Well I'm a hands on kind of guy.
I knew a guy back in the early 80's who was going to buy the latest and
greatest computer as soon as it came out. Every time I saw him he would talk
about another computer he heard of that he was going to buy as soon as it
came out.
I bought 3 books. One on 8080 assembly, one on 6502 assembly and one on 6800
assembly. (There was no Internet back then) Then I built this computer and
bought that computer, soldered kits, built wire-wrap boards, wrote programs
in 1802 assembly, 6502 assembly, basic, forth, disassembled operating
systems, made a lot of mistakes and learned a LOT.
I don't know if that guy ever bought a computer, probably not, but I
parlayed a lot of tinkering and a Journeyman's card into a career in
electronics and had a lot of fun along the way.
Personally I'd get;
A loupe and a table mounted lamp / magnifying glass.
Some de-soldering braid,
A Solder Sucker,
A Small soldering Iron, 30 Watt with a 1/16 tip,
A flux pen (a felt tip pen with flux.),
A SMT soldering kit
http://www.cpcares.com/ESM200K.html for $22 ( I'm Cheep)
( Or one of the $60 to $100 "SMT soldering kits" if you're not.)
And melt some solder
I looked it the sites you posted and they provide the basics. After that it'
s a mater of practice, hands on. Of course that's just my opinion and
everybody has one.
Thanks for checking over those web pages, it's good to know that
someone experienced thinks those pages are on the right track. Over
the past few days I've been reading those web pages, along with
dozens of other threads and web pages on SMD assembly and test
equipment.
One web page suggested getting the kind of magnifying eyeglasses that
watchmakers or jewelers use but I may go with one of those third hand
clamps with a built in and position adjustable magnifying glass. I saw
one at a surplus electronics store today for $5. It was a little light
on construction and the magnifying glass only had a plastic lens so I
think I'll try to find a better one.
I've found a few interesting newsgroup threads about SMD assembly,
which I've pasted to the end of this post. I think I'll see if I can
find the "hoof" tip mentioned in the threads.
........................
What you need is FLUX - I solder these kind of things with a moderate
sized iron, regular (0.028) solder, and flux.
Get a corner pin located, tack solder, locate other corner, tack
solder
(just put a little solder on the tip of you iron) -flux the pins on a
side you didn't tack, and then drag the tip and solder along, repeat,
and clean with flux remover -I learned this from a lady who did
commercial rework on SMD's for a lving - I've put 0.5mm parts on with
not problem pretty quick. Now a 201 resitor or cap is another story -
I'm a tombstoner. Anyone know how to do these things well?
..............
Andrew,
I totally agree with what you've said below. I used to do i486 and
Pentium mainboard rework by the palet before and this is exactly what
we
do from 8 pin SOIC to 208 pin QFPs. Flux, right heat, medium soldering
iron tip (small one don't deliver that much heat) and 63/37 solder
will
do the job. The result is almost like that of the production ones
after
cleaning up the excess flux.
As for the braid, I use it for stubborn solder bridges and I don't
recommend the shotgun approach of filling everything with solder then
clean up with the braid as what some has suggested. You'll end up with
misaligned pins and damaged ugly board.
For SMT resistors and caps, if you have two irons then just put one
tip
on each end and lift or you can buy those fancy tips.
PJ
..........
You'll find there are several techniques. From trial & error (and
later
a little advice from a rework tech at Intel), here's mine for working
with 0.5mm pitch, 128-pin SMDs:
* Flux the pads
* Position the piece
* *Very light* downward pressure to prevent shifting
* Place a small bit of solder on the iron tip
* Tack one corner pin
* Ensure device is positioned properly
* Tack opposite corner
* Flux the pins
* Place a small amount of solder on the iron
* Stroke each pin away from the body toward the tip
- Flux will help the solder wick around/under the pin
- The stroke guides solder balls to the tip of the foot
- You can do several pins at once if the tip is wide
* Cleanup with solder braid
Some key tricks:
- I didn't have good success with the "blob it on, run to the end of
the
row" technique at lower temperatures. The pin-by-pin technique is a
little more tedious, but more consistent with fine-pitch devices.
- *Don't* use a very fine tip. I started with a narrow-tip 1/32"
"screwdriver" tip, but discovered that it had problems transferring
enough heat on larger packages. A conical 1/32" screwdriver tip
worked
much better, as did a common 1/8" conical screwdriver tip.
- Good tinning on the tip is key, since you want the solder to flow
off
smoothly, not ball up and come off in globs. If you do many, you may
find yourself replacing the tip regularly. There are good tricks to
prolonging the life of the tip's tinning - search google for
'soldering
iron tip tinning'. Basically, cover the tip in solder when it's idle
in
the stand to prevent oxidation; wipe it off before you start a joint,
not after.
- You don't need thin-gauge solder, since you're applying it to the
tip,
not the pad. Some folks prefer paste solder, but I've had better
success with wire solder.
- Use a flux pen, like MG Chemicals' (Fry's Electronics). It goes on
thin, applies easily, makes less mess.
- Flux is your best friend here. You're bound to get bridges or
solder
globs behind pins. They can be coaxed out with flux, an outward
stroking motion, and braid to remove excess.
- Rather than using a stereo microscope, I use a jeweller's magnifying
visor in the strongest strength to do the soldering, with a jeweller's
loupe for inspection. Micromark.com sells both, and the loupe
attaches
to the visor.
- Bright lighting is good. I use a small 20W halogen desk lamp on an
arm to position it close to the work and move it around to minimize
shadows on the pin edges.
- Use a temp controlled iron, set to ~220 C. Check the specs on your
parts for maximum soldering temperature and time tolerances.
- If you'd like some practice, check out the dummy parts at
http://www.practicalcomponents.com and practice first on a spare PCB.
They supply exact mechanical parts for about $1 each - worthwhile if
your live parts are $10-$30.
......................
Metcal makes a "hoof tip" just for this. It looks like a medium-small
conical tip that has a flat on one side. When you put solder on it, a
nice juicy blob parks on the flat, and as you run the pointy tip down
the row of fluxed pins, the solder slurps off onto each pin in just
the right amount. My people solder 240-pin FPGAs in just a minute or
two this way.
If anybody is doing any serious amount of soldering/desoldering,
Metcal gear is well worth it.
John
................
I'm using this thing (its equivalent from Weller) to solder 100 pin
FPGAs
and it does work. But you need flux to prevent solder from spilling
over
multiple pins and shorting them together. I also found that this works
better
with higher temperature, I do it at around 400C.
Soldered in about 600 over the years this way.
Siol
...............
Do you happen to have the tip number handy? I'm using a conical tip
with a flat grind on it ("screwdriver" tip), but I haven't seen a hoof
tip from Weller like John describes.
Oh, one other tip: Metcal makes two hoofers, big and small, and my
people prefer the big one. It holds more solder and works great on the
fine-pitch parts.
All this stuff is counter-intuitive.
...............
Ever heard of rework paste? just clean up the pads and tin them paint
on
the rework paste then place the component on the pads, you can then
either
do every pin with your iron or use a hot air pen to fix the device
afterwards clean up with some isoprop and a brush, Ive fitted loads od
chips
with this method and I might say with pin spacings of much less that
1mm
,,,,,,, good luck
..........