There are quite a few problems with via in pad. 
        1. Having a via in a pad will not give you a flat pad, possibly
reducing the reliability to the solder joint, very bad for fine pitch parts.
(unless this is a micro via)
        2. You will be forced to plug or fill the via (again unless it is a
micro via or blind via).
        3. There is also a process that will cap a via during the plating
process, again you will not have a flat pad. 
        If one is trying to decide if using via in pad is use full, just
remember the more processes you add to the board the more costly the design
will become, along with it's complexity, check with your board vender. It is
sometimes less expensive to add layers then going to a more complex design.

Regards,

Ted

-----Original Message-----
From: Dwight Harm [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, February 20, 2002 9:17 PM
To: Protel EDA Forum
Subject: Re: [PEDA] how does smt work ??


I'm relatively new at PCB layout, so I'd like to verify -- aren't
under-the-component vias fairly common nowadays, particularly with
fine-pitch ICs and BGAs?  The autorouter puts 'em there all the time, so it
MUST be ok! ;)

> -----Original Message-----
> From: Thomas [mailto:[EMAIL PROTECTED]]
> Sent: Wednesday, February 20, 2002 3:19 PM
>
<snip>
> The reason you may not notice the vias is that they may be tented (covered
> with solder mask) or under the component (bad design practice).

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