Inspection joins test in a single system

Offering a solution for verifying limited-access boards where not every joint is visible, Goepel Electronic (Jena, Germany; http://www.goepel.com) has incorporated both automated-optical inspection (AOI) and boundary-scan test (BST) into its OptiCon AdvancedLine and SpeedLine inspection systems. The company claims that with adequate planning during design, manufacturers can use this combination to attain nearly 100% fault coverage. They can eliminate in-circuit test and the accompanying bed-of-nails fixtures—avoiding a significant expense, a production bottleneck, and a storage headache.

AOI and BST are primarily complementary, with only a few overlapping failure-recognition modes, plus an interactive mode that finds faults that neither AOI nor BST can locate alone.

Kokott acknowledges that stand-alone AOI systems can be deployed with more flexibility than can the combined AOI/BST system. AOI-only systems can be deployed after solder-paste deposition, after automated pick-and-place, after manual placement, and after solder reflow. In contrast, the combined system can only operate near the end of the production process, when electrical test normally takes place. Similarly, x-ray systems can evaluate the BGA solder joints that are invisible to AOI systems. He notes, however, that such alternatives are expensive ones, costing upwards of $200,000, vs. $70,000 for the AOI/BST combination.

Combining the two techniques also concentrates fault data, keeping it within one host workstation that controls both the optical and boundary-scan tests. With alternatives, fault data is scattered among various workstations controlling inspection and electrical test. With the data in one place, engineers can more readily identify process or design improvements to prevent future faults and lower manufacturing costs. In addition, by eliminating the fixture and program-preparation delays that in-circuit test demands, the combined approach allows manufacturers to rapidly test prototypes, so engineers can enter ramp-up with known test procedures and fault-free boards.

Benefiting most from Goepel's systems, says Kokott, are boards heavily populated by boundary-scan devices or devices tested by conventional boundary-scan techniques, such as interconnection test or cluster test. OEMs who manufacture their own products benefit because designers can create the boundary-scan tests themselves, shortening time-to-market.

Because AOI takes far longer than BST, AOI basically determines maximum throughput rates. Although each technique finds faults the other does not, there is some overlap (figure). To increase throughput—if boundary-scan circuitry is available—test engineers can shorten the AOI step by transferring detection of some faults to BST.