Semiconductor Light Emitting Device Package Thermal Stress Reduction
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Solution Overview
Problem
The high manufacturing costs and reliability issues of semiconductor light emitting device packages, particularly due to thermal stress from differences in thermal expansion coefficients between the lead frame structure and the semiconductor light-emitting device, as well as the occurrence of solder remelting and yellowing with epoxy resin.
Innovation Solution
A semiconductor light emitting device package design featuring a lead frame structure with grooves, using a silicon molding compound resin portion and eutectic bonding without solder, which reduces thermal stress and eliminates yellowing, and includes a phosphor layer for wavelength conversion on a ceramic substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If epoxy resin is used for packaging, then manufacturing cost is reduced, but yellowing occurs and reliability deteriorates
Solution Approach 1:
The patent changes the material parameter from epoxy resin to silicon molding compound, which has different chemical composition and physical properties. This parameter change eliminates the yellowing issue while maintaining low manufacturing cost, as silicon molding compound does not exhibit the yellowing characteristic of epoxy resin under thermal and UV exposure.
Solution Approach 2:
The patent employs silicon molding compound as a composite material that combines the benefits of low cost with improved reliability. This material composition provides both the economical aspect needed for manufacturing and the stability required to prevent yellowing, thus resolving the contradiction between cost and reliability.
2Device complexity
If lead frame structure is used, then manufacturing simplicity is improved, but thermal stress increases due to thermal expansion coefficient difference
Solution Approach 1:
The patent applies local quality by introducing grooves at specific locations on the lead frame surface. These grooves are locally positioned to provide stress relief exactly where thermal expansion differences create maximum stress, while maintaining the overall simplicity of the lead frame structure. The grooves act as localized features that address the thermal stress problem without complicating the entire package design.
Solution Approach 2:
The patent directly addresses thermal expansion by designing grooves into the lead frame structure that accommodate differential thermal expansion between the lead frame and the light-emitting device. The grooves provide expansion space and stress relief pathways, allowing the materials to expand and contract at different rates without generating excessive thermal stress.
3Strength
If solder is used for bonding, then bonding strength is improved, but solder remelting occurs under high temperature
Solution Approach 1:
The patent replaces traditional solder with a eutectic bonding structure that uses a eutectic alloy layer. This bonding material is designed to melt at a specific temperature and be replaced by direct metal-to-metal bonding, effectively making the initial solder layer a temporary bonding solution that is replaced by a more reliable permanent bond, thus eliminating the remelting problem.
Solution Approach 2:
The patent utilizes phase transitions of the eutectic alloy during the bonding process. The eutectic material melts at a controlled temperature to facilitate bonding, then solidifies to create a strong joint. This controlled phase transition allows for reliable bonding while preventing remelting under normal operating conditions, as the bonding structure is designed to remain stable above the eutectic melting point.
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 significantly reduces thermal stress, lowers manufacturing costs, and enhances reliability by eliminating solder remelting and yellowing, making the semiconductor light emitting device package suitable for applications requiring high reliability, such as automotive lighting.
Implementation Method 1
thermal stress from differences in thermal expansion coefficients between the lead frame structure and the semiconductor light-emitting device
Implementation Method 2
A phosphor layer is disposed on an upper surface of the semiconductor light-emitting device
Implementation Method 3
using a silicon molding compound resin portion and eutectic bonding without solder
Data Source
AI summary
A semiconductor light emitting device package includes a lead frame structure including a first lead frame and a second lead frame. A resin portion is adjacent to side surfaces of the first lead frame and the second lead frame. A semiconductor light-emitting device is mounted on the first lead frame and the second lead frame, in the form of a flip chip, by eutectic bonding. Each of the first lead frame and the second lead frame has a plurality of first grooves extended in a first direction.