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SMT-Jan2017

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74 SMT Magazine • January 2017 ate controls and parameters that will fit the product appli- cations. Las Marias: What about plat- ing? How does plating affect your assembly process? Dulang: Plating is one of the critical parameters. If plat- ing does not comply with the specifications, then there is a strong possibility to encounter assembly problems. Plating can cause functional test fail- ures due to connectivity issues. The worst reliabil- ity failure is the intermittent failure due to cracks. Compatibility of surface plating to solder paste and component plating are ver y critical points. Las Marias: Are there parameters to consider when it comes to plating and/or surface finishing that will help optimize your assembly process? Apolinario: The parameters are the right selection of surface finish, then PCB pad cleanliness. Plating thickness should be considered to optimize the as - sembly process and testing, as well as handling and shelf life. Las Marias: How do surface finishes impact solder - ability? Apolinario: Solder finishes have a significant im- pact on solderability, most especially on those fine- pitch lead and more complex components such BGAs, LGAs, and flip chips. That's why the selec- tion of the surface finish is not easy; the surface plating should be determined based on the prod- uct application and complexity. First, the planari- ty of surface finish should be properly assessed; an uneven surface is not fit for complex components such BGAs. Then, the handling sensitivity—ex- posed surface finish might create contamination that will impact solderability. And lastly, the reli- ability of assemblies. Las Marias: What about shelf life? Apolinario: The PCB shelf life depends on the type of surface finish and thickness. Proper packaging should be considered to prevent any excess mois - ture and ensure prolonged shelf life. There are standards written on how to treat the PCB if it exceeded the shelf life; more often, customers de- cide and recommend actions on how to handle end of shelf life. The quality and integrity of the solder and connection slightly varies as the shelf life nears its expiration. Las Marias: How do you and your customers deter- mine which surface finish would be best suited to your needs? Apolinario: In most cases, customer requirements depend on the product application, standards reg - ulation, manufacturability or complexity of pro- cess, cost, reliability, rework, and the environment where the product will most exposed. Dulang: The overall product assembly process must be considered. For example, does the prod - uct have COB process? Some surface finishes are wire bondable while others are not. Therefore, what wire to use, aluminum or gold? The environ- ment upon where the product will be applied also needs to be considered as it can affect reliability. Las Marias: What trends do you see in surface fin - ishes? Apolinario: As the complexity of surface-mount components increases, we see the trend toward ENIG finish. Even though it is expensive, it has the advantage of being able to handle more com- plex surface-mount components such BGAs, flip chips, and LGAs. ENIG is compliant with ROHS and WEEE, which are now standard requirements for the industry, especially in the automotive and industrial sectors. However, given the challenges on productivity, cost and quality, most industries are also considering alternative finish such im- mersion silver, which has the same advantages as ENIG but not as expensive. Las Marias: Thank you, gentlemen. Apolinario: Thank you, Stephen. SMT PLATING AND SURFACE FINISH: ASSEMBLERS' POV Joemar Apolinario Dnichols Dulang

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