Article 4: “How to hand solder a SOIC” by Anthony Burch

This article describes how to solder a Small Outline IC, or SOIC.The details of the process are covered, including chip placement, tacking, soldering and solder bridge removal.

You can also use this technique for soldering any fine-pitch or closely spaced gull wing pins, like those on Quad Flat Packs, or J-Lead pins, like those found on some memory chips.

Pick up the chip using a vacuum pickup tool and place it on the board. It does not need to be too accurate at this stage.

Next, line the legs of the chip up with the pads on the board. Wear a head magnifier while you are doing this, so that you can see it better. Do the alignment by just putting a finger on each side of the chip and carefully move it until you can see that the legs are lined up with the pads. The next step is to tack the chip down to the board.

To tack the chip down onto the board, start by putting a little blob of solder onto the tip of your soldering iron. Use a small chisel tip on your soldering iron for this step.

Then carefully hold down the chip, for example using the edge of the vacuum pickup tool, and gently touch the solder blob onto one of the corner pads.

Don’t let the actual soldering iron tip touch the legs. You just want some contact of the solder to the leg and pad. The objective at this stage is not to make a good solder joint but simply to get some solder onto the leg and pad to hold the chip down to the board.

For the next step make sure that you are wearing some “powder free latex gloves” to avoid getting flux on your hands.

Take a gel flux syringe and apply flux to all the pads on both sides of the chip. Put on a reasonably good amount of flux. The chip is now ready for soldering.

There will be a lot of solder fumes during the soldering, so make sure that you are wearing a face respirator and have good ventilation in your work area.

Turn the board so that the non-solder blob side is facing you.

Put some solder into the reservoir tip of the iron. You don’t necessarily need to fill up the reservoir. As long as there is a small amount of solder there, the solder will flow out onto the pins and pads when the tip comes into contact with them.

Next, just run the iron slowly across the feet of the pins. Of course, don’t press down too hard – just guide the iron along. It is OK to run the iron back along some of the pins if you feel that there may not have been solder coverage of some of the pads.

Once that edge is soldered, wipe the tip of the iron on a damp sponge. This removes the dross or residue that builds up on the iron tip as you solder.

Turn the board around, load up the reservoir tip of the iron with solder again, and solder the other edge.

If you can see that you have created some solder bridges on some of the pins during soldering, wipe the iron tip again. Put a little more flux just on those pins and then bring down the tip of the iron to suck away the excess solder from the joints.

After cleaning the flux residue from the board it is important to check all the way around the chip again for solder bridges. If there are any bridges, apply flux gel just to those pins and use the reservoir tip to suck away the excess solder. Once done, clean and inspect the board again.

That completes the description of the SOIC soldering process, including chip placement, tacking, the soldering and solder bridge removal.


About the Author

There are many low cost tools and techniques for soldering small batches of printed circuit boards or one-off prototypes. Some of these techniques are well known while others have been invented and reinvented by small tech companies and advanced hobbyists. A few good tips can be worth their weight in gold (not just their weight in solder). Discover the tips that can save you days of soldering time or thousands of dollars in outsourcing costs. Anthony’s site has many videos that reveal exactly these kinds of valuable soldering tips. Go to http://SuperSolderingSecrets.com