Superconductive Multi-Chip Module Bonding for Cryogenic Reliability
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Solution Overview
Problem
Existing multichip module fabrication techniques for superconducting circuits face challenges with thermal cycling, vibration tolerance, and adhesion issues due to differential thermal expansion and the fragility of temperature-sensitive components, leading to unreliable bonds and mechanical instability.
Innovation Solution
A non-conductive adhesive with matched thermal expansion coefficients between the chip and substrate is used to bond wafers, eliminating the need for solder reflow and providing a reworkable bond, ensuring mechanical stability and electrical conductivity across a broad temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder reflow is used to bond wafers to substrate, then electrical and mechanical bonding is achieved, but temperature-sensitive electronics are damaged and thermal cycling reliability is poor
Solution Approach 1:
The patent changes the bonding temperature parameter from high (solder reflow above melting point) to low (adhesive bonding below 100°C), protecting temperature-sensitive superconducting electronics while achieving reliable mechanical and electrical bonding through adhesive materials with matched thermal expansion coefficients
Solution Approach 2:
The patent introduces an adhesive layer as an intermediary bonding material between the wafer and substrate, replacing direct solder bonding. This adhesive mediator enables mechanical and electrical connection without exposing electronics to high temperatures, and its thermal expansion is matched to both bonding surfaces to ensure thermal cycling reliability
2Temperature
If filler material is added between wafer and substrate to enhance thermal conductivity, then heat dissipation is improved, but the reflow process is impaired and bonding reliability decreases
Solution Approach 1:
The patent extracts and eliminates the filler material from the bonding interface, demonstrating that it is not needed when adhesive bonding is used instead of solder reflow. The adhesive itself provides adequate thermal management without interfering with the bonding process or causing reliability issues
Solution Approach 2:
The patent converts the potential harm of poor thermal conductivity without filler into a benefit by using the adhesive material itself as the thermal management solution, achieving adequate heat dissipation while maintaining bonding integrity and avoiding the harmful effects of filler materials during the bonding process
3Adaptability or versatility
If multiple wafers are used to achieve complex functionality, then functional density increases, but mechanical stability and alignment precision decrease
Solution Approach 1:
The patent divides the complex functionality into multiple separate wafers that are bonded to a common substrate, allowing each wafer to be optimized for its specific function while the substrate provides mechanical stability and precise alignment through adhesive bonding with matched thermal expansion
Solution Approach 2:
The patent uses composite adhesive materials with specifically matched thermal expansion coefficients to bond multiple wafers to the substrate, creating a composite structure that maintains mechanical stability and alignment precision across the multi-wafer assembly during thermal cycling
4Ease of manufacture
If standard adhesive bonding is used without thermal expansion matching, then manufacturing is simplified, but thermal cycling causes delamination and bond failure
Solution Approach 1:
The patent changes the thermal expansion parameter of the adhesive material to match both the wafer and substrate, creating a thermally matched bonding system that prevents delamination and bond failure during thermal cycling while maintaining ease of manufacture through adhesive bonding processes
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
The adhesive bonding technique enhances the mechanical stability and reliability of multichip modules under thermal cycling and vibration, maintaining electrical conductivity from room temperature to cryogenic conditions, and allows for reworkability, improving yield and reducing the risk of bond failure.
Implementation Method 1
A non-conductive adhesive with matched thermal expansion coefficients between the chip and substrate is used to bond wafers
Implementation Method 2
corresponding sets of predefined electrical contacts are maintained in relative compression by a cured adhesive
Data Source
AI summary
A method for electrically interconnecting two substrates, each having a corresponding set of preformed electrical contacts, the substrates comprising an electronic circuit, and the resulting module, is provided. A liquid curable adhesive is provided over the set of contacts of a first substrate, and the set of electrical contacts of the second substrate is aligned with the set of electrical contacts of the first substrate. The sets of electrical contacts of the first and second substrate are compressed to displace the liquid curable adhesive from the inter-contact region, and provide electrical communication between the respective sets of electrical contacts. The liquid curable adhesive is then cured to form a solid matrix which maintains a relative compression between the respective sets of electrical contacts. One embodiment of the module comprises a high-speed superconducting circuit which operates at cryogenic temperatures.