A microelectronic unit 12 includes a substrate 20 and an electrically conductive element 40. The substrate 20 can have a CTE less than 10 ppm/°C, a major surface 21 having a recess 30 not extending through the substrate, and a material 50 having a modulus of elasticity less than 10 GPa disposed within the recess. The electrically conductive element 40 can include a joining portion 42 overlying the recess 30 and extending from an anchor portion 41 supported by the substrate 20. The joining portion 42 can be at least partially exposed at the major surface 21 for connection to a component 14 external to the microelectronic unit 12.