56

Solder Balls
The causes of solder balls are many and they have always been present on the bottom side of printed board. It has been the increase in the use of no clean low residue soldering which has focused the attention on the problem. Regardless of the cause, if they will not adhere to the solder mask when leaving the solder wave the problem is mostly eliminated. Selecting the best solder mask is the best solution to making a board design robust. In this example the solder balling is random and more likely the result of solder balls spitting or bouncing up from the solder wave. This is caused by volatile materials still remaining from the flux or the height of the wave separation. Try using a piece of white card placed over the wave. Leave it there with the wave running but without boards being processed. Then try the same test with boards going through the machine. This will pinpoint the cause of the problem.