Lead Frame Protrusion Design for Resin Adhesion
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Solution Overview
Problem
Existing lead frames for semiconductor elements face issues with resin peeling off due to thermal expansion, contraction, and vibration, particularly in QFN and LED packages, where the current methods of forming protrusions with flat or arc-like profiles are insufficient in ensuring strong adhesiveness between the resin and the lead frame.
Innovation Solution
A lead frame design featuring protrusions on the semiconductor-mounting and terminal parts with a thick, rounded top end and a slanted downward projection, increasing the contact area between the metal substrate and resin, thereby enhancing adhesiveness and tolerance to stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protrusion is formed on the terminal part to improve resin adhesiveness, then the adhesiveness is improved, but the top end of the protrusion becomes sharp which causes cracks in the sealing resin
Solution Approach 1:
The patent applies curvature by forming the top end of the protrusion with a rounded shape instead of a sharp edge. Specifically, the protrusion top end has a radius of curvature of 0.01 to 0.05 times the protrusion width, which eliminates stress concentration points and prevents crack initiation in the sealing resin while maintaining effective resin anchoring through the protrusion structure
2Object-affected harmful factors
If the protrusion top end is made flat or arc-like to prevent cracks, then crack occurrence is reduced, but the contact area with resin is reduced which lowers adhesiveness
Solution Approach 1:
The patent applies local quality by creating different surface characteristics at different locations of the protrusion. The top end has a rounded shape with controlled radius of curvature to prevent cracks, while the lateral sides maintain a roughened surface with increased surface area to enhance resin mechanical interlocking and chemical adhesion, thus achieving both crack prevention and high adhesiveness
3Reliability
If resin is designed to overhang the lead frame edge to prevent peeling, then peeling resistance is improved, but resin still peels off due to thermal expansion, contraction, and vibration from friction during cutting
Solution Approach 1:
The patent applies beforehand cushioning by forming protrusions on the terminal parts before resin packaging. These protrusions create mechanical interlocking structures that anchor the resin to the lead frame. The rounded top ends prevent stress concentration during subsequent thermal expansion, contraction, and vibration, thus cushioning against peeling forces before they can cause damage
Data Source
AI summary
A lead frame for mounting semiconductor element includes a protrusion that is horizontally projects from edges of the upper and lower surfaces of a semiconductor-mounting part or a terminal part of the lead frame and that is provided on a lateral side of at least one of the semiconductor-mounting part or the terminal part of the lead frame, wherein the top end of the protrusion is substantially flat or the profile of the cross section of the top end is arc-shaped, and the top end of the protrusion is thick.