Dual-Layer Resin Packaging for LED Wire Bond Stress Relief
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Solution Overview
Problem
Conventional light-emitting devices packaged with clear resin without fillers become brittle and prone to wire breakage due to thermal expansion differences between metal and resin, leading to mechanical weakness and reduced optical efficiency.
Innovation Solution
A light-emitting device is designed with a lead frame and die paddle, where a softer silicone resin covers only the necking area of the wire bond, while a harder epoxy resin covers the rest, enhancing mechanical strength and optical properties by minimizing light absorption and refraction losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If clear resin without fillers is used to package the chip, then light transmittance efficiency is improved, but mechanical strength deteriorates due to brittleness and wire breakage
Solution Approach 1:
The packaging structure is divided into multiple resin layers with different properties: a first resin layer (softer, higher elongation) and a second resin layer (harder, better optical properties). This segmentation allows each layer to fulfill different functions - the first layer provides mechanical flexibility and stress relief, while the second layer ensures light transmittance efficiency.
Solution Approach 2:
Different regions of the packaging structure are assigned different material properties. The first resin layer is positioned at the wire bonding area where mechanical stress occurs, providing local flexibility. The second resin layer covers the light emitting area where optical performance is critical, ensuring local transparency and light efficiency.
2Strength
If harder resin is used to improve mechanical strength, then wire breakage resistance improves, but optical properties deteriorate due to increased light absorption
Solution Approach 1:
The resin packaging is segmented into two distinct layers: the first resin layer provides mechanical strength and wire protection, while the second resin layer is optimized for optical transparency. This segmentation resolves the contradiction by assigning mechanical and optical functions to different layers rather than requiring a single material to excel at both.
Solution Approach 2:
The invention uses a composite resin structure combining two different resin materials with complementary properties. The first resin (softer, more flexible) complements the second resin (harder, more transparent) to create a composite packaging system that achieves both mechanical strength and optical efficiency.
3Reliability
If soft resin covers the whole die and wire, then mechanical deformation buffer is improved, but optical efficiency deteriorates due to increased light absorption and refraction
Solution Approach 1:
The resin coverage is segmented spatially: the first soft resin layer is applied only to the wire bonding area where mechanical stress occurs, while the second hard resin layer covers the light emitting area. This segmentation ensures mechanical protection is provided where needed without compromising optical efficiency in the light path.
Solution Approach 2:
The soft resin is extracted from the light path by limiting its coverage to only the wire bonding area. This removes the source of light absorption and refraction losses while retaining the mechanical buffering function where it is most needed - at the wire bonding interface subject to thermal stress.
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 provides improved mechanical strength and optical efficiency by reducing stress on the wire bonds and minimizing light absorption, allowing more light to be coupled out from the light-emitting die.
Implementation Method 1
When the packaged chip is exposed to thermal attacks, the coefficient of thermal expansion (CTE) difference between the metal and the resin will cause pull/push stress onto the bonded wire
Implementation Method 2
losses by absorption and refraction on such passing are reduced
Data Source
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).