Circuits Assembly - August 2008 - (Page 41)

Cracks, head-on-pillow (HOP) and knuckling are gross yet common defects that cause intermittent failures and are impossible to catch with AOI and difficult to detect with 3-D x-ray. Failure analysis can support process modification to prevent this. NPI. The reliability analysis lab also supports NPI by providing data that can be used in product qualification. Typically customers provide two assemblies for this part of the qualification process. One area of focus is BGAs, as solder joints aren’t visible without destructive testing. The lab cross-sections and verifies the BGA center and outside perimeters reflowed adequately. Failure analysis also helps processes evolve to support emerging customer requirements. For instance, continued miniaturization is driving highly complex assembly such as package on package. In this situation, a BGA is placed and a second BGA is flux-dipped and placed on top of the first BGA. There is now a triple stack BGA, adding to the already challenging component Δ T. Vapor phase works well with those technologies because it reflows evenly at 230 oC using SAC 305; however, other SAC formulations require higher temperatures. The lab is currently analyzing a specially formulated 235°C boiling point fluid in order to provide the best options to support these future customer needs. Quality issues. Perhaps one of the areas in which laboratory service is most effective in contributing to enhanced throughput is its ability to help engineering determine the root cause of quality issues through failure analysis. The product and process validation techniques discussed earlier help optimize processes from the start, but even with a robust process, additional defects may occur. Often these circuitsassembly.com Getting Lean Figure 1. Cross-section analysis showed that a customer’s final assembly process was placing unacceptable levels of strain on the solder joints. defects arise not from the EMS process, but from issues in a supplier’s process or in handling at the customer. Failure analysis resources can help quickly identify the issue. The following examples illustrate how these defects can arise: In one case, analysis indicated field failures were the result of the customer’s final assembly process (Figure 1). The analysis monitored the strain in each of the processes through ICT and functional test at the contractor, and strain in each of the customer’s processes. The result showed the root cause of the failures was a screw mounted next to the BGA during the customer’s final assembly process. Strain gauge analysis showed excessive and constant strain was applied to the BGA in question once the final assembly housing was fully installed, resulting in fractured solder joints and open circuit connections. The problem was quickly resolved, and it helped solidify the customer relationship because the recommended process modifications were based on quantitative analysis. Supplier-related issues also can cause hard-to-identify defects. Some issues occur when suppliers are out of spec. For instance, in one case a customer’s product was leaking lithium fluid in the field. The problem was an issue in the battery supplier’s assembly process. Production opera- Figure 2. Analysis of this leaking battery determined the supplier’s production operators were crimping and pinching the battery seal in final assembly. tors were actually crimping and pinching the battery seal in final assembly (Figure 2). Once the failure analysis data were presented, the supplier took responsibility, and modified the batter assembly process, improving yield and reliability. What started as an assembly workmanship concern in the eyes of the customer resulted in a supply base issue; an issue where root cause was identified and permanent corrective action was taken. This type of customer/supplier/ manufacturer problem-solving partnership would never have been possible without the use of undisputable quantitative analysis provided through reliability laboratory services. While reliability analysis isn’t traditionally thought of in terms of Lean manufacturing, these examples demonstrate how its use helps minimize process variability, development and speed manufacturing and quality issue resolution. The net effect is improved customer quality, enhanced manufacturing and resource efficiency, leading to improved throughput. n References 1. Chris Munroe, “The Advantages of Vapor Phase Processing in RoHS-Compliant Assembly,” SMTA International Proceedings, August 2008. Circuits Assembly AUGUST 2008 41 http://circuitsassembly.com

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Circuits Assembly - August 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Screen Printing Better Manufacturing Auditing a Fabricatior Cutting Machine Programming Time Simultaneous Acoustic Imaging and Surface Mapping Tech Tips Soldering Test and Inspection Process Doctor Pb-Free Lessons Learned Getting Lean Component Advances Product Spotlight Ad Index Assembly Insider Techincal Abstracts

Circuits Assembly - August 2008

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