MATERIAL SELECTION AND ITS IMPACT ON COPLANARITY OF SPRING PIN PROBE HEADS

摘要

Spring probe (pin) is becoming one of the major contactor technologies in WLCSP probe head testing due to its increased compliance versus traditional contactors. The pin to pin coplanarity of a spring pin probe head is determined by various factors and housing material is one of the primary factors. This paper introduces the results of a study conducted at Smiths Connectors (IDI) on spring pin probe head housing materials. The compression spring of a spring pin is preloaded when mounted on a test board. This preload force pushes the probe head housing up and causes its bowing. The quantity of spring pins, housing structure, and housing material are major factors to influence the bowing. To select an optimal material, extensive finite element analysis (FEA) were performed to simulate the probe head housing deformation under external preload. Typically probe heads have a large quantity of cavity holes for spring pins, which can affect FEA accuracy. A specific methodology is applied and the measurement results indicate FEA can accurately predict housing bowing. The FEA results indicate that a thermoplastic composite material with a higher flexural modulus of elasticity has less bowing and lower contactor tip coplanarity. Another character of thermoplastic composite materials, water absorption, can significantly affect contactor cavity true position and probe head performance. When selecting higher flexural modulus material, lower water absorption must be considered as well.