Resin Semiconductor Package Structure for Heat Sink Torque Load
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Solution Overview
Problem
Semiconductor devices with resin cases face challenges in preventing deformation of heat sinks due to high fastening torque, as existing stress-relief methods are ineffective or lead to separation or cracking, especially when using a collar or metal layer formation is difficult on resin materials.
Innovation Solution
Incorporating a high-rigidity plate-shaped surface pressure absorbing member within the resin case, formed integrally by insert molding, which interposes between the bolt and heat sink, providing increased adhesion and distributing stress to prevent deformation and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high fastening torque is applied to fasten the semiconductor device to the heat sink, then the cooling performance is improved, but the heat sink deforms due to stress concentration
Solution Approach 1:
A collar made of rigid material is inserted into the fastening hole as an intermediary component between the fastening bolt and the heat sink. This collar distributes the surface pressure over a larger area, preventing stress concentration that would cause heat sink deformation, while still allowing high fastening torque to be applied for optimal cooling performance.
Solution Approach 2:
The collar is pre-installed into the fastening hole of the resin case before the final assembly. This preliminary placement ensures that the stress-distributing structure is already in position to protect the heat sink from deformation when the high fastening torque is subsequently applied during assembly.
2Shape
If a collar is inserted into the fastening hole to prevent heat sink deformation, then the heat sink is protected from stress, but the collar separates from the case under high fastening torque
Solution Approach 1:
The collar and the resin case are integrally formed through insert molding, merging two previously separate components into a single unified structure. This integral formation eliminates the interface between the collar and case, preventing separation under high fastening torque while maintaining the collar's stress-distributing function.
Solution Approach 2:
The integrated structure combines the rigid collar material with the resin case material through insert molding, creating a composite assembly where the rigid collar provides stress distribution and the resin provides structural integration, achieving both deformation prevention and attachment strength.
3Stress or pressure
If a metal layer is formed on the resin case to relieve stress, then the stress concentration is reduced, but it is difficult to form a metal layer on resin material
Solution Approach 1:
Instead of forming a permanent metal layer on the resin case, a disposable collar made of rigid material is inserted into the fastening hole. This collar serves the same stress-distributing function but is easier to manufacture and assemble than a metal-coated resin case, avoiding the complex and costly metal layer formation process.
Data Source
AI summary
A semiconductor device includes a semiconductor element, a heat sink on which the semiconductor element is mounted, and a case made of resin, the case being mounted on the heat sink and containing the semiconductor element. A fastening hole is formed passing through the case and the heat sink. The case includes a surface pressure absorbing member on a portion including the fastening hole in plan view, the surface pressure absorbing member having a plate shape and being higher in rigidity than the resin.