Semiconductor Device Metal Spacer Bonding Stress Buffer
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Solution Overview
Problem
Fatigue degradation of the bonding material between semiconductor elements and lead frames in semiconductor devices leads to crack formation, which can adversely affect the semiconductor element, especially due to differences in thermal expansion coefficients, resulting in increased electric resistance and potential damage.
Innovation Solution
A metal spacer is introduced between the semiconductor element and the lead frame, bonded with a first bonding material, and the metal spacer and lead frame are bonded with a second bonding material of lower strength, ensuring that cracks occur in the bonding part between the lead frame and the metal spacer, thereby minimizing damage to the semiconductor element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bonding material directly bonds the semiconductor element and the lead frame, then the structure is simple and manufacturing is easy, but fatigue degradation leads to crack formation that directly damages the semiconductor element
Solution Approach 1:
A metal spacer is introduced as an intermediary component between the semiconductor element and the lead frame. The metal spacer serves as a mediator that absorbs stress and prevents direct transmission of cracks to the semiconductor element, thereby protecting it while maintaining a manageable device structure.
Solution Approach 2:
The bonding structure is segmented into multiple distinct layers: a first bonding material bonding the semiconductor element to the metal spacer, and a second bonding material bonding the metal spacer to the lead frame. This segmentation allows each bonding material to be optimized for its specific function and location, improving overall reliability.
2Reliability
If a metal spacer with two bonding materials is introduced to protect the semiconductor element, then crack damage to the semiconductor element is reduced, but the device structure becomes more complex and manufacturing becomes more difficult
Solution Approach 1:
Different bonding materials are used at different locations: the first bonding material (with higher heat resistance and strength) is used where the semiconductor element contacts the metal spacer, while the second bonding material (with lower strength to absorb stress) is used where the metal spacer contacts the lead frame. This local differentiation optimizes protection while managing manufacturing complexity.
3Reliability
If the second bonding material has lower strength than the first bonding material, then cracks occur in the bonding part between lead frame and metal spacer first, minimizing damage to the semiconductor element, but the overall bonding strength of the structure is reduced
Solution Approach 1:
The second bonding material is deliberately designed with lower strength to act as a stress-absorbing cushion that fails first under thermal cycling stress. This beforehand cushioning prevents stronger bonds from failing and transmitting damage to the semiconductor element, sacrificing localized bond strength for overall system reliability.
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 configuration reduces the impact of crack formation on the semiconductor element by absorbing stress and buffering thermal expansion differences, thereby extending the lifespan of the bonding material and maintaining the semiconductor element's performance.
Implementation Method 1
the semiconductor element and the metal spacer are bonded by a first bonding material
Implementation Method 2
the metal spacer and the lead frame are bonded by a second bonding material
Implementation Method 3
distortion caused by a difference between the coefficient of thermal expansion of the lead frame and the coefficient of thermal expansion of the semiconductor element is absorbed by the broken bonding part
Implementation Method 4
Because the semiconductor element and the lead frame have different coefficients of thermal expansion, stress is repeatedly applied to the bonding material in a heat cycle generated by the semiconductor element
Data Source
AI summary
A semiconductor device includes a transistor, lead frames, a metal spacer, one surface of which is bonded to the transistor by a first bonding material and the other surface of which is bonded to the lead frame by a second bonding material, and a plastic mold. The plastic mold packages the transistor and the metal spacer. One surface of each of the lead frames is attached to the plastic mold. Strength of the second bonding material is lower than strength of the first bonding material. According to the above configuration, when stress is repeatedly applied to the semiconductor device, a crack occurs earlier in the second bonding material than in the first bonding material. The stress is buffered at the first bonding material.