Airborne electronics equipment fastener joint failure study

Wherever multiple pieces of material are attached together, interfacial thermal resistance exists. In order to achieve maximum interfacial heat transfer, highest possible interfacial pressure is desired. However, due to the constraints of the material property, there is a practical limit of interfacial pressure. In many cases, the interfacial pressure is achieved by using fasteners. When the fastener is tightened the stress and elasticity of the material will create a preload, thus the interfacial pressure. This paper studies two kinds of fastener failures in electronics: loss of preload and excessive preload. Loss of preload (or loose) is easier to understand and may be visible by inspection. Excessive preload failure is much harder to detect and comprehend, thus often ignored. This paper is researching the common failures of the electronic packaging associated with the fastener torque values. The study presents an engineering solution regarding torque values and locking mechanisms. It also presents a simplified conservative engineering calculation method regarding interfacial thermal resistance based on test data.