Solderability failure on LGA/QFN: the standards and customers are often at odds.
There is no requirement for the side terminations to be solderable based on IPC-A-610 requirements; however, customers often like to see a joint, and it makes automatic optical inspection (AOI) possible. Poor solderability of the edge termination is typically caused by the lack of a protective coating like tin on the surface of the copper lead frame or resin smearing during component singulation. Solderability is best tested using a wetting balance or in production with paste and a glass slide for reflow simulation.
These are typical defects shown in the National Physical Laboratory's interactive assembly and soldering defects database. The database (http://defects-database.npl.co.uk), available to all this publication's readers, allows engineers to search and view countless defects and solutions, or to submit defects online. To complement the defect of the month, NPL features the "Defect Video of the Month," presented online by Bob Willis. This describes over 20 different failure modes, many with video examples of the defect occurring in real time.
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CHRIS HUNT is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); email@example.com. His column appears monthly.
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|Title Annotation:||THE DEFECTS DATABASE|
|Publication:||Printed Circuit Design & Fab|
|Date:||Aug 1, 2012|
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