Development of a soldering/inspection workcell for surface mount devices

Abstract

The small focused spot size and localized heating possible with laser soldering makes it an attractive alternative technique for bonding surface mount devices with small lead pitch onto a printed wiring board. Using a Nd:YAG laser, we have applied this technique to reflow soldering 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 component 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.