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April 2004

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Subject:
From:
"Morse, Carrie" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 26 Apr 2004 09:33:11 -0400
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I stand corrected.
I used Methylene Chloride.
Sorry for the confusion. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Saturday, April 24, 2004 8:04 AM
To: [log in to unmask]
Subject: Re: [TN] White Discoloration -- Excessive Heat, Insufficiently
Cured SM, or, Both?

WHOA!!!!!!!!!!!!!!!!!!!!!!!!!!!!

IMPORTANT!

Methyl chloroform is a popular but incorrect name for
1,1,1-trichloroethane (TCA), a relatively mild but unstable solvent and
fairly useless for cure testing.

Methylene chloride, aka dichloromethane (DCM), is a totally different
beast and is more aggressive and better for cure testing.

TCA is an ozone-depleting solvent and a controlled substance under the
Montreal Protocol. As such, it has not been available in developed
countries since 1 Jan 1996. Its instability gives it, assuming correct
stabilisation, a useful lifetime of ~2 years. If your stuff was made
before 1996, you can reckon it is useless, as a solvent, by now. In most
countries, you are bound to have existing stocks and waste solvent
destroyed by an approved destructor. You are probably not allowed to
simply store it passively or to landfill it. Please check with your
local authorities.

Brian

Morse, Carrie wrote:
> Wow,
> Thanks to everyone for all the info.
> I have a new update.  We tried 4 things based on a number of
> recommendations:
> 1.  Applied flux and hit the area with an iron.  The discoloration 
> went away.  But, we have such a large area on so many boards there is 
> no real way to get this done in a timely fashion.  In addition, we 
> scratched the area up pretty well, so, either way, it looks bad.
> 2.  We tried to re-wave the board.  The discoloration got 
> whiter/hazier 3.  Used Methyl Chloroform to test for permanency.  No 
> mask was evident on the swab which tells me the mask is cured.
> 4.  Lastly, we baked a board at 250F for 45 minutes -- no change.
>
> So...Any ideas what it is or if it is detrimental?
> Any suggestions?
> It's Friday...If anyone can suggest the boards are OK and I can feel 
> comfortable to ship that would be fine by me.
>
> -Carrie
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Gregg Klawson
> Sent: Friday, April 23, 2004 11:50 AM
> To: [log in to unmask]
> Subject: Re: [TN] White Discoloration -- Excessive Heat, 
> Insufficiently Cured SM, or, Both?
>
> Carrie,
>
> Some info from one SM mfr, this may help.
>
> http://www.enthone.com/electronics/pdf/Imup5.pdf
>
> -- Gregg
>
> At 02:27 PM 4/22/2004, Morse, Carrie wrote:
>
>>Here's the status.  I baked the boards for 45min @ 250F and...I still 
>>have the white haze.  No change.  So, What do you all think?
>>(IOW--HELP!!!!)
>>
>>-Carrie
>>
>>-----Original Message-----
>>From: Brian Ellis [mailto:[log in to unmask]]
>>Sent: Thursday, April 22, 2004 2:06 AM
>>To: TechNet E-Mail Forum.; Morse, Carrie
>>Subject: Re: [TN] White Discoloration -- Excessive Heat, 
>>Insufficiently
>
>
>>Cured SM, or, Both?
>>
>>I'm not saying that this is the cause, but another possibility is 
>>hydrolysis of the uncured solder mask. If the boards are coated and 
>>then stored in a humid atmosphere before development (either before or

>>after
>>exposure) for more than an hour or two, then some components in the 
>>chemistry may absorb sufficient humidity to hydrolyse, partially 
>>upsetting the polymerisation.
>>
>>I suggest methylene chloride would be better than acetone for a wipe 
>>test, but it depends on the chemistry of the LPI.
>>
>>Brian
>>
>>Morse, Carrie wrote:
>>
>>>We are wave soldering a LPI board and seeing a Whitish Discoloration
>>>-- Haze like -- only in the areas that the board has seen OA flux and
>>
>>wave.
>>
>>>We are using a wave pallet and the areas not exposed do not exhibit 
>>>this phenomena.  This board is also processed through SMT for one 
>>>side
>>
>>>and we do not see this around any of the SMT.
>>>
>>>We have not seen this problem in the past, and, the Wave operator 
>>>states that the wave recipe has not changed.
>>>
>>>So, I am wondering -- if LPI is not fully cured, will it turn white 
>>>when exposed to OA flux and Wave?
>>>Also, what IS the max temp LPI should be able to see and for how long

>>>without discoloring?
>>>We've done an Acetone test, but, it comes up clean and....I think I 
>>>read in a previous posting that the Acetone may not be an effective 
>>>test for LPI.  Is that true?  If so, What IS an effective test?
>>>
>>>I'm headed to the Omega tester to see "how clean" the board is.
>>>
>>>All advice is welcome!
>>>
>>>-Carrie
>>>
>
>
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