We had this happen a while back and it was posted here on the net. We were
real concerned and stopped production to find out what happened. It was
caused by the flux attacking the surface of the solder mask and it only
showed up after wave solder. We had the boards sent to an outside inspection
service and the report came back saying it was only a 'surface etch' (much
like a fine sand blast on glass) and had no effect on the solder mask other
than cosmetic. I can send you the inspection report if you need it.
Tom Parkinson - Quality System Manager - CIT
WinTronics, Inc.
Ph: 724-981-5770 Ext. 235
Fax: 724-981-1772
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Morse, Carrie
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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