Author Topic: Myth busting solder-flux cleaning with isopropanol alcohol  (Read 131484 times)

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Online rhb

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #75 on: December 18, 2018, 11:37:08 pm »
I had a Harbor Freight PIR sensor night light that had stopped working and been tossed in the junk bin.  I pulled it out yesterday to see if I could scavenge a AA batter holder and in the process took it apart.

It's a pretty simple device, so I thought I should be able to diagnose the fault.  In looking at it I noticed some flux residue.  So I cleaned it with a spray of isopropyl and an old toothbrush.

Now it works.  So I'll have to put it back together instead of removing the PIR to play with. :(

The surprising part was how little flux residue there was and that what I noticed was not close to the sensor or op amp, just the on-off-auto switch area.  I cleaned the whole board, so there may have been some I did not notice
 

Offline T3sl4co1l

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #76 on: December 19, 2018, 07:06:19 pm »
PIR detectors are pyroelectric, i.e., the electric field on a crystal changes with temperature.  Electric field means very high impedances, low leakage -- exceptionally so at the rates of change used here (low Hz).

If that's seen at board level or not, depends on if the sensor is internally buffered.  I think that's not uncommon, so you get a PIR module that looks very much like an electret mic: an internal JFET follower on the capacitive (charge based) element, giving reasonable circuit values (continuous current (fractional mA?) instead of charge).  Board contamination could still be a problem, but it would have to be much worse to kill operation.  Or the circuit is just that badly designed (you can always make a circuit worse; you can't always make a circuit better!).

Tim
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Offline SeanB

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #77 on: December 19, 2018, 07:46:39 pm »
No clean flux, or water soluble flux poorly cleaned, will leave a residue that affects high impedance circuits. as the detector typically use 100k or higher value resistors to get gain, any board leakage on either top or bottom will cause incorrect operation. Might work when new, but after a few months of absorbing ambient humidity and rain there will be conductive paths that are not intended. Clean board and give a coat of some conformal coating, or just mask off the pyro detector top with painters tape and spray board top and bottom, avoiding the variable resistors using more tape, and they will last for years.
 

Online rhb

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #78 on: December 19, 2018, 11:11:38 pm »
The circuit is very similar to the example in the datasheet for the PIR D203B sensor.  But it's driving an LED and timer circuit rather than a relay and uses an LP324 quad op amp.  It also has a sensor to keep it from turning on if the room lights are on

Putting it back together was a huge pain.  Every time I soldered a wire back on, another one broke off.  But I did eventually get it back together and it works just fine.  So I washed the "NG" written on the back off and put it to use.

I've not had trouble once the muck was cleaned off.  I did have to reclean a CD player after a few months, but that was several years ago.  It's never had a problem since.
 

Offline TheNewLab

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #79 on: January 07, 2019, 08:59:08 am »
I did a little video on common alternatives

TLDR version:  Use real flux cleaner (or isopropyl if you don't have it)


You really should have included brake cleaner in your test. Cleans at least as well as the MGC product with zero board or component damage, and MUCH cheaper. I swear by it now.
I am also about to buy an ultrasonic cleaner and wonder to bath solution to use.
1st, some auto parts, and Iknow what to use,
2nd electronic parts and boards, and that I do not know.
Does Brake cleanerreally  work that well and is safe on circuit boards?
IF so, that would be ideal. Do you dilute it?
 

Offline TheNewLab

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #80 on: January 07, 2019, 09:05:34 am »
Also, regarding ISO alcohol. I use 99% and I am not always happy. Some have mentioned how bought flux cleaner has additional chemicals
Can I make up a solution combining alcohol with other chemicals to make flux cleaning and PCB cleaning MORE effective?


or, some special blend that will not blow up or poison me?

I know acetone works on some stuff, I don't think PCBs though
ANd Naphtha (lighter fluid is great for plastics..but only for plastics as I understand.

So many questions?
one more:  any ultrasonic  homebrew solutions for electronics ?
 

Offline chickenHeadKnob

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #81 on: January 07, 2019, 11:03:58 am »
I did a little video on common alternatives

TLDR version:  Use real flux cleaner (or isopropyl if you don't have it)


You really should have included brake cleaner in your test. Cleans at least as well as the MGC product with zero board or component damage, and MUCH cheaper. I swear by it now.

Well I just gave this stuff: (Certified Brake Cleaner non-chlorinated) a try - https://www.canadiantire.ca/en/pdp/certified-non-chlorinated-brake-cleaner-390-g-0381430p.html
Certified appears to be a Canadian Tire house brand, it is just Heptane and Carbon Dioxide. First impression is that it works very well!, not egregiously smelly or toxic and cheap and locally abundant. Winner!

My test was not a full soldered board. Just recently I bought some Rose's metal from Russia. This is low temp. Bismuth/tin/lead that melts around 97 degrees Celsius, and it comes  from the seller in drops (small blobs). I wanted it in the form of wire so I can  hold it while using it to solder the lids on hermetic boxes I am making so I coated the drops with MG-835 liquid rosinRA flux and heated them on a hot plated griddle. I use a black and decker brand teflon surface 24 inch breakfast griddle as my hot plate. I got the drops warm enough to melt them and get them to coalesce into 10mm wide ribbons, which should be as good as wire. The flux never got to smoke temp. so this is not the same as hardened burned on flux typically seen on PCB's.

I let the hot plate cool down, peeled off the rose's metal and let the flux harden for a day. I scraped off as much as I could before hitting it with the brake cleaner. There was still a layer of hard powdery flux stuck on the teflon that came off like magic with the brake cleaner but admittedly this is not as a good test as a real PCB.
 

Online rhb

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #82 on: January 07, 2019, 03:19:38 pm »
One of these might help:

https://www.seattlefindings.com/Draw-Plate-Round-10-32-Gauge_p_4067.html

The normal routine is to make a narrow mold, cast an ingot and then successively draw until you get the desired diameter.  That's what jewelers have done for thousands of years and still do regularly all around the world.

A piece of 10 AWG copper wire pulled straight and pressed into plaster of paris that is almost set should work for the mold.  You can probably melt the drops in the mold with a hot air gun.
 
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Offline chickenHeadKnob

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #83 on: January 08, 2019, 03:51:08 am »
The normal routine is to make a narrow mold, cast an ingot and then successively draw until you get the desired diameter.  That's what jewelers have done for thousands of years and still do regularly all around the world.

A piece of 10 AWG copper wire pulled straight and pressed into plaster of paris that is almost set should work for the mold.  You can probably melt the drops in the mold with a hot air gun.

Thanks, a few similar approaches occurred to me. Rose's metal is new to me as it is the first time handling it. It is surprisingly hard and non-ductile, I don't think it will draw well. Plaster of paris is a good idea. As it turned out the teflon prevented the molten metal from alloying with the underlying aluminum and I could steer the liquid around with a popsicle stick to get ribbons so my hasty approach gave quick functional results.
 

Online rhb

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #84 on: January 08, 2019, 01:09:23 pm »
If it work hardens while drawing it will be really difficult to anneal without melting it.  It may be hard from being quenched in water to form the drops.

Jewelers commonly use solder in sheet form.  So another option is to cast a wire ingot and then either draw if out with a hammer and anvil or compressing it in a vise to make a thin ribbon that you can cut with nippers.

The plaster of paris mold should be baked in an oven at 250 F for several hours before use to make sure it is dry.
 

Offline T3sl4co1l

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #85 on: January 08, 2019, 01:40:21 pm »
A quick look at the literature suggests elongation (a measure of ductility) should be very good indeed.  You may have to go slowly, however (which implies the large elongation is due to creep).

Tim
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Offline chickenHeadKnob

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #86 on: January 08, 2019, 03:16:24 pm »
A quick look at the literature suggests elongation (a measure of ductility) should be very good indeed.  You may have to go slowly, however (which implies the large elongation is due to creep).

Tim
I have to play some more. i don't know the purity of the stuff I have, I always have some doubt when buying from ebay. One of my goals was to use the griddle and a thermocouple to ascertain the melting point to get a gauge on the quality. Well I screwed that up, somehow the thermocouple via my Brymen 869 was giving wild readings, plausible one moment implausible the next. I cranked up the heat after getting impatient and over shot 110+ degrees, then things started melting too quickly.
 
 I had a small container of water and a sponge and was using the sponge to drip water onto the griddle as a sanity temp test and the water drops were boiling off quickly when the metal started to melt. The water and sponge were also intended as a quench once I had the metal in the form I wanted. As the metal cooled a network of crystals could be seen forming, indicating to me that one component was coming out of alloying solution first and that the final result may not be all that homogenous. Once solid I tried bending it. It feels like something inbetween pot metal/white metal and standard 63/37 solder.

I feel embarrassed derailing this thread from the flux removal topic :-[
 

Offline grantb5

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #87 on: January 08, 2019, 03:47:57 pm »
I feel embarrassed derailing this thread from the flux removal topic :-[

Start a new one or bring it back on topic when you sort your current issues. :)
 

Offline T3sl4co1l

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #88 on: January 08, 2019, 06:30:25 pm »
Eutectic shouldn't be forming visible crystals.  Maybe you have rather more pure bismuth than you were expecting?  It should still be on the soft side if the melting point is obviously not that high, though, AFAIK...

If you leave a strip of the stuff cantilevered out, does it bend slowly over time?

Tim
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Bringing a project to life?  Send me a message!
 

Online Ian.M

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Re: Myth busting solder-flux cleaning with isopropanol alcohol
« Reply #89 on: January 08, 2019, 09:36:26 pm »
The traditional Rose's alloy is non-eutectic.   See http://www.che.uc.edu/jensen/w.%20b.%20jensen/reprints/178.%20Fusible%20Alloys.pdf

You should be able to melt it under water in a glass beaker, with anti-bumping granules added so you cant superheat it by more than a few deg C.   If not, it not what its supposed to be.

I'm curious how effective the rosin RA flux was at such a low temerature.
 


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