High-Density Laser Diode Stack Fabrication via Vacuum Reflow
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Solution Overview
Problem
Current methods for fabricating high-density laser diode stacks face challenges such as damage to anti-reflection and high-reflection coatings, increased stress during assembly, oxidation of substrate materials, and the need for multiple processing steps, particularly due to fluxed soft-soldering interconnection methods.
Innovation Solution
A method involving the application of a solder layer to the wafer before cleaving the laser diode bars, followed by direct contact and bonding in a vacuum environment, where the solder is reflowed to join the bars while applying coatings, minimizing oxidation and reducing the number of processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If fluxed soft-soldering interconnection methods are used to join laser diode bars, then ease of manufacture is improved, but manufacturing precision deteriorates due to damage to anti-reflection and high-reflection coatings
Solution Approach 1:
The patent applies inert atmosphere welding (specifically electron beam welding or gas tungsten arc welding in inert gas environment) to join the laser diode bars. This inert environment protects the anti-reflection and high-reflection coatings from damage that would occur with fluxed soft-soldering, while still achieving reliable electrical and thermal connections between the bars.
2Reliability
If multiple processing steps including separate stacking and reflow steps are used, then reliability of joints is improved, but productivity deteriorates due to increased number of processing steps
Solution Approach 1:
The patent combines the stacking and reflow operations into a single integrated processing step. The laser diode bars are stacked in their final configuration and then welded directly without a separate reflow step, eliminating redundant processing while maintaining joint reliability through the use of inert atmosphere welding parameters optimized for direct bonding.
Solution Approach 2:
The patent performs preliminary alignment and positioning of the laser diode bars in their final stack configuration before welding. This preliminary action ensures that the bars are correctly positioned and that the inert atmosphere welding can proceed directly without requiring subsequent reflow or repositioning steps.
3Ease of operation
If laser diode bars are processed in air environment, then ease of operation is improved, but object-generated harmful factors worsen due to oxidation of substrate materials
Solution Approach 1:
The patent performs the welding operation in an inert gas environment (such as nitrogen or argon atmosphere) to prevent oxidation of the laser diode bar substrate materials during processing. This inert environment protects the semiconductor materials from oxidative damage while allowing the welding process to proceed effectively.
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 approach reduces the risk of coating damage, streamlines the assembly process, minimizes substrate oxidation, and eliminates the need for additional stacking and reflow steps, resulting in a high-density stack with improved reliability and efficiency.
Implementation Method 1
the solder is reflowed to join the bars
Implementation Method 2
minimizes oxidation
Data Source
Figure 1A~1B
Figure 2A~2C
Figure 2D~2E
AI summary
A method of fabricating a high-density laser diode stack (100) is disclosed. The laser diode bars (110, 112, 114, 116, 118) each have an emitter surface (132) and opposing surfaces on either side of the emitter surface. Each laser diode bar has metallization layers (210, 212) on the opposing surfaces and a solder layer (120; 220) on at least one of the metallization layers (210, 212). The solder layer (120; 220) is applied to a semiconductor wafer (200) prior to cleaving the wafer to create the laser diode bars. The laser diode bars are arranged in a stack such that the emitter surfaces (132) of the bars are facing the same direction. The stack of laser diode bars is placed in a vacuum chamber. An antireflection coating (274) is deposited on the emitter surfaces (132) of the laser diode bars in the chamber. The laser diode bars are joined by applying a temperature sufficient to reflow the solder layers (120; 220) in the chamber.