--- Smith Russell MSM LAPO US
<[log in to unmask]> wrote:
> Peter:
>
>
> Wooa Buckeroo snatch a reign on that bronco..:-)
>
> Not all LPI requires debubbling. And wouldn't the
> physical thickness of
> the mask, and the viscosity and flow characteristics
> and the gas
> permeability of the mask also have major impacts?
I don't know if all masks need debubbling but all of
the mask we currently use and ones we have used in the
past required the debubbling step. Your next
statement (thickness, viscosity and flow
characteristics) are exactly why you need the
debubbling step. The mask is much thicker at the edge
of the trace. There are volatiles that must be dried
out of the mask.
> (I this doesn't start a war),
> To make a statement that the observations of
> moisture etc. are based on
> peoples inexperience with LPI , well don't you feel
> that's assuming just a
> little to much on your part? One of those kind folks
> that offered their
> opinion might be a developer of the technology.
Here's the deal. I am a fabricator. The picture
shown is a textbook case of poor debubbling. If
someone wants to chase down the possiblities of
moisture, contamination go for it. (Of course you
will then have to explain why the moisture only
happens at the edge of a trace) But if you want to cut
to the chase and address the problem, start with the
debubbling process and work backwards from there.
> (That's one of the things
> so liked, yet so feared with E-mail the anonymity
> of it all.)
>
> Just for future reference you seem to be an
> expert in LPI.( It's
> Always good to know a few.) It might be helpful
> for me if I have
> questions in the future if I know many
> manufacturers of LPI have you had
> the opportunity to apply. Also which of the
> application techniques have you
> used.? ( I might be the only one here that doesn't
> know so sorry if this is
> redundant, but humor me.)
I don't quite understand what you are asking here so
if I miss the point email me back and I'll give it
another try..
As stated before I am a fabricator. Where an LPI
expert might be able to advise me on how their product
is manufactured and how they think it should be
processed, I am the one stuck with figuring out the
fine points of actually processing the material in a
manufacturing environment, not the lab.
Masks that we currently use are Lea Ronal OPSR 5600,
Ciba Geigy 77MA. We have tried Coates, Taiyo and
Electra in the past. We apply the mask with a double
sided DP10 coater, expose in a 8kw Byers printer and
expose with a ATO TECH 547XL.
>
> Just a comment from my operational experience : Even
> though you might not
> have seen a void in the mask , try taking product
> that looks like that and
> do some thermal shock testing, they get really ugly
> really fast .
>
> I agree that a board that ugly should never leave
> the house....
> "Rejectable" or not. Personally if I saw a board
> like that in my auto
> airbag system I would be a tad worried..!!!!! :-)
> Russ Smith
I'd be worried that you were taking your auto airbag
system apart:)
>
> ----------
> From: Peter Menuez
> To: [log in to unmask]
> Subject: Re: [TN] "Bubbly Soldermask..."
> Date: Thursday, July 27, 2000 7:47PM
>
> 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-
> > >
> > >
> >
>
##############################################################
> > > TechNet Mail List provided as a free service by
> > IPC using LISTSERV 1.8c
> > >
> >
>
##############################################################
>
=== message truncated ===
__________________________________________________
Do You Yahoo!?
Kick off your party with Yahoo! Invites.
http://invites.yahoo.com/
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Keach Sasamori at [log in to unmask] or
847-509-9700 ext.5315
##############################################################
|
