Multichip Module Adhesive Bonding for Cryogenic Thermal Cycling
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing multichip module fabrication techniques for superconducting circuits face issues with thermal cycling, vibration tolerance, and adhesion reliability due to differential thermal expansion and the use of temperature-sensitive materials, leading to bond failures and reduced functionality.
Innovation Solution
A non-conductive adhesive with matched thermal expansion coefficients for silicon wafers is used to bond chips to substrates, eliminating the need for solder reflow and providing a reworkable bond, enhancing mechanical stability and electrical conductivity across a broad temperature range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder reflow bonding is used to attach wafers to substrates, then electrical and mechanical bonding is achieved, but temperature-sensitive electronics are damaged due to heating above reflow temperature
Solution Approach 1:
The patent changes the bonding mechanism from thermal solder reflow to cold adhesive bonding. Instead of heating above solder reflow temperature, a non-conductive adhesive is applied at room temperature or cryogenic temperatures to bond the wafer to the substrate. This parameter change in bonding temperature protects temperature-sensitive superconducting electronics while achieving reliable mechanical and electrical attachment through the adhesive material.
Solution Approach 2:
The patent replaces the thermal-mechanical solder reflow process with a chemical-mechanical adhesive bonding process. The solder reflow process relies on thermal energy to melt and reflow solder material, while the adhesive process uses chemical bonding at lower temperatures. This substitution eliminates the harmful thermal effects while maintaining the mechanical bonding function.
2Temperature
If filler material is added between wafer and substrate before reflow, then thermal conductivity is enhanced, but reflow process is impaired
Solution Approach 1:
The patent extracts the filler material from the pre-reflow stage and applies it after the bonding process. Instead of placing filler between wafer and substrate before solder reflow (which interferes with the reflow process), the non-conductive adhesive is applied as the bonding medium itself without requiring subsequent reflow heating. This eliminates the conflict between filler presence and reflow processing while still achieving the thermal conductivity enhancement.
3Strength
If wafer and substrate have mismatched thermal coefficients of expansion, then bonding is achieved, but thermal cycling causes bond failures
Solution Approach 1:
The patent introduces a non-conductive adhesive as an intermediary material between the wafer and substrate. This adhesive layer acts as a compliant intermediate that can accommodate differential thermal expansion between the wafer and substrate during thermal cycling. The adhesive's mechanical properties allow it to absorb the stress from CTE mismatch, preventing bond failures while maintaining reliable electrical and mechanical connection.
4Productivity
If multiple wafers are used to achieve complex functionality, then functional density increases, but mechanical stability and alignment under vibration deteriorate
Solution Approach 1:
The patent merges multiple wafers into a single multichip module assembly bonded to a common substrate using the non-conductive adhesive. This unified structure provides mechanical stability and maintains alignment between multiple wafers under vibration and thermal cycling. The adhesive bonding creates a rigid yet compliant connection that preserves the mechanical integrity of the multi-wafer assembly, enabling high functional density without sacrificing stability.
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 method improves the mechanical stability and reliability of multichip modules under thermal cycling and vibration, maintaining electrical conductivity from room temperature to cryogenic temperatures, and allows for reworkability, increasing yield and package density.
Implementation Method 1
A non-conductive adhesive with matched thermal expansion coefficients for silicon wafers is used to bond chips to substrates
Implementation Method 2
A non-conductive adhesive with matched thermal expansion coefficients for silicon wafers is used to bond chips to substrates
Implementation Method 3
compressing the chip and substrate to displace the liquid curable adhesive between the contacts and form electrical pathways
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.