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March 1998

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Subject:
From:
Ruben Irizarry <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 16 Mar 1998 14:12:31 -0700
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Hi I will try to help you.
Solder Balls it has been the most common and the most complex reflow
soldering problem. During reflow, small spherical solder powder particles
of various diameters, are formed away from the main solder pool, do not
coalesce and remain on the board after solidification. There are many
possible causes such as:

Smearing of paste on the PCB from an inadequate printing process (stencil
underside wiping between prints can often alleviate this), excessive
exposure of paste to an oxidizing environment, inadequate heating (too slow
and uneven), too rapid a heating rate and too long a preheat profile,
prompting paste dry-out. Other causes of solder ball formation include an
interaction between the solder mask (as you said) and paste, insufficient
flux activity, too many fines (undersized powder particles) and
inappropriate volatiles in the flux for the specified reflow process.

The presence of solder balls on the PCB is of concern because of their
potential for creating circuit shorts and/or leakage currents. They also
represent the possibility of insufficient solder in an adjacent joint that
ought to have been part of a well-formed connection.

I hope this will help you,

Rub?n E. Irizarry-Guzm?n
Operations Engineer




[log in to unmask] on 03/16/98 08:06:30 AM

Please respond to [log in to unmask]; Please respond to [log in to unmask]

To:   [log in to unmask]
cc:    (bcc: Ruben Irizarry)
Subject:  [TN] Causes & Corrective Actions for Solder Balls




Good day all,

I have a question relative to solder balls and hope that someone can
shed some light on this issue.

1.  What causes solder balls?
2.  Could solder balls be the result of incompatiability between flux
and soldermask?
3.  How do you eliminate solder balls?
4.  What is the IPC acceptability standards for solder balls?

Any feedback would be greatly appreciated.  Thanks to all that offer
assistance.

Best Regards

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