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April 2004

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Subject:
From:
Jeffrey Bush <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 22 Apr 2004 15:29:02 -0400
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This must be slightly under cured causing flux to attach the surface.
Using Meth Chloride, make a puddle on the soldermask surface and let sit
for 30 seconds - then rub with a q-tip as see if the mask comes off the
board.  The degree of cure will be indicated by the amount of mask
dissolving in the solution - more in the q-tip mean less cured.  If this
is not apparent, the cause may be from another source - what type of
soldermask is used in the board.  The mask manufacturer will be able to
provide the compatibility info with your flux.  



Jeffrey Bush
Director, Quality Assurance and Technical Support

                          76 Technology Drive - POB 1890
                             Brattleboro, Vermont 05302-1890
                                Tel. 802.257.4571.21 Fax. 802.257.0011
                                    [log in to unmask]
                              http://www.vtcircuits.com	



-----Original Message-----
From: Morse, Carrie [mailto:[log in to unmask]] 
Sent: Thursday, April 22, 2004 2:28 PM
To: [log in to unmask]
Subject: Re: [TN] White Discoloration -- Excessive Heat, Insufficiently
Cured SM, or, Both?


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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