Packages are changing, forcing SPI, AOI and test to keep up.

New package types are appearing everywhere and are driving the need for testing and inspection at various points in the production line. Preventing defects is now as important as detecting defects. Many assemblers include a variety of test and inspection equipment in their lines: SPI, AOI, AXI, ICT. The combination of systems used depends on applications, budgets and so on. From a supplier’s point of view, keeping algorithms, imaging techniques and testing techniques up to date with packages are musts.

Starting with SPI, we can see examples of this evolution. Many articles in literature with data support the fact that paste print errors can contribute to downstream defects through a compounding effect of paste geometry and manufacturing variables. Capturing these defects or monitoring process variation to prevent defects early can save money and time in rework, increase production quality and, of course, help prevent defects altogether (e.g., tombstoning, from uneven paste). Environmental, technological and economic trends push the SPI market through smaller form factors, changes in material sets for Pb-free, and cost-reduction demands. Recent use of advanced packages such as fine-pitch BGA, CSP, 0201 and 01005 devices are driving the evolution of this step.

Similar to the SPI situation, the AOI market is competing for repeatable and accurate measurements while still meeting line beat-rates with quality inspection and versatility. Continual advancements in the imaging chain of an AOI system is required to keep up with resolution needs driven by smaller components and packages. Another industry-wide packaging-related challenge for AOI is related to low contrast components. Examples of such components are white parts on white ceramic boards, small SOTs on dark boards, or any case where the component has a poor contrast to the background. Algorithm enhancements can improve the low contrast situation (Figure 1).


Customers are driving test innovation, too. A recent AXI example: the QFN. Because these devices are relatively low cost, QFN packages are seeing more use, for example, in leadframe-based CSPs. Currently, only generic test requirements for QFNs exist. More quality testing and inspection is needed. Because the QFN has hidden joints (Figure 2), x-ray is the best in-process method of inspection. In this case, a major OEM actually helped to develop an algorithm addressing QFNs and reducing false call rates.


New packages also challenge ICT, mainly from reduced vectorless test coverage and eroding test point access. In response, most ICT vendors have enhanced traditional vectorless test using better measurement hardware and noise reduction techniques. However, even these will suffer as leadframes shrink, disappear or get shielded by heatsinks. Vectorless test, which dramatically reduces the dependency on leadframes, is one way to resolve that issue.

New ICT probing techniques are compatible with Pb-free processes and facilitate test point access on dense or high-speed boards where ICT was not possible. They permit more probing options and therefore simplify and reduce the cost of ICT fixtures. They also simplify DfT by eliminating the need to reroute signal paths during layout to accommodate traditional test pads.

Stacy Kalisz Johnson is product marketing engineer at Agilent (agilent.com); stacy_johnson@agilent.com.

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