The standards and customers are often at odds.

Quad flat no lead (QFN) and land grid array (LGA) packages often do not have solderable side terminations or are poorly solderable due to the component manufacturing process. The lack of a wettable surface is due to the package separation process, leaving exposed base material on the exposed edges of the lead frame or smearing resin on the plated surfaces.

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://defectsdatabase.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.

Chris Hunt is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); This e-mail address is being protected from spambots. You need JavaScript enabled to view it . His column appears monthly.