Lead Frame Silver Gold Plating for Epoxy Bleed and Corrosion
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Solution Overview
Problem
Conventional lead frames have both surface layers formed of the same material, leading to issues such as epoxy bleed out, reduced adhesive strength, and increased risk of discoloration and migration, which affect the reliability and performance of semiconductor packages.
Innovation Solution
A lead frame with different characteristics on its upper and lower surfaces, featuring a silver plating layer on the upper surface for enhanced adhesive strength and a gold plating layer on the lower surface for improved corrosion resistance and solderability, along with specific layer structures and manufacturing processes to achieve these properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If both surface layers of the lead frame are formed of the same material, then the manufacturing process is simple and cost-effective, but the upper surface and lower surface have the same characteristics which causes epoxy bleed out, reduced adhesive strength, and increased risk of discoloration and migration
Solution Approach 1:
The patent applies different plating materials to different surfaces of the lead frame based on their specific functional requirements. The upper surface uses silver plating for epoxy compatibility and adhesive strength, while the lower surface uses gold plating for corrosion resistance and solderability. This local differentiation of material properties resolves the contradiction by optimizing each surface for its specific function rather than using a uniform material throughout.
Solution Approach 2:
The lead frame employs a composite plating structure with multiple layers including silver plating on the upper surface and gold plating on the lower surface. This composite approach combines the advantages of different materials (silver's epoxy compatibility and gold's corrosion resistance) into a single integrated component, achieving superior overall performance while addressing the specific requirements of each surface.
2Strength
If silver plating is applied on the upper surface, then adhesive strength with mold resin and bonding wires is enhanced, but the complexity of the plating process increases
Solution Approach 1:
Silver plating is selectively applied only to the upper surface of the lead frame where adhesive strength with mold resin and bonding wires is critical. This localized application of silver plating enhances the specific functional requirement (adhesive strength) while limiting the complexity increase to only the necessary areas, rather than applying complex multi-layer plating to the entire component.
3Reliability
If gold plating is applied on the lower surface, then corrosion resistance and solder wettability are improved, but the manufacturing complexity increases
Solution Approach 1:
Gold plating is selectively applied only to the lower surface of the lead frame where corrosion resistance and solder wettability are most critical for external connections. This localized gold plating approach optimizes the specific functional requirements (corrosion resistance and solderability) while minimizing the overall manufacturing complexity by avoiding unnecessary gold plating on other surfaces.
4Strength
If the upper surface is made rougher, then adhesive strength with mold resin is enhanced, but the surface finish complexity increases
Solution Approach 1:
The upper surface of the lead frame is selectively roughened to enhance adhesive strength with mold resin, while the lower surface maintains a different finish appropriate for its function. This localized surface treatment approach optimizes the adhesive properties where needed without unnecessarily complicating the surface finish control across the entire component.
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
The solution effectively suppresses epoxy bleed out, strengthens bonding with wires and mold resin, prevents discoloration, and enhances solder wettability and migration resistance, thereby improving the mounting reliability of semiconductor packages.
Implementation Method 1
an upper outermost plating layer of an upper part of the lead frame is a silver plating layer including silver
Implementation Method 2
a lower outermost plating layer of a lower part of the lead frame is a gold plating layer including gold
Implementation Method 3
At least one of the upper surface of the base material and an upper surface of the upper first layer is formed to be rougher than at least one of the lower surface of the base material and a lower surface of the lower first layer
Implementation Method 4
both surface layers of the lead frame are formed of plating layers consisting of the same material
Data Source
AI summary
There is provided a lead frame including a plurality of plating layers formed on both an upper surface and a lower surface of a base material including a metal, wherein an upper outermost plating layer of an upper part of the lead frame is a silver plating layer including silver, and a lower outermost plating layer of a lower part of the lead frame is a gold plating layer including gold.