Andre,

     One other thing that can contribute to solder beading aside from paste
deposition and pick and place issues is the slumping characteristics of your
paste...more specifically, the "hot slump" characteristics. All pastes slump
during the heating prior to reflow to some extent (most people would be pretty
suprized how much paste hot slumps if they could see it), but when it's really
excessive what happens is that some of the paste will still wind up beneath
the component body, which is precisely what you've been trying to avoid with
all the custom aperture modifications.

You may want to consider a different paste, or maybe increasing the % metals
content of your paste (reducing the flux content tends to reduce hot slumping)
to try and reduce the solder beads you're seeing.

Have you talked with your solder paste vendor about your problem yet? I know
it depends who your rep is, but it's been my experience that those guys love
to come in play with us big guys to try and work a problem through...they
usually learn something more about their own product and it beats pounding the
sidewalk trying to sell somebody else some paste.

Good luck!

-Steve Gregory-

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