An interconnect substrate has formed thereon a first plurality of conductive leads (108-1...108-J) and a second plurality of conductive leads (109-1...109-K). A plurality of cells (106-1,1...106-J,K) are formed in the substrate, each cell having a number of bonding pads (107-1...107-M) formed on the surface of the substrate above the region of the substrate in which the cell is formed, thereby to allow a plurality of integrated circuit chips and electrical components to be attached to the substrate and electrically connected to the cells. Devices and programming elements in the substrate or in integrated circuits mounted on the substrate allow selected connections to be formed between selected ones of the conductive leads to be connected electrically thereby to allow selected components mounted on the substrate to be electrically interconnected. Other devices in the substrate or in integrated circuits mounted on the substrate allow testing of the components mounted on the substrate to determine their performance and the checking of the integrity of the connections formed between conductive leads.