Sn Alloy Intermetallic Layer for Power Module Solder Durability
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Solution Overview
Problem
Power modules with solder layers bonded to circuit layers composed of aluminum or copper alloys experience cracking and increased thermal resistance when subjected to power cycles, leading to reliability issues, especially in high-power applications like wind power generators and electric vehicles.
Innovation Solution
A power module configuration where a Sn alloy layer with a specific composition of Ni and Cu (0.5% to 10% Ni and 30% to 40% Cu) is formed at the interface between the solder and circuit layers, enhancing the durability and stability of the solder layer, and including an intermetallic compound of (Cu, Ni)6Sn5 to prevent breakage and thermal resistance increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni plating film is formed on the surface of the circuit layer and solder material is provided on the Ni plating film to bond the semiconductor element to the circuit layer, then the bonding between the semiconductor element and circuit layer is achieved, but cracks are initiated in the solder layer during power cycles and thermal resistance increases
Solution Approach 1:
The patent applies composite materials by creating a multi-layer intermetallic compound structure at the interface between the solder layer and copper circuit layer. Specifically, it forms a Cu6Sn5 layer and a (Cu,Ni)6Sn5 layer in a laminated arrangement, where each layer serves different functions: the Cu6Sn5 layer provides basic bonding while the (Cu,Ni)6Sn5 layer containing Ni suppresses crack initiation during power cycles. This composite intermetallic structure resolves the contradiction by combining materials with complementary properties to achieve both bonding strength and cycle durability.
Solution Approach 2:
The patent applies local quality by concentrating the Ni element specifically at the interface region between the solder layer and copper circuit layer, rather than distributing it uniformly throughout the entire structure. The Ni is localized in the (Cu,Ni)6Sn5 intermetallic compound layer formed at this critical interface, where it specifically addresses the crack initiation problem. This localized approach improves solder layer integrity at the most vulnerable point without requiring Ni throughout the entire bonding structure.
2Reliability
If the circuit layer is composed of copper or copper alloy, then good electrical conductivity is achieved, but cracks are initiated in the solder during power cycles leading to increased thermal resistance
Solution Approach 1:
The patent applies the intermediary principle by introducing a Ni-containing intermetallic compound layer ((Cu,Ni)6Sn5) as a mediator between the copper circuit layer and the solder layer. This intermediate layer acts as a buffer that suppresses crack initiation during power cycles. The Ni element in this intermediary layer modifies the interface properties, reducing the harmful thermal stress effects that would otherwise cause cracks in the solder layer, thereby protecting the bonding interface while maintaining good electrical conductivity of the copper circuit layer.
3Temperature
If power cycle loading is applied to the power module, then the power module operates under realistic conditions, but thermal stress causes solder layer breakage and thermal resistance increase
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the intermetallic compound layer at the solder-copper interface. Specifically, it changes the stoichiometry and phase composition by controlling the Ni content to form a (Cu,Ni)6Sn5 layer with specific properties. This compositional parameter change in the intermetallic layer alters its thermal and mechanical properties, enabling it to better withstand thermal stress during power cycles and prevent solder layer breakage while maintaining bonding strength.
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 solution effectively suppresses solder layer breakage and maintains high reliability even after 100,000 power cycles, with a thermal resistance increase rate less than 10%, ensuring the power module's performance and longevity.
Implementation Method 1
forming a Sn alloy layer including Ni and Cu at the interface between the solder layer and the circuit layer
Implementation Method 2
the interface between the solder layer and the circuit layer is strengthened by forming a Sn alloy layer including Ni and Cu
Implementation Method 3
the circuit layer and the power device (semiconductor element) are bonded through the solder material
Implementation Method 4
a heat sink such as a radiator plate or a cooler is provided on the other surface of the power module substrate to radiate heat from the power device
Implementation Method 5
the metal layer and the aforementioned heat sink such as a radiator plate or a cooler are bonded to each other
Data Source
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AI summary
In a power module according to the present invention, a copper layer composed of copper or a copper alloy is provided at a surface of a circuit layer (12) onto which a semiconductor element (3) is bonded, and a solder layer (20) formed by using a solder material is formed between the circuit layer (12) and the semiconductor element (3). An alloy layer (21) containing Sn as a main component, 0.5% by mass or more and 10% by mass or less of Ni, and 30% by mass or more and 40% by mass or less of Cu is formed at the interface between the solder layer (20) and the circuit layer (12), the thickness of the alloy layer (21) is set to be within a range of 2 µm or more and 20 µm or less, and a thermal resistance increase rate is less than 10% after loading a power cycles 100,000 times under a condition where an energization time is 5 seconds and a temperature difference is 80°C in a power cycle test.