Hi, Gary -

step stencils are an idea to apply different solder paste depot thickness
across one board in one strike, where crude SO or PLCC type packages with
demand for lots of solder are mated with fine pitch T-SOP or T-QFP packages.
The former get large wet paste thickness from the thick region of the
stencil (to avoid possible opens after soldering), while the latter get
lower paste print thickness (to avoid possible bridging).

But to my knowledge the step stencils are not widely used, due to
- higher cost as compared to uniform thickness stencils
- danger of solder paste smearing at least close to the steps
- difficulty of cleaning the stepped stencil underside
  (the steps cannot be on the upper side)
- increased wear on the squeegee due to pressure variation over its length.

For SMD adhesive application there are polymer stencils on the market, which
allow the application of different drop amounts AND hights barely by
different openings. The stencils are rather thick (and rather expensive) but
give astonishing results suitabel for the above mentioned packes with great
variations in demand for amounts. Ask Mark Whitmore at DEK for more details
(I don't get provisions from him).

Best regards,

Thomas Ahrens
[log in to unmask]

-----Ursprüngliche Nachricht-----
Von: Smith, Gary <[log in to unmask]>
An: [log in to unmask] <[log in to unmask]>
Datum: Donnerstag, 10. August 2000 16:29
Betreff: Re: [TN] Blow Holes


>Can anyone tell me if step stencils are used only for solder paste
>applications or are they used also (or only) for adhesive application??
>
>Thanks
>
>-Gary
>
>##############################################################
>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
>##############################################################

##############################################################
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
##############################################################