Extending Pads for Circuit Board Solder Joint Strength
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Solution Overview
Problem
Conventional circuit board structures are limited in the number of conductive traces that can pass between solder pads due to the constraints of the solder mask layer openings, leading to insufficient routing area and potential weak solder joints from inadequate solder ball wetting.
Innovation Solution
A method of fabricating a circuit board with solder pads and conductive traces where the pads' width matches the traces', and forming extending pads on an insulating layer with a larger projection area to cover adjacent traces, allowing multiple conductive traces to pass through and ensuring sufficient solder ball wetting area without altering the solder pad shape or size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the solder pad width is increased to provide sufficient wetting area for solder balls, then the solder joint strength is improved, but the number of conductive traces that can pass between adjacent solder pads decreases
Solution Approach 1:
The solder pad structure is segmented into two distinct parts: the original solder pad (exposed through solder mask opening) and the extending pad (formed on the insulating layer). This segmentation allows the solder pad width to be reduced for better trace routing while the extending pad provides the necessary wetting area for solder balls, thus resolving the contradiction between solder joint strength and trace density.
Solution Approach 2:
The extending pad extends the solder pad area in the horizontal plane (another dimension) rather than increasing the vertical height. This dimensional extension provides additional wetting area without affecting the vertical structure, allowing more conductive traces to pass between adjacent solder pads while maintaining sufficient solder ball wetting area.
2Productivity
If the pitch between solder mask openings is reduced to increase the number of conductive traces, then the routing density is improved, but the wetting area for solder balls becomes insufficient
Solution Approach 1:
By segmenting the solder pad into the original pad and extending pad, the invention allows the pitch between solder mask openings to be reduced for higher routing density while the extending pad compensates for the reduced wetting area, maintaining sufficient solder ball wetting area and joint strength.
Solution Approach 2:
The extending pad acts as an intermediary structure that mediates between the reduced pitch (for higher density) and the required wetting area (for joint strength). It provides the additional area needed for solder ball wetting without requiring increased pitch between solder mask openings.
3Ease of manufacture
If conventional SMD solder pads are used with fixed dimensions, then the fabrication process is simple, but the routing area between adjacent solder pads is constrained
Solution Approach 1:
The solder pad structure is segmented into the original pad (defined by solder mask opening) and the extending pad (formed subsequently on the insulating layer). This segmentation enables increased routing area between adjacent solder pads while maintaining a relatively simple fabrication process using standard semiconductor manufacturing techniques.
Data Source
AI summary
A circuit board structure and a method for fabricating the same are disclosed, including providing a core board having conductive traces and solder pads respectively formed thereon, wherein width of the solder pads corresponds to that of the conductive traces, and pitch between adjacent solder pads is made wide enough to allow multiple conductive traces to pass through; forming on the core board an insulating layer with openings for exposing the solder pads therefrom; forming on the insulating layer a plurality of extending pads electrically connected to the solder pads respectively, wherein the projection area of the extending pads is larger than that of the corresponding solder pads and covers conductive traces adjacent to the corresponding solder pads. Thus, more conductive traces are allowed to pass between adjacent solder pads and meanwhile, the extending pads provide an effective solder ball wetting area for achieving good solder joints and sufficient height after collapse.