I have seen this on a number of occasions. In every case it has been
corrected by correcting an incorrect profile.
The problem is caused by the paste reaching the reflow zone prior to it
being dried properly - the solution therefore would be to slow the process
down and give the paste longer to dry prior to reflow.
It is also a good idea to check the solderability of your PCBs as if this
were a problem or if you had solder mask on the pads, then again the same
result could occur. But my bet is that you can eliminate these balls by
looking at your profile.
Let us know how you get on.
Neil
Neil Atkinson - Quality Manager
Stadium Electronic Controls (UK)
-----Original Message-----
From: Marsico, James [mailto:[log in to unmask]]
Sent: 15 August 2001 11:53
Subject: Re: solder balls
The process is standard SMT with convection reflow using
water soluble flux
and a very aggressive in-line aqueous cleaner. The solder
balls seem to be
stuck under the chip components. They are very difficult to
see, you have
to actually tilt the board sideways and look under the
components.
Jim Marsico
Senior Engineer
Production Engineering
EDO Electronics Systems Group
[log in to unmask] <mailto:[log in to unmask]>
631-595-5879
-----Original Message-----
From: Lush, Dorothy [SMTP:[log in to unmask]]
<mailto:[SMTP:[log in to unmask]]>
Sent: Tuesday, August 14, 2001 5:06 PM
To: 'TechNet E-Mail Forum.'; 'Marsico, James'
Subject: RE: solder balls
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]]
<mailto:[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] <mailto:[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]>
<mailto:[log in to unmask]
<mailto:[log in to unmask]> >
> 631-595-5879
>
>
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