A power electronics assembly for an electric motor controller. The power electronics assembly comprises an insulated metal substrate, a composite material substrate, and a bolt having a bolt head and a bolt shaft for mechanically coupling the composite material substrate to the insulated metal substrate. The power electronics assembly also includes an electrically conductive sleeve configured to be held between a first electrical contact carried by the insulated metal substrate and a second electrical contact carried by the composite material substrate and the bolt is configured to clamp the composite material substrate to the insulated metal substrate to force the electrically conductive sleeve against the first electrical contact and the second electrical contact.