DEVELOPMENT OF A SOLDERING INSPECTION WORKCELL FOR SURFACE-MOUNT DEVICES/

The small focused spot size and-localized heating possible with laser soldering makes it an attractive alternative technique for bonding sur face mount devices with small lead pitch onto a printed wiring board. Using a Nd:YAG laser, we have applied this technique to reflow solderi ng of a test device-a 224-pin quad ceramic chip (lead spacing 25 mil)- onto pretinned substrates. The soldering step was incorporated into a larger workcell, in which an Adept robot was used to place the compone nt in position and also to scan the laser beam, delivered via a fiber, over the leads to be soldered. The mobile laser head was modified to accept a miniature CCD camera coupled to a Cognex vision system, which allowed coincident viewing of the soldering process and postsoldering inspection of the joints.