Light Emitting Device Lead Frame Resin Coverage
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Solution Overview
Problem
Light emitting devices with exposed leads on long-side lateral surfaces are prone to cracking under bending stress due to greater warpage at these surfaces, leading to potential damage and reduced reliability.
Innovation Solution
A light emitting device design featuring a resin package with leads only exposed on short-side lateral surfaces, where the resin part covers the long-side lateral surfaces, reducing stress concentration and enhancing the structural integrity of the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If leads are exposed on long-side lateral surfaces, then ease of connection is improved, but crack resistance deteriorates due to greater warpage at these surfaces under bending stress
Solution Approach 1:
A resin layer is introduced as an intermediary between the lead and the external environment on the long-side lateral surfaces. This resin layer absorbs and distributes bending stresses, preventing direct stress concentration at the lead-resin interface and eliminating the warpage-induced crack problem while maintaining lead exposure for connections at the short sides.
Solution Approach 2:
The lead exposure configuration is made asymmetric: leads are exposed only on the short-side lateral surfaces where warpage is minimal, while the long-side lateral surfaces are covered with resin. This local differentiation optimizes both connection accessibility (at short sides) and crack resistance (by protecting long sides from stress concentration).
2Ease of operation
If leads are exposed on long-side lateral surfaces, then ease of connection is improved, but structural integrity deteriorates due to stress concentration at the mold member near the leads
Solution Approach 1:
The resin layer serves as a stress-distributing intermediary that covers the lead on long-side lateral surfaces, preventing stress concentration at the mold member-lead interface. This intermediary layer transfers bending stresses away from critical regions, maintaining structural integrity while allowing lead exposure at short sides for connections.
Solution Approach 2:
The resin coating on long-side lateral surfaces provides beforehand cushioning by absorbing and distributing bending stresses before they can concentrate at the lead-mold member interface. This preventive measure protects the structural integrity against future bending stresses while maintaining connection accessibility at short sides.
3Reliability
If resin covers long-side lateral surfaces, then crack resistance is improved, but ease of connection deteriorates
Solution Approach 1:
The resin coverage is applied selectively only on long-side lateral surfaces where warpage and stress concentration occur, while short-side lateral surfaces maintain lead exposure for connections. This localized differentiation resolves the contradiction by providing crack resistance where needed without compromising connection accessibility.
Solution Approach 2:
The lateral surfaces are segmented into two functional zones: long-side surfaces covered with resin for crack resistance, and short-side surfaces with exposed leads for easy connection. This segmentation allows each zone to optimize its specific function without interfering with the other.
Data Source
AI summary
A light emitting device includes a resin package having a rectangular shape in a top view and two short-side lateral surfaces and two long-side lateral surfaces. The two short-side lateral surfaces include a first external surface and a second external surface located on an opposite side from the first external surface. The two long-side lateral surfaces include a third external surface and a fourth external lateral surface located on an opposite side from the third external lateral surface. The lead is not exposed on the third external lateral surface nor the fourth external lateral surface. The first lead is exposed at the first external lateral surface and the second external lateral surface, respectively flush with the resin member at the first external lateral surface and the second external lateral surface. The second lead is exposed at the second external lateral surface, flush with the resin part at the second external lateral surface.