Pyrolytic Graphite Substrate Orientation for Laser Diode CTE Matching
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Solution Overview
Problem
Current CTE-matched substrates for semiconductor laser diodes are expensive and difficult to produce, limiting high-volume batch process packaging due to high strain and thermal conductivity issues.
Innovation Solution
A pyrolytic graphite (PG) substrate with a crystalline structure oriented at a specific angle to match the coefficient of thermal expansion (CTE) of GaAs laser diodes, providing excellent thermal conductivity and ease of machining for low-cost, high-density packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If CuW pseudoalloy substrates are used to match CTE of GaAs laser diodes, then stress between laser diode and substrate is reduced, but manufacturing cost increases and machining difficulty increases
Solution Approach 1:
The patent changes the material parameters by selecting pyrolytic graphite with specific crystalline orientations (basal plane angles of 0°, 30°, 45°, 60°, or 90° relative to the longitudinal axis) to achieve CTE matching with GaAs laser diodes. This allows tuning the thermal expansion characteristics without relying on difficult-to-machine CuW pseudoalloys, thereby reducing stress while improving manufacturability.
2Reliability
If Cu—Mo—Cu laminated composites are used to match CTE, then stress between laser diode and substrate is reduced, but packaging density decreases due to minimum thickness constraints
Solution Approach 1:
The patent utilizes the anisotropic thermal expansion properties of pyrolytic graphite by orienting the basal plane at specific angles to achieve CTE matching. This single-layer approach eliminates the need for multi-layer Cu—Mo—Cu composites with minimum thickness constraints, enabling thinner substrates and higher packaging density while maintaining stress reduction.
3Ease of manufacture
If pyrolytic graphite substrate with optimized basal plane orientation is used, then manufacturing cost decreases and packaging density increases, but stress matching between laser diode and substrate may worsen
Solution Approach 1:
The patent systematically evaluates different basal plane orientations (0°, 30°, 45°, 60°, 90°) of pyrolytic graphite to identify optimal angles that achieve both cost-effectiveness and stress matching. By tuning the orientation parameter, the solution finds the optimal balance between manufacturing advantages and stress reduction requirements for GaAs laser diodes.
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 PG substrate reduces stress between laser diodes and substrates, enabling efficient thermal management and batch processing, improving manufacturing costs and yields while maintaining diode efficiency.
Implementation Method 1
a basal plane oriented at a pre-determined orientation angle as measured from a longitudinal axis of a heat generating material to be mounted on a surface of the PG substrate, so that a coefficient of thermal expansion (CTE) of the PG substrate is substantially matched with a CTE of the material
Implementation Method 2
These submounts typically must be CTE-matched to the semiconductor chip to achieve low strain, and also must provide good thermal conductivity
Data Source
AI summary
A pyrolytic graphite (PG) substrate and laser diode package includes a substrate body having a PG crystalline structure with a basal plane oriented at a pre-determined orientation angle as measured from a longitudinal axis of a heat generating material, such as a laser diode, mounted on a surface of the PG substrate, so that a coefficient of thermal expansion (CTE) of the PG substrate is substantially matched with a CTE of the material.