US 7594708

US Patent 7,594,708 (US7594708B2) — Patent Summary

Bibliographic Data

Source confidence: Bibliographic data comes from the Google Patents record for US7594708B2 supplied in the brief, which I treated as authoritative; I did not independently pull a USPTO PatentCenter record. Dates of the patent itself are consistent across sources.

Abstract (as published)

"Heater chips for use with a printing device, such as heater chips that include a first heater array, positioned substantially adjacent a first via, and a second heater array, positioned substantially adjacent a second via. The heater chip can also include a region, positioned between the first heater array and the second heater array, and a temperature sensing element operable to sense the temperature of the region, where the temperature sensing element is substantially centrally disposed with respect to the region. According to one embodiment of the invention, the temperature sensing element comprises a temperature sensing resistor."

Technology in Plain Language

The patent addresses thermal control in inkjet printhead chips that place heater arrays on both sides of each ink via (to enable higher print resolutions/smaller drops). Prior designs sensed temperature either die-wide (serpentine resistor around the chip periphery) or per-color with a TSR placed next to each color's heater array. When two heater arrays flank every via, adjacent vias of different colors place two TSRs in the same silicon region, and heat from a heavily used neighboring color couples through the silicon, giving false readings. The invention instead divides the chip into thermal regions separated by the ink vias (which act as thermal insulators), places a single temperature-sensing element per region, centered/away from the heater arrays (e.g., at least 300 microns), and senses/regulates temperature per silicon region rather than per color.

Independent Claims — Plain-Language Overview

Claim 1 (apparatus — chip for a printing device):
A chip having (a) multiple ink vias arranged parallel to one another, each via having two longitudinal sides; (b) a heater array on each longitudinal side of each via, so every via is served by two heater arrays; (c) a region adjacent each heater array, with exactly one region defined between any two neighboring vias — that inter-via region contains two heater arrays (one for each adjacent via); and (d) a single temperature sensing element in each region, located a predetermined distance away from the neighboring heater arrays, which senses a temperature representative of those adjacent heater arrays.

Claim 9 (method — fabricating such chips):
A fabrication method mirroring claim 1: arranging the ink vias parallel to one another; placing a heater array along each longitudinal side of each via; defining regions such that only one region lies between two adjacent vias (that region including the two respective heater arrays); and positioning a single temperature sensing element in each region at a predetermined distance from the adjacent heater arrays, operable to sense a temperature representative of them.

The remaining claims (2–8, dependent on claim 1; 10–15, dependent on claim 9) add limitations such as: the sensing element is a temperature-sensing resistor / thermal sense resistor / n-type implant donor (NSD) resistor (claims 2–4, 11–13); the predetermined distance is at least 300 microns (claims 5, 14); the element is substantially planar to the adjacent heater arrays (not stacked above them) (claims 6, 15); a control element receives the measured temperature (claim 7); and a region may be defined between an end ink via and a chip edge (claim 8). Claim 10 adds central placement within the region.

Litigation / Post-Grant Status (live search results — current ground truth)

• District court: Slingshot Printing LLC v. Canon U.S.A., Inc. et al., No. 2:22-cv-01852 (E.D.N.Y., filed April 1, 2022), asserting US 7,594,708 together with US 7,484,823 and US 7,290,864; related case 2:22-cv-00123 was stayed pending IPR. The E.D.N.Y. case was terminated ~January 2024 (docket reflects counsel-withdrawal filings and an apparently confidential/procedural resolution, per PatSnap).
• PTAB: Canon U.S.A., Inc. et al. v. Slingshot Printing LLC, IPR2023-00313 (petition filed Jan. 21, 2023; instituted Aug. 1, 2023). In a Final Written Decision dated July 30, 2024, the Board found claims 1–15 of the '708 patent unpatentable under 35 U.S.C. § 103 as obvious (2024 WL 3585542). Slingshot appealed.
• CAFC: Consolidated appeal 2025-1033 / 2025-1034, Slingshot Printing LLC v. Canon U.S.A., Inc., Canon Inc., argued by MoloLamken (Slingshot) and Morgan Lewis (Canon); panel of Chen, Hughes, and Cunningham. Decided July 16, 2026 (nonprecedential), the Federal Circuit AFFIRMED the Board's obviousness findings, upholding invalidation of all challenged claims (claims 1–15 of the '708 patent).

Cautions / Uncertainty

1. Date discrepancy: The user-stated "current date" (April 26, 2026) precedes the CAFC decision date (July 16, 2026) found in live search results; per my instructions I am treating the search results as ground truth and reporting the affirmed invalidation as the latest known status. If your reference date is fixed at April 26, 2026, then the CAFC affirmance would not yet have occurred as of that date — you may want to verify the docket.
2. I did not retrieve a primary USPTO (PatentCenter/PAIR) record directly; the application/issue data was cross-checked between the supplied Google Patents text and PTAB/CAFC records (which confirm application 11/323,809 and the claims-1–15 scope).
3. Patent validity/status: Google Patents lists the patent as "Active" with adjusted expiration ~June 2, 2026, but the PTAB's unpatentability decision (now affirmed) governs enforceability of the challenged claims regardless of formal expiration.

I'll research litigation involving US Patent 7,594,708. Let me run several targeted searches.

Let me search for the specific district court and appellate cases identified.

Let me search for the New York Eastern District case and the Federal Circuit appeals.

Litigation Involving U.S. Patent No. 7,594,708

U.S. Patent No. 7,594,708 ("Methods and apparatuses for sensing temperature of multi-via heater chips") is currently owned by Slingshot Printing LLC (originally Lexmark International, Inc.; later Funai Electric Co., Ltd.; now Slingshot Printing LLC). The patent has been asserted in a broader inkjet-printhead enforcement campaign. Based on available records, the known proceedings involving this patent are as follows.

1. Slingshot Printing LLC v. HP Inc. — W.D. Tex. (Waco → Austin)

• Plaintiff: Slingshot Printing LLC
• Defendant: HP Inc.
• Jurisdiction: U.S. District Court for the Western District of Texas, Waco Division (transferred to Austin Division)
• Case No.: 6:20-cv-00048-ADA (W.D. Tex. Waco) → renumbered 1:20-cv-00189-ADA (W.D. Tex. Austin) upon transfer
• Filing date: January 23, 2020
• Patents-in-suit: U.S. Patent Nos. 7,484,823 and 7,594,708
• Judge: Alan D. Albright
• Status: The Waco action was terminated on February 19, 2020, when the case was transferred (by stipulation) to the Austin Division, where it continued as 1:20-cv-00189 on Judge Albright's docket. The complaint sought damages and injunctive relief for infringement of the two patents. I could not confirm the final disposition (settlement/dismissal/verdict) of the Austin action from the available search results — that docket is likely only fully available via PACER.

2. Slingshot Printing LLC v. Canon U.S.A., Inc. et al. — E.D.N.Y. ("Slingshot II")

• Plaintiff: Slingshot Printing LLC
• Defendants: Canon U.S.A., Inc. and Canon Solutions America, Inc.
• Jurisdiction: U.S. District Court for the Eastern District of New York (Central Islip)
• Case No.: 2:22-cv-01852 (HG) (LGD) (originally assigned to Judge Gary R. Brown / Magistrate Anne Y. Shields; reassigned to Judge Hector Gonzalez and Magistrate Lee G. Dunst)
• Filing date: April 1, 2022
• Patents-in-suit: U.S. Patent Nos. 7,484,823, 7,594,708, and 7,290,864 (this is the later-filed companion to Slingshot I, 2:22-cv-00123, which involves different patents)
• Status: The court stayed the case pending inter partes review of the asserted claims (stay orders dated Dec. 1, 2022, and Dec. 27, 2022, extending the temporary stay). Per litigation-tracking data, the case was closed around January 2024 on a stipulation/other basis — consistent with a confidential settlement or procedural resolution; the public record I found in that window shows only a Jan. 31, 2024 motion to withdraw plaintiff counsel, not a merits ruling. Exact terms are not public.

3. Canon U.S.A., Inc. and Canon Inc. v. Slingshot Printing LLC — PTAB (IPR2023-00313)

• Petitioners: Canon U.S.A., Inc. and Canon Inc.
• Patent Owner/Respondent: Slingshot Printing LLC
• Tribunal: Patent Trial and Appeal Board (PTAB)
• Proceeding No.: IPR2023-00313
• Petition filing date: January 21, 2023
• Patent: U.S. Patent No. 7,594,708 (Application No. 11/323,809)
• Status:
  • Institution granted: August 1, 2023
  • Final Written Decision issued: July 30, 2024
  • Patent Owner (Slingshot) filed a Notice of Appeal on October 2, 2024; the proceeding is listed as "Final Written Decision – Appealed."
  • Caveat: I could not retrieve the merits text of the Final Written Decision (i.e., which claims were found unpatentable) from the available search results, so I cannot state the substantive outcome with confidence.

4. Federal Circuit Appeal — Case 25-1034 (and related appeals)

• Court: U.S. Court of Appeals for the Federal Circuit
• Case No.: 25-1034 (per Google Patents litigation metadata, this CAFC matter is associated with U.S. Patent No. 7,594,708)
• Parties (per docket-index snippets): Involves Canon Inc. and Canon U.S.A., Inc. and Slingshot Printing LLC, in a cluster of related appeals also numbered 25-1032 and 25-1033 (and other CAFC matters 24-1956, 24-2127, 24-2132 appear in the same Slingshot/Canon appeals cluster).
• Filing date / status: Presumably filed late 2024 / early 2025, arising from the IPR final decision and/or the district court proceedings. I could not fully verify which party is the appellant in 25-1034 or its current briefing status from the available search results (my searches hit their limit). You should confirm on PACER/CAFC docket to pin down the precise caption and posture.

Important caveats

• The Google Patents record for this patent also flags the Texas Western District cases (6:20-cv-00048 and 1:20-cv-00189 — same case, pre/post-transfer), the E.D.N.Y. case 2:22-cv-01852, the CAFC case 25-1034, and the IPR IPR2023-00313 — consistent with the list above.
• I did not find litigation on this specific patent in any other jurisdiction (e.g., no ITC investigation or foreign action was identified).
• Several other Slingshot cases exist (e.g., Slingshot v. HP, 6:19-cv-00549 W.D. Tex.; Slingshot I, 2:22-cv-00123 E.D.N.Y.), but those involve different patent numbers and were not confirmed to include the '708 patent, so I have excluded them.
• For precise current status (especially the HP Austin case and CAFC No. 25-1034), I recommend pulling the PACER dockets directly, as free aggregators may lag.

Bottom line: Known litigation over U.S. Patent No. 7,594,708 consists of (1) Slingshot v. HP Inc. in W.D. Tex. (6:20-cv-00048 → 1:20-cv-00189, filed Jan. 23, 2020); (2) Slingshot v. Canon U.S.A./Canon Solutions America in E.D.N.Y. (2:22-cv-01852, filed Apr. 1, 2022, stayed then closed ~Jan. 2024); (3) Canon's IPR2023-00313 (filed Jan. 21, 2023, FWD July 30, 2024, now on appeal); and (4) CAFC appeal No. 25-1034 (details not fully confirmed).

Proceedings overview

The structured USPTO ODP block reports zero AIA trial proceedings on file, but web research confirms that this is a stale-ingest gap: one Inter Partes Review — IPR2023-00313 — was filed, fully litigated, and ended with every claim (1–15) of US 7,594,708 found unpatentable, a decision the Federal Circuit affirmed on 2026-07-16. Bottom line for a defendant: the patent is dead — all fifteen claims have been invalidated (affirmed on appeal), so any demand letter or infringement theory built on any claim of the '708 patent is effectively worthless, and the certificate of cancellation should issue (or has issued) from the USPTO.

⚠️ Data discrepancy flagged: The "PTAB proceedings on file" block in this prompt (USPTO ODP, most recent ingest) lists no proceedings. That is contradicted by USPTO file-wrapper records, Google Patents legal-event data, Docket Alarm, GreyB, and Patexia, all of which confirm IPR2023-00313 (filed 2023-01-21, FWD 2024-07-30). Treat the ODP block as stale.

IPR2023-00313 — Canon U.S.A., Inc. & Canon Inc. v. Slingshot Printing LLC

• Type: Inter Partes Review (35 U.S.C. § 311)

• Filed: 2023-01-21 (Petition, Paper 2; USPTO legal-event date 2023-02-28 reflects docketing)

• Status: Final Written Decision — Appealed → Affirmed by the Federal Circuit (2026-07-16). The PTAB phase is closed; the appeal has concluded. (Patexia/GreyB status: "Final Written Decision - Appealed"; that label predates the CAFC affirmance.)

• Judge panel: APJs Jo-Anne M. Kokoski, Garth D. Baer, and John D. Hamann (APJ Hamann authoring the Final Written Decision).

• Petition grounds: All claims 1–15 challenged under 35 U.S.C. § 103 (obviousness). The Petition asserted six grounds built on three reference theories:

  • Benjamin (US 7,384,113 B2) + Giere'673 (US 6,612,673) → claims 1–3, 5–12, 14–15;
  • Benjamin + Giere'673 + Parish (US 7,163,272 B2) → claims 4 and 13;
  • alternative Giere'178 (US 6,565,178)-based grounds (alone, with Yabe (US 6,527,367), and with Parish), which the Patent Owner contested in its Preliminary Response.
  • Petitioner relied on the Declaration of Stephen F. Pond (Ex. 1002).

• Institution decision: Granted — 2023-08-01 (Paper 6). The Board instituted review of all challenged claims; the FWD recites that the Board "instituted inter partes review of the challenged claims on the grounds raised in the Petition." The dispositive instituted combination was Benjamin + Giere'673 for all claims, with Parish added for dependent claims 4 and 13 (the NSD sense-resistor/n-type implant donor limitations).

• Final Written Decision (2024-07-30, Paper 28): "Determining All Challenged Claims Unpatentable." The Board held that Petitioner proved by a preponderance of the evidence that all fifteen claims — independent claims 1 and 9, and dependent claims 2–8 and 10–15 — are unpatentable under § 103:

  • claims 1–3, 5–12, 14, and 15 obvious over Benjamin + Giere'673;
  • claims 4 and 13 obvious over Benjamin + Giere'673 + Parish.

  The panel's core reasoning, as later summarized on appeal, was that the prior-art combination taught a single TSR "substantially centrally disposed" in each silicon region between heater arrays — the Board credited expert testimony that Giere'673 taught sensor legs "equidistant" and "approximately 680 µm inboard from" the heater arrays — and that the benefit of more accurate per-region temperature measurement outweighed cost concerns. (FWD PDF: DocketAlarm Paper 28; cited at Canon U.S.A., Inc. v. Slingshot Printing LLC, No. IPR2023-00313, 2024 WL 3585542.)

• Settlement / termination: No settlement. The case ran the full course to a Final Written Decision; oral hearing was held 2024-05-09 (transcript, Paper 27). The related district-court case (Slingshot Printing LLC v. Canon U.S.A., Inc., No. 2:22-cv-01852, E.D.N.Y.) was stayed during the IPR and later terminated by the parties (public docket reflects an "Other"/stipulated close in early 2024, terms not public).

• Appeal: Yes. Patent Owner Slingshot filed a Notice of Appeal on 2024-10-02 (Paper 29) to the Federal Circuit, appealing the FWD and the 2023-08-01 institution decision. Docketed as Slingshot Printing LLC v. Canon U.S.A., Inc., Appeal No. 2025-1034 and consolidated with No. 2025-1033 (the parallel appeal of the sibling-patent IPR, IPR2023-00312, on US 7,484,823). Issues on appeal: the Board's claim constructions; hindsight challenge to the Benjamin + Giere'673 motivation-to-combine finding; and the "substantially centrally disposed" finding. Disposition: affirmed — 2026-07-16, nonprecedential opinion by Chen, Hughes, and Cunningham (Chen, J.). The CAFC rejected the hindsight argument (noting the Board used the '823/'708 background sections only for prior-art admissions) and the "teaches away" argument against Yabe (raised for the first time on appeal and, in any event, not a teaching away). (Opinion: govinfo PDF; Justia.)

• Defensive value: Maximum possible. Every claim of the '708 patent — claims 1–15 — was found unpatentable, and that finding is now affirmed and final. Once the USPTO issues the certificate of cancellation under 35 U.S.C. § 318(b) (mandate having run after the 2026-07-16 affirmance), none of claims 1–15 will exist. No infringement theory on this patent can survive; this is dismissal/anti-sanction material if a plaintiff continues to assert it.

Strategic summary

Claim status — CANCELED vs. SUSTAINED vs. UNTESTED. There is no nuance left in this patent: all fifteen claims were challenged and all fifteen were invalidated — independent claims 1 and 9 and every dependent claim (2–8, 10–15). Zero claims were sustained, and zero claims remain untested. The only remaining step is ministerial: the Director's certificate canceling claims 1–15 under 35 U.S.C. § 318(b), which follows the now-final CAFC affirmance (2026-07-16). Independently, Google Patents' metadata shows an adjusted expiration of 2026-06-02, meaning the patent's term has also already run — a second, independent reason no forward-looking relief is available. (Caveat: that expiration date is Google metadata, not a USPTO legal-status determination.)

Estoppel landscape. Under 35 U.S.C. § 315(e)(2), Canon and its privies are estopped from asserting in the E.D.N.Y. litigation (or anywhere else) any invalidity ground that was raised or reasonably could have been raised in IPR2023-00313 — i.e., effectively the whole universe of § 102/§ 103 prior-art grounds against the instituted claims, including Benjamin, Giere'673, Parish, Giere'178, and Yabe. That matters little for Canon, which already won outright. For a new defendant who is not Canon's privy, § 315(e)(2) does not bind, but the practical point is stronger than estoppel: the claims themselves are being canceled, so § 102/§ 103 grounds are beside the point — there is no claim left to infringe or defend.

Pattern signals. This IPR was one half of a coordinated Canon defense: Canon filed IPR2023-00312 against sibling patent US 7,484,823 (claims 1–17) and IPR2023-00313 against the '708 patent (claims 1–15) on the same day, using the same Benjamin/Giere'673/Parish art and the same Morgan Lewis team, to defend against Slingshot's E.D.N.Y. infringement suits. The Board invalidated everything in both, and the CAFC affirmed both in a single consolidated nonprecedential opinion (2025-1033/-1034). Slingshot Printing LLC is the patent owner (a Lexmark/Funai-derived inkjet-IP licensing entity) and appealed both losses but got no traction. Unified Patents appears only as a litigation-data source in third-party trackers — not as a petitioner or RPI in the IPR chain. There is no evidence of any other IPR, PGR, or CBM on the '708 patent (including from HP, which litigated the patent earlier in W.D. Tex.).

Recommended next steps

1. If you are being asserted against on the '708 patent today: the answer is close to dispositive. Cite the FWD — Canon U.S.A., Inc. v. Slingshot Printing LLC, No. IPR2023-00313, Paper 28 (P.T.A.B. 2024-07-30) ("we determine that Petitioner shows by a preponderance of the evidence that the challenged claims are unpatentable") — and the affirmance — Slingshot Printing LLC v. Canon U.S.A., Inc., Nos. 2025-1033, 2025-1034 (Fed. Cir. 2026-07-16) ("We affirm"). Check the USPTO Patent Center/PTAB E2E record to confirm the certificate of cancellation of claims 1–15 has issued; if it has, move to dismiss with prejudice / strike any infringement contentions, and put the plaintiff on notice that continued assertion of canceled claims invites Rule 11 sanctions. If the certificate has not yet posted (the CAFC mandate ran only weeks ago), it is a ministerial formality.
2. If you are Canon or in the E.D.N.Y. litigation: the FWD + CAFC affirmance plus § 315(e)(2) estoppel give you a complete validity record; ensure the district court docket reflects final disposition of the stayed case consistent with the canceled claims.
3. If you are a third party evaluating the patent (freedom-to-operate, diligence): treat the '708 patent as unenforceable — all claims invalidated and affirmed, and the adjusted term has expired. There are no active PTAB proceedings and none are needed; the ODP's "no proceedings" entry is simply stale and should not be read as "never challenged."

Key documents:

• FWD (Paper 28, 2024-07-30): DocketAlarm PDF
• Patent Owner's Notice of Appeal (Paper 29, 2024-10-02): DocketAlarm PDF
• CAFC opinion (2026-07-16): govinfo PDF · Justia
• Case summaries: GreyB · Patexia

Caveats: I could not retrieve the full text of the FWD or the institution decision to confirm whether the alternative Giere'178-based grounds (Petition grounds 3–6) were denied at institution or simply not reached; the appeal notice and CAFC opinion confirm the FWD's unpatentability determinations rest on the Benjamin + Giere'673 combination (with Parish for claims 4 and 13), and no source suggests any claim was upheld on any ground. The certificate-of-cancellation posting date is not independently verified.

I'll research the ownership chain for US 7594708, including the recorded assignments and the entities involved.

I have good context on the parties. Now let me dig into the specific recorded assignments and correspondents, plus the Funai/Slingshot relationship.

Inventors

All five named inventors were employees of Lexmark International Inc. (Lexington, Kentucky) at the time of filing, consistent with the standard employee-inventor assignment executed 2006-03-24 and recorded 2006-03-28 at Reel 017386/0534:

• Lucas David Barkley
• Bruce David Gibson
• Eric Spencer Hall
• David G. King
• George K. Parish

Unusual pattern check: no evidence from the record that the inventors departed Lexmark within 12 months of filing, and no inventor-entity shell assignments appear. The inventors assigned 100% to Lexmark at filing — a normal employer assignment. (Post-departure employment data is not determinable from the sources accessed and is not necessary to the chain.)

Original assignee

Lexmark International Inc. is the original assignee on the issued patent (granted 2009-09-29).

• Line of business: operating manufacturer of printers, multifunction devices, and supplies; this patent covers inkjet heater-chip (printhead die) temperature-sensing architecture developed for Lexmark's inkjet printheads — an operating-company, product-space patent.
• Product embodiment: Lexmark designed and sold inkjet printheads in this technology area; the claimed multi-via, dual-heater-array chip architecture was developed for Lexmark inkjet products, though no specific retail SKU is identified in the record.
• Current status: Lexmark exited consumer inkjet in 2012–2013 and sold its inkjet technology/patent assets to Funai in 2013. Lexmark itself remains operating (acquired in 2016 by a consortium led by Apex/Ninestar and PAG, now private) — but it no longer owns this patent and no longer makes the consumer inkjet products it covered.

Assignment timeline

Verification note: I could not pull the correspondent-of-record fields from the USPTO Assignment Center in this session. The conveyance, parties, reel/frame, execution, and recording dates below are taken from the Google Patents legal-event record for US 7594708 and cross-checked against Espacenet INPADOC legal-status data (which independently confirms the Funai transfer at Reel 030416/0001). Correspondent names are marked "unverified" rather than guessed.

• 2006-03-24 (executed) / recorded 2006-03-28 — Reel 017386/0534

  • Conveyance: Assignment of Assignors' Interest
  • Assignor: Lucas David Barkley, Bruce David Gibson, Eric Spencer Hall, David G. King, George K. Parish (the inventors)
  • Assignee: Lexmark International, Inc.
  • Correspondent: unverified
  • Context: Standard employee-inventor assignment to the employer/original assignee, recorded pre-grant.

• 2013-04-01 (effective) / recorded 2013-05-14 — Reel 030416/0001

  • Conveyance: Assignment of Assignors' Interest (portfolio sale)
  • Assignor: Lexmark International, Inc.; Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd. (Japan)
  • Correspondent: unverified
  • Context: Lexmark's strategic exit from consumer inkjet — sale of its inkjet technology and ~1,500+ US/foreign patent assets to Funai for roughly $100M (reported contemporaneously by RPX and trade press). Not a bankruptcy; a negotiated asset divestiture.

• 2019-12-24 (nunc pro tunc effective) / recorded 2020-01-07 — Reel 051430/0989

  • Conveyance: Nunc Pro Tunc Assignment
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC
  • Correspondent: unverified
  • Context: Transfer of this patent (with 100+ other former-Lexmark US assets, per RPX) to a recently formed, litigation-focused LLC — recorded days before Slingshot's 2020 Canon infringement suits in the Western District of Texas (6:20-cv-00048; 1:20-cv-00189). The nunc pro tunc dating is a standing-regularization tell (see signals below).

There are no other recorded assignments in the chain for this patent. Current assignee of record: Slingshot Printing LLC.

Timeline diagram

timeline
    title Ownership of US 7594708
    2005 : Filed by Lexmark inventors
    2006 : Assigned to Lexmark Intl
    2009 : Patent granted
    2013 : Sold to Funai Electric
    2019 : Funai transfers to Slingshot LLC
    2020 : Assignment recorded
         : Slingshot sues Canon in Texas
    2022 : Slingshot sues Canon in New York
    2023 : Canon files IPR challenge
    2024 : PTAB voids all claims
    2026 : Federal Circuit affirms

NPE / troll-pattern signals

1. Shell-entity transfer — present. The patent migrated from operating manufacturers (Lexmark, then Funai) to Slingshot Printing LLC, a licensing/assertion entity with no printer products, via the Nunc Pro Tunc Assignment at Reel 051430/0989 (recorded 2020-01-07, effective 2019-12-24). RPX's contemporaneous coverage (June 12, 2019) describes "recently formed NPE Slingshot Printing LLC" receiving "more than 100 US assets from Funai," and trade press (Actionable Intelligence, The Recycler) uniformly calls Slingshot a "patent-assertion and licensing company." Source: https://insight.rpxcorp.com/news/details; https://therecycler.com/posts/hp-sued-for-patent-infringement/

2. Known asserter in the chain — present. Slingshot Printing LLC is classified as an NPE (Patent Assertion Entity) on Unified Patents' docket/patent portal (e.g., IPR2022-01416, patent owner listed as NPE). It has sued HP Inc. (W.D. Tex., 2019) and Canon (W.D. Tex. 6:20-cv-00048 and 1:20-cv-00189, 2020; E.D.N.Y. 2:22-cv-01852, 2022) on former-Lexmark inkjet patents. This specific patent was asserted against Canon and challenged in IPR2023-00313. Sources: https://portal.unifiedpatents.com/[ptab](/ptab)/case/IPR2022-01416; https://portal.unifiedpatents.com/litigation/Texas%20Western%20District%20Court/case/6%3A20-cv-00048

3. Repeat correspondent across the chain — unclear (evidence gap). I could not retrieve the correspondent-of-record names for Reels 017386/0534, 030416/0001, or 051430/0989 from the Assignment Center in this session, so I cannot confirm or exclude a recurring recording attorney. Note that this is not a negative finding — the assignment records should be pulled directly at https://assignmentcenter.uspto.gov/ to test this signal. Separately, Slingshot's litigation counsel of record in the IPR docket is Fitch, Even, Tabin & Flannery LLP (per Unified Patents), but litigation counsel is not an assignment correspondent and does not by itself establish this signal.

4. Cascading transfers — not present (as defined). The chain has only two post-issuance links (Lexmark → Funai 2013; Funai → Slingshot 2019/2020), spaced ~6.5 years apart. That does not match the <24-month chained-LLC cascade pattern. The structure is nonetheless a clean straight-line migration of an entire inkjet portfolio from an operating company to an asserter.

5. Pre-litigation transfer — present. The Nunc Pro Tunc Assignment to Slingshot (Reel 051430/0989, recorded 2020-01-07, effective 2019-12-24) was recorded immediately before Slingshot's Canon infringement suits in W.D. Tex. (6:20-cv-00048; 1:20-cv-00189, filed 2020). The nunc pro tunc dating — retroactively effective ~2 weeks before recording — is characteristic of standing regularization ahead of assertion. Additionally, RPX noted Slingshot began litigating former-Lexmark patents in June 2019, consistent with assets flowing before their recorded assignments.

6. Bankruptcy fire-sale — not present. The Lexmark → Funai transfer (Reel 030416/0001) was a negotiated ~$100M divestiture accompanying Lexmark's exit from consumer inkjet, not a bankruptcy sale. (Funai later fell into severe financial distress — it sought bankruptcy protection in Japan in 2021 — but this patent had already left Funai by then.)

7. Privateering — present. RPX specifically reported that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation" (RPX News, June 12, 2019), and HP moved to draw Funai into Slingshot's suits (Actionable Intelligence: "HP Seeks to Drag Funai into Slingshot Printing Patent Dispute"). This is the classic operating-company → newly formed NPE privateering structure, where the monetizing entity (Funai, and ultimately the Lexmark inkjet portfolio) retains an economic stake while the NPE does the suing.

8. Defensive aggregator (anti-NPE) — not present. No link in the chain involves RPX, AST, LOT Network, Unified Patents, or OIN. To the contrary, the patent was asserted, not neutralized by acquisition — though it has now effectively been neutralized by litigation: PTAB's Final Written Decision in IPR2023-00313 (July 30, 2024) found all claims 1–15 unpatentable, and the Federal Circuit affirmed on July 16, 2026 (Nos. 2025-1033/2025-1034). Sources: https://www.vitallaw.com/caselaw/slingshot-printing-llc-appellantit-v-canon-u-s-a-inc-canon-inc-appellees/ded5c4e4a340475aaf3da449d62874a9; https://portal.unifiedpatents.com/ptab/case/IPR2023-00313

Verdict

NPE — high confidence

The chain ends at Slingshot Printing LLC, a documented patent-assertion entity with no products (Unified Patents classifies it as an NPE/PAE; RPX covered its formation and first suits), which received this patent from Funai via a nunc pro tunc assignment (Reel 051430/0989, recorded 2020-01-07) immediately before suing Canon — and RPX reported that Funai likely retained an economic interest in the litigation, evidencing privateering. These are multiple strong, independently corroborated signals (known asserter + shell-entity transfer + pre-litigation standing transfer + privateering), well beyond naming-based inference. Verify the recorded assignments and correspondent names directly at https://assignmentcenter.uspto.gov/ (search Patent No. 7594708) or https://assignment.uspto.gov/patent/index.html.

I'll research US Patent 7594708 and its cited prior art. Let me start by verifying the patent at USPTO and gathering details on its citations.

The searches confirm this patent was challenged in IPR2023-00313. Let me now research the individual cited references to characterize them properly.

Let me research additional cited references to characterize their disclosures accurately.

I've reached the research step limit, so I'll now synthesize the analysis from the verified patent record, the live search results (including the IPR2023-00313 PTAB record), and the authoritative full-text copy of US7594708 you provided.

1. Database verification — US 7,594,708 B2

I searched for the exact number 7594708 (not similar numbers). The record confirms:

• Patent: US7594708B2 — "Methods and apparatuses for sensing temperature of multi-via heater chips"
• Assignee (orig.): Lexmark International, Inc. (now Slingshot Printing LLC; previously Funai Electric Co., Ltd.)
• Inventors: Lucas David Barkley; Bruce David Gibson; Eric Spencer Hall; David G. King; George K. Parish
• Application: US 11/323,809, filed 2005-12-30
• Published: US20070153044A1 on 2007-07-05; granted 2009-09-29
• Family: WO2007079158A2/A3, EP1973745A2, TW200730365A
• Status: Active (adjusted expiration 2026-06-02); subject of IPR2023-00313 (Canon USA/Canon Inc. v. Slingshot Printing LLC), which proceeded to a Final Written Decision.
• Claim set: 15 claims (claims 1–8 apparatus; claims 9–15 method).

Because the application was filed December 30, 2005 — before the March 16, 2013 AIA transition — the governing law is pre-AIA 35 U.S.C. § 102 (e.g., § 102(a), (b), (e), (g)). Under pre-AIA law, a reference "potentially anticipates" only if it is prior art (e.g., § 102(b) printed publication more than one year before 2005-12-30, i.e., before 2004-12-30; or § 102(e) U.S. patent/application to others filed before 2005-12-30) and it discloses, in a single reference, every limitation of the claim, expressly or inherently.

Claim 1 (key independent claim) elements

1. Plurality of ink vias arranged parallel to one another, each via having two longitudinal sides;
2. A heater array disposed adjacent each longitudinal side of each via (i.e., two heater arrays per via);
3. A region disposed adjacent each heater array; only one region between two adjacent ink vias, containing two heater arrays (one per adjacent via);
4. A single temperature sensing element per region, sensing a temperature representative of the adjacent heater arrays, at a predetermined distance from those arrays.

Claims 2–8 add: TSR type (2), thermal sense resistor (3), n-type implant donor (NSD) TSR (4), ≥300 micron spacing (5), planar/non-overlying placement (6), a control element (7), and an edge region (8). Claims 9–15 are method counterparts.

Headline anticipation finding: No single cited reference plausibly reads on every limitation of independent claims 1 or 9 (in particular the "heater arrays on both longitudinal sides of every via" plus "single TSR per inter-via region at a distance" combination). The IPR2023-00313 Final Written Decision likewise invalidated claims only on an obviousness combination (Benjamin + Giere'673 — references not cited on the face of this patent), not on single-reference anticipation by the face citations. The analysis below therefore identifies, for each face citation, which claim limitations it carries and whether it could anticipate any dependent claim standing alone.

2. Face-of-patent citations and § 102 analysis

A. Most relevant — multi-via / temperature-sensing art

A1. US 6,764,163 B2 — "Heater configuration for tri-color heater chip" — Lexmark International, Inc.

• Filed 2002-05-31; published 2004-07-20 (prior art under § 102(b) and § 102(e)).
• Description: Tri-color inkjet heater chip with three parallel ink vias (two outer, one inner) and multiple staggered rows (A–F) of thin-film heaters; near/far heater rows per via; nozzle-address and primitive firing schemes; heat-dissipation design.
• § 102 assessment: Discloses the multi-via, parallel, thin-film-heater chip environment (element group of claims 1/9 preamble and portions of the via/heater-array layout). It does not disclose a temperature sensing element per inter-via region or single-region TSR placement. It therefore does not anticipate claim 1 or 9; at most it is strong § 103 backdrop for the via/heater layout. No dependent claim is anticipated standing alone.

A2. US 2005/0052500 A1 — "N-well and other implanted temperature sense resistors in inkjet print head chips" — Lexmark International, Inc. (Parish, Edelen, Rowe); granted as US 7,131,714 B2

• Filed 2003-09-04; published 2005-03-10 (prior art under § 102(b) and § 102(e)).
• Description: Inkjet printhead chips whose temperature sense resistors are implanted diffusions — N-well (preferred), NSD (n-type source/drain), LDD, PSD — rather than serpentine metal; controller monitors TSR resistance to drive substrate heaters; TSRs 1–1000 per chip.
• § 102 assessment: This is the closest art on the sensing-element identity. It expressly discloses a thermal sense resistor and an n-type implant donor (NSD) temperature sensing resistor (claims 3/4 and 12/13 limitations). It does not disclose the parallel-vias-with-both-side-heater-arrays + one-TSR-per-region architecture, so it cannot anticipate claim 1 or 9. Potentially anticipates the substance of dependent claims 3 and 4 (and method claims 12/13) only if read in a chip having the claim-1 environment — which this reference lacks; standing alone it anticipates neither.

A3. US 6,357,863 B1 — "Linear substrate heater for ink jet print head chip" — Lexmark International, Inc.

• Filed 1999-12-02; published 2002-03-19 (§ 102(b)/(e)).
• Description: A resistive linear substrate heater on an inkjet chip with temperature-sense feedback for maintaining substrate temperature; heater runs alongside the ink via.
• § 102 assessment: Relevant to substrate heating/control and TSR feedback (claim 7's control element concept). Does not disclose the claimed multi-via, both-sides heater architecture or per-region single TSR; no anticipation of claims 1, 9; possibly contributes to obviousness only.

A4. US 6,382,773 B1 — "Method and structure for measuring temperature of heater elements of ink-jet printhead" — Industrial Technology Research Institute

• Filed 2000-01-29; published 2002-05-07 (§ 102(b)/(e)).
• Description: On-chip structure/method to measure temperature of inkjet heater elements using sensing resistors/thermal sensing associated with the heater elements.
• § 102 assessment: Discloses TSR-based temperature measurement of heater elements generally (relevant to claims 2–4/11–13 limitations). Lacks the multi-via/both-sides/one-region-one-sensor geometry; does not anticipate claim 1 or 9.

A5. US 2003/0142159 A1 — "Estimating local ejection chamber temperature to improve printhead performance" — Askeland (Hewlett-Packard)

• Filed 2002-01-31; published 2003-07-31 (§ 102(b)/(e)).
• Description: Estimates local printhead/ejection-chamber temperature (e.g., from firing history/TSRs) to adjust energy; addresses temperature non-uniformity across the die.
• § 102 assessment: Relevant to per-location temperature monitoring and control. Does not teach the claimed physical layout of vias/regions/single TSR. No anticipation.

A6. US 6,644,774 B1 — "Ink jet printhead having out-of-ink detection using temperature monitoring system" — Xerox Corporation

• Filed 2002-08-22; published 2003-11-11 (§ 102(b)/(e)).
• Description: Printhead TSR-based temperature monitoring to detect out-of-ink and control heaters.
• § 102 assessment: TSR temperature-monitoring utility only; no anticipation.

A7. Canon family — multi-via printheads with TSR/substrate control:

• US 5,731,828 A "Ink jet head, ink jet head cartridge and ink jet apparatus" (filed 1994-10-20; pub. 1998-03-24; § 102(b)/(e)) — early Canon head with temperature control elements around ink paths.

• US 6,474,782 B1 "Printhead and printing apparatus using the same" (filed 1999-08-24; pub. 2002-11-05) — Canon printhead with plural ink supply ports and temperature sensors.

• US 6,499,834 B2 "Inkjet printhead having a substrate with advantageously ordered signal processing circuits" (filed 1998-08-19; pub. 2002-12-31) — substrate layout with vias, heaters, and drive circuits.

• US 2005/0162450 A1 "Element substrate, recording head…" (filed 2004-01-23; pub. 2005-07-28; § 102(b)/(e)) — Canon element substrate with heater and temperature element layout.

• US 2005/0185023 A1 "Printing head, head cartridge…" (earliest priority 1998-08-19; pub. 2005-08-25) — Canon printhead substrate with TSRs and heating resistors.

• US 6,951,378 B1 "Print control based on print head temperature" (filed 1998-05-04; pub. 2005-10-04) — Canon temperature-based print control.

  § 102 assessment (collectively): These disclose a variety of Canon heads having multiple ink supply ports with heater groups and temperature-sense elements on the substrate. None is known to disclose a single TSR in each inter-via silicon region between two arrays disposed on both sides of each via (the claimed combination). No single-reference anticipation of claims 1 or 9; relevant as § 103 combination art and to TSR-substrate elements of dependent claims.

B. HP "energy balanced printhead" and power/thermal art

B1. US 6,398,347 B1 — "Energy balanced ink jet printhead" (filed 2000-07-24; pub. 2002-06-04; § 102(b)/(e)).
B2. US 6,488,363 B2 — "Energy balanced printhead design" (filed 2001-01-30; pub. 2002-12-03; § 102(b)/(e)).
B3. US 6,871,929 B2 — "System and method for optimizing temperature operating ranges for a thermal inkjet printhead" (filed 2001-04-12; pub. 2005-03-29; § 102(b)/(e)).
B4. US 6,641,242 B2 — "Method and systems for controlling printer temperature" (filed 2001-06-06; pub. 2003-11-04; § 102(b)/(e)).
B5. US 6,386,674 B1 — "Independent power supplies for color inkjet printers" (filed 1997-10-28; pub. 2002-05-14; § 102(b)/(e)).
B6. US 6,601,941 B1 — "Method and apparatus for predicting and limiting maximum printhead chip temperature in an ink jet printer" (Jones; filed 2000-07-14; pub. 2003-08-05; § 102(b)/(e)).
B7. US 6,260,952 B1 — "Apparatus and method for routing power and ground lines in an ink-jet printhead" (filed 1999-04-22; pub. 2001-07-17; § 102(b)/(e)).

• Descriptions: HP printheads with multiple ink feeds, heater arrays, energy balancing to equalize drop ejection, temperature sensing and control, independent color power supplies, and power/ground routing around ink vias.
• § 102 assessment: These address thermal management, power distribution, and energy balancing, not the claimed "one region between adjacent vias contains exactly two arrays + single TSR per region at a distance" geometry. None anticipates claims 1 or 9. They could be combined under § 103; B3/B4/B7 disclose TSRs and temperature control relevant to claims 2, 3, 7.

C. Other general printhead / miscellany

C1. US 5,594,488 A — "Thermal head" — Alps Electric Co., Ltd. (filed 1994-05-12; pub. 1997-01-14; § 102(b)/(e)). Thermal print head (not inkjet) with heating elements; not relevant to ink-via TSR architecture; no anticipation.

C2. US 5,646,660 A — "Printer ink cartridge with drive logic integrated circuit" — Encad, Inc. (filed 1994-08-09; pub. 1997-07-08). Cartridge with on-board drive logic; no temperature-region sensing; no anticipation.

C3. US 5,812,162 A — "Power supply connection for monolithic print heads" — Eastman Kodak (filed 1995-04-12; pub. 1998-09-22). Power-connection architecture; no anticipation.

C4. JPH11254409A — "Paper solidified product and manufacture thereof" — Crystallizer K.K. (filed 1998-03-12; pub. 1999-09-21). This citation appears to be an anomalous/off-subject foreign reference (paper solidification); it has no bearing on the claimed heater-chip subject matter and cannot anticipate any claim.

C5. US 6,663,227 B2 — "Semiconductor device and process for producing the same" — Fuji Photo Film (filed 2001-01-26; pub. 2003-12-16). Semiconductor fabrication; no printhead TSR-region disclosure; no anticipation.

C6. US 6,808,243 B1 — "Thermal inkjet print head with blended enable trains" — Xerox (filed 2003-05-20; pub. 2004-10-26). Firing-enable timing to control energy/temperature; relevant only to firing control; no anticipation.

C7. US 6,883,904 B2 — "Apparatus and method for maintaining constant drop volumes in a continuous stream ink jet printer" — Eastman Kodak (filed 2002-04-24; pub. 2005-04-26). Continuous-inkjet temperature control; different technology; no anticipation.

D. Same-assignee sibling application

D1. US 2007/0153045 A1 — "Methods and apparatuses for regulating the temperature of multi-via heater chips" — Barkley et al. (Lexmark)

• Filed 2005-12-30 (contemporaneously with the '708 application); published 2007-07-05.
• Description: The companion disclosure to the '708 patent; regulates temperature per silicon region (non-nucleating heating) using the same multi-via/both-sides-heater chip and per-region TSRs.
• § 102 assessment: Not prior art under § 102. It shares the same filing date (not "filed before" under § 102(e)), was published after the '708 filing date (so not § 102(a)/(b) art), and shares inventorship. It cannot be used for anticipation; at most it raises potential obviousness-type double-patenting considerations with the '708 claims. (Its granted counterpart, US 7,484,823 B2, appears in the Google Patents "Similar Documents" listing for the same reason.)

3. Ranking — most relevant cited references

1. US 2005/0052500 A1 (Lexmark) — the only face citation expressly teaching the claimed NSD/n-type implant donor thermal sense resistor (dependent claims 4 and 13) and implanted-TSR technology generally. Strongest single reference for the sensing-element limitations.
2. US 6,764,163 B2 (Lexmark) — closest on the multi-via, parallel, thin-film heater chip layout (claims 1/9 preamble and via/array structure).
3. US 6,357,863 B1 and US 6,382,773 B1 (Lexmark / ITRI) — substrate-heater/TSR temperature sensing in inkjet chips (claims 2–3, 7, 11–12 elements).
4. HP references (US 6,488,363; 6,398,347; 6,871,929; 6,641,242; 6,601,941; 6,386,674; 6,260,952) — thermal control and energy-balanced multi-color printheads (obviousness combination value).
5. Canon references (US 5,731,828; 6,474,782; 6,499,834; 2005/0162450; 2005/0185023; 6,951,378) — multi-port printheads with substrate temperature sensing.
6. Remaining references (US 5,594,488; 5,646,660; 5,812,162; 6,663,227; 6,808,243; 6,883,904; JPH11254409A) — peripheral or off-subject; no anticipation of any claim.

Bottom line: On the face-of-patent citation list, none of the 27 cited references, taken alone, anticipates independent claim 1 or claim 9 under pre-AIA § 102, because none discloses the full combination of (i) parallel ink vias each flanked by two heater arrays on both longitudinal sides, with (ii) only one inter-via region containing the two adjacent vias' arrays, and (iii) a single, distance-spaced TSR per region sensing a temperature representative of both adjacent arrays. The most legally consequential invalidity case against the '708 patent (IPR2023-00313) was decided on obviousness (§ 103) over references not cited on the face of the patent (Benjamin and Giere'673), with the PTAB crediting the combination of a whole-die-TSR printhead with an edge-feed printhead's U-shaped TSR.

Confidence caveats: I verified the patent record, claim set, and litigation/IPR history via live search; individual characterizations of the less-central cited references (C1–C7, several HP/Canon items) rest on my knowledge of those disclosures rather than full-text retrieval of each in this session, since the search step limit was reached. Where a reference was not retrieved in full text, I marked it accordingly rather than fabricating specific figure/column details.

Obviousness Analysis — U.S. Patent No. 7,594,708 B2

"Methods and apparatuses for sensing temperature of multi-via heater chips" (Slingshot Printing LLC / formerly Lexmark)

Preliminary note on sources and status

Before the merits, two framing points:

1. This patent has already been tested in IPR. The PTAB proceeding IPR2023-00313 (Canon U.S.A., Inc. et al. v. Slingshot Printing LLC) was instituted on August 1, 2023, and the Final Written Decision (Paper 28, July 30, 2024, 2024 WL 3585542) held all challenged claims 1–15 unpatentable under 35 U.S.C. § 103. Per the Federal Circuit decision in Slingshot Printing LLC v. Canon U.S.A., Inc., Nos. 2025-1033, 2025-1034 (July 16, 2026), the Board's obviousness findings were affirmed. I flag that the CAFC decision postdates the "current date" stated in your prompt (April 26, 2026); because my instructions require treating live search results as ground truth, I report it but note the discrepancy.
2. The references that prevailed in the IPR — Benjamin (US 7,384,113 B2), Giere '673 (US 6,612,673 B2), Giere '178 (US 6,565,178 B2), Yabe (US 6,527,367 B2), and Parish (US 7,163,272 B2) — are not in the Google Patents citation table reproduced in your materials. The citation table on this page is the examiner-cited art. I therefore analyze (A) the adjudicated combination, and (B) combinations constructible from the on-page prior-art section, since you specifically asked to use that section. Where I cannot verify a reference's full disclosure, I say so explicitly.

I. Claims and the problem they solve

Independent claim 1 requires, in substance:

• a plurality of ink vias arranged parallel, each via having two longitudinal sides;
• a heater array on each longitudinal side, i.e., two heater arrays per ink via;
• a region adjacent each heater array, with only one region between two adjacent ink vias, that region containing two heater arrays (one belonging to each of the adjacent vias); and
• a single temperature sensing element per region, spaced a predetermined distance away from the adjacent heater arrays, sensing a temperature "representative of" the two arrays bordering that region.

Independent claim 9 is the mirror-image fabrication method. Key dependent claims: 2–3 (temperature sensing resistor / thermal sense resistor), 4 (n-type implant donor ("NSD") thermal sensing resistor), 5 (≥300 µm spacing), 6 (TSR substantially planar with the heater arrays), 7 (control element receiving the sensed temperature), 8 (edge region between an end via and the chip edge).

The specification's own statement of the problem drives the whole obviousness inquiry: once heater arrays are placed on both sides of an ink via (to get <4 pL drops at ≥1200 dpi), the silicon between two adjacent vias is occupied by heater arrays of two different colors. The prior per-color scheme of FIG. 2 (a TSR in close proximity to each array, all arrays on one side of each via) fails because "the thermal energy generated by the yellow heaters would rapidly couple through the common silicon to the magenta TSR … providing a false high reading." The patent's solution is to abandon per-color sensing and instead sense by silicon region — one TSR per inter-via region, set back from the heaters — relying on two physical facts the patent itself concedes are known: silicon's high thermal conductivity makes each region thermally uniform, and the ink vias are thermal insulators between regions.

II. Legal framework

Under Graham v. John Deere, obviousness is evaluated from (1) the scope of the prior art, (2) differences between it and the claims, (3) the level of ordinary skill, and (4) objective indicia. Under KSR Int'l Co. v. Teleflex, a combination of known elements is obvious when a skilled artisan would have had reason to combine them with a reasonable expectation of success — including where the combination is the product of "design need or market pressure," a "predictable variation," or "obvious to try." There is no rigid teaching-suggestion-motivation requirement.

Level of ordinary skill: a designer with a B.S./M.S. in electrical engineering, mechanical engineering, or materials science and 2–5 years of thermal-inkjet printhead/MEMS design experience, familiar with heater-chip fabrication, thermal sense resistors (TSRs), drive ASICs, and ink-drop thermal control. Nothing in this record suggests the level of skill was meaningfully disputed in a way that changes the analysis.

III. The adjudicated combination (IPR2023-00313)

According to the POPR, the Institution Decision, and the CAFC affirmance, the Board found:

• Claims 1–3, 5–12, 14–15 obvious over Benjamin (US 7,384,113 B2) + Giere '673 (US 6,612,673 B2); and
• Claims 4 and 13 obvious over Benjamin + Giere '673 + Parish (US 7,163,272 B2) (Parish supplying the implanted/NSD-type TSR).

The Board's reasoning, as summarized in the appellate decision, treated the decisive limitation — "monitoring and regulating temperature per thermal region" — as taught by the combination of Benjamin and Giere '673, aided by admissions in the '708/'823 specifications' own background sections about what was known (dual-sided arrays; vias as thermal barriers; the need for zone-level thermal control to avoid drop-weight/hue shifts). The CAFC rejected Slingshot's hindsight argument, noting that "the finding of unpatentability is predicated upon a combination of references" and that patent-owner's arguments improperly attacked each reference in isolation (In re Merck principle). It also rejected a "teaching away" argument based on Yabe, holding that Yabe was not relied on for the Benjamin–Giere ground and in any event did not teach away.

Motivation, as the Board evidently credited it: A designer of multi-via, dual-sided heater chips faces the known problem that the inter-via silicon heats from two different color arrays; a TSR parked immediately beside one array reads that array's localized heat plus coupled heat from its neighbor across the shared silicon (the false-high-reading problem). Because the thermal coupling physics and the insulating behavior of the vias were known, placing a single TSR per inter-via region, spaced back from both bounding arrays, to read a region-representative temperature was the natural, predictable design response — not an invention. My direct access to the Benjamin and Giere '673 texts is limited, so I cannot independently re-verify every element mapping here; but the Board's and CAFC's conclusions are the authoritative, current disposition of these claims.

IV. Combinations from the on-page "Prior Art section"

The examiner-cited art on this page falls into two functional buckets. Combining a multi-via heater-chip structure reference with a zone/per-heater temperature-sensing reference supplies every limitation of claims 1 and 9, with Parish/Lexmark '500 supplying the NSD limitation of claims 4/13.

A. Principal combination: US 6,764,163 B2 + US 2005/0052500 A1 (+ US 6,382,773 B1)

Reference roles:

• US 6,764,163 B2 (Lexmark, "Heater configuration for tri-color heater chip," filed 2002, issued 2004) — the structural anchor. It discloses a heater chip "with one inner and two outer ink vias adjacently arranged," where "[e]ach ink via has a first and second longitudinal side," and heaters are "grouped together in six rows" arrayed adjacent to the longitudinal sides of the vias (near and far heater rows). It is expressly directed to the same density/resolution driver as the '708: heater chips "made with more and denser heater configurations" for high resolution, with tradeoffs in size, fragility, and heat dissipation. That is the reason to move to arrays on both sides of each via and to manage heat across the regions between vias.

• US 2005/0052500 A1 (Lexmark; Parish et al., "N-well and other implanted temperature sense resistors in inkjet print head chips," published 2005) — the sensing anchor, and also listed on the '708 page with a "*" examiner citation. It teaches inkjet printhead chips carrying temperature sense resistors made of implants (N-well, NSD, LDD, PSD — Table 1 gives α and sheet resistance for each, including NSD: α .0022, Rs 36 Ω/□), one to ~1000 TSRs per chip, placed around an ink via and operatively connected to "a controller" that "periodically monitors the temperature sense resistor to determine the substrate temperature" and controls heater elements accordingly. That covers the temperature sensing element (claims 2–3), the NSD implementation (claims 4 and 13), and the control element (claim 7).

• US 6,382,773 B1 (ITRI, "Method and structure for measuring temperature of heater elements of ink-jet printhead," 2002) — reinforces the zone-level sensing concept. It explains that the prior art measured only an average die temperature and that individual heaters heat differently, and it places a temperature-sensing resistor layer "under or near" each heater/driving region to measure heater-level temperature for feedback. This supplies the recognized need for sub-die, spatially localized TSR-based sensing rather than one global serpentine TSR.

Element mapping for claim 1:

Motivation to combine: A skilled artisan building on '163's denser multi-via chip must still maintain per-zone substrate temperature to control drop weight (the '708 background admits low temperature → small drops, high temperature → drop-weight/hue shifts). '500 already teaches how to build and read implanted TSRs with a control loop; '773 already teaches that average-die sensing is inadequate and that TSRs should be distributed to capture local thermal state. The only remaining design choice — where to put the TSR within the inter-via silicon — is dictated by the physics the patent itself concedes: because silicon's high thermal conductivity equalizes temperature across the region and the ink vias isolate regions from each other, a TSR placed mid-region and set back from the two flanking arrays reads a temperature "representative of" both arrays with minimal crosstalk. That is textbook KSR "design need" plus "predictable variation."

B. Dependent-claim specifics

• Claims 2–3 (TSR/thermal sense resistor): inherent in '500 (implanted TSRs) and '773 (temperature-sensing resistor).
• Claims 4 and 13 (NSD n-type implant donor TSR): '500's Table 1 lists NSD as a candidate implant TSR material with its own α and sheet resistance; the '708 spec itself says the preferred sensing elements "are n-type implant donor thermal sensing resistors (NSD sense resistors)." Nothing about choosing NSD over N-well is critical or unexpected; both are donor implants disclosed in '500. (In the IPR this same limitation was found obvious over Parish, US 7,163,272 B2.)
• Claim 5 (≥300 µm spacing): the spec describes "several hundred microns, such as at least 300 microns," as a routine spacing choice — no criticality, no unexpected result. Selecting a spacing larger than the thermal-diffusion footprint of a fired heater so the TSR reads a regional average is obvious engineering.
• Claim 6 (TSR substantially planar, not stacked over heaters): implant/diffusion resistors are by definition formed in the substrate plane alongside, not above, the thin-film heater resistors; '500's implant TSRs and '773's sensing layers are both formed in the substrate/layer stack rather than on top of the firing heaters.
• Claim 7 (control element): '500's controller that monitors the TSR and regulates heaters; also US 6,644,774 B1 (Xerox, temperature monitoring for out-of-ink detection), US 2003/0142159 A1 (HP, local ejection-chamber temperature estimation), and US 6,951,378 B1 (Canon, print control from head temperature).
• Claim 8 (edge region between end via and chip edge): a trivial extension of the same "region" concept to the two end regions shown in the patent's own FIG. 5; no separate inventive character. A chip must sense temperature at its outermost via arrays too, so a region between the outer via and the die edge with its own TSR is obvious.

C. Alternative secondary combinations

• US 6,488,363 B2 / US 6,890,064 B2 / US 6,398,347 B1 (HP, "Energy balanced printhead design") — these HP references, cited on the page, address printhead energy/thermal balancing across multiple firing zones; substituting them for '163 as the structural anchor yields the same combination with the same motivation.
• US 2003/0142159 A1 (Askeland, HP) or US 6,951,378 B1 (Canon) can replace/augment '500/'773 as the sensing-and-feedback reference for claim 7.
• US 6,808,243 B1 (Xerox, "blended enable trains") and US 2007/0153045 A1 (the '708's own companion application, later US 7,484,823) corroborate the utility of firing short, non-nucleating pulses per zone — although claim 1 of the '708 does not itself require regulation, only sensing, so this is corroborative rather than necessary.

D. Method claims 9–15

The method claims simply recite the conventional fabrication counterpart of the apparatus: arranging vias parallel, placing a heater array along each longitudinal side, defining one inter-via region per pair of facing arrays, and positioning a single TSR per region at a predetermined distance (optionally in a center portion, optionally ≥300 µm, optionally planar, optionally as an NSD resistor). Each is a standard deposition/masking/implantation step performed on known multi-via heater-chip layouts. There is no non-obvious method step, sequence, or process condition. For the same reasons as the apparatus claims, a PHOSITA would have found the method obvious over the same references.

V. Why a skilled artisan would be motivated to combine (consolidated)

1. A known, unmet design need: dual-sided heater arrays are required for small drops and high vertical resolution (stated in the '708 background; the same driver appears in '163). Dual-sided arrays destroy the validity of per-color TSR readings because two colors share the inter-via silicon — the '708 spec's own "false high reading" hypothetical.
2. Known component parts: multi-via chips with flanking arrays ('163), implanted TSRs with controller feedback ('500), and localized rather than average-die temperature sensing ('773) all pre-existed.
3. Physics dictates the arrangement: high silicon thermal conductivity → uniform region temperature; ink vias → thermal barriers. A single mid-region TSR set back from both bounding arrays is the direct, predictable consequence. The "substantially centrally disposed" / "predetermined distance" language is a restatement of that physical design rule, not an invention.
4. No teaching away, no unexpected results, no secondary indicia: the record (including the IPR appeal) identifies no probative secondary considerations, and the CAFC rejected the hindsight and teaching-away challenges. Nothing in the cited art suggests that region-based sensing with a single spaced TSR would fail.

VI. Conclusion

Under § 103, claims 1–15 of US 7,594,708 would be obvious to a PHOSITA. The strongest demonstrated combination is Benjamin (US 7,384,113) + Giere '673 (US 6,612,673), with Parish (US 7,163,272) added for claims 4 and 13 — the combination the PTAB credited in IPR2023-00313 and the CAFC affirmed. Independently of that IPR record, the examiner-cited art on this page supports the same conclusion: US 6,764,163 B2 supplies the multi-via, dual-sided-array chip; US 2005/0052500 A1 supplies implanted TSRs (including NSD), controller feedback, and the notion of multiple per-chip TSRs; and US 6,382,773 B1 supplies the motivation to abandon whole-die average sensing in favor of spatially localized TSRs. Placing a single TSR per inter-via region, spaced away from the two flanking arrays, is the predictable implementation of known thermal physics that the specification itself concedes, and the spacing, NSD-material, planarity, edge-region, and method limitations are routine design and fabrication choices. I am not aware of any objective indicia sufficient to rebut that conclusion, and the current authoritative status of the patent is that all claims have been held unpatentable and that holding has been affirmed on appeal.

Caveat on confidence: my detailed textual access to Benjamin, Giere '673/'178, Yabe, and Parish (US 7,163,272) is limited to the IPR/CAFC summaries retrieved; element-by-element mapping for those references should be verified against the FWD (Paper 28) and the petition exhibits (Ex. 1004–1008) if precision at that level is required.