bit of hot air soldering.

[graffian]

Last time I tried my honkkong phuey hot air gun was to remove an ic, I burnt the board and still couldn't get the little blighter to move.
I have some very old solder paste , it has the constancy of salami. I added flux to a bit of paste so it was about as smooth as non crunchy peanut butter[I am hungry].
Last time I tried the solder paste, I melted the goo holding it together, the little balls blew all over the place.
The new softer mix works.

 

[Red'n'Black]

Looks tidy. Is that an Arduino or similar?

I've never had much luck with hot air and paste for hand soldering, as you say it just balls up and blows everywhere. Usually use the smallest iron tip I can get, 0.2mm solder and a magnifier.

For removing ICs, as you say it's difficult to get enough heat into the board to melt the solder (especially unleaded) without charring it. Removing as much of the unleaded solder as possible with braid, then adding leaded, helps a lot. There is some stuff called ChipQuik with an even lower melting point, but I've never tried it.

We have the RS 250W hot air guns at work, those are about right. I tried one of the DIY paint stripper types once, brutal, it just incinerated everything

 

[ajlelectronics]

I have found that heating the back of the board helps with IC removal.

 

[Chris Snow]

Board pre heaters make things much easier. As does decent paste. If the solder balls are flying around you're paste is expired.

If you're damaging the substrate you must be way too hot.

The technique I use is to go around the outside of component in circles to get some heat into the board. Then hit the component briefly with heat and pick it up with tweezers.

 

[voipio]

There is definitely an art to reworking these types of component, and even more so with BGAs!! Heating the back of the board definitely helps, plus using hot air tips suited for the job.

This kind of thing:

https://cpc.farnell.com/duratool/d03329/station-hot-air-bs-plug/dp/SD01139?st=hot air rework

is not hugely expensive and comes with a couple of round nozzles, plus nozzles for 10x10mm and 15x15mm QFP devices.

 

[Screwdriver]

Board pre heaters make things much easier. As does decent paste. If the solder balls are flying around you're paste is expired.

If you're damaging the substrate you must be way too hot.

The technique I use is to go around the outside of component in circles to get some heat into the board. Then hit the component briefly with heat and pick it up with tweezers.

That's interesting so, just for future reference, are most of these components happy at a temperature that would melt solder?

 

[Red'n'Black]

That's interesting so, just for future reference, are most of these components happy at a temperature that would melt solder?

Yes, but not for very long. Most part data sheets have a 'reflow temperature profile' somewhere in the back, it peaks at 260C for maybe 10 seconds.

 

[Wightsparks]

There is definitely an art to reworking these types of component, and even more so with BGAs!! Heating the back of the board definitely helps, plus using hot air tips suited for the job.

This kind of thing:

https://cpc.farnell.com/duratool/d03329/station-hot-air-bs-plug/dp/SD01139?st=hot air rework

is not hugely expensive and comes with a couple of round nozzles, plus nozzles for 10x10mm and 15x15mm QFP devices.

Wow that's great, I am looking at getting into immobiliser/key programming, possibly with some board repair and looking to set up a hot air/soldering station. That looks like reasonable quality kit for much less than I expected.

 

[graffian]

It's an ATmega chip.
The temp was set at 215ºC, and I relied on distance to ramp the temp in. I was thinking a few degrees more might be
good, But it did it reasonably quickly so probably better to stick with it. I should blow on a thermocouple with the hot
air thingieand see what temp settings, flow and distance do.

I applied the paste by wiping it across the pads, with a pair of tweezers, surface tension pulls the solder to a pad when it melts.
I didn't get the smear of paste at anything like anything like a uniform thickness. You can see how there is loads of
solder on one pad - corner pad in the pic- and there is another [not in the pic] that has a tiny bit under the pin but
most of that pad looks completely clean.

Yes the paste is a little out of date, I bought it as out of date paste about 20 years ago, it's got a little more out of date since.
I was wondering about the flux, mine is made in Colimfrmia so I guess it's not the best.

 

[voipio]

The temperature settings for hot air devices are often unreliable, in that they have quite a bit of overshoot as the sensor warms up. For desoldering with the Duratool device (linked to above) the temperature needs to be set somewhere in the 300-350degC mark, and is fairly stable once it settles at temperature.

 

[Chris Snow]

That's interesting so, just for future reference, are most of these components happy at a temperature that would melt solder?

Most SMT components are designed to survive 3-4 reflow cycles which look something like this.
PTH (through hole) however are generally not, so beware using hot air near them.

I applied the paste by wiping it across the pads, with a pair of tweezers, surface tension pulls the solder to a pad when it melts.

Use a syringe with a fine needle, you can deposit paste fairly controllably.
if you want to make life easier buy one of these

JBC DPM-A Solder Paste Hand Dispenser

JBC Solder Paste Hand Dispenser DPM-A

kaisertech.co.uk

Yes the paste is a little out of date, I bought it as out of date paste about 20 years ago, it's got a little more out of date since.

Ready for the bin then! if you keep it in the fridge it can last ages, need to warm to room temp pre use though.

 

[Screwdriver]

Very pretty graph but no labels to say what it is.

Source?

 

[ajlelectronics]

Applying solder paste can be done with the end of a wooden skewer.

 

[Member 32799]

put a big beat of new solder around the chip to get more thermal mass to the pins , preheat above your stove the pcb , quick and hot 350 c push it it with tweezers of …. Possible with and without hot air gun

 

[graffian]

The temperature settings for hot air devices are often unreliable, in that they have quite a bit of overshoot as the sensor warms up. For desoldering with the Duratool device (linked to above) the temperature needs to be set somewhere in the 300-350degC mark, and is fairly stable once it settles at temperature.

I was at something like 350ºC when I was burning the board, it was doing it pretty quickly.
I just tried blowing on a thermocouple with elCheapy thing-a third of the price of the duratool one- set at 225º.
at 2" away it got to 215º
at 1" away it got to 230º
at very close it got to 246º

Ready for the bin, I have half a kilo of it.

The reflow chart thingie is quite usefull, if I didn't exceed 215º I would have been OK maintaining that for something like 45s.
I was probably only seconds at that temp, once the chip had given a little shake and pulled itself in line I started backing off with the air.
Should you take the temperature above the temp the chip moves around on the molten solder?

I bought the hot air thing to stick a load of LEDs on. With an iron it was difficult to orientate them, I managed to
solder one on sideways and I melted the plastic cases of all of them, not a lot of contact poking out of them.
The hot air did a great job, plonk the leds in roughly the right spot and the surface tension pulled them onto the pads.

 

[Chris Snow]

Very pretty graph but no labels to say what it is.

Source?

https://bltcircuitservices.co.uk/wp-content/uploads/2017/06/LFS-UFP-T4-ZQ-Non-Refrigeration.pdf

The paste we use at work, was only really to give an idea of what a reflow profile looks like, now realise I forgot to say what it was!!

 

[Chris Snow]

Ready for the bin, seems add some flux and it's fine. And more to the point I have half a kilo of it.

I tried this with some old paste some years ago, it just doesn't really act the same, the solder balls didn't flow properly and would fly all over the place.

I probably have a few kilo's of crusty paste if anyone wants some...

 

[Screwdriver]

By sheer coincidence this just popped up on my YouTube subscription:

every day is a school day.

 

[Red'n'Black]

Yes, but not for very long. Most part data sheets have a 'reflow temperature profile' somewhere in the back, it peaks at 260C for maybe 10 seconds.

Here's a typical one: