Nuts and Volts - January 2009

■ Installation of surface mount chip.

■ Application of solder to one pad.

I usually go back and re-solder the first pin since it may be messed up from re-positioning the part.

NOTE: Some people prefer to use a small dot of glue to hold each component in place before soldering. If this works out well for you, use that method but keep in mind it adds another step and can make rework more troublesome down the road if you have to replace any parts.

Working with Fine Pitch Parts

Care needs to be taken to ensure that there are no solder bridges causing shorts. When dealing with fine pitch parts, do not be concerned about solder bridges at first. Since the pitch is so close on these pins, just solder each side without worrying about solder bridges and let it cool before going on to the next side. When done, let the whole component cool. Then, go back over each side with solder wick to remove the excess solder. This will remove most of the solder and leave just enough to make a proper connection. Repeat the process if solder bridges still exist.

Solder wick is your friend when working with surface mount parts. If you ever get a bridge or too much solder on a connection, just use the wick to remove the excess. In the event you remove too much, you can always add more solder and repeat the process. Be sure to let the component cool between each side so the part will not be damaged by excessive heat. The results can be fantastic if you take your time.

■ Removal of excess solder.

you only want to sever the lead without nicking the PCB. That may not be a problem if there are no traces underneath the chip but it is always best to assume there are and be very careful during the process. When I was removing an SX28 processor, the leads were thin so I only needed to cut one side and then bend the chip up and down to break off the other side. With the chip out of the way, the rest of the preparation was easy.

Just put a fresh bead of solder down with the iron and all the leads end up sticking to the soldering iron. Just wipe them off on your sponge. The last step is to go over the pads with solder wick so they are all flat again, ready

Replacing Surface Mount Parts

Sometimes you may need to replace a surface mount component. There is one method I have found works very well for fine pitch parts. I use a sharp utility knife to cut the leads right at the body of the part. It requires a steady hand since