Hi Brian, You have a new one in publication? Where can I get it? Steve -----Original Message----- From: Brian Ellis [mailto:[log in to unmask]] Sent: Thursday, May 23, 2013 10:30 AM To: TechNet E-Mail Forum; Steve Gregory Subject: Re: [TN] White Residue Disappears with heat gun, what does that mean? You will then want a new, signed, copy! :D Brian On 23.05.2013 19:13, Steve Gregory wrote: > 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] > ______________________________________________________________________ > ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. 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