Then try the same test with boards going through the machine. Leave it there with the wave running but without boards being processed. Try using a piece of white card placed over the wave. This is caused by volatile materials still remaining from the flux or the height of the wave separation. In Figure 7, 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 excessive back flow in air or too high a drop in nitrogen environments.įigure 6: More solder balls caused by spitting. Solder balls are caused by gassing and spitting of the flux on the surface of the wave or by solder literally bouncing back from the solder wave. ![]() Selecting the best solder mask is the best solution to making a board design robust. Regardless of the cause, if the solder balls do not adhere to the solder mask when leaving the solder wave, the problem is mostly eliminated. It has been the increase of the use of no clean low residue soldering that has focused more attention on the problem. The causes of solder balls are numerous, and they have always been present on the bottom side of printed boards. The compatibility of the resist and flux should be examined often the mask can contribute to solder ball adhesion.įigure 5: Solder balls on this board were caused by spitting from the surface of the wave. Ideally there should be minimal bubbles visible below the glass when it contacts the wave. Using a glass plate over the wave should show up the gassing problem. If the preheat is incorrectly set or the quantity of flux applied increases, the evaporation of the solvent from the flux may be affected. If the solder is falling a distance from the printed board as the wave separates, the solder can literally splash back from the bath. This type of defect is normally caused by spitting from the surface of the wave, which is associated with wave soldering parameters. In Figure 5, the position of the balls is random. ![]() Solder balls are caused by a number of process parameters. In the past, the solder balls were washed off the board surface during cleaning, out of sight out of mind! Solder balling during wave soldering has always been around, but the elimination of cleaning after the soldering operation has made it more visible as a process problem. If the solder resist is thin, solder can wet during wave contact and leave a ball.įigure 4: Solder on a resist can wet during wave contact and leave a ball. As the tin/lead becomes liquid during reflow or wave soldering, the tin/lead expands. ![]() It is caused by squeeze out of the tin/lead from under the solder mask. The example in Figure 4 is on a track and cannot be just knocked off. In Figure 3, a solder ball is attached to the base of the board on the edge of the resist and must have attached itself to the resist as it separated from the pin.įigure 3: Another solder ball attached to the edge of a resist.Ĭare should be taken with some solder balls. ![]() In Figure 2 shown a solder ball is attached to the base of the board on the edge of the resist and must have attached itself to the resist as it separated from the pin.įigure 2: This solder ball must have attached itself to the resist as it separated from the pin. Solder balls can be ejected from the joint area during soldering due to excessive outgassing of the PCB. Solder balling can be caused by poor process conditions with gassing from the flux during wave contact or excessive turbulence as the solder flows back into the bath which causes spitting. Care must be taken to ensure operators recognize the difference as any attempt to remove this type of ball manually will result in a damaged track.įigure 1: Manual removal of this solder attachment will damage the track. The coating may have failed as it was applied over a tin/lead coating on the tracking or due to poor print thickness control. The solder has wet the track due to failure of the resist coating. Solder Balls or Solder Balling on a Printed Circuit BoardĪlthough a solder ball is present in Figure 1, it should have been referred to as a solder attachment rather than a ball.
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