NPL defect of the month

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9 November 2011 News Manufacturing / Production Technology, Hardware & Services

The accompanying photograph, taken from the NPL defect database (http://defectsdatabase.npl.co.uk) shows the surface of a nickel pad on a printed board after stripping the gold from the nickel surface.

The image shows limited evidence of corrosion on the nickel surface at the grain boundaries on a bare board. Some evidence of gold is also still visible. Solder joint failures when examined normally show far more corrosion around the nickel boundary. There is still a lot of debate on the subject of ‘black pad,’ but changes to nickel chemistry and better control have reduced solder joint failures.

Unfortunately many gold failures are attributed to black pad issues when clearly they are not. Close cooperation is necessary with the PCB supplier and its chemistry supplier to determine the cause of the problem. One should always ask to review the chemistry supplier’s audit reports conducted at the PCB supplier’s premises. Independent analysis may also be required if the assembly processes are considered the root cause of any joint failure. Things which should be reviewed include the PCB fabrication process, the reflow temperature and time in a liquid state for the solder paste.

November’s featured NPL defect video analyses methods of assembling package-on-package boards, and can be found at www.dataweek.co.za/video

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NPL defect of the month

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