Semiconductor Lead Plating for Solder Wettability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Leadless-package semiconductor devices with copper lead frames face issues due to oxidation, resulting in poor solder wettability and insufficient mounting strength to circuit boards.
Innovation Solution
A semiconductor device with a semiconductor element, leads, and a sealing resin, where a first plating layer covers the lead back surface and a second plating layer covers the lead end surface, both exposed from the resin, enhancing solder wettability and mounting strength through electroplating and electroless plating processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a copper lead frame is used in a leadless-package semiconductor device, then size and thickness reduction is achieved, but the lead frame oxidizes in the atmosphere forming a copper oxide film with poor solder wettability
Solution Approach 1:
The patent applies composite materials by combining copper lead frame with multiple plating layers (first plating layer and second plating layer). The copper provides electrical conductivity and mechanical strength, while the plating layers (containing tin, nickel, and gold) provide oxidation resistance and solder wettability. This composite structure resolves the contradiction by maintaining the size benefits of copper while adding protective functional layers.
Solution Approach 2:
The patent changes the surface parameters of the lead frame by applying plating layers with specific material compositions and thicknesses. The first plating layer contains tin at 5-20 mass% and nickel at 80-45 mass%, while the second plating layer contains gold at 8-30 mass%, nickel at 65-90 mass%, and phosphorus at 2-8 mass%. These parameter changes transform the surface properties to achieve both oxidation resistance and solder wettability while maintaining device compactness.
2Ease of operation
If the lead frame is exposed from the sealing resin, then external connection is enabled, but the exposed surface oxidizes and reduces mounting strength
Solution Approach 1:
The patent uses composite plating layers on the exposed lead frame surfaces. The first plating layer with tin and nickel provides a base protective barrier, while the second plating layer with gold, nickel, and phosphorus provides enhanced oxidation resistance and solder wettability. This composite approach maintains external connection functionality while protecting against oxidation to preserve mounting strength.
Solution Approach 2:
The patent applies different plating layer configurations to different locations: the first plating layer covers the lead back surface, while the second plating layer covers the lead end surface. This local quality approach targets oxidation protection and solder wettability enhancement specifically at the exposed connection surfaces that require external connection, without unnecessarily complicating covered areas.
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 the solder bonding strength and mounting reliability of the semiconductor device to circuit boards by using plating layers with higher solder wettability, specifically tin for the first plating layer and a Ni-P-Au laminated layer for the second plating layer.
Implementation Method 1
A first plating layer is formed by electroplating to cover the back surface of the lead frame
Implementation Method 2
A second plating layer is formed, with the protective tape attached, by electroless plating to cover the lead end surface
Data Source
AI summary
A semiconductor device includes a semiconductor element, a plurality of leads electrically connected to the semiconductor element and one of which supports the semiconductor element, a sealing resin covering the semiconductor element and a portion of each leads, and first and second plating layers exposed from the sealing resin. The sealing resin includes a resin side surface facing in a first direction perpendicular to the thickness direction. At least one of the leads has a lead end surface connected to its back surface and flush with the resin side surface. The first plating layer covers the back surface of the lead. The second plating layer covers the lead end surface and projects in the first direction relative to the resin side surface. An edge of the second plating layer overlaps with the first plating layer as viewed in the first direction.