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SMT electronics assembly manufacturing forum.

Solder balls after wave soldering

Istv�n Dominik


Solder balls after wave soldering | 28 January, 2000


I have problems with the SMD boards during wave soldering. Mainly between the pins of the SOICs there are small solder balls. Maybe somebody had the same problem and could solve it. Please give me some ideas what causes this problem and how it is possible to prevent it.


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mike d


Re: Solder balls after wave soldering | 28 January, 2000


One possible reason for this is that you are using a water soluble flux in your wave solder machine. If you are and the boards are not pre heated long enough, the water in the flux does not evaporate before hitting the wave. When the water hits the wave it instantly boils, shooting little balls of solder everywhere.

Just my thoughts,

Mike Deeney

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Roni H.


Re: Solder balls after wave soldering | 30 January, 2000


The major reason is that the flux is still "wet", you should fix the temp. profile (specialy preheat zone) so the evaporation of flux carriers will be better (anyway not to much !).

Recommended: 1st preheat zone heating to ~70C , 2nd&3rd preheat zones heating to ~110C slowly (before soldering) - measured on CS !!

Good luck Roni

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Steve Harshbarger


Re: Solder balls after wave soldering | 2 February, 2000


The advise from both Roni and Mike sounds right on the money.

The problem is most likely that your PCB is not completely dry (the flux has not completely evaporated) in the area where these solder balls occur. You have a number of different options that may resolve your problem.

- The easiest is to start by checking your top side PCB temperature. This temperature is checked just prior to the PCB entering into the solder wave. **Note - make sure you check this temperature on a PCB that has the solder ball problems, and was put through your fluxing process. Top side temperature can change by as much as 40 degrees, depending on PCB type and if flux was applied.** Most alcohol based no clean fluxes typically run around 210F and most water soluble fluxes typically run around 180F. Your flux manufacturer should have a recommended temperature. If you are running to low a temperature - SOLDER BALLS.

- If you have confirmed your top side temperature is ok, the next option you may want to consider is changing to a convection preheater. Adding some air movement in the preheat area will help to dry the flux on the PCB faster.

- If you are running water based flux (VOC free), the steps I mentioned above may still not be enough to resolve your problem. Unfortunately water based flux does not evaporate as easily as alcohol based flux. It may be necessary to use a spray fluxing system. Spray fluxers allow you to put a very thin coating of flux on your PCB (approximately 75% less flux than a foam fluxer applies). 75% less flux on, means 75% less to evaporate. With proper heating, I have never seen this fail to eliminate solder balls.

Good Luck, Steve Harshbarger

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reflow oven profiler