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
>>
>>
>>
>>
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