Characterization of Harmonic Generation by Spring Contacts in Mobile Devices

Spring contacts are used in mobile communication devices to connect metal planes near the antennas. Inappropriate design of the spring contacts will cause harmonic generation at the contact which can deteriorate receiver sensitivity at the harmonic frequency. In this article, the passive radio frequency (RF) harmonic generation phenomenon on spring contacts is studied. A spring contact harmonic generation measurement system is developed. The measurement system comprises of spring contact test vehicle, force sensor, xyz-stage with step motors, and RF path. The factors that may have an impact on the spring contact harmonic generation, such as contact material, contact force, and contact resistance are investigated. It is found that the overall harmonics generated at the spring contact decreased as the contact force increased. The gold-to-gold contact is found to be superior to the stainless-steel contacts. Indications are found that the nonlinearity at the stainless-steel spring contact is the combination of metal-insulator-metal junctions and p-n junctions formed by the surface oxide layer on the stainless steel. Recommendations to reduce the harmonic generation are discussed.