ECE 1013 – Lab
Guide to Electronics Soldering
by Chase Robinson
In this guide, we will
1) learn what soldering is, the tools used, and how to do it
2) discuss common soldering problems and their solutions
Table of Contents
FOREWORD, COPYRIGHT, AND THANKS… ...................................................................................................................................... 3
OVERVIEW .................................................................................................................................................................................... 4
WHAT IS ELECTRONICS SOLDERING? ............................................................................................................................................................ 4
PB VS PB-FREE ELECTRONICS SOLDER ........................................................................................................................................................... 4
SOLDERING TOOLS ........................................................................................................................................................................ 5
SOLDERING IRON ........................................................................................................................................................................................ 6
SOLDERING STATION .................................................................................................................................................................................... 6
REUSABLE SOLDERING TIPS ............................................................................................................................................................................. 6
SOLDER .................................................................................................................................................................................................. 8
FLUX .................................................................................................................................................................................................... 10
BRASS SPONGE TIP CLEANER ......................................................................................................................................................................... 13
TIP TINNER ............................................................................................................................................................................................. 13
DE-SOLDER BRAID / WICK ........................................................................................................................................................................... 14
FLUSH CUTTERS........................................................................................................................................................................................ 14
WIRE STRIPPER ........................................................................................................................................................................................ 15
TWEEZERS .............................................................................................................................................................................................. 16
PLIERS SET .............................................................................................................................................................................................. 16
HELPING HAND ........................................................................................................................................................................................ 17
DIGITAL MULTIMETER ................................................................................................................................................................................ 17
SOLDERING PROCESS................................................................................................................................................................... 18
HOW TO SOLDER:................................................................................................................................................................................... 18
OTHER SOLDERING TECHNIQUES TO KNOW ................................................................................................................................................. 25
GENERAL SOLDERING ADVICE ................................................................................................................................................................... 27
THE IDEAL SOLDER JOINT............................................................................................................................................................. 28
TRICKS FOR CONSISTENTLY GOOD RESULTS: ................................................................................................................................................ 28
COMMON PROBLEMS: ................................................................................................................................................................ 28
IMPROPERLY PLACING COMPONENTS ......................................................................................................................................................... 29
INSUFFICIENT WETTING ........................................................................................................................................................................... 30
OVER-SOLDERING .................................................................................................................................................................................. 31
UNDER-SOLDERING ................................................................................................................................................................................ 32
DISTURBING THE JOINT ............................................................................................................................................................................ 33
COLD JOINTS ......................................................................................................................................................................................... 34
OVERHEATING ....................................................................................................................................................................................... 35
SOLDER BRIDGES .................................................................................................................................................................................... 36
LIFTED PADS.......................................................................................................................................................................................... 37
2
Foreword, Copyright, and Thanks…
This guide was created for you, the learner.
It was made with a lot of resources that I accessed for free, so in that spirit, this guide is likewise released under the
Creative Commons “Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)” license.
Link to the license deed (in the figure below): https://creativecommons.org/licenses/by-nc-sa/4.0/
Link to the license legal code: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
See the figure for the terms of this license, but briefly:
You are free to share, copy, distribute, and make
derivatives of this work in any medium or form, as long as:
1. You give appropriate credit, indicate if changes were
made to it, and provide a link to the license,
2. The use must be non-commercial, and
3. Any remixes or derivatives of this work that you create
must also be provided freely under this same
“CC BY-NC-SA 4.0” license.
The best teacher is personal experience, but this soldering
guide will hopefully serve as a good starting point for this
foundational electrical and computer engineering skill.
Thanks for reading! I hope you find it helpful.
–
Chase Robinson
For questions or feedback, you can reach me by email at car248@msstate.edu
3
Overview
What is Electronics Soldering?
Examine the Printed Circuit Board (PCB) of any electronic device and you'll see
dozens (or potentially hundreds!) of components. Look closer, and you'll find
that each part is secured in place by little mounds of metal.
This is called a Solder Joint!
Soldering is the act of using melted metal “solder” to form a physical and
electrical connection between two metal surfaces. Without soldering,
electrical signals will not have a reliable path between components on a PCB.
Lead pronounced led, or “L-EH-D”
vs
lead: pronounced lēd, or “L-EE-D”
In this guide, we discuss Lead (the element) and leads (the metal wires attached to components).
For clarity, the elemental symbol 'Pb' is added in all instances we refer to Lead (Pb), the element.
If "(Pb)" is not included, the text is referring to a component's wire lead.
mid-late 1800s
Pb vs Pb-Free Electronics Solder
Historically, electronics solder was an alloy of Lead (chemical symbol: "Pb") and Tin (Sn),
with trace amounts of other metals. Lead (Pb) was used due to its low melting point.
However, the irreversible harm of Lead (Pb) exposure, increased seepage of Lead (Pb) from
landfills due to accumulating e-waste, and the added complications of recycling materials
that contain Lead (Pb) have led to regulations in many countries banning the use of
Lead(Pb)-solder in most electronics.
Lead(Pb)-solder is still used in high-stakes industries such as aerospace due to certain
properties that are not relevant here. For most devices, modern Lead(Pb)-free alloys of Tin
(Sn), Silver (Ag), and Copper (Cu) are just as effective and easy to use, but safer.
Lead(Pb)-solder is still sold, but we only supply and recommend Lead(Pb)-Free types.
Pb-solder is used for all
electronics soldering
1896
Electric-powered
soldering iron invented
(American Electrical
Heater Company)
1936
PCB is invented
(Paul Eisler, Australia)
1996
First Pb-free
solder patented
2006
E.U. bans Pb-solder
4
Soldering Tools
A basic kit may include:
#
Item
1x
Soldering Iron & Station
4x
Soldering Tips (variety pack)
1x
Lead-Free Solder (Tube)
1x
Flux (pen)
1x
Flux (tub)
1x
Brass Sponge Tip Cleaner w/ Base
1x
Brass Sponge (refill)
1x
Tip Tinner
1x
Solder Braid / Wick
1x
Flush Cutter
1x
Wire Stripper
1x
Tweezers
1x
Pliers Set
1x
Helping Hand
1x
Digital Multimeter
1x
Soldering Practice Kit
This is a general guide to common tools.
The kit you receive may differ!
5
Soldering Iron
Primary tool for soldering. It consists of a handle and
heating element. Basic models include 1-3 temperature
settings. More practical versions include an adjustment
knob for finer control. All models have replaceable tips.
Soldering Station
This is a more advanced version of a soldering iron, and typically includes features
like dial-temperature control, a resting stand, and a cleaning station. We stock
models that are affordable and reliable for many years with proper care.
Reusable Soldering Tips
Soldering Tips are typically made of a copper metal core plated with an Iron alloy. A variety of shapes exist, but most are
fairly versatile. Odds are, you will find one or two styles you like best and use them most. Changing tips frequently while
in a soldering session is not efficient or practical.
The most common tip types are Conical, Chisel, Knife, and Needle; but specialty tips exist for other, more unique
applications. The main things to consider when choosing a tip are your needs for heat transfer and working space.
Heat will transfer more
quickly when the area of
contact shared between the
surface and tip is larger. For
this reason, chisel tips can
make quick work of soldering
large wires. They can also
cause irreparable damage to
small SMD parts and
sensitive circuit chips. In
most cases, a conical or
needle tip works best.
a
b
c
d
e
A variety of soldering tips exist. Common types include:
Conical (a & b), Needle (c), Chisel (d), and Bevel (e) tips.
6
Common Tip Types
Conical Tips (B-Series)
Conical Tips are good general-purpose tips. They provide heat
application to a relatively focused area, so it may take slightly
more time to apply heat to larger pads and wires. Conical tips can
be used for nearly any soldering job, but may be too large to work
efficiently with smaller SMD components).
Needle Tips (I-Series)
When soldering IC pins individually, working with tightly grouped parts, or soldering small
SMD components, try using a Needle Tip. The small contact area means heat transfer takes
more time, so there is less risk of damaging heat-sensitive microchips.
Chisel Tips (D-Series)
This type of soldering tip can be great for general purpose soldering or for larger jobs,
depending on the tip's width. Wider tips are better for soldering large-gauge wires and desoldering grouped components. Chisel tips are, however, more likely to make accidental
contact with other joints near the work site, potentially causing damage or forming bridges.
The best chisel tip for general purpose use is one whose width allows the application of
directed heat to the pin and pad of one joint evenly and simultaneously, without contacting
nearby joints or components in the process.
Bevel Tips (C-Series)
Bevel tips have a small divot/recess on the working surface of the tip. This concavity holds
small amounts of solder for depositing on pins during the drag soldering process.
Bevel tips can also be used to fix solder bridges.
Specialty Tips
Specialty Tips include things like Bent Conical tips (for reaching difficult-to-access components), Knife tips (used for "drag
soldering"), and other variations of the above styles. They outperform the standard tips only in specific circumstances.
7
Changing Tips
With proper care, the same tip can be used for many years. Sometimes you might want to change to tip size to fit the
job. To change tips, first make sure your iron is completely cool. Unscrew the cap that secures the tips in place. Remove
the old tip and replace it with the one you would like to use. Tighten the cap until it is snug, but do not over-tighten it!
Solder
A variety of solder types exist. Not all solder is suitable for
electronics, so this section serves to help you identify what kind of
solder you should purchase as an ECE student. Solder is sold by
these criteria: 1) Composition and 2) Contents of Solder Core.
Solder Types, by Composition
Lead (Pb) Alloy Solders
Generally, a blend of ~60/40 Tin (Sn) and Lead (Pb), with trace amounts of other metals.
The melting points range 180˚C – 190˚C (or 356˚F – 374˚F).
As noted, Pb-solder is being phased out in many countries due to the permanent negative health + environmental effects.
Lead(Pb)-Free Solders
Pb-Free solders are generally made as a blend of Tin-Silver-Copper (Sn-Ag-Cu, or SAC), or a Tin-Copper or Tin-Silver alloy.
The melting points typically range from ~217˚C – 250˚C (or 423˚F – 482˚F).
Modern Pb-free solders with flux cores work as well or better than Pb-solder.
Solders with Core Additives
Some solder contains an inner core of flux to aid in wetting. More about these below.
8
Solders Types, by Contents of Core
Solid Core
Solid Core solder is the same composition all the way through.
There is no core of flux, so flux must be applied to the joint
manually to ensure proper wetting occurs. This makes solidcore solder a bit more difficult to use, requiring more care and
manual dexterity, but it can be done well with enough practice.
Rosin-Flux Core
Rosin Core solder is the go-to option for electronics soldering.
The flux core aids in wetting, and makes soldering significantly
easier than when using solid-core solder.
Acid-Flux Core
Acid Flux Core solder is not used for electronics soldering! It is for copper pipes and sheet metal.
Acid-based flux is aggressive and strong. Its high corrosiveness can damage PCBs!
Be careful when purchasing solder from retail stores!
Most big-box stores (such as Lowes, Walmart, etc.)
only sell welding (acid core) solder, not electronics (Rosin-Flux) solder.
9
Flux
What is flux?
Flux is a chemical compound used when welding or otherwise joining metals together. For Electronics Soldering, flux is
usually liquid or semi-solid, and either Rosin-based (from pine byproducts) or water-soluble.
Flux serves a few purposes; these include:
1) remove oxidation from metal surfaces (oxidation is described next on this page),
2) temporarily prevent the metal’s exposure to oxygen (thus preventing any new oxidation), and
3) improves the wetting (melting/flowing) of solder.
Oxidation
Solder alone is an acceptable joiner, but the soldering
process needs flux to work effectively because of oxidation.
Oxidation is a chemical reaction involving the movement of
electrons between surface metal ions and water. The metaloxygen bonds formed are very strong.
The new compounds are “metal-oxides”. Eventually, a
barrier of these oxidation products (commonly known as
rust) builds up on the metal surface.
Solder needs a clean and dry surface to form a strong bond,
but this barrier not only prevents hot solder from bonding, it
also makes heat transfer less efficient.
So, even though you apply a hot iron to both at the same
time, an oxidized pad may not get hot, while the
component you are trying to solder over-heats.
10
Oxidation prevents complete contact and
bonding. The bond-resistant surface may
cause the solder to “bead” against the
corrosion, like water on a rain jacket.
Flux is a reducing agent (something you'll
learn about in Chemistry) which means it
can reverse oxidation. Flux dissolves metaloxide molecules, leaving a metal surface
that is clean and receptive to bonding. Flux
also improves the “wetting” of solder,
meaning it helps the solder melt/flow.
Sometimes flux can leave a sticky residue. You should always remove this residue because it will collect dust and debris,
like wire clippings. To clean a PCB, disconnect any power sources then apply Isopropyl Alcohol (either 70% or 99% will
work) to a cotton swab and wipe the flux away. Allow all surfaces to air dry before reconnecting any power sources!
A soldering kit might include different kinds of flux. A common combination is flux in the form of a pen and a dipping tub.
11
Flux Pens
A flux pen is mostly used when de- or re-soldering.
To use: remove the cap and place the felt tip where
the flux should be applied, then gently depress the
tip to allow flux to flow through the felt to the PCB.
Be careful not to press down too hard or for too
long, as it can quickly overrun the working area.
Flux Dipping Tubs
A dipping tub is most useful for cleaning soldering tips, but can also be dabbed with a
toothpick or similar implement to apply small quantities of flux to a work surface. A
single tub should last a considerable amount of time. Use it anytime you want to “reset”
a soldering tip (be sure to follow this up by re-tinning the tip immediately)
You can dip your soldering tip into
the tub while hot, just do it quickly so
that as little smoke as possible forms.
Use your fume extractor
to capture the vapors!
Common Properties of Flux:
Activity
Activity is another word for reactivity; it describes flux's ability to remove oxidation. Highly active fluxes are often
reserved for heavy cleaning use-cases. For like-new components, Low to Moderate activity is sufficient.
Corrosivity
While Activity and Corrosivity are related, they are not the same. Fluxes that are highly corrosive are usually also highly
active. In most cases, a highly corrosive flux is only necessary for electronics when cleaning severely corroded boards
that have been exposed to the outdoor elements for long periods of time.
Cleanability
Some fluxes leave a sticky residue that must be cleaned with alcohol or other solvents. Some can be cleaned with only
water. Other so-called “No-Clean” fluxes don’t leave much of a residue at all, when used properly.
Conductivity
Rare for electronics solder, but good to be aware of. Flux with conductive ingredients must be cleaned away after use.
12
Brass Sponge Tip Cleaner
The brass sponge is an effective cleaning tool for your soldering tips.
To clean a tip, insert and remove the tip from the brass sponge repeatedly.
As the sponge is used, you
may need to change the angle
or position of insertion so that
fresh areas of brass are used.
Watch out; wear eye protection!
Try to only insert the soldering tip
into the sponge in a straight line.
Insertion at an angle can push loops of
the brass sponge aside, causing a
springing action that will fling bits of
solder into the air at surprising speeds.
At some point, you will need to "freshen up" the brass sponge. Wear gloves and eye protection, then remove the brass sponge
from the base. Gently squeeze and massage the sponge between your hands over a trash can, allowing the loosened solder
pieces to fall out. Afterward, the sponge can be put back in place or flipped around to provide fresh areas for use.
Tip Tinner
Tip Tinner is a mild acid mixed with solder powder.
Use it to quickly clean and maintain soldering tips. It works by de-oxidizing the
metal surface and providing fresh solder to bind immediately to the tip.
To use: insert a hot soldering iron gently into the
tinner. Press until the working surface of the tip is
beneath the surface of the tinner material, and
then pull the tip back out.
Catch the vapors with your fume extractor!
13
De-Solder Braid / Wick
A De-Solder Braid is used when de-soldering a joint. It
works by “wicking away” melted solder from a joint.
To use, lightly press the soldering tip to the wick over the
joint to be de-soldered. When the solder melts, it will be
adsorbed onto the wick in a short time. At this point,
remove the wick and soldering tip from the PCB. Clean the
joint if any residue remains.
Sometimes adding flux can help when de-soldering!
Flush Cutters
Flush Cutters are used to cut wires closely, and to trim
component leads after soldering them to a PCB. While their
name says "flush", the leads you cut should not be perfectly
flush with the solder.
It's a good idea to leave at least 2-3 millimeters protruding from the top of the solder joint. This provides a number of
minor benefits, including making it easier to test connections with a multimeter and de-/re-solder.
14
Wire Stripper
This is perhaps the most versatile tool in standard kits.
Its primary purpose is removing the insulation from wire, but its plier-like
end can be used for crimping and bending wire, while the cutter can be
used to snip wires and de-soldering braids. There is also a locking feature,
should you wish to hold onto something while keeping your hands free.
Bending and cutting wire are self-explanatory, but the technique for stripping wires is described below:
1) Notice the half-circles cut into each opposing face of the wire stripper.
2) Using the numbers for AWG (American Wire Gauge) or mm (millimeter)
on the face, place the wire in the appropriate "slot" such that about
1cm (0.4 in.) remains exposed on the face (image 'a', below).
3) Close the wire strippers around the wire carefully. If you've chosen the
correct size, the cutting edge will only slice into the insulation.
4) Hold the tool firmly and, with gentle but firm force, pull the long end
of the wire perpendicular (90˚) away from the wire stripper (image 'b').
The metal core should begin to slide out of the insulation (image 'c').
5) Pull the wire until the end is free of its shield (image ‘d').
The size of Breadboard- and Arduinocompatible wires is 22 AWG (0.6 mm)
a)
b)
c)
d)
15
Tweezers
A variety of types exist, each best suited for certain purposes. Tweezers
with flat ends are good for flattening braided wires for joining, or
holding on to a through-hole component.
Bent and Needle-Tip tweezers are good for getting into tight areas and,
with delicate handling, holding small SMD parts in place while soldering.
Pliers Set
A variety of types are often included.
There are small flush cutters, for working in tight
spaces, like inside an electronic device's case.
Standard pliers can be used for manipulating wire in
various ways or used as a heat sink while soldering.
Needle-nose pliers can be used to make small wire
manipulations and reach into tight spaces.
Wide-nose pliers make great heat sinks for sensitive
components, and are excellent for crimping wires.
16
Helping Hand
Helping Hands come in various styles, some more
“helpful” than others. The most useful types will have
multiple, independent arms with many individual joints
that are sturdy but still flexible. Some more advanced
models even come with accessories, like a weighted
base, USB-powered flashlight, or magnifying glass.
Digital Multimeter
One of the tools you’ll reach for frequently is a Digital Multimeter.
With it, many circuit problems can be diagnosed quickly.
A basic multimeter will be capable of measuring or testing
1) AC and DC Voltage, in Volts (V)
2) DC Current, in Amps (A)
3) Resistance, in Ohms (Ω), and
4) Continuity (yes or no)
This versatile tool will be covered in more depth in future labs.
If your multimeter stops working properly, consider:
1) It could be a circuit anomaly, like an interfering signal.
Test something you know the approximate value of (small, regulated power source, resistors of known value, etc).
2) If it is still giving inconsistent values, the batteries may be low! Replace them with new batteries and try again.
3) If it happened suddenly, you may have blown the fuse! See your device’s instruction manual for instructions.
17
Soldering Process
How to Solder:
0) Safety First!
Do
•
•
•
•
•
•
•
Always return the Soldering Iron to its resting stand when not actively soldering.
Solder in a well-ventilated area (not a dorm or bedroom). Use the fume extractor to catch soldering fumes from the air!
Use the protective silicone mat when soldering!
Always wash your hands with soap and warm water after soldering or handling components and circuit boards!
Be cautious of hanging cables and hot irons when walking around the lab!
Make sure any belongings of yours are tucked out of the way of any walking paths!
Ask questions if you are confused on what to do.
Don't
•
•
•
•
•
Don’t touch the heating element or soldering tip when hot.
Don't let the hot parts of the soldering iron come in contact with any cables, the table surface, other objects, or a person.
Don't allow your cables (from your computer, soldering iron, air filter, etc) to hang over the table edge.
Don’t leave a hot iron unattended!
Don’t eat or drink while in a soldering session, and don’t do so without washing your hands with warm soap and water first!
18
I: Set Up your Work Space
Arrange things in front of you according to your preferences. As a right-handed user, I personally find it easiest to arrange
things as diagramed below. Notice the area highlighted by the blue arc in the Figure below. This arc represents the
comfortable reaching range for you. Keep the items you use frequently here. I prefer to keep the tools shown below out
and ready, while other tools (like the tweezers, pliers, etc.) are usually kept in my toolbox until needed.
EXAMPLE WORK STATION LAYOUT
(top-down view)
Set out the tools you will need, and leave anything you won’t use frequently in your toolbox. You can organize your work
space nearly anyway that feels comfortable to you. The main concerns are to 1) make sure that the fume extractor is close
enough to your soldering action to catch the vapors you create, and 2) be tidy in how things are laid in front of you.
Besides the Soldering Iron itself, the items you will most often use when soldering include:
•
•
•
•
•
Fume Extractor
Protective Silicone Mat
Helping Hands
Solder
Tip Tinner
•
•
•
•
•
Brass Sponge
Flux (tub or pen, depending on the task)
Wire Strippers
Multimeter
Computer or Paper references
19
Before you begin, ensure that no cables are hanging over the table edges and that your arrangement does not encroach
into any neighbors’ work space. When you are ready to start:
1) Plug the Soldering unit in, adjust the temperature to your preferred setting, and turn the iron on.
For Lead(Pb)-Free solder, try 217˚C – 227˚C (or 423˚F – 441˚F)
The precise dial setting varies for each model. You will know it is at the right
temperature when solder only takes 1-3 seconds to flow (melt).
2) It will take 8 - 15 minutes for the iron to reach its set heat level each time it is turned on from room
temperature. When it is ready, solder will melt fairly quickly once held to the hot tip.
Water and electronics are not friends; be careful!
Dry up any stray water ASAP.
In the meantime, finish setting up.
3) Ready the sponge. It should be damp, but not wet!
The sponge should not drip when held upright.
4) Clean the iron's tip of dust by wiping it on the damp sponge.
5) Test the iron’s temperature.
Touch a small amount of solder to the iron's tip. If it does not melt within 1-3 seconds, wait a few
minutes longer for temperature to rise. Once it melts as described, apply solder to the tip until
there is a thin layer of fresh solder covering the working surface of the tip (see figure)
This is called "Tinning" the tip.
Tin your tip:
1) when starting a soldering session,
2) every ~5-10 minutes while soldering, and
3) immediately after switching the iron off.
Tin this area
Having trouble tinning, even at a good temperature?
If a particular dial setting usually works for you, the iron has had time to warm up
(~15 minutes from cold), and solder still isn’t melting, there may be tip oxidation!
Try using the brass sponge and tip tinner on your hot soldering tip, then try again.
In the future, you can prevent this from happening by tinning at the end of the session.
20
II: Prepare the Surface
For excessive oxidation (restoring old devices, or those exposed to the
elements for extended periods), a higher activity flux may be needed.
6) Clean up and dry any components or areas of the work site that have dust, residue, or visible
oxidation before soldering.
7) Blow off any dust (into the fume extractor, ideally). Use Isopropyl Alcohol to clean flux residue.
Apply a small amount of low or moderate activity flux to oxidized areas, then clean with alcohol.
III: Access the Schematic
Every circuit is carefully designed! Many calculations and simulations are used to pre-check a design so that the right
amount of current travels through the right paths, at the right times. To prevent errors and irreversible damage, these
plans must be followed exactly, with parts that closely match the schematic (within the tolerance of values allowed).
Make the Circuit Schematic easily accessible during your soldering session. Computer or paper is fine.
There are two very important things you must know before soldering any component:
Its proper 1) Position and 2) Orientation.
Position
This factor refers to each part’s location in the circuit and on the PCB. It is of course critical to solder them into the correct
locations so that the design is followed, but one should also think about how parts are positioned relative to each other.
For instance, you may want to solder small resistors first and large capacitors after, or you may wish to solder a microchip
onto the board before adding other parts that might get in the way of the chip’s small and tightly-grouped pins.
In addition, the leads of some parts (like transistors, LEDs, and some capacitors) must each be in a certain spot to work.
When this “polarity” matters, good designers print symbols on the PCB so parts can be placed facing the right direction.
Orientation
The second factor is a part’s orientation on the PCB. Ideally, each component will be soldered flat against or parallel to
the PCB surface, and centered in place.
There are a few exceptions. Some resistors need to be soldered vertically, and other parts may require a certain height
from the PCB for fit or temperature purposes, but most parts can be soldered as described here.
21
IV: Prepare to Solder
It is almost time to start soldering. Just a few final steps and tips before you begin!
Acquire the part you wish to solder
8) Double check all part values before soldering! Similar parts are very easy to mix up.
Some schematics show the actual value for the part in the circuit (e.g. “220 Ω”), while others use an alphanumeric
placeholder. For example, resistors might be labeled R1, R2, R3, etc.; or capacitors listed as C1, C2, etc.
Stabilize the PCB, then Secure the Component into Place
9) Use a Helping Hands unit to hold the PCB at a favorable angle for soldering.
10) Place one component into position on the PCB. It’s often be helpful to secure it, too, before
soldering. Check the box below for common and unconventional ways to secure your parts.
Tips for Holding Components while Soldering
Flat Surface
Bend a Lead
Stack something flat (and non-flammable)
underneath to rest the assembly on.
Bend one or more leads to secure the part
until the first joint is soldered. Straighten each
remaining lead before soldering it. Adjust as
needed to remain flat.
Putty
Tape
Putty is a great way to hold parts in position.
Blu-Tack is a popular brand. Place the part,
then and press the putty around the part on
the non-soldering side of the PCB to secure it.
The best tapes to use can be easily
repositioned and will leave no residue.
For example, consider using Electrical tape,
masking tape, or plumber’s tape.
Clip or Clothespin
Hold one lead on the soldering side securely
with the clip. Solder the other lead, then
remove the clip, adjust the part as needed,
and solder the remaining lead.
Combine Methods
Use one trick for the first lead, and another for
the next, or try multiple at the same time.
22
11) Once you feel confident the part is secured, continue with the instructions below
V: Apply Heat briefly, then Add Solder
12) Using a pen-holding grip with your preferred hand, take hold of the handle of the soldering iron.
Don’t apply heat for too long!
Many parts can be damaged easily.
If solder won’t flow after ~3 seconds of
heat, STOP! Let the area cool, then apply a
small amount of flux before trying again.
13) Identify which lead and pad you will
solder. Gently touch the hot tip of the
soldering iron to the pad and lead for
~1-3 sec
14) Add solder by gently pressing it
where the pin and pad meet, but on the
opposite side of the pad from the iron’s
tip.
(see the diagram to the left)
Touching the solder to the pin AND pad simultaneously in this location (instead of to the iron itself)
helps prevent one of the biggest causes of poor soldering: insufficiently wetted joints.
VI: Ensure Even Heating
15) Stop adding solder when just enough covers
the joint, but keep the hot tip in place for 1-2
more seconds to make sure that the pin, pad,
and solder all reach the same temperature.
Doing this helps create stronger bonds
between the metals as they cool together.
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VII: Allow Joint to Cool, then Inspect for Quality
16) Let the joint cool, then check that it conforms to characteristics of a good quality solder joint.
It’s significantly easier to add
more solder than to remove excess!
Add just a small amount of solder
at a time to avoid over-soldering.
17) Before you decide you are finished
soldering any PCB, check all joints.
Look for errors like those in the Common
Problems section. Fix the mistakes.
VIII: Clean Up
18) When you are finished soldering for the day, turn the iron off and immediately tin the tip!
19) Clean up any flux residue
remaining on the board. Clip long
leads and dispose of clippings.
20) Finally, tidy up your workstation
and put away all tools/equipment.
Then go wash your hands with
soap and warm water!
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Other Soldering Techniques to Know
Drag Soldering
This is an efficient way to solder parts with lots of closely-arranged pins, like microchips!
1) To Drag Solder, you will need either a Knife– or Bevel–style tip
The area highlighted in blue is the “dragging face” (see diagrams) –>
2) Beginning with a hot iron tip, apply solder (a little more
than what you would use when tinning) to the dragging face.
An example solder on a knife-style tip is shown to the left.
3) With the component secured in its place, identify a
group of ~2-4 pins to solder. Rest the tip’s edge across
the pins near (but not touching!) the microchip for
1-2 seconds. (see the blue line, in the diagram) –>
4) Next, slowly and smoothly drag the tip towards the outer edges
of the pads while keeping contact. When you reach the end of the
pad, pull the soldering tip up and away.
5) Repeat for any remaining pins.
If you accidentally create a solder bridge, try the dragging technique without
the added solder on the tip (this will draw solder onto the tip and away from the pins).
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De-Soldering
De-Soldering is exactly what it sounds like: removing solder from a joint when fixing mistakes or replacing damaged parts.
1) To de-solder, first get your de-soldering braid.
2) Place a clean end of the braid against the joint.
3) Gently press a hot tip down onto the braid at the joint.
4) The
braid,
solder,
and
joint
should
reach a similar temperature for best results!
all
If possible, touch the pad or pin AND the braid
with the soldering tip, for quicker de-soldering.
5) Once the solder has melted and wicked to the braid,
smoothly pull the braid and iron away.
6) Let the PCB and component cool before removing solder again!
For big wires or faster de-soldering, use a
larger tip for greater heat transfer.
Be mindful of sensitive parts!
Use a smaller tip for these, or try a drag
de-soldering technique for microchips.
Be sure to use clip off the ends of the braid once it becomes
saturated with solder, as needed.
7) Repeat the steps above until a satisfactory amount of
solder has been removed.
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General Soldering Advice
Resist the urge to dump components out onto the work surface.
Only retrieve the next few parts you are about to solder!
This will vary with the solder alloy’s characteristics and core
type, but one can generally reheat the same solder joint 2-4
times before it will need new flux to wet.
A few more resolders after that, and you might consider desoldering the joint and starting over with fresh solder.
If the same joint requires more than one complete soldering or desoldering action (3–5 seconds of heat for the process), make sure
to let the area cool completely before starting again!
Wait a bit longer for the parts to cool than you think you need to.
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The Ideal Solder Joint
Tricks for Consistently Good Results:
There are several main features of an ideal joint that you should strive for. The first and most important factor is the
wetting angle. Wetting is the term used to describe the physical process of solder melting to a completely liquid state.
Proper wetting is needed to form strong bonds between the pin, pad, and solder metals. Without proper wetting, the
bonds between the metal types will be weak and susceptible to breakage. The proper wetting angle results in a shape
that is similar to a volcano, meaning, the solder should form a gentle concave slope from the outer edges of the pad to a
roughly equal distance up the pin. Clip any excess length off the end of the pin such that, for the total length on the solderside of the board, about 1/3 of the pin’s length is exposed, and the remaining 2/3 is covered in solder.
Other keys to a good quality solder joint include:
•
Use the right temperature!
o A properly tinned tip, at the right temp,
will melt solder in 2-3 seconds.
•
Keep the tip properly tinned!
o Tin the tip manually with solder, or use the
tip tinner! Tin frequently (every ~5-8 min).
•
A Brass Sponge –> Tip Tinner combo can help
“reset” almost any iron tip for good soldering.
Dip in flux after using the brass if the tip has
been extra stubborn about getting tinned.
Common Problems:
This final section of this guide will highlight frequently made mistakes, offer repair
suggestions, and advise preventative measures for the issue at hand.
For soldering coursework, check each assignment’s rubric for information on how soldering is graded.
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Improperly Placing Components
One of the most important problems to avoid is improperly placed components. The successful operation of every device depends on
each piece being soldered in the correct location and orientation. This also impact’s the device’s longevity. Parts should be soldered
in position (ideally unbendable or only barely movable), and with proper soldering technique to ensure lasting connections.
How to Identify:
Most components should be aligned flat against the PCB, and secured perpendicular or parallel
to the board. There are a few exceptions (vertical resistors, for example)
Components that do not fit these criteria are susceptible to being bent and broken during casual use.
How to Fix and Prevent:
How to Fix:
1) Re-Heat and Re-Position Angled Parts
a. Re-heat a pin(s) and, as the solder liquifies, bend the part closer to its proper angle.
b. Next, re-heat another joint and continue to bend the part closer. Return to each pin as needed,
re-heating and re-positioning as needed until the part is in its best alignment.
2) De-Solder Backwards or Severely-Angled Parts
a. Use a de-soldering technique to fix these bigger mistakes. You may only have to
de-solder some of the pins before the first technique above will begin working.
Prevention:
• Double- or triple-check schematics and part orientation before soldering.
• Keep each part stable until its soldering joints have set.
• Use soldering aids (e.g. tape, putty, etc.) to secure parts while soldering.
• Consider what order you will solder parts in, to prevent issues with access space.
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Insufficient Wetting
This is probably the most common issue seen in beginner
soldering practices. Luckily, it is very simple to prevent and fix!
Typically occurs when the solder, pin, and/or pad do not reach the same temperature. A surface layer of liquid
solder is cooled too quickly, forming a thin "skin" of partially solidified solder. This layer doesn’t bond well with
other surfaces, and the result is a weak connection between the two metals.
How to Identify:
This type of mistake is best identified by the “bubble” of solder that forms, like water on a rain coat.
A cooler temperature pin or pad can cause the solder to form a skin, preventing a bond. Often times, solder
will bond well to one surface, but not the other. This indicates uneven heating of the pin and pad!
(pad)
(pad)
(both)
(pad)
(pad)
(pad)
(part)
(pad)
(pin)
How to Fix and Prevent:
How to Fix:
1) Re-Heat, but More Evenly
a. Apply a balanced application of heat to the pin and pad for 3-4 seconds
b. A second or two after the solder has melted, withdraw from the joint and check it.
c. If another attempt is needed, a touch of flux might help.
Prevention:
• For one-off errors, simply try heating a bit longer before or after adding solder.
• If one joint is repeatedly not bonding to solder, identify the contributor to blame (pin, or pad), add flux,
and heat that area up for an additional second or two before following the steps above.
• If this happens frequently, turn your iron temperature up a little.
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Over-Soldering
This happens when too much solder is applied to a joint. It isn’t the easiest to fix, but it’s very easy to prevent!
How to Identify:
An over-soldered joints will have a round (convex) surface, and the solder may extend well
beyond the pad or encroach into the space of another pin or pad. The solder may also hide the
pin, or seep down into a through-hole opening to the other side of the board.
✓
How to Fix and Prevent:
How to Fix:
1) A Freshly-Cleaned (and un-tinned) Tip
a. A tip fresh out of the brass sponge can wick small amounts of solder away from a joint.
b. Clean the hot tip, but don’t tin it (much, if you have to).
c. Touch the tip to the solder to melt it, and once the solder flows withdraw the iron.
d. Dip the tip in the brass sponge before the next attempt (if needed).
2) De-Soldering Braid
a. In excessive cases, try de-soldering with the solder braid / wick.
Prevention:
• Apply solder to joints at a slower rate.
• Use a smaller-diameter solder (for example, when soldering little Surface-Mount components).
• Use a smaller soldering tip, so less solder is available to flow into the joint when working
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Under-Soldering
How to Identify:
An under-soldered joint may be too flat, or have a surface with a steep, convex slope.
In other cases, the solder may not completely cover the pad or fully surround the pin.
How to Fix and Prevent:
How to Fix:
1) Re-Heat and Add More Solder
a. Apply a hot soldering tip to the joint until the solder flows.
b. Add a small amount of new solder until the right amount is present at the joint, then stop.
c. Withdraw the iron’s tip after an additional second or so of heat to the joint.
Prevention:
• If this is a persistent issue, try adding solder at a slightly greater pace than you have been.
Sometimes a joint can appear under-soldered, when in reality the liquid
solder has leaked through the pin’s hole onto the other side of the PCB.
Don’t add too much solder at once before checking the joint.
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Disturbing the Joint
How to Identify:
These can best be identified by their frosted, rough, and/or lumpy appearance. They will occur
when motion interrupts the crystallization process required to form strong metal bonds.
Disturbed joints are weak and may cause problems in your circuit over the lifetime of the device.
How to Fix and Prevent:
How to Fix: (note: you will often need to re-position the part while fixing this type of joint)
1) Re-solder + Stabilize
a. Heat the joint long enough to sufficiently wet the solder and bring the pin+pad to temperature.
b. Gently pull the iron’s tip away from the joint, and allow the joint to set and cool undisturbed
Prevention:
• Each component should be secured carefully before (and while) soldering! Helping hands, putty, tape,
and other methods are the best way to prevent disturbed joints.
This happens frequently in joints that are over-worked.
After reheating solder a few times, apply additional flux to the worksite.
If joints continue to look disturbed despite great care, they might be a
Cold Joints from a low soldering temperature. See the next page!
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Cold Joints
How to Identify:
Cold joints will appear frosted and lumpy; most commonly, they will have a characteristic “peak” that
occurs when the iron tip is pulled away. Cold Joints might also resemble an insufficiently wetted joint in
areas where the solder contacts the pin or pad. It occurs when the solder solidifies too quickly, or when it
does not reach a high enough temperature first before cooling to a solid.
How to Fix and Prevent:
How to Fix:
1) Re-Heat
a. Heat the pin, pad, and solder for a longer time to ensure it reaches the proper temperature.
Prevention:
• Avoid raising your iron’s temperature except as a final troubleshooting option.
• Check for drafts of air that may be prematurely cooling the joint.
• Sometimes, a larger tip style can prevent this problem when soldering larger items, like wires.
o The more tip surface area in contact with the joint, the more heat is transferred from the tip.
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Overheating
Small parts and microchip pins are more susceptible to this than large pads and wires.
How to Identify:
Typically, joints that get too hot will leave evidence in the form of a brown or black sooty deposit.
Often the flux is responsible for this, but it is also possible to char or burn the PCB’s protective mask.
In addition to the soot, the solder may also appear crumply (due to the flux burning off), or frosted.
How to Fix and Prevent:
How to Fix:
1) First, Clean the Area
a. If the joint appears scorched in any way, use Isopropyl Alcohol on a cotton swab or folded
paper towel to clean up any Flux residue and sooty material
b. Allow the site to air dry fully
2) Then Re-Solder, with Caution
a. Areas that reach high temperatures should be treated delicately. A copper trace or pad is more
likely to peel away from the PCB after a scorching event.
Prevention:
• Apply heat for less time, or use a lower soldering temperature setting.
• Use a smaller soldering tip, so heat is transferred more slowly to your joints.
• Use a Heat Sink to prevent damage.
o When soldering the lead or pin of a sensitive component, hold pliers to the lead between the
heat and the component’s body. The pliers will absorb extra heat, helping to prevent damage.
35
Solder Bridges
Solder Bridges can cause damage to active circuits! Make sure your
PCB is bridge-free before connecting any power sources.
The cause is often using too much solder, but bridges can also be made via accidental contact to other joints.
How to Identify:
A solder bridge is a real-life short circuit defined by any unintended electrical connection between
nearby elements on a PCB. This most commonly occurs when soldering microchips or other closelyarranged pins and pads, such as those often found in Surface-Mount designs.
Unsure if you have a bridge? Use the multimeter’s continuity/diode tester setting!
Touch one probe to each joint of the suspected bridge. If continuity is positive, it is most likely bridged (check schematic).
How to Fix and Prevent:
How to Fix:
1) Partial De-Solder
a. Try first wicking a small amount of solder away from the joints with a freshly cleaned tip (via
brass sponge). Apply a hot tip to the solder, and pull away a second or two after it melts.
b. If the bridge is still present, use the brass sponge again before repeating.
2) Complete De-Soldering
a. Follow the steps for De-Soldering, then re-solder the joints (but more carefully)
Prevention:
• Apply less solder to closely-spaced soldering locations, so the solder doesn’t flow outside its pad
• Mind the direction solder is pulled when removing a hot tip
36
Lifted Pads
This can be a very difficult repair to make!
Do your absolute best to prevent this.
Lifted pads are caused by single extreme heat events, or by repeated exposure to moderate temperatures through
several heat-cool cycles (resoldering the same joint too much).
How to Identify:
This is one that is very easy to recognize once it happens; look for peeling or hanging traces.
The trick is spotting these before it’s too late. Just before the pad pulls away from the PCB, you will
notice the margins of the pad gain a small shadow underneath the lip of the pad (see image, below right)
How to Fix and Prevent:
How to Fix:
1) Conductive Tape
a. A small piece of conductive copper tape can re-connect the trace and the pad.
b. Remove as much evidence of overheating as possible, if present (apply flux, then clean).
c. You may need to gently scrape away some PCB mask to expose the metal part of the trace.
2) Jumper Wire
a. In the worst of cases, you can often still salvage the board by using a jumper wire.
b. Connect the parts directly (lead to lead) using a jumper wire, if possible. Check schematic!
c. Otherwise, Scrape away an area of PCB mask or apply flux, if needed.
d. Take a small wire and solder a connection between the wire+part.
e. Then solder a connection between the wire+trace (or to wherever the trace leads).
Prevention:
• Use less heat, either by heating for a shorter time or using a lower temperature
• Be more careful when soldering so re-soldering is not necessary
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