Power Semiconductor Module Stress Absorption
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Solution Overview
Problem
Existing power semiconductor modules suffer from voltage endurance degradation and semiconductor chip characteristic variation due to thermal expansion of silicon gel, leading to airtightness loss and contamination, as the cover plate made of fragile materials like polyphenylene sulfide cracks under thermal stress.
Innovation Solution
A power semiconductor module design where the printed board has a lower elastic coefficient and thickness than the cover plate, allowing it to absorb stress from silicon gel expansion, preventing cover plate displacement and cracking, with optional use of glass epoxy FR4 or flexible printed circuit film to enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a cover plate made of polyphenylene sulfide (PPS) is used to suppress the upper control board downward, then the control board is retained in position, but the cover plate cracks under thermal stress from silicon gel expansion
Solution Approach 1:
A new layer is introduced between the silicon gel and the cover plate to act as a stress-absorbing intermediary. This layer has a coefficient of thermal expansion similar to silicon gel, so it expands and contracts with the gel during temperature cycles, preventing stress transmission to the cover plate and eliminating cracks while maintaining board suppression functionality
Solution Approach 2:
The coefficient of thermal expansion parameter is matched between the new layer and silicon gel, creating thermal compatibility. This parameter matching ensures that both materials expand and contract at similar rates during temperature cycles, preventing differential expansion stress from cracking the cover plate
2Reliability
If silicon gel is used as sealing material to cover control circuit components, then sealing and protection are provided, but thermal expansion of silicon gel causes displacement and cracking of the cover plate
Solution Approach 1:
A new stress-absorbing layer is positioned between the silicon gel and cover plate to mediate their interaction during thermal cycles. This intermediary layer absorbs the dimensional changes of the silicon gel through matched thermal expansion properties, preventing stress concentration that would cause cover plate cracking and maintaining overall structural stability
Solution Approach 2:
The invention utilizes thermal expansion principles by selecting a material for the new layer whose coefficient of thermal expansion matches that of silicon gel. This ensures synchronized expansion and contraction during temperature cycling, converting potentially harmful differential expansion into benign coordinated movement that preserves structural integrity
3Shape
If the cover plate is made to suppress the control board, then board displacement is prevented, but the fragile material cracks under stress transformation
Solution Approach 1:
A stress-absorbing intermediate layer is introduced between the silicon gel and cover plate to decouple their mechanical interaction. This layer absorbs expansion stresses through matched thermal properties, preventing stress transmission to the cover plate while allowing it to maintain its shape-forming suppression function on the control board
Solution Approach 2:
The new stress-absorbing layer acts as a pre-positioned cushion between the expanding silicon gel and the cover plate. This cushioning layer anticipates and absorbs thermal expansion stresses before they reach the cover plate, preventing crack initiation and protecting the structural integrity of the cover plate during temperature cycles
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 design effectively prevents voltage endurance degradation and semiconductor chip characteristic variation by absorbing thermal stress, maintaining module airtightness and reliability, even under heat cycles, and reduces the risk of cover plate cracking.
Implementation Method 1
the printed board is transformable according to expansion/contraction of the silicon gel in a heat cycle and the stress applied by the silicon gel is absorbed by the printed board
Implementation Method 2
By applying a heat cycle to the module structured as disclosed in JP-A-2000-68446, the thermally expanded silicon gel 12 is displaced upwardly
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A power semiconductor module comprises a power circuit portion having a power semiconductor chip (113, 111) located on an upper surface of a base (108) having a case (500) on an outer periphery of the base; a printed board (102) with a circuit component mounted thereon, located above the power circuit potion with a space therebetween; a supporter (1031, 1032) which couples the printed board (102) with a cover plate (105) located on an upper portion of the case (500); and silicon gel (101) which is filled in the semiconductor module. An elastic coefficient of all or part of the printed board (102) is smaller than that of the cover plate (105).