Utilising Shear Stress Modelling in Reliability Studies of Polymeric Interconnections in Electronics

Polymeric interconnections in electronics are used in various applications and consequently, they may be exposed to various environments during their life-time. Accelerated life tests are typically used to study their reliability in different environments. However, the tests are fairly time consuming and often expensive. If modelling with accurate results could be utilised when studying reliability, time and cost savings could be achieved as the need for actual testing would decrease. In this study possibilities to utilise shear stress modelling in the prediction of polymeric interconnection reliability under humid and thermal environments were investigated. It was observed that if the failure mechanism of the polymeric interconnections is related to shear stresses, shear stress modelling can be utilised in reliability studies in thermal environments. For example, delamination may be one manifestation of failure mechanisms related to shear stress. If the materials or dimensions of polymeric interconnections are changed so that failure mechanisms will not change, shear stress modelling together with the reliability data of the initial structure can be used to estimate failure times and places of the new structure. On the other hand, if the failure mechanism of the polymeric interconnection is related to thermal expansion of the adhesive matrix, strain modelling which calculates the changes in thickness of an adhesive layer between contacts seems feasible in reliability studies. In addition it was observed in this study that reliability prediction of polymeric interconnections in humid environments is extremely difficult due to the numerous factors causing failures in humid environments. It was not possible to use shear stress modelling alone, as the factors causing failure are not only related to shear stresses. However, if shear stress modelling together with adhesion measurements is used, estimation of failure times in a constant humidity test seems to be possible.