AS SEEN IN - Phoenix|x-ray
The Magazine for Electronics Assembly UNTIL VERY RECENTLY, COSTLY 3-D SYSTEMS WERE NEEDED TO FIND NUMEROUS SUBTLE DEFECTS. TODAY, NEW 2-D WITH OVHM SYSTEMS OFFER AN INEXPENSIVE ALTERNATIVE IN MANY INSTANCES. By Holger Roth May 2001 www.smtmag.com 3-D or 2-D- Choosing with Today’s Technology Recently, this question arose during a presentation: Competitors are pushing three-dimensional (3-D) X-ray inspection as the best way to inspect ball grid arrays (BGA) and chip scale packages (CSP). Do I need to spend the extra money to ensure my production quality? My answer, as usual, was yes — and no. That decision depends greatly on what is being manufactured. For more than 95 percent of manufacturers, twodimensional (2-D) X-ray actually is a better solution. The question then follows: Are we one of the 5 percent who need 3-D? This article offers information to help ascertain the answer to that question. Test Criteria and Requirements X-ray inspection, whether offline manual or inline automated, verifies the functional integrity of assemblies after the soldering process. X-ray inspection finds: • Solder bridges (shorts) • Missing or undersized solder joints (voids) • Misalignments • Open solder joints In practice, BGA bridges, missing joints and misalignments can be found and recognized by either an operator or an automated software package, using a top-down view without rotating or tilting the board. Open solder joints, however, are in contrast to these rough solder joints, and typically require an inspection in oblique view at higher magnification. Under such inspection, either a gap in the solder joint can be AS SEEN IN seen directly, or the shape of a solder mass will indicate insufficient pad wetting (the board pad, in most cases). Using the oblique view to inspect smaller solder joints such as fine-pitch ball grid array (FBGA), microBGA CSPs and flip chips frequently provides insufficient magnification because of the long distance separating the solder joints from the X-ray source due to sample tilting. This can be overcome only if the X-ray system has a high geometrical magnification even at angled inspection or oblique view at highest magnification (OVHM). Automated BGA solder joint evaluations are performed simply by comparing the measured data with threshold values. Thus, all X-ray images can be quickly, accurately and repeatedly determined for pass-fail conditions — making even semiautomated 100 percent sorting possible.