Soldering a SMD to a PC board is not as difficult as it might seem. Follow these steps, and you will have a neat, professional looking job when done.
First, you must identify pin 1. One or more of the following identifies pin 1:
♦ Dot lasered or stamped on the SMD in one corner
♦ Notch on the end
♦ Beveled edge or beveled edge with a groove at pin 1
Orient U3 on the board with pin 1 to the trace with the dot beside it. The tool of choice to
do this is a pair of tweezers. If your hands are not that steady (as mine are), try using a jeweler’s
screwdriver or toothpick. Fingers are too big, and the chip may have a tendency to stick to your
finger, making placement difficult. The chips are very light and can easily be moved or catapulted
off to who-knows-where. Take your time and be patient.
If you find it difficult to position the chip because it keeps "falling off", you may find it necessary to take some solder-wick and clean the traces on which the SMD sits. During the manufacturing phase that tins the board, the solder may be thick enough that round edges have formed on the edge of the pattern. This is normal. By cleaning the pad with solder wick, it will become flat once again and placement of the part will be much easier.
Warning! - Do NOT use tape (cellophane or otherwise) to help secure the chip to the board during soldering. Many people are not aware of this, but the act of pulling a small piece of tape out of the dispenser generates around 400 to 500 volts of static electricity. Cellophane tape can and will damage the IC. Even though the chip may work, it becomes what is known as the "walking dead". In a year or so, it will mysteriously stop working. Don't take the chance!
|Identify pin 1 and position on the PC board|
In the following, be careful NOT to touch the lead from the SMD with the tip of the iron.
With the tip of the iron, heat one of the corner traces where the SMD sits. Carefully feed a
small amount of 0.015 diameter solder to the tip of the iron. Capillary action should cause
the solder to flow along the trace and to the lead of the SMD. Use as little solder as possible.
Remove the iron and allow to cool.
|Solder one of the corner pins to the PC board|
If all goes well, the SMD should not have moved and one of the corner leads should now be securely soldered to the board. Using a magnifier, carefully inspect the SMD chip for alignment. This will be your last chance to fix anything easily. If the chip is misaligned or improperly oriented, re-heat the trace (again, NOT the lead) with the iron and slide the chip off the pad. Clean the pad with some solder wick, and begin again.
|Alignment of chip looks good.|
Assuming alignment and orientation is good, in like manner, solder the remaining leads of the SMD.
|Solder remaining pins using same capillary action as before.|
Check the soldering with a magnifier for solder-bridges, cold solder joints, and too much solder. If anything looks suspicious, use solder wick to clean the connection, and then re-solder.
When everything looks good, you're done. Congratulations!Next Step
If a chip ever fails and has to be replaced, the following procedure works well and does not stress the PC board.
|Using a sharp pair of small cutters or something similar, clip the SMD leads as close to the body of the chip as possible. The body of the chip can now be removed easily.|
|Use solder-wick to remove the pins and solder from the PC board.|