AVR-Chat

I am going to try a project using the SMT version of the Atmega16.  This
will be my first SMT project.

I must admit, I’m a bit nervous at the thought of not being able to pull the
processor out of a socket to replace it – not that I’ve ever had to in the
past, but at least I knew the option was there  :-)

I note that, in the datasheet - near the top where it shows the pin
assignments, it shows the TQFP (gull wing) package along with "NOTE: Bottom
pad should be soldered to ground." with an arrow to a large pad on the
bottom of the package.  This note does not appear near the end of the
datasheet where they show the package dimensions.

What is the reason for this pad to Gnd - thermal stability?

In a home environment how does one solder this pad - provide a hole under
the part and solder from the back side?  Would thermal/conducting grease
work rather than soldering?

My application does not use a lot of output drive so heat dissipation should
not be a consideration ...


Another issue:  In the past I have only used commercial prototyping boards
with the processor already in place.  I had never noticed that, in the
through-hole part, there are two "GND" pins.  The TQFP package has three VCC
and three GND pins.

I assume that good design requires that all of these pins be connected
(i.e.: connecting one won't work)?  Do all the VCC pins require their own
decoupling or will one do (and if so, which one?) ?

I'm looking forward to designing a board with 603 size resistors that are
WAY smaller than my usual 3/8" long beasts.  I'll be able to get a whole lot
more in the board area provided by the free version of Eagle PCB  :-)

Thanks in advance for the help ...
 
Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844
http://www.whitetrout.net/Chuck