Hi Phillip -

I'll take a stab at your #4:

**4)  We have run a no clean process for five years without ever having a 
failure related to solderballs, but we have been asked to eliminate solderballs 
entirely.  Is this too much to ask from a no clean process?**

***The folks I have talked with and the technical articles I have found on the 
subject of solderballing seem to fall into two camps: 

(camp 1): Solderballs are part of a no-clean process and can be avoided if you 
characterize your solder process very well and select/understand the low residue
flux vehicle that you are using

(camp 2): Solderballs are an inevitable part of a no-clean process and provided 
that one can show they do not cause a reliability problem in the products use 
environment no one is concern about their presence.

We have one program that has been using low residue materials and has just now 
completed our internal "qual" for using a no-clean process flow. We did have 
solderballs but were able to eliminate them (and yes I mean eliminate them 
99.99999%) with some process changes and some assembly design changes. The 
product is simple 50 mil pitch technology so making the jump to a no-clean 
process flow wasn't very challenging - I suspect had it been 16 or 20mil pitch 
technology things would have not gone as smooth. 

Who asked you to eliminate the solderballs? An internal or external customer and
was there a technical reason or just an risk assessment concern? I believe in 
the camp 2 philosophy but live in a camp 1 environment. Hopefully other 
TechNetee's can relate their experiences.



Dave Hillman
Rockwell Collins
[log in to unmask]





______________________________ Reply Separator _________________________________
Subject: RE: SOLDER BALLS (on SMT)
Author:  [log in to unmask] at ccmgw1
Date:    2/6/97 9:34 PM


1)  Has the question posed by Tom Olafsson below ever been answered?  I 
could not find any follow up in the archive.
     
2)  Has anyone published a report on SMT solderballing, such as causes and 
cures?  I have seen a lot of correspondence on the wavesolder generated 
solderballs, but I am looking for a cure to what we call "squeezeballs" 
(usually found on the sides of 1206 chip caps and resistors.  We are about 
to initiate a DOE to solve the problem by varying the solderpaste print 
shapes (home plate shapes, etc), stencil thickness, as well as three other 
parameters.
     
3)  How is the J-STD-001 defect for solderballs supposed to be 
interpreted........anotherwards if the solderball is encapsulated and 
doesn't reduce the minimum design electrical clearance, can it be larger 
than .005"?
     
4)  We have run a no clean process for five years without ever having a 
failure related to solderballs, but we have been asked to eliminate 
solderballs entirely.  Is this too much to ask from a no clean process?
     
5)  Does anyone have a good method for removing solderballs from the sides 
of chip caps without running the risk of losing it under some other 
component?  Use of a vacuum desoldering device has been suggested but the 
tips aren't small enough to reach in between a lot of the components.
     
     
All suggestions or responses will be appreciated.
     
Regards,
     
     
Phillip A. Bavaro
Senior Manufacturing Engineer
[log in to unmask]
(619) 658-2542
     
_______________________________
     
     
     
     
At 5:51 PM -0000 10/16/96, [log in to unmask] wrote:
>Do any of you know of or have a checklist (at a high level) of what should 
>be investigated if solder balls left on PCB assemblies after reflow?  What 
>is typically the most common cause that should be investigated first?
>
>Thanks,
>
>Tom Olafsson
>Teradyne Inc.
>[log in to unmask]
>
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