The ChipQuik SMD Removal Kit (www.chipquik.com) allows you to quickly and easily remove surface mount components such as PLCC, SOIC,TSOP, QFP, and discrete packages.The primary component of the kit is a low-melting temperature solder (requiring less than 300 degrees F) that reduces the overall melting temperature of the solder on the SMD pads. Essentially, this enables you to just lift the part right off the PCB.
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ARNING: H
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ARMPlease read through this example completely before attempting SMD removal on an actual device. When removing the device, be careful to not scratch or damage any of the sur- rounding components or pull up any PCB traces. Using the ChipQuik SMD rework package makes it easy to remove the fine-pitch memory device. After following the instructions on the package (which consists of simply applying a standard no-clean flux to the SMD pins and then applying a low-melting-point solder), you can easily remove the surface mount part from the board. Use rubbing alcohol to remove any residual from the solder pads. Verify that the solder pads are clean and free from cuts or solder jumps before proceeding to the next step of the hack.
Figure 2.33 shows the contents of the basic ChipQuik SMD Removal Kit, from top to bottom: alcohol pads for cleaning the cir- cuit board after device removal, the special low-melting temperature alloy, standard no- clean flux, and application syringe.
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Electrical Engineering Basics • Chapter 2 37
Figure 2.33
ChipQuik SMD Removal Kit ContentsFigure 2.34 shows the circuit board before the SMD part removal. Our target device to remove is the largest device on the board, the Winbond WTS701EM/T 56-pin TSOP IC.
The first step is to assemble the syringe, which contains the no-clean flux. Simply insert the plunger into the syringe and push down to dispense the compound (see Figure 2.35).The flux should be applied evenly across all the pins on the package you will be removing (see Figure 2.36). Flux is a chemical compound used to assist in the soldering or removal of electronic components or other metals. It has three primary functions:
1. Cleans metals surfaces to assist the
flow of filler metals (solder) over base metals (device pins)
2. Assists with heat transfer from heat source (soldering iron) to metal sur- face (device pins)
3. Helps in the removal of surface metal oxides (created by oxygen in the air when the metal reaches high temperatures)
Once the flux is evenly spread over the pins of the target device, the next step is to apply the special ChipQuik alloy to the device (see Figure 2.37).This step is just like soldering: Apply heat to the pins of the device and the alloy at the same time.The alloy has a melting point of approximately 300 degrees F, which is quite low.You should not have to heat the alloy with the soldering iron for very long before it begins to melt. The molten alloy should flow around and under the device pins (see Figure 2.38).
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38 Chapter 2 • Electrical Engineering Basics
Figure 2.34
Circuit Board Before Part RemovalFigure 2.35
Applying Flux to the LeadsFigure 2.36
Chip with Flux AppliedStarting at one end of the device, simply heat and apply the alloy. Repeat for the other side(s) of the device.The flux will help with ensuring a nice flow of the alloy onto the device pins. Ensure that the alloy has come in contact with every single pin by gently moving the soldering iron around the edges of the device. Avoid touching nearby com- ponents on the PCB with the soldering iron.
Now that the alloy has been properly applied to all pins of the device, it is time to remove the device from the board. After making sure that the alloy is still molten by reheating all of it with the soldering iron, gently slide the component off the board (see Figure 2.39).You can use a small jew- eler’s flathead screwdriver to help with the task. If the device is stuck, reheat the alloy and wiggle the part back and forth to help the alloy flow under- neath the pads of the device and loosen the con- nections.
The final step in the desoldering process is to clean the circuit board.This step is important because it will remove any impurities left behind from the ChipQuik process and leave you ready for the next step in your hardware hack.
First, use the soldering iron to remove any stray alloy left on the device pads or anywhere else on the circuit board. Next, apply a thin, even layer of flux to all of the pads that the device was just soldered to. Use the included alcohol swab or a flux remover spray to remove the flux and clean the area (see Figure 2.40).
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Electrical Engineering Basics • Chapter 2 39
Figure 2.37
Applying Heat and Alloy to the LeadsFigure 2.38
Chip with Alloy AppliedFigure 2.39
Removing the Device from the BoardThe desoldering process is now complete.The surface mount device has been removed and the cir- cuit board cleaned (see Figure 2.41). If you intend to reuse the device you just removed, use the sol- dering iron to remove any stray alloy or solder left over on and in between the pins and ensure there are no solder bridges between pins. If you do not want to reuse the device, simply throw it away.