Basic Prototyping & Assembly Guide

Soldering Basics Guide

by Leif Erickson

This prototyping and assembly guide will help beginners and students obtain satisfactory results, when soldering electronic components. If you have little or no experience of using a soldering iron, then I recommend that you practice your soldering technique on some old surplus components and clean copper-clad (protoboard), or old circuit boards, before experimenting with a real project. This will help you to avoid the risk of disappointment when you start to assemble your first prototypes. If you've never soldered before, then read on!

Learn how to solder, like a Pro!

If there ever was a skill that needed to be practiced, it was Basic Soldering! This is the most fundamental skill that is overlooked by many electronic shops and labs. Many shops now give a "solder test" to prospective applicants. And with good reason!!

There are many ways to make a solder joint, but only one way to make a perfect joint! "The bigger the blob the better the job", is not one of them, especially with Surface Mount Devices.

Practice on some scrap boards before trying it on something you don't want to lift up pads or traces on. The glue holding the pads and traces onto the pcb, becomes molten soon after! the solder melts!! The smaller the pad, the faster it will come off!, or lift up or slide over to next trace. This gives you a rule - ONLY 3-6 seconds on a pad with a soldering tip!! Or it may come off on your tip!! Then try to put it back onto the board!! TRY Using a little super glue under the pad, and a 1-3 second touch may put it back down. BUT DON'T BREATHE THAT SMOKE! It has cyanides in it!! Poisonous!!!

Its a simple physical and chemical reaction, to form a clean electrical connection. Melting a 63% lead/37% tin mixture we call solder(with some flux mixed in) and "flow" the molten mixture onto 2 separate parts, and join them together. The parts and board should be cleaned first. Using a green scrubbing pad on leads can help if they look oxidized, but watch it on pcb's! The flux will clean some of the dirt and oxidation off the pad and lead when heated, as it is a corrosive acid. This is the bubbling you see and the smoke - DO NOT BREATHE THE SMOKE!! This should be done in a well ventilated area. Lots of shops are not! Hands and face should be washed before eating or touching yourself, after soldering! The acid residue and lead fumes are on your skin!!

You should find a way to secure the pcb so it won't move. A small bench vise can be purchased in many electronic catalogs. Or a small wooden frame clamped on a bench may work. Good lighting is a must, and maybe a magnifier lamp for inspection. The head mounted visor with flip down magnifiers are good too! They look dorkey, but they help a lot! Optivisor is what brand I use.

You can pre-bend the passive component leads first to alleviate the stress when stretching the leads into the holes. It also looks better! Put your parts through the holes and bend them over a little and take care not to have the leads bending down to the hole on the top of pad. Lead should go straight thru the center of the hole. The leads on the back will act as a heat sink to the pads and vias, so leave them on. Unless you have access to a part bender and cutter! Production shops may have these. Hobbyists may buy a plastic lead bender from any electronics catalog or Radio Shack.

It is possible, BUT NOT MANDATORY,to use a lower temperature setting and lower melting point solder for SMD parts. 350-500 degree F melting point solder or solder paste could be used. The paste is harder to control, and may be messier to use on SMD parts. Use a thin diameter solder on SMD parts, 0.015-.020". You can get water based flux, that can be washed off, or, no-clean flux, that is supposed to be less corrosive. Rosin core flux is harder to clean off, and is semi-corrosive to parts and people. Regular solder melts around 450-500 degrees and then starts to flow, so SMD parts are also put together with this, so DON'T HEAT THEM TOO LONG! CAPS ARE THE EASIEST TO DESTROY!

Place your tip on the pad and lead, wait one second, then put solder to the lead and pad, not the tip. Move solder a bit till it starts flowing, then when it looks like enough solder forms your shiny little volcano, get out of there! Most parts have a 10 second max lead life at 650-750 degrees F, so, remember the 3-6 second rule for soldering.

It just takes a quick dab of solder, as the lead and pad is smaller, You just want to flow the lower part of lead to pad, not cover the whole lead. Sometimes there is enough solder on the pad to almost "tack" solder the lead onto pad. Start with a flat clean pad, and flow a little solder onto 1 pad, and hold part with tweezers, while flowing 1 side, and be sure its flat on board. Caps are extremely susceptible to cracking, if heated too much or pushed too hard while soldering. Inspect ALL your caps after soldering, for this. The end caps are held on with solder to the layers inside, and they melt or separate while soldering. BE CAREFUL!

The metal tweezers can act as a heat sink also, curved ones are best. You can put curved side down, hold part on the length of it, steady your hand/tip on pcb, and tack 1 side. Larger more rigid curved or straight tweezers may work better, than the finer ones, for picking up parts. Depends on your preference.

To place resistors, caps and diodes use above process. SOT23 transistors and other 3 legged devices are similar. Tack 1 lead down, be sure it's flat on the board, before proceeding. IC's are a little different. You have to tack 1 lead on, AFTER "registering" all the leads, on ALL the pads. Tack opposite corners, while checking all the leads to pads, and don't forget where Pin #1 goes! Its harder to take off a chip, than put it on!! This goes for any type of chip, 4 pins to as large as you want to solder. Check Pin #1, then solder the rest of the leads on, using the least amount of solder. Pin # 1 is on the side of the chip with a beveled side, and possibly a dot in the plastic package. You want to be able to see the lead on top, not solder (for a professional job).

In circuits with reliability questions, you should trim leads and bend lead over to edge of the pad before soldering, to be safe. If its your own project at home, think about troubleshooting a bad joint on a board. Same goes for work, too. Finding a bad solder joint is not a really fun way to spend your time.

Clean up your flux on the board using isopropyl alcohol, or find a good chemical cleaner at Radio Shack or any electronic catalog. USE CHEMICAL CLEANERS IN WELL VENTILATED AREAS. THEY CAN ATTACK SOME PLASTICS ALSO!! SOME JUST GO BRITTLE AND FALL APART! Use a cleaning brush, found at hardware stores or electronics stores, with the silver tubing handle, and black bristles. They are sold by the handfuls. Cut the bristles so they are about 1/2 inch long, or so. They become more stiff, and will clean the flux off better. There is a trick little unit that has the different chemical spray cans, and a cleaning brush that is connected to the can by metal tubing, so you can spray the cleaner onto pcb, while scrubbing flux off.

Inspect all your soldering, when done, with a magnifying glass. Look for a separation around the lead and the cone tip of solder joint, or pad. A sloping or slightly concave, cone shaped joint, like a tiny volcano, with the lead coming out of the top is best. Clean and shiny is what it should look like! Any grainy or bubbly looking solder should be cleaned off pad and lead, and re-soldered. Use a solder sucker, or desoldering braid. Re-flowing a joint will only make it worse, and possibly heat up the pad and it will fall off.

For wiring the smd parts and other prototype circuits, there are a few kinds of wire to use. Depending on the SMD lead size, most wiring can be done with 30 to 38 gauge solid wire, or the enamel coated magnet or coil wire. PVC hook-up wire,(not good heat resistant insulation) Kynar,(better) and Teflon (more heat resistant) insulation type wire wrap wire(more expensive), or use a multistrand wire, strip off insulation, and tear apart the wire strands with out kinking them.

These are good wire sizes also. Look for telephone wire pieces trimmed off by the phone boxes, they are sometimes fine enough, or use for ground and power, or other hook-ups.

Soldering onto ground planes, or big pads, is a bigger chore, you pre-tin the wire ends, but not all the way to the insulation. Leave room for wire to bend, not all soldered to insulation. Leave some slack in your wiring to components. You may need to move it, or it could break off if too tight and vibrating in a machine. Try to route wiring neatly from the start, use small pieces of wire to wrap up bundles to board holes. Use the wire clippings for other projects. Making ground and power runs on this and other circuits, on the white prototyping boards for jumpers, make test points on the board, etc...

Other ways to solder with surface mount parts: Use a heat gun, or hot plate, to warm up whole or part of a board, (preferably both, heat both sides at same time) use a soldering rework station, costing a few thousand dollars... Some use their ovens to solder parts using solder paste. Infrared lamps may work also.

A Metcal iron is a very good, but $300-700 iron, and tips cost $22-60 each. Weller and others are now selling irons similar to the Metcal series. Constant heat to the tip, and soldering in 5-10 seconds from a cold start! You can solder to a 'real penny' with one of these faster than any other kind, even the huge stained glass type irons(50-200 Watts).

Check out EBAY auctions and flea markets in large cities for used Metcals. Some are floating around at decent prices. I got an older Metcal system, (with the wrong iron holder-the tweezers) for less than $100 with shipping. The tips are available too. The larger Metcals are better for exteneded usage so stay away from the little SP200? system. It uses different tips, the larger ones, MX500 type, all use the same tips. Many to choose from! Pull a chip off with one swipe! They have the hoof tips for soldering the chip side all at once! Go to Metcal.com for lots of soldering info! Links here someplace...

Have you seen the NEW cold tip soldering iron on TV? Heats up in seconds only when on metal? and cools off in 2 seconds to the touch?!?!? Ceramic Space shuttle type tip? And battery operated!! Not sure if its any good for SMD work, but its portable!!

Prototyping a circuit is basically an art form. Each circuit can take many different layouts, but which one is "BEST"? Remember Ohm's Laws, Kirchoff's Laws, and electromagnetic Laws(sometimes called "phenomona"), when building and laying out GROUND and POWER runs. Lay out these 2 like a tree. Use a main trunk for the higher current, then branch out to each area or circuit. No return to the trunk from end of branch, is best, for EMC and other grounding considerations. This is a study on to itself.

PLEASE READ UP ON THIS when and where you can on line!! It is a very important subject to learn early on in engineering! All wires radiate some kind of frequency(ies), depending on the signal going thru it, at the time. Clock and PLL and memory bus signals give off different types of interference to adjacent signals, all depending on trace size, length, thickness and over top of any traces or grounds on opposite side, and type of pc board material, that becomes a capacitor(s)! Very complex RF stuff here!! We are just learning to solder and build circuits!

I am adding a Guitar Amp build page and a Zenith 8G005 Restoration page. Both are just starting, and have just basic info right now, and some pix along the way. Most of the info can be found on my links pages. Its how I figured out what I am getting ready to do with the guitar amps and the TransOceanics. Taking som etime, but hey, I'm OLD, they say... Its easier to build the amps and figure out the rest of the radio circuits after that. I am almost done recapping the 1st 8G005, but other things always get priority.. ..the links to these pages are on other pages right now. Working on them all right now. Lots more TUBE RELATED Links pages, Guitar and Audio Amps!

NEW!

Transistor markings Info :
American and Japanese transistors that are Electronic Industries Association registered, are assigned specific part numbers. Each EIA number has 5 parts to it. 1. It describes device type. Number tells active electronic connections, plus one.
2: Shows part is registered.
3: Gives device polarity and applications.
2SA = Transistor, Hi Frequency, PNP
2SB = Transistor, Low Frequency, PNP
2SC = Transistor, Hi Frequency, NPN
2SD = Transistor, Low Frequency, NPN
2SJ = FET, P Channel
2SK = FET, N Channel
3SK = MOSFET, N Channel
3N = MOSFETS, Dual Triacs
SN = Opto devices

4: EIA/EIAJ reference numbers, are assigned in order of registration, and not to be a reliable guide of device specifications.

5: A letter suffix to part #, usually means an improvement of specifications. A "B" version is newer/better than an "A", or no suffix at all.

The alpha-numeric codes below part #, is a LOT/date code, telling when wafers were built, what line, time, etc...

Getting into deeper subjects:

For an interesting side project, consider what you "know" about electro-magnetics, see what you find out about online searches for Nikola Tesla, Stubblefield, and other 100 year old scientist/engineers way ahead of their time! Make Power from wires in the ground?? See how little is known about their experiments, and how much may be in use already. Search for scalar technology and any words showing up in Tesla searches about his experiments.

The Earth is one BIG iron(metallic) core? with a north and south pole. Our magnetic field protects us from most of the "Radiation" from the sun. Except during solar eruptions, that can cause blackouts here, if strong enough! Wonder why? The storm disrupts our fields, and moving fields do what? Look up SOHO, HAARP, and ELF, Astronomy, Radio Telescopes, Hubble, JPL, NASA, free energy on google.com

There is a New Capacitors Article to read also, see link below!

NEW Capacitor Article-more coming!

For those eager to read up on the EMC/EMI world of "Black Magic" and the "Art of grounding" - Start your journey by, clicking the link below!