PCB Pad Opening Shapes for Uniform Solder Distribution
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Solution Overview
Problem
Printed wiring boards with both non-solder mask defined (NSMD) and solder mask defined (SMD) pads exhibit lower semiconductor element mounting yield due to variations in exposed conductor areas, which affect solder paste distribution and height during the mounting process.
Innovation Solution
The solution involves forming pads with both SMD and NSMD structures on a printed wiring board and correcting the shape of the openings in the resin insulation layer to ensure uniform exposed conductor areas, either by covering lead lines with solder resist or adjusting the opening shapes to match the exposed areas of both pad types, thereby maintaining the exposed conductor areas within a 15% difference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If both NSMD and SMD pads are formed on the printed wiring board, then the versatility of the board is improved, but the mounting yield deteriorates due to variations in exposed conductor areas
Solution Approach 1:
The patent applies local quality by differentiating the opening shapes in the resin insulation layer according to the pad types. For NSMD pads, the opening shape is adjusted to compensate for the presence of lead lines, while for SMD pads, the opening shape corresponds to the pad geometry. This localized differentiation ensures that both pad types achieve substantially equal exposed conductor areas, resolving the contradiction between versatility and mounting yield.
2Manufacturing precision
If the opening shapes are adjusted to match exposed areas, then the manufacturing precision is improved, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by modifying the opening shape parameters (area, perimeter, curvature) in the resin insulation layer based on the pad type and lead line configuration. By calculating and adjusting these geometric parameters, the patent achieves uniform exposed conductor areas across different pad types while managing the complexity through systematic parameter adjustment rather than ad-hoc modifications.
Data Source
AI summary
A wiring board includes a substrate, pads formed on an electronic-component mounting surface of the substrate, and a resin insulation layer covering the electronic-component mounting surface and having opening portions such that the opening portions are exposing the pads, respectively. The pads include a non-solder mask defined pad having a wiring portion and a non-solder mask defined pad having no wiring portion, and the opening portions are formed such that the non-solder mask defined pads have exposed conductor areas which have substantially same areas inside the opening portions.