[time-nuts] PCB design questions thread II

[Keith Payea]

A really good way to handle the pad on the bottom of the part is to put a
hole through the board right there.  You usually need a bunch of vias to tie
the pad to the ground plane on the bottom of the board anyway.  Put one hole
large enough for your soldering iron tip to reach in and touch the underside
of the part.  When installing the part, solder the regular pads first, then
flip the board over and solder the central pad.

This is sort of self limiting too.  If you apply too much heat for too long,
the part desolders itself and falls off!

Adding the extra hole is recommended by some of the vendors.  I've used it
sucessfully with 2.4GHz band radios and it works great.

	Keith 

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Paddock
Sent: Monday, June 02, 2008 6:24 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] PCB design questions thread II



> How do you cope with SMT parts (eg high frequency ADCs) with metal
> thermal transfer /ground connections under the package itself?

"How to succeed the first time with ultra-small QFN packages"
http://www.wirelessnetdesignline.com/showArticle.jhtml?articleID=202800018


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