PCB Pad Solder Resist Design for Tight Pitch
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Solution Overview
Problem
The challenge is to reduce the gap between component mounting pads on printed circuit boards while improving reliability and increasing the number of mounting pads to accommodate the shrinking size and weight demands of mobile devices.
Innovation Solution
A printed circuit board design featuring a first insulating layer with first and second pads, where the solder resist layer has specific openings exposing portions of the pads, allowing for a closed region with side surfaces covered and an open region with side surfaces exposed, thereby reducing the gap between pads and enhancing reliability by ensuring proper electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the gap between component mounting pads is reduced to accommodate more pads on smaller boards, then the number of mounting pads increases, but the reliability of electrical connections deteriorates due to increased risk of short circuits
Solution Approach 1:
The solder resist layer is selectively removed to create closed regions around specific pads, providing localized protection where needed. This allows different pads to have different protection levels - some with full side surface coverage and others with partial coverage - optimizing both density and reliability for different connection requirements
Solution Approach 2:
The solder resist layer is divided into multiple regions: closed regions that fully cover pad side surfaces to prevent short circuits, and open regions that expose side surfaces for pads requiring different protection levels. This segmentation allows simultaneous optimization of different pad areas for density and reliability
2Area of stationary object
If the gap between pads is narrowed to reduce board size, then the board area decreases, but the manufacturing precision requirements increase due to tighter spacing
Solution Approach 1:
The solder resist layer is formed and patterned before final pad assembly, pre-establishing protective barriers around pads. This preliminary protection structure prevents manufacturing variations from causing short circuits during subsequent assembly processes
Solution Approach 2:
The closed regions of the solder resist layer act as preventive barriers that cushion against potential short circuits caused by manufacturing tolerances. By providing this protective buffer in advance, the design accommodates tighter pad spacing without proportionally increasing precision requirements
Data Source
AI summary
A printed circuit board includes a first insulating layer, a plurality of first and second pads disposed on the first insulating layer, and a solder resist layer disposed on the first insulating layer, the solder resist layer having a plurality of first and second openings respectively exposing at least portions of the plurality of first and second pads. The first pad has a closed region having a side surface covered by the solder resist layer, and an open region having a side surface exposed by the first opening. The second pad has only a closed region having a side surface covered by the solder resist layer.