I'll put my 50 grams worth in...
As a general rule, I avoid re-using solder paste.  It has been on the stencil,
exposed to air and is not what you took out of the jar.   Oh sure it will work
- it'll print, have tack, reflow and solder, but you will likely, eventually
notice an increase in defects.

The biggest sin is to take the old paste off the stencil and mix it in with
new (virgin) paste. If you have to re-use it, keep it in a separate container.
Never mix it.

As far as the exposed paste drying up a bit, some people remedy this by
"adding a bit of solvent".  Hey, this is not Sherwin-Williams.  If you've ever
been to a solder paste manufacturer you will see that the manufacturing
procedures are very exacting and precise - and not repicable on most factory
floors.

I recommend my clients purchase solder paste in cartridges rather than jars.
You're not exposing the whole container to air when you extract what you need
and it's very difficult for someone to mixed used paste with the new (not that
it likely hasn't been tried).

Other current printing limitations not withstanding I am very enthusiastic
about the direct printing technology that has been introduced by DEK (Pro-
Flow), MPM (Rheometric Pump) and Fuji (they've had a version of this for some
time).  One of the benefits of the methodology is preservation of solder paste
thus extending work life and tack time.

Also, be sure to monitor and control the temperature and humidity of the
manufacturing floor in compliance with the range recommended by the solder
paste manufacturer.

Phil Zarrow
ITM, Inc.
Durham, NH
www.ITM-SMT.com

################################################################
TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################

################################################################
TechNet E-Mail Forum 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's web site (http://www.ipc.org) "On-Line Services" section for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################