Hi Tom:
If the solder is visible I would pick them up with braided wire. If they are at a place that is hard to get to and do not violate minimum electrical spacing and they are going to be encapsulated with CC then, I would not worry about them. Solder balls can be a potential for shorts if not encapsulated.
Regards,
Ramon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jack Crawford
Sent: Monday, October 04, 2004 3:12 PM
To: [log in to unmask]
Subject: Re: [TN] solder balls wedged under low profile SMD
Tom, both Rev B and C to 610 had so many words associated with solder
ball criteria that it's hard to see the real requirements. Rev D will
be much clearer with the following:
5.2.6.1 Soldering Anomalies - Excess Solder - Solder Balls/Solder Fines
Solder balls are spheres of solder that remain after the soldering
process. Solder fines are typically small balls of the original solder
paste metal screen size that have splattered around the connection
during the reflow process.
Target - Class 1,2,3
* No evidence of solder balls on the printed wiring assembly.
Acceptable - Class 1,2,3
* Solder balls are entrapped/encapsulated..
* Solder balls do not violate minimum electrical clearance.
Note: Entrapped/encapsulated/attached is intended to mean that normal
service environment of the product will not cause a solder ball to
become dislodged.
Acceptable - Class 1
Process Indicator - Class 2,3
* More than five solder balls per 600 mm2 [0.93 in2].
Defect - Class 1,2,3
* Solder balls violate minimum electrical clearance.
* Solder balls are not entrapped in no-clean residue or encapsulated
with conformal coating, or not attached (soldered) to a metal surface,
Figures 5-45 through 5-48.
Note that there are really only two considerations--the solder balls
aren't loose or aren't likely to break loose in the normal service
environment, and they aren't of a size or location that will cause a
short or violate minimum electrical clearance. It's no difference from
the criteria in Rev C, just stated much clearer.
I hope this helps.
Jack
Jack Crawford, IOM
IPC Director Certification and Assembly Technology
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Tom Gervascio
Sent: Monday, October 04, 2004 1:56 PM
To: [log in to unmask]
Subject: [TN] solder balls wedged under low profile SMD
Are solder balls a defect or process indicator? The solder balls were
are observing are mid chip solder balls on low profile SMD resistors and
caps. The mid chip balls typically wash off and X ray does find a few
solder balls wedged under SMD devices (right now about 8 per board). I
think they are process indicators and do not need touch-up (I really
think desoldering the part and resoldering the part is more deleterious
to reliability than these entrapped solder balls.
I went over the IPC-A-610C and found the following pertaining to solder
balls.
Para 6.5.3.1 and Para 12.4.10 Excess solder. Target condition is no
evidence of solder balls on the printed wiring assembly
Acceptable condition Class
1/Process Indicator Class2,3. Entrapped or encapsulated solder balls
that are within 0.005 inch of lands or conductors, or exceed 0.0051 inch
in diameter.
Tom Gervascio
Senior Process Engineer
Sparton Electronics
(352) 540-4040
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