Lead Frame Plating Sequence for Oxidation-Resistant Bond Pads
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Solution Overview
Problem
Lead frames made of copper are susceptible to corrosion, leading to oxidation of exposed leads, which affects electrical performance and solder connections, and are difficult to fully plate with tin, resulting in non-plated areas and manufacturing challenges.
Innovation Solution
A method involving nickel plating followed by a masking process to prevent tin plating from contacting the nickel, ensuring full coverage of leads with tin before forming a package casing, thereby protecting against oxidation and enabling reliable mass production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper lead frames are used, then electrical conductivity and cost-effectiveness are improved, but susceptibility to corrosion and oxidation worsens
Solution Approach 1:
The patent applies composite materials by combining copper lead frames with tin plating and nickel plating layers. The copper base provides electrical conductivity and cost-effectiveness, while the tin and nickel plating layers provide corrosion and oxidation resistance, creating a multi-layer composite structure that resolves the contradiction between electrical performance and corrosion susceptibility.
Solution Approach 2:
The patent changes the surface parameters of the copper lead frame by applying different plating layers with specific thicknesses and compositions. The tin plating (5-20 micrometers) and nickel plating (1-5 micrometers) modify the surface properties to resist corrosion while maintaining the underlying copper's electrical conductivity, thus resolving the contradiction through parameter modification.
2Object-affected harmful factors
If tin plating is applied to lead frames, then protection against oxidation is improved, but difficulty in achieving full coverage of leads worsens
Solution Approach 1:
The patent applies preliminary action by first depositing a nickel plating layer before applying the tin plating. The nickel layer serves as a preparatory step that creates a uniform, adherent base surface that facilitates complete and uniform tin plating coverage on complex lead frame geometries, preventing non-plated areas and ensuring full protection.
Solution Approach 2:
The nickel plating layer acts as an intermediary between the copper lead frame and the tin plating. This intermediate layer improves the wettability and adhesion of tin to the copper surface, enabling complete coverage of leads including difficult-to-reach areas, thus resolving the manufacturing difficulty of achieving full plating coverage.
3Object-affected harmful factors
If multiple plating layers are deposited, then protection against corrosion and oxidation is improved, but manufacturing complexity and process time worsen
Solution Approach 1:
The nickel plating is applied as a preliminary layer before tin plating, creating a standardized two-step process that can be automated. This preliminary action establishes a consistent base layer that simplifies subsequent tin plating operations, making the overall multi-layer process more controllable and less complex despite the additional layer.
Solution Approach 2:
The patent merges the corrosion protection function into a standardized nickel-tin plating system that can be applied in a single manufacturing sequence. By combining the protective functions of nickel (adhesion and corrosion resistance) and tin (oxidation resistance and solderability) into one integrated plating process, the complexity is managed through process integration rather than separate operations.
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
Ensures full plating of lead frame leads with tin, improving reliability and electrical performance while allowing for cost-effective, high-volume manufacturing of lead frame packaged devices.
Implementation Method 1
depositing a nickel plating on each wire bond area to form nickel-plated bond pads
Implementation Method 2
depositing a plating masking material on the nickel plating to form a masking layer on the nickel plating
Implementation Method 3
depositing a tin plating on the lead frame, including on the plurality of leads
Implementation Method 4
Lead frames made of copper are susceptible to corrosion, leading to oxidation of exposed leads
Data Source
AI summary
A method of fabricating a lead frame packaged device includes providing a lead frame including at least one wire bond area and a plurality of leads extending from the at least one wire bond area, wherein each wire bond area includes a plurality of bond pads; depositing a nickel plating on each wire bond area to form nickel-plated bond pads; depositing a plating masking material on the nickel plating to form a masking layer on the nickel plating; depositing a tin plating on the lead frame, including on the plurality of leads, wherein the plating masking material prevents the tin plating from making contact with the nickel plating; removing the masking layer from the lead frame to expose the nickel plating on each wire bond area; attaching a die to the lead frame; and forming wire bonds between the die and the nickel-plated bond pads.