--- "Carano,Michael"
>
> Peter,
>
> How does one blame the plating on this issue? The
> fabricator has nothing to
> say about board design, which has a major effect on
> overplating.
You are right, board design has everything to do with
plating thickness. To this point many customers are
unaware of the effect and seem to do everything in
their power to make our lives harder. <grin>
We have the same problems (of course) but have started
to ask customer permission to add copper to the
boards, especially with isolated circuitry. This has
been met with limited success.
> Without
> sectioning, we can't say anything about overplating
> at this time,. With
> respect to what looks like thin mask over the trace,
> that to should be
> determined with sectioning. In most cases that I
> have seen, a pseudo thin
> mask area actually is a pull back of the pigment of
> the mask, not the mask
> itself.
Absolutley. But as you can see, we did not have a
cross section to look at and I made an assumption.
Also, in a follow up email it was pointed out that
this CM had blow holes and pin holes which indicates
light plating.
>
> As far as debubbling goes, that may be true for
> curtain coating of the mask.
> In screenable LPI and Spray, the flash off (tack
> dry) is a very critical
> step in eliminating bubbles.
Ok, in our experience we allow the board to debubble
for about 15 minutes before we put the boards into
tack dry.
>
> Best regards,
>
ditto
Pete Menuez
> Mike Carano
>
> -----Original Message-----
> From: Peter Menuez [SMTP:[log in to unmask]]
> Sent: Thursday, July 27, 2000 6:48 PM
> To: [log in to unmask]
> Subject: Re: [TN] "Bubbly Soldermask..."
>
> First of all the pictures you show look pretty bad
> and
> I don't believe I would ever ship something like
> these. However, I want to point out that these may
> not
> be 'rejectable'.
>
> After coating LPI there is a hold time to allow the
> mask to debubble. This debubble time varies on
> many
> things but primarily on the thickness of the copper
> trace.
>
> Think about the geometry of the trace. If the
> trace
> was 1oz (.0014") the mask would cover fairly evenly
> and there would be little or no mask build up at
> the
> trace. At the trace thickness increases the trace
> acts as a dam forcing the mask to build up along
> the
> trace. This is exactly what you are showing in the
> pictures. The fact that the mask is very thin (most
> pigment removed) at the top of the trace is a good
> indicator that there is high copper here.)
>
> The debubbling hold time is designed to allow the
> volatiles (solvents) to escape the mask. What it
> looks like in your picture is that the boards were
> not
> debubbled long enough before they were tack cured.
> What you have left are small dots where the solvent
> was forced out of the mask leaving behind a puddle
> of
> mask.
> I have done a considerable amount of cross
> sectioning
> on this anomaly and have yet to find a void in the
> mask.
>
> I glanced over several of the emails responding to
> your original question and suggest that
> contamination, curing, moisture etc. are based on
> peoples inexperience with LPI's. This is a classic
> debubbling issue.
>
> I said in my opening statement that these boards
> may
> not be rejectable. They are rejectable for the
> simple
> reason that they are ugly but probably not
> rejectable
> for performance issues. If you cross section these
> puddles you will see that there is more mask
> present
> (rather than less which would be the case with a
> void). If you have more mask you have more
> insulation
> and in fact your insulation performance would be
> increased. Ok, this is pretty weak but...
>
> The area I would concentrated on with your supplier
> are: a) control of the plating process and
> b) if there is anything you could do to help
> them
> control the plating (robber buss/thief area)
>
> pete menuez
> [log in to unmask]
>
>
>
>
>
> --- Brian Ellis <[log in to unmask]> wrote:
> > Steve
> >
> > This is incredible. Change your supplier as top
> > priority :-) Seriously, as the others
> > say, the "bubbles" are probably due to
> solvent/water
> > entrapment in the track corners.
> > However, I see another problem which may/may not
> be
> > related. Am I correct in thinking
> > that it has been hot and humid where you are,
> > lately? If so, it would seem that there
> > has been hygroscopic contamination left on the
> > board. On your first photo, see the
> > myriad white points between the tracks? This
> looks
> > like vesication to me. The most
> > common cause is hygroscopic contamination (ionic
> or
> > non-ionic) which pumps atmospheric
> > humidty across the mask layer (all polymers can
> > allow humidity through). The osmotic
> > pressure rises until it actually lifts the mask
> off
> > the surface, locally, forming a
> > vesicle or, if you like, a microblister (see my
> book
> > for detailed explanation). This
> > could possibly be the cause of your bubbles along
> > the track edges, as well, although
> > these seem rather gross: the photo I use to
> > illustrate vesication also has bubbles
> > along some of the track edges, but the vesication
> > between the tracks is on a similar
> > scale. Whatever, it is a totally unacceptable
> fault.
> >
> > Brian
> >
> > "Stephen R. Gregory" wrote:
> >
> > > Hi all!
> > >
> > > We just got some boards in at receiving
> inspection
> > that have thousands of
> > > little "bubbles" in the soldermask all over the
> > boards...they seem to
> > > concentrate all along the edges of the features
> of
> > the board. You can see
> > > pictures of it at:
> > >
> > >
> >
>
>
http://www.driveway.com/share?sid=e25a88c4.8e904&name=Pictures
> > >
> > > One picture is bubblemask.jpg, the other is
> > bubblemask2.jpg...what would
> > > cause that? It's a LPI...don't know the brand
> > name. I'm thinking that either
> > > the boards weren't dry or cleaned well prior to
> > soldermasking them. I'm
> > > rejecting the boards of course...
> > >
> > > My freedrive is filling up fast with all the
> > pictures of the "pretty boards"
> > > that we get from our vendors!!!
> > >
> > > -Steve Gregory-
> > >
> > >
> >
>
>
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