Roughened Silver Plating on Copper Lead Frame
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Solution Overview
Problem
Conventional lead frames with silver plating suffer from poor adhesion to sealing resin due to inadequate surface roughening, which can lead to peeling off under shock or heat, and require thick plating layers to prevent copper diffusion, making them unsuitable for high-density packaging.
Innovation Solution
A lead frame with a copper-based substrate and a roughened silver plating layer having acicular projections as the outermost layer, where the crystal direction occupies a largest proportion, enhancing adhesion and allowing for thinner plating layers while reducing cost and processing time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the surface of the lead frame substrate is roughened by microetching to improve adhesion to sealing resin, then adhesion is improved, but impurity residue called smut is generated when using copper alloy substrates
Solution Approach 1:
The invention changes the chemical composition parameters of the copper alloy substrate by controlling the silicon content to be 3 mass% or less. This parameter change prevents the generation of smut impurity residue during the microetching process while maintaining the ability to form a roughened surface for improved adhesion to sealing resin.
2Object-affected harmful factors
If a thick plating layer of precious metal is formed directly on copper alloy substrate to prevent copper diffusion, then copper diffusion is prevented, but cost increases and plating layer thickness cannot be reduced for high-density packaging
Solution Approach 1:
The invention changes the chemical composition parameters of the copper alloy substrate by limiting silicon content to 3 mass% or less. This parameter change enables the formation of a roughened surface that improves adhesion, allowing the use of thinner plating layers (reducing precious metal quantity) while maintaining effective copper diffusion prevention through the enhanced surface morphology.
3Quantity of substance
If a nickel undercoat layer is formed to prevent copper diffusion and reduce plating layer thickness, then plating layer thickness is reduced, but adhesion to resin cannot be improved without additional roughening processes
Solution Approach 1:
The invention changes the chemical composition parameters of the copper alloy substrate by controlling silicon content to 3 mass% or less. This enables successful microetching of the nickel undercoat layer to create a roughened surface that provides both copper diffusion prevention and improved adhesion to sealing resin, eliminating the need for additional roughening processes.
Solution Approach 2:
The invention performs preliminary roughening of the nickel undercoat layer through microetching before forming the precious metal plating layer. This preliminary action creates the necessary surface morphology for good adhesion to sealing resin while the nickel layer continues to provide copper diffusion prevention, allowing thinner overall plating structures.
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 significantly improves adhesion to sealing resin, reduces the total thickness of plating layers, and enhances productivity by minimizing copper diffusion and processing costs.
Implementation Method 1
the surface of the lead frame substrate is roughened to have concavities and convexities by microetching, to produce a physical anchor effect, thereby improving adhesion to sealing resin
Implementation Method 2
it is necessary to make the thickness of the plating layer made of a precious metal or a precious metal alloy 2 μm or more... a plating layer made of nickel or an alloy containing nickel, which prevents copper diffusion
Data Source
AI summary
A lead frame includes, as an outermost plating layer, a roughened silver plating layer having acicular projections and covering the entire surface of a lead frame substrate made of a copper-based material. The roughened silver plating layer has a crystal structure in which the crystal direction <101> occupies a largest proportion among the crystal directions <001>, <111>, and <101>. The lead frame can be manufactured with improved productivity owing to reduction in cost and operation time, and achieves remarkably high adhesion to sealing resin while keeping the total thickness of plating layers including the silver plating layer to be thin.