Quad Flat Pack Surface Mount Chip: Removal, Repair and Replacement
This Instructable will guide those unfamiliar with QFP (Quad Flat Pack) chips and their design, summarizing the removal process from start to finish.
QFP chips have existed for some time now, but due to the complexity of the chip, its high pin count, and the easily warped materials it is made of, removal tends to do more damage, than good. The repair aspect of this guide will cover some of the simple techniques to force chip functionality once again, even if it is for a few moments to determine point of failure in a system.
When it comes to removal, you must be mindful of all nearby components, as many that lead to these type of chips are extremely small, with a low heat tolerance (I learned this the hard way). Also recall that not all PCB's that mount these chips are single layered, the reverse side may also have an array of chips that my literally fall off while heating components for removal.
Step 1: Assemble Your Tools
Depending on the tools you have available, you will have to use varying methods for removal.
If you have a heat gun, proceed to step #5
If you only have a soldering iron, continue to step #2
These tools will be needed regardless of the methods used.
- Solder Wick
- Solder (Lead free, unless your soldering iron is low power)
- Soldering iron fine tip head (or QFP shaped tip)
- Flux pen
- Magnifying glass
- Miniature suction cup
- Small stand clamp
Step 2: Soldering Method: Fine Tip
If you have a tip that fits over your soldering iron for the particular chip, then you may attach that, and proceed to step #3.
If you have the fine tip, then prepare by adding flux to the chips pins, the more liberal the better. Follow up by placing your suction tool in place, attaching it to the clamp as to not accidentally move the chip.
Allow the soldering iron to heat up, placing upright if corded, or in the coil, to prevent damaging any nearby items. Position your magnifying glass as to see the pins and the gap between them. Continue by individually applying the iron lightly to the pins one at a time, while simultaneously feeding solder onto the tip. Make sure to control the amount of solder you place on the tip as to not "gunk" up the pins with too much solder even for the wick. This will be tedious, and will need to be taken slowly in order to be accurate and not overheat or damage pins. Since the tip will likely be shaky try to avoid placing the tip incorrectly and connect two pins. If you do connect them, it is usually not noticeable and may result in a short when powering on the board. Once complete, layer the pins with copper wick and apply light pressure with your soldering iron. It will absorb any additional solder from the pins and only allow the solder under the foot of the pin, to remain allowing for a secure bond that is unlikely to short.
Step 3: Solder Method Prep: Shaped Tip
As this is the most complex of the methods, an additional prep step is required.
Prepare strips of wick to absorb the solder that will melt. In the case of the QFP shaped tip, layer the edges and cover each row of pins. Ensure that your wick does not contact other components or this may cause destruction of said components.
Check the tip temperature by placing a very small piece of solder on it, it should melt instantly and emit a light colored fume, be sure to avoid this.
Step 4: Solder Method: Shaped Tip
Since we have now prepared the tip, apply light pressure to the surrounding of the chip, being sure to limit your movements as the tip is shaped to the size of chip and wont need much adjustment. Since the tip is already heated, the pins should instantly melt and then be easily removable. Since the tip we have prevents us from using the normal suction cup, we will have to remove it immediately after lifting the tip off of the chip. This can be done with a pair of tweezers on the edge, with a majority of the solder that has melted sticking to the old chip. Alternatively, placing a bent pair of paper clips under the chips edges to lift it on off uniformly.
Step 5: Heat Gun Method
IT IS NOT ADVISED TO USE THIS METHOD IF YOU HAVE MULTIPLE (SMALL) COMPONENTS NEARBY
Depending on the PCB layout, using the heat gun method will result in multiple components melting and thus shifting off their slot. This can be difficult to repair so it is advised not to use this unless all the components nearby are heat resistant or if you have a cup that will capture all the excess heat and focus it on the chip in question.
First off, begin by placing the cup you have or some aluminium foil on the PCB, surrounding the chip. Once the chip is cupped or isolated, you can turn on your heat gun, and set the heat to 750 degrees. This may seem overkill but will allow you to heat the chip up in a matter of seconds. The heat gun will use a large amount of power, so if you have typical incandescent bulbs it will likely flicker, this is fine, but do not put any further load on your circuit. Let the gun heat up, you can check this, if it does not have an indicator, by using a thermometer and placing it on the metal tip of the gun. Once heated, place your suction cup attached to your tweezers and place it on the chip. Aim your heat gun down, place the heat gun as show in the image, going around the cup until you can feel some slack in the chip. Make sure not to move the chip while it is only slack, in this case you may end up pulling pins off, or removing lines inside the PCB. Lightly pull directly upward and allow the chip separate from the board. You have successfully removed the chip!