Total separation is cause for investigation.

The conformal coating has separated from the surface of the plastic QFN/LGA body, which is not uncommon on many plastic parts. Devices often have molding release agents on the surface that make coating adhesion difficult to maintain, and minor loss or separation may not normally be reworked. In this case, the root cause should be established, as all the coating on the device has completely lifted.

Cleaning the board assembly after soldering may overcome the problem in future production runs, or it might not, unless a proper assessment is conducted on the cleaning process compatibility. The next batch of parts might not have the problem, and, convinced, you will be cleaning for life. The fault can be seen on most conformal coatings, more likely on thinner coating, although the poor adhesion will still be apparent on thicker coating that may not be so easily displaced.

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.

Dr. Davide Di Maio 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.