Hot air gun tools

Den fredag den 18. marts 2016 kl. 02.10.18 UTC+1 skrev George Herold:

at one put we had to pull a lot of transistors off pcbs, I took some ~2mm copper sheet and made a tip for a soldering iron that could melt all the joint at the same time, with that it was a few seconds to per part

-Lasse

A classic surface mount hot air rework station would do the job.

In 1988 I got Cambridge Instruments to buy a Groatmore hot-air rework tool, but Google doesn't know about it.

looks similar.

There are 11 pins... getting them all tinned and heat conducting.. besides complicated.

George H.

Yeah sorry for the bad title, I've got a hot air rework station. Just a blower tool spreads the heat out too much and everything near the switch unsolders too. (the switch is rather massive compared to the bits around it.) George H.

Do you have a vacuum desoldering station?

A couple of out of the box thoughts. Probably worthless , but might trigge r you to think of something better.

1. how about trying to shield the rest of the PCB. Maybe some 1/16 or 1/8 aluminum with a hole big enough for the switch that will shield the rest of the components from the heat. Sheet Rock might be better ,but would not last very long. The aluminum could be dunked in water between uses to cool it.
2. You might also think about using a propane torch. I have used one to sal vage parts off PCB's. It is pretty tricky to get enough heat and still not burn the board. So try using a propane torch on some totally scrap boards and see what you think.

Yes, that's the problem. If the part has a lot more thermal mass than the board, it is going to desolder stuff on the board first. Confining the hot air to the part's terminals will help up to a point. But, you may end up blistering the board before the switch comes off.

I have made some custom desoldering tools for such situations. (Having a CNC mill can be handy.) I have an ancient Ungar iron that has a 1/4-20 thread on the end of the heater. I take a block of copper bar and drill and tap a 1/4-20 hole in the back of the copper, and machine the front to fit around the part's through holes. In this case you'd want 11 holes in the right pattern, make them just a bit larger than the switch's pins. File the business end flat, and tin it as the iron heats up, then apply solder liberaly and place it over the switch's pins. The switch will generally unsolder and pull out in about 3 seconds. WAY faster than the air tool, once the iron is heated up. And, no risk of burning the board or making other parts fall off. But, I wouldn't do this for just a couple switches, but if you have more than a dozen, it would be well worth the time to make.

Jon

I do much the same using an aluminum foil heat shield. Just hide the leads that you don't want to get hot under the foil and they'll stay fairly cool.

Yep. That's what I usually do when I'm worried about melting nearby plastic parts. However, if you really need to reduce the heat affected zone, I suggest an infrared desoldering station: instead of a hot air desoldering station.

Load the connector pins up with a HEAP of solder, a great big blob. Use your iron(s) to melt the blob, pull the switch. Clean up the blob.

sheet rock lasts: 10mm has 20min fire rating.

yeah, when you hear the substrate popping it's done!. I've used propane succesfully to replace parts on single layer boards,

if you want to replace the switch cut the old one up and remove the pins one at a time.

Sounds like a PITA. If you don't need to keep the switches you might be able to snip off the pins then work on them individually.

I don't know if you will get enough heat transfer otherwise without direct contact to the pins. If you can make your brass tube do this it should work, maybe with a bit of extra solder/flux.

I have seen someone hold the circuit board over a solder wave to do this. Watch those fingers!....

Group reply,

Thanks all, We do have a vacuum soldering gun, but I've never used it.

The fixture on the end of a big iron.. maybe even my Weller heat gun could work.

Re: Destroy switch and remove pins one by one is my typical modus operandi, In this case I wanted to keep the switch in tact.

The hot air gun work fine. About ~1 minute of heat and I could wiggle the switch,

George H.

That's good. I was musing about making a dam around the switch pins - say using RTV silicone - then filling it with some high boiling point liquid - olive oil maybe at 300'C - which you could heat with an iron or your hot air. I wonder if that would have worked?

Cheers

Here's mine: You really should learn to use it. The problem is that you need to find a tip where the hole will fit around the rotary switch pin. The tip in the above photo will work nicely for component leads, but will not fit anything larger.

I can't be sure without a photo, but 1 minute seems much too long. I can usually remove SMT components after a few seconds of hot air. Larger components might take 20 seconds maximum. Are you sure you have it set to 440C and not 440F? If C, it's too hot. If F, it's to cold:

(a starting temperature recommended by Weller), the mass of solder and copper closest to the iron tip will heat quickly, but it will take some time for that heat to spread.

I'll post my settings when I get to the office.

Does the vacuum pump do any better than my big blue solder sucker? I use that a lot, but around pins like this it almost always leaves a little solder where the pin touches the plated hole.

he switch,

I did some later at 420 C, but it took longer. I had the air flow dialed d own to 3 (out of 10.. whatever that means... sparkfun hot air gun.) I didn't want a lot of hot air blowing back on my hand... (did you see my smoke stack arrangement?)

A minute seemed like a good time, it took me a lot longer than that with just blowing hot air. The one problem was that it would take a while for all the pins to come loose. There's always one that takes longer to come free. I'm thinking a more symmetric air path may help. (I've got the air input tacked to the side of the smoke stack.)

Turn's out I'm (or someone) is going to have to do ~200 of these. A few spacers and a longer 2-56 screw and I should be good to go. But that will wait for Monday, I'm going to watch some hockey and drink beer.

George H.

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Sorry for the delay. Things have been a bit hectic for me lately.

The vacuum pump has the advantage of maintaining the heat around the connection for much longer than the thermally insulated solder sucker. Both will tend to instantly turn the solder into dross, but the vacuum pump can suck it into the glass cylinder faster and longer. The mechanical piston solder sucker compensates by using more vacuum, which seems to lift pads more often. The metal tip of the vacuum pump type tends to last longer than the PTFE tip of the mechanical piston solder sucker. I would prefer to use the vacuum pump variety, except that it takes too long to heat up and I hate cleaning out the dross.

I never made it to my office to check on the hot air desoldering station temperatures. I have a pair of leather welders gloves next to my hot air desoldering station. They're needed for reflowing BGA chips, which tends to blow hot air back at my hands.

Yes and I didn't like it. If your switch pins are arranged in a circle, you want two concentric cylinders that straddle the pins. The only hot air that is delivered goes between the rings. No air in the middle and no air on the outside. It's much the same as the reflow nozzles for SMT desoldering. Something like these, except instead of square, they should be circular to match your switch footprint: If you're going to be doing a large number of switches, I would consider a custom or home made nozzle.

Do you have a cheap IR thermometer? You may want to check your temperature. As I vaguely recall, there was about a 50C drop between the nozzle temperature and the work temperature.

Wear gloves and forget the smoke stack. If you want all the pins to come out at once, use a custom nozzle with concentric cylinders.

Definitely build a custom nozzle. Instead of making it out of brass or steel, I suggest you just turn and drill an aluminum rod with air holes to match the switch pins. You don't need a nozzle that will work with every available switch, just one for the immediate problem switch. Also drill some small pin holes into the business end of the cylinder, into which you pound a few small pins. The pins will prevent the aluminum cylinder from hitting the PCB and scorching the board. It will also prevent the solder connection from creating back pressure that will blow solder up into the aluminum nozzle. Also, be sure to buy an oxy-acetylene torch tip cleaner to clean out the holes in the aluminum cylinder. If confused, I can scribble a drawing if you give me some clue as to the rotary switch footprint.

Oh, it's a weekend. I didn't notice.

I have a better and easier idea.

Start with a 1/4" or thicker slab of G10/FR4 material (width of a hose clamp). If you don't have any, build some up from old PCB boards. Drill to fit over the rotary switch pin pattern. Chamfer the holes to prevent any sharp edges that might burn off. Find some metal tubing (stainless, steel, brass, copper, aluminum in order of preference) and cut to fit into the holes. Use an automotive flaring tool to flare the tubing ends and flatten with hammer. These should also hold the sandwich together if you used old scrap PCB's. For cleaning, have a drill bit or acetylene torch tip cleaner handy that fits the tubing.

Mill a circular area around the drill holes to form a circular disk. The center of this disk will receive more hot air than the edge, so some kind of conical structure pointing into the air flow needs to be added in the middle (if there are no switch pins in the area) to deflect the hot air towards the edge of the disk.

Using whatever sheet metal you can find, make a funnel like affair to adapt the circular disk diameter to the air gun nozzle diameter. Use hose clamps on both ends to secure. It might be useful to add a strip of sheet metal around the circumference to act as an air dam.

The rest is playing with the temperature and air speed so that it works. My guess(tm) that the time to build this custom nozzle will be justified by quicker and cleaner desoldering times. I can do a scribbling if my description is incomprehensible.

On Sat, 19 Mar 2016 17:51:30 -0700, Jeff Liebermann Gave us:

If you are doing heat shrink, no problem. If you are reflowing solder and expecting to not have failed components, you will need a calibrated hot air 'gun'.

I always pre-heat the assembly as well to reduce the shock introduced by the gun at the time of use.

I heat up the ESD mat and table underneath it, and then the bottom side of the PCB, then the top side, THEN perform the chip attachment with the hot air 'pen'.

I use this

It comes with some of those tips you hunted up. $75 is cheap for a calibrated tool.

This one is better and cost less: