PCB Pad Barrier Layer for Fine-Pitch Galvanic Corrosion Prevention
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Solution Overview
Problem
Existing printed circuit boards face issues with galvanic corrosion during the formation of metal posts, leading to defects and reduced reliability, especially when fine pitches are required for connections between chips and the board.
Innovation Solution
The printed circuit board design includes a barrier layer between the pad and the metal post, preventing direct contact with the surface treatment layer, and using a conductive material with a lower standard reduction potential to prevent galvanic corrosion, along with a seed layer for plating, ensuring reliable connections with fine pitches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a surface treatment layer is formed on the pad to improve connection reliability, then connection reliability is improved, but galvanic corrosion occurs during metal post formation
Solution Approach 1:
A barrier layer is introduced as an intermediary between the pad and the surface treatment layer. This barrier layer prevents direct contact between dissimilar metals (pad metal and surface treatment layer metal), thereby eliminating the galvanic corrosion pathway while maintaining the connection reliability provided by the surface treatment layer.
Solution Approach 2:
The original direct contact structure between the pad and surface treatment layer is segmented by inserting a barrier layer. This segmentation separates the two metal layers that would otherwise create a galvanic cell, allowing each layer to perform its function without causing corrosion to the other.
2Adaptability or versatility
If fine pitch pads are formed to enable chip connections, then connection capability is improved, but manufacturing precision requirements increase
Solution Approach 1:
The barrier layer is formed on the pad surface before the surface treatment layer is applied. This preliminary action ensures that the pad is properly prepared and protected from the beginning of the stacking process, which is crucial for maintaining precision in fine pitch applications where alignment tolerances are tight.
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 effectively prevents galvanic corrosion, ensuring reliable and defect-free connections for fine-pitch components, enhancing the reliability and performance of the circuit board.
Implementation Method 1
a first barrier layer disposed on the second portion of the first pad corresponding to the first opening; a first surface treatment layer disposed on the first barrier layer... a second barrier layer disposed between the second pad and the metal post
Implementation Method 2
a seed layer disposed on the barrier layer and extending along the barrier layer; and a metal post disposed on the seed layer
Data Source
AI summary
A printed circuit board includes: an insulating portion; a first pad disposed on the bottom of the insulating portion; a first solder resist layer disposed on the bottom of the insulating portion, covering at least a portion of the first pad, and having a first opening in at least a portion of the first pad; a first barrier layer disposed on a portion of the first pad corresponding to the first opening; a first surface treatment layer disposed on the first barrier layer; a second pad disposed on the top of the insulating portion; a second solder resist layer disposed on the top of the insulating portion, covering at least a portion of the second pad; a metal post disposed on the second pad; and a second barrier layer disposed between the second pad and the metal post.