I received a hot air rework station as a birthday gift.
It's a Gordak 8586D- nothing super fancy, Cyclone FPV has them for about $40- but it's more than adequate for my needs.

I'm super excited to be able to learn a new skill. This will significantly up my repair abilities from what I could do with a fine tip soldering iron.

Please don't consider this thread to be a, "how to"- this is more of a record/journal of my journey and frustrations while learning this new skill. I've got just about enough experience with troubleshooting and repair to be dangerous. Those of you that have experience with hot air, I'd love hints, tips, and constructive criticism. I kinda feel like I'm learning how to solder all over again. It's fun.

Anyhow, these are what I think will be useful tools & supplies that I already own from doing non-super tiny repair work:

Headmount magnifying glasses (can't really hold a magnifying glass and solder at the same time.)
Solder wick (i hate this stuff. it works well with ton of flux, but I prefer my desoldering gun- but my desoldering gun is a bit too big for super tiny things)
A variety of flux- MG 836LFNC liquid flux, Kester 186-18 liquid flux, MG 8341 flux paste.
A bunch of fine point tweezers.
Suction pens for the grabbing of components.
A couple different types of solder paste.
A variety of fine point and grabber probes for my multimeter.
A cheap $10 ebay ultrasonic glasses/jewelry cleaner (I fill this with 99% Isopropyl Alcohol to clean boards)
99% Isopropyl Alcohol (see above )
13.8v DC power supply, and 5v/9v buck converters.
A cheap $10 diy LCR/ESR meter (I originally built this to match transistors for audio amplifiers, but it's also super handy for identifying unknown components, checking the value of capacitors in circuit, checking to make sure that antennas don't have any hidden internal damage, doing a quick test to make sure that motor windings all measure within an acceptable range and aren't burnt out, and a whole bunch of other things. next to my multimeter, it's one of my most used devices.)
Small and large PCB holders, bluetak, etc.
Copper foil (to repair/replace damaged pads and traces)
5 minute epoxy (to attach the foil above)
Solder mask (I'm pretty sure this is just glorified UV glue. I should do some tests to see if it is somehow less conductive, or if it is just a pretty green color)
Various small gauges of magnet wire (I have this for fixing speaker coils, but it also works great as jumper wires)

Alright, on to the new tool.
The manual is in Chinese. Cool, I mean, it's a soldering station. Can't be that hard to figure out, right?
We're not going to talk about how long it took me to realize that, "SLP" meant sleep, and the reason it wasn't responding to buttons was because I had to actually pick the thing up from the holder.

I put some solder paste on the first row of resistors on a practice smd board. Placed the resistors.

I honestly have *no* clue what to set my air temp and flow at. I know I can't just blast it like I do with a soldering iron, so I'm starting out with an air temp of 375, airflow at 30%.

Cool! First row of resistors soldered in place. Turns out that this is not as easy as it looks in all of those youtube videos. Looks like I used a bit too much solder paste- things are a bit blobby.

Okay, lets try an IC- dropped the airflow down to 25%. Instead of straight solder paste, I made a mix of about 50/50 solder paste and liquid flux.

Yes! looks good. Gotta watch my airflow though. I was either too close or I had it too high- I had to come at it from a couple angles to get it to work- but once I got the right angle, it just pulled right into place.

I need to do a lot more practicing with the initial hot air soldering, and then a whole bunch of practicing removing those bits and reinstalling them. 

I got a little cocky and decided to try repairing an old F3 FC that I had already written off as a parts board... We're not going to talk about that. Practice is important.

Quote:I got a little cocky and decided to try repairing an old F3 FC that I had already written off as a parts board... We're not going to talk about that.

Can I guess? Mosfet shorted so bad it cooked itself into the PCB?

Heat and blow on full and that sucker is just sitting there like NOPE.

(17-Jul-2022, 04:38 PM)sevro Wrote: Can I guess? Mosfet shorted so bad it cooked itself into the PCB?

Heat and blow on full and that sucker is just sitting there like NOPE.

Hah! No, some things that used to be on the board… aren’t anymore.

I’ll get some good practice putting them all back where they should be. Good thing I’m in the habit of taking detailed photos of boards before I start working on them.

Even the pros end up blowing components off the board when they didn't mean to. I've seen at least one by Louis Rossmann and another by Paul Daniels where that exact thing happened followed by a few choice words

It’s amazing how quickly things can go from, “Hey, this is cool, I totally got this!” to “@?&&?$!(!!!”. Good fun though.

There is a first time for everything.

My first was replacing a UFL on a Crossfire receiver.

Too much airflow, blew off a super tiny capacitor never to be found (as NorthbridgeFix says: "To the ninth dimension").

After I replaced the UFL connector I did not have a tactile button any more The tactile part of the button had melted away.

Good thing this house has brick walls else I was going to punch a hole through it

One thing we have to remember watching pcb repair videos online is that you have to focus on phone repairs videos as they are similar to pcbs we work on in terms of size and component density.

Do not watch videos of people working on old single sided pcbs that are the size of an A4 or A3 size sheet of paper with more than 10mm gaps between components.

Thanks, I’ll definitely focus on phone repair videos.

Who needs buttons anyway?

I’m gonna have one hell of a blister on my left hand tomorrow.

This is most definitely not the same as repairing pulled up traces/pads and whatnot. This takes a whole different skill set than hitting something with a fine tip soldering iron.

Some things seem to work great with straight solder paste, other things seem to work best with a mix of solder paste and flux- but it’s a real fine line between getting enough solder on pads and bridging pins below the visible outside bits.

Other things seem to work best by pre-tinning tiny pads and pins, and not using solder paste.

It takes significantly more time/heat to remove a component than it does to set one, and it takes no time at all to blow off a small capacitor or resistor.

Seriously, no time at all. Don’t look away or sneeze.

I was hoping that this would be a, “look, I fixed a flight controller!” response to this thread, but that was wishful thinking and I have a very long way to go to learn this skill. Good thing I have some practice boards and some random old computer bits that I don’t care about. I really need to use those bits to practice on and not be like, “Hold my beer!” and try to work on something that I actually care about.

The picture below is a tiny little bit of a wire or component lead that managed to somehow fly up and embed itself into the outer base of my thumb. It’s a good reminder that eye protection is important, because that would really suck if it embedded itself into one of my eyeballs.

I have only used solder paste 5 times probably for actually fixing stuff. And it does more harm than good at times.

Getting the quantity correct is a challenge and often you end up shorting the pads/legs of the component you are soldering or the components nearby.

The cleanup is more more painful than actually replacing the component with a soldering iron and solder wire.

It makes more sense to tin the pads with a soldering iron, place the component roughly in the correct position and then use hot air to melt the solder in place. Once you see the solder start to melt, let go of the component so it can get sucked into place by the solder on the pads.

The majority of people that actually use solder paste is on BGA chips and they use a stencil to apply the paste which only coats the pads on the chip and the stencil ensures you have the correct quantity required.

Add to that, another situation where we will use solder paste is on single sided boards where we pick and place components on a smd hot plate. Again this will only work for single sided pcbs.

For double sided boards we will need to use a reflow oven, and basically we will apply solder paste to the pads and place components on one side, place the board in the oven and once the programmed reflow process is complete (smd components soldered on one side) we will flip the pcb and repeat the process on the other side.

(19-Jul-2022, 09:12 AM)kafie1980 Wrote: It makes more sense to tin the pads with a soldering iron, place the component roughly in the correct position and then use hot air to melt the solder in place. Once you see the solder start to melt, let go of the component so it can get sucked into place by the solder on the pads.

Yes. This. Thank you.
I’ve been struggling with the solder paste and ratio of solder paste to flux- every other time I hit it with hot air it’s either perfect or awful- too much or too little solder.
I’m pretty damn good with a soldering iron though, and I’ve got no issues tinning tiny pads or pins. Ima stop over complicating things and combine my current skills with this new thing.

I've also never used solder paste for anything. If you watch a lot of the pros they just use the technique that kafie mentioned by tinning the pads on the board, adding flux, and then just letting the hot air melt the solder and pull the component into place.

Rather than potentially destroy a fixable FC, I decided to do some more work on a practice board tonight.

My goal was to solder in place two rows of tiny resistors.
Rather than using solder paste I used a bunch of flux and pre-tinned the pads.

I dropped my airflow down to 20% because I had a whole bunch of loose little smd resistors on the board.

Hit it with hot air- some worked great, other took a bit of nudging or removing and replacing with tweezers to get them in the right position to pull into place.

I’m thinking solder paste is actually useful with hot air on a fresh pad. I’ve been using solder paste for a few years to pre tin super tiny pads. It doesn’t seem to work so well for chips or anything with lots of fine small pins- but for placing tiny things it does have enough grip to hold it place.

For replacement of something that was already installed- yeah, a whole bunch of flux and making sure pads and pins are pre-tinned works much better than solder paste.

My main problem with solder paste is that I can’t be sure exactly how much solder is where I want it, and if there is slightly too much it can easy slip under something and bridge it where I can’t see/fix.

Those resistors in your example and even capacitors on most of the PCBs in our hobby can become a pain if you have to hot air or solder iron a whole bunch of them.

Is there a better tool for the job, yes there is. They are known as "hot tweezers". Google them, I am sure you will be surprised how easy it makes the job. The branded ones are pricey in the $200+ range. The cheaper ones are garbage to the point I have not seen many positive reviews on them.

For removing chips, there is another tool you can add to your arsenal that can help removing components from PCBs. Its called "low melt solder". Looks like regular solder but has a very very low melting point and some brands claim below 100 degress centigrade. Spread some of it on the pins or pads and it takes very little heat to separate the component. You do not even need hot air, solder a quick run of the iron across the pins/pads. The low melt solder remains in a melted state for more than 5 to 10 seconds depending on how much heat has been provided. Keep in mind this is only for component removal and do not use this to actually solder anything.

The hot tweezers are fancy, but they seem horribly overpriced for what they are.

Thanks for that low melt solder tip! I think that’s going to come in very handy.