Aluminum-Copper Clad Power Module for SiC Reliability
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Solution Overview
Problem
Power modules handling high voltages and currents face challenges with aluminum wire bonding due to thermal stress and reliability issues, especially with silicon carbide semiconductors, as copper wire bonding is difficult and prone to damage and thermal stress at high temperatures.
Innovation Solution
A power module design using an aluminum-copper clad metal laminate sheet with intermetallic compounds formed between the aluminum and copper layers, where the aluminum layer is bonded to the semiconductor chip and the copper layer to the substrate, reducing thermal stress and preventing embrittlement and crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper wires are used for bonding to achieve higher current-carrying capacity and compactness, then the current-carrying capacity is improved, but the wire bonding process becomes difficult and may cause damage to the surface electrode due to copper's hardness
Solution Approach 1:
An aluminum foil is placed on the surface of the power semiconductor chip as an intermediary layer. The soft aluminum foil facilitates easy wire bonding with copper wires, while the copper wire provides high current-carrying capacity. The aluminum foil acts as a mediator that enables the bonding process without direct contact between hard copper wires and the fragile surface electrode.
Solution Approach 2:
The solution combines aluminum and copper materials in a layered structure. The aluminum layer provides deformability for bonding, while the copper wire provides high current-carrying capacity. This composite approach leverages the complementary properties of both materials to resolve the contradiction between bonding ease and current capacity.
2Volume of moving object
If copper wire bonding is performed directly to achieve compactness, then the device size is reduced, but thermal stress at the bonded interface becomes large at high operating temperatures above 250°C
Solution Approach 1:
The solution changes the material parameter (thermal expansion coefficient) by introducing an aluminum layer between the chip and copper wire. Aluminum has a thermal expansion coefficient closer to that of silicon carbide chips, reducing thermal stress during temperature cycling. This parameter change maintains compactness while improving reliability at high temperatures.
3Ease of manufacture
If aluminum foil is placed on the chip surface to prevent bonding damage, then the bonding process becomes easier, but grain boundaries become apparent above 175°C due to recrystallization leading to fracture risk
Solution Approach 1:
A buffer plate with thermal expansion coefficient matching the semiconductor chip is introduced as an intermediary between the aluminum foil and the chip. This buffer plate prevents direct thermal stress transmission to the aluminum, avoiding grain boundary fracture at high temperatures while maintaining the bonding benefits of aluminum foil.
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 design enhances the reliability of power modules by reducing thermal stress and preventing damage during wire bonding, maintaining the aluminum layer's lower recrystallization temperature and thermal resistance, and suppressing intermetallic compound formation, ensuring stable operation and extended lifespan.
Implementation Method 1
intermetallic compounds having a thickness of 5 μm to 100 μm are formed between the two layers of the metal laminate sheet
Data Source
AI summary
A power module is fabricated, employing a clad metal that is formed by pressure-laminating aluminum and copper, in such a manner that the aluminum layer of the clad metal is bonded such as by ultrasonic bonding to the surface electrode of the power semiconductor chip and a wire is bonded to the copper layer thereof to establish electrical circuit. The clad metal is thermally treated in advance at a temperature higher than the operating temperature of the power semiconductor chip to sufficiently form intermetallic compounds at the interface between the aluminum layer and the copper layer for the intermetallic compounds so as not to grow in thickness after the bonding processes.