Active Device Prescreening for Hybrids

An investigation was conducted to find ways to reduce the number of active device failures so common in hybrid manufacturing. It was determined that a very substantial reduction in these failures can be achieved with the proper procurement, inspection, and testing of the active device chips prior to the assembly into the hybrid. A high reliability production line which uses this approach has resulted in dierelated in-process repairs which amount to only 29 percent of all the repairs, whereas the corresponding figure for another line without the above controls is 60 percent. This is mainly achieved through a) the control of the purchased active device chips through stringent procurement specifications (including wafer probing); b) incoming inspection which includes sample testing for electrical and mechanical parameters; c) visual examination of all the active device chips prior to usage; and d) mounting on headers and testing electrically all devices which have been found, through previous history, to have a high fallout rate; this comprises about 1/3 of all the transistor chips used; the devices are subsequently removed from the headers and installed in hybrids.