Lead Electrode Stepped Flange Resin Adhesion
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Solution Overview
Problem
In surface mounting resin-sealed light-emitting apparatuses, the peeling of lead electrodes due to thermal strains is a persistent issue, particularly at rectangular or acute angular portions, which affects adhesion and leads to lifting, and existing solutions either impair adhesion or hinder miniaturization.
Innovation Solution
A light-emitting apparatus with a recessed stepped portion on the upper surface of the lead electrode, offset from the secured semiconductor light-emitting device, featuring a flange portion with an approximately acute angular cross-section, which is formed by half pressing, preventing peeling and lifting without enlarging the electrode width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the upper portion of the edge portion of the lead electrode is rounded in cross section to improve adhesion, then adhesion is improved, but the edge portion lifts off due to thermal expansion pressure during wire bonding
Solution Approach 1:
The patent applies different cross-sectional shapes to different portions of the lead electrode. The lower portion (embedded in resin) has a rounded cross section to maximize adhesion, while the upper portion (subject to wire bonding pressure) has a flat cross section to resist lifting. This local differentiation resolves the contradiction between adhesion and positional stability.
2Reliability
If stepped portions are formed entirely on the outer surface of the inner edge portion of the lead frame to prevent lifting, then lifting is prevented, but the area of the lead frame is increased, hindering miniaturization
Solution Approach 1:
Instead of forming stepped portions on the entire outer surface, the patent forms them only on specific portions of the inner edge portion that are most prone to lifting. This localized approach provides sufficient anti-lifting functionality while minimizing the area increase, enabling miniaturization.
Solution Approach 2:
The patent applies stepped portions only where necessary (partial action) rather than uniformly across the entire lead frame. This selective application prevents over-design and unnecessary area increase while still achieving the goal of preventing lifting at critical locations.
3Reliability
If the lead electrode shape is designed to eliminate rectangular or acute angular portions to reduce thermal stress concentration, then thermal stress is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent replaces acute angular portions with curved surfaces, particularly at the corners of the lead electrode. This curvature eliminates stress concentration points caused by sharp angles while maintaining a shape that is relatively easy to manufacture using standard forming processes.
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 effectively prevents peeling and lifting of the lead electrode due to thermal strains, ensuring high reliability and miniaturization of the light-emitting apparatus while maintaining adhesion and reducing the risk of adhesive flow-out.
Implementation Method 1
the epoxy resin and the lead electrodes are different from each other in expansion coefficient, and when the temperature of the device increases, for example, during reflow step in mounting process of the light-emitting apparatus, strains are generated in these parts by stresses due to the heat
Data Source
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AI summary
A light-emitting apparatus is disclosed in which a lead electrode (121a) is held by a resin package (11) having a cup portion formed therein, a light-emitting device (131) is secured on the surface of the lead electrode within the cup portion, and a light-transmitting member 15 is filled in the cup portion so as to seal the light-emitting device. A recessed stepped portion (121b) is formed in that region of the upper surface of the lead electrode held by the resin package which is offset from the secured portion of the semiconductor light-emitting device, the edge portion of the bottom surface of the stepped portion laterally protrudes into the resin package, forming a flange portion (121c), and a vertical cross section of the protruding edge portion forms an approximately acute angle.