Using a Hot Air Rework Station for PCB Repair

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Rarely will a printed circuit board design be perfect—often, chips and components must be removed and replaced during the troubleshooting process. Removing an integrated circuit without damage is nearly impossible without a hot air station.

The Right Tools

Solder rework requires a few tools above and beyond a basic soldering setup. For larger chips and a higher probability of success, start with a basic toolkit and add a few additional tools. The basic tools include:

  1. Hot air solder rework station (adjustable temperature and airflow controls are essential)
  2. Solder wick
  3. Solder paste (for resoldering)
  4. Solder flux
  5. Soldering iron (with adjustable temperature control)
  6. Tweezers

To make solder rework easier, add:

  1. Hot air rework nozzle attachments (specific to the chips that will be removed)
  2. Chip-Quik
  3. Hot Plate
  4. Stereomicroscope

Prepping for Resoldering

For a component to be soldered on to the same pads as a previous component, prepare the site carefully for the soldering. Often a sizable amount of solder remains on the PCB pads, which keeps the IC raised and prevents all of the pins from being correctly soldered. If the IC has a bottom pad in the center then the solder there can also raise the IC or even create hard-to-fix solder bridges if it gets pushed out when the IC is pressed to the surface. The pads can be cleaned up and leveled quickly by passing a solder-free soldering iron over them and removing the excess solder.

Rework

There are a couple of ways to quickly remove an IC using a hot air rework station. The most basic, and one of the easiest to use, techniques is to apply hot air to the component using a circular motion so that the solder on all of the components melts at about the same time. Once the solder is melted, remove the component with a pair of tweezers.

Another technique, which is especially useful for larger ICs, is to use Chip-Quik, a very-low-temperature solder that melts at a much lower temperature than standard solder. When melted with standard solder they mix and the solder stays liquid for several seconds which provides plenty of time to remove the IC.

Another technique to remove an IC begins with physically clipping any pins the component has that are sticking out of it. Clipping all of the pins allows the IC to be removed and either hot air or a soldering iron is able to remove the remains of the pins.

Dangers of Solder Rework

Using a hot air solder rework station to remove components is not entirely without risk. The most common things that go wrong are:

  1. Damaging nearby components: No all components can withstand the heat required for removing an IC over the time period that it can take to melt the solder on the IC. Using heat shields like aluminum foil can help to prevent damage to nearby parts.
  2. Damaging the PCB board: When the hot air nozzle is held stationary for a long time to heat up a larger pin or pad the PCB may heat up too much and start to delaminate. The best way to avoid this is to heat up components a little slower so that the board around it has more time to adjust to the temperature change (or heat up a larger area of the board with a circular motion). Heating a PCB very rapidly is just like dropping an ice cube into a warm glass of water—avoid rapid thermal stresses whenever possible.