Compressible Membrane for Thermal Stress Isolation in Lead Frames
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Solution Overview
Problem
The mismatch in thermal expansion coefficients between metal electrically conductive parts and their overmolded plastic components leads to undesired relative expansions and mechanical stress during operation, potentially causing damage and failure in electrical devices.
Innovation Solution
Incorporating a compressible membrane with a higher compressibility than the overmold material between the electrically conductive member and the overmold material to absorb relative thermal expansion, thereby decoupling the two and reducing mechanical stress transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plastic material is used to overmold metal electrically conductive parts, then protection against exposure to outside elements is improved, but mechanical stress and relative expansion damage occur due to different coefficients of thermal expansion
Solution Approach 1:
A membrane is introduced as an intermediary layer between the metal electrically conductive member and the plastic overmold material. This membrane has a coefficient of thermal expansion intermediate between the metal and plastic, allowing it to accommodate relative expansion differences and prevent mechanical stress while maintaining the protective function of the overmold.
Solution Approach 2:
The patent changes the physical parameters of the interface between dissimilar materials by introducing a membrane with specific mechanical and thermal properties. The membrane's elasticity and intermediate thermal expansion coefficient allow it to deform and absorb stress, changing the stress distribution parameters in the assembly.
2Reliability
If a rigid overmold structure is used to encase electrical connections, then protection is improved, but stress concentration and potential failure occur due to thermal expansion mismatch
Solution Approach 1:
The patent uses a flexible membrane as a thin film between the rigid metal component and the rigid plastic overmold. This flexible film can deform to accommodate thermal expansion differences, preventing stress concentration while still providing protection for the electrical connections.
Solution Approach 2:
The membrane acts as a pre-positioned cushioning element that anticipates and absorbs the thermal expansion stresses before they can concentrate and cause failure. By placing this compliant layer in advance, the design prevents rather than remedies the stress concentration problem.
3Ease of manufacture
If dissimilar materials with different thermal expansion coefficients are directly bonded, then manufacturing simplicity is maintained, but relative expansion causes undesired stress and potential failure
Solution Approach 1:
The membrane serves as an intermediary bonding layer that is compatible with both the metal substrate and the plastic overmold material. This intermediate layer maintains the manufacturability of the overmolding process while eliminating the direct bonding problem between dissimilar materials with mismatched thermal expansion coefficients.
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 membrane effectively absorbs thermal expansion differences, reducing mechanical stress and vibrations transferred to the overmold material, ensuring even distribution of stress and preventing overstressed areas, thus enhancing the reliability and durability of electrical devices.
Implementation Method 1
The different materials may have different coefficients of thermal expansion. Different thermal coefficients of thermal expansion may result in undesired relative expansions during operation.
Implementation Method 2
The membrane has a compressibility greater that a compressibility of the overmold material such that at least a portion of relative thermal expansion between the electrically conductive member relative to the overmold material is absorbed by the membrane.
Data Source
AI summary
An electrical device includes an electrically conductive member, an overmold material disposed about a portion of the electrically conductive member and a membrane disposed between the overmold material and at least a portion of the electrically conductive member. The membrane has a compressibility greater that a compressibility of the overmold material such that at least a portion of relative thermal expansion between the electrically conductive member relative to the overmold material is absorbed by the membrane.