Sorry for the following wordiness:

It really is as simple as depicted in the Seattle Robotics Society articl=
e.=20
I've done several boards using this method and they all turned out perfec=
tly=20
with no solder bridges or unsoldered pins.  No touchups required as of ye=
t.=20
I've found it easier to place the solder on each pad separately instead o=
f=20
the direct line across the entire row.  A neighbor of mine works at a=20
hospital and brings me 3 or 5 cc syringes and long 21 gage needles.  It's=
=20
nice that the needles are long because I have more control using my other=
=20
hand to keep it steady. They're very sharp & need a slight grind on the t=
ip=20
to make it just flat enough to lay a perfect flat strip of paste across t=
he=20
width of each pad.  I keep the big syringe gotten from Digikey in the fri=
dge=20
all the time, and put only a small amount of paste in the smaller 3cc=20
syringe when I'm doing a project.  This is a must because the tip will cl=
og=20
some time during the process and the smaller diameter syringe gives much=20
more pressure to push out the clog than the large diameter syringe that I=
=20
got from Digikey.  It also allows much more control in the amount of past=
e=20
applied.

The solder paste from Digikey is indeed expensive, but well worth it.  Th=
ey=20
offer 2 varieties that come in the small syringe.  One is water-soluble, =
as=20
the Seattle Robotics article used, and the other is a no-clean flux versi=
on.=20
Use the no-clean version!  The water-soluble type must be washed in a rat=
her=20
vigorous manner afterward.  I discovered this after finding excess leakag=
e=20
across caps where I wasn't able to fully clean away the flux from under t=
he=20
devices by simply running it under the faucet (with brush & flux remover =
of=20
course).  A call to Kester tech support verified that it must be cleaned =
in=20
a cleaning system with a particular mild detergent, much like puting it i=
n a=20
dishwasher.  He said that the no-clean version is the way to go for=20
home/small lab.  I've been using the same batch of paste for close to 2=20
years and it still works as well as the day I got it, probably because I'=
m=20
careful to not allow any air to get in the container and it's stored in t=
he=20
fridge in a tip-down fashion.  Always put the caps back on top & bottom=20
after transferring to the smaller syringe.

I've also successfully used a small hot air gun that my mother happened t=
o=20
have for embossing greeting cards.  Costs about $25 U.S.  It has a pretty=
=20
small diameter outlet and the airflow can be adjusted to low flow.  Doing=
 it=20
this way is perfect for a single device at a time and for desoldering tha=
t=20
device.  The air will push it around a bit so you must be careful to dire=
ct=20
the airflow directly downward over the part. Even then I hold a wooden=20
toothpic in the other hand to help keep the device in place should it flo=
at=20
away before the process is complete.  It is delightfully surprising to se=
e=20
how professional looking the job is when complete.

Oh, and another very important tip: don't try any of this if you've had m=
ore=20
than 1 cup of coffee or after a night of heavy drinking. And besides a go=
od=20
set of tweezers, sharp wooden toothpicks are your friends.  And a good cl=
ean=20
magnifying glass is worth its weight in gold. Don't even bother wasting $=
40=20
for a little vacuum pick-up tool.

That's all I have to say about that.

Rick



> >hard to find seller, digykey give doubled price and delayed delivery.
>>More trouble=A3=ACIt needs low T storage and half year life.
>
> Well, that is two of the problems with solder paste, its shelf life and
> storage temperature.
>
>> .5mm RA solder+iron for SSOP each pin solding or solder paste+hot gun?
>>I have very good constant temperature solding iron. But,
>>such huge pin count is really tough job. So, solder paste is better?
>
> This is where you have to decide just how many you need to do.
>
> However some people find that using a normal iron with a spade tip, the=
y=20
> can
> first solder the corner pins on a package so it does not move, then run
> along the pins with a larger spade tip, and solder, then remove the exc=
ess
> solder with solder wick.This can be a faster process than soldering eac=
h=20
> pin
> separately, but does need some care, as very fine pitch TSSOP packages =
can
> have their leads pushed off the pad by the tip of the iron.
>
> You may like to look at the following web sites, if you haven't already.
> http://www.geocities.com/vk3em/smtguide/smtguide.htm
> http://www.seattlerobotics.org/encoder/200006/oven_art.htm
>
> --=20
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>=20


--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist