Dear Technetters,

        Currently we have changed to use PCB with OSP (Organic
        Solderability Preservative) finished instead of HASL (Hot Air
        Solder Leveling) finished, the PCB is a single side one, CEM-1
        or CEM-4 material, mixed technology with through hole and
        surface mount component, which then go through wave soldering
        process. The PCB itself has some big copper land/trace design
        for high current flow which patterned with circular opening by
        solder resist in order to increase overall trace thickness but
        not create solder coalesce problem, the circular pads is 1mm
        in diameter and with 1.5mm centre to centre distance. After
        the wave soldering, all the through hole lead solder joint and
        surface mount device seems no difference in quality when
        compare with the HASL finished board, but a random solder
        skipping happened on those circular pad opening, the skip
        solder area can be readily take up solder by applying solder
        wire with solder iron, the question is :

        1. What is the root cause of such problem? Flux (the flux
        using is a rma no clean type)? Machine setting? Pad design or
        others?

        2. The way to eliminate this problem, but if it cannot,can we
        just let the skip solder pad (with copper expose) remain
        unsolder, will this create reliability problem? What I heard
        from some of the OSP supplier that this should be OK.


        Thanks in advance,
        WM Cheng

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