Hi,
I am planning a job where I need to manually solder surface mount ICs. Some
of these ICs have pins that are only 0.5mm apart! I'm worried that this
will be impossible to solder manually.
I've looked on the web - people tell me it is possible to solder SMDs but
I'm worried their talking about older SMDs with pin-to-pin distances of more
like 1mm.
I'm a relatively skilled soldering iron user.
Is it possible to manually solder ICs with pins only 0.5mm apart?
Thanks,
Jack
The pads MUST NOT have any applied solder on them. If they do,
remove it all with solderwick. (the bumps from the solder will not
allow the chip to lie flat.)
Align the IC, solder one corner pin to hold it down. Solder the
opposite corner down. Don't worry if the solder joins several pins.
Make absolutely sure it's aligned properly, and all the pins are
resting on the pads. Now apply enough solder that all the pins are
covered, even if they are all shorted together.
Here's the neat part: Take some "solderwick" (the braided stuff you
use for removing solder) and remove all the solder! It doesn't really
take it all off, it leaves the required amount underneath the "feet"
of the pins. If you look in a microscope, you'll find that you have
almost perfectly soldered pins. There will be trouble if the pins
didn't all touch the pads prior to soldering. Chips intended for
surface mount must have good co-planarity, so be very gentle handling
them. If you bend the leads for than a few thousands of an inch, you
can expect trouble.
If you have a good touch with an iron, and are using good liquid
flux (RMA type, you must remove the residual flux afterward using a
solvent like isopropyl alcohol), you can zoom thin solder along the
pins, and it will not short them out. I believe it's absolutely
necessary to use the proper liquid flux in order to pull this off, and
it does need a bit of practice. You'll need the solderwick to remove
shorted pins. I figure if you're using solderwick anyhow, then do the
first method and not lose any sleep over it.
I have successfully soldered QFP80's this way, the most difficult
part is the alignment to the pads.
This is not a fast way to solder, but it doesn't need any fancy
equipment.
To show how crude you can get, instead of using our hot air reflow
stations (several thousand $ each), I demonstrated soldering a QFP80
using an old crappy soldering GUN, along with the solderwick removal.
The final results were just as good, under close inspection with a
microscope, and they easily met the IPC/EIA J-STD-001C soldering
standards. (Don't do this with a good chip! The soldering guns can
damage chips because of electrostatic discharge (ESD) from the
capacitive coupling to the power line.)
-Paul
...............................................................
Paul
Somewhere in the Nova Scotia fog
ANTISPAM - Please remove the m's in my email address