>-----------------------------------------------------
I encountered a similar problem with a previous employer some years ago.
I procured some basic paint stripper from a major home repair retailer. It
was the the "super thick" formulation. I masked-off the to-be-stripped area
with kapton tape (masked slightly undersized, as I recall, as some stripper
will inevitably sneak under the tape). Applied the stripper sparingly with
a swab or other suitable applicator. Observed the LPI, and when it began to
bubble/blister, easily removed the softened mask with a swab. I remember
approx. 5-10 minutes for the stripper to do its job. Stubborn bits may
require a poke with an orange stick, toothpick, etc. Really stubborn bits,
or especially thick coatings, may require a second stripper application.
Generously cleaned & rinsed the area with IPA and DI. Dried & tinned the
exposed copper plane.
Of course, this was all done in a properly ventilated area, wearing all
pertinent safety gear. This worked quite well, as an engineering-controlled
process.
Hope this helps. => ells
>---------------------------------------------------
On Wed, 30 Mar 2005 13:42:27 -0600, Genny Gibbard <[log in to unmask]>
wrote:
>Another thing along the same lines - but doesn't do it as neat as what you
>did, Steve, is apply some solder to some solder wick and rub the solderwick
>back and forth on the board, using a soldering iron - removes mask and tins
>the underlying copper in one step...
>
>Similar to Ramon's suggestion - heat is applied, and the abrasiveness of the
>wick scrapes the soldermask off, but might be slightly less abusive to the
>iron tip than the suggestion below.
>
>-----Original Message-----
>From: Dehoyos, Ramon [mailto:[log in to unmask]]
>Sent: 30-Mar-05 1:17 PM
>To: [log in to unmask]
>Subject: Re: [TN] Selective LPI soldermask removal...
>
>
> Hi Steve:
> I have used on green LPI, a heat gun and a somewhat
>sharp wide solder iron tip. Move the heat around the area and scrap the
>masking with the tip. It comes off very fast.
> Regards,
> Ramon
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Stephen Gregory
>Sent: Wednesday, March 30, 2005 1:59 PM
>To: [log in to unmask]
>Subject: Re: [TN] Selective LPI soldermask removal...
>
>
>I messed up the URL in my email, some may have figured that
>out. But it's: http://www.stevezeva.homestead.com
>
>
>Kind regards,
>
>-Steve Gregory-
>Senior Process Engineer
>LaBarge Incorporated
>Tulsa, Oklahoma
>(918) 459-2285
>(918) 459-2350 FAX
>
>
>|---------+----------------------------->
>| | Jeffrey Bush |
>| | <Jeffrey.Bush@VTCI|
>| | RCUITS.COM> |
>| | Sent by: TechNet |
>| | <[log in to unmask]> |
>| | |
>| | |
>| | 03/30/2005 12:39 |
>| | PM |
>| | Please respond to |
>| | TechNet E-Mail |
>| | Forum; Please |
>| | respond to Jeffrey|
>| | Bush |
>| | |
>|---------+----------------------------->
>
>>---------------------------------------------------------------------------
>-----------------------------------|
> |
>|
> | To: [log in to unmask]
>|
> | cc:
>|
> | Subject: Re: [TN] Selective LPI soldermask removal...
>|
>
>>---------------------------------------------------------------------------
>-----------------------------------|
>
>
>
>
>We could do this for you with laser.
>
>Jeffrey Bush
>Director, Quality Assurance and Technical Support
>
>VERMONT CIRCUITS INCORPORATED
> 76 Technology Drive - POB 1890
> Brattleboro, Vermont 05302
> Voice: 802.257.4571.21 Fax: 802.257.0011
> http://www.vtcircuits.com
>
>
>-----Original Message-----
>From: Stephen Gregory [mailto:[log in to unmask]]
>Sent: Wednesday, March 30, 2005 12:25 PM
>To: [log in to unmask]
>Subject: [TN] Selective LPI soldermask removal...
>
>Happy "Hump-day"!
>
>I might have asked the list about this over a year ago, I can't
>remember.
>But I have this
>assembly that goes into a Radar system. There's a device on the assembly
>that has to
>be sitting over the metal of the top layer plane, with no solder mask on
>the board beneath
>the footprint of the device for it to work properly. Unfortunately, the
>solder mask file in the
>gerbers didn't reflect this. So at the time (over a year ago), I
>reworked
>the boards that we
>had to correct the problem...and let me tell you, it's a REAL PIA!
>
>Go to: http://www.stevzeva.homestead.com and look at "Mask Removal", and
>"After Tinning"
>to see what I'm trying to do.
>
>I did this over a year ago, and we got an order for these assemblies
>again...but the gerber never
>got corrected, and I get to do this again. WHOOPEE!
>
>I have to remove the solder mask beneath where the device is going to be
>installed, and then
>I solder coat the area to cover the exposed copper. I'm removing the
>solder
>mask very, very
>carefully with a Dremel and a very fine abrasive tip, and I'm using an
>exacto knife with various
>blades. This is all being done tediously under a microscope to prevent
>the
>copper from being
>removed from the plane. We have a micro-blaster here to remove conformal
>coating, but it can't
>get down to the bare copper. That's why I'm using the Dremel and exacto
>knife. This time when
>the board house did their micro-etch or pumice scrub just prior to
>applying
>the solder mask, they
>really did a good job! That mask is on there, and meant to stay put! I'm
>really having a hell of a
>time doing this on these latest fabs.
>
>Is there any other way to remove this coating in the area that I need
>to?
>I'm thinking maybe a
>laser. Does anybody know where I would go to get this done, and about
>what
>it would cost?
>There's only 5-boards that I need this done to, but it takes me a couple
>of
>hours with each board
>to complete the job.
>
>Kind regards,
>
>-Steve Gregory-
>Senior Process Engineer
>LaBarge Incorporated
>Tulsa, Oklahoma
>(918) 459-2285
>(918) 459-2350 FAX
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