Flange Mount FET Grounding via PWB Cut-Out and Heat Sink
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Solution Overview
Problem
High frequency flange mount transistors experience gain and power degradation due to ineffective grounding and heat transfer when mounted on printed wiring boards, as existing mounting techniques fail to provide close proximity to the PWB ground and inadequate thermal conductivity.
Innovation Solution
A cut-out is formed in the PWB with conductive plating and vias extending between its surfaces, and a heat sink element with a shoulder contacts the cut-out edge, enhancing grounding and heat transfer, eliminating the need for a separate copper strap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat sink boss extends from the chassis to contact the FET, then heat transfer is improved, but the RF ground return path from the FET flange to the PWB increases
Solution Approach 1:
The grounding path is segmented into two separate paths: one for RF grounding (through the PWB ground plane) and one for heat sinking (through the heat sink boss to chassis). This segmentation allows each function to be optimized independently, resolving the contradiction between heat transfer and RF grounding.
Solution Approach 2:
The FET flange serves as an intermediary element that simultaneously contacts both the PWB ground plane (for RF grounding) and the heat sink boss (for heat transfer). This intermediary structure enables both grounding and heat sinking functions without requiring direct connection between the heat sink boss and PWB ground.
2Reliability
If the FET is mounted with flange on PWB surface, then electrical connection is achieved, but heat transfer to chassis is insufficient
Solution Approach 1:
The mounting structure merges two functions: the FET flange provides both electrical connection to the PWB ground plane and mechanical support for the heat sink boss. This combining of grounding and heat sinking functions at the FET flange interface resolves the contradiction between electrical connection and heat transfer efficiency.
3Reliability
If heat sink boss is not connected to PWB ground, then RF grounding path is improved, but heat transfer effectiveness is reduced
Solution Approach 1:
The grounding and heat sinking functions are segmented into separate pathways: RF grounding through the PWB ground plane and heat transfer through the heat sink boss to chassis. This segmentation resolves the apparent contradiction by allowing each function to operate through its own optimized path without interference.
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 improves electrical conductivity and heat transfer, reducing power degradation at higher frequencies and enhancing thermal management for flange mount FETs.
Implementation Method 1
One or more vias also extend between the top and bottom surfaces of the cut-out and are exposed along its edge. An FET is placed in the cut-out and into contact with a heat sink element which is designed to enhance grounding of the FET
Implementation Method 2
a heat sink element which is designed to enhance grounding of the FET and improve the transfer of heat to the chassis or other metal support structure for the PWB
Data Source
AI summary
An apparatus for improved grounding and heat transfer between flange mount field effect transistors and printed wiring boards is provided comprising a cut-out formed in the printed wiring board, extending between its top and bottom surfaces, defining an edge which is covered or plated with a conductive material at least in some areas. One or more vias also extend between the top and bottom surfaces of the cut-out and are exposed along the edge. A field effect transistor is placed in the cut-out and into contact with a heat sink element designed to enhance grounding of the field effect transistor and improve the transfer of heat to the chassis or other metal support structure for the printed wiring board.