Screw Joint Analysis in Radio Frequency Filters

Abstract: Filter devices are central elements of radio units utilized for modern-day telecommunication. Leakages of radio waves and passive intermodulation are evolving more prominent as the frequency bands become crowded. The study in this thesis investigates the screw joints in the filter assembly to determine the influential parameters on the connection between the filter lid and its chassis. The clamp and release torque are vital factors in the resulting pre-load force. Besides the geometrical characteristics of the chassis andthe self-threading screw, the friction and surface roughness on the filter lid are significant contributors. Extensive testing revealed that increasing the countersink in the lead holeand applying the lubricant Molykote 1000 Paste increase the consequent clamp torque. After numerous cycles of thermal shock testing, the release torque does not show significant dissimilarities between the tested parameter combinations. A surface roughness test shows that applying a silver coating to the filter lid increases its surface roughness and thereby the friction of the screw head on the surface. In conclusion, the pre-load force will increase by changing the parameters as mentioned above, while it requires further testing to make a suggestion regarding the effect of the silver coating on the filter lid.