Side-Emitting Laser PCB Window Assembly for Low-Stress Encapsulation
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Solution Overview
Problem
Existing semiconductor laser packaging using hard epoxy creates stress and contamination issues, leading to degradation of the laser facet in high temperature and humidity environments, and results in light reflection loss due to the inability to apply anti-reflection coatings.
Innovation Solution
A glass window assembly with a bracket is used to encapsulate the side-emitting laser chip on a printed circuit board, allowing for the use of a low-stress, low-contaminant potting compound and an anti-reflective coating to reduce stress and improve optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hard epoxy encapsulation is used to protect the laser chip, then the laser chip is protected from environmental damage, but residual stress is created on the laser chip causing performance degradation and delamination
Solution Approach 1:
The encapsulation system is divided into two separate components: a rigid support structure (PCB with mounting holes) that provides mechanical protection and environmental sealing, and a soft stress-absorbing encapsulant (silicone rubber or fluorosilicone rubber) that cushions the laser chip without creating excessive stress. This segmentation allows each component to perform its specialized function optimally.
Solution Approach 2:
The invention uses composite material construction combining a rigid support structure (PCB made of rigid materials like aluminum or plastic with metal reinforcement) and a soft elastomeric encapsulant (silicone rubber compound with specific durometer 20-40 Shore A). This composite approach combines the protective benefits of rigid materials with the stress-absorbing properties of soft materials, resolving the contradiction between protection and stress reduction.
2Illumination intensity
If polish-able hard epoxy is used to encapsulate the laser chip, then the front surface can be polished for better light transmission, but light reflection loss occurs and anti-reflection coating cannot be applied
Solution Approach 1:
The invention changes the surface parameter of the encapsulant from a hard, non-coatable surface to a soft, coatable elastomeric surface. The soft encapsulant material (silicone rubber) provides a surface that can be coated with anti-reflection coatings, thereby reducing light reflection loss while maintaining good light transmission properties.
3Ease of manufacture
If UV cure epoxy is used to hold the epoxy in shape during curing, then the epoxy location is fixed on the PCB, but contaminants including the cure agent cause degradation of the laser front facet in high temperature and humidity environments
Solution Approach 1:
The invention changes the chemical composition parameter of the encapsulant from UV-cure epoxy (which contains harmful cure agents) to a moisture-cure or adhesive-bonded elastomeric material (silicone rubber or fluorosilicone rubber). This material change eliminates the contaminants that cause laser facet degradation while maintaining the ability to fix the encapsulant in the desired location during assembly.
Solution Approach 2:
The soft encapsulant material (silicone rubber or fluorosilicone rubber) creates a chemically inert environment around the laser chip, protecting it from degradation by moisture and other environmental contaminants. These materials do not release harmful cure agents like UV epoxy does, thereby maintaining laser facet stability in high temperature and humidity conditions.
Data Source
AI summary
A chip-onboard assembly for a side-looking optical component is mounted on a mounting surface of a printed circuit board (PCB) and includes a window assembly mounted to the PCB. The window assembly includes a glass window and a window holding bracket. The bracket has a first walled portion, a second walled portion attached to the first walled portion, and a third walled portion opposite the second wall portion. The first walled portion further has a cutaway section configured to accommodate the glass window. An optical encapsulant covers the covering the side-looking optical component. The glass window is attached to the side-looking optical component CoB assembly.