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
- 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:
- Clean the PCB pads if it has been sitting around for a while. A Plastic Eraser is good for this.
- Place the board on an ESD work matt.
- 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.
- Dab the tinned pads with your flux pen
- 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.
- 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.
- 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.
- 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.
- Starting with the pin next to the tinned pad, gentle place the soldering iron tip against the pad and solder
- When the solder melts, count “1 and 2” and remove the tip and move to the next pin
- DO NOT Push any solder into the joint, ever. You end up with too much solder
- 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.