I agree - charring has the potential to become a "conductive trace the
product design team didn't plan" so any amount of charring needs to be
understood from  a potential failure location.

Dave


On Wed, Jun 18, 2014 at 10:02 AM, Wayne Thayer <[log in to unmask]> wrote:

> I think we've avoided Ed's original question about pleading for leniency on
> charring.
>
> I, for one, have been "burned" several times by a very small amount of
> laser
> charring residue providing enough conductivity to fail isolation.  Carbon
> conducts electricity very well!  So even if you can't see the char you
> should
> be skeptical.
>
> Cleaning off charring is possible, but arduous.  An aggressive oxidizing
> plasma cycle can be qualified to do most of it, but often aggressive
> mechanical agitation with alcohol or some other fluid is also needed.
>
> Wayne
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of David Hillman
> Sent: Wednesday, June 18, 2014 10:28 AM
> To: [log in to unmask]
> Subject: Re: [TN] Laser depanelization
>
> Hi Ed - we are just starting to investigate and qualify laser depaneling
> for
> some of our boards. We have not observed the level of charring that you
> had in
> the photo you provided on our test samples. I recommend talking with your
> laser depaneling provider about their process parameter selections - you
> should not be having that level of burning.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
> On Tue, Jun 17, 2014 at 5:41 PM, Ed Popielarski <
> [log in to unmask]>
> wrote:
>
> > Hi all,
> >
> > One of our aerospace customers is requesting boards depanelized from
> > support frames.
> >
> > I looked into router, but the conformal coating tends to smear and
> > will be a significant FOD issue later.
> >
> > We are willing to invest in laser, however, the result is a bit of
> > charring on the edge, not much of a surprise. Unfortunately, this
> > example http://stevezeva.homestead.com/Capture.JPG was rejected on
> > IPC-A-610-Rev E Para. 10.7.4 "Solder Mask Coating-Discoloration"
> > "Burned or charred solder mask material.
> >
> > In my opinion, this is not within the "spirit of the law" since there
> > are no specific provisions for laser depanelization, only marking.
> >
> > Anyone know of some way around this?
> >
> > Ed Popielarski
> > Engineering Manager
> >
> > [cid:[log in to unmask]]
> >                                970 NE 21st Ct.
> >                               Oak Harbor, Wa. 98277
> >
> >                               Ph: 360-675-1322
> >                               Fx: 206-624-0695
> >                               Cl: 949-581-6601
> >
> >        "It's one kind of victory to slay a beast, move a mountain, and
> > cross a chasm, but it's another kind altogether to realize that the
> > beast, the mountain, and the chasm were of your own design."
> >
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> > pn=0.011188,0.033023&ctz=420&t=m&z=16&iwloc=A
> >
> >
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