PCB Sacrificial Pad Mitigates Galvanic Corrosion
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Solution Overview
Problem
Galvanic corrosion between gold and copper patterns on Printed Circuit Boards (PCBs) during the Organic Solderability Preservative (OSP) process leads to over-etching and damage of copper traces, rendering the PCB inoperable.
Innovation Solution
Modifying the PCB by exposing additional copper areas or adding sacrificial copper patterns to reduce the gold-to-copper area ratio, thereby mitigating galvanic corrosion during the OSP process by increasing the copper area exposed to the soft etching solution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If soft etching is performed during the OSP process to prepare bare copper, then the copper surface is cleaned and prepared for OSP, but galvanic corrosion occurs between gold features and copper traces causing over-etching and breaks in copper traces
Solution Approach 1:
The patent introduces a sacrificial copper pattern as an intermediary element that is electrically connected between the gold feature and the copper trace. This sacrificial pattern acts as a mediator that absorbs the galvanic corrosion current, protecting the functional copper trace from corrosion during the OSP soft etching process
Solution Approach 2:
The sacrificial copper pattern is designed to be consumed or corroded preferentially during the OSP process. This disposable copper element sacrifices itself to protect the more valuable copper trace, aligning with the principle of using cheap, short-living objects to protect critical components
2Reliability
If the gold feature area is large relative to the copper trace area, then the electrical connection capability is maintained, but the galvanic corrosion rate increases causing copper trace damage
Solution Approach 1:
The patent segments the copper connection path into multiple parts: the original copper trace and the additional sacrificial copper pattern. This segmentation allows the corrosion current to be distributed across multiple copper areas, reducing the corrosion rate on any single copper trace while maintaining overall electrical connectivity
Solution Approach 2:
The patent addresses the area ratio problem by adding a spatial dimension to the solution. Instead of changing the gold feature area, it adds an additional copper pattern in a different spatial location that is electrically connected, effectively increasing the total copper area without modifying the original gold-to-copper area ratio
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
Significantly reduces the corrosion rate of copper traces, preventing damage and ensuring reliable electrical signal transmission across the PCB by lowering the gold-to-copper area ratio below a threshold.
Implementation Method 1
galvanic corrosion between the gold features and the copper traces can over-etch the copper traces
Implementation Method 2
During soft etching, galvanic corrosion between the gold features and the copper traces can over-etch the copper traces
Data Source
AI summary
In one example, the present application describes a Printed Circuit Board (PCB) that mitigates galvanic corrosion during an Organic Solderability Preservative (OSP) process used during fabrication of the PCB. The PCB includes a first metal pattern and a second metal pattern electrically coupled to each other, where the first and second metal patterns are different metals. The first metal pattern has a first area that is exposed by a solder mask layer, and the second metal pattern has a second area that is exposed by the solder mask area. A ratio of the first area to the second area is less than a threshold ratio to mitigate the galvanic corrosion of the second metal pattern exposed on the PCB during the OSP process.