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).

In article ,
ken scharf wrote:

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.

I've seen people recommend this as the preferred hand-soldering
approach for dealing with small-pitch surface mount parts. Don't
worry about creating bridges... use a bit of liquid flux on the pins,
get a nice blob of fresh solder onto the tip of the iron, and then
just gently drag the molten solder-ball along the pins and get them
soldered to the traces. Then, go back over it with solder-wick and a
bit more liquid flux, and wick away the excess.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Dave Platt wrote:
In article ,
ken scharf wrote:

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.

I've seen people recommend this as the preferred hand-soldering
approach for dealing with small-pitch surface mount parts. Don't
worry about creating bridges... use a bit of liquid flux on the pins,
get a nice blob of fresh solder onto the tip of the iron, and then
just gently drag the molten solder-ball along the pins and get them
soldered to the traces. Then, go back over it with solder-wick and a
bit more liquid flux, and wick away the excess.

I did smear the pc lands under the chip with paste flux first. Not a
heavy coat, just lightly applied. It does help.
I've watched the technicians at work hand solder even finer pitch chips.
One young woman has very good close in eyesight and works without a
magnifier. She does have to clean up with the solder-wick, but makes
machine like perfect solder connections. (she makes it look EASY!)
Whats hard is doing an entire board in one sitting without getting a
visual version of writer's cramp. (eye strain)

On 2006-12-28, ken scharf wrote:
I've watched the technicians at work hand solder even finer pitch chips.
One young woman has very good close in eyesight and works without a
magnifier. She does have to clean up with the solder-wick, but makes
machine like perfect solder connections. (she makes it look EASY!)
Whats hard is doing an entire board in one sitting without getting a
visual version of writer's cramp. (eye strain)

After you've done it enough under a microscope you learn what is going
to happen and you can do a lot of it without even being able to see it,
by timing and feel. Like you said in another post, there's also the
part where you get used to how disgusting any solder joint looks under
sufficient magnification...

--
Ben Jackson AD7GD

http://www.ben.com/

One thing you might try "next time"...

Pre-tin the PC pads by heating them with a heat gun, (being careful to
not overheat the board) and applying a very small amount of solder to
each pad. If you can get the IC pins all lined up with their PC board
pads, tack solder one of the corner pins (or one that is easiest to
solder without bridging). Use a toothpick (or some other device) to
apply gentle down pressure to the IC to keep it from moving. Use the
heat gun again (carefully) until the solder melts and the chip should
"settle" down into the molten solder. Keep the heat gun moving around
all pins to be sure all get down into molten solder. If you happen to
have a piece of copper clad PC board, you can practice by putting some
solder blobs on it and putting the leads of some sort of junkbox parts
on to the solder and heat it up with the heat gun, apply the down
pressure to the component and you can get the feel of how far the heat
gun should be away from the board and the length of time it takes to
melt the solder...

Scott
N0EDV

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).

ken scharf wrote:


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).

It's MUCH easier to begin with the easy parts! Start with the largest
chip caps and resistors, continue with the rest of the simple passives,
and then the largest ICs (largest pin spacing).

Finally, when you've honed your SMD skills, solder the large ICs with
the small pin spacings.

And give up the industrial-strength coffee for the duration :-)


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:
ken scharf wrote:


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).

It's MUCH easier to begin with the easy parts! Start with the largest
chip caps and resistors, continue with the rest of the simple passives,
and then the largest ICs (largest pin spacing).

Finally, when you've honed your SMD skills, solder the large ICs with
the small pin spacings.

And give up the industrial-strength coffee for the duration :-)


For some reason the instructions that came with the DDS-60 kit have you
solder all the ic's on first, then the resistors and caps.

After thinking I had done a good job on the AD9851 I put the board under
my binocular microscope for a close in look. I saw what looked like
microscopic solder bridges between the chip leads. I was able to remove
these with a stiff piece of paper slid between the chip leads. I still
see strange 'hair like' structures all over the board under the
microscope. I may be seeing dust, bits of flux, who knows! The
microscopic world is strange, especially in 3D.

Personally, I'd do the DDS chip first, before the resistors and
capacitors. One of the tricks I use is to clean the IC pins with rubbing
Alcohol after soldering and removing shorts.

Then, I apply a hot air gun, SLOWLY bringing the temperature up on the
pins of the IC. I try to get to barely melting the solder, but not burning
the main board. A slow application allows the IC to heat up gradually.

This tends to remove the hairline solder bridges and clean up between the
pins of the IC. Since the main DDS chip is the only part on the board, I
don't have to worry about heating up and blowing the resistors and
capacitors clean off the board !!!

I can, and have, used this same method on a completely assembled board,
but I have to pay close attention to the small parts, the tend to want to
blow away. In that case, I build a heat shield with tin foil and I press
it down on the board all around the IC I want to solder flow and that
usually keeps the other parts on the board where I want them.


This all takes a delicate touch, it's pretty easy to get things too hot,
but it does provide nice and clean solder joints.


Jim Pennell
N6BIU


--

23:10 Pacific Time Zone
Dec 28 2006

International Time
07:10 UTC
29.12.2006

I've been working on a high-power HF autotuner design that I'd just
about shelved because of the necessity of soldering the DDS chip. (it
uses an internal RF source to power the phase detector)

This thread has helped a lot. When time permits I may order up some
parts and give it a try. I have a good-quality magnifier lamp and a
fine-point temp-controlled pencil, what I don't have is OEM eye lenses
and flexible finger joints... ;-)

Jim, N7CXI

ken scharf wrote:
Ian White GM3SEK wrote:
ken scharf wrote:

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).

It's MUCH easier to begin with the easy parts! Start with the largest
chip caps and resistors, continue with the rest of the simple passives,
and then the largest ICs (largest pin spacing).

Finally, when you've honed your SMD skills, solder the large ICs with
the small pin spacings.

And give up the industrial-strength coffee for the duration :-)


For some reason the instructions that came with the DDS-60 kit have you
solder all the ic's on first, then the resistors and caps.

After thinking I had done a good job on the AD9851 I put the board under
my binocular microscope for a close in look. I saw what looked like
microscopic solder bridges between the chip leads. I was able to remove
these with a stiff piece of paper slid between the chip leads. I still
see strange 'hair like' structures all over the board under the
microscope. I may be seeing dust, bits of flux, who knows! The
microscopic world is strange, especially in 3D.

Jim Barber wrote:
I've been working on a high-power HF autotuner design that I'd just
about shelved because of the necessity of soldering the DDS chip. (it
uses an internal RF source to power the phase detector)

This thread has helped a lot. When time permits I may order up some
parts and give it a try. I have a good-quality magnifier lamp and a
fine-point temp-controlled pencil, what I don't have is OEM eye lenses
and flexible finger joints... ;-)

Most of my SMD work is done using half-moon reading glasses - the
strongest and cheapest available from the drugstore - in front of my
normal glasses. When not in use, they hang from a neck cord.

After publishing this suggestion, a very generous person *gave* me a
professional-quality binocular microscope. This is wonderful for big
jobs like assembling a whole new board... but to be honest, I still tend
to use the double glasses more, because the "setup process" is much
quicker.

You will find that the tip of the soldering iron becomes much steadier
when seen under the magnifier. This feedback loop is a wonderful thing,
especially if you give it the best possible chance to work:

* "Use the scope, Luke!" - learn to concentrate exclusively on what
you're SEEING. This is harder than it seems, because for normal
soldering we also rely a lot on our sense of touch, and automatically
tend to press the tip of the iron against the parts being soldered. With
SMD this is a disaster - it simply pushes the parts out of position - so
you need to break that habit and concentrate on using ONLY your eyes.

* Steady your arm against the edge of the bench, so you're not trying to
stabilize your whole body.

* Stay off the caffeine - it creates a fine tremor that the brain cannot
stabilize (too much "noise" in the feedback loop).



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek