Jason,
I have seen similar results during cleaning process evaluations. In my
case, clear residue was residual flux that remains in the small spaces
common to fine-pitch parts after the cleaning solvent has evaporated. You
might be seeing the Non-volatile Residue. Evaporation is slowest in the
small spaces, especially between solder pad and solder mask. In addition,
capillary forces will draw and hold liquid there making it slow to
evaporate. This was solved by longer cleaning time (to get more flux off)
and better rinsing/drying to rinse away the "dirty" flux removing solvent
and get rid of the NVR.
I am surprised that your vapor degreasing process alone is not adequate to
get rid of flux residue. The vapors should penetrate and get to all
surfaces. Either the part is in vapor too short a time or you are seeing
residue left by the secondary wash/rinse in "contaminated" terpene.
We use Kyzen Ionox I3330 at 140 deg. F followed by a clean Isopropyl alcohol
spray rinse. Without the clean IPA rinse, our boards would look like yours.
Hope this helps,
> Rainer G. Blomberg
> Staff Production Engineer
> Space Systems - Clearwater
> Honeywell International, Inc.
> * Phone (727) 539-5534
> * Fax (727) 539-4469
> * Email [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Jason Gregory
Sent: Wednesday, March 09, 2005 6:37 PM
To: [log in to unmask]
Subject: Re: [TN] Cleaning residues off of PCB
Photo posted. Thanks Steve!
You can see (barely - sorry bad photo) some halo-ing around the leads. Like
I said, no other detection in open areas or two leaded devices just finer
pitch, multi-leaded devices.
Follow the link
http://www.stevezeva.homestead.com/files/residue_closeup.jpg
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of David D. Hillman
Sent: Wednesday, March 09, 2005 4:05 PM
To: [log in to unmask]
Subject: Re: [TN] Cleaning residues off of PCB
Hi Jason! Can you send a photo to Steve for posting? A visual would help.
Dave Hillman
Rockwell Collins
[log in to unmask]
Hello all,
We have some boards that I am requiring some advice on cleaning residues.
The PCBs were soldered with SN96 (Sn96.5/Ag3.5). The first pass of the
boards look great. However, the second pass looked very suspicious. We are
seeing residue that looks like dried, puddled flux residue around most of
the leads. The areas mostly affected are multi-leaded components and there
is no evidence of this residue in open (non-populated) areas of the board.
If we take something like a probe or tweezers and move them along the areas
of concern, then it flakes off, but not real easily. I am afraid to do this
in fear of damaging the laminate (these are expensive boards). We have tried
re-fluxing them with aggressive RMA flux and re-reflowing them, but to no
avail. I have just tried soaking them, for 15 minutes, in a 50/50 solution
of distilled white vinegar and DI water, but again, to no avail.
Does anyone have any suggestions as to something else to use that's
aggressive, but not damaging to polyimide (or the solder joints)?
TIA,
Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]
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