PTAB

IPR2017-01649

Broadcom Corp v. Tessera Inc

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Key Events
Petition
petition

1. Case Identification

2. Patent Overview

  • Title: Methods of Encapsulating a Semiconductor Chip Using a Settable Encapsulant
  • Brief Description: The ’605 patent describes methods for encapsulating a semiconductor chip package. The process involves placing a chip on a dielectric layer into a mold and injecting a thixotropic composition that becomes less viscous under shear to fill the space, then regains viscosity to prevent leakage when the mold is removed.

3. Grounds for Unpatentability

Ground 1: Obviousness over Kovac and Wang - Claims 1-3 are obvious over Kovac in view of Wang, as evidenced by DiStefano.

  • Prior Art Relied Upon: Kovac (International Publication No. WO 96/09746), Wang (Patent 5,817,545), and DiStefano (Patent 5,455,390).
  • Core Argument for this Ground:
    • Prior Art Mapping: Petitioner argued that the combination of Kovac and Wang disclosed all limitations of the challenged claims. Kovac taught a method for making a chip-size package by disposing a "compliant thixotropic material" between a semiconductor chip and a substrate. Petitioner contended that Kovac’s suggestion to "close the edges of the assembly" to trap this filler material would have led a person of ordinary skill in the art (POSITA) to use a known molding process for underfill encapsulation, as explicitly taught by Wang.
      • For independent claim 1, Kovac disclosed providing a dielectric layer with a microelectronic element and using a "thixotropic material" as an encapsulant. Wang taught placing such an assembly into a mold and "sealingly engaging" the mold against the substrate to prevent leakage during encapsulation. Petitioner asserted that injecting Kovac's thixotropic material using Wang's pressure-based molding process would inherently apply a shearing force, reducing the material's viscosity as required by the claim. Kovac disclosed disposing the material to fill the area between the chip and substrate and subsequently curing it. Petitioner argued that the claimed steps of waiting for the composition to regain viscosity and removing the assembly from the mold before final curing were obvious modifications taught by Wang to improve manufacturing efficiency and throughput.
      • For dependent claim 2, Kovac was alleged to explicitly teach that its dielectric layer is "flexible."
      • For dependent claim 3, Kovac disclosed that its flexible layer is preferably made from "Kapton." DiStefano was cited as evidence that a POSITA would have known that Kapton is a polyimide material.
    • Motivation to Combine: Petitioner argued a POSITA would combine Kovac and Wang to implement Kovac's general suggestion of "closing the edges" of the assembly. Wang provided a specific, well-known molding technique suitable for the type of underfill encapsulation described in Kovac. The motivation was to achieve predictable and improved results, such as preventing encapsulant leakage, controlling the final fillet shape, and enabling the use of a vacuum to eliminate voids—a problem addressed by both references. Applying Wang's established molding process to Kovac's package was presented as a straightforward application of a known technique to solve a known problem.
    • Expectation of Success: A POSITA would have had a reasonable expectation of success in combining the references. The combination involved applying a standard underfill molding process (Wang) to a conventional semiconductor package (Kovac) using compatible materials. The result—an encapsulated chip with a controlled fillet shape—was predictable and desirable.

4. Key Claim Construction Positions

  • Petitioner dedicated significant argument to the construction of "a thixotropic composition" as used in all claims. While not conceding the term was definite, Petitioner proposed for purposes of the inter partes review (IPR) that the term should be construed based on the patent’s specification and examples. The proposed construction was: "a material with a high initial viscosity at 25°C (i.e., room temperature), and sufficient pseudoplastic properties when sheared to lower its viscosity enough to completely fill the area between the at least one microelectronic element and the dielectric layer, and which must regain viscosity approximating its initial viscosity when the shear force is removed so as to prevent any visible flow." This construction was central to Petitioner's argument that Kovac's "compliant thixotropic material" met the claim limitation, as it was described as being "sufficiently thixotropic" to prevent flow-out.

5. Relief Requested

  • Petitioner requested institution of an IPR and cancellation of claims 1-3 of the ’605 patent as unpatentable under 35 U.S.C. §103.