Vectronics VEC-1500K User Manual

IMPORTANT WARRANTY INFORMATION! PLEASE READ

Return Policy on Kits When Not Purchased Directly From Vectronics: Before continuing any further with your VEC kit check with your Dealer about their return policy. If your Dealer allows returns, your kit must be returned before you begin construction.

Return Policy on Kits When Purchased Directly From Vectronics: Your VEC kit may be returned to the factory in its pre-assembled condition only. The reason for this stipulation is, once you begin installing and soldering parts, you essentially take over the role of the device's manufacturer. From this point on, neither Vectronics nor its dealers can reasonably be held accountable for the quality or the outcome of your work. Because of this, Vectronics cannot accept return of any kit-in-progress or completed work as a warranty item for any reason whatsoever. If you are a new or inexperienced kit builder, we urge you to read the manual carefully and determine whether or not you're ready to take on the job. If you wish to change your mind and return your kit, you may--but you must do it before you begin construction, and within ten (10) working days of the time it arrives.

Vectronics Warrants: Your kit contains each item specified in the parts list.

Missing Parts: If you determine, during your pre-construction inventory, that any part is

missing, please contact Vectronics and we'll send the missing item to you free of charge. However, before you contact Vectronics, please look carefully to confirm you haven't misread the marking on one of the other items provided with the kit. Also, make certain an alternative part hasn't been substituted for the item you're missing. If a specific part is no longer available, or if Engineering has determined that an alternative component is more suitable, Vectronics reserves the right to make substitutions at any time. In most cases, these changes will be clearly noted in an addendum to the manual.

Defective Parts: Today's electronic parts are physically and electrically resilient, and defective components are rare. However, if you discover an item during your pre-construction inventory that's obviously broken or unserviceable, we'll replace it. Just return the part to Vectronics at the address below accompanied with an explanation. Upon receipt, we'll test it. If it's defective and appears unused, we'll ship you a new one right away at no charge.

Missing or Defective Parts After You Begin Assembly: Parts and materials lost or damaged after construction begins are not covered under the terms of this warranty. However, most parts supplied with VEC kits are relatively inexpensive and Vectronics can replace them for a reasonable charge. Simply contact the factory with a complete description. We'll process your order quickly and get you back on track.

Factory Repair After You Begin Assembly: Kits-in progress and completed kits are specifically excluded from coverage by the Vectronics warranty. However, as a service to

customers, technicians are available to evaluate and repair malfunctioning kits for a minimum service fee of $18.00 (½ hour rate) plus $7.00 shipping and handling (prices subject to change). To qualify for repair service, your kit must be fully completed, unmodified, and the printed circuit board assembled using rosin-core solder. In the event your repair will require more than an hour to fix (or $36.00, subject to change), our technicians will contact you in advance by telephone before performing the work. Defective units should be shipped prepaid to: Vectronics

300 Industrial Park Road Starkville, MS 39759

When shipping, pack your kit well and include the minimum payment plus shipping and handling charges ($25.00 total). No work can be performed without pre-payment. Also, provide a valid UPS return address and a day time phone number where you may be reached.

Table of Contents

INTRODUCTION .............................................................. 1

VECTRONICS SOLDERING COURSE LESSONS.......... 2

LESSON 1

Solder Alloys And Wire....................................................................... 2

LESSON 2

Kinds of Flux ....................................................................................... 6

LESSON 3

Soldering--Health and Safety ............................................................... 11

LESSON 4

Soldering Irons..................................................................................... 13

LESSON 5

Soldering Iron Tips .............................................................................. 19

LESSON 6

Tip and Iron Maintenance .................................................................... 21

LESSON 7

Soldering Applications......................................................................... 24

LESSON 8

Component Handling and Preparation ................................................. 32

LESSON 9

Desoldering for Repair or Replacement............................................... 36

VECTRONICS SOLDERING COURSE QUIZZES ........... 39

Lesson 1 Solder Alloys and Wire....................................................... 39

Lesson 2 Kinds of Flux ...................................................................... 40

Lesson 3 Soldering Health and Safety................................................ 41

Lesson 4 Soldering Irons.................................................................... 42

Lesson 5 Soldering Iron Tips ............................................................. 43

Lesson 6 Iron and Tip Maintenance................................................... 44

Lesson 7 Soldering Applications........................................................ 45

Lesson 8 Component Handling and Preparation ................................ 46

Lesson 9 Desoldering for Repair and Replacement ........................... 47

Answers to quizzes............................................................................... 48

VECTRONICS SOLDER COURSE LAB .......................... 49

Parts List .............................................................................................. 49

Parts Placement Diagram ..................................................................... 50

Step-By-Step Assembly Instructions.................................................... 50

Operating Instructions.......................................................................... 60

In Case of Difficulty............................................................................. 60

Theory of Operation............................................................................. 61

Specifications ....................................................................................... 61

Schematic............................................................................................. 62

INTRODUCTION

Like technology itself, the art and science of soldering has advanced a great deal over the years. This course covers all the latest tools, techniques, and materials you'll need for "through-hole" style PC board assembly and repair. By the time you complete it, you'll be ready to tackle a wide range of jobs on the bench and in the field.

Before you begin work, take a few minutes to browse through the course manual. As you will see, this course contains three main sections. In the first main section, you'll find nine short and detailed lessons that cover topics like solders and fluxes, product safety, soldering irons, circuit boards, component handling, and much more. The next section contains quizzes to reinforce the material you've read in each lesson. Be sure to use this section; it can be a valuable study aid.

In last section of this course, you'll find step-by-step instructions for the laboratory portion of the course. This exercise requires a well-lighted and uncluttered workspace along with some basic soldering tools and materials. Make a list of the items you'll need to complete the lab, and round them up ahead of time.

To avoid "information overload", limit reading to one lesson per study session. The more carefully you work, the more you'll remember later on--when it really counts.

VECTRONICS SOLDERING COURSE LESSONS

LESSON 1

Solder Alloys And Wire

A few short years ago, choosing the right type of solder was easy--you bought "rosin core" for electronics and "acid core" for plumbing. These days, it's a little more complex! Distributors now offer a wide range of solder alloys, wire sizes, core types, and fluxes--not to mention many supplemental soldering aids and chemicals. While all of these options let you select products especially matched to every job, the choices can get confusing. In this session, we'll survey a range of solder products used for electronic bench work--and look at how to use them safely.

Properties and Characteristics of Common Solder Alloys: Over time, solder has proven to be the most efficient and economical way to connect individual electronic components together into complex patterns of circuitry. To find out why it works so well, we'll start with a definition. The McGraw-Hill Electronics Dictionary defines "solder" this way:

Solder (1.) An alloy that can be melted at a fairly low temperature, for joining metals which have much higher melting point. An alloy of lead and tin in approximately equal proportions is the solder most often used for making permanent joints in electronic circuits.

Solder is unique because it's a solid at room temperature, but melts easily to bond with other metals. Once cool, it provides a strong mechanical joint to hold components in place, and it provides a low-resistance electrical path for efficient electrical flow. Best of all, the soldering process is reversible. If you want to replace a component or move a wire later on, you can do it. Little wonder soldering is the process of choice for a wide range of assembly tasks ranging from the laboratory bench to the manufacturing production-line!

The Three States of Solder: Solder does more than simply "melt" as it gets hot. Solder alloys exhibit three distinct physical states during the heating and cooling process. These are:

Solid State: At room temperature, solder behaves as a "frozen" metal--it's solid and mechanically stable. The exact temperature where solder begins to "thaw" depends upon the mixture of metals in the alloy. Most electronic solders change state at between 360 and 420 degrees F.

Plastic State

: As solder begins to "melt", it first changes into a pasty, unstable, soft material. If a cooling solder joint is vibrated or moved while in the plastic state, the resulting connection will appear dull, grainy, and the joint may fracture. To prevent fractures, most electronic solders are specially formulated to minimize their "plastic-state" temperature range. This makes the transition from a liquid to a solid more rapid.

Liquidous State: As temperature rises, solder changes from a plastic paste to a thick, syrupy, molten liquid. This is called the liquidous state. When solder is in the liquidous state, it can flow, "wet", and adhere to many electrically conductive metals such a copper, tin, silver, and brass. However, electronic solders don't adhere to all conductive metals. It won't stick to aluminum, for example. The metals it adheres to are called solderable metals.

Composition of Solder Alloys: We've said that most solder alloys consist of near-equal mixtures of tin and lead. Normally, pure tin melts at 450-degrees F and pure lead melts at 621 degrees F. However, when we combine the two into an alloy, the melting point becomes lower. The actual temperature depends upon percentage of tin to lead--as measured by weight. The two alloys used most commonly for electronic solder are:

60/40 Alloy: Solder containing 60% tin and 40% lead begins to melt at around 374 degrees F with a plastic range of 13 degrees F. This mix provides a relatively low melting point, which helps to limit thermal stress on sensitive electronic components. The 60/40 alloy also provides superior wetting on solderable metals. "Wetting" refers to liquidous solder's ability to spread over the surface of another metal and adhere to it. In addition to superior wetting, 60/40 solder has a moderate ability to bridge short gaps between metal surfaces. "Gapping" is especially useful for assembly jobs where contact between conductive surfaces may be loose or incomplete.

63/37 Solder: Solder containing a mixture of 63% tin and 37% lead begins to melt at around 364 degrees F--slightly lower than the 60/40 alloy. The 63/37 alloy is unique because it has an extremely narrow plastic-state temperature range--only a degree or two. Because of this characteristic, the transition from a liquidous state to a solid state is virtually instantaneous. Alloys that "set" this quickly during cooling are called eutectic (you-tech-tic) solders. The 63/37 alloy exhibits less gapping and less movement from contraction during cooling.

Both alloys are extremely popular for general-purpose hand soldering. The 60/40 alloy generally works better for single-sided circuit board assembly, handwiring, larger connector installations, and any other application where superior wetting or moderate gapping is beneficial. The 63/37 alloy works better for assembling crowded multi-layer PC boards and for making surface-mount repairs. These are applications where gapping could cause unwanted short-

circuits and where joint contraction might move tiny surface-mount parts out of position during cooling. As a rule, however, either type may be used interchangeably for most bench applications.

Specialty Solders: In addition to the popular 60/40 and 63/37 alloys, electronics distributors now offer a variety of specialty solders. Specialty solders have unique properties that are well matched to specific electronic applications. Here are some of the more popular types:

2% Silver Solder: This lead/tin/silver alloy provides a somewhat higher melting point, improved conductivity, and increased strength over 60/40 and 63/37 solders. The 2% alloy works well where added joint durability is needed, or in applications where high operating temperatures and strong electrical currents may work together to melt conventional solders.

Low-Temperature Solder: This alloy melts at a significantly lower temperature than 63/37 or 60/40, reducing the risk of thermal damage to unusually heatsensitive electronic components. The most popular low-temp formula combines a mix of 43% tin, 43% lead, and 14% bismuth into an alloy that melts at 295-325 degrees F. Some low-temperature solders are highly toxic, so be sure to read instructions carefully before using them.

Lead-free Solder: Lead is a toxic substance that accumulates in the body. Because of this, leaded solders can't be used in some applications or handled by people who are medically at-risk for lead contamination. As an alternative, Tin/antimony solder alloys provide a low-toxicity bond for electronic applications where environmental protection or medical safety is important. A tin/silver alloy may also fulfill this requirement.

Commonly Available Forms of Solder

Wire solder comes in a variety of standard diameters and core configurations. Most have one or more hollow cores filled with flux. Flux is an essential chemical agent used to free metal surfaces of oxides during heating. Dispensing flux via a hollow core in the solder wire controls the delivery rate and ensures uniform flux dispersion over the connection.

Solder Wire Size: Standard wire diameters for solder range from a thick .125inch (11 gauge) wire to a hair-fine .010-inch (31 gauge) wire. Here is a list of standard solder diameters shown:

Diameter Gauge

.125" 11

.093" 13

.062" 16

Diameter

Gauge

.050" 18

Single Core

Multi-Core

Solid

.040" 19

.031" 21

.025" 23

.020" 25

.015" 28

.010" 31

As you can see, there's a lot of them! However, most distributors carry only a few of the more popular sizes. As a rule of thumb, solder manufacturers recommend using the largest wire size with the highest flux percentage practical to ensure good iron tinning and adequate flux delivery. In general, when solder wire is too large for the job, you'll have difficulty controlling how much melted solder is applied to the joint. When the wire is too small, you'll have difficulty feeding enough solder onto the connection with a single well-controlled hand movement.

In practice, many technicians like to keep a roll of .020-inch 63/37 for intricate surface-mount work and a roll of .031 or .040-inch 60/40 for general bench use. Large high-power component assembly require a thicker solder--.062-inch for example--to provide rapid coverage of the joint area. Ultimately, the ideal wire size depends on the task and on your personal preference.

Type of Core: In addition to the ten standard wire diameters, solders also come in three core types--single core, multi-core, and solid core. Single-core solder has one hollow cavity at its center filled with flux. Multi-core solder has several smaller-diameter flux cavities clustered around the center. The manufacturers of multi-core products claim better flux dispersion, but--in practice--both single and multi-cores work acceptably well. Solid-core solder has no flux cavity. When using solid-core solders, you must apply a flux paste to connections by hand using a brush or syringe.

Size of Core: Not all flux cores are the same size. The core-size of wire solder is especially important because it controls the amount of flux delivered to each connection. Core size may be specified as a number (Kester No. 66), a generic name ("regular"), or a flux percentage (3.3%). Flux percentage is based on the weight of the flux as compared to the weight of 60/40 alloy. Three "manufacturer's standard" core sizes are shown below:

Regular

Medium

Small

3.3%

No. 66

2.2%

No. 56

1.1%

No. 50

For general bench work and field repairs, "regular-core " (3.3%) solder delivers the most flux, providing the fastest chemical action and best preparation of metal surfaces. For hand assembly operations where metals are highly solderable and surfaces pre-cleaned, 2.2% or even 1.1% solder will do the job--and leave less residue behind for clean-up.

It's always important to check core size when you select a roll of solder. Solder wires with low flux delivery may perform poorly on unprepared surfaces, and may also cause your iron to "de-wet". De-wetting (or loss of tinning) is a condition where solder no longer adheres to the tip because there isn't enough flux available to keep it free of oxides. If forced use solder with a medium or small core for general bench work, apply supplemental flux to each connection before heating. This will protect your iron and to ensure adequate joint preparation.

LESSON 2

Kinds of Flux

Flux is essential for successful hand-soldering. However, not all fluxes have the same chemical composition or working characteristics. Different formulations do the job in slightly different ways. In this section, we'll take a closer look at what flux does, and cover the various types of flux in common use for hand soldering.

How Flux Works: When exposed to air, most "raw" solderable metals quickly attract oxygen molecules and form a layer of oxide. Once oxide forms, the surface is rendered chemically "passive". This means no molecular bonding sites are available for combining with other metals! If you apply solder to a passive oxidized surface, it will bead up into a ball and pull away--much like water on a freshly waxed automobile (Figure-A). This process is called retraction. Solder retracts because there are no bonding sites on the surface where it can take hold and hang on. Instead, a ball forms because internal cohesion attracts the solder molecules toward each other.

Metallic oxide

A. Cohesive forces pull solder into a ball. B. Adhesive forces spread solder out.

Solder

retracts from

surface.

Oxide-free

Solder "wets" surface.

Base Metal

Flux is a specially-formulated chemical agent that removes oxide to expose the base metal underneath. Once oxide is removed, the surface becomes chemically "active" (Figure-B). This means the molecular bonding sites are restored and the surface is again free to combine with other metals. When liquidous solder is applied to an activated surface, powerful molecular forces take over--pulling the solder downward and forcing it outward to cover the area in a process called adhesion. When solder adheres to a chemically active surface, we say it wets the surface. Complete wetting is essential for good solder connections.

In addition to removing oxides, flux has a second job--to form a protective coating over the newly-activated metal. Although flux is a semi-solid at room temperature, it melts and spreads well below the melting temperature of solder. This allows it to flow ahead of liquidous solder--activating the surface and locking out air to prevent re-contamination.

Finally, it's important to remember that flux isn't a "cleaning agent". Flux removes oxides through chemical action and floats them off the surface in a chemical suspension. If metal is dirty, greasy, or contaminated in other ways, it should be cleaned prior to applying flux. Also, note that flux residue contains the oxides it has removed after the solder connection is made. In some applications, these deposits may need to be removed through cleaning.

Common Types of Flux

Fluxes fall into two general categories--inorganic and organic. Inorganic, or "acid-core" types, are normally used for plumbing and are far too corrosive for electronic applications! Most electronic solder fluxes are organic. Organic flux falls into three classes: rosin, water-soluble organic, and solvent soluble organic. Of those groups, rosin flux is most common. Rosin is a natural substance produced by pine trees that contains abietic (a-bee-tic) acid. Rosin fluxes are classified by their degree of chemical activity and residue conductivity. Some rosins are mild and poorly-conductive, while others are very aggressive and more conductive. The two most-common rosin fluxes are RMA and RA:

RMA Flux: "Rosin--mildly activated" flux (RMA) is a good choice for assembling products made from highly solderable metals. The cleaning action of RMA is adequate for hand assembly in a well-controlled manufacturing environment, but generally insufficient for general bench and field work where

oxidation is more prevalent. The residue from RMA flux is relatively nonconductive and non-corrosive.

RA Flux: "Rosin--fully activated" flux (RA) is the most widely-used flux, and clearly the best choice for bench and field work. RA flux delivers more aggressive cleaning action, and it activates a wider range of solderable metals than RMA. Although RA residue is more conductive and corrosive than RMA, it is also "self-encapsulating". This characteristic isolates corrosive agents from air and moisture to prevent long-term contamination. On the down side, encapsulation may interfere with probe contact during testing procedures, and its protection may fail to hold up when exposed to extreme humidity and moisture.

Other rosin flux formulations are available, but rarely used for hand soldering. For example, "R" flux (non-activated rosin) is too mild for most practical applications, and "highly-activated RA" leaves a highly corrosive residue that must be removed immediately after use. In addition to the popular RMA and RA rosin fluxes, other formulations such as water-soluble and no-clean flux are now widely available in wire solders.

No-Clean Flux: "No-clean" flux contains few solids (2-5%), and leaves only a small trace of non-corrosive and non-conductive residue behind. This, in turn, eliminates the need for cleaning after the job is completed. No-clean flux is less aggressive than RA, which reduces its usefulness for general field and bench work where oxidation my be poorly controlled. However, "no-clean" works very well for hand-assembling new circuit boards, and is especially popular with technicians and engineers for surface-mount prototype work.

Water-Soluble Flux: This organic water-soluble flux consists of citric, glutamic, or lactic acids dissolved in a water or alcohol base. On the plus side, water-soluble flux is more aggressive that rosin fluxes, and it successfully activates some metals that RA flux cannot. On the negative side, water-soluble fluxes leave organic acids and salts behind which are potentially corrosive and conductive--and these must be removed immediately after use. Of course, removal is relatively easy, since only water and mild non-toxic cleaning agents are needed to do the job.

Supplemental Flux

When hand soldering, flux is delivered primarily through the core of solder wire. In some cases, "core flux" may not provide sufficient chemical action to get the job done, and additional flux is needed to fully prepare the area. Supplemental fluxes are available from distributors in most popular types (RMA, RA, noclean, etc.), and may be dispensed as a paste or liquid--depending upon packaging.

Flux Jar

Flux Syringe Flux Pen

Flux Pastes are most often packaged in a small jars or a plastic syringes. Jar paste is applied to larger areas with a flux brush, and to miniature surfaces and with a wooden toothpick. Patse-filled syringes come with special applicator tips which offer controlled flow-rate and pin-point placement. Replacement tips are available in a variety of sizes. Syringes provide convenient packaging, and they work well for a wide range of tasks. The flux pen delivers flux as a liquid, much like a felt-tip marker delivers ink. Pens are especially convenient for miniature PC board and surface-mount work. Supplemental pastes and liquids may evaporate and dry out when exposed to air for long periods. Be sure to cap or cover all flux containers when not in use. Refrigerating during prolonged periods of non-use helps extend shelf life.

PC Board Cleaners and Flux Removal Solvents

Most off-the-shelf cleaners are formulated for removing rosin-core flux residues (RMA and RA). Although cleaning is routine during automated PC board assembly, residue removal may not be required for general purpose bench and field hand-soldering jobs. That's because RMA and RA fluxes are selfencapsulating, and "no-clean" fluxes leave no harmful residue behind.

If cleaning is needed to satisfy a cosmetic or technical requirement, consider using an alternative to older-style CFC-based organic solvents. While CFCs are very effective, the price, toxicity, and environmental impact may not be justified. Less-toxic organic solvents, alkaline saponifiers (sap-on-a-fires), and emulsion cleaners are now available to do the job with minimal risk. Organic solvents dissolve rosin deposits, while saponifiers and emulsion cleaners convert them into water-washable substances.

Before using any flux removal product, read instructions carefully! Most organic solvents require adequate ventilation and other safety precautions for safe use. A stiff-bristle brush is usually needed to remove particles and debris (a discarded toothbrush works well for this). After handling cleaning chemicals, be sure to clean hands thoroughly before eating or smoking. Finally, never improvise by using solvents not specified for flux removal. These may expose you to a needless health hazard, and may also damage chemical-sensitive plastics on the PC board!

Purchasing and Using Solder--A Quick Review

By now, you're probably getting the idea that "grabbing any old roll of solder" to do a job might not yield the best results! Before you select a product, ask yourself the following questions:

1. Is the solder alloy right for the job?

2. Is the wire size matched to the task (too small, to big)?

3. Is the core type acceptable (single, multi, or solid?)

4. Is the core size going to deliver the right amount of flux?

5. Is the type of flux right for the application?

6. Is supplemental flux needed?

7. Will the flux residue require removal?

8. If so, what type of cleaning product is best?

You probably won't always be able to find exactly what you want! However, if you understand solder specification and what they mean, substitution should be easy. For example, for most routine PC board hand-soldering jobs, a 60/40 alloy in a .031" or .040" wire size with a 3.3% (regular) RA flux core works well. From that starting point, you can add other solders to accommodate specific tasks. For example, a 63/37 alloy in a .020" wire size with 3.3% RA (or "noclean") flux works well for surface-mount applications. And, a roll of "fat" 60/40 might come in handy for assembling high-power equipment with large components.

When forced to use "SE" (or someone else's) solder, always read the label first! If the flux is unaggressive or the core size "small", use supplemental flux (usually RA). If the flux is highly-activated RA or water-soluble, remove the residue afterward. Finally, if it's acid core or the roll's unmarked, put it back and find something else. It always pays to be an informed consumer!

LESSON 3

Soldering--Health and Safety

Industrial hygienists evaluate occupational safety in terms of acute and chronic health hazards. Acute hazards relate to immediate threats from traumatic injury. A misplaced cable that causes someone to trip and fall downstairs is an acute health hazard. Chronic hazards relate to long-term threats from toxic agents. A chemical known to cause cancer after prolonged exposure to its fumes is a chronic health hazard. Soldering isn't regarded as a high-risk activity in either category, but there are hazards you need to know about and avoid.

Acute Hazards

Burns: The most obvious short-term health hazard associated with solder is

heat. Iron tips typically operate at 600-800 degrees F, and the temperature of molten solder exceeds 350 degrees F. Moreover, liquidous solder can spatter over a wide area without warning. Either of these heat sources can inflict painful burns and even permanent injury.

To reduce your vulnerability to heat-related injuries, always wear appropriate clothing and eye protection (no shorts or tanks tops if you value your skin). In the event of accidental skin contact with a hot iron or hot solder, immediately run cold water over the burn area. This first-aid response cools skin rapidly to limit tissue damage, and anesthetizes damaged nerve endings to reduce pain! Never apply butter or any other substance--only ice or a cool wet towel. If severe blistering or wounding breaks the skin barrier, seek further medical attention as soon as possible to prevent secondary infection. Also, have any eye injury resulting from a solder spatter checked at once--no matter how minor.

Electric Shock: Electrocution is a second acute hazard associated with soldering and solder irons. Most thermostatically-controlled solder stations supply low voltage to soldering tools, greatly reducing the risk of injury. However, solder-station control units, self-contained desoldering tools, and unregulated bench irons usually connect directly to the 110-volt AC line. Inspect plugs and power cords frequently for heat damage, iron burns, or wear. Also, confirm the integrity of power-plug grounds. Damaged power cords should always be replaced, and never repaired using electrical tape or shrink tubing! Finally, never attempt soldering operations on a piece of electronic equipment while it is connected to a power source!

Chronic Hazards

Lead Poisoning: Lead is a toxic substance that accumulates in the body over

time. If toxic levels are reached, the impact on health will be serious. Medical outcomes may include damage to productive organs, cancer, birth defects, colic, kidney disease, paralysis, brain damage, and even death! Fortunately, electronic soldering is done at temperatures well below the "fuming point" of lead, so lead vapors pose little threat to your health. Mishandling lead-bearing solder wire presents a greater long-term hazard. Each time you use solder wire, a small quantity of lead is transferred to your fingers. This, in turn, may be ingested when you handle food or smoke cigarettes. Although the amount of lead transferred may be small, it can accumulate to dangerous levels over time. To prevent unwanted lead from accumulating in your system, it's extremely important to wash your hands thoroughly after handling solder--especially before eating or smoking!

Flux Fume Inhalation: Solder fluxes may also present a chronic health hazard. Some flux vapors contain mineral acids that are irritating to the skin and toxic to inhale. Repeated exposure may produce asthma-like repertory symptoms or chronic throat irritation. To minimize your exposure to flux vapors, ventilate the area around your soldering station. A small portable air-filter, or a larger ducted ventilation system, work well for removing airborne irritants. If ventilation is unavailable, avoid breathing in visible plumes of smoke or strong-smelling vapors. Even a small fan aimed across your work area will help to blow irritants clear and reduce exposure.

Other Workplace Hazards: In addition to solder, electronic work areas usually harbor a collection of flux solvents, degreasing chemicals, and PC board etching chemicals. Also, high-speed drilling and abrasive cleaning of PC boards generates airborne particles of epoxy and copper dust. Most of these substances present one or more health hazard, ranging from mild respiratory irritation to severe or deadly toxic effects. Be sure to obtain and read MSDS information (hazardous material data sheets) for all chemicals stored in your work area. Know how to use them properly, and know what to do in case of an accidental spill or over-exposure!

LESSON 4

Soldering Irons

Types of Irons: There are a lot of different soldering irons out there, and choosing the right one can be as confusing as choosing the right roll of solder! Electronic distributors offer products ranging from ten-dollar hobby irons to microprocessor-driven rework stations costing several thousand dollars. All soldering irons do pretty much the same thing--heat connections and melt solder alloys. But, there are differences in how they do the job--and how well they do it! Here's a survey of the popular hand-soldering irons in use today.

Low-Cost Hobby Iron: These are simple low-cost consumer products intended for home-owners and beginning-hobbyists. Most provide a two-wire power cord connected directly to a fixed-output 110-volt 30-40 Watt heating element. Iron tips are ungrounded and unsuited for working with static-sensitive components. Elements and tips aren't designed for continuous use, and replacement parts may be hard to find--making these products "throw-aways" when they fail (not suitable for lab or shop use).

Handle

Power Cord

Barrel

Tip

Heating Element

Unregulated 110-volt Professional Iron: These irons work on the same

principle as low-cost hobby irons, but the heating elements and tips are higher quality and designed for continuous use. Power cords may be two-wire (isolated tip) or three wire (grounded tip). Tips and elements are easily replaced, and a variety of wattages and tip styles may be used with the same basic handle assembly. Some "high-end" 110-volt irons may have thermostatic temperature control, but most will not.

Shield

Cord

Main Body

Cartridge Socket

Grip

Removable Heat Cartridge

Replaceable Tip

Transformer Powered Soldering Station: Transformer-powered soldering irons run on low voltage. Typically, a transformer unit enclosed in a separate bench-top control box converts 110-volts to 24 volts. Irons plug into a socket on the front panel of the box, allowing for rapid substitutions. Virtually all transformer-powered stations use three-wire AC cords and provide grounded iron tips. Grounded tips bleed off electro-static discharge (ESD) that might otherwise build up on the iron and damage sensitive electronic parts during construction.

Two kinds of temperature control are popular, depending on the solder station's model and manufacturer. One method uses magnetic-thermostat switching with a temperature-sensitive element built into the iron's tip. The type of tip you install controls temperature. The classic "Weller Soldering Station", an industry mainstay for over 30 years, uses the magnetic thermostat design.

Other soldering stations use an electronic thermostat that provides continuously adjustable temperature control. All thermostatically-controlled irons apply element power on demand to maintain a more constant tip temperature. This is an important feature not found on lower-cost unregulated irons.

Transformer Unit

TEMP

800

700

Thermostat Control

600

PWR

Mini-Irons: With the advent of surface-mount technology and increased

miniaturization, a smaller version of the conventional soldering iron has gained popularity. Light-weight "mini-irons" (or soldering pencils) outfitted with ultrafine tips reach into tight spots where other irons can't reach. Mini-irons are available in both unregulated and thermostatically-controlled models.

Min-Iron

Alternative Soldering Irons: For field work or quick bench jobs, many people

prefer to use a "no-plug-in, fast heat" alternative to the traditional iron. The most common energy sources for these irons include internal rechargeable NiCd batteries and liquid butane fuel. Portable types may not deliver the power and

temperature regulation of a transformer powered bench station, but they get small jobs done quickly without need for running extension cords or removing equipment from remote locations. Another type of alternative iron, the triggeroperated soldering gun, has been around for many years. These days, batterypowered versions are especially popular.

Butane Iron

Battery-Powered Gun

Battery-Powered Iron

High-Capacity Irons: High-output irons are characterized by powerful heating

elements (100 watts or more), elevated tip temperatures (up to 1000-degrees F), and massive tips. These "Big-Bertha" irons are especially useful for heating large surface areas, heavy-gauge wiring, and certain types of RF-cable coaxial connectors. Most shops and labs have one tucked away for special jobs. Highoutput irons can inflict severe burns very quickly, and must be handled with plenty of respect!

High-Capacity Iron

Other specialized resistance-soldering systems are sometimes used for connector installation--especially in manufacturing. Resistance soldering units consist of a powerful low-voltage high-current transformer connected to a special clamp-on hand-tool. When the hand-tool is clamped on, it literally turns the entire metallic part into a heating element! Heating is uniform and fast with these systems.

How Soldering Irons Work: A soldering iron has two jobs. First, it generates thermal energy (or heat) by means of a heating element. Second, it stores up and transfers that heat to a solder connection via the tip. Prior to contact with a solderable connection, the iron pre-heats well above the melting temperature of solder (typically 600-800-degrees F). As it heats, a substantial reservoir of thermal energy becomes stored in the barrel and tip. Upon contact, an energy exchange takes place that simultaneously heats up the solder joint and cools down the iron. Most of the heat required to complete an average connection comes from stored energy alone. However, the element assists by pumping new thermal energy into the tip to slow its rate of cooling. Once tip contact is broken, the element immediately begins to reheat the iron, restoring an energy reservoir in preparation for the next connection.

Solderable Metals

in Connection

Cool

Heat Sink

Heat Source

Tip

Solderable Metals

in Connection

Element

Heat Source Heat

Tip

Hot

Exchange

Mass, Temperature, and Thermal Energy: The amount of heat energy stored

by your iron depends on several factors, but the two most important ones are the tip's mass and the tip's temperature.

Mass: As the iron's element pumps heat energy into the barrel and tip, the molecules move faster--causing the tip to get hotter. When the iron makes contact with a cold connection, heat energy is liberated and the molecules start to slow down. The greater the metallic mass, or the more molecules you have in your tip, the more thermal energy it will store for every degree of temperature rise. An iron with a big tip stores more thermal energy for every degree of temperature rise than a small one. That's because more molecules are available.

Temperature: The higher the tip's temperature rises, the more thermal energy you can store (per ounce, gram, or whatever). That's because it takes more energy to make a fixed number of molecules move faster. Conversely, the further the temperature drops, the more energy you can liberate. Faster-moving molecules have more energy to give off.

To put this in perspective, say you need to heat a connection to 400 degrees F so it will melt solder. It makes sense that a 800-degree F tip will contribute more thermal energy to the heating process than an identical tip heated to only 600degrees F. However, a more massive tip heated to 600-degrees F could contribute the same amount of energy as the less massive 800-degree F tip-because more storage mass is available in the bigger tip.

600-F

Thermal energy storage depends on

both MASS and TEMPERATURE.

800-F

Without getting into BTUs (British Thermal Units) and the finer points of hermodynamics, we can generalize the concept and say:

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