Warning:  Do not expose children to lead alloys and dangerously hot soldering irons.  Be more safety consious for others because they aren’t as aware of the hazards of soldering.

Opinions with 60 years soldering experience in electronics equipment maintenance shops, research labs, and NASA equipment manufacturing shops.  Use the references for more information.


Al Washington 12 June, 2014


The weather station owner may find the need to solder.  Some may need skills to repair or replace a circuit component.  Others are assembling a kit of parts where everything is included.  Some may design a circuit and produce the component board including drilling and etching.  Hopefully this soldering course will provide some information so that you’ll solder safely and with confidence


Some definitions:
1 DIY as used in this course is ‘Do It Yourself’ and sometimes is the ‘Do-It-Yourselfer’, the person.
2 Wetting is when a liquid spreads out evenly over a surface without forming droplets.
3 When heat is removed from the work, the alloy solidifies, not dries.  Turning from a liquid to a solid.


Solder is pronounced [sod-er].  Bonding materials by soldering, brazing and welding are sometimes confused.  Soldering is a process of bonding items by flowing a low temperature melting alloy on the surface and filling the void between the parts with solid metal. Soldering uses temperatures below 700°F. Brazing uses temperatures above 700°F but below the melting point of the items that are bonded.  Welding is a process of melting and fusing the items that are bonded.




Soldering is a very dangerous task involving high temperatures, lead alloys, vapors, fumes, acid, harsh chemicals, and tools that may cause injury.  This course suggests that the untrained person get hands on training from an expert solderer before attempting to solder.

The kitchen table is not the appropriate place to solder

Eye protection should always be used in case anything goes the wrong way.  Side shields are needed on prescription glasses for necessary protection.  Also consider and protect observers who may be near to the soldering.

Children should not be permitted in the vicinity of soldering because of the possibility of burns from the high temperatures and the possible exposure to a large quantity of lead.  Children should not be exposed to lead alloys that may be used in soldering.  If solder containing lead is used, everyone should know the hazards.  The soldering iron and the work piece is hot without any visible warning.  Children won’t know that the work area is hot.

Soldering will produce fumes of lead, tin and other alloys.  Work in adequately ventilated areas or use respiratory equipment.  Some exposure may cause harm to an unborn child, reduce fertility, cause respiratory and skin sensitivity, affect brain development in children.  Other hazards must be read on the MSDS

Please don’t ever give a child the possibility of pulling a hot soldering iron down on to them from a work table.         THINK


Material Safety Data Sheet        MSDS


The MSDS is a multipage document for each chemical or product.  The MSDS provides information for products used in the workplace.  It is the go to place providing specifications and safe handling, toxic information, health hazards, fire fighting, first aid procedures.  The DIY should be familiar with MSDS on solders, fluxes, and cleaners used.  All products have an MSDS.  There is even an MSDS for water.


All hazards and precautions can’t be included in this short course.  Links to several MSDS are for example only.  Not responsible for information supplied by other publishers.
CIGWELD Tin-Lead solder wire MSDS techdata/msdscigweld_tinlead.pdf
Tin/Lead Alloys-Solder MSDS techdata/msds_tin_lead_solder.pdf
Also find MSDS on fluxes & cleaners used when soldering.


Prevention and treatment of burns


When using a hot soldering iron and hot parts, it is almost inevitable that the technician will someday get burned.  There are ways to lessen the severity of burns to fingers/hands.

First, be aware of the hot dangerous places and when they are hot, how long it takes parts to cool after joining.  Of course the iron tip will be hot when in use.  The parts that have been soldered or unsoldered will remain hot and dangerous for a minute or so after the iron is removed.  Always watch where your hand is reaching.  Don’t blindly reach for the soldering iron because you may contact the hot part.  The iron should be returned to the soldering iron holder and not placed on a table top. 

These burn treatment procedures are the result of many years training and supervising electronic technicians in maintenance and manufacturing shops.  Treatment of small burns applies to burns from hand soldering irons and also to home kitchen burns from hot oil splatter or hot cookie sheets.

You may have been taught to get some ice or a stick of butter to soothe the burn.  Maybe you intend to pinch off an aloe stem or buy some burn treatment? That’s bad advice.  Those take too long to begin treatment and are the worst suggestions for first treatment for small burns.  You need to control the burn while it is in progress before it can cause damage.  You can get instant treatment in 2 seconds if you know what to do. 

We don’t react quick enough to prevent burns.  It takes several seconds to realize the pain is a burn from a hot object.  First, you hear the sizzle, then you feel pain,  a few seconds later you deduct that the pain is a burn.  Then you react by dropping the hot object. 

If the soldering iron is 500°F, and your finger touches it; ouch it’s difficult to think that.  The outer layer of dermis becomes almost 500°F from heat conduction from the iron.  The heat migrates down into the body heating the flesh layer by layer to hotter and hotter temperatures.  You’ve now removed your digit from the iron but the flesh remains hot.  The longer the layers stay hot, the more burn damage occurs.  We have to get the flesh cooled in a hurry. 

You can rush to the sink for cold water; get some ice; apply burn treatment cream.  Too late.  Your finger is now toasted.

Develop and practice a reflex to instantly cool the burned site.  The burn site is at 500°F.  Your mouth is 98°F.  Put your burn into your mouth and that will reduce the flesh temperature from 500°F to 98°F within 2 seconds.

OK, so your finger is dirty and won’t taste good.  Would you rather have a burned finger that will be in pain for weeks?

You hear the sizzle, feel the pain, insert finger in mouth. 
It’ll hurt for awhile.  Keep the burned site moist until you can get to a faucet for running cold water.  Then do your normal aloe or burn treatment cream.  In a day, you won’t notice the burned area.  You’ve prevented discomfort from a minor soldering iron burn. 


Before soldering, set up a glass of water.  If you’re unfortunate to get burned, just dip your fingers into the water.  Instant relief, no burn.  It’s better than sucking on your thumb.  But who prepares for a hazardous task like soldering?

Keep the children away from soldering.  The irons may not have an indicator lamp showing that it’s hot.  It doesn’t smoke, make bubble and boiling sounds.  Soldering tools are apparatus for responsible adults. 

May your burns be minor and just a learning experience.


Soldering tools


a. Eye protection  Before investing in tools, take stock of your eye protection.  If you don’t use prescribed glasses, purchase a comfortable pair of quality safety glasses with side shields.  If you wear prescribed eyeware, they should also protect your eyes from debris injury.  You will need protection from hot fragments, objects ejected when clipping, and splattered solvents/cleaners.


b. Soldering iron  The soldering iron can range from just a few dollars for a blister pack soldering kit similar to a wood burning tool to a professional solder/unsolder station with a hefty price tag.  pRS1C-2160671w345

Match your iron to the task you have.  For a training project soldering axial lead through hole electronic components, you should select a 25 Watt AC line powered iron.  When you have more experience soldering, invest in another iron that has features such as thermostat controlled.  Isotip makes an excellent battery powered iron with interchangeable sizes of tips.  The battery is recharged from the AC line. 


Some irons have screw in interchangeable heaters.  The heaters have screw on tips of several shapes and sizes.

A more expWeller1erienced technician may need a thermostatically heat controlled soldering station. 







Electronic soldering irons differ from stained glass soldering irons mainly by Wattage.  Stained glass artists use larger irons that have the capacity to heat larger areas.  Their solders are larger solid wire with no flux core.  They apply flux before soldering. 
Wood burning tools are also similar to soldering irons.  They may have similar capacity but offer different tip selections.  Wood burning irons also have hot knife selections.  If your iron is compatible, you may be able to buy wood burning tips for your soldering iron.  How cool is that?
Again, match your tool selection to the work. 


c. Soldering iron holder The holder must raise the hot tip above the table work surface to prevent charring.  Don’t accept an iron holder that doesn’t have a cage or wire spiral that will prevent anything from touching the hot parts of the soldering iron.  A simple stand isn’t good enough.

bad_stand  This simple soldering iron stand simply props the iron up away from the table top.  It is not acceptable because it won’t protect a person’s hands from touching the hot iron.  Find a holder with a cage that covers the hot parts.


d. Wet cellulose sponge    Soldering stations almost always include a cellulose sponge in a water tight tray.  If your tools don’t have the sponge, buy a tray and fit it with a small cellulose sponge.  Cellulose resists melting from the hot iron.  Wet the sponge with as much water as it will hold.  Don’t squeeze water from the sponge.  You can add water to the tray to make the sponge saturated.
When a replacement sponge is needed, buy a large cellulose sponge and trim it to fit.  The sponge will be hard when dry and can be trimmed with a razor or X-Acto blade.
The reason for a saturated sponge is to provide enough water to give the hot iron a thermal shock when it is wiped.  The fast, but short, reduction in tip temperature loosens scale or debris that has settled on the tip.  You should hear a hiss sizzle as the hot tip touches the wet sponge.  Two quick wipes are sufficient.  The iron has enough heating capacity to quickly recover from this reduction in temperature. .

e. Heat sink tool, anti-wicking tool        heatsink1
We can prevent soldering heat from conducting through the component leads causing heat damage to semiconductors.  Semiconductors are susceptible from soldering heat damage.  These heat sinks are made from aluminum which readily conducts heat away from the component.  Clamp the heat sink as near to the component body as possible.  The heat sink is removed as soon as the soldering is completed.

f. Static strap                           antistaticstrap The anti-static wrist strap dissipates charges that build on a person’s body.  The wrist strap makes contact with the person’s skin and the other end of the cable plug or clip connects to a ground connection point on the workbench.  Controlling static charges is vital when handling metalic oxide or field effect solid state devices or any equipment containing those components.  A safe precaution is to always use a static strap. 
Use a commercial static strap; do not make your own.  Manufactured straps  have internal resistance which makes them safe for the user when working on energized equipment.

g. Cup or glass of cool water      DSCN1778 The glass of water is for burn safety.  Use a wide mouth open cup  or glass of water.  Keep it near the soldering iron to dip fingers if you’re unfortunate to have a burn accident.

h. Solder sucker                     soldersucker   A hand operated vacuum device that will remove molten solder from a terminal or pad.  Heat the point with your soldering iron, quickly place the sucker tip over the hot solder and press the button.  A plunger inside causes a vacuum which sucks the molten solder inside.  Press the other button to cock it for the next removal.  Occasionally open the barrel and remove the solder debris.

This is an alternative to using solder wick.  .

i. Soldering aids                       solderingaidsSoldering aids are available in an assortment of reamers, brushes, hook tips, fork tips, and scrapers.  These are the hand tools for positioning wires or component leads on terminals or brushing, scraping for soldering or solder removal. 

We Electronics Technicians use tools designed specifically for small electronics components.  We also find use of surgical knives, hemostats, dental cleaning, mirrors, jewelers screwdrivers, gunsmith tools, optical/camera clamps, modeling/clay tools, and artists tools.  If it works, adopt it. 


Soldering alloys and fluxes


A do-it-yourself technician will probably use solder in wire form.  Manufacturing has other forms such as bars heated to liquid, solder paste, preformed solder shapes.  The wire form used for electronics construction or repair usually has an inner core of rosin flux.  Ensure that you are getting a rosin flux core solder and not acid core which are not for electronics applications.
Electronics parts suppliers are a better source of rosin core solders in several wire sizes.  Hardware stores has acid core solders.
ROHS lead free solders comply with the European Union directive directing manufacturers to reduce certain chemicals in products.

Varieties of solders are too numerous to list here.  Tin is the major component.  Lead is the next highest ingredient when it is used in lead solders.  Silver, copper, and Indium are ingredients in some solders.  You select the metal alloy to suit the job you are making.  Silver requires a higher temperature and is stronger.  Copper is an ingredient that preserves your soldering iron tip, prevents the tip from sacrificing copper to the work.  Solder specifications show the melting temperature and the solidus temperature. 

A soldering flux is a metal surface cleaning fluid or a paste.  Some fluxes are inactive and some are acid.  Acid based fluxes are not acceptable for use in electronic devices. The acid flux must be neutralized or it will cause corrosion of the equipment.  Soldering can be easier if the surface is prepped by using a liquid flux dropper or a flux pen.  This removes dirt, grease or corrosion from the surface to be joined.  Sometimes additional flux is used on difficult to solder surfaces such as solar panels.
We normally use a solder wire form which has an inner core of solid flux.  Additional flux isn’t normally needed.  The flux is activated when the soldering iron melts the alloy and liquefies the flux. The flux flows over the surface and is replaced with the molten metal. 
Flux build up on cicuit pads is unsightly.  It can be removed with 91% alcohol on a stiff brush or Q-tip.  If a large amount of flux remains, it may be brittle and can be chipped away with a soldering aid & wire brush.
a.      Lead free solder.  This is ROHS compliant solder specified by the European Union Directive for reducing hazardous chemicals in disposition.  The lead has been replaced with silver and trace amounts of other elements. A common Sn/Ag/Cu alloy has a melting point of 423°F.
b.     Lead alloy Solder This is a ‘soft solder’.  Major ingredients are tin (Sn) and lead(Pb). Common types are 60/40 tin/lead, 50/50 common to stained glass work, 63/37 lowest melting temperature.  63/37 tin/lead is a eutectic solder, it’s melting point and solidus point are both at 361°F.
c.     Solder wick is a length of braided copper tubing that is flattened and impregnated with a dried rosin flux.

Several widths are available from 0.030” wide to 0.190” wide.  This is used for removing solder from a terminal or component pad.  Solid copper braid works best because it has the most surface area of copper to pull the solder.  First, flex the solder wick to ‘activate’ the impregnated dried flux.  Place the solder wick flat on the area of solder to be removed.  Apply the flat area of the soldering iron tip to the top surface of the solder wick.  Move, rock, soldering iron tip side to side to achieve maximum contact of the iron tip to the wick.  When the heat is transferred through the copper wick to the solder, the copper will wick the solder from the terminal into the copper braid.  Sometimes it may help to ‘prime’ the wick with fresh solder..Remove the wick braid before removing the hot iron.  You will need to move the wick along to expose more wick as it fills with solder.  Cut off the solder filled wick with diagonal cutters to start again with a fresh wick.  The wicking process should take only a few seconds.  Watch for overheating damage of the component that solder is being removed.
In this topic ‘wick’ is a noun and a verb.  Wick is a product used for desoldering.  The verb wick is the process of drawing solder away from the terminal.
See also Solder sucker topic.
d.     Liquid flux or flux pen
Mil standards that regulate soldering alloys


Through Hole Soldering


a. The mechanical bond.  Use appropriate size smooth jaw needle nose pliers, bent tip pliers, round jaw pliers, flush cutting diagonal pliers, etc to create a most perfect position of the lead.  The component should be firmly held before solder is applied.  Most components are mounted and secured in place by their component leads.  The components should not depend on the solder to keep them in place.  A solid mechanical connection must be made before soldering.  The component lead should be brought around the terminal stud 270° only.  Do not multiple wrap the lead around a terminal.  The minimum wrap allows easy removal of failed components without damage to the terminal stud or the board.  A firmly mounted component won’t allow any movement while the solder is solidfying.  Movement in the joint while cooling will cause a ‘cold solder joint’.

High Wattage axial lead power resistors should be mounted above the circuit board.  Use the axial leads as stand-offs.  These power resistors are designed to handle internal heating by dissipating the heat to the surrounding air.  If the power resistor is in contact with the board, it may char the board over time. 

Most components leads should be straight for 0.2” to 0.4” before bending 90° to be fastened to the board.  This prevents stress on the lead where it enters the component.

space reserved for describing the Davis supercap failure due to improper lead bending

Wire insulation should be dressed to stop at the edge of the board pad.  Insulation should not be deformed or burned during the soldering process.  Insulation of the wires should not be in contact with the solder. 


b. The electrical connection  The solder bond should provide a low resistance path between all components connected at the joint.  If the joint wasn’t clean before soldering or is a granulated cold joint, it can add significant resistance in the circuit.  A cracked joint due to vibration during its service life can corrode and become a ‘rectifying’ junction.  A recitifying junction provides low resistance in one current flow direction while high resistance in the other direction.  This is the same as if a diode were placed in the circuit; and the device fails.  Most cracked or cold joints can be repaired simply by reheating with the soldering iron and a little flux.  A cracked joint is difficult to spot as a hairline in the solder above stressed component leads.  Defective solder joints are difficult to troubleshoot.  You can see that a wire is firmly in place; but it may not be properly electrically connected.




c. The soldering process           tools_Header_Joints640

The soldering illustration is owned by Bill Earl from https://learn.adafruit.com/assets/1978


1.      mechanical cleaning  The items that are to be bonded must have a clean surface.  The solder adheres to the surfaces by ‘wetting’ If you are tinning insulated stranded wire, first clip 1/4” or more from the end of the insulated wire to get to bright copper wires for easier tinning.  If copper is dark, it can be brightned with a rubber eraser, brass brush or with steel wool for large areas.  The cleaning operation may leave its own debris that must also be removed.  Chemicals may be used in this first cleaning but they may need to be washed and dried. Clean copper is pink. Copper is a very active element.  Copper will remain clean for only a day.  It oxidizes quickly.  The lowly ‘Pots & Pans’ helper in a restaurant has to clean the copper pots every single day with salt and vinegar.
2.     flux application  Always use a flux core solder.  There will be sufficient flux without needing to apply more.  If you apply additional flux, the excess will need to be cleaned from the work.  Liquid flux has a solvent base which evaporates leaving the rosin as residue.  The rosin is non-conductive but may become dirty and cause less than optimum performance of the circuit.
Some difficult to solder items such as solar panels may need to be pre-fluxed with a liquid or paste so that the solder will flow quickly and without much mechanical pressure from the iron.
3.      heat application  Remove the soldering iron from its holder.  Wipe the iron tip on a very wet cellulose sponge listening for the hiss as the heat evaporates water.  This is very important to temperature shock the iron tip and loosen debris on the tip.  Wiping will remove most of solder that remained after the last soldering operation.
NEVER FLICK,FLING, THROW MOLTEN SOLDER FROM THE IRON!  To do so is like random firing of a weapon.  It is dangerous and unnecessary. Inspect the iron occasionally for pitting and areas that are not tinned.
4.     solder alloy delivery  Heat and alloy application occurs simultaneously.  Bring the solder wire to the work while touching the iron to the same point.  Apply pressure with the iron against the work and the end of the solder.  Start a molten solder bridge between the iron and the work.  You want maximum contact for quick heat transfer to the work.  Do not lay the iron on top of the solder wire.  This will heat the inner flux core and cause spitting of the flux which is dangerous to the technician and contaminates components.  Remove the solder and iron together.  Watch for a shiny surface when the solder becomes solid.  If the work is moved, it will become a ‘cold solder joint’ with a grainy appearance.  Fix the cold solder joint by applying a very small bit of solder & flux while heating.  A cold solder joint is resistive and unreliable.
More solder on a joint is not better.  Apply only enough solder to give a good contour around the joint.  A ball shaped joint is unacceptable.  You should see the shape of the wire as it bends around a terminal.


5.     post cleaning and inspection  Watch the joint cooling as soon as the soldering iron is removed.  The solder surface should remain shiny.  A dull or grainy appearance may have been caused by the components moving before the alloy solidified.
Inspect for the proper quantity of solder and the contour over the pad and component leads.  Add more solder or remove with a wick to get the perfect joint.
Check for solder bridges between board pads and traces.  Remove excess solder with a solder sucker or with a wick.
Look at the component side of a circuit board to be sure that the component is properly placed, usually firmly against the board, not moved away during the soldering process.


Surface Mount Device Soldering  


a. The mechanical bond.  Surface mounted components have no excess lead length.  To build a circuit, the components are mounted on a circuit board or a chip carrier board which adapts the small components to a larger circuit board.  The surface mounted devices will be hereafter referred to as SMD.  Passive SMD are resistors, capacitors, diodes, LEDS, inductors.  Active SMD are integrated circuits, transistors, and sensors.  Switches and actuators are sometimes packaged as SMD.


b. The electrical connection  The solder bond provides a low resistance path between the component and the circuit board.


c.. The soldering process   Select one lead of a component or a corner lead of a large package; apply a small dot of solder to the corner circuit board pad before placing the component.  Place the component in its proper orientation.  Hold it in place with gentle pressure on the device with a tweezer, probe, etc and apply heat at the lead/pad junction for 1.5 seconds.  The component should settle down through the solder to the base metal pad.  Remove the soldering iron while continuing to hold the component in place with the probe.
Inspect that component terminal and next solder the diagonally opposite terminal on a multi pin device by adding solder while applying heat.  Repeat on the remaining component terminals.


1.      mechanical cleaning The circuit board must be thoroughly cleaned and tinned before the components are placed.  An amount of solder is applied to the pad.  The cleaning process can use alcohol or a solvent depending on the board.  A silk screened board may not tolerate a solvent.  Tinning is the process of applying a small amount of solder to the SMD pads on the circuit board.   Some DIY may be assembling a kit of parts.  Others make our own boards. 


2.     flux application  An adequate amount of flux should be applied in the solder core or using a flux applicator.


3.      heat application  An adequate amount of heat is necessary to make a quick solder.  Be sure that the iron is clean, the solder wire is clean, and the iron tip is clean and tinned.  The SMD can be soldered manually with a small tip soldering iron or by heating the entire circuit board in a preheated oven.  Hot air should be investigated as a method of small job soldering.


4.     solder alloy delivery The solder alloy can be applied before the component is placed above the cooled solder before heating in an oven.  Or the solder alloy can be applied similarily to the lead/pad junction as with through hole soldering.


5.     post cleaning and inspection  Check for solder bridges between board traces.  Components and circuit boards have smaller clearances which make it more likely to bridge between pads/traces.  Check that the component didn’t move during the soldering or oven process.  The component pins should be in perfect alignment with the board pads.


The Ten Commandments for soldering

1  When touching the work with the iron, try to contact the part of the greater mass with the flat (larger) part of the tip while trying to touch the part of the smaller mass with the side or edge (smaller part).

2  Immediately on tool-to-work contact, create a fast heat bridge by placing the core solder in the gap.  This will melt the flux and then some solder, which will permit localized wetting for rapid heat flow.

3  Once the core solder starts melting, draw it around the joint in the direction of flow (good for large connections).  If the fillet is small, feed the solder steadily to the junction of tip and work.

4  Remove the solder first, provided that sufficient metal has been added to the joint.

5  Next, remove the iron, but only after the solder has reached the desired contour as dictated by surface tension.

6  Allow the solder to freeze without vibration to avoid disturbed joints.

7  Always place the heat (soldering iron tip) on the side opposite insulation and heat sensitive components

8  Do not melt solder on top of the soldering iron tip and carry it to the work (puddling), unless the work was prefluxed.

9  Do not place the soldering iron on top of core solder or interpose core solder between the work and the tip; flux will spit and not run onto the connection.

10 Do not pull or push on solder joint for inspection.

The Ten Commandments of Soldering is from “Solders and Soldering”, Howard H. Manko




Solderable materials


Many materials can be soldered if the surfaces are prepared and the propper flux and alloys are used..  We normally solder to a copper surface or to components that have been tin plated.  Tinning a wire or component means that we are precoating it with molten solder (which is tin).  It is possible to solder to stainless steel, brass, silver, gold.  We can even solder to ceramic, graphite, and glass.  Those are specialities that the DIY won’t need.  A tin/lead solder will easily adhere to a gold plated surface.  However, soldering to gold contact areas of components is not acceptable.  The amalgam of gold and tin is brittle and the solder joint will fail prematurely.  The gold plating must be mechanically removed (scraped) before soldering to it.


Relating lead alloy soldering, to homes with lead found in old painted walls:
we are required to control access during the removal of lead paint from structures.  The lead in old walls may be a small  amount of lead compared to our soldering supply of lead.  We may purchase a lead alloy solder in a 1 pound roll.  How many square feet of walls would contain the same quantity of  lead?  My point is that we must be considerate of exposure to and control our use of lead alloy solders. 


Solders and Soldering, Howard H. Manko  0-07-039970-0
Soldering Manual, American Welding Society 0-87171-151-6

Suggested How To Solder links:


This is a project shared with members of the WxForum.  www.wxforum.net   You can contribute to the information by replying to the topic on WxForum.


LAST CHANGED ON 2014.06.12