Solder balls on solder side!!

Are you using a water based flux? Are the solder balls mainly around or near non-plated holes or near the edges of the PCB?

If so the preheat must be set so the water content of the flux is fully evaporated before the board hits the solder wave. If water remains on the PCB then as the PCB hits the wave the water instantly vapourizes, causing pressure between the wave and the underside of the PCB.

Where there are gaps such as non-plated holes etc. then this pressure is rapidly released, causing the molten solder to spit, resulting in solder balls on the top side.

Another place for this problem to occur is if you are using wave solder pallets, particularly if they have masking features for plated mounting holes or similar. Larger amounts of flux can become trapped between the PCB and these features as a result of capilliary action. This is more difficult to evaporate. Balling on the top side around the edges of the PCB may indicate this problem. You may also find a lot of solder balls in the pallet where the PCB is supported.

Hope this is helpful,

Regards,

Pete B.

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Please advise what kind of the solder mask, glossy or matt?

Matt finished can reduce the solder ball significant. Check Enthone, Enplate DSR Series.

Good Luck!

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If we were talking about a single board problem, we�d be thinking about the laminate, but since you imply the problem is broad-based across multiple assemblies, consider the following machine parameters: * Crank-up preheat time / temperature to drive off flux solvent. * Adjust flux specific gravity, if it�s high * Perform machine maintenance on pump or wave level control * Turn-down conveyor speed * Check if tinning oil is loaded with water

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