In this tutorial I will describe a technique for soldering to fine pitch SMD pads. Using this approach I was able to solder a wire to a 0.3mm (~ 12mil ) pad.
1) Start by tinning the pads:
- place liquid flux on the pads
- take a "ball" of solder on the soldering iron tip and gently touch the pads, if you get to much solder connecting the pads, just "wipe it off" with a clean soldering iron
- the pads that have fresh flux will attract the solder
- the tinned pads should have small "pillows" of solder on top of them.
2) The wire should be thinner than the pad. You can get a thin wire by separating a thicker stranded wire. Tin the wire the same way as you tinned the pads
- first place liquid flux on the wire
- next touch the wire with a soldering tip that has some solder on it
3) This is the main step, the main idea is to mask the pad being soldered with 3 pieces of temperature resistant tape (Kapton tape).
The setup looks "dirty" when magnified, because of the sticky flux, you clean it up usually at the end with alcohol.
