An apparatus is described for burn-in and/or functional testing of microelectronic circuits of unsingulated wafers. A large number of power, ground, and signal connections can be made to a large number of contacts on a wafer. The apparatus has a cartridge that allows for fanning-in of electric paths. A distribution board has a plurality of interfaces that are strategically positioned to provide a dense configuration. The interfaces are connected through flexible attachments to an array of first connector modules. Each one of the first connector modules can be independently connected to a respective one of a plurality of second connector modules, thereby reducing stresses on a frame of the apparatus. Further features include for example a piston that allows for tight control of forces exerted by terminals onto contacts of a wafer.