Dr. Chris Hunt

A new pad shape could increase soldering speed with less stress to the board.

Although products designed for high-temperature applications with organic substrates can withstand high soldering temperatures, can they still be damaged? Damage can occur if soldering times or temperatures are too high or, in the case of soldering irons, the tip comes in contact with the surface of the board or pad for an excessive period of time.

During automated soldering the program that defines the tip’s contact position and force must be refined. If not, due to change in position of the board, change of tip, poor product tooling or system drift, the soldering iron tip will cause damage to the board. It is also possible for damage to occur if the z position of the tool tip is poorly controlled with no pressure sensing.

FIGURE 1 shows damage to the surface of the solder mask caused by the tool. It is, however, possible to change the shape of the pad so it has a teardrop shape or a tail opening in the solder mask where the tip can land and make contact. This makes good thermal contact between the solder on the tip and the pad, increasing the speed of soldering without damage to the board surface.

These are typical defects shown in the National Physical Laboratory’s interactive assembly and soldering defects database. The database, 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.

Dr. CHRIS HUNT is with the National Physical Laboratory Industry and Innovation division (npl.co.uk); chris.hunt@npl.co.uk. His column appears monthly.



Figure 1. Soldering iron-related solder mask damage.

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