Sn-Cu-Ni Solder Layer for Power Module Thermal Stability
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Solution Overview
Problem
Power modules with soldered semiconductor devices experience increased thermal resistance and solder layer cracking due to power cycles, particularly when using aluminum or copper alloy circuit layers with Ni plating, leading to reliability issues in high-power applications like wind power and electric vehicles.
Innovation Solution
A power module design with a solder layer composed of Sn as the main component, containing 0.01-1.0% by mass of Ni and 0.1-5.0% by mass of Cu, and an average crystal grain size of 0.1-10 µm, which disperses precipitate particles of intermetallic compounds like (Cu, Ni)6Sn5, reducing crack propagation and thermal resistance increase during power cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Ni plating film is formed on the circuit layer surface and solder material is arranged on the Ni plating film to bond the semiconductor device, then the bonding between circuit layer and semiconductor device is achieved, but cracks are initiated in the solder layer during power cycles leading to increased thermal resistance
Solution Approach 1:
The invention changes the chemical composition parameters of the solder material by specifying precise ranges of Sn (96.0-99.99 wt%), Cu (0.1-5.0 wt%), and Ni (0.01-1.0 wt%). This compositional parameter optimization prevents excessive intermetallic compound formation and suppresses crack initiation during power cycles, directly resolving the contradiction between achieving reliable bonding and maintaining crack resistance.
Solution Approach 2:
The invention creates a composite solder material system combining Sn as the base metal with controlled additions of Cu and Ni. This composite structure forms a eutectic composition that melts at a specific temperature range and creates a balanced microstructure with appropriate intermetallic compound distribution, achieving both strong bonding and crack resistance during thermal cycling.
2Use of energy by moving object
If the circuit layer is composed of copper or copper alloy, then good electrical conductivity is achieved, but cracks are initiated in the solder and thermal resistance is likely to increase when power cycle is loaded
Solution Approach 1:
The invention optimizes the solder composition parameters to contain 0.1-5.0 wt% Cu and 0.01-1.0 wt% Ni, which creates a balanced intermetallic compound formation rate. This parameter control ensures good electrical conductivity through the copper circuit layer while preventing excessive intermetallic growth that would cause cracks and thermal resistance increase during power cycles.
3Power
If higher power devices are mounted on the power module to control wind power generation or electric vehicles, then the power handling capability is improved, but the reliability with respect to power cycle must be further improved
Solution Approach 1:
The invention specifies precise compositional parameters for the solder material (Sn: 96.0-99.99 wt%, Cu: 0.1-5.0 wt%, Ni: 0.01-1.0 wt%) that create a eutectic system with optimal thermal and mechanical properties. This parameter optimization enables the solder to withstand the severe thermal cycling conditions generated by high-power devices while maintaining reliable electrical and thermal connections.
Solution Approach 2:
The invention develops a composite solder material with Sn-Cu-Ni combination that forms a controlled microstructure of intermetallic compounds. This composite structure provides both the electrical conductivity needed for high-power applications and the thermal stability required to maintain reliability under severe power cycle conditions.
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 cracking and maintains high reliability by reducing thermal resistance increase rates under repeated power cycles, ensuring the power module's integrity and performance in high-power applications.
Implementation Method 1
a power module obtained by bonding a circuit layer including a copper layer composed of copper or a copper alloy and a semiconductor device together using a solder material
Implementation Method 2
precipitate particles composed of an intermetallic compound including Cu, Ni, and Sn ((Cu, Ni)6Sn5 in the present embodiment) are dispersed in the solder layer
Implementation Method 3
a copper layer composed of copper or a copper alloy is formed on the surface of the circuit layer to which the semiconductor device is bonded
Data Source
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AI summary
A power module is provided with a copper layer composed of copper or a copper alloy on a surface of a circuit layer (12) to which a semiconductor device (3) is bonded, and a solder layer (20) that is formed by using a solder material is formed between the circuit layer (12) and the semiconductor device (3). An average crystal grain size which is measured by EBSD measurement in a region having a thickness of up to 30 µm from the surface of the circuit layer (12) in the solder layer (20) is 10 pm or less, the solder layer (20) has a composition that contains Sn as a main component, 0.01 to 1.0% by mass of Ni, and 0.1 to 5.0% by mass of Cu, and a thermal resistance increase rate when a power cycle is loaded 100,000 times under conditions of a conduction duration of 5 seconds and a temperature difference of 80°C is less than 10% in a power cycle test.