Lead Frame Half-Etching Design for Deformation Control
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Solution Overview
Problem
Multi-row lead frames, particularly QFN and LED-type, face deformation issues due to insufficient strength from half-etching, which affects cutting processability and resin filling, as the strain from half-etching is unevenly distributed, leading to deformation and clogging during the dicing process.
Innovation Solution
A lead frame design where a first site connected to the dam bar has the same plate thickness as the metal plate, and a second site adjoining the dam bar has a smaller plate thickness, allowing for controlled half-etching patterns to reduce strain and facilitate cutting and resin filling, while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If half-etching is applied to dam bars and leads to improve cutting processability, then cutting efficiency is improved, but deformation and warp increase due to uneven strain distribution
Solution Approach 1:
The patent applies local quality by differentiating the plate thickness of the dam bar into multiple regions: a first region with the same thickness as the base metal plate, and a second region with reduced thickness. This local differentiation allows the cutting portion to be thin for easy cutting while the support portion remains thick for structural stability, thereby resolving the contradiction between cutting efficiency and deformation control.
2Ease of manufacture
If dam bar thickness is reduced to facilitate cutting, then cutting processability is improved, but strength and structural integrity deteriorate
Solution Approach 1:
The dam bar is segmented into functionally distinct regions: a first site that maintains full thickness for structural support, and a second site with reduced thickness for cutting. This segmentation allows each region to fulfill its specific function optimally, enabling easy cutting without compromising overall structural integrity.
Solution Approach 2:
Different thickness characteristics are assigned to different portions of the dam bar. The first region retains the original thickness to provide strength, while the second region has reduced thickness to facilitate cutting, thus achieving both ease of manufacture and maintained strength.
3Loss of substance
If leads are made long and thin to reduce material usage, then material efficiency is improved, but deformation liability increases
Solution Approach 1:
The lead structure employs local quality by creating a thickness gradient: the portion connected to the dam bar maintains greater thickness for strength and deformation resistance, while distal portions can be thinner to reduce material usage. This localized thickness variation allows the lead to be both material-efficient and deformation-resistant.
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
This design significantly reduces deformation and warp, enhances cutting process efficiency, and ensures complete resin filling around semiconductor elements, with a defect rate reduction from 100% to 0.2% in comparative tests.
Implementation Method 1
subjecting the metal plate to half-etching treatment with a predetermined pattern from at least one side of the metal plate, to thereby form a first site, which is defined as surrounded by sides of the dam bar along a width direction of the lead at an end portion thereof at which connection is made with the dam bar and sides of the dam bar along a width direction thereof, having the same plate thickness as the plate thickness of the metal plate, and a second site, which adjoins the first site in the dam bar and is not connected with the lead, having a plate thickness smaller than the plate thickness of the metal plate
Data Source
AI summary
A lead frame constitutes a product unit in a multi-row lead frame and has a dam bar and a lead connected together. The dam bar has a first site where connection is made with the lead and a second site adjoining the first site without connection with the lead. A predetermined range in the lead near a connecting portion with the dam bar and the second site in the dam bar have a plate thickness smaller than that of the first site having a same plate thickness as a metal plate as a material from which the dam bar and the lead are made.