Brian Koo asked:

>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.

For this sort of frequently asked question, rather than asking 1,800 list
subscribers (and this is the _second time_ today), go to
http://jefry.ipc.org/SCRIPTS/WA.EXE?S1=technet and put in "solder balls".
You will get all kinds of theories and secret fixes to reduce solder balls.

My opinion is that you should modify the stencil apertures for all your
chip style components, because when you put the part down, the volume
displacement of the chip style (as opposed to leaded components) will force
enough paste out between the pads to assure that you can have solder ball
formation at reflow, no matter what profile you have. Go to a "home plate"
design on the pad, your problem will pretty much disappear.

Your stencil fabricator can probably help you with this, even if you have
no control over the pastemask artwork.

But you being in the Silicon Valley, there is no excuse for not knowing
this obvious stuff, though. I thought you could just ask the guy next to
you in traffic and get this answer. ;-)


cheers,


Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

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