Optical Subassembly Thermistor Mounting on FPC
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional receiver optical subassemblies (ROSA) face challenges in temperature sensing and bias voltage adjustment for avalanche photodiodes (APDs) due to space constraints and high costs in butterfly packages, while co-axial packages are cheaper but lack space for thermistors, limiting lead pins and increasing costs for die thermistors.
Innovation Solution
The optical subassembly employs a flexible printed circuit board to mount a thermistor outside the co-axial package, connecting it via lead pins to sense the temperature of the APD, allowing for effective temperature sensing without additional space within the package, using chip thermistors to reduce costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thermistor is installed inside the co-axial package to sense APD temperature, then temperature sensing function is achieved, but the package space is insufficient and lead pin count is limited to 4-6 pins
Solution Approach 1:
The thermistor is extracted from the internal package space and mounted on the external circuit board instead. This extraction resolves the space conflict by placing the temperature sensing component outside the co-axial package while maintaining its functional integration through external circuit connections.
Solution Approach 2:
The thermistor mounting location is moved from the internal three-dimensional space to the external two-dimensional circuit board surface. This dimensional transition allows the package to maintain its compact co-axial structure while accommodating the thermistor externally with minimal impact on the overall form factor.
2Measurement precision
If a die thermistor is used for temperature sensing, then sensing precision is improved, but the cost increases significantly
Solution Approach 1:
The patent substitutes expensive die thermistors with cheaper chip thermistors that provide adequate temperature sensing precision for the application. This substitution significantly reduces manufacturing costs while maintaining sufficient measurement accuracy for bias voltage compensation in optical receivers.
3Reliability
If the number of lead pins is increased to accommodate thermistor connections, then temperature sensing capability is improved, but the package outer diameter must be increased beyond 5.6mm
Solution Approach 1:
The thermistor and its connection requirements are extracted from the package interior to the external circuit board. This allows the package to maintain its standard 4-5.6mm diameter with 4-6 lead pins, while the thermistor connections are established externally without requiring additional pins through the package body.
4Reliability
If a butterfly package is used instead of co-axial package to accommodate thermistor, then temperature sensing space is sufficient, but the price becomes expensive
Solution Approach 1:
The thermistor mounting function is extracted from the package structure itself and relocated to an external circuit board. This allows the use of the simpler, cheaper co-axial package instead of the more complex and expensive butterfly package, while still providing adequate space for thermistor installation on the external board.
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 enables temperature sensing of the APD with a thermistor outside the package, increasing the number of available lead pins and reducing costs by using chip thermistors, while maintaining signal quality and impedance matching for high-speed optical communication systems.
Implementation Method 1
a thermistor (125) is mounted on a flexible printed circuit board (120)... The thermistor installed in the package senses the case temperature of the package, which corresponds to the operating temperature of the APD
Implementation Method 2
connecting it via lead pins to sense the temperature of the APD... connected to a via hole provided on the flexible printed circuit board, and this via hole is directly soldered to the stem
Data Source
AI summary
The present invention is to provide an optical subassembly with a co-axial package that enables to sense the temperature of the devices mounted within the subassembly with a relatively inexpensive chip thermistor. The subassembly includes a co-axial package and a FPC board to connect the subassembly to the outer circuit. The thermistor is mounted on the FPC board such that one electrode thereof is connected to a pattern formed on a surface opposite to a surface facing the subassembly and the other electrode is soldered to a via hole connecting two surfaces of the FPC board and this via hole is soldered directly to the subassembly.