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I have built a QMX Rev 2 and am having trouble with off-scale peaks in the SWR.? I've rewound T501 and T507.? I've found I can pretin the leads before I install the transformers.? I've been cleaning the board with 91% Isopropyl Alcohol and a brush around the soldering pads.? Last night I cleaned the whole board and the USB connection no longer worked. This morning I tried again and the USB port is working.? I am not used to working with SMD components.? Have I damaged the board using IPA?? I've ordered?MG Chemicals 4140A flux remover in hopes of cleaning the remaining residue.? What do you guys use or recommend?
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Hello,
I seriously doubt that you can damage a circuit board with isopropanol. In 25+ years of using it (for cleaning, lol), I was never able to do any damage to any board, with or without SMD's, including PC motherboards.
Besides, MG Chemicals 4140 flux remover also contains isopropanol.
Under normal circumstances, alcohol does not conduct electricity, buuut... when mixed with dissolved flux, maybe it conducts just enough to bamboozle the USB port from QMX. When dried out, the problem just... evaporated :-)
Just IMO.
Regards,
YO3GFH
op. Adrian
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I normally use IPA?and a toothbrush, but depending on how well sealed the on-board components are (or if it's not a PCB) sometimes?I use chlorine-free spray brake cleaner and Scotchbrite from the auto parts store.
73 Jim N6OTQ
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I have used non-chlorinated brake parts cleaner for years with zero issues.? Be aware that it CAN damage some plastic parts, but I've never had any issues using it on PCBs. I spray, scrub with a toothbrush/acid brush, then spray again to rinse.? Typically, I use Auto Zone store brand NON- CHLORINATED.?
?
Mike
WM4B
On 01/22/2024 12:53 PM EST Adrian YO3GFH via groups.io <p_adr@...> wrote:
?
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Hello,
I seriously doubt that you can damage a circuit board with isopropanol. In 25+ years of using it (for cleaning, lol), I was never able to do any damage to any board, with or without SMD's, including PC motherboards.
Besides, MG Chemicals 4140 flux remover also contains isopropanol.
Under normal circumstances, alcohol does not conduct electricity, buuut... when mixed with dissolved flux, maybe it conducts just enough to bamboozle the USB port from QMX. When dried out, the problem just... evaporated :-)
Just IMO.
Regards,
YO3GFH
op. Adrian
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Removal of flux is not necessary since it is non-conducting.
Removing it looks nicer but does not improve the function. To
inspect for solder bridges its better to use a strong light and
magnification. Sandy KB3EOF
On 1/22/24 11:59, John Norton wrote:
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Show quoted text
I have built a QMX Rev 2 and am having trouble with off-scale
peaks in the SWR.? I've rewound T501 and T507.? I've found I can
pretin the leads before I install the transformers.? I've been
cleaning the board with 91% Isopropyl Alcohol and a brush around
the soldering pads.? Last night I cleaned the whole board and the
USB connection no longer worked. This morning I tried again and
the USB port is working.? I am not used to working with SMD
components.? Have I damaged the board using IPA?? I've ordered?MG
Chemicals 4140A flux remover in hopes of cleaning the remaining
residue.? What do you guys use or recommend?
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I normally use IPA?and a toothbrush, but depending on how well sealed the on-board components are (or if it's not a PCB) sometimes?I use chlorine-free spray brake cleaner and Scotchbrite from the auto parts store. In another life, I worked at prototyping "broadband service gateways", now known as routers, and nearly 100% of our boards were failing for a time, due to spray cleaners being used to remove flux from unstable boards. Visually almost everything was perfect, but circuit after circuit tested bad. Finally after several dozen failed prototypes, one fellow had a board connected, and started twisting it around, discovering numerous intermittent connections. The evaporation of spray cleaners, and subsequent chilling, caused boards, and parts to shrink and distort, breaking solder bonds, pins, and pads, cracking traces, even shattering parts. I built up another board, and tested it before cleaning. Perfect. I sprayed is down while we all carefully watched and listened, and we could hear crackling noises, and watched as the board bowed roughly 1/4" as the solvent evaporated, then warm, and return to normal, something not noticed as boards were sprayed down, and set aside. The solution was to use slightly warmed isopropanol a.k.a. isopropyl alcohol (NEVER called IPA, that's a beer, and isopropyl alcohol is two words, not three, the acronym doesn't work), and an acid brush (horsehair) to gently clean the board. Kurt
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Kurt,
I've always used IP and an acid brush to clean circuit boards of flux but I have not built any boards that used SMD parts as small as these. I've a film on the board that I'm trying to remove.? ?I'll be using the flux remover in a quart bottle so no problem with temperature.? On the other hand your diatribe about using IPA as an abbreviation was not well received.
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Jim,
I used brake cleaner on an old pre-fiberglass phenolic board and had problems with the AC section of a VTVM damping the movement when the probes were removed.? I cut isolation slots in the board to solve the issue.? Never again will I use brake cleaner.
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On Mon, Jan 22, 2024 at 04:04 PM, John Norton wrote:
I've always used IP and an acid brush to clean circuit boards of flux but I have not built any boards that used SMD parts as small as these
IPA (there, I said it!) and an acid brush works for the smallest components, down to 0201 (my limit!) anyway.? Go easy so as to ot dislodge components.? Spot clean with acetone (NOT fingernail polish remover) for stubborn, burnt flux.? It is OK if there is a thin film of flux left, with the exception of certain high-impedance circuits which require scrupulous cleanliness.?? Even used with an ultrasonic cleaner isopropyl won't hurt anything except potentiometers and other unsealed components.?? The commercial flux removers seem to have "hotter" solvents but are pretty costly and possibly environmentally questionable. 73, Don N2VGU
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My goto cleaner has always been IP but the white film left behind bothered me. So I started using Q-tips moistened with distilled water to clean off the IP film residue which does a great job.
The debate about cleaning flux off boards has been raging for decades. I never trusted flux residue on high-frequency circuits and especially high-impedance circuits. Working in a high-reliability group for 17 years, we had an unbreakable rule that all boards had to be immaculately clean. Whether this was absolutely necessary could still be debated but the one big plus of cleaning off the flux was for visual inspection of solder connections. Seeing that shiny solder connection with the proper-sized fillets was very reassuring for the QA people. Of course, those shiny connections disappeared after ROHS requirements were implemented but I still like seeing nice-looking fillets even if they¡¯re somewhat dull.
Tony - AC9QY
Jim,
I used brake cleaner on an old pre-Fiberglas phenolic board and had problems with the AC section of a VTVM damping the movement when the probes were removed.? I cut isolation slots in the board to solve the issue.? Never again will I use brake cleaner.
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I've always used IP and an acid brush to clean circuit boards of flux but I have not built any boards that used SMD parts as small as these. I haven't looked at the QMX, I'm here for another product. We were using 0603 and 0201 ~25 years ago, the 0201 were very easy to damage with board stresses. I've a film on the board that I'm trying to remove.? ?I'll be using the flux remover in a quart bottle so no problem with temperature Another option is CRC QD electronic cleaner for really stubborn gunk, sprayed into a container, I use stainless steel condiment cups, then dip a q-tip, or brush into the solvent: The cleaner is pricey at auto parts stores, sometimes over $20 per can, but WalMart is a good source, typically around 5-7 dollars. On the other hand your diatribe about using IPA as an abbreviation was not well received. Kurt
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I have always used IPA to clean PCBs and not had an issue other than as the IPA evaporates it tends to cool the board and you may get condensation, so you need to wait until this has disappeared before applying power. ? Back in the day when cleaning audio or video tape heads with solvent, same issue.? You had to wait at least 10 minutes before putting a tape in to play or the condensation would take the tape oxide from the tape and put it back on the head ? Graham ZL1CE
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I had the same problem.? After trying several different products, found out that 99% isopropyl alcohol worked really well.? It's not easy to find, or cheap, but it was the only thing that worked for me.?
On Mon, Jan 22, 2024, 17:40 Graham (ZL1CE) < grahamw@...> wrote: I have always used IPA to clean PCBs and not had an issue other than as the IPA evaporates it tends to cool the board and you may get condensation, so you need to wait until this has disappeared before applying power. ? Back in the day when cleaning audio or video tape heads with solvent, same issue.? You had to wait at least 10 minutes before putting a tape in to play or the condensation would take the tape oxide from the tape and put it back on the head ? Graham ZL1CE
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I want to thank everyone for their suggestions.? I'll try the commercial flux remover since it's already ordered.? I will also try and find 99% IPA with distilled water rinse.? I used IPA because?
I found it in a Electronics Design article about cleaning circuit boards. :)? Special thanks to Kurt for his continued suggestions and sense of humor.? I was really worried about the SMAnce components.? I've been a Controls engineer for the last 35 years developing analog boards, programming PLCs? - robots, and developing custom HMIs.? Not exactly working with miniture QMX boards.
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Hi Sandy,
I never removed flux residue, but now I¡¯m a firm believer in doing so and it¡¯s due to an experience I had in building multiple Hi-Per Mite active audio filters. ?I built two Hi-Per Mites and I noticed the frequency response between the two units sounded different. ?When I built both units I measured all capacitors and resistors prior to assembly to make sure they were very close to nominal values. ?I then swapped the op amp and the audio amp IC but noticed no change in frequency response (they still sounded different and neither units frequency response changed when I swapped the ICs). ?I then built a third one and cleaned it using isopropyl alcohol and this 3rd unit had a frequency response that I liked and it was identical to one of my first two that I built. ?I then cleaned the odd ball unit (the one I did not like) with isopropyl alcohol and now I can¡¯t tell a difference in frequency response between any of the 3 units. ?I then went and cleaned the one unit that had not yet been cleaned and it had no impact. ?Bottom line is that I had to clean one of the units to bring it inline with the other two units and this is something I had chased for a long time. ?I¡¯m now a firm believer in cleaning the flux residue.
Just FYI, Don wd8dsb
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I use isopropyl alcohol too and it works well.
But for my last kit, I took the advice of folks here in this forum and switched to the Kester leaded no clean solder.
It made a huge difference -- no cleaning was necessary (as the name suggests).
73, Mike KK7ER
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I may be the odd man out using only Ethanol to clean circuit boards. This is a byproduct known as "heads" from a distilling hobby, that provides a libation for a thirsty Scottish friend. I will say that the reflux still, that can produce about 95% Ethanol, does clean well in that concentration, however, I always wait a bit for the remaining moisture to dry before connecting electrons. This liquid also works well for removing bug splatter from the front of cars in summer.
Dave VE3KCL
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I use IPA as its easily available and does the job.??
If I see white film that means either the IPA has become loaded with flux
or oil and a fresh brush is needed.? Repeat as needed.? For difficult cases?
(BOARD ONLY) I use Ethanol, Acetone, or MEK carefully.
Reason I say board only is some device packages are not compatible
with more aggressive solvents.? Its easier to take care.
--
Allison
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Post online only,?
direct email will go to a bit bucket.
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I have a friend who keeps shorting boards with Iso. I never do. I use 99% and dry with compressed air. The compressor has a line drier as well but that is because I use it to spray lacquer. I don¡¯t think the drier is needed for PCB work.?
--
Colin - K6JTH?
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Mike Besemer - WM4B
Donald S Brant Jr
Graham (ZL1CE)
VE3KCL
Colin Kaminski