Dual-Layer Resin Packaging for LED Wire Bond Stress Relief
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Solution Overview
Problem
Conventional light-emitting devices face issues with wire breakage due to thermal stress caused by the coefficient of thermal expansion (CTE) difference between metal and resin, and there is a need for improved optical and mechanical properties.
Innovation Solution
A light-emitting device design where a softer silicone resin covers only the necking area of the wire bond, while a harder epoxy resin covers the rest, providing mechanical buffer and maintaining optimal optical properties by minimizing light absorption and refraction losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If clear resin without filler is used to package the chip, then light transmittance efficiency is improved, but wire breakage resistance deteriorates due to hard and brittle resin after curing
Solution Approach 1:
The resin packaging is divided into two distinct layers: a first resin layer (epoxy with filler) providing mechanical strength and wire breakage resistance, and a second resin layer (clear epoxy without filler) providing high light transmittance. This segmentation allows each layer to specialize in one function, resolving the contradiction between mechanical protection and optical performance.
Solution Approach 2:
Different regions of the resin packaging are assigned different material properties: the first resin layer (bottom layer) uses epoxy resin with filler particles for mechanical strength where wire bonding occurs, while the second resin layer (top layer) uses clear epoxy without filler for maximum light transmittance where light exits. This local differentiation of material quality optimizes both mechanical and optical performance in their respective zones.
2Strength
If resin hardness is increased to improve mechanical strength, then wire breakage resistance is improved, but stress from thermal expansion difference worsens
Solution Approach 1:
The first resin layer uses epoxy resin with filler particles providing high mechanical strength and wire breakage resistance at the bonding interface. The second resin layer uses softer clear epoxy without filler that can better accommodate thermal expansion differences. This local differentiation of hardness allows the system to have both strong mechanical support where needed and thermal stress accommodation where required.
3Reliability
If soft resin covers the whole die and wire, then wire breakage resistance is improved, but optical properties deteriorate due to light absorption and refraction
Solution Approach 1:
The resin packaging is segmented into two layers with distinct functions: the first resin layer (epoxy with filler) provides mechanical strength and wire breakage resistance, while the second resin layer (clear epoxy without filler) provides high light transmittance. This segmentation eliminates the problem of soft resin interfering with optical properties while maintaining wire protection through the first layer.
Solution Approach 2:
The region where light exits (covered by the second resin layer) is assigned high optical quality with clear epoxy free of filler particles for maximum transmittance. The region where mechanical strength is needed (first resin layer at the bonding interface) uses epoxy with filler for protection. This local quality differentiation ensures that soft resin does not interfere with optical performance in the light path.
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 configuration enhances mechanical strength and optical performance by reducing stress on the wire bonds and maximizing light transmission, thereby improving the reliability and efficiency of the light-emitting device.
Implementation Method 1
the first (softer) resin such as silicone will provide buffer for mechanical deformation during the thermal attack
Implementation Method 2
with the hard resin generally having superior optical properties over the soft resin, in particular a better transparency, less light is absorbed
Data Source
Figure 1~2
Figure 3
AI summary
A light-emitting device (100A) includes: a lead frame (110) including a die paddle (111) and a lead (112) spaced apart from each other; a light-emitting die (120) attached on the die paddle (111); a wire (130) bonding the light-emitting die (120) to the lead (112), wherein a first end (131) of the wire (130) and a region of the light-emitting die (120) to which the first end (131) of the wire (130) is bonded form a first necking area (141); a first resin cover (150a) covering the first necking area (141); and a second resin cover (160) covering the first resin cover (150a), the light-emitting die (120), and the wire (130). The first resin cover (150a) has a hardness lower than a hardness of the second resin cover (160).