I have had severe problems with paste height despite having a good stencil
design and metal squeegee when: 1) there were soldermask height issues
(generally fab production process produced mask lumps on every via which are
located in the greatest number next to fine-pitched parts); and/or 2) there
was something wrong with the printing machine. Printing in the x-y direction
can be fine and even stencil release but the height can be way off. And,
believe me SMT phase of production can build hundreds of assemblies and
never alert the engineer or find the root cause or deal with the
consequences.
Dorothy Lush
> ----------
> From: Stephen R. Gregory[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;[log in to unmask]
> Sent: Tuesday, July 31, 2001 8:19 PM
> To: [log in to unmask]
> 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
>
>
>
>
>
---------------------------------------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
---------------------------------------------------------------------------------
|
