You can stencil the glue as an alternative to dispensing.  Several adhesive
mfg's make stencil capable adhesives for smt.  We use a 6mil stencil with
apertures sized to the component types.  The reflow oven is used to cure the
glue, following mfg's recommendations.

The advantages are:
1. No need for additional equipment, i.e. dispenser.
2. Faster cycle times for adhesive application with stencil vs. dispense
3. No need for special pallets at wavesolder

The draw backs are:
1. Missing glue, leading to missing component.  The apertures are typically
small and can become clogged with the thick adhesive, resulting in a skip.
2. Misaligned components.  Glue, unlike solder paste, is unforgiving.
3. Handling damage.  The boards must be handled with extra care not to knock
parts off.
4. Soldering issues with bottom side SMT components.  This type of design
narrows the process window.

If the design is done correctly you can use double sided reflow and then use
a selective solder pallet for the through hole components.

The advantages to this method are:
1. Use of known processes.
2. Reduction of handling and wavesolder related defects.

The disadvantages are:
1. Restraints on the PCB design
2. Need for special pallets

Regards,
Steve Schiera

-----Original Message-----
From: Danny Harkins [mailto:[log in to unmask]]
Sent: Monday, February 12, 2001 1:29 PM
Subject: SMT Wavesolder & via in a pad


Hello All,

I am needing information (help) on two issues:

     1. We have a board that has all SMT/Thruhole parts on the
primary side. We would like to add some SMT parts to the secondary
side, i.e. 0805's, SO8's and SO16's. How could we go about doing
this and still run thru the wavesolder? We do not have a glue
dispenser.

     2. We have had some designers ask about putting via's in an
SMT land. What is the consensus on this?

I appreciate any help, advice you may have.
Thanks,

---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------