Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Air bubbles in solder joints



Air bubbles in solder joints | 30 October, 2002

Hi, I have received a report form a board supplier, analysing the reuslts form non wetting problems we have been expereincing with their boards. I assumed it was due to the gold layer being too thin, thus allowing the nicklel layer to be exposed and thus not easy to solder to. However, the report suggets that the cause of the problem is in the pre heat stage of the reflow process, where the flux has not had enough time to vapourise and clean the surface for soldering??!!! This does not sit well with me as we run another suppliers boards, exactly the same board design, and we expereince no problmes with the same profile. Now the question I am asking is, wrt the cross sectional analysis, should these always have air bubbles present in the solder fillet formation? My expereince and tehcnical sessions I have been involved with suggestes up to 20% of a solder joint can have voids ( or air bubbles) without any detreimental affect on the solder fillet quality. Further to that, the air bubbles have no relation to the way the flux activity works on the PCB. The submitted report shows signs of silicon and carbon containination, and the report suggestes the flux from the solder paste is not being released out of the solder paste to clean the PCB finish.( whichh I think is a load of crap) Any assisitance or guidelines in relation to this problem would be very much appreciated.

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Air bubbles in solder joints | 31 October, 2002

Being very new to SMT I won't assume I know what the problem is but.... I had lots of air pockets in solder joints, 95% of the boards. Everyone I spoke to thought it was a problem with my process but when one board was sent to our supplier they admitted to some experimentation in their process which led to something not being cleaned (if I remember correctly) from a layer inside the board. The heat brought some of the residual chemicals to the surface through small pits in the vias and through holes, this would blow through the solder leaving nice little holes.

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