Coated Copper Foil Interlayer for Low-Temperature Sintered Bonding
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Solution Overview
Problem
Existing interconnect materials for high-temperature applications in power semiconductor devices face challenges such as high cost, low electromigration resistance, and thermo-mechanical instability, while alternatives like silver sintering have drawbacks like high cost and susceptibility to oxidation.
Innovation Solution
A coated metal foil comprising copper or copper alloy with internal pores and an organic binder is used to form a copper-containing interlayer, enabling sintering with low temperature and pressure, and providing high thermal and electrical conductivity with improved thermo-mechanical fatigue resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper is used as interconnect material, then cost is reduced and electrical/thermal conductivity is improved, but oxidation resistance deteriorates
Solution Approach 1:
An organic binder coating is applied to the copper flake surfaces to serve as a protective intermediary layer that prevents oxidation while allowing the copper to maintain its excellent electrical and thermal conductivity properties
Solution Approach 2:
The invention creates a composite structure combining copper flakes with an organic binder coating, where the copper provides electrical and thermal conductivity while the organic coating provides oxidation resistance
2Temperature
If silver sintering is used, then bonding temperature is reduced, but cost increases and electromigration resistance deteriorates
Solution Approach 1:
The invention modifies the bonding process parameters by using a two-stage approach: initial bonding at reduced temperature followed by heat treatment at higher temperature, which enables copper-based materials to achieve both low bonding temperature benefits and high temperature stability with improved electromigration resistance
3Temperature
If TLP bonding is used, then high-temperature bonding is achieved, but thermo-mechanical fracture resistance deteriorates due to brittle IMC microstructure
Solution Approach 1:
By implementing a two-stage thermal process with controlled temperature progression and holding times, the invention transforms the microstructure from brittle intermetallic compounds to a more ductile copper-rich structure that maintains high-temperature capability while improving fracture resistance
Solution Approach 2:
The heat treatment process induces phase transitions in the bonded joint, transforming the microstructure from brittle intermetallic phases to more ductile copper-rich phases that better resist thermo-mechanical fracture
4Ease of manufacture
If copper flakes with organic binder are used, then sintering temperature and pressure are reduced, but oxidation resistance during processing deteriorates
Solution Approach 1:
The organic binder coating serves as a dual-function intermediary that facilitates low-temperature sintering while simultaneously protecting the copper flakes from oxidation during the sintering process
Solution Approach 2:
The organic binder coating provides self-protection against oxidation during sintering, eliminating the need for additional protective atmospheres or complex processing equipment
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 coated metal foil allows for efficient bonding with short sintering times, low residual organics, and enhanced mechanical and thermal integrity, addressing the limitations of existing interconnect materials.
Implementation Method 1
The use of PEG600 in the paste formulations was reported to enable the in situ reduction of Cu oxides during sintering
Implementation Method 2
During sintering, it is possible to realize a connection, which consists of one metal throughout
Implementation Method 3
Besides the high thermal conductivity of the material
Implementation Method 4
nearly the same electrical and thermal conductivities
Data Source
AI summary
A coated metal foil for forming a copper-containing interlayer between a first solid substrate and a second solid substrate or between a solid substrate. The coated metal foil includes a metal foil of copper or of a first copper alloy or of a copper plated nickel-iron alloy. The metal foil has a first surface and a second surface. The metal foil has a composition coated on the first surface and/or the second surface of the metal foil. The composition includes an organic binder and flakes of copper or the first or a second copper alloy. The flakes include internal pores.