Steve,

        We have designed a number of boards with controlled depth holes.
        Does your vendor do a quality on this type of hole? If so,
        would you mind giving me their name?

                                Thank you,

                                Richard
                                [EMAIL PROTECTED]



-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Friday, November 30, 2001 4:49 AM
To: Protel EDA Forum
Subject: Re: [PEDA] Blind and buried via's Mayhem


In a message dated 11/29/01 5:47:09 PM Eastern Standard Time, 
[EMAIL PROTECTED] writes:


> >1. Can I use a hole pair that goes through the prepreg, but
> >does not go through the core material above or below that
> >level?  I just don't see how it can be manufactured.
> 
> No.  At least not to my knowledge.  My understanding of the process is
that 
> 
> basically you can only use blind vias on cores.  You may not connect cores

> to one another except with full through-hole vias.
> Exception:  If you have 2 internal cores you can prepreg these together
and 
> 
> then drill through them... plate to connect these cores together, and then

> prepreg more cores to the outside of that unit, through-hole drill the 
> whole thing and plate again, etc, etc, etc.
> 
> 
> 

Actually there is another way. On a recent job which had lots of blind and 
buried vias, the fab house called up and said they actually prefer to use 
"controlled depth drilling". They wanted to do, for instance, a via from 
layer 1 (top of first core) to layer 3 (top of second core) by laminating
the 
whole board together and then drilling down to the nominal depth of the 
middle of the copper on layer 3. I was skeptical be he said that such 
precison depth drilling is routine for them.  You need to talk to your fab 
house to see what's practical, and how much it costs.

Steve Hendrix


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