In a message dated 5/26/98 5:41:52 PM Pacific Daylight Time,
[log in to unmask] writes:
>>TechNet,
I am having trouble with solder balls dinging metal squegee blades on the
second
pass of some double-sided boards. The solder balls usually form due to vias
on
the first pass. Is there any good, quick method for a stencil print operator
to
assure that there are no solder balls on a board before it is printed, so the
blades will remain in good condition. Would performing a wipe of the board
with
an alcohol wipe effect the quality of the print? Thank you in advance for
any
suggestions that you might have.
Sincerely,
Brian Geijsbeek<<
Hello there Brian,
Okay...here ya' go, first, get some 80-grit sandpaper, then use a lotta
elbow grease, and sand them pesky balls offa the board!! What's that? Whaddya
mean no way? Awwwww......you're no fun!!
Seriously, it sounds to me like you do got one heck of a solderball
problem if it's bad enough for them to ding a stainless steel metal squeegee.
It also sounds to me like the fab shop that built these boards for you did
something that's causing the solder balls from the via's.
I'm guessing now because you didn't actually mention it, but did they
HASL the board and then go back and tent the via's? Because if that's what's
happened, there's no way your going to get all the balls off...what's
happening is that the plating is reflowing beneath the mask and then out
gassing thru a break in the via tent and giving you the little balls that
you're seeing... some of them are going to be bonded to the anular pads, and
others are just adhered to the mask. The ones that are bonded to any metal are
the ones that are tough to remove.
But moreover, what I would be concerned about is not just the solderball
problem you're seeing, (because it sounds to me like you're building product
with these fabs) but what's going on inside that little cavity that's been
somewhat enclosed by soldermask...is there any flux or flux residues trapped
in there? Something to worry about...
You know, I've only seen this sort of thing happen when they've put mask
plugs on both sides of the board tenting the via's...that's not necessary,
only one side of the board needs to be tented (if it's being done for
improving vacuum at ICT).
C-ya!
-Steve Gregory-
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