Printed Wiring Board Residual Stress Reduction via Layer Thickness Gradient
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Solution Overview
Problem
Existing printed wiring boards face issues with residual stress accumulation and warpage due to differences in processing steps across build-up layers, leading to potential disconnections and reduced reliability in conductor layers and via conductors.
Innovation Solution
The design incorporates multiple build-up layers with varying resin insulating and conductor layer thicknesses, where each layer acts as a buffer to distribute and reduce stress, with via conductors and lands formed to enhance connectivity and reliability, and the use of solder resist layers and metal posts for component mounting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform thickness is used for all resin insulating layers across build-up layers, then manufacturing process is simplified, but residual stress accumulates and causes warpage
Solution Approach 1:
The patent applies local quality by varying the thickness of resin insulating layers at different positions and build-up stages. Specifically, the first resin insulating layer has a greater thickness than the second resin insulating layer, creating non-uniform local properties that compensate for processing-induced stress differences across the multi-layer structure, thereby reducing overall warpage while maintaining manufacturing feasibility.
2Reliability
If different processing steps are applied to different build-up layers, then connection reliability is improved, but residual stress and warpage increase
Solution Approach 1:
The patent applies parameter changes by modifying the thickness parameter of resin insulating layers across different build-up layers. The first resin insulating layer is designed with greater thickness compared to the second resin insulating layer, creating a gradient structure that balances the differential stress effects from varied processing steps, thereby maintaining connection reliability while mitigating residual stress accumulation.
3Stability of the object's composition
If thicker resin insulating layers are used throughout, then stress distribution is improved, but overall board thickness and complexity increase
Solution Approach 1:
The patent applies local quality by strategically varying resin insulating layer thickness rather than uniformly increasing all layers. The first resin insulating layer has greater thickness where stress concentration occurs, while the second resin insulating layer has reduced thickness, creating a optimized non-uniform structure that improves stress distribution without proportionally increasing overall board complexity.
Data Source
AI summary
A printed wiring board includes a first build-up layer having first insulating layer, conductor layer and via conductor, a second build-up layer formed on the first build-up layer and having second insulating layer, conductor layer and via conductor, a third build-up layer formed on the second build-up layer and having third insulating layer, conductor layer and via conductor, and a fourth build-up layer formed on the third build-up layer and having fourth insulating layer, conductor layer and via conductor. The first insulating layer has a thickness that is larger than a thickness of the second insulating layer, the thickness of the second insulating layer is larger than a thickness of the third insulating layer, the thickness of the second insulating layer is larger than a thickness of the fourth insulating layer, and the thickness of the fourth insulating layer is larger than the thickness of the third insulating layer.