Area distributed soldering of flexible and rigid printed circuit boards

A design process which was developed to facilitate area-distributed soldering of a flexible printed circuit to a circuit pack in an inspectable and repairable manner is described. In the design, solder joints are formed between surface-mount pads on a rigid printed-circuit board and plated through holes on a flexible printed circuit. The joints are formed by heating both the flexible printed circuit and the printed circuit board to reflow temperatures and then allowing solder that has been deposited on the surface mount pads to rise through the plated through holes. Because solder rises up through the plated through holes to the exterior surface of the flexible printed circuit, spherical solder caps are clearly visible and inspectable. Solder joints are also easily repaired since the flexible printed circuit can be reheated to reflow one or all of the solder joints.>