micro vias (laser type) at least as explained to me DO NOT go all the
way thru
they only go from an outside layer to the next adjacent inner layer
to me this seems to limit their usefulness because you then have to
typically transition to a standard via which would have to be buried to
be useful, esp. in the case of a dense bgas
micro vias do allow hole in smd pad, they are too small to bother the
paste much
I think they were 5 mil dia and 2 mils deep, consult shop
the smallest mech via I have found running around here is 18 mil via
diameter, finished hole size should be spec'd as 0 to 10 mils, this
allows vendor choice and means they don't need to guarantee that the via
is not plugged or blocked by plating.
these feature sizes are associated with 4/4 rules which are to be
avoided if possible
more buildable minimums would be 20 mil via, 5/5 rules
we just did a job with a bunch of big dense 1mm BGAs and the trace
density was such that we had to go to 4/4 to minimize layers to a
thickness which would still insert into a PCI conn!
protel could not route this board but spectra could (service was by Mike
Reagan who did a very nice job)
someday it would be nice to have variable trace/gap rules by area so
that the rest of the board didn't also have to be 4/4
Dennis Saputelli
John Haddy wrote:
>
> I don't know whether there is a standard definition, but I
> would regard it as a hole that couldn't be made reliably
> using a standard drill-then-plate process.
>
> i.e. smaller than about 0.25mm finished hole size in a
> 0.5mm diameter land.
>
> John Haddy
>
> > -----Original Message-----
> > From: Brian Guralnick [mailto:[EMAIL PROTECTED]]
> > Sent: Tuesday, 15 May 2001 8:05 AM
> > To: Protel EDA Forum
> > Subject: [PEDA] What size is a micro VIA
> >
> >
> > Hi all,
> >
> > What diameter is considered a micro-Via?
> >
> > Thanks,
> > _____________
> > Brian Guralnick
> >
> >
> >
> >
--
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