Charles Barker asked:

>Are there any recommended stencil "pad" design guidelines available for
>creating pad patterns for adhesive application when wave soldering SMD's
>on the
>bottom side of boards?
>
>We are looking at giving stenciling a try for the first time.

You'll be glad you did. Now that we do it, we will never go back to the
dipsenser, it is so much faster, less trouble overall, and the results are
generally better, too. Of course, if you have 5 pick and place machines
waiting on a glue dispensing robot like we did, you have to do something.

We don't use pads. I've seen it recommended. If you put them on the board,
I'm sure you will have even better results, but we did not do so because
re-spinning a board here sometimes takes an act of Congress as we have
"OEM" product versions under customer rev control.

We went with a laminated two layer 0.006" + 0.006" stencil. The artwork was
prepared to open apertures around the discrete-populated areas, which had
one each 0.030" dia. round apertures (these go through only one layer). The
apertures for the SO parts go through both stencil layers and are 0.060"
dia ( 2 per) to give taller dots, accomodating the higher belly standoff of
the SO parts.

IMO round dots are best as you have the optimum ratio between the wall
surface of your stencil and surface area of the dot, permitting better
"release", and easier cleaning.

We use a 60 durometer urethane squeegee, and Heraeus PD 860002 S adhesive
dispensed from a big cartridge with a "caulk gun".

The only difficulty we have had is cleaning the stencil, which we do 90% by
simply wiping with a lint free non-woven rag, and final clean with IPA and
a rag. It's a little messy, but we can print 300 or more dots in 15
seconds, with almost no stringing or other dispense-type problems. The dots
have proven to be better than our syringe/pump robotic dispenser at holding
parts through wave solder.

You could call:
John McMaster at Heraeus 610-825-6050
Calvin Schweitzer at Utz Engineering (stencil fab) 201-778-4560

regards,

Jerry Cupples
Interphase Corporation
Dallas, TX
http://www.iphase.com/