Profiled Leadframe in Reflective Package for LED Assembly
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Solution Overview
Problem
Existing packaged light emitting devices face challenges in manufacturing ease and assembly complexity, with issues such as tarnishing of reflective metal layers and weak adhesion of mould compounds leading to reduced reflectivity and delamination risks.
Innovation Solution
A packaged light emitting device with a profiled leadframe embedded in a reflective material, featuring solder bonding areas covered with solder but not the surrounding reflective material, which acts as a solder resist for self-alignment, and wirebonding areas for improved assembly and thermal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a silver reflective metal layer is used on the leadframe, then reflectivity is improved, but tarnishing occurs leading to reduced reflectivity and adhesion problems with mould compound
Solution Approach 1:
The leadframe surface is segmented into distinct functional zones: wirebonding areas with silver coating for electrical connection, solder bonding areas with tin coating for mechanical attachment, and reflective areas with aluminium coating for light reflection. This segmentation allows each area to have optimized properties for its specific function, preventing the adhesion problems that occur when silver is used across the entire surface.
Solution Approach 2:
Different metal coatings are applied to different regions of the leadframe based on local functional requirements. The wirebonding areas receive silver coating for optimal electrical contact, solder areas receive tin coating for reliable soldering, and reflective areas receive aluminium coating for maximum reflectivity. This local quality approach ensures that each region has the appropriate material properties without compromising overall reliability.
2Ease of manufacture
If a simple package structure is used, then manufacturing is simplified, but additional wirebonding steps are required increasing assembly complexity
Solution Approach 1:
The package structure merges multiple functions into a single integrated leadframe component. The leadframe simultaneously provides electrical connection (through integrated pads), mechanical support (through integrated mounting structures), and light reflection (through integrated reflective surfaces). This merging eliminates the need for separate wirebonding steps and additional components, reducing assembly complexity while maintaining manufacturing simplicity.
Solution Approach 2:
The leadframe is designed as a multi-functional component that performs multiple roles: it serves as the electrical interconnection structure, the mechanical support framework, the light reflector, and the mounting substrate for the light emitting device. This universality reduces the number of separate components and assembly steps required, simplifying both manufacturing and assembly processes.
3Manufacturing precision
If solder is applied to the mounting surface, then bonding area is defined, but solder may spread to reflective material reducing reflectivity
Solution Approach 1:
A solder resist coating is applied as an intermediary layer between the solder and the reflective aluminium areas. This solder resist acts as a barrier that prevents solder from spreading onto the reflective surfaces during the soldering process. The solder resist is applied only in non-reflective areas where solder bonding is required, allowing precise definition of bonding areas while preserving the reflectivity of adjacent aluminium regions.
Solution Approach 2:
The solder resist coating provides a visual distinction between areas that should receive solder and areas that should remain reflective. The different color or appearance of the solder resist compared to the reflective aluminium surface allows for easy identification and control of solder application boundaries, ensuring that solder is applied only to appropriate areas and reflectivity is maintained where needed.
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 simplifies the assembly process, enhances reflectivity by preventing tarnishing, and improves thermal and electrical performance with self-aligned solder and direct copper leadframe connections, reducing assembly complexity and enhancing reliability.
Implementation Method 1
A package body comprising reflective material incorporating a profiled leadframe and defining a continuous and flat mounting surface
Implementation Method 2
the reflective material surrounding the at least one solder bonding area may act as a solder relief or solder resist giving rise to self-alignment of the solder because wetting of regions with solder apart from the solder bonding area is prevented or reduced
Implementation Method 3
A very common approach is to use light emitting diodes (LEDs), which are in increasing use for a number of applications in view of their efficiency in generating light
Implementation Method 4
Where broad spectrum light, for example white light is required, this can be achieved from VCSEL and VECSEL type devices using phosphors
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
A packaged light emitting device die (20) includes a package body having a profiled leadframe (10) embedded in a body (12) of reflecting material. The leadframe (10) is exposed on mounting surface (14) only on at least one solder bonding area (16). Solder (22) is present only on the at least one solder bonding area (16) and not elsewhere. The reflecting material provides the reflecting parts of the package so there is no need for a reflective layer to be deposited on leadframe (10). Moreover, the reflecting material can function as a solder resist to self-align the solder (22) to the at least one solder bonding area (16).