Electronic repair often requires the removal and replacement of integrated circuits (ICs). Circuit boards can be divided into two broad categories: those with through-mounted ICs and those with surface mount ICs. The common removal techniques involve cutting the ICs out of the board, using thermal tweezers to remove them, or using hot air as a removal tool. While hot air soldering/desoldering stations can also be used to install ICs, technicians more commonly use soldering irons. Such stations are most likely to be used in commercial or industrial electronic repair rather than a home workshop.
- Skill level:
- Moderately Challenging
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Things you need
- Flush cutters
- Cotton swabs
- Solder wick
- Solder sucker tool
- Temperature controlled soldering iron
- Rosin core solder
- Rosin flux
- Thermal tweezers
- Hot air desoldering station
- 10X hand magnifier
Clip off the leads of a through hole IC near the body with a pair of flush cutters. Heat the solder joint with a soldering iron and pull each lead out of the board with tweezers. Remove the excess solder with a solder sucker tool. Clean the board with alcohol and cotton swabs.
Clip off the leads of a surface mounted IC using the same method as with through mounted ICs if the leads are large enough to clip safely. Finely spaced leads such as those on flash memory chips can be removed with thermal tweezers. Note the manufacturer's maximum safe temperature as exceeding it, or applying heat for too long can damage the circuit board by lifting its pads. Tin the tweezers with solder as the molten metal facilitates heat transfer.
Place the nozzle or hood of a hot air desoldering station over the IC if it has finely spaced leads. This method reduces the risk of damaging a circuit board and works well for removing multiple ICs quickly. It is strongly recommended to have some formal training in the use of these stations.
Remove the IC chip
Wipe the circuit board with alcohol and cotton swabs to clean it. Apply flux to the pads.
Align a surface mount IC and centre it over the pads. Clip the leads of through mount components to match the rest on the board. Touch the soldering iron tip on each joint and apply enough solder to wet the joint and form a concave fillet. This is an indication of sufficient solder. If the fillet doesn't form, there's not enough solder. A convex joint indicates too much solder. Limit the application of heat to no more than five seconds.
Wipe the circuit board with more alcohol and cotton swabs to remove excess flux. Inspect the repair under magnification. Look for solder bridges, solder balls, debris and cold solder joints. Solder bridges join two adjacent leads with a single solder blob. Solder balls appear to be tiny round balls that can short adjacent leads just as a solder bridge. Cold solder joints look dull and lumpy. They indicate that the solder moved as it was cooling, causing crystallisation. Cold solder joints will fail prematurely. Rework as necessary by heating and reflowing the solder, but be careful about applying too much heat as it can damage the board or the ICs.
Install the Replacement IC
Tips and warnings
- Alcohol is flammable. Keep it away from the hot soldering iron.
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