A tightly packed three-dimensional electronic system or subsystem comprising multiple stacks of semiconductor elements is described. The system is repairable because the elements connect together using re-workable flip chip connectors; each flip chip connector comprises a conductive spring element on one side and a corresponding well filled with solder on the other side. The spring elements relieve stresses at the interfaces and allow the component stacks to remain flat; they also provide vertical compliance for easing assembly of elements that have been imperfectly thinned or planarized. Semiconductor integration platforms may be used to integrate active and passive devices, multi-layer interconnections, through wafer connections, I/O plugs, and terminals for attachment of other semiconductor elements or cables.