Hi, Tony,
When I first read your posting, I bet myself a beer that you were using
laser drilled blind vias. I also bet myself that they were probably below
0.012" - are they? How deep do they go? You will have great difficulty
filling a small-diameter, blind laser-drilled via with this epoxy, or any
other, unless you can do it in a vacuum. The problem is being able to
displace the air inside the hole.
Dupont CB100 (now CB101, by the way) has a very small particle size, and is
specifically designed to fill small holes well. Any alternatives I have
heard of have larger particles and don't fill holes nearly as well. If you
have to keep the via-in-pad design, you may be faced with fabricating the
board with conventional drilling. This will mean laminating the layers
containing your blind vias and processing them as through holes. These can
then be filled successfully and outgassed, ground flat, etc., before the
remaining layers are laminated onto the stack, drilled and plated. It's
quite possible to fill holes up to 0.025" diameter and only 0.007" deep
with CB100/101, without the over-plated pads popping off during reflow.
The only other reason I can think of why pads would come off is if the
plating adhesion to the epoxy is faulty and you have a large CTE mismatch
between the BGA and the substrate material. Differential expansion could be
pulling weak pads off (??). Plating to CB100/101 is usually very
successful, so I can't say why plating adhesion should be bad - if it is.
Good luck
Peter
tony steinke <[log in to unmask]> 30/05/2002 04:09 AM
Sent by: TechNet <[log in to unmask]>
Please respond to "TechNet E-Mail Forum."; Please respond to tony steinke
To: [log in to unmask]
cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
Subject: Re: [TN] conductive blind via plug
Don, Russ, Rush
The application is a blind via under BGA pad. The process sequence is:
Lase via
electroless
full panel electroplate
CB100(lase vias only)
flash electroplate
drill
electroless
image
pattern plate
strip/etch
Thanks for the input.
Tony Steinke
----- Original Message -----
From: Don Vischulis
To: tony steinke
Sent: Wednesday, May 29, 2002 9:49 AM
Subject: RE: [TN] conductive blind via plug
Tony,
Please supply process details. The manufacturing sequence may be part of
the root problem.
Don Vischulis
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of tony steinke
Sent: Wednesday, May 29, 2002 11:33 AM
To: [log in to unmask]
Subject: [TN] conductive blind via plug
Techies,
We have done some initial testing on the DuPont CB100 conductive via plug
with blind via application and so far have been unsuccessful. The blind
via is approximately .016 diameter and .030 in depth. The biggest problem
we are experiencing is getting adhesion(BGA pads popping off) with
copper plating after the CB100 has been applied. Is there
another type of conductive blind via plug recipe on the market.
Thanks for any comments
Tony Steinke
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