Soldering LPC2100 devices

Started by Leon Heller February 3, 2004
After a few messy attempts (they worked, though), I've just about got the
hang of soldering devices like the LPC2100, using a technique called 'drag
soldering'. Although I use an expensive Metcal soldering system and a stereo
microscope, you can manage with an ordinary temperature-controlled soldering
iron and a decent magnifier if you have good eyesight. You should have two
tips for the soldering iron, a very pointy one (I use a 0.4 mm tip) and a
wider one, say 1.5 mm. You also need some liquid flux (I use Electrolube
SMF12P - it comes in an applicator pen with a felt tip).

1. Apply liquid flux to the pads.
2. Position the chip correctly on the pads. The flux should help to hold it
in place.
3. Insert the pointy tip, heat up the soldering iron and make sure the tip
is clean and freshly tinned.
3. Solder one corner pin. There should be enough solder on the pad, you just
need to reflow it.
4. Check the lead alignment and adjust the chip position if necessary. There
should be enough 'give' in the lead you have soldered.
5. Solder a lead on the opposite corner.
6. Recheck the lead alignment, adjust the chip position if necessary.
7. Apply more flux to all the leads.
8. Insert the larger tip and heat up the iron. Make sure the tip is clean
and freshly tinned
9. Apply some solder to the tip and drag it slowly along one row of leads,
you need a very light touch and a reasonably constant speed. Repeat for the
other rows. Don't worry about solder bridges at this stage.
10. Remove any solder bridges with desolder braid.
11. Carefully inspect all the joints and redo any suspect ones with the
pointy tip and some fine solder, if necessary. I poke the leads with the tip
of a scalpel whilst observing them under the microscope.
12. Remove the flux with IPA and re-inspect.

The joints should be shiny with a nice fillet of solder.

I actually use a Metcal 'mini hoof' tip for drag-soldering. It's shaped like
a horse's hoof and can be fed with just the right amount of solder for a
complete row. Plenty of flux is the key to success with this technique.


Leon Heller, G1HSM
My low-cost Philips LPC210x ARM development system:

An Engineer's Guide to the LPC2100 Series