How to build a reliable PCB - Fuel Economy, Hypermiling, EcoModding News and Forum

MPaulHolmes · 02-02-2010, 01:47 PM

This is going to be where Clyde, an industry expert, with many years of experience, is going to put his helpful suggestions on soldering, and general assembly of reliable pcbs. It's an important topic that is often ignored.

williamson · 02-03-2010, 11:44 AM

Topic: Solder: The US Military does not allow lead-free. The only reason we have lead-free is that old electronics fill the land-fill. Lead-free does not solder as well as lead. A special solder is used. If you are hand-soldering, try to not buy lead-free parts.

Topic: Solder iron: PCB's are made by gluing a sheet of 1 to 4 oz. copper sheet to an epoxy sheet. So your copper runs on your delivered PCB are glued on. Therfor you should use an iron temperature controlled at 700 deg. Don't hold the iron on the joint longer than needed, and don't PUSH sideways on the joint. Weller irons on ebay are the best, but for some reason they demand almost a "NEW" price! You can buy a "scope cheaper!

williamson · 02-04-2010, 11:35 AM

Topic: Soldering; The industry standard iron is Weller WTCPT.
Topic: Solder removal: There are two ways: 1. solder wick: this is a roll of small copper braid. This braid is laid down on the joint and the tip is applied on top. The heated bare copper melts the solder, and it wicks up the braid. After use, the coated braid is cut off and discarded. All military repair work demands this method. It is a huge pain in the butt. Frankly, I only use the second method.
2. A "Solderpullt". This is the industry stand brand. The problem with this tool is that when it triggers on the hot clad run, it can tear or dislodge the run. So I would call this the BAD-BOY approach. The only help I can offer is to not press the tip hard into the joint.

RobertSmalls · 02-04-2010, 06:12 PM

There's no arguing that lead-tin solder outperforms tin-antimony and other lead-free solders. But I use the lead free stuff despite the 20°C higher melting point. Firstly, because it's readily avaiable. Secondly, because lead is harmful to humans and I don't want to be exposed to it while working on a circuit board. Thirdly, if you use lead, your project is destined to become hazardous waste, which is difficult to dispose of.

Leaded solders are illegal in the more civilized jurisdictions, including California and the EU.

Soldering is coming to be an important skill for all EcoModders, EV operators and otherwise. I'll be learning a bit more by trial and error, and hopefully from the tips here, as I'm assembling a PCB for my Honda.

williamson · 02-05-2010, 03:36 PM

Mr. Smalls is absolutely right. We have 100 years of technicians soldering, and I've never heard of one getting lead poisoning. One should wash your hands after handling lead solder. Each person viewing this site will have to decide his own priorities, when it comes to lead-free. Lead-free is the future. First, we only make one PCB. Any production of more than a few boards should be lead-free. This site is called "a reliable". As stated earlier, the military doesn't allow it because of "wetting". So if you are inexperienced in soldering, you should take into account that lead-free may not "wet" as well. To put this topic to bed, you've heard both sides, and I say, try to do lead-free, if you can.
Topic: "Wetting": In production, parts are sealed in air-tight bags, with a production date sealed in the bag, so it can't be changed. Product is opened and soldered the same day, because old parts develope an oxide coating, that impairs Wetting. We buy left-over parts, that could have spent years on the shelf. So if the component leads look dull, you could clean them just before soldering.

williamson · 02-06-2010, 03:31 PM

Topic: Electrolytic caps: Never buy 'lytics from a manufacturer whose name starts with an "X". Almost all Chinese company names start with "X". The parts are cheaper. Buy only Japanese, such as Nichicon, or Panasonic. Or any Japanese co. Try to buy 105 degree parts. 'lytics fail by drying out. Therefor higher temp parts last longer, and quality sealed parts, ditto. Ten or twenty years ago, people were cleaning PCB's with fluerines. They leaked past the wire leeds on "lytics and quickly destroyed the cap. So epoxy end seals were invented. They work, but usually cost a penny more. If you look under your caps and you see black epoxy, instead of rubber, you know why. Chinese resistors start with "X" but they are fine, and now may be your only source!

williamson · 02-06-2010, 03:38 PM

Topic: board cleaning: When I worked in electronics, I asked an engineer at Kester Solder about board cleaning. He said there was no reason to clean a board of ordinary flux, except for good looks. He said Heathkit and Knight kits were around for years with no cleaning. There have been "No clean" fluxes. They stay on the board and "work" because they are meant to be transparent. Unless you overheat them with an iron. THEN they turn black and very hard to remove. If you choose to go the better route of "lead-free", ask the solder manufacturer if the board must be cleaned.

williamson · 02-07-2010, 05:22 PM

Topic: resistor reliability: small, leaded resistors are a ceramic tube with crimped-on end caps. The carbon coating is then applied. The only failure mode for this construction (the only choice) is to apply a bending force to the end caps. You can buy a bending tool. This tool is a tapered plastic strip, about 5 inches long, with descending widths, to put your part on, and then bend the leads down. If you bend too close to the body, you will loosen the end caps. If your PCB is laid out with minimum leed spacing, you can get into trouble. I don't think anyone can bend a leed with this tool and not tug on the end caps. The SAFEST method is to specify the leed spacing which allows you to use a pair of small needle nose pliers, to hold the leed close the the body, and bend the FREE end.

williamson · 02-08-2010, 12:43 PM

Topic:Parts sources; Mouser seems the best first try. Lower prices than "D". also, odd stuff from "All Electronics", Jameco", and "Futurlec". On that last one, make sure you go to the USA one. My son has a chemical engineering degree from Johns-Hopkins, and he is the VP- Sales for a PCB company. He said that hand-soldering lead-free is 100 times harder than lead-tin. One problem is that if you buy a lead-free PCB that has all the surface-mount parts already mounted, and the PCB is lead-free, then you have to add the remaining thru-hole parts by hand. Then you have to pay attention to "Wetting". Forwarned is forarmed!

williamson · 02-09-2010, 02:43 PM

Topic: heat-shrink tubing: If you strip the insulation from a wire, and then solder the end, and the wire can move, such as being within a car, the wire will only move at its weakest point. This is the tiny section of wire which has been striped of insulation. Therefor, when soldering a wire, slip a short piece (read one-half inch) of heat-shink tubing over the wire and down over the terminal. You can shrink the tubing with your iron. In industry, the tubing is shrunk by a heat gun (read:blow-dryer). The tubing is sold by as supplied inside diameter. It comes in many chemistries. For our work, the cheapest chemistry is best. That's usually Polyolifin.The most typical diameter is 1/8 inch. You can solder two wires together "in mid air" by sleeving the joint.