Wiring Board Pad Retraction for Crack Prevention
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Solution Overview
Problem
The existing wiring boards face challenges in miniaturization and connection reliability due to the large size of external connection pads, which leads to potential cracks and degradation in performance, especially when subjected to stress from heat shrinkage of resin.
Innovation Solution
The wiring board design features external connection pads with their outer peripheral edges retracted from the surface plated layer toward the center, reducing the resin amount between pads and vias and preventing crack propagation, thus maintaining connection reliability and preventing performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the external connection pad is formed larger than the opening portion of the solder resist layer, then the pad can be properly exposed for connection, but the wiring cannot be miniaturized
Solution Approach 1:
Instead of making the pad larger than the opening (conventional approach), the invention inverts the relationship by making the opening larger than the pad. The opening portion of the solder resist layer extends beyond the outer peripheral edge of the pad, allowing the pad to be smaller while still achieving proper exposure and connection functionality.
2Manufacturing precision
If the external connection pad is formed in a large size, then the pad can be properly connected, but the connection reliability of the via is lowered due to crack formation and heat shrinkage stress
Solution Approach 1:
The invention inverts the conventional size relationship by making the opening larger than the pad, which enables the pad to be formed in a smaller size. This smaller pad size reduces the amount of resin between the pad and via, thereby minimizing heat shrinkage stress and preventing crack formation, which improves via connection reliability.
3Ease of manufacture
If the surface plated layer and pad have the same size, then the plating is uniform, but cracks easily propagate toward the interior of the insulating layer along the side face of the pad
Solution Approach 1:
The invention applies local quality by creating a size difference between the pad and opening portion. The opening portion of the solder resist layer is made larger than the pad, providing a local protective structure that prevents crack propagation into the insulating layer while maintaining uniform plating on the pad surface.
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 design enables miniaturization of wirings, enhances connection reliability by reducing resin-induced stress, and prevents deep crack penetration into the insulating layer, thereby maintaining the performance of the wiring board.
Implementation Method 1
A surface plated layer is formed by thinly plating nickel (Ni), gold (Au), and the like from the side of the pad.
Implementation Method 2
there is a possibility that the connection reliability of the via is lowered by, for example, formation of a crack in a connecting portion between the pads and the via and due to stress caused by heat shrinkage of the resin.
Data Source
AI summary
A wiring board includes: wiring layers; insulating layers disposed between the wiring layers; and external connection pads respectively including surface plated layers, for connecting to an external circuit. In each of the external connection pads in one face of the wiring board, an outer peripheral edge of the external connection pad is retracted from an outer peripheral edge of the surface plated layer toward a center of the external connection pad.