Surface Mount parts have been around for a long time, but are just now becoming popular among hobbyists and students. With a little practice, you will find that using surface mount parts is easy and something that is well within your abilities.

The reason we are moving to surface mount parts is that most of the new devices, especially microcontrollers, are based on SMT (Surface Mount Technology). For example, the part shown in the picture above has 112 pins on it. To do this as a standard DIP, the part would be nearly 7 inches in length! That is just too big. With SMT, this part is a little under 1 square inch.

This section will describe the basics for soldering surface mount parts onto my kits.

There is a video available that shows you this processes. The video is approximately 4mb in length, and runs for about 2 minutes. You will need RealPlayer or other software capable of showing a movie in the RealPlayer format. To view the video

It doesn't view very well streamed from my ISP's server.

Soldering SMT Parts

There are two basic techniques for soldering surface mount parts. One uses a soldering iron, the other uses an oven. The oven or baking method requires a bit of practice. I prefer to use a soldering iron, and that is what I am going to describe here.

The boards that I sell have a solder reflow finish. This means that the boards have a thin layer of solder plating across all of the pads. This makes the solder techinque work out quite well. The basic idea is that you will place parts onto the board, then heat the pins of the part so the solder reflow sticks to the part. In most cases, you shouldn't add solder to the joint.

To do this solder technique, you will need

You also might want to consider a magnifier of some sort as the pins on these parts are pretty small. I use a swing arm lamp that has a magnification lens on it.

Soldering the surface mount part is fairly easy, but does require care. The key is to use a 'dry' soldering iron. Clean the tip with a wet sponge to remove any residue and solder from the iron.

The board you are soldering to should have a thin layer of reflowed solder on all of the traces and pads. The reflowed solder is what will hold the chip in place. Avoid adding any additional solder, especially on parts with close pin spacing.

The order of operations is:

1. Apply a thin coat of paste flux to the SMT pads on the board. The flux will help your parts
2. Place your part on the SMT pads. Carefully align the pins so they appear to be centered in the pads. Take special care that you have located pin 1 on your part, and you have aligned it with pin 1 of your PCB. Aligning the part requires a little patience, but it shouldn't be too difficult.
3. Clean the tip of your solder iron with a wet sponge. There should be a nice clean tip without 'extra' solder on it.
4. You should now tack your part in place. Only do 1 pin here as you will be checking the alignment in a seperate step. Touch your solder iron to a corner pin of your SMT part and let it heat for a couple of seconds.
5. Repeat for an opposing corner pin.
6. Recheck your alignment of all the pins. They should all line up as close to centered on their pads as possible.A trick that I like to use is to hold the board up to a light source to backlight it. This allows you to see how the pins align to the pads. It is also a great way to check for short circuits and solder bridges.
   
   
   
   
7. Now that all of the pads are aligned, you can heat each pin on the part. Remember, you are using the solder reflowed on the board to mount the part. Adding additional solder is a tricky propostion that usually results in a messy solder bridge!
8. Each pin gets a second or two of heat. I usually drag my solder iron across the pins slowly which heats each pin in turn. 
9. I will often go back and reheat the part one additional time, just to be sure I did heat everything. This shouldn't take you very long.
10. Check to see if you created a solder bridge anywhere by closely inspecting your work. I often hold the board up to a lamp so the light shines through the board (backlighting it). It helps you to see solder bridges and that everything is aligned.

Thats all there is to it. If you do make a mess by having too much solder, I have had the best luck removing the extra solder by using solder wick.

Soldering Surface Mount Capacitors

Most of my kits use surface mount capacitors. Surface mount caps are available in a wide range of sizes, some of them barely visible to the unassisted eye. My kits typically use capacitors in the 1206 case, which is one of the larger sizes. These can be mounted just like the SMT instructions above.

As an additional step, I usually add a touch of solder to each capacitor. This just helps hold them down a little better. It probably isn't required, but if you would like, you can do the same. Adding a touch of solder is fairly easy. Just reheat one side at a time, and touch a little bit of rosin core solder. You only need to add a small amount to get the result in the drawing below.

I must admit, most of my attempts at doing this result in much more solder than shown, but that is OK. As long as you don't overheat the cap or create a short, you should be fine.