Hi Chuck,

Thank you for the input. The mask is a LPI, not a dry film, I double
checked the fab notes to be sure. I'll have a chance to look at the next
lot of boards soon as we are expecting the next delivery shortly...

Steve

On Wed, Nov 11, 2015 at 1:17 PM, Chuck Brummer <[log in to unmask]> wrote:

> Steve,
>
> Appears that the lamination of DFSM has forced the SM into the holes.  If
> the spray pressure at develop is not adequate it will not clear the mask
> from the barrels.
> Suggest you tell you supplier that this is a problem even if you do not
> reject the parts.  They can rework easily if they mask is not cured.
> If I am incorrect, this is screened mask (of your you images looks very
> much like dry film, the other seems a little rough and might be liquid)
> they are spraying mask when the screen "snaps off" and contaminates the pad.
>
> Based on your need you are making a good decision but I would still give
> feedback to the board supplier.
>
>
> Chuck Brummer
> Medical Flex, EMSD
> 8357 Canoga Ave, Canoga Park, CA 91304-2605
> Office: +1 818 734-4930 | Mobile: +1 805 890-8452
> [log in to unmask]
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
> Sent: Tuesday, November 10, 2015 10:32 AM
> To: [log in to unmask]
> Subject: [EXTERNAL] [TN] Unusual solder mask defect...
>
> Hi All,
>
> We just ran across a soldermask defect that I'm having trouble trying to
> figure out how it may have been caused. We build a .093" thick 8-layer
> assembly for a customer that is pretty picky as far as barrel fill is
> concerned. So we started noticing a problem on one lead of a component that
> we kept seeing no top solder fillet on that usually didn't have a problem.
> Upon further investigation we saw that there was a solder mask ring down
> inside the barrel:
>
> http://stevezeva.homestead.com/Soldermask_plug.jpg
>
> So then I pulled the bare boards that we had in stock and found this:
>
> http://stevezeva.homestead.com/Soldermask_plug_2.jpg
>
> I would say that at least 2/3rds of the boards I looked at had this
> problem. What's kind of weird is that this mask ring would appear at the
> top of the barrel and sometimes at the bottom, but always the same hole.
> The mask is an LPI, and what I'm having a hard time understanding is that
> the mask seems so well imaged around circumference of the pad, how does it
> get cured inside the barrel like that? And why is the ring sometimes at the
> top of the barrel and others down at the bottom?
>
> I was able to clear the plug by carefully using a .033" drill bit under a
> microscope so that I didn't damage anything else in the barrel. I double
> checked the gerbers and there are no inner layer connections, the only
> connection is the trace that you see on the outer layer in the photo.
> Because of time constraints we could not send the boards back to the fab
> vendor (even though I wanted to), but we put the next shipment on hold
> until they inspected for the problem. Why doesn't it surprise me that they
> said that they didn't see the problem? Sheesh...
>
> So I'm just trying to understand what in the process could have caused
> this, a scratch in the artwork maybe?
>
> Steve
>
> --
>
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