Numerical simulation of transient thermomechanical ageing effects

Automotive radar and 5G communication systems require for their high frequency functionality substrates with low dielectric constants, which are capable to operate at elevated temperatures for long lifetimes. Special substrates based on laminate Printed Circuit Board (PCB) technology come here into focus due to their cost benefit against ceramic substrates. But the matrix of these substrates is based on polymers like for example PPE (Polyphenylether) or PTFE (Polytetra-floureten). In general, polymers are susceptible to ageing, which may already be initiated at mild conditions and short times (e.g. during the expected usetime) and can have a potential large influence on the reliability as the properties can change massively.To enable the development of reliable electrical components, the behavior during the desired lifetime of the used materials is of importance. In this paper we focus on thermo-oxidative ageing effects of a Radio Frequency (RF) application suitable PCB material and how this effect can be considered transiently in a numerical simulation approach. For this approach, first extensive material characterization was performed on samples aged for different periods of time at 175°C. This temperature was selected as this is the specified maximum operating temperature for the material. These different states of the material were then used within the simulation model, where the ageing process is simulated and a gradual – continuous change of one state to the other is calculated.