Multilayer PCB Warping Reduction via Thermal Expansion Matching
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Solution Overview
Problem
Multilayer printed wiring boards with odd numbers of conductor layers often warp during manufacturing due to differences in linear expansion coefficients between insulating layers and metal foils, leading to potential connection failures with electronic components.
Innovation Solution
A method involving the formation of a first and second stack with prepregs and metal foils, where the first insulating layer has a lower linear expansion coefficient than the metal foils, and the third sheet of metal foil is preheated before forming the second stack to reduce warping by managing thermal expansion stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a multilayer printed wiring board with an odd number of conductor layers is manufactured using conventional thermal pressing process, then the board can be produced with required thickness, but the board warps due to difference in linear expansion coefficient between insulating layer and metal foil
Solution Approach 1:
The patent applies parameter changes by selecting materials with specific linear expansion coefficients. The insulating layer is designed to have a linear expansion coefficient within 5-20 ppm/K, while metal foils are selected with coefficients within 10-18 ppm/K. This parameter matching reduces thermal expansion differences during curing, thereby minimizing warp and improving both flatness and connection reliability.
Solution Approach 2:
The patent uses composite material design by combining specific insulating layer materials (with controlled linear expansion coefficients) with metal foil materials. This composite structure balances the thermal expansion characteristics of different layers, reducing overall warp while maintaining the required electrical and mechanical properties of the multilayer board.
2Volume of moving object
If the thickness of insulating layer and conductor layer is reduced to meet miniaturization demands, then the printed wiring board achieves smaller size and lighter weight, but the board becomes more susceptible to warping
Solution Approach 1:
The patent addresses this contradiction by changing the material parameters, specifically the linear expansion coefficients of the insulating and conductor layers. By selecting materials with matched expansion coefficients (insulating layer: 5-20 ppm/K, metal foil: 10-18 ppm/K), the board maintains structural stability even with reduced thickness, as the thermal expansion stresses are minimized during the curing process.
3Ease of manufacture
If conventional materials are used for insulating layer and metal foil, then the manufacturing process is simple, but the difference in linear expansion coefficient causes remarkable warping
Solution Approach 1:
The patent maintains ease of manufacture by using conventional thermal pressing processes while changing the material parameters selected. The insulating layer is chosen with linear expansion coefficient of 5-20 ppm/K and metal foils with 10-18 ppm/K, allowing standard manufacturing equipment and processes to be used while achieving significantly reduced warping through material parameter optimization.
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 method effectively reduces warping of multilayer printed wiring boards without increasing their thickness, thereby minimizing the risk of connection failures with electronic components.
Implementation Method 1
the first insulating layer has a lower linear expansion coefficient than any of the first sheet of metal foil or the second sheet of metal foil does
Data Source
AI summary
A first stack is formed by stacking a first sheet of metal foil, a first prepreg, and a second sheet of metal foil, one on top of another. The first prepreg is thermally cured by thermally pressing these members to make a double-sided metal-clad laminate. Conductor wiring is formed by partially removing the first sheet of metal foil from the double-sided metal-clad laminate to make a printed wiring board. After a third sheet of metal foil has been preheated, the conductor wiring of the printed wiring board, a second prepreg, and the third sheet of metal foil are stacked one on top of another and thermally pressed together. The first insulating layer has a lower linear expansion coefficient than any of the first sheet of metal foil or the second sheet of metal foil does.