Agilent looks at inspection trends

Kent Dinkel, imaging marketing manager

Jeff Harrell, AOI product manager Photos courtesy of Agilent Technologies.

Q: How has inspection changed in the past few years?

Dinkel: One of the biggest changes is the growth of AOI and AXI on the same process line. In process placement, AOI is more versatile. You traditionally placed it after wave or reflow solder to look for the presence or absence of components, for the correct components and correct positioning, and at visible solder joints. But boards have become increasingly complex. Hidden joints, fine-pitch gull-wing heels, through-hole connectors, and RF shielding challenge this approach.

Harrell: You can also place AOI upstream. It can verify paste volume on boards before placing components, for example. A 2-D AOI system looks at the solder position on the pad and for deposit-area and bridging faults. Three-dimensional techniques permit more thoroughly assessing solder volume, which can determine good joint formation and, ultimately, board function.

After component placement and before wave or reflow, AOI looks again at component position, polarity, and identity. Some manufacturers perform AOI after placing only some components, examining the components as well as the solder paste on pads that will later be covered by BGAs. And many still perform post-reflow inspection. People want to take advantage of the machine's flexibility, buying only one AOI system for all process locations, if possible. We offer a "unified platform." You might use it with a 3-D analysis head at one point and an illumination-based head somewhere else.

Dinkel: AXI placement is more fixed—examining solder joints post-reflow or post-wave. It is also more expensive and slower, so you have to make sure it will justify its cost. X-ray offers 2-D or 3-D imaging and either automatic or semi-automatic operation. Automatic 2-D systems work best with less-complex single-sided boards. They lose effectiveness in double-sided applications. Three-dimensional systems can separate top and bottom side joints and can identify defects where 2-D systems are blind. Some manufacturers offer semi-automatic "2.5-D," combining 2-D inspection, oblique viewing, and software algorithms to make the analysis more 3-D-like. These solutions work well in off-line applications, such as failure analysis, but they are generally not fast or automatic enough for high-volume production.

Q: Where is the balance point between post-reflow AOI and AXI?

Harrell: You still see AOI more often in board manufacturing because of its throughput and cost advantages. As visual access to joints declines, we expect that situation to change. The balance also depends on board value and customer intention. Is the goal process analysis and defect prevention where you see pre- and post-reflow AOI more often or defect detection, which favors x-ray? How important are the cost of field failure and complete fault coverage—say an enterprise-level server or router vs. a cell phone? At the low end, most people emphasize AOI. As the board value and cost of escapes increases, AXI becomes more common.