How to build a reliable PCB

[williamson]

Topic: component spec's: This is a touchy area. If you buy a kit, the components are included. No problem. If you buy a PCB and a parts list, the exact part #'s should be purchased. Substitutions should not be made, except with the approval of the designer. After all, this site is "reliable". Resistors have a spec of "cl-cl"(clean lead to clean lead). They are conformal coated. The coating goes down the leads. This spec guarantees that you can solder this close to the body. The same is true of dipped film capacitors. BTW, dipped capacitors are the best buy for reliability vs. price. But they are not capable of high currents, as in a controller or P. supply ( in a high current location). There, Polypropylene caps are specified. This is true of electrolytics, also. Only some are rated for high ripple current. Potentiometers deserve special mention. Some are specified as being "sealed." But the fine print takes away what the header gives. They are sealed only for certain solvents, and for certain immersion times. Sealed pots usually cost more.

[williamson]

Tweety posted that I am wrong on a few issues. I can't see how we can let my posting be in error and not correct it because this site is supposed to teach. Facts are facts. They are right or wrong. Opinions are shades of gray. To those, we are all entitled. Can tweety please post any facts where I am wrong, so I can correct my error? I found an inconsequential error: I wrote :Florene". This is a gas. I meant Floride, as in Carbon-tetra-floride, a solvent. Tweety: thanks for your help. Kindest regards to all.

[williamson]

Topic: Newbie solderers vs skilled. Newbie solderers (NBS) don't know what wetting is, or, they cannot identify it as quickly as a highly experienced solderer (ES). A decision to remove the heat is made in an instant. One not sure keeps the heat on, to be sure. Poor wetting causes a weak joint that may crack under stress. Even NBS can guess at that. Well, if the PCB sits in a stereo cabinet, all well and good. Let him solder unreliably. The car doesn't crash. But if the PCB receives constant jarring, as being in a very light-weight electric car, a crack is more likely, and could result in who-knows-what output from the controller. (I'm selling fear)! So a skilled solderer can start using lead-free without any problems, or fear. To him I say: Absolutely go lead-free, since you know what your doing (looking for wetting)!

[williamson]

Topic: Wetting:I assume my audience is building a controller. I just ordered a controller kit from Paul. 'Nuff said. I also assume that you have no or little experience in soldering, or, you don't want a BIG head-ache! There are other problems in soldering, but I don't want to scare you. A common problem is solder bridges, where you use too much solder because you really need more flux to be sure of wetting. This problem is greatly diminished by using a solder masked PCB, which are almost universal today. So it is likely you have automechanic experience, and that's why you're building an electric car. If you have welding experience, then you'll be happy to learn you already know Wetting! The puddle must melt into both surfaces to bond with them. Jfitzpat has accurately described how the iron is put on the joint, heated and then the solder flows in. You have to have the heat flow to both sides of the joint to cause LIQUID SOLDER to be in contact with all surfaces. These surfaces, that is, the PCB and the component lead have a coating that melts. This is those parts doing their job. Now you just add melted solder to fill in the gaps. BUT not stick up. It's a fillet weld! I think someone should be able to get useless PCB's to practice on. Maybe Paul, on request can ship NG PCB's. If I'm not speaking out of turn. The postage is a fair price.

[williamson]

"Watch out for that open manhole cover!" "I didn't see that, thanks". This topic is how to reliably solder with lead-free solder. Don't take it as negative, if I point out the pitfalls. What can I do to make a reliable PCB? Well, the only positive step, is to learn to solder. Can you learn that here by reading? If you stick-weld, you know reading doesn't make you a welder. It's an art. A skill. You have to learn a skill. If I told you how to solder, and you thought you were a skilled solderer, I would be doing you harm. you"re free to buy the kit a posted. I don't know the first thing about the kit, but I have faith. You can get scap PCB's and practice, and if you want, you can mail me your efforts and I will call you back with any comments. It's safer to take the long route, than jump right in and solder Pauls kit. This isn't negative about being a first-time solderer. I recommend you learn, and then jump in with confidence! Now, the pitfalls to watch out for in lead-free soldering: When you are a Newbie, you might keep the iron on the joint longer than an old-timer, looking for wetting. Learn wetting on a junk PCB. Semiconductors don't like a lot of heat. The diode MBR60l45CTG, which is typical, says "lead temperature for soldering purposes: 260 C for 10 seconds. The typical iron temp. for lead solder is 700 F. The typical temp. for lead-free is 750 F. which is 400 C. Jfitzpat mentioned that the Radio Shack lead-free solder has no-clean flux. This flux is a slight compromise on performance, at the expense of being "invisible" Actually, it is only transparent! BUT, my experience has been that if you heat it too much (and SUPPOSED to know what I'M doing!) it turns very dark brown, and nearly insoluble in anything short of AQUA REGIA! (just kidding) I recommend rosin flux, and don't clean.

[williamson]

I find a typo in the above post; You're free to buy the kit (how to solder) that I posted earlier.

[williamson]

Topic: Lead-free works! In industry, there are very tightly controlled proceedures to be followed, such as the applicable section of ISO-9000 #1 Volume production on a surface mount production line using specifically designed equipment #2 The process is monitored by Production Engineers. #3 New parts are used with no oxidation of the solder surfaces. #4 The Quality Control Dept. checks the PCB's The result is that all the electronics in the world are made with lead-free solder-except our military. But, I wouldn't be surprised that when the risks are reduced to lead solder levels, that will change! Hopefully soon.

[williamson]

The post by Paul on 2-18 about the military experience with lead-free, should be read by all. But the post aludes to an excellent compromise FOR US! the author said that adding 3% lead made good soldering. A second thing that might make inhibit the tin wiskers might be comformal coating.

Topic: conformal coating. This is a spray-on from an aerosol can (freon-free). All you do is bake the finished pcb board at about 180 degrees for 24 hours, to drive out the moisture-and any volatile compounds. There is (I was reliably told) moisture within the PCB that takes a while to leave. I'll check this out. Military electronics are coated. Commercial electronics must be coated when they are used near a body of salt-water. Only the thinnest coating you can spray on, is sufficient. In a car, you have dirty air and road salt. I would call it an absolute necessity to coat all pcb's in an electric car!!

[dcb]

re: leadfree, the biggest hurdle for the hobbyist in my opinion is just getting it in hobby sized quantities. The minimum order is like $40.

I did get my hands on a small sample of glowcore after numerous emails to the manufacturer, and it seemed to work ok w just a regular iron, but it definitely takes some getting used to.

[williamson]

There is an excellent site that teaches: electronicprojectdesign. The topics are, among many,:"Soldering tips","soldering techniques", "conformal coating" They mention curing time, but we would read the can. Some coatings cure at room temp. They also say to bake hotter and shorter, but WE are in no hurry.