Abstract: A multi-chip module (MCM) includes chip sub-modules that are fabricated as self-contained testable entities. The chip sub-modules plug into respective sockets in a frame of the MCM. Each chip sub-module may be tested before being plugged into the MCM. A chip sub-module may include an IC chip, such as a processor, mounted to an sub-module organic substrate that provides interconnects to the chip. The frame into which each chip sub-module plugs sits on a mini-card organic substrate that interconnects the chip sub-modules together. The MCM may include a downstop between the mini-card organic substrate and a system board to limit or prevent solder creep of solder connections between the mini-card organic substrate and the system board.