Cleaning circuit boards

[Topless]

Are there "don'ts" when it comes to cleaning circuit boards? I've been spraying with windex, followed by a damp rag, followed by a dry rag, and it seems to work. But I feel like I'm violating the essence of electronics by such crude methods, lol.

There are also gaps in the green board where metal is showing through. Is it a good idea to paint these areas? And if so, water-based latex acrylic or oil? Yes, these are the questions I ask myself in moments like these.

Thank you!

[dinghyguy]

in my opinion the best thing you can do for the taillight circuit boards is drill out the rivets holding the sockets on, clean the oxidation off, solder the sockets carefully to the board and install small nuts and bolts to mechanically make sure the solder joint is supported. That with cleaning the socket insides and the connectors to the board will give you bright and stable rear lighting as long as the wiring and rear ground are in good condition. It made a huge difference to mine when i did it and i was amazed at how much crud was under the sockets.

cheers
dinghyguy

[RRoller123]

While we are at it, let's review the basic solders that are used? The ONLY one that makes any sense for nearly all electronic PCB applications is the Eutectic mix, commonly sold as "63/37" Tin Lead mix by Wt%. The chart shows why: The Eutectic point on the chart is that inverse triangle, where the solder transitions from a solid to a liquid directly, without going through a pasty range (Alpha plus liquid, or Beta plus liquid. Alpha and Beta are different solid crystalline forms of the alloy) . And this point is also the minimum melt temperature to get the solder liquid. The further one goes to either side, the higher the melting point, and the longer the pasty range. Makes soldering a PITA.

Even a 60/40 alloy, that was sold as an "electronic" solder (I was trying to use it up yesterday, as I have a bunch left over from years ago) works like carp compared to the eutectic.

Use an RMA (Rosin Mildly Activated), or RA, (Rosin Activated) flux and you should be fine. R (Rosin, no activators) is awful, basically does nothing. Solder can be bought with these various rosin cores already inside. Indicated on the label. On fine circuit boards, we required a good cleaning for anything in the RA range, but I always just leave it on or give it a quick wash with a solvent, and the RA doesn't cause any corrosion. These flux acids are only activated by elevated temperature.

There are are also "No Clean" solders that are sold, but imho, most of them suck outside of the factory, where we used them almost exclusively. So I use RMA or RA, start with a clean soldering surface, a good iron with a clean tip screwed down securely (Butane as a heat source is fine) and it all works as it should. If trying to solder to a large mass, like a Tab or something, the right shaped tip (spade) and a high power iron may be necessary to get enough heat into the joint quickly enough to get it to wet before the heat flow damages nearby materials in the PCB.

(what is interesting is that the alloy melts at a lower temperature than either of its components alone. Pretty common, but not intuitive.)

[SteinOnkel]

Not to highjack your thread, but RRoller if you could give me some feedback on my methods that would be much appreciated. You seem to be an expert in the field and I'm always looking to improve.

https://youtu.be/6JqpI-oe0K4

https://youtu.be/GFTfteg6J48

[18Fiatsandcounting]

(what is interesting is that the alloy melts at a lower temperature than either of its components alone. Pretty common, but not intuitive.)

I think this might be similar to freezing point depression seen with mixtures of components in a solution, and I guess I'll have to dig out my physical chemistry textbook and review the sections on the Clausius-Clapeyron equation. Shucks, I thought I had the afternoon off....

I think the (simplistic) answer to your question above is that the energy (temperature) needed to melt an alloy is less because the structure has already been "weakened" somewhat by the fact that the alloy contains two components and thus its crystalline structure is not as ordered as for the pure metals. So for example, lead has a particular structure and melts at temperature T1. Tin has another structure that melts at temperature T2. Combine them into an alloy, and the structure of the resulting alloy is less robust than either metal individually, so its melting temperature (energy required) is less than T1 or T2.

-Bryan

[RRoller123]

You have hit upon it exactly!

I may have been an expert about 23 years ago, not anymore....... LOL. I actually was a Wave Solder Engineer and consultant to a couple of companies at one point. But this was way back in the day.. War Stories... Saved the ass of one NH Telecom startup company on one looksee, and unfortunately the poor fellow running that show had no idea what he was doing and he lost that job, but he did stay in the company, so I didn't feel all that bad..... They went on to be a huge telecom success.

One afternoon about 5 O'Clock on the last day of a quarter, (decades ago) I get a call from one of our customers, their Ops Manager, who says he had to build and ship 700 units by midnight. I though he was joking. I was the Facilities Engineer/Tech Ops Manager/Industrial Engineer/etc etc, employee #2, you know how it is, and we were doing pretty well by then, had lasted a couple of years and had about 80 employees, shipping about $75 million a year. He said he had the boards all stuffed and would I wavesolder them for him right now, tonight? And he would take them back, finish building them, and test and ship them before midnight. I thought he was joking, but he was a good guy and I liked him, so I said, sure, bring them over when you have them ready and "make sure you bring a case of beer". I left the wave up and running, just in case he wasn't kidding and actually showed up.

Well he showed up at about 7:30, with about 500 boards in racks, stuffed (how he kept the parts in those holes while driving over I will never know). He couldn't get 700 ready, but damn if he didn't have about 500 stuffed and ready for wave! My shop was empty, I was the only one still there (no 2nd shift at the time) so we put the case of beer up on the top of the wave and I showed him how to "Catch" while I "Pitched". Well we got totally hammered, soldered all the boards by about 10:30, and he left, driving much more slowly than when he came, and I found out a few days later that about 300 boards flew through first pass test and they were shipped and he made his quarter. (I think they unplugged the clock on the wall......) Sorted out the non FPT yield units later. We never mentioned the case of beer up on top of the Wave, but I wish we had had camera phones back then.

Just an aside, my plant was the second in the United States to put in fully closed loop aqueous cleaning for SMT printed circuit boards. (Northern Telecom in Santa Clara was first) Literally no sewer drain. Back in the 80's, I forget when exactly. The amount of lead waste was so little (a few rags for wiping down stencils , and the depleted DI columns, filters, etc, that we met all the requirements to not even require an operating permit from the EPA or the MA authorities (we were classified as a VSQG). All we really had been waiting for was the paste flux chemistry to become available, and when it did (a friend of mine in the chemistry world around here (Boston) helped to develope it), we worked with the cleaning guys (remember Hollis and Electrovert? I am not sure if they even exist anymore), we bought the equipment and went for it. Worked out well, and I gave a bunch of papers at conferences etc.

And then the dog bit, I had had enough after the 5th startup, and here we are today, I am now covered in sawdust instead of lead dust, and Fiat parts.

God those days were fun, I love war stories, especially when having gotten old in the meantime, and been locked up for over a month.

[18Fiatsandcounting]

...And then the dog bit...

I thought you said your dawg does not bite (and you know the rest). Wait for it....

....


Patience, patience....

...That is not my dog.

-Bryan

[RRoller123]

and Lead dust made a lot more dough than Saw dust, but that is completely ok.

[RRoller123]

Not to highjack your thread, but RRoller if you could give me some feedback on my methods that would be much appreciated. You seem to be an expert in the field and I'm always looking to improve.

https://youtu.be/6JqpI-oe0K4

https://youtu.be/GFTfteg6J48

That first one, the flex circuit.. we never manufactured those. But there was a convention of thought on these things back in the day. [There is a local company here that does it (Tech Etch)]. Almost all of this technology that I was ever aware of was exclusively for military purposes, and uses a different POLYIMIDE base than std commercial PCBs. We decided to stay commercial exclusively, and never went into it. In a weapon like a missile, for instance, that only needs to fire once and last a couple minutes at most, makes sense. But apparently the VW folks are not too happy with it. The flex circuit in the video does not look like a Polyimide base, but I of course can't be sure. Polyimide is a brown color, and this is blue, but it might be the solder mask. Blue is an odd color though, green here in the states, and everywhere else that I saw. We had an idea once to use a red or blue mask for our prototype boards, so the customer could tell them apart, different generations of prototype being different colors, in the lab or Beta sites, whatever. But it never went over well, because they never wanted to pay for the setup charges for the board manufacturer to breakdown, clean, setup the screen printer with the new color, run a few protos, then break it all down, clean it and set it back up with green. I can't say I blame them.

The second one, .... I am amazed at what people will do, looks great, but you need a PhD to pull this off. The soldering and crimp techniques look fine. Those little boards are good, but you can burn them, be careful. Lots of power applied for a short time, with a good flux and eutectic solder and it should work. I was always terrible at it myself, but I was pretty good at hiring people who were good at it.

[18Fiatsandcounting]

Not to highjack your thread, but RRoller if you could give me some feedback on my methods that would be much appreciated. You seem to be an expert in the field and I'm always looking to improve.

https://youtu.be/6JqpI-oe0K4

https://youtu.be/GFTfteg6J48

Awesome work Steiny, and I'll be interested in how it turns out. I'll just note that my '69 Chevy truck also has a similar flexible circuit foil for it's instrument cluster, and yes indeed, those copper "lines" do break with age. Not being as inventive as you, I've just jumpered the break with a wire.

-Bryan

[RRoller123]

I suspect that the constant vibration in an automotive environment, even while maybe low amplitude (hopefully), and the points somewhere along those flex circuits where natural frequencies are hit, combined with the very thin Cu traces, causes this. The cost savings better have been worth it of all this flex in cars. Now if Chevy (GM really) could just fix that damned heater fan speed assy unit. What the hell is up with that?

Man, Steiny that fix looks incredible, I hope it works! You deserve the medal for that. There's a lot of work right there. The only general guideline that I can offer when making individual solder joints at single connections (something I was never all that good at, I am a wavesolder guy) is to size the MASS of the soldering iron tip, and the SHAPE of the tip, to match the needs of the joint. And have a lot of reserve power behind the tip. Soldering to a large tab requires not only a lot of power behind the tip, but the right physical shape to transfer that heat to the joint as fast as possible. Large contact area needs large mass of the tip and a large reserve power source to get the depleted heat right back in as quickly as possible. In a wavesolder machine, the power going in compared to the individual joint is essentially infinite, so it doesn't matter at all, but with an iron, it makes a huge difference.

I have found (and was quite surprised by this) that even with my butane powered iron, the 60/40 alloy performed like siht compared to the eutectic 63/37, even with the iron well heated up and just soldering individual wires together.

One more war story, I used to pull the "Johnny Tremain" trick on my folks at the nearby assy line. Remember reading Johnny Tremain in Junior High? He was Paul Revere's apprentice. Accidentally plunged his hand into a molten silver cauldron. Horrible. Anyway, I had a pair of gloves that would withstand a nuclear explosion, and every once in awhile I would pretend to slip, and shove my hand down into the molten pot, with about 700 pounds of flowing solder in it at about 500F. My God the look on their faces as I made a fake howl. Jeezus the stupid stuff we did back then. Thank God I haven't grown up even yet.

[spider2081]

I was always terrible at it myself, but I was pretty good at hiring people who were good at it.

I think soldering is a skill that does not lend itself well as a "self taught" skill.

My fist job after high school was at an auto radiator manufacturing company where I was taught to solder coppers and brass using acid flux.
I then joined the service and was taught to solder electrical connectors and components with non corrosive flux.
I don't think I would have ever developed the skills if I tried to learn by trying.
A properly completed solder connection is a metallurgical bond.

[18Fiatsandcounting]

Now if Chevy (GM really) could just fix that damned heater fan speed assy unit. What the hell is up with that?

I think what you're referring to is the resistor network that allows the fan to work with OFF-LOW-MED-HIGH. It's comprised of some nichrome (or similar) resistance wires, and this stuff doesn't solder. So, they just crimp this nichrome wire onto the lugs, and (of course) with age the mechanical connection loosens and corrodes and your heater fan speed thingie doesn't do squat any more.

-Bryan

[RRoller123]

Exactly, it's a POS, and you have to buy a whole expensive unit to replace it. Probably changed 4 of them over the years in my cars. But not quite bad enough to lose them as brand.... funny how that works.