Non-linear deflection analysis of pin-on-package testing using FEA

Abstract

Integrated circuit packages are tested for component function before shipped to customers. The testing involves probing of the package leads with Pogo pins/spring probes having sharp-edge tips manufactured from harder BeCu or Pd alloys. The spring-controlled pins forced onto the pad surface penetrate the surface oxide layers to establish electrical contact with the metal underneath for assessment of test parameters. However, this also can lead to form scratch marks and pad cracks on the lead surfaces and achieving good contact with minimum damage to pad surfaces is important. Also pin tips tend to deform due to mechanical interactions with the package lead & wear upon continuous insertions. Since reliability testing over millions of insertions can be a very time consuming process, here's, an attempt to utilise simulation method/approach to quantify plunger pin insertion induced stress/strain at the pin-pad interfaces & evaluate variations in tip profile on probe and pad performance in a standard manner. This paper describes a non-linear contact analysis of spring-loaded palladium vertical probes with wedge & crown tip profiles insertion onto lead surface during package testing and evaluating penetration induced deformation, stress and strain at contacting interfaces of both probe tip and pad and compared with indentation measurements. The non-linear analysis involves Bilinear Isotropic hardening plasticity (BISO) elasto-plastic material and rough contacts in Ansys Workbench environment.