Light Emitting Device Lead Frame Geometry for Thermal Management
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Solution Overview
Problem
Light-emitting devices with surface-mounted structures face challenges in achieving good heat dissipation while preventing delamination between the lead and the resin molded body due to material differences in linear expansion coefficients, leading to insufficient adhesiveness and thermal resistance issues, especially in high-power consumption applications.
Innovation Solution
The design includes a light-emitting device with a lead frame configuration where the first lead has a bonding region and an outer edge extending parallel to a direction, with the light-emitting element bonded to the bonding region, and a molded body with specific side surfaces and recesses that expose the bonding and electrical connection regions, featuring bent lead portions and a narrowing width across the bonding region to reduce thermal resistance and prevent delamination, using materials like copper-based alloys and thermoplastic resins with fillers for improved reflectance and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a resin molded body is used to cover the light-emitting element, then the light-emitting device achieves a compact structure and protection, but delamination occurs between the lead and resin due to mismatched linear expansion coefficients
Solution Approach 1:
The patent modifies the linear expansion coefficient of the resin molded body by adding specific fillers (such as metal powders, ceramic particles, or glass beads) to match it closer to that of the lead frame. This parameter change reduces thermal stress during temperature cycling and prevents delamination between the lead and resin interfaces.
Solution Approach 2:
The patent creates a composite resin material by combining base resin with fillers having different thermal expansion properties. This composite structure allows tuning of the overall linear expansion coefficient to bridge the gap between metal lead and organic resin, maintaining reliable adhesion under thermal stress.
2Temperature
If the lead width is increased to improve heat dissipation, then thermal resistance decreases, but the device size increases
Solution Approach 1:
The patent applies different lead widths at different locations: wider lead sections under the light-emitting element for optimal heat dissipation, and narrower lead sections at protruding terminals for compact packaging and circuit board mounting. This localized quality variation optimizes both thermal performance and device size.
3Power
If high-power light-emitting elements are used to increase output, then illumination intensity improves, but heat generation increases leading to delamination risk
Solution Approach 1:
The patent adjusts the resin's linear expansion coefficient through filler addition to better match the lead frame, reducing thermal stress accumulation during temperature cycles caused by high-power operation. This parameter modification enables reliable operation at higher power levels without delamination.
Solution Approach 2:
The patent converts the harmful thermal expansion mismatch into a beneficial matched system by carefully selecting fillers whose combined effect creates a resin with linear expansion properties intermediate between metal and organic materials, turning the potential failure mechanism into a stable thermal interface.
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 heat dissipation, reduces thermal resistance, and prevents lead pull-out and delamination, enabling high output power and efficient light extraction while maintaining a compact size, suitable for use in illumination and display devices.
Implementation Method 1
a light-emitting element (40) bonded to the bonding region (10m)
Implementation Method 2
using materials like copper-based alloys and thermoplastic resins with fillers for improved reflectance
Implementation Method 3
it is necessary to keep good heat dissipation while preventing delamination between the lead and the resin molded body
Data Source
AI summary
A light-emitting device includes: a first lead including a bonding region and a first outer edge extending generally parallel to a first direction; a light-emitting element bonded to the bonding region; a second lead including an electrical connection region connected to the light-emitting element; and a molded body including a first side surface generally perpendicular to the first direction, a second side surface provided on a side opposite to the first side surface and being generally perpendicular to the first direction, a lower surface, and a recess provided in a surface opposite to the lower surface, the molded body being formed so that one end portion of the first lead protrudes from the first side surface, the other end portion of the first lead and an end portion of the second lead each protrude from the second side surface, and the bonding region and the electrical connection region are exposed from a bottom surface of the recess. The one end portion of the first lead and the end portion of the second lead each are bent downward, the other end portion of the first lead are bent upward or downward, and a width of the first lead across the bonding region in a second direction perpendicular to the first direction are narrower than a width of the one end portion and wider than a width of the other end portion.