High standoff parts are more susceptible to improper wave height.

Figure 1 shows a solder skip, due mainly to incorrect wave height, as there is no evidence of solder on the pad or the termination. This may be a Pb-free joint, but the principle behind the defect is the same. If there had been solder on the termination, the process parameters may have been correct, and problems with the pad solderability may have been present.

In the past, skips on this type of capacitor have also been seen with different component suppliers and different lead forms. This type of component has the highest standoff of any component. When investigating skips, look at the design, differences in component lead form and process issues like flux gassing and wave height.

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.