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How to Replace an SMD

Integrated circuits provide complex manipulation of data and processing. The electronics industry has gone through many package designs but the surface mounted device (SMD) has become popular for large volume customers. Machines insert SMDs during the board manufacturing process. Like most electronic products, at some point they will fail. Repairing electronic products is expensive when considering technician time and parts. You can gain an appreciation for the difficulty of replacing a single SMD on one of the boards.

Things You'll Need

Solder flux
Low temperature alloy solder
Soldering iron
Pair of tweezers or small dental pick
Cotton swabs
Isopropyl alcohol
Component paste
Magnifier
Hot air gun or blow dryer
60/40 solder
Low wattage soldering iron (15W) with smallest chisel tip available
Solder brush

Instructions

Removing SMD
- 1
  Coat the leads on the SMD with flux. Flux helps solder to flow and not ball up when heated.
- 2
  Apply a special solder made of an alloy of tin, bismuth, lead and indium to the solder joints connecting the leads to the pads on the board using a small soldering iron. This type of solder has a lower melting point than traditional 60/40 solder. The alloy solder forms an amalgam with other types of solder and lowers the melting point to well below the boiling point of water. This reduction of the melting point significantly reduces the chances of damaging the pads on the board during the removal of the SMD.
- 3
  Heat the leads on the SMD until the new solder has melted and then lift the SMD off the board using a pair of tweezers or small dental pick.
- 4
  Dip a cotton swab in flux and clean the residue from the board. Perform a final wipe with a second swab dipped in alcohol.
Replacing SMD
- 5
  Place a small dab of paste on the board side of the SMD and using tweezers and a magnifier align the SMD in place. Position the leads over the pads.
- 6
  Allow the paste to harden for at least a few hours. This will hold the SMD in position while you solder the leads in place.
- 7
  Heat the underside of the board using a hot air gun or blow dryer. The goal is to heat the SMD and pads to approximately 150 degrees Fahrenheit. Once you have done this, the solder will melt quicker when you begin to attach the leads to the pads.
- 8
  Form a small ball of solder at the corner of the SMD using a low wattage soldering iron equipped with the smallest chisel tip you can find. Drag the ball of solder along the edge of the SMD without making contact with the pads or the leads with the tip.
- 9
  Move slow enough that the solder just melts as the tip arrives at the lead. This may take a bit of practice but once you have the technique down, it virtually eliminates the formation of solder bridges.
- 10
  Clean up the board in the area in which you replaced the SMD. Use a solder brush and an alcohol swab.
- 11
  Examine each lead and pad of the SMD to ensure the solder links the two and that there are no solder bridges between adjacent leads or pads.

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