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August 2001

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From:
"d. terstegge" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 1 Aug 2001 11:50:07 +0200
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Hi Technetters,

Having a solid set-up procedure (like Steve mentions) is the key issue here. But how about making proto's all the time, some of them hardly manufacturable, like flex-rigid boards without a carrier or boards with solderpads within 0.5 mm of the board-edges ?  Setting up the machine means some improvisation then.....
For an engineer it's quite easy to see if set-up is incorrect, but for the average operator a height- measurement helps in identifying such a problem. 
For average, flat and rigid boards I agree with Steve (as long as metal blades are used).

Howard: measuring a value a little higher then the stencil thickness is normal. Maybe someone else can give an explanation for this is, because I don't remember :-{

Kind regards,

Daan Terstegge
SMT Centre
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net


>>> "Stephen R. Gregory" <[log in to unmask]> 08/01 5:19 am >>>
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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