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Inclusion Voiding in Gull Wing Solder Joints
Analysis Lab |
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Authored By:T.L. Lewis, C.O. Ndiaye, J.R. Wilcox IBM Corporation USA TranscriptSolder voiding in ball grid array solder joints has been well characterized and documented in IPC-A-610 and IPC-7095 which define industry recommended BGA solder workmanship criteria and methods of inspection. Solder voiding limits associated with other, non-BGA, surface mount technology solder joint types however are neither well defined nor well understood in the industry. According to IPC guidelines, the amount and size of solder voids are simply to be specified by customer/vendor agreement. In the absence of well-defined voiding criteria, the morphology of solder joint fillets seen in final visual inspection often becomes the sole arbiter of solder workmanship and quality. Among the various SMT solder interconnect designs used in IBM applications, one of the more common SMT leaded structures is the Gull Wing design found on SMT connectors. Three distinct types of solder voiding have been observed in these gull wing solder joints: solder inclusion voids, solder exclusion voids, and solidification hot tears. The most prevalent of the three has been inclusion voids, also known as solder process voids. This paper provides definitions of the different voiding types encountered in gull wing solder joint geometries. It further provides corresponding reliability data that support some level of inclusion voiding in these solder joints and identifies the final criteria being applied for certain IBM Server applications. SummarySolder voiding in ball grid array (BGA) solder joints has been well characterized and documented in IPC-A-610 and IPC-7095 which define industry recommended BGA solder workmanship criteria and methods of inspection. Solder voiding limits associated with other, non-BGA, Surface Mount Technology (SMT) solder joint types however are neither well defined nor well understood in the industry. According to IPC guidelines, the amount and size of solder voids are simply to be specified by customer/vendor agreement. In the absence of well defined voiding criteria though, the morphology of solder joint fillets seen in final visual inspection often becomes the sole arbiter of solder workmanship and quality. Among the various SMT solder interconnect designs used in IBM applications, one of the more common SMT leaded structures is the Gull Wing design found on SMT connectors. Three distinct types of solder voiding have been observed in these Gull Wing solder joints: solder inclusion voids, solder exclusion voids, and solidification hot tears. The most prevalent of the three has been inclusion voids, also known as solder process voids. Such solder inclusion voids in SMT leaded solder joints have been observed using either IR/convection or vapor phase reflow processes. This paper provides definitions of the different voiding types encountered in Gull Wing solder joint geometries. It further provides corresponding reliability data that support some level of inclusion voiding in these solder joints and identifies the final criteria being applied for certain IBM Server applications. Such acceptance criteria can be applied using various available x-ray inspection techniques on a production or sample basis. The bulk of supporting data to date has been gathered through RoHS server exempt SnPb eutectic soldering operations but it is expected to provide a reasonable baseline for pending Pb-free solder applications. ConclusionsWhile solder voiding in BGA solder joints has been extensively investigated and characterized, solder voiding phenomena in other SMT soldering configurations and their reliability impact have not been as clearly identified. In SMT gull-wing lead solder joints similar voiding to that reported in BGA joints has been observed but gull-wing joints also include other void types not characteristic of BGA joints. Solder voids types most commonly observed in the gull-wing lead solder joints of SMT array connectors are:
Initially Published in the IPC Proceedings |
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