Package-On-Package (PoP) Solder Short FA TechniqueAuthors: Afaq Ahmed, B.E., MBA, Mohammad Nizam Othman, Fazli Haidir
Company: Celestica Malaysia Sdn Bhd
Date Published: 4/14/2015 Conference: Symposium
PoP package board-assembly has its own challenge. Typically a solder ball to solder ball short would happen if things go wrong during assembly. This is just one type of failure mechanism, other usual problems associated with BGA assembly would happen too. For hairline short, typical X-ray tool would not help if those shorts are fine enough to be missed by X-ray. In that context, PoP failure analysis is very challenging. A lapping technique was used to vertically grind from memory side to the point where all solder joints were visible from top. Mounting epoxy was used through a vacuum-impregnation to hold the solder joints.
Looking from the top, for solder ball joint to solder ball joint hairline short, frozen in-place by molding epoxy becomes easy to see through a microscope as all the interconnections can be viewed simultaneously.
Once a solder-to-solder short is visually identified, SEM and EDX was used to confirm the shorting material to be solder. Further checks on memory BGA showed presence of fiber material between the balls. This its concluded that solder bridged through the fiber during the assembly of memory BGA chip to Processor chip.
PoP, SEM, EDX, Failure Analysis, Solder ball to Solder Ball Short
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