Hi all,

 

I know we've talked about this before, but I seem to forget the fine details lately. (blame it on me getting old or something),

 

Anyways, we've got a different (newer)cleaner and we've just gotten it going over the last few days. The cleaner is close-looped which is different than the way the old cleaner operated. Had a little foaming issue that was solved by putting in another carbon bed. But today I washed a board after it had come off the wave, and the bottom surface of the board had what I call "Zebra Stripes" of what looked like white residue along the bottom of the board. They are pretty much shadows of the conveyer mesh chain that the board was sitting on through the cleaner:

 

http://stevezeva.homestead.com/ZebraStripes.jpg

 

I ran the board through the Omegameter we have and of course it passed at 4.3 µg NaCl/sq. in.. I took the board out of the Omegameter tank and the stripes were gone, which didn't puzzle me too much. Boards always seem to come sparkly clean out of an Omegameter tank. 

 

I ran the board through the cleaner again and the white stripes re-appeared. Our cleaner is a Austin America Microjet, our water is at 13 megohm, I'm running 135 F. in my wash at a belt speed of 2 fpm. My dry section is 100 F. We're using a Indium 1095 water soluble flux in a foam fluxer in our wave. 

 

I remembered something from the TechNet a long time ago about heating the board with a heat gun to see if the white residue disappears. I searched the archives and found this from Bill Kenyon:

 

"Quick identification of the (solder mask) residue- if it is the white powder fumed silica used to thicken liquid solder masks, you will often see it appear as Brian has noted. If the solder mask is undercured, any cleaning step may strip off part of the green solder mask, exposing the white thickener powder (typical trade name is 'Cab-O-Sil"). Heat the white area with a heat gun. If the residue is the Cab-O-Sil, the heat softened solder mask will allow the Cab-O-Sil to sink back into the green solder mask. Residue disappears, problem is insufficient UV cure during solder mask processing."

So I tried that, and the stripes disappeared. I cleared almost all of the stripes with the heat gun and re-ran the board through the cleaner and the stripes pretty much stayed gone...I can barely see a shadow of them. The information that Bill Kenyon shared with us was from quite some time ago, but that still applies, correct? 

 

Steve Gregory

 


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