We recently started to use wave-soldering. As total newbies in that field, we got successful results most of the time. Howewer, this batch of PCB's had a lot of resdiue, as shown on the picture. Most of it is most likely flux, but on some areas even some soldering alloy is visible (marked red on the picture). It's a leaded soldering wave with foam fluxer and IR pre-heat. Any suggestions will be helpful. Also, if someone knows a good on-line tutorial on wave soldering (how-to's, do's and dont's) I would appreciate a link to it.
This looks more like webbing and not flux residue. Webbing is caused by not enough flux to protect the surface resulting in oxide webs sticking to the board surface.
The insufficient flux can be caused by:
- Weak flux foam head - Air knife pressure too high collapsing the foam head - Hot boards or carriers collapsing the foam head - Preheating too high burning the flux - Single flowing wave (no back drainage for oxide elimination)
Giving us some more info on your machine settings would be helpful.
thanks for the response. I might add some more information - we succesfully soldered some boards with the same settings of belt speed, pre-heat temp. etc. This batch of boards differs from the previous in a way that they are 4-layer. Maybe it has something to do with it (perhaps board was not pre-heated enough due to bigger thermal mass)?
Belt speed was 120mm/min (0.8"/sec). I checked the wave width with tempered glass and it is about 40mm. What I can't check is the PCB temp. after pre-heat. As I have understood, it should be about 100 deg.C, but I have no means to verify it.
"Webbing" is definitely partially made of solder alloy, as I have removed it from the PCB by hand (it melts on the soldering iron tip)...
You also need to check if your flux is properly wetting the board. Flux dewetting on the surface can also cause webbing. You can check that with spraying flux on the board surface and watch the wetting behavior.
Certainly does look like solder deposit across the board. Check to see if fluxing correctly. Best way is to hand flux the PCB ensuring you put plenty on. IF you still get the same result then probably down to resist absorbing the flux due to porous resist. It can also be caused by the board only just skimming the wave but this is normally only on the front edge not all over the board hope it helps Cheers Greg York BLT Circuit Services
I had seen such effect caused by the wave itself, where the exposed wave surface was coated by a thin dull oxide layer which then adhered to the bottom side of PCB during wave soldering. You could verify if the wave surface is clean metal when the PCB contacts the wave. During wave soldering, the leading board edge should push out this oxidized surface layer to allow clean metal exposure to PCB.