Too bad you don't have the ability to document the assembly/reflow
process so the EMS doesn't have to "cry like a little baby". 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nowland, Russell
Howard (Russell)
Sent: Tuesday, February 27, 2007 1:37 PM
To: [log in to unmask]
Subject: Re: [TN] Via in Pad question

Carl,

The question is how bad do you want to do it?  It would take more than a
few paragraphs to explain how to do it.  I have built VIP assemblies for
~18 years and it is doable using older technology 50 mil pitch and
discretes down to 0805 without filling the vias.  You have to have a
good PWB supplier with good hole quality and good hole cleanliness or
you will out gas causing a lot of problems.  You can go finer using
smaller drills but your cost goes up and it becomes harder to plate the
holes.  

Your EMS' will cry like a little baby too.  You also have to learn how
to design your stencils to compensate for the solder loss.

Like I said it is not a quick to learn process and there can be pitfalls
along the way.

If you have to do it do yourself a favor and fill the vias.

We had very little problems when we were an OEM and now that we use
EMS's it is a pain. 


Russell Nowland
Alcatel-Lucent           
Supply Base Engineer
Address: 14000 Quail Spring Parkway, Suite 300 Oklahoma City, OK 73134
email: [log in to unmask]
Desk: 405-302-1660
Cell: 405-203-0034
Fax: 405-302-1622

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Carl VanWormer
Sent: Tuesday, February 27, 2007 10:58 AM
To: [log in to unmask]
Subject: [TN] Via in Pad question

I am looking for guidance on using vias in pads of surface mount
components.  The concept is great for high speed design, since it gives
the least inductance for mounting bypass caps.  It sounds easy, but I'm
sure there are some pitfalls and there may be some rules I will break.
Any guidance towards documents on this combination would be appreciated.
Also, any stories to scare me away from this approach will be fun to
hear.

Later,
Carl





Carl Van Wormer
Cipher Systems
1800 NW 169th Place, Suite B-100
Beaverton, OR  97006
Phone (503)-617-7447 extension 20    

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