The latest addition to the database shows a flip chip component reflowed using a Pb-free process to a standard laminate printed board. Based on optical inspection, a question was raised over one of the joints at the far left and the fiber contamination. The component was x-rayed and the solder joints were found to be satisfactory. Small fibers like the one in Figure 1 are not uncommon on the surface of printed boards. They can be airborne contamination held in place by the flux applied prior to flip-chip placement. Random in-process inspection of boards prior to component placement and inspection of bare boards for cleanliness could be considered remedies.

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database (http://defectsdatabase.npl.co.uk), which is available to all Circuits Assembly 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); defectsdatabase@npl.co.uk.