Jorge,
Why don't you try a water soluble masking on the via's? That is what we
do and it works for us. After cleaning, the holes are ready for test.
The Masking is: Wondermask by Techspray P/N 2204-8SQ. Yes, this adds one
more step to the process but saves a lot of touchup later. I hope this
info is of value.

Patty Olinger 
Manufacturing Engineer
Projects Unlimited
(937)918-2267
[log in to unmask]


-----Original Message-----
From: Jorge Rodriguez [mailto:[log in to unmask]]
Sent: Friday, January 11, 2002 2:10 PM
To: [log in to unmask]
Subject: [TN] Solder Balls on Wave Solder


Technetters,

        My company is having a solder ball problem on the wave solder.
The
issue is primarily caused by overly large un-masked  vias on both sides.
The
via diameter is 25 mils with an annular ring of 25 mils on a .062"
board.
On the wave solder process, the flux gets entrapped inside the vias and
no
matter what we do on the pre-heating section there still flux remaining
inside that causes the solder to explode into tiny solder balls when it
gets
to the laminar section of the wave, like a volcano effect on the
component
side. These boards have also a good amount of the same vias under fine
pitch
QFP devices , this narrows our process window  if we want to heat the
board
even more. Heating the board more on the preheaters to resolve the
solder
ball problem leads on re-reflowing of the leads of those devices and
quality
problems as a result of that, the QFP pins pop up and become
un-soldered.
The customer does not want to use smaller vias or get them masked off
since
vias are used for test and rework purposes, they want to be able to
insert
wires inside the vias in case they need to change the board
configuration.
Any ideas on what to do with the wave process to resolve this issue?


        Any ideas would be greatly appreciated.



Jorge Rodriguez
Process Engineer
Varian Electronics Manufacturing
615 South River Drive
Tempe, AZ 85281
Phone: (480) 968-6790 X 4258
Fax: (480) 829-4000
E-mail: [log in to unmask]

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information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
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