Hi to all,

Earl's experience of using 1.5 mil plating in a PTH via without lands is
intriguing.  I would surely love to use landless vias in my designs.  Not
being a PCB fabricator, I have a few naive questions about this.

1) In order to get this much copper in the holes, does this mean that the
outer layers will necessarily plate up to 2 oz. or more finished weight?
Would a pulse plating process avoid this overplating on the outer layers to
any significant degree without causing other problems?

2) Is this technique practical with via sizes in use today?  Specifically, I
have been specifying 0.010" FHS +0.003"/-0.010" for 7/7 mil line/space
boards and 0.008" FHS +0.003/-0.008" for 5/5 mil line/space boards.
Obviously, plated shut vias are OK with me.

3) You mentioned that the ductility of the copper must be high, which is
logical.  What special measures are needed to insure this?

4) Are there any special issues in tenting vias made this way?  I like to
tent the vias with LPI mask, but my fabricators seem equally divided on this
(a whole separate topic):  some say no reliability problems and we do it
every day, some say the boards will die a horrible death.  The gloom and
doom fabricators suggest first plugging the vias with SR1000 and then using
LPI with openings that encroach on the SR1000 plugs.  The other fabricators
call this a ridiculous waste of money.  Who should I believe?

Regards,

Seth Goodman
Goodman Associates, LLC
tel 608.833.9933
fax 608.833.9966

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