HOW-TO: Soldering SOIC devices by hand

The secret to good SMT soldering is not to heat the IC too much and not to use too much solder.

The following is the method I use to solder SOIC IC. Some of the steps and techniques will be applicable to other Surface mount Devices, but hopefully these will be covered off in other How-Tos
Tools required:

  • ESD work environment
  • ESD Tweezers
  • Soldering Iron with a chisel tip (I use 2-2.4mm tip)
  • Fine Solder 0.5mm diam is really good, 0.7mm diam will do
  • Liquid Flux Pen
  • Plastic Eraser

Now for the good stuff:

  1. Clean the PCB pads if it has been sitting around for a while. A Plastic Eraser is good for this.
  2. Place the board on an ESD work matt.
  3. Tin 2 diagonally opposite pads, for example 16 and 8 or 20 and 10.
    • You just want a small amount of solder in the pads and I try and make one of them a ground pin.
  4. Dab the tinned pads with your flux pen
  5. Place the IC on the pads, paying particular attention to the pin alignment to the pads.
    • Don’t forget to check Pin1 is on the right pad.
  6. Holding the IC in place by gently pushing downward on the IC body with a pair 0f tweezers, solder the pins on the tinned pads. Do not add additional solder.
  7. Now check the IC for alignment again, cause now is the time to make corrections.
    • To realign, gently apply the soldering iron to a pad and when the solder if molten, move the IC a small amount. Reapply heat to the other pad to release any stress in the IC leg.
  8. Place a straight section of solder against the un-soldered pins of the IC. I actually place it so that the Solder doesn’t touch the pad, but sits on the lowers section of the IC leg.
  9. Starting with the pin next to the tinned pad, gentle place the soldering iron tip against the pad and solder
  10. When the solder melts, count “1 and 2” and remove the tip and move to the next pin
  11. DO NOT Push any solder into the joint, ever. You end up with too much solder
  12. Repeat for the other side of the IC.

If this sounds complicated, then believe me it is not.  Have a go.  you will find you get in the swing of this real quickly.  As I stated in the beginning, the secret to good SMD soldering is not to heat the IC too much and not to use too much solder.  Good luck.

This entry was posted in TOT - tools of the trade and tagged , , . Bookmark the permalink.