Circuit Board Insert Molding Stress Buffering
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Solution Overview
Problem
Conventional insert molding methods for circuit boards in sensor modules can cause deformation and cracking due to excessive load from the mold, especially when the resin shrinks, as the mounting area of semiconductor parts is not adequately protected from resin flow, leading to stress and potential board deformation.
Innovation Solution
Incorporating a member with a lower elastic modulus than the circuit board into the mold clamp portion and joint areas to reduce the applied load and thermal stress, using materials like thermosetting or thermoplastic resins with fillers such as glass or mica, which can be mixed with the resin to ensure the member's softer properties align with the circuit board's requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If insert molding is performed on the circuit board without adequate protection, then the housing can be formed efficiently, but the circuit board deforms and cracks due to excessive resin shrinkage stress
Solution Approach 1:
A resin sheet is introduced as an intermediary layer between the circuit board and the molding resin. This resin sheet absorbs and distributes the shrinkage stress during molding, preventing direct transmission of excessive forces to the circuit board. The resin sheet acts as a buffer that protects the circuit board from deformation and cracking while still allowing the housing to be formed efficiently.
Solution Approach 2:
The resin sheet is placed on the circuit board before the insert molding process begins. This pre-positioned cushioning layer is specifically designed to absorb the anticipated shrinkage stress during molding, providing protective cushioning in advance. The resin sheet's material properties are selected to match the circuit board's thermal and mechanical characteristics, ensuring it can withstand the molding process without transmitting harmful stresses.
2Stability of the object's composition
If the mold clamp portion applies high load to secure the circuit board, then the board remains stable during molding, but deformation and cracks occur due to excessive stress
Solution Approach 1:
The resin sheet serves as a mediator between the mold clamp portion and the circuit board. When the mold applies clamping force, the resin sheet distributes this load over a larger area and reduces peak stresses on the circuit board. This intermediary layer prevents direct concentration of forces that would cause deformation or cracking, while still maintaining adequate stability during the molding process.
Solution Approach 2:
The resin sheet's material parameters are specifically selected to match or be compatible with the circuit board's elastic modulus and thermal expansion coefficient. By adjusting the resin sheet's thickness and material composition, the overall stiffness and stress distribution characteristics of the circuit board assembly are modified. This parameter optimization allows the mold clamp to apply sufficient load for stability without exceeding the circuit board's strength limits.
3Reliability
If the resin shrinks during cooling, then the housing solidifies properly, but excessive shrinkage stress deforms the circuit board
Solution Approach 1:
The resin sheet acts as a stress-absorbing intermediary during the resin shrinkage phase. As the molding resin cools and shrinks, the resin sheet provides a compliant interface that accommodates volume changes without transmitting excessive stresses to the circuit board. This intermediary layer allows the housing to solidify properly while protecting the circuit board's dimensional accuracy.
Solution Approach 2:
The resin sheet's thermal and mechanical parameters are optimized to bridge the gap between the circuit board and the molding resin. Its thermal expansion coefficient and elastic modulus are selected to minimize stress transmission during the cooling and solidification process. The resin sheet's thickness and material composition are tuned to allow controlled deformation that absorbs shrinkage stresses, ensuring the circuit board maintains its dimensional accuracy while the housing solidifies reliably.
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 approach effectively suppresses deformation and crack formation in the circuit board during the insert molding process by distributing the resin's shrinkage stress more evenly, thereby enhancing the manufacturing yield and preventing separation at the joint portions.
Implementation Method 1
distributing the resin's shrinkage stress more evenly
Implementation Method 2
Incorporating a member with a lower elastic modulus than the circuit board into the mold clamp portion and joint areas to reduce the applied load and thermal stress
Implementation Method 3
Conventional insert molding methods for circuit boards in sensor modules
Implementation Method 4
using materials like thermosetting or thermoplastic resins with fillers such as glass or mica
Implementation Method 5
Incorporating a member with a lower elastic modulus than the circuit board into the mold clamp portion
Implementation Method 6
using materials like thermosetting or thermoplastic resins with fillers such as glass or mica, which can be mixed with the resin
Data Source
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AI summary
In a module in which a circuit board is integrally insert molded with a housing while semiconductor parts mounted on the circuit board are exposed, deformation of the circuit board caused by pressure on the circuit board by a mold for blocking the molding resin is reduced. In the module in which the circuit board is integrally insert molded with the housing while the semiconductor parts mounted on the circuit board are exposed, the deformation of the circuit board is reduced by placing a material, which has an elastic modulus smaller than the elastic modulus of the printed circuit board, in the projection area of the mold holding portion on the circuit board.