ken scharf wrote:
I bought one of these kits to make use of a sample AD9851 chip I got
from Analog Devices a few years ago.
http://www.amqrp.org/kits/dds60/index.html
I knew it was hopeless to bread board something with this chip, but even
with a PC board soldering something with such close lead spacing is a
challenge (especially when you're past 50 with failing close in vision
and less than rock solid stable hands). Still I figured I'd give it a
try. Armed with the smallest soldering tip available for my Weller
PES51 soldering station, a good magnifier lamp AND a binocular
microscope I gave it a try to solder the chip to the board.
Well there is good news and bad news. The bad news is that it is
impossible to solder the chip by hand without creating solder bridges.
The good news is that I did a good enough job to get the chip 99%
perfectly centered on the solder pads, and you can remove the solder
bridges with solder wick without removing the chip from the PC board.
It would have been easier with thiner solder (I had .021" dia solder)
and a thiner soldering iron tip, but inspection with the microscope
shows no shorts, and it looks like all the pins are properly soldered.
Naked eye it doesn't look pretty but it should work.
Now to solder those chip caps and resistors! (They should be easier,
the AD9851 was the worst part to place with the tight spacing, all the
other parts have lead spacing at least twice as wide).
Be sure to more or less "drown" the pins to be soldered with flux. If you
get solder bridges, you probably have to little flux applied - really slob
the flux on the pins. When you think you have enough of flux, add more...
Any bridges are corrected with solder wick.
The AD98xx can be soldered with a 0.5mm ceramic tip. Get one of these cheap
( 10$ ) magnifying visors, especially if you are half blind as I am...
The AD9851 is one of the easiest SMD IC's to solder as there are pins only
on two sides.
Besides... We have been using SMD's since the early eighties now so stop
whinging over it, adapt! They wont go away and they actually improve most
RF designs!
//Dan, M0DFI