Superconducting Circuit Contacts With Cryogenic Adhesive Bonding
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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 use of temperature-sensitive materials, 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, which enhances mechanical stability and reliability under cryogenic conditions.
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 deteriorates
Solution Approach 1:
The patent changes the bonding temperature parameter from high (solder reflow above 200°C) to low (adhesive bonding below 100°C), enabling temperature-sensitive superconducting electronics to survive the bonding process while achieving reliable mechanical and electrical attachment that withstands thermal cycling
Solution Approach 2:
The patent introduces an adhesive layer as an intermediary bonding material between the wafer and substrate, replacing the direct solder bonding approach. This adhesive mediator enables reliable bonding at lower temperatures and provides damping that improves thermal cycling reliability
2Strength
If low melting temperature alloy is used for bonding, then electrical and mechanical connection is achieved, but adhesion reliability deteriorates due to differential thermal expansion
Solution Approach 1:
The patent uses a composite adhesive material that combines polymer matrix with filler particles, creating a material with tailored properties including reduced thermal expansion and improved adhesion. This composite structure resolves the conflict between maintaining electrical connection and achieving adhesion reliability under thermal stress
Solution Approach 2:
The patent explicitly addresses thermal expansion by selecting adhesive materials with coefficient of thermal expansion (CTE) matched to the superconducting wafer and substrate. This CTE matching prevents differential expansion stresses that would cause adhesion failure during thermal cycling, while maintaining reliable electrical connection
3Ease of manufacture
If no filler material is used between wafer and substrate, then reflow process is simplified, but thermal conductivity deteriorates
Solution Approach 1:
The patent merges the bonding and thermal management functions into a single adhesive layer. The adhesive simultaneously provides mechanical bonding, thermal conduction, and electrical insulation where needed, eliminating the need for separate filler materials and simplifying the manufacturing process while maintaining excellent thermal conductivity
4Ease of repair
If adhesive bonding is used instead of solder reflow, then reworkability is improved, but manufacturing precision may deteriorate
Solution Approach 1:
The patent uses a two-stage bonding approach: first, temporary alignment fixtures provide precise positioning during assembly; second, the adhesive provides permanent bonding after alignment is achieved. This dynamic process enables both high manufacturing precision during assembly and reworkability afterward, as the adhesive bond can be reversed if needed
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, allowing for high-speed data transmission and increased yield by maintaining electrical conductivity across a broad temperature range, including cryogenic temperatures, and enabling reworkability.
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
A non-conductive adhesive with matched thermal expansion coefficients between the chip and substrate is used to bond wafers
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.