fast way to unsolder mosfets?

[SpeedEBikes]

I was wondering if anybody could offer tips for unsoldering potentially good TO-220 mosfets. I've managed to desolder them using a solder sucker and copper braid to get most of the solder out followed by slowly teasing them out going round and round on the legs with a soldering iron. But it is slow and tedious.

Is there a tool or a technique to pop them out quick and easy?

 

[steveo]

Hey

first make sure the controller your taking apart is completly of of power, I solder all 3 legs of the fet together, then heat it and pull the fet quickly while its hot.


-steveo

 

[amberwolf]

If you don't care about the PCB they're mounted in, they can be very quickly removed without damage to the MOSFETs by leaving them bolted to their heatsink, ensuring the heatsink is not fastened to the PCB, then heating the PCB with a palm-sized butane torch in a single pass fast enough to not set it on fire but to melt the solder on the leads, while pulling the heatsink directly vertically away from the PCB. This usually requires mounting the PCB itself in a vise, so you don't burn your hand trying to hold it.

If the heatsink gets hot before you've removed them from the boards, you're probably going too slowly at heating the PCB, or the PCB is a multilayer with thermal, ground, and power planes all carrying the heat away too fast (in which case you will need to solder-suck as much solder as you can away from each pin first, using one of the vacuum-type suckers rather than braid, if possible).

 

[liveforphysics]

I mask off the board, put the "chisel" tip on my heatgun, hold the board upside down, and take a pass over the back side. The FETs drop out effortlessly.

I removed the crap FETs from a 12fet infinion controller with about 5 minutes of masking the board, and 1 minute of actually running the heat gun.

 

[SpeedEBikes]

lfp, I take it by heat gun you mean a typical sold at Home Depot paint stripping gun. I've got one that I use for shrink wrap but was afraid to try it for desoldering. I was considering buying a "hot air rework station" but I've never used one and I thought they were primarily for taking off smd chips and didn't know if I'd find it useful or not.

What do you mask with? Aluminum foil? Or the somewhat expensive kapton tape? Does it matter how thick it is? I've seen 1 mil, 2 mil, etc.

 

[rkosiorek]

i use an old Hakko 707 desoldering station. if it ever dies i'll have to buy something new as it has been discontinued. they recommend this as a replacement.


it has a built in vacuum pump. the heated tip is hollow and when you squeeze the trigger it sucks the solder up into that glass tube.

i also have a hot air re-work gun. it works well for surface mount but it just doesn't have the power to melt the quantity of solder on both sides of the board for large leads like FETs.

i may have to try the heat gun idea though. i think i'd try to mask using fairly thick foil though.

rick

 

[wrobinson0413]

.

 

[dontsendbubbamail]

I mask off the board, put the "chisel" tip on my heatgun, hold the board upside down, and take a pass over the back side. The FETs drop out effortlessly.

I removed the crap FETs from a 12fet infinion controller with about 5 minutes of masking the board, and 1 minute of actually running the heat gun.

How about a picture of that heat gun? Personally I lifted a trace and a few pads while trying to unsolder fets. This was using one of those spring loaded solder suckers and a Radio Shack desoldering irons.

Bubba.

 

[SpeedEBikes]

Rick, thanks for the suggestion of the Hakko 808. A quick googling finds lots of positive reviews of it. I've been using an adjustable temp Hakko soldering iron for many years and I've been very happy with it. I'll probably give the heat gun a try first, but I think I'll be ordering an 808 fairly soon.

 

[rkosiorek]

it is also not a perfect solution. i have still managed to lift a few pads using a desoldering station. but i have to admit it does require more effort.

another thing i suggest you buy at the same time is a "PIN VISE" and a few really small drill bits.

View attachment 1

it is like a really tiny drill chuck to hold really tiny drill bits. just perfect to hold the tiny drills you may need to really clean out the through holes on a circuit board. like #60 (1.02mm dia.). big hobby stores have them. but machinists supply places have them for cheap.

and don't overlook some of the essential "accessories" like the long thin file thingie you'll need to keep the hole clear in the heating element.



it's about $5.00 direct from Hakko. they also have fancy cleaners for the nozzles but i just use one of the ones you get for oxy-acetelyne torches. or i use the previously mentioned pin vise with an appropriatetly sized drill.

rick