Tips on PCB Stuffing

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During the course of 2008, all of London Power's kits acquired PCBs. The newer Power Scaling Kits have them, and the older kit, our PSK-1, also had a PCB.

Certain methods of handling components and installing them can make the already "easy" task of PCB assembly even simpler.

With any kit or project, it is best to organize the components. If it is a kit, empty the parts out of the bag, identify them, group them, and make sure everything is present. Look at the kit notes and make sure you have a reasonable understanding of what will be involved. Kit notes are not intended to be circuit tutorials - that is what the books are for - but they will show you how to assemble the given circuit and how to tie it in to other circuits as appropriate.

Some components stay cool during operation, so they can be pushed all the way down to the PCB. That is, their leads are inserted into the holes, and the body of the component made to rest on the PCB. On the solder-side - also called the "foil side" or "copper side" - before installing the components, bend their leads outward or inward slightly. This will keep the part from falling off the board when you flip it over to solder the leads.

Install a few components at a time, starting with parts that mount fully pressed down to the PCB. This includes diodes and low-wattage resistors (1/4W, 1/2W, 600mW).

When soldering each lead, a proper connection should take less than ten seconds. Prior to soldering, add solder to the tip of the iron and then wipe the soldering iron tip on a wet sponge. This removes the solder you just applied and "wets" the tip - primes it with solder so it can more easily heat the solder you wish to apply to the connection. Touch the tip to the lead and trace. Touch the solder to the tip and then move it to the opposite side of the lead. Solder will flow around the lead and cover the pad. This should happen in just a few seconds. As soon as the solder has flowed all the way around the pad, remove the iron.

You can solder several connections in a row with each treatment of the iron tip. Never wipe the iron tip on the sponge prior to placing the iron in the holder. Leave it dirty, and even add some solder to the tip just before placing it in the holder. At the beginning of the next set of connections, wipe the tip on the sponge. Double check that the tip is shiny with solder and no dirt is present on the tip.

Trim the excess leads of the components you've just installed. Use flush-cutting snips to cut the leads just at the peak of the solder slope around the lead. There is no benefit in leaving long leads, and in fact, longer leads may cause electrical hazard or failure.

After all of the short components are mounted, move to taller items. If there are semiconductors other than diodes, now is the time to mount them. Push the leads through the holes but leave at least 1/4" (6mm) above the PCB. The splaying of the leads going through the holes will provide enough friction to hold the parts in place when you flip the board over. Again, solder quickly but effectively. Do not cut across multiple leads of transistors, etc. This can reduce the effective spacing of the leads. Snip each lead individually.

Power resistors must be mounted with space between their body and the PCB. Just because a flame-proof resistor won't burst into flames, one cannot assume that it won't get hot enough to burn the PCB. Half-an-inch or 12mm is good here. Hold the resistor body between your thumb and finger. Use your other hand to gently bend the leads perpendicular to the body. They should curve out away from the body rather than bend at a sharp angle. Insert the leads into the holes and push the part down. You must squeeze the leads slightly at the body as you push the leads farther down. This keeps tension on the leads so that the resistor will not fall out when you turn the board over for soldering.

Next, mount taller parts, or heavier and bulkier parts. This includes small transformers, caps, tube sockets, pots, relays, fuse clips, etc. Some components are subject to external forces (tube sockets, fuse holders) while others can impart forces onto the board due to their weight (transformers, large caps). In either case, once the leads are pushed through the PCB, bend the protruding lead over for mechanical retention of the part. Then solder as usual.

Secure the PCB using metal stand-offs and/or metal bolts and nuts. Plastic mounts can be microphonic.

Note that it is important not to bend most component leads right at the body of the component. For devices with short leads that must be formed, use needle-nose pliers to bend the leads as required. Do not bend leads to precisely align with the holes in the board lest the part falls out when you flip it over to solder.

See also PCBs - Colour Considerations and PCBs vs. Hand-Wiring

About London Power

London Power was founded in 1990 by Kevin O'Connor, after two decades of research into innovative audio amplification techniques. Kevin is an audio designer, author and speaker, known for his proprietary methodology called Power Scaling, and for his eleven books on audio subjects. Whether you seek amps, kits or information, you'll find useful answers here on not just the "how" but the "why" of audio amplifier design. Please enjoy the information on this site, and don't hesitate to contact us with questions.

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