I agree, it sound like someone is forcing the old " we must use SPC on..."
argument. My first response to that argument would always be "WHY?".
SPC is a really useful tool but when you are trying to use SPC for the sake
of it you only end up making it a dirty word.
Mistake proof and have solid systems, if you can't mistake proof and you
have critical measures which have caused you problems in the past, consider
SPC - but always keep an eye on technology developments which may be able to
eliminate your need for SPC.
My view is that measuring is expensive and non value adding and should only
be done where there is no other way!
Cheers,
Neil
Neil Atkinson - Quality Manager
Stadium Electronic Controls Division
Stephen House, Brenda Road, Hartlepool TS25 2BQ (UK)
e-mail: [log in to unmask]
-----Original Message-----
From: Stephen R. Gregory [mailto:[log in to unmask]]
Sent: 01 August 2001 04:19
Subject: Re: Solder Paste Measurements
Hi All!
Just want to "muddy the waters" a bit...
How many of you that use metal squeegees, and pretty much have your stencil
thickness down (as far as specifying thickness for a given pitch) have found
that it is really "crucial" to measure your paste thickness?
I for one, have found that when I spend the time and the money on equipment
to measure paste thickness, when using metal squeegee blades, and having a
solid set-up procedure, that I'm spending a bunch of time and money
measuring
things that are always good...meaning that time could be spent better
elsewhere as long as you use metal squeegee blades, and have a good
procedure
in place ensures that the printer is set-up correctly..which is not rocket
science...
Am I over simplifying things? It's always worked for me since the advent of
metal squeegees...I don't know how you can go wrong with a metal blade. Look
at the gerbers you're given, see if they match the pad geometries, and then
get the stencil made. Things are pretty straight forward after that...
-Steve Gregory-
Howard, in the past, I was forced to use to use and invest in smaller, less
expensive systems (I've since been lucky to have nice EXPENSIVE
toys-teehee). One of my favorite tools has always been the benchtop
Cyberoptics unit. I don't remember the model name, I'm sure it's on their
website, or a price figure. But I do know it was cheaper than most systems.
The beauty of it is it shoots a laser at an angle, laser is viewable on
monitor and is deflected by paste height. You line up the reference lines
on the screen and get pretty true paste height. If your using 1:1 apertures
or if you're doing aperaure reductions, you can calculate your volume.
Hope I've helped.
Jason Gregory
SCI Systems, Inc.
Software Specialist - NPI Group
(256)882-4107 x3728
[log in to unmask]
>>> [log in to unmask] 07/31/01 11:49 AM >>>
Hi Howard,
I've always found measuring solder paste volume to be very difficult. Yes,
numbers can be generated, but even taking large amounts of data doesn't
guarantee the correct impression. Generally, regardless of equipment used,
the best results one can hope for are for trends, which at best could be
described to be of the order of -1 or +1 from true. It's not a bad thing to
try but don't expect absolute results.
Best regards,
Andrew Hoggan
BBA Associates Ltd
www.bba-associates.ltd
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Howard Watson
Sent: 31 July 2001 14:47
To: [log in to unmask]
Subject: [TN] Solder Paste Measurements
Dear Technetters,
My question is: how do you measure solder paste height and volume
accurately? My situation is with using the VisionMaster Model 150A, I am
having trouble obtaining reasonably accurate measurements. The VisionMaster
is a small bench topsystem that uses a template consisting of a "region of
interest" (the solder paste), and reference regions (the areas on each side
of the pad). Because there are inconsistencies in the PCB (HASL finish),
like raised areas from traces, valleys surrounding the pad, and
irregularities in the solder mask, the readings I get cannot possibly be
true. Many times the measured readings for weighted average height are over
7.5 mils using a 6 mil screen and 9.5 mils using an 8 mil screen. The
process specifics are Multicore NC-40 paste, shore 94-97 polyurethane
blades, DEK 265 Infinity, and correct squeegee pressures, print gap, etc..
I believe the bricks are good, I just ca! n't use the measurements for SPC
as it shows the process to be out of control.
In theory, polyurethane blades should "scoop" if anything, leaving a
shorter brick than the stencil thickness. It seems logical to me that the
best way to obtain accurate measurements would be to use the pad as a
reference region and measure the height from the pad, but the VisionMaster
system does not allow me to do this. Does anyone have knowledge or
recommendations on what I can do here? How do the more expensive systems
measure solder paste? Oh yea, spending $$ on new equipment is not a real
good option at this point!
Thanks in advance for the assistance,
Howard Watson
Manufacturing Engineer
AMETEK/Dixson
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