> -----Original Message-----
> From: Dennis Saputelli [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, 15 May 2001 10:07 AM
> To: Protel EDA Forum
> Subject: Re: [PEDA] What size is a micro VIA
>
>
> 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
Assuming that the microvia is part of a build-up technology, I'd regard
this as a major benefit! Since all drilled vias become buried vias (I'm
referring to a polyimide type buildup over a traditional FR4 stack),
the entire component mounting surfaces are free from those pesky holes
that prevent you from placing the component just where you want it!
>
> micro vias do allow hole in smd pad, they are too small to bother the
> paste much
and, (combined with smaller trace widths) they massively increase the
available routing channels.
...
>
> 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
It is possible to set rules with effect limited to region or component. I
use this to allow 5/5 rules under a microBGA, while the rest of the board
is 6/6. I've got no idea whether an autorouter would take note of this,
since I handcraft my boards (being compact, with high speed digital plus
microwave radio components, the layout is as critical as the circuit
design).
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* To post a message: mailto:[EMAIL PROTECTED]
*
* To leave this list visit:
* http://www.techservinc.com/protelusers/subscrib.html
* - or email -
* mailto:[EMAIL PROTECTED]?body=leave%20proteledaforum
*
* Contact the list manager:
* mailto:[EMAIL PROTECTED]
*
* Browse or Search previous postings:
* http://www.mail-archive.com/[email protected]
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
