PCB Conductive Layer Design for Wire Bonding
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Solution Overview
Problem
Current printed circuit boards face challenges in ensuring an appropriate conductive layer thickness for wire bonding environments, particularly when mounting wire bonding chips with microcircuits, as existing methods do not adequately support the necessary thickness and structure for efficient bonding.
Innovation Solution
A printed circuit board design featuring a conductive layer with a nickel (Ni) layer embedded in the insulation layer and a gold (Au) layer on top, where the nickel layer protrudes from the solder resist layer, ensuring a suitable thickness and width for wire bonding, and incorporating palladium (Pd) layers for enhanced bonding capabilities, along with a manufacturing method that involves forming and thinning the solder resist layer to prevent overhanging and ensure proper bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conductive layer thickness is increased to ensure appropriate thickness for wire bonding environment, then the wire bonding capability is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The conductive layer is segmented into multiple functional sub-layers: a base conductive layer embedded in the insulation layer, a nickel conductive layer for wire bonding contact, and a gold conductive layer for corrosion resistance and bonding surface. This segmentation allows each layer to be optimized for its specific function while collectively providing the required thickness and capability for wire bonding.
Solution Approach 2:
The patent employs composite material structure by combining different metallic materials (nickel and gold) in a layered configuration. The nickel layer provides mechanical strength and bonding surface, while the gold layer provides corrosion resistance and excellent electrical conductivity. This composite structure achieves the required wire bonding capability without excessive overall thickness.
2Ease of operation
If the solder resist layer is made thinner to prevent overhanging and ensure proper bonding, then the wire bonding process is improved, but the protective function of the solder resist layer is reduced
Solution Approach 1:
The solder resist layer is designed with non-uniform thickness: it is thinner in the region where wire bonding occurs to prevent overhanging and allow proper bonding tool access, while maintaining adequate thickness in other areas to provide necessary protective functions. This local variation in thickness optimizes both the wire bonding process and the protective function.
3Ease of operation
If the nickel conductive layer protrudes from the solder resist layer to ensure suitable thickness for wire bonding, then the bonding surface availability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The nickel conductive layer is formed to protrude from the solder resist layer in advance, before the wire bonding process. This preliminary protrusion ensures that the bonding surface is already available and properly positioned, eliminating the need for complex alignment adjustments during the bonding process and reducing manufacturing precision requirements.
Data Source
AI summary
A printed circuit board includes an insulation layer having a first surface and a second surface which are opposite to each other, a first connection pad which is embedded in the insulation layer and has a surface recessed from the first surface of the insulation layer, a conductive layer which is located on the first connection pad and has a part embedded in the insulation layer and another part protruding from the first surface of the insulation layer, and a first solder resist layer which is located on the first surface of the insulation layer and has a surface which is at a level equal to or lower than a surface of the conductive layer.