Lead Frame Step Surface Geometry to Prevent Burr Shorting
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Solution Overview
Problem
The presence of burrs during the cutting of leads in a lead frame strip can lead to short circuits between adjacent leads, which are typically electrically isolated.
Innovation Solution
A lead frame strip design with leads having a lower surface, an upper surface, and a step surface recessed relative to the upper surface, forming a convex upward shape in vertical cross-section, which reduces the likelihood of burrs and subsequent short circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If leads are cut at predetermined positions to obtain singulated semiconductor devices, then productivity is improved, but burrs are formed causing short circuits between adjacent leads
Solution Approach 1:
The lead structure is designed with different surface qualities at different locations: the upper surface is flat for normal operations, while the lower surface features a convex portion that protrudes toward adjacent leads. This local structural differentiation ensures that during cutting, the convex portion makes contact first, preventing burrs from forming on the flat upper surface that would cause short circuits, while still allowing efficient singulation.
2Reliability
If a convex upward step surface is formed on leads, then short circuit risk is reduced, but manufacturing complexity increases
Solution Approach 1:
The convex portion is pre-formed on the lower surface of the lead during the lead fabrication process, before the cutting operation. This preliminary structural preparation ensures that during subsequent cutting, the convex portion automatically makes contact first, eliminating the need for complex real-time control systems or additional protective mechanisms during the cutting process.
Data Source
AI summary
A lead frame strip includes a frame portion and a plurality of leads projecting from an inner edge of the frame portion to an inside of the frame portion, wherein each of the leads has a lower surface, an upper surface opposite the lower surface, and a step surface recessed relative to the upper surface toward the lower surface, and wherein the step surface is convex upward in a vertical cross-section that is taken through the step surface perpendicularly to a direction in which the leads project.