Hi Mike, Unfortunately a lot of what we build here is consigned stuff...customer supplied boards and parts. So often times I won't even know who built the fabs. One of the questions I have is; by using the heat gun am I actually curing the mask? Why doesn't that happen during reflow or wave solder? Brian, Guess what? I found a used copy of your book on Amazon that I'm buying. It should arrive in 2-3 weeks. It will be one that I'm going to study.... Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Fenner Sent: Thursday, May 23, 2013 3:34 AM To: [log in to unmask] Subject: Re: [TN] White Residue Disappears with heat gun, what does that mean? I agree it probably is under cured resist, but as Brian says it may not be. If you were using a no clean and had this the explanation could be unremoved resin which is melting back to its normal translucent state, the white would be analogous to the water mark left by a coffee (tea for me) cup on a polished table. Probably not too bad a risk. The downside with unremoved water soluble flux residues is much higher. You need to be more certain. So you have done a simple test and have an indicative, but not absolute result. So you need to do some more work. If it is under cured resist then boards from a different batch may not show it, so all else being the same it's your board supplier's problem. You could also try finishing off the cure by baking some unpopulated boards for say a couple of hours at 100C. If it goes away on the baked boards, but not on unbaked boards then it's your PCB suppliers problem. Meanwhile you have a keep you going fix till the problem is rectified. Another thought is - has PCB supplier changed the resist in some way, if it is now shinier than before this may be highlighting an existing problem. So you could also contact your PCB supplier outline the problem, ignore the never had that before etc, ask them to collaborate with you to identify the problem by elimination all possible causes. Anyway their contribution in the elimination process would be to supply a batch which is definitely cured and do another side by side test. No doubt you already doing that though. Best Wishes Mike -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis Sent: Thursday, May 23, 2013 7:38 AM To: [log in to unmask] Subject: Re: [TN] White Residue Disappears with heat gun, what does that mean? There are a number of potential causes. A common one is the exposure of solder mask fillers because the cleaning removes the surface molecules of the solder mask. This is largely cosmetic but it may mean the mask is insufficiently cured. As you state (or I did in the earlier exchange!), heat will allow the filler to sink in. Another common cause is that a resin (synthetic or rosin) or carboxylic activator from the flux has spread and hydrolysed. This indicates a potential incompatibility of the flux and cleaning chemistries. This was common in the days of cleaning DIN 8511 F-SW32 type fluxes in CFC-113 azeotropes, as well as aqueous cleaning of many modern fluxes. The residues, which are not necessarily ionic, may form a hydrogen bond to low MW components of the solder mask whose surface may be incompletely polymerised. There are five pages devoted to these phenomena described in more detail in my book from p. 157 ff. You should determine the cause and take measures to eliminate it, rather than work in the dark. This means a series of systematic diagnostic tests and can be a painful process because you may have combinations of up to about half-a-dozen contributory factors, some of which may require expensive analyses. Empirical trial-and-error is usually unsatisfactory. Hope this helps. Brian On 23.05.2013 02:37, Steve Gregory wrote: > 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 ?g 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 > > > > > ______________________________________________________________________ > This email has been scanned by the Symantec Email Security.cloud service. > For more information please contact helpdesk at x2960 or > [log in to unmask] > ______________________________________________________________________ > ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________