Reworkable IC Assembly via Interposer and Selective Underfill
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Solution Overview
Problem
The existing flip chip packaging technology faces challenges in reworkability due to the coefficient of thermal expansion mismatch between integrated circuit chips and substrates, which prevents the removal or reworking of integrated circuit chips, especially in multichip packaging, as conventional underfill adhesives inhibit the ability to rework or clean individual contacts.
Innovation Solution
An interposer substrate assembly is introduced, where the interposer has a thermal expansion coefficient matching the integrated circuit chip, reducing strain on electrical contacts and allowing for reworkability by using an adhesive material between the interposer and substrate while eliminating adhesive between the interposer and chip, utilizing low-melt electrical contacts for easy removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If underfill adhesive is used to reduce strain on electrical contacts due to CTE mismatch, then reliability of electrical contacts is improved, but reworkability of integrated circuit chip is significantly inhibited
Solution Approach 1:
The patent divides the bonding structure into two segments: the integrated circuit chip bonds directly to the substrate without underfill adhesive, while a separate underfill adhesive layer is applied only between the substrate and the surrounding support structure. This segmentation allows the electrical contacts to be free of adhesive interference for reworkability, while still providing strain relief through the peripheral underfill.
Solution Approach 2:
The underfill adhesive is extracted from the critical bonding interface between the chip and substrate, and relocated to only the peripheral support structure. This extraction removes the harmful effect of adhesive on reworkability while preserving the beneficial strain-relief function in non-critical areas.
2Stress or pressure
If underfill adhesive is used to address coefficient of thermal expansion mismatch, then strain on electrical contacts is reduced, but ability to remove or clean individual contacts is significantly inhibited
Solution Approach 1:
The underfill adhesive is applied with local quality differentiation: it is present in the peripheral support structure where strain relief is needed, but deliberately absent from the central area where electrical contacts are located. This localized application allows contact removal and cleaning operations to proceed freely while maintaining strain relief where required.
3Stress or pressure
If adhesive material is used to bond interposer to substrate, then strain on first plurality of electrical contacts is reduced, but reworkability of integrated circuit chip assembly is inhibited
Solution Approach 1:
The patent introduces an interposer as an intermediary component between the integrated circuit chip and the substrate. The underfill adhesive bonds the interposer to the substrate, creating a compliant intermediate structure that absorbs thermal expansion strain. The chip itself remains adhesive-free, allowing reworkability while the interposer mediates the strain through its adhesive-bonded connection to the substrate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables commercially viable, reworkable electronic device assemblies with reduced thermal and mechanical stresses, allowing for the removal and replacement of defective chips without affecting the underlying interposer substrate assembly, thereby enhancing the financial profitability of packaging.
Implementation Method 1
The adhesive material bonds the interposer to the substrate and reduces strain on the first plurality of electrical contacts resulting from the coefficient of thermal expansion mismatch between the first and second materials
Implementation Method 2
there is a coefficient of thermal expansion mismatch between the integrated circuit chip and substrate... the interposer includes a second material having a second thermal expansivity. The second thermal expansivity is different from the first thermal expansivity
Data Source
AI summary
An electronic device assembly is provided which includes a substrate, an interposer and an integrated circuit chip. The substrate is fabricated of a first material having a first thermal expansivity, and the interposer and integrated circuit chip are fabricated of a second material having a second thermal expansivity. The second thermal expansivity is different from the first thermal expansivity so that there is a coefficient of thermal expansion mismatch between the substrate and the interposer or chip. The interposer is coupled to the substrate via a first plurality of electrical contacts and an underfill adhesive at least partially surrounding the electrical contacts to bond the interposer to the substrate and thereby reduce strain on the first plurality of electrical contacts. The integrated circuit chip is coupled to the interposer via a second plurality of electrical contacts only, without use of an adhesive surrounding the second plurality of electrical contacts.