Consider a dip paste for resoldering components after rework.

Figure 1 is a good example of solder balling under a BGA that is certainly outside of IPC criteria. The ball will have undoubtedly reduced the insulation separation distance below the minimum for the product design. The solder ball is most likely the result of using paste to rework the part, with excessive paste resulting in a solder ball. In such cases, it’s worth looking at the new range of dip pastes for rework, as they can eliminate rework stencils.

Reworking the component to remove the solder ball may be an extreme response, however. With care and a height pressure air line, the ball could probably be removed without removing the component. It’s worth a try. Inspect the component location afterward using optical or x-ray equipment.

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.