Small balls on boards after wave soldering.

Is there anybody to help me ? We have small balls appearing on the boards soldered by wave soldering machine and it looks that use of nitrogen is linked to the problem (because without nitrogen, we have no more problems). That remind you something ? Let me know. Thanks. Philippe.

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| Is there anybody to help me ? | We have small balls appearing on the boards soldered by | wave soldering machine and it looks that use of nitrogen | is linked to the problem (because without nitrogen, we have no more | problems). | That remind you something ? Let me know. | Thanks. | Philippe. Small solderballs on the solder side of the board are usually a function of the soldermask or the flux. If the mask is not fully cured, or its got higher than usual porosity, small amounts of trapped moisture will be released when it contacts the wave and cause balling problems. Not fully drying the flux (if you're using a VOC-free) will also cause solder balling. Are there small balls around the nozzle of the wave? If there are, it's probably the flux. You might need to reprofile the board. I've never heard of nitrogen causing solder balls, but the surface tension difference that promotes better wetting to components could be exacerbating the problem. I occaisionally get bridging of TO-220's under nitrogen, so I turn the nitrogen flow down just a little (like from 600 scfh to 400 scfh at the wave) and the bridging goes away. I guess a little microdross can be a good thing! You could try turning your flow rate down a little and check the effect on the process. Running a 1000 ppm environment instead of a 50 ppm one isn't going to generate a whole lot more dross or defects, but it could be enough to keep balls from sticking.

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| Is there anybody to help me ? | We have small balls appearing on the boards soldered by | wave soldering machine and it looks that use of nitrogen | is linked to the problem (because without nitrogen, we have no more | problems). | That remind you something ? Let me know. | Thanks. | Philippe. Solder mask cure is important, as Chris stated. You can determine cure using IPC-TM-650 methods wherein methyline chloride is used to ascertain epoxy solder mask type cure. There is no method to determine dry film solder mask cure and this often is a problem that should have gone away with advent of LPI, etc.. Earl Moon - Proof Of Design

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