Nonplanar LED Lead Frames for Reflow-Resistant Encapsulation
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Solution Overview
Problem
Conventional LED packages face challenges with solder reflow, leading to issues such as unwanted scattering surfaces, decreased mechanical and electrical integrity, and reduced adhesion of encapsulant materials, particularly in outdoor applications.
Innovation Solution
Lead frame structures with nonplanar features within the package housing recesses, including raised projections and indentations, enhance adhesion and confinement of encapsulant materials, controlling solder reflow and improving mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional planar lead frame structures are used, then manufacturing is simple, but solder reflow causes unwanted scattering surfaces and decreased mechanical integrity
Solution Approach 1:
The patent applies curvature by forming nonplanar features (protrusions and indentations) on the lead frame structure. These curved and three-dimensional features provide mechanical reinforcement against solder reflow forces while maintaining manufacturing feasibility through standard forming processes, thereby improving reliability without excessive complexity.
Solution Approach 2:
The patent transitions from a two-dimensional planar lead frame to a three-dimensional nonplanar structure by adding protrusions and indentations that extend vertically from the lead frame plane. This dimensional enhancement provides additional mechanical strength and solder reflow resistance while the features are integrated into the existing lead frame geometry.
2Reliability
If conventional planar lead frame structures are used, then encapsulant adhesion is reduced, but adding nonplanar features increases manufacturing complexity
Solution Approach 1:
The nonplanar features with curved surfaces increase the surface area and provide mechanical interlocking for the encapsulant material. These curved protrusions and indentations enhance adhesion through geometric interlocking while being formable using standard metal forming techniques, balancing manufacturing ease with improved adhesion.
Solution Approach 2:
The nonplanar features create a textured surface topology that increases effective surface area and provides mechanical interlocking for the encapsulant. While not truly porous, the three-dimensional features serve a similar function by increasing surface complexity that enhances material adhesion without requiring actual porosity.
3Reliability
If nonplanar lead frame features are added, then solder reflow is controlled and adhesion is enhanced, but device complexity increases
Solution Approach 1:
The curved nonplanar features create a three-dimensional topology that provides mechanical resistance to solder reflow forces. The protrusions and indentations act as physical barriers and anchoring points that control solder flow while being integrated into the lead frame structure, managing complexity through functional integration.
Solution Approach 2:
The nonplanar features serve multiple functions simultaneously: they provide mechanical reinforcement against solder reflow, increase encapsulant adhesion through enhanced surface area and interlocking, and maintain structural integrity. This multi-functionality reduces the need for separate components, managing overall device complexity.
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 nonplanar lead frame structures effectively mitigate solder reflow, enhance encapsulant adhesion, and maintain electrical and mechanical integrity, reducing unwanted scattering and improving LED package performance.
Implementation Method 1
features positioned within a recess of a package housing and proximate mounting areas of LED chips within the recess. The features may include nonplanar shapes relative to a floor of the recess that promote increased adhesion with an encapsulant in the recess
Implementation Method 2
mitigating effects of reflow when the package is later bonded at a device level. The features may be arranged in rows, as islands, or even as random structures along portions of the leads
Data Source
AI summary
Light-emitting diode (LED) devices and more particularly lead frame structures for reflow mitigation in LED packages are disclosed. Lead frame structures include various features positioned within a recess of a package housing and proximate mounting areas of LED chips within the recess. The features may include nonplanar shapes relative to a floor of the recess that promote increased adhesion with an encapsulant in the recess while also mitigating effects of reflow when the package is later bonded at a device level. Exemplary nonplanar shapes include portions of leads that extend upward into the recess and/or portions of leads that extend downward below the floor of the recess. The features may be arranged in rows, as islands, or even as random structures along portions of the leads.