A thinly plated hole could be susceptible to PTH lead damage.

The latest addition to the database is delamination on the surface of a board assembly. A microsection (Figure 1) shows a plated through-hole with a through-hole lead after soldering using a PbSn process. Prior to sectioning, the board had shown evidence of minor delamination and measling around the pad area on the board subsurface. The board was being produced in medium volume for a consumer product.

Mechanical strain or damage may occur during pin insertion. The soldering temperature or the time to solder may have been excessive, causing board expansion. The image in Figure 1 is not very clear, but based on the examination and comparison of the relative dimensions, the plating in the hole is thin, probably less than 20 µm. There is evidence of delamination/separation of the glass bundles at the hole-copper interface.

Close examination of the microsection and the rest of the board will be required for root cause analysis. There are a number of possible causes, and along with the board examination, all the process details would be reviewed, or even the assembly/soldering operation audited.

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 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.

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