In a message dated 11/10/98 11:30:36 AM Pacific Standard Time, briankoo@AQS-
INC.COM writes:

<< Dear Technet users,
 I am experiencing some solder balls on some of PCBs' that we are
 assemblying now.  We set the temperature according to recommended
 thermal profile based on Supermole which we are using to set first time
 processing board.  Certain times, we do not see any solder balls for
 same PCB, but we are seeing solderballs that we ran last night.
 Mostly,  balls are appear near capacitor location.

 We are contract manufacturer in San Jose.  Please respond to my email.
 Thank you.

 Brian Koo
  >>
Hello there Brian!

     Don't that kinda' stuff make ya' crazy? Set something up one day and it's
running fine, come back in the next and everything goes to hell in a hand-
basket! Makes ya' wonder sometimes don't it?

     Well, if you've been running this board before without any solderball
problems, tells me that your stencil is okay, and if you've plotted the board
with a supermole and the setpoints are the same on your oven as the settings
when you plotted it, tells me that your profile is okay too. You didn't change
paste either, and I'm assuming that nothing with the board has changed
either...(just going down my list of variables here).

     About the only other variables that I can think of that might have an
affect whether or not you'll solderball is:

1. Print deposition - Nobody's changed the squeegee blades on you have they?
Going from plastic to metal squeegees you'll find that you print thicker
paste...you don't have that scoop-out anymore. How about the wipe during the
print stroke? Has that changed? If in the beginning the printer was set-up
giving you a clean wipe and then the next set-up you maybe didn't have so
clean a wipe might give you enough additional volume to cause a solderball or
two.

2. You said that it was occuring on the capacitors, did the capacitor change?
Maybe what had happened was that the capacitor reel ran out and the new reel
changed to a thicker one on swing shift, which would cause the placement force
to be greater than it was with the old ones. You might be on the razors edge
as far as the volume of solder paste being printed and not get any solder
balling, but when the paste gets squished out off the pads from too much
placement force that'll give you solderballs too.

This one's a "toughie"...to have something be running good for you and then go
wacko is always a pain. Something has changed in between the time it was
running good for you and now. It's just finding out what....

Hope this helps,

-Steve Gregory-

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