Re: ATM Sputter Coater?

[John Dykins <dykins@UDel.Edu>]

James Lerch wrote:

> BTW, anyone have a 'Rule of Thumb" guide for diffusion pump to chamber size?
> This could be handy for evaluating the above system's potential.
> 


The description does not mention the diffusion /turbo pump nor the
height of the bell jar. If the bell jar is say 2 cu ft then a 4 inch
diff would be fine.
If the bell jar is glass then hope for adequate protection in case of
implosion.

Generally it is best to go for the biggest diff pump and the smallest
chamber to pump down quickly and handle gas loads without choking, e.g.
due to filament heating and high voltage discharge. Apart from the
volume, a large chamber has a large surface area which will adsorb 
water vapor when at atmospheric pressure. In fact water vapor is usually
the major constituent remaining in a vacuum system.
 
Other considerations, 
Look for a diff/turbo pump with a large throat diameter, i.e. area, for
fast pumpdown.
The tube from diff pump to chamber should be short and  be the same
diameter as the diff pump.
The rotary pumping speed should be at least 4 cu ft /min to handle the
gas loads
James' system is a good example of the above, I would guess that it used
a 4 inch pump and maybe a 1-2 cu ft chamber and the rotary does not look
small.