23.pdf

Contents

23.1 Electronic Shop Safety

23.1.1 Soldering safety

23.1.2 Chemicals

23.2 Tools And Their Use

23.2.1 Sources of Tools

23.2.2 Tool Descriptions and Uses

23.3 Soldering Tools and Techniques

23.3.1 Soldering Irons

23.3.2 Solder

23.3.3 Soldering

23.3.4 Desoldering

23.4 Surface Mount Technology (SMT)

23.5 Electronic Circuits

23.5.1 Electrostatic Discharge (ESD)

23.5.2 Electronics Construction Techniques

23.5.3 Printed-Circuit Boards

23.5.4 From Schematic to Working Circuit

23.5.5 Other Construction Techniques

23.6 Mechanical Fabrication

23.6.1 Cutting and Bending Sheet Metal

23.6.2 Finishing Aluminum

23.6.3 Chassis Working

23.6.4 Drilling Techniques

23.6.5 Construction Notes

23.4.1 Equipment Needed

23.4.2 Surface-Mount Parts

23.4.3 SMT Soldering Basics

23.4.4 Removing SMT Components

Chapter 23

Circuit Construction

23.1 Electronic Shop Safety

Building, repairing and modifying equipment in home workshops is a longstanding

ham radio tradition. In fact, in the early days, building your own equipment was the only

option available. While times and interests change, home construction of radio equipment

and related accessories remains popular and enjoyable. Building your own gear need not

be hazardous if you become familiar with the hazards, learn how to perform the necessary

functions and follow some basic safe practices including the ones listed below. Let’s start

with our own abilities:

Consider your state of mind. Working on projects or troubleshooting (especially where

high voltage is present) requires concentration. Don’t work when you’re tired or distracted.

Be realistic about your ability to focus on the job at hand. Put another way, if we aren’t able

to be highly alert, we should put off doing hazardous work until we are able to focus on the

hazards.

Think! Pay attention to what you are doing. No list of safety rules can cover all possibilities.

Safety is always your responsibility. You must think about what you are doing, how it relates

to the tools and the specific situation at hand. When working with tools, avoid creating situ-

ations in which you can be injured or the project damaged if things don’t go “just right.”

Take your time. If you hurry, not only will you make more mistakes and possibly spoil the

appearance of your new equipment, you won’t have time to think things through. Always

plan ahead. Do not work with shop tools if you can’t concentrate on what you are doing —

it’s not a race!

Protect yourself. Use of drills, saws, grinders and other wood- or metal-working equip-

ment can release small fragments that could cause serious eye damage. Always wear safety

glasses or goggles when doing work that might present a flying object hazard and that includes

soldering, where small bits of molten solder can be flung a surprising distance. If you use

hammers, wire-cutters, chisels and other hand tools, you will also need the protection that

safety eyewear offers. Dress appropriately — loose clothing (or even hair) can be caught in

exposed rotating equipment such as drill presses.

Don’t work alone. Have someone nearby who can help if you get into trouble when work-

ing with dangerous equipment, chemicals or voltages.

Know what to do in an emergency. Despite your best efforts to be careful, accidents may

still occur from time to time. Ensure that everyone in your household knows basic first aid

procedures and understands how to summon help in an emergency. They should also know

where to find and how to safely shut down electrical power in your shack and shop. Get

medical help when necessary. Every workshop should contain a good first-aid kit. Keep an

eye-wash kit near any dangerous chemicals or power tools that can create chips or splinters.

If you become injured, apply first aid and then seek medical help if you are not sure that

you are okay. Even a small burn or scratch on your eye can develop into a serious problem

if not treated promptly.

What about the equipment and tools involved in shop work? Here are some basic safety

considerations that apply to them, as well:

Read instructions and manuals carefully…and follow them. The manufacturers of tools are the

most knowledgeable about how to use their products safely. Tap their knowledge by carefully

reading all operating instructions and warnings. Avoiding injuries with power tools requires

Home construction of electron-

ics projects can be a fun part of

Amateur Radio. Some say that

hams don’t build things nowadays;

this just isn’t so! A recent ARRL

survey shows that more than

half of active hams build some

electronic projects. When you go

to any ham flea market, you see

row after row of dealers selling

electronic components; people

are leaving those tables with

bags of parts. They must be doing

something with them!

Even experienced construc-

tors will find valuable tips in this

chapter. It discusses tools and

their uses, electronic construc-

tion techniques, tells how to turn

a schematic into a working circuit

and then summarizes common

mechanical construction practices.

Originally written and compiled by

Ed Hare, W1RFI, this chapter was

updated by Jim Duffey, KK6MC

with contributions from Chuck

Adams, K7QO.

Circuit Construction

23.1

safe tool design as well as proper operation by

the user. Keep the instructions in a place where

you can refer to them in the future.

Respect safety features of the equipment

you work on and use. Never disable any safety

feature of any tool. If you do, sooner or later

you or someone else will make the mistake the

safety feature was designed to prevent.

Keep your shop or work area neat and or-

ganized. A messy shop is a dangerous shop. A

knife left laying in a drawer can cut someone

looking for another tool; a hammer left on top

of a shelf can fall down at the worst possible

moment; a sharp tool left on a chair can be a

dangerous surprise for the weary constructor

who sits down.

Keep your tools in good condition. Always

take care of your investment. Store tools in a

way to prevent damage or use by untrained

persons (young children, for example). Keep

the cutting edges of saws, chisels and drill

bits sharp. Protect metal surfaces from corro-

sion. Frequently inspect the cords and plugs

of electrical equipment and make any neces-

sary repairs. If you find that your power cord

is becoming frayed, repair it right away. One

solution is to buy a replacement cord with a

molded connector already attached.

Make sure your shop is well ventilated.

Paint, solvents, cleaners or other chemicals

can create dangerous fumes. If you feel dizzy,

get into fresh air immediately, and seek medi-

cal help if you do not recover quickly.

Respect power tools. Power tools are not

forgiving. A drill can go through your hand

a lot easier than metal. A power saw can

remove a finger with ease. Keep away from

the business end of power tools. Tuck in your

shirt, roll up your sleeves and remove your tie

before using any power tool. If you have long

hair, tie it back so it can’t become entangled

in power equipment.

fumes is also hazardous. When smoking was

common, it was not uncommon to see techni-

cians who smoked light cigarettes with their

soldering iron. This should not be done.

Soldering equipment gets hot ! Be care-

ful. Treat a soldering iron as you would any

other hot object. A soldering iron stand is

helpful, preferably one that has a cage that

surrounds the hot tip of the iron. Here’s a help-

ful tip — if the soldering iron gets knocked

off the bench, train yourself not to grab for

it because the chances are good that you’ll

grab the hot end!

Generally, solder used for electronic com-

ponents contains a flux that assists the solder

in making a thoroughly wetted joint. (Never

use acid-flux, as described in the section on

soldering.) When heated, the flux gives off a

vapor in the form of a light gray smoke-like

plume. This flux vapor, which often contains

aldehydes, is a strong irritant and can cause

potentially serious problems to persons who

may have respiratory sensitivity conditions

including those who suffer from asthma. In

most cases it is relatively easy to use a small

fan to move the flux vapor away from your

eyes and face. Opening a window provides

additional air exchange. In extreme cases use

an organic vapor cartridge respirator.

Solvents are often used to remove excess

flux after the parts have cooled to room tem-

perature. Minimize skin contact with solvents

by wearing molded gloves resistant to the

solvent. If you use a solvent to remove flux,

it is best to use the mildest one that does the

job. Isopropyl alcohol, or rubbing alcohol, is

often sufficient. Some water-soluble solder

fluxes can be removed with water.

Observe these precautions to protect your-

self and others:

• Properly ventilate the work area. If you

can smell fumes, you are breathing them.

• Wash your hands after soldering, espe-

cially before handling food.

• Minimize direct contact with flux and

flux solvents. Wear disposable surgical

gloves when handling solvents.

For more information about soldering haz-

ards and the ways to make soldering safer,

see “Making Soldering Safer,” by Brian P.

Bergeron, MD, NU1N (Mar 1991 QST , pp

28-30) and “More on Safer Soldering,” by

Gary E. Meyers, K9CZB (Aug 1991 QST ,

p 42).

Read the information that accompanies the

chemical and follow the manufacturer’s rec-

ommended safety practices. If you would like

more information than is printed on the label,

ask for a material safety data sheet (MSDS).

Material safety data sheets are available on the

Internet from several sources, such as www.

meridianeng.com/datasheets.html . Manu-

facturers of brand-name chemical products

usually post an MSDS on their product Web

sites.

Store chemicals properly, away from sun-

light and sources of heat. Secure their con-

tainers to prevent spills and so that children

and untrained persons will not gain access.

Always keep containers labeled so there is

no confusion about the contents. It is best to

use the container in which the chemical was

purchased. If you transfer solvents to other

containers, such as wash bottles, label the new

container with exactly what it contains.

Handle chemicals carefully to avoid spills.

Clean up any spills or leaks promptly but don’t

overexpose yourself in the process. Never

dispose of chemicals in household sinks or

drains. Instead, contact your local waste plant

operator, transfer station or fire department to

determine the proper disposal procedures for

your area. Many communities have house-

hold hazardous waste collection programs.

Of course, the best solution is to only buy the

amount of chemical that you will need, and

use it all if possible. Always label any waste

chemicals, especially if they are no longer

in their original containers. Oil-filled capaci-

tors and transformers were once commonly

filled with oil containing PCBs. Never dispose

of any such items that may contain PCBs in

landfills.

Always use recommended personal protec-

tive equipment (such as gloves, face shield,

splash goggles and aprons). If corrosives (ac-

ids or caustics) are splashed on you immedi-

ately rinse with cold water for a minimum

of 15 minutes to flush the skin thoroughly.

If splashed in the eyes, direct a gentle stream

of cold water into the eyes for at least 15

minutes. Gently lift the eyelids so trapped

liquids can be flushed completely. Start flush-

ing before removing contaminated clothing.

Seek professional medical assistance. If using

hazardous chemicals, it is unwise to work

alone since people splashed with chemicals

need the calm influence of another person.

Food and chemicals don’t mix. Keep food,

drinks and cigarettes away from areas where

chemicals are used and don’t bring chemicals

to places where you eat.

Table 23.1 summarizes the uses and haz-

ards of chemicals used in the ham shack. It

includes preventive measures that can mini-

mize risk. Additional safe chemical handling

information can be found on the Internet at

www2.umdnj.edu/eohssweb/aiha/techni-

cal/msds.htm .

23.1.1 Soldering Safety

Soldering requires a certain degree of

practice and, of course, the right tools. What

potential hazards are involved?

Since the solder used for virtually all elec-

tronic components is a lead-tin alloy, the first

thing in most people’s minds is lead, a well-

known health hazard. There are two primary

ways lead might enter our bodies when solder-

ing: we could breathe lead fumes into our lungs

or we could ingest (swallow) lead or lead-

contaminated food. Inhalation of lead fumes is

extremely unlikely because the temperatures

ordinarily used in electronic soldering are far

below those needed to vaporize lead. Never-

theless, since lead is soft and we may tend to

handle it with our fingers, contaminating our

food is a real possibility. For this reason, wash

your hands carefully after any soldering (or

touching of solder connections).

Handling lead or breathing soldering

23.1.2 Chemicals

We can’t seem to live without the use of

chemicals, even in the electronics age and a

number of chemicals are used every day by

amateurs without causing ill effects. A sen-

sible approach is to become knowledgeable

of the hazards associated with the chemicals

we use and treat them with respect. Here are

a few key suggestions:

23.2

Chapter 23

Table 23.1

Properties and Hazards of Chemicals often used in the Shack or Workshop

Generic Chemical Name

Purpose or Use

Hazards

Ways to Minimize Risks

Lead-tin solder

Bonding electrical

Lead exposure

Always wash hands after

components

(mostly from hand contact)

soldering or touching solder.

Flux exposure (inhalation)

Use good ventilation.

Isopropyl alcohol

Flux remover

Dermatitis (skin rash)

Wear molded gloves suitable

for solvents.

Vapor inhalation

Use good ventilation and

avoid aerosol generation.

Fire hazard

Use good ventilation, limit use to

small amounts, keep ignition

sources away, dispose of

rags only in tightly sealed

metal cans.

Freons

Circuit cooling and

Vapor inhalation

Use adequate ventilation.

general solvent

Dermatitis

Wear molded gloves suitable

for solvents.

Phenols and

Enameled wire/

Strong skin corrosive

Avoid skin contact; wear

methylene chloride

paint stripper

suitable molded gloves; use

adequate ventilation.

Beryllium oxide

Ceramic insulator that

Toxic when in ine dust

Avoid grinding, sawing or

can conduct heat well

form and inhaled

reducing to dust form.

Beryllium metal

Lightweight metal,

Same as beryllium oxide

Avoid grinding, sawing,

alloyed with copper

welding or reducing to dust.

Contact supplier for special

procedures.

Various paints

Finishing

Exposures to solvents

Adequate ventilation; use

respirator when spraying.

Exposures to sensitizers

Adequate ventilation and

(especially urethane paint)

use respirator.

Exposure to toxic metals

Adequate ventilation and

(lead, cadmium, chrome,

use respirator.

and so on) in pigments

Fire hazard (especially

Adequate ventilation;

when spray painting)

control of residues; eliminate

ignition sources.

Ferric chloride

Printed circuit

Skin and eye contact

Use suitable containers;

board etchant

wear splash goggles and

molded gloves suitable for acids.

Ammonium persulphate

Printed circuit

Skin and eye contact

Use suitable containers;

and mercuric chloride

board etchants

wear splash goggles and

molded gloves suitable for acids.

Epoxy resins

General purpose

Dermatitis and possible

Avoid skin contact. Mix

cement or paint

sensitizer

only amount needed.

Sulfuric acid

Electrolyte in

Strong corrosive when

Always wear splash goggles and

lead-acid batteries

on skin or eyes.

molded plastic gloves (PVC) when

Will release hydrogen

handling. Keep ignition sources

when charging (ire,

away from battery when charging.

explosion hazard).

Use adequate ventilation.

Circuit Construction

23.3

23.2 Tools and Their Use

All electronic construction makes use of

tools, from mechanical tools for chassis fab-

rication to the soldering tools used for circuit

assembly. A good understanding of tools and

their uses will enable you to perform most

construction tasks.

While sophisticated and expensive tools

often work better or more quickly than simple

hand tools, with proper use, simple hand tools

can turn out a fine piece of equipment. Table

23.2 lists tools indispensable for construction

of electronic equipment. These tools can be

used to perform nearly any construction task.

Add tools to your collection from time to

time, as finances permit.

Radio equipment. (The ARRL’s Technical

Information Service at www.arrl.org/tis lists

numerous sources of tools and supplies.) Bar-

gains are available at ham flea markets or

local neighborhood sales, but beware! Some

flea-market bargains are really shoddy and

won’t work very well or last very long. Some

used tools are offered for sale because the

owner is not happy with their performance.

There is no substitute for quality! A high-

quality tool, while a bit more expensive, will

last a lifetime. Poor quality tools don’t last

long and often do a poor job even when brand

new. You don’t need to buy machinist-grade

tools, but stay away from cheap tools; they are

not the bargains they might appear to be.

Dull or broken tools can be safety hazards.

Tools that are in good condition do the work

for you; tools that are misused or dull are

difficult to use.

Store tools in a dry place. Tools do not fit

in with most living-room decors, so they are

often relegated to the basement or garage.

Unfortunately, many basements or garages

are not good places to store tools; dampness

and dust are not good for tools. If your tools

are stored in a damp place, use a dehumidifier.

Sometimes you can minimize rust by keeping

your tools lightly oiled, but this is a second-

best solution. If you oil your tools, they may

not rust, but you will end up covered in oil

every time you use them. Wax or silicone

spray is a better alternative.

Store tools neatly. A messy toolbox, with

tools strewn about haphazardly, can be more

than an inconvenience. You may waste a lot

of time looking for the right tool and sharp

23.2.1 Sources of Tools

Electronic-supply houses, mail-order/Web

stores and most hardware stores carry the

tools required to build or service Amateur

CARE OF TOOLS

The proper care of tools is more than a

matter of pride. Tools that have not been cared

for properly will not last long or work well.

Table 23.2

Recommended Tools and Materials

Simple Hand Tools

Screwdrivers

Slotted, 3-in, 1 ⁄ 8 -in blade

Slotted, 8-in, 1 ⁄ 8 -in blade

Slotted, 3-in, 3 ⁄ 16 -in blade

Slotted, stubby, 1 ⁄ 4 -in blade

Slotted, 4-in, 1 ⁄ 4 -in blade

Slotted, 6-in, 5 ⁄ 16 -in blade

Phillips, 2 1 ⁄ 2 -in, #0 (pocket clip)

Phillips, 3-in, #1

Phillips, stubby, #2

Phillips, 4-in, #2

Long-shank screwdriver with holding clip on

blade

Jeweler’s set

Right-angle, slotted and Phillips

Pliers, Sockets and Wrenches

Long-nose pliers, 6- and 4-in

Diagonal cutters, 6- and 4-in

Channel-lock pliers, 6-in

Slip-joint pliers

Locking pliers (Vise Grip or equivalent)

Socket nut-driver set, 1 ⁄ 16 - to 1 ⁄ 2 -in

Set of socket wrenches for hex nuts

Allen (hex) wrench set

Wrench set

Adjustable wrenches, 6- and 10-in

Tweezers, regular and reverse-action

Retrieval tool/parts holder, lexible claw

Retrieval tool, magnetic

Cutting and Grinding Tools

File set consisting of lat, round, half-round,

and triangular. Large and miniature types

recommended

Burnishing tool

Wire strippers

Wire crimper

Hemostat, straight

Scissors

Tin shears, 10-in

Hacksaw and blades

Soldering iron, 200-W, 5 ⁄ 8 -in tip

Solder, 60/40, rosin core

Soldering gun, with assorted tips

Desoldering tool

Desoldering wick

Safety

Safety glasses

Hearing protector, earphones or earplugs

Fire extinguisher

First-aid kit

Useful Materials

Medium-weight machine oil

Contact cleaner, liquid or spray can

RTV sealant or equivalent

Electrical tape, vinyl plastic

Sandpaper, assorted

Emery cloth

Steel wool, assorted

Cleaning pad, Scotchbrite or equivalent

Cleaners and degreasers

Contact lubricant

Sheet aluminum, solid and perforated, 16- or

18-gauge, for brackets and shielding.

Aluminum angle stock, 1 ⁄ 2 × 1 ⁄ 2 -in and 1 ⁄ 4 -in

diameter round brass or aluminum rod (for

shaft extensions)

Machine screws: Round-head and lat

head, with nuts and lockwashers to it.

Most useful sizes: 4-40, 6-32 and 8-32, in

lengths from 1 ⁄ 4 -in to 1 1 ⁄ 2 in (Nickel-plated

steel is satisfactory except in strong RF

ields, where brass should be used.)

Bakelite, Lucite, polystyrene and copper-clad

PC-board scraps.

Soldering lugs, panel bearings, rubber

grommets, terminal-lug wiring strips,

varnished-cambric insulating tubing, heat-

shrinkable tubing

Shielded and unshielded wire

Tinned bare wire, #22, #14 and #12

Enameled wire, #20 through #30

Hand nibbling tool (for chassis-hole cutting)

Scratch awl or scriber (for marking metal)

Heavy-duty jackknife

Knife blade set (X-ACTO or equivalent)

Machine-screw taps, #4-40 through #10-32

thread

Socket punches, 1 ⁄ 2 in, 5 ⁄ 8 in, 3 ⁄ 4 in, 1 1 ⁄ 8 in,

1 1 ⁄ 4 in, and 1 1 ⁄ 2 in

Tapered reamer, T-handle, 1 ⁄ 2 -in maximum

width

Deburring tool

Miscellaneous Hand Tools

Combination square, 12-in, for layout work

Hammer, ball-peen, 12-oz head

Hammer, tack

Bench vise, 4-in jaws or larger

Center punch

Plastic alignment tools

Mirror, inspection

Flashlight, penlight and standard

Magnifying glass

Ruler or tape measure

Dental pick

Calipers

Brush, wire

Brush, soft

Small paintbrush

IC-puller tool

Hand-Powered Tools

Hand drill, 1 ⁄ 4 -in chuck or larger

High-speed drill bits, #60 through 3 ⁄ 8 -in

diameter

Power Tools

Motor-driven emery wheel for grinding

Electric drill, hand-held

Drill press

Miniature electric motor tool (Dremel or

equivalent) and accessory drill press

Soldering Tools and Supplies

Soldering pencil, 30-W, 1 ⁄ 8 -in tip

23.4

Chapter 23

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