Printed Wiring Board Stress Distribution via Insulating Layer Opening
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Solution Overview
Problem
The increasing demand for smaller and more functional electronic devices has led to thinner wirings on printed circuit boards, which are prone to stress and breakage due to thermal deformation, as existing technologies fail to adequately address the stress distribution and concentration issues at the junctions between lands and wirings.
Innovation Solution
A printed wiring board design featuring a conductive layer with lands and thinner wirings, where an insulating layer is strategically opened to expose the land and wiring edges, allowing solder connection while dispersing stress along the opening edge, reducing the likelihood of breakage by distributing stress over a longer continuous region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If thinner wirings are employed to reduce the size of the printed circuit board, then the size of the electronic device is reduced, but the wiring becomes more prone to breakage due to stress concentration
Solution Approach 1:
The insulating layer is selectively removed only from specific regions (the land and the wiring drawn from it) while maintaining coverage over other areas. This localized modification allows solder to flow around and strengthen the wiring at the critical stress concentration point without requiring changes to the entire board structure, thus improving wiring strength while maintaining thin wiring dimensions for compact device size.
Solution Approach 2:
The insulating layer is removed in advance before the soldering process, creating a prepared surface that allows solder to naturally flow around and adhere to the wiring during the subsequent soldering step. This preliminary preparation ensures that the wiring is pre-positioned and pre-prepared to receive solder reinforcement, improving its stress resistance before thermal deformation occurs during operation.
2Ease of manufacture
If the insulating layer is completely removed to expose the wiring for solder connection, then solder joining is improved, but the wiring becomes more vulnerable to stress and breakage
Solution Approach 1:
Instead of completely removing the insulating layer, the invention applies localized removal only where solder connection is needed (at the land and wiring interface). The insulating layer remains intact in other regions, providing continuous protection and stress distribution. This selective approach achieves adequate solder joining while maintaining the protective function of the insulating layer to prevent wiring breakage.
3Strength
If solder flows around into the side surface of the land to improve joining strength, then resistance against warping and bending is improved, but the process complexity increases
Solution Approach 1:
The insulating layer is removed in advance to create a prepared surface that facilitates natural solder flow during the soldering process. This preliminary preparation eliminates the need for complex process controls to achieve solder infiltration, as the solder naturally flows around the land and wiring during standard reflow soldering, achieving improved joining strength without increasing process complexity.
Data Source
AI summary
Provided is a printed wiring board comprising: a substrate; a conductive layer including a land and a wiring and formed on a surface of the substrate, the wiring having a width smaller than the land and drawn from the land; and an insulating layer formed on the conductive layer. The insulating layer has an opening corresponding to a position of the land, and an edge of the opening runs above the land and above one of edges in a width direction of the wiring.