Even if you never upgrade to a modified FET, you might want to replace the FETs in the car before a big race. FETs like any other components wear over time. I have found that the car goes slightly faster after a FET change. Not by much, but can be felt, or so I feel. Sometimes a car goes slower just before a FET goes out too.
Here is a good article by Atomic Mods on how to install FETs. http://web.archive.org/web/20080123122226/http://www.atomicmods.com/custom.aspx?id=18
They make it sound so easy. In actually doing an install, there were some trials and errors. Here is what I found.
Absolute minimal equipment:
Solder - .032" or thinner solder - 62/36/2 with 2% silver bearing kind is prefered. 63/37 is next for low melting temperature. 60/40 rosin solder core may be used if nothing else is found. SMT boards are coated from the factory. Silver bearing solder will replenish that coating during removal and install. For repeated install and removal, silver bearing solder should be used. Look for the solder that advertise as no clean.
Solder wick - The smallest you can find. Around .030" wide. Chemtronic is suppose to be the best.
Flux - Do not use acid flux. For electronic use, almost all are Rosin flux. Use flux that are advertised as no cleaning or no harmful residue since is almost impossible to clean under the FET after soldering. Get both paste and liquid, but liquid if you only have one. McMaster sells a liquid flux already in a needle applicator. For paste, Kestler SP44 paste is a good choice since it leaves no corrosive residue.
Soldering Iron - Small under 20 watt soldering iron is the common choice. However, as long as you can reach the contacts, even a 40 watt iron will work fine. Some will argue that it even works better than those tiny bitsy solder because you get the job done faster and hence less heat damage.
Almost required equipment:
Circuit board holder / magnifying glass - Is a pain to balance the board on books etc.
Magnifying headband - Harbor Freight sells a Magnifier Headstrap with Lights for only $5.99 pretty nice quality works good. No excuse not to get one.
Small desk lamp for plenty of light
Nice to have equipment:
Butane soldering iron with hot air attachment - A Weller P2KC portasol can make a poor man's hot air desoldering tool. Works way better than desoldering wick.
Bausch & Lomb Hastings Triplet 10X Lope - Nice for inspecting the work. Cost around $35 on ebay.
Anti-static work pad - You are suppose to have anti static work surface, but many people have done it without.
Dream equipment:
Hotair Station $80 - $1K
Rework Station with hotair and de-solder vaccum $$
Flow bench / Fume Extractor - Keep soldering fumes from destroying your brains.
Step by Step:
Remove the top cover and switch holder. Flip the circuit board over and hold it in the circuit board holder.
First order of business which is also the most difficult and potentially damaging is removing the old FETs. Remember, once the solder is hot, the glue that glue the electronic trace to the board is already melted and has only about 20% of its original strength. Strong arm removal tactics can cause the circuits to lift off the circuit board. Even if replacement of FETs tracing may break next time you remove the FETs.
FET Removal Options:
Soldering the FET on is actually the easy part. Removal of the FET is where the most damage can occure. There are many methods to remove an IC. Here is a count down of the methods:.
Method #4: Use X-Acto knife to cut the legs off of the FET using many pass. This is time consuming and do cause stress to the circuit board tracings. Least prefered.
Method #3: Solder wick to remove most of the solder then pop the component off. This is the most common technique. Remember to place some liquid flux on the solder wick. Flux works as a wetting agent and works wonders in pulling the solder into the wick. I usually use a high power solder to desolder. Small solder just don't have the heat to heat up the wick and solder on the joint. Use very gentle pressure on the solder iron, otherwise the circuit board glue also gets squeezed out. Is impossible to get rid of the solder under the legs of the FET. Use a pick or small screw driver to pry up one leg at a time.Usually, the chip will pop off hold your breath that the trace does not come with it.
Method #2: Hot air removal. Most people don't care to spend money on a hot air station, but using a propane solder iron with hot air tip does the job quite well. Practice on some junk circuit boards. Heat until the solder is melted, then just remove the chip. Works like magic. Leaves the circuit looking like new. Might want to have a heat shield to protect that plastic looking box next to the FET. I used some aluminum foil wraped over a business card as a heat shield. The down side to using hot air with the propane solder gun is it takes maybe 20 seconds to heat up the solder to remove it. I would like to apply heat as quick as possible to prevent possible damage to surrounding electronics. On the plus side, hot air makes a very clean removal with minimal stress to the electronic trace.
Board looks new after fets are removed. No left over flux from the solder wick to deal with.
And the best Method #1:This is what I call the chops sticks technique. I think this is the latest best method to remove FETs. Use two soldering iron like a pair of chopsticks. (Now, if money is no object, you can buy a hot tweezer that does the same thing, but looks like it will cost several hundreds of dollars. See link on the bottom.) Use them one on each side to heat all the legs of the chip at the same time, then just pick the chip up using the soldering irons. Clean, fast and simple. Hint: Put a drop of solder on each iron before using it. It will heat the solder joint up almost instantly, and allow you to remove the FET in the minimal amount of time for least impact to the chip and circuit board.
Best Method FET removal video:
Board Preparation:
After desoldering the old FET, the remaining solder will be in various shaps and forms. Don't resolder another FET there on uneven surface. Flaten the solder on the circuit board by dragging a solder wick across the pads. Work from the outside to inside so you don't damage the trace. The pads on the circuit board should be nice and flat with minimum solder on it. When you solder the FET on, it will sit close to the circuit board with minimum solder between it and the circuit board trace for minimal resistance and maximum heat conduction and strength.
After flatening out the solder pads, they are nice and clean ready for new FETs that stay close to the circuit board with minmal solder on the joint.
Install New FETs:
Before soldering new FETs on, you need flux. It will help solder wick underneath the feet on the FETs. Soldering paste works great here. The paste is sticky, and helps in positioning of the FETs also. Liquid flux can be used, but it tend to go away quickly once you start to solder.
Remember, the dot on the FET goes on the right side in the picture below for both chips. See also the picture on the FETs page. After carefully positioning the fet, put a glob of solder on the iron, and contact the glob of solder onto one leg of the FET. That will melt the solder under the leg to fasten the FET as well as add some more solder to the joint. Do the opposite corner next. Solder another leg or two, then wait for the FET to cool before going on. After all the legs are soldered, re-melt all the solder to get a good joint. Use some liquid flux if some solder are not getting under the feet of the FET. Let the board cool, do the second FET, and you are done.
First drop of solder.
Install
complete
Compare with the factory wave solder job. FET job is definitely not as perfect, but not too bad either. BTW, the solder job on the mini-z is much better than one on the Radio Shack X-Mods.
Factory FET solder.
Tips:
When applying heat to electronic components, use soldering iron with high enough heat so solder melts immediately, and the joint is made in minimal amount of time. Using an soldering iron with too low a temperature will require application of heat to the component for a long time that can leads to damage. To speed up heating up of the joint, place a blob of solder on the tip before touching it to the joint. The blob of solder will allow solder iron to transfer heat faster to the joint so you don't have to hold the iron to the FET for a long time.
Before powering on for the first time, make sure you verify that all connections are solid. You can blow the FET if the gate connection to the P-Channel is not made when you turn on the power. You will create an instant short in that FET. P-channel depends on voltage to turn off, so if there is no connection, it is always turned on, and when the N-channel is turned on by the controller, then there would be a short. A quick way to check connection is to use an ohm meter. Place one probe on the leg of the FET, and another on the point shown in the circuit board below. Make sure there is continuity.
Useful Links:
Excellent source for difficult to find solder supplies: http://web.archive.org/web/20080123122226/http://www.wassco.com/
Source for soldering equipments: http://web.archive.org/web/20080123122226/http://www.action-electronics.com/index.htm
Hints on working on SMT components: http://web.archive.org/web/20080123122226/http://www.piclist.com/techref/smds.htm
Chip Quick - Alternate way of FET removal: http://web.archive.org/web/20080123122226/http://www.howardelectronics.com/chipquik/products.html
Heated Tweezers - Another way to remove FET: http://web.archive.org/web/20080123122226/http://www.howardelectronics.com/jbc/microtweezers.html