Hi Jorge,

I'm not sure I understand the difference between solder beads and solder
balls, are the beads smaller?

Water soluble paste will pick up moisture and lose structure in high (>50%
RH) humidity conditions.

You could be getting excessive flux flow out during reflow preheat and with
it small individual particles of solder powder washing out and creating
micro-balling.

Or

You could have a volcanic effect whereby the paste explodes during the
reflow process spattering solder balls all over, this is also likely if
there has been an increase in moisture content in the paste.

Or

The powder in the paste is not particularly good and is not fusing properly
and creating a lot of micro-balls.

Could be anything really. What paste are you using?

Best regards,

Andrew Hoggan
BBA Associates Ltd
www.bba-associates.com



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jorge Rodriguez
Sent: 21 August 2001 19:57
To: [log in to unmask]
Subject: [TN] Solder Beads (not solder balls)


Fellow technetters,

We are having tons of issues with solder beading, even on boards were we
didn't have the issue before. We're clueless, we suspect of the solder paste
(63-37 Water Soluble), it looks slumpy amd watery, but we're not sure. I
know solder beading can be solved by designing the stencils with home-base
aperture, but what we're seeing here is across the board, not just one
particular assembly but several. Does anyone have experience dealing with an
issue like this?, could solder beading caused by the oven profile or is it
more like solder paste related?


Any comments would be appreciated.


Jorge Rodriguez
Process Engineer
Varian Electronics Manufacturing
E-mail: [log in to unmask]

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