Pencil butane torch for Surface Mount desolder?

I've only used full size hot air gun and protective masking-off before. I prefer the short sharp shock of full size rather than the "proper" pulse jet type things, presumably for rework only really.

Couldn't resist one in a pound shop, unbelievably precisely small spot of flame and also adjustable (upwards), amazing engineering, minimum about 1mm diameter. For SM salvaging rather than just removal, any other tips from actual users? Seems necessary to hold the pcb vertical in a vice and hold the pencil with flame upwards about 20 degrees of angle so butane liquid is not at the outlet. Mask off surrounding areas (including body of IC) with PTFE or woven glass matt cut to fit the paricular situation. Sub mm tungsten wire or something strong enough in those dimensions to push under the IC or the pins , to loop around, and tug on while heating. Freezer spray blast just prior to heating pins.

For DIP do one side of pins at a time, while tugging ? Scalpel blade , perhaps bent, under pins ? What sort of lighting is best ie to see the flame but also the work?

Reply to
N_Cook
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Don't stint on the removal tool -- a cheap and chippy chopper is not a good choice. You also need a big black block for proper support.

Reply to
William Sommerwerck

That torch produces plenty of temperature but not nearly enough heat.

I use two hot air guns, one aimed at the back of the board and one on the front. (The copper ground planes act as heat sinks, so you need to pour a bunch of thermal energy into the area in question in order to get sufficient heat rise to melt solder.)

I normally heat up the back of the board before I even start the 'front side' air gun. Two guns are more convenient than one. Most of the time however, I can use the same gun for both. Heat the back thoroughly and then concentrate on the front.

I dab a little solder paste in the area. That is my local 'thermometer'. When it melts, I know I'm only seconds away from 'liftoff'.

Strip some 30 ga. wirewrap wire to route underneath BGAs. You can form a cradle to gently lift the device off the board.

--Winston

Reply to
Winston

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Do you have a particular rationale for freeze blasting prior to rework? I think the resulting thermal shock would increase the likelihood of damage. Reflow ovens have temperature ramps for a reason. As long as you aren't charring the numbers off the package with a bernz-o-matic until it falls off the board, you are safe heating the entire device to reflow temp. That's how it was put on in the first place. Just do it uniformly and gradually.

If you are serious about salvaging QFP/TSOP/TSSOP devices, you might want to look into a regular size heat gun with a nozzle designed for these packages. An OKi is about 500 bucks but you can get a cheap chinese knockoff for under 200. If you really want to do it quickly and safely I'd recommend getting a solder tip for each package. But this could run you anywhere from 200-1500 depending on what you've got to start with.

But if you're like me and you are salvaging chips because you don't have the cash to buy new ones, then I suggest you look into chip-quik. It's low-temperature solder you "blob" over the leads with an ordinary iron. It stays liquid for 10-30 seconds so you can do a few laps around the device with your pencil iron, then grab the device with forceps and pluck it right off the board. You can set your iron a lot lower if you have an adjustment.

I used to use that tungsten wire trick (steel or ordinary enameled magnet wire works great too) but chip quik is much faster and less traumatic to the device.

I routinely use chip quik these days to upgrade 80-pin microcontrollers. I am not salvaging them but the lower heat causes less damage to the board, and that saves me trouble later.

Reply to
stickyfox

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Some interesting ideas there. I don't often meet ground planes but if I do , how do you gauge the rear heat ? I like the solder paste indicator.

Reply to
N_Cook

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Do you have a particular rationale for freeze blasting prior to rework? I think the resulting thermal shock would increase the likelihood of damage. Reflow ovens have temperature ramps for a reason. As long as you aren't charring the numbers off the package with a bernz-o-matic until it falls off the board, you are safe heating the entire device to reflow temp. That's how it was put on in the first place. Just do it uniformly and gradually.

If you are serious about salvaging QFP/TSOP/TSSOP devices, you might want to look into a regular size heat gun with a nozzle designed for these packages. An OKi is about 500 bucks but you can get a cheap chinese knockoff for under 200. If you really want to do it quickly and safely I'd recommend getting a solder tip for each package. But this could run you anywhere from 200-1500 depending on what you've got to start with.

But if you're like me and you are salvaging chips because you don't have the cash to buy new ones, then I suggest you look into chip-quik. It's low-temperature solder you "blob" over the leads with an ordinary iron. It stays liquid for 10-30 seconds so you can do a few laps around the device with your pencil iron, then grab the device with forceps and pluck it right off the board. You can set your iron a lot lower if you have an adjustment.

I used to use that tungsten wire trick (steel or ordinary enameled magnet wire works great too) but chip quik is much faster and less traumatic to the device.

I routinely use chip quik these days to upgrade 80-pin microcontrollers. I am not salvaging them but the lower heat causes less damage to the board, and that saves me trouble later.

OOOOOOOOO

I'm probably to old to change my ways now unless a proven advantage to do so. I like to go in and out as quick as possible with hot air source having heated up for 30 seconds before applying. No known failures in reuse from pre-freezing. I like the way they come off in their 0.1mm tugsten wire strops and they can be placed in the palm of the hand, IC body face down, and be just warm , not hot.

Reply to
N_Cook

You're on the right track. Get a pencil torch with a catalytic "hot air" tip. I use a Weller PortaSol. MUCH better ratio of temperature to heat delivered. Works way better than I'd expected. Preheting the board closer to solder temperature with a big hot air gun or temperature controlled hot plate makes it even easier.

Reply to
mike

(...)

I have not been measuring the temperature at all. I've been relying on experience to know that I've heated up the back side of the board 'sufficiently' but not so much as to loosen components.

I've been eyeing these Tempilstiks to get a better idea:

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One could mark the board with three crayons of increasing melting temperature and get a better idea when to start pulling on the BGA.

It works 'better than nothing'. Of course the virgin solder melts at a much lower temperature than does the used solder.

--Winston

Reply to
Winston

Another reason to investigate these , but 1/2 deg C resolution fine for that purpose. For general fault hotspot monitoring 0.1 deg C resolution ones would be more useful but too expensive. Another gizmo I must get around to trying. Using the pyrometer of a PIR unit , setting in an insulated tube shroud for pointing and then analogue fashion monitor the output in a relative way, absolute temp not required for that purpose.

Reply to
N_Cook

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In this situation would thore remote IR thermometers pick up the temp of the board or the much higher temp of the hot air above it , but in line of "sight" of the sensor?

Reply to
N_Cook

(...)

I dunno. Plus / minus 10 C is all that is necessary. Your real indication is when you can lift the BGA off the board without undue drama.

I understand that PIRs are A.C. devices, so one would have to be adept at 'blinking' the shroud at the target while capturing the resulting pulse from the PIR. As you say below, there is a much better solution.

That is a good experiment to do.

I *guess* that the infrared emissivity of nitrogen *at that temperature* is low enough that the infrared from the PCB would swamp it out. I do not know for sure.

Product Idea! An infrared sensor mounted to your headband magnifier.

Lensed LCD chart presented as a heads-up display in your magnifier continuously scrolls to show temperature at the center of your crosshairs.

--Winston

Reply to
Winston

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The "ac" action is from the effect of the facetted mirrors in the PIR, producing signal change when a moving warm object moves across the boundaries of facet projected areas , a bit like fly's multi-lens eye structured as a movement sensor

Reply to
N_Cook

(...)

The way I misunderstand it is that the raw output of the sensor itself is A.C. With or without the faceted lens, a hot object presented to the sensor itself will result in a pulse, not a D.C. offset as one expects of a Si photocell, for example.

I'm here to learn however, so I am open to new information.

:)

--Winston

Reply to
Winston

I tap the board to encourage components to 'unstick' from the molten solder.

Yeah, PIR detector is hopeless at absolute temperature. What it does instead is rely on the warm body moving in and out of the lensed zones to create an AC IR signal. That's why they have that fresnel lens thing on them to define the IR zones.

Hmm, seen the price of a point-at-target IR thermometer? Add a couple more times that for the headsup display? Not cheap :(

Grant.

--
http://bugs.id.au/
Reply to
Grant

$10 on sale at Harbor Freight.

--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.
Reply to
Michael A. Terrell

(....)

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Thirty smackers? Looks hackable too.

--Winston

Reply to
Winston

Nice. I was thinking more of the 'brand name' pricing, 10 or more times that ;)

Grant.

--
http://bugs.id.au/
Reply to
Grant

The uSoft version *is* pricey.

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--Winston

Reply to
Winston

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