I like Loan's answer because solderballs normally form in the middle along
the side of the chip component and not underneath. The normal solderball is
formed when solder follows the flux under the component during reflow then
is "squeezed" out to the side when the molten solder solidifies, shrinks and
pulls the chip flush to the board surface. I could see the pulling down
action stopped by, say, epoxy or soldermask non-existence or over presence.
Are these balls being formed during SMD or solderwave do you think? An
aqueous SMT paste process usually will wash this ball away. No-clean paste
requires not forming them in the first place (and only allowing them to stay
if they are imbedded in flux and less than a certain size, etc.) by
controlling stencil aperature, solder printing(x-y and z(volume)), solder
choice and oven profile. Is this an aqueous or no-clean solder paste/process
we are talking about?

Dorothy Lush
Manufacturing Engineer

> ----------
> From:         Marsico, James[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Marsico, James
> Sent:         Tuesday, August 14, 2001 12:34 PM
> To:   [log in to unmask]
> Subject:      soldr balls
>
> Here's a relatively basic SMT question, but we've haven't experienced this
> before.  We're seeing solder balls under (way under, in the center) chip
> components.  Any recommendations?
>
> Jim Marsico
> Senior Engineer
> Production Engineering
> EDO Electronics Systems Group
> [log in to unmask] <mailto:[log in to unmask]>
> 631-595-5879
>
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