How to build a reliable PCB

[williamson]

misc.: Never use a flush-cutter to trim leads on a pcb. They can tear a run. In industry, this is one of the absolute no-no's. You can use a small computer fan to blow the fumes from the flux, away from you. Flux exists in lead or lead-free. It's not the lead fumes. Lead doesn't vaporize at these temps. The differance between solid and standed wire is that solid wire does not withstand vibration, or frequent bending. It can only be used where the wire undergoes no motion. When you insert a component, you then bend the leads to hold it in place. Only bend the leads enough to hold the part, maybe 20 or 30 degrees. If you bend it close to the pcb, you may cause a solder bridge to the next pad. also, you may not be able to cut the lead at the top of the solder. The lead may touch something! Solder braid can be purchased at Jameco, a good Co. for small quantities of unusual (and common) parts. P/N153462, $2.25. As I posted, solder-wicking is the professional way, but I would never do it. When, if you conformal coat, only a single spray layer is needed. A thin film!

[williamson]

I strongly recommend conformal coating. The spec says 1 mil (.001 inch) gives 1200 volts insulation. So you put it on like hair-spay. Miller-Stephenson is a very reputable supplier. Their P/N is MS-470C.

[williamson]

High voltage circuits should also be conformal coated. The failure mechanism is totaly differant, but--. A low-level control board has circuits that are susceptable to leakage currents from salt air and road mist. A 144 volt board could develope an arc-trace across the board, following along the contamination. This would be not only destructive, but could be a fire. FR-4 is only "fire-retardent"! Most coatings are rated for about 1KV per .001" thick coating. This would be even more important for an AC controller at 300 volts. I think Digikey sells a 12 oz. can for about $20.00 They aren't the last choice.

[williamson]

Solder: Only buy .032 or thinner solder. Don't use any thicker solder, even if your paid to use it: You can't control the amount applied-not even a well-skilled professional could. Install resistotors first. This is for two reasons: First: small parts are installed first because you can't get your fingers in between big parts, second: Resistors conduct electricity, and dissapate any electro-static charge on the PCB. Next, Diodes, then caps, then transistors ( labeled "Q"s) Always last, is the IC"s.

[ChedMpls]

I am soldering the cougar control board and i am having lots of trouble with heat. Most parts and holes get soldered straight away with my (25w, 750F) radio shack iron. But the legs/holes that are connected to the large copper ground planes will NOT heat up enough to melt leaded solder. I went out and bought a 50w 900F Velleman soldering "station" (cheap $20) and cranked up to 900F it sometimes melts the solder if i hold it on the joint for 30 SECONDS OR MORE. C'mon - shouldn't an iron melt solder in a few seconds on this size board? Do i need more watts or do i need 1000F to get everything hot enough to solder?

I cannot finish this pcb until i get an iron that works !!!

[williamson]

Dear ChedMpls: I built this controller, but I used a Weller soldering station. On the internet, these sell for almost new list price. What a rip-off. But since the Weller tip is temperature controlled, I assume that when I put it on the power semiconductor legs, it greatly increased the heat to bring the parts to 700 deg. I had no problem at 700 deg. All normal soldering is done at 700 deg. You dont want more than 700 deg. You can lift the clad off the board! It's only glued on. You can damage semiconductors with too much heat, or with holding the iron on too long. Just look at the data sheet of semiconductors. But getting to your problem: first, you might have a pencil point tip that doesn't transfer heat thru such a tiny tip, second, you may have an oxide covered tip. You have to wipe the tip on a wet sponge often, to wipe of any oxidation, or CRUD. Lastly, sad to say, you may not have an iron that holds 700 deg, either due to poor or non-existant temperature control, or the heating element isn't as large as a Weller. Also, in the instructions, it says to use a 180-250 iron to solder some large stuff. Read your directions. If you need a large iron for these steps, you can use it for the legs. The instructions call out 180 watts, min. I used a 100/140 watt duel heat Weller gun, and hade no problem. Kindest regards, Williamson

[ChedMpls]

thanks for that advice, W.
i AM using a pencil tip iron because these holes/pads on the pcb seem very small to me and i am afraid of touching the solder mask with a large tip. is the pencil tip a rookie mistake?
Did you use the 100/140 weller "gun" on the control board or just the power board? the tips on the "guns" look HUGE!

[Greg Fordyce]

I used a larger tip (2mm) for soldering to the ground plane. That seemed to work well. Maybe the pcb design could be improved to help prevent this problem. Recently I got a kit from Sparkfun and for pins connected to the ground plane they had a isolation ring but with 4 small connections to the pad in a cross shape. This made the ground pin electrically connected to the ground plane, but gave heat isolation for soldering. Worked very well.

[williamson]

Reply for Ched and Greg: The pencil tip is the right one for the control board. The 180 watt gun is called for in the instructions, for the power board. They recommend one for, I think 29.99. Good recommendations! Having a star pattern around ground plane holes is standard PCB layout proceedure, to stop the heat loss.

[1-ev.com]

I think visual may help....

http://store.curiousinventor.com/gui...r/heat_solder/