Soldering Guide

Soldering Guide
Competency	Soldering
Difficulty	Beginner
Time Required	1-2 hours (practice) + 30 minutes (theory)
Prerequisites	None - complete beginner friendly
Materials Needed	Soldering iron ($20-50), lead-free solder, safety glasses, ventilation, practice kit or perfboard
Next Steps	SimpleBot PCB assembly, Soldering Techniques

Soldering Guide is your introduction to the hands-on technique of joining electronic components with molten metal. This tutorial covers everything you need to safely and successfully solder through-hole components for SimpleBot and other BRS robots.

By the end of this tutorial, you'll be able to:

Set up and safely operate a soldering iron
Create reliable solder joints on through-hole components
Recognize good joints vs cold joints vs bridges
Solder wires to terminals and pads
Troubleshoot common soldering problems

This tutorial is hands-on. Plan to spend 1-2 hours practicing before attempting your first real PCB.

Part 1: Safety First

Soldering involves high temperatures and fumes. Before you start:

Essential Safety Rules

Wear safety glasses - Solder can spatter, component leads fly when clipped
Ventilate your workspace - Work near open window or use fume extractor
Never touch the iron tip - Reaches 300-400°C (572-752°F)
Use a proper iron stand - Never lay hot iron on desk
Keep flammable materials away - No paper, plastic, or fabric near hot iron
Wash hands after soldering - Especially important with leaded solder
Never leave hot iron unattended - Turn off or unplug when leaving

Understanding the Hazards

Burns - Iron tip can cause instant, serious injury; handle only by the insulated grip
Fumes - Flux produces irritating smoke containing rosin or other compounds
Lead exposure - Traditional 60/40 solder contains lead; use lead-free or handle carefully
Fire - Hot iron can ignite paper, plastic, sponges left in contact
Eye injury - Clipped component leads can fly across room at high speed

If you get burned: Cool immediately under cold running water for 10+ minutes. Seek medical attention for serious burns.

Part 2: Tools and Materials

Soldering Iron Selection

You need a temperature-controlled soldering iron for electronics work:

Recommended irons ($20-50):

Hakko FX-888D ($90) - Industry standard, very reliable
Pinecil ($30) - Portable, USB-C powered, excellent value
TS100 ($50) - Portable, battery-compatible
Weller WLC100 ($40) - Basic analog temperature control

Avoid:

Non-temperature-controlled irons (too hot, damage components)
High-wattage soldering guns (too powerful for electronics)
Ultra-cheap irons under $15 (unreliable temperature, poor tips)

Tip selection: Start with a chisel or cone tip (1-2mm). Avoid fine needle tips for beginners.

Solder Selection

Lead-free solder (SAC305: 96.5% Sn, 3% Ag, 0.5% Cu) - Recommended, melts at 217°C
Leaded solder (60/40: 60% Sn, 40% Pb) - Easier for beginners, melts at 183°C, but contains lead
Diameter - 0.8mm for most electronics work (0.5mm for fine-pitch, 1.0mm for larger joints)
Flux core - All electronic solder has rosin flux core (essential for good flow)

For learning: Leaded solder is easier to work with (lower temperature, better flow). Use lead-free for production projects. Wash hands after handling either type.

Additional Essential Tools

Solder stand - Holds hot iron safely
Brass wool or wet sponge - Clean iron tip (brass wool better, doesn't cool tip)
Safety glasses - Protect eyes from solder spatter and flying leads
Wire cutters - Flush-cut type for trimming component leads
Practice board - Perfboard or through-hole practice kit

Helpful But Not Essential

Helping hands - Third hand with alligator clips to hold work
Magnifying glass - Inspect joints for defects
Solder wick - Braided copper removes excess solder
Flux pen - Extra flux improves difficult joints
Desoldering pump - Sucks up molten solder for removal

Part 3: Iron Setup and Maintenance

First Time Setup

Read iron manual - Temperature settings vary by model
Install tip - Most irons come with tip installed; tighten securely
Set temperature - 350°C (662°F) for lead-free, 320°C (608°F) for leaded
Place in stand - Secure stand location away from flammable materials

Tinning the Tip (Critical Step!)

Tinning means coating the tip with a thin layer of solder. This:

Protects tip from oxidation
Improves heat transfer to joints
Extends tip lifetime

Tinning procedure:

Heat iron to working temperature (2-3 minutes)
Clean tip on brass wool or damp sponge
Immediately apply solder to tip - should melt and coat tip surface
Wipe excess on brass wool, leaving thin shiny coating
Tip should be shiny silver, not black or brown

Re-tin every 3-5 joints to maintain performance. Always tin before turning off iron.

Tip Cleaning

Clean tip before every joint:

Brass wool (preferred) - Wipe tip, doesn't cool it down
Damp sponge - Wipe tip, cools it temporarily (recovers quickly)

Never use file, sandpaper, or abrasive - damages tip plating!

Tip Maintenance

Oxidation - Black or brown crusty coating prevents heat transfer
Prevention - Keep tip tinned at all times, clean frequently
Recovery - Use tip cleaner/activator (Hakko FS-100) or replace tip

When to replace tip:

Pitting or holes in plating (copper core visible)
Can't maintain tinning even after cleaning
Tips are consumable ($5-10) and last 6-12 months with proper care

Part 4: Making Your First Solder Joint

The Basic Technique

Creating a solder joint has four steps:

Heat the joint (not the solder)
Apply solder to the joint (not the iron)
Wait for solder to flow (1-2 seconds)
Remove iron and hold steady (2-3 seconds while cooling)

Step-by-Step: Through-Hole Resistor

Setup:

Insert resistor leads through perfboard holes
Bend leads slightly on bottom to hold in place
Position board so you can access solder side

Soldering:

Clean and tin iron tip
Touch iron to both pad and component lead (contact both!)
Wait 0.5-1 second for heat transfer
Apply solder wire to the junction of pad and lead (not to iron tip)
Solder should melt and flow smoothly around lead and onto pad
Remove solder wire (joint should have small amount of solder)
Remove iron (total contact time 2-3 seconds)
Hold component steady for 2-3 seconds while solder solidifies
Solder changes from shiny-liquid to matte-solid when cooled

What you should see:

Solder flows smoothly onto pad and up component lead
Forms concave "fillet" shape (like volcano)
Shiny, smooth surface after cooling
No excess solder (blob) or insufficient solder (barely wetting)

Common Mistakes (And How to Fix Them)

Mistake 1: Cold Joint

Appearance: Dull, grainy, crystalline surface
Cause: Insufficient heat - solder didn't flow properly
Fix: Re-heat joint until solder melts and flows smoothly

Mistake 2: Too Much Solder

Appearance: Large blob obscuring pad and lead
Fix: Remove excess with solder wick (see Part 7)

Mistake 3: Disturbed Joint

Appearance: Cracks, irregular surface
Cause: Component moved before solder fully solidified
Fix: Re-heat until solder melts, hold steady while cooling

Mistake 4: Insufficient Solder

Appearance: Solder barely touches pad or lead, no fillet
Fix: Re-heat and add more solder

Mistake 5: Solder Won't Flow

Cause: Dirty/oxidized surfaces or insufficient heat
Fix: Clean surfaces, increase temperature 10-20°C, use flux

Part 5: Recognizing Good Solder Joints

The "Ideal" Solder Joint

A properly made through-hole solder joint has:

Shiny surface - Smooth, reflective (not dull or grainy)
Concave fillet - Solder flows up lead in smooth curve (volcano shape)
Complete wetting - Solder visibly adheres to both pad and lead
Appropriate amount - Enough to form fillet, not a blob
Pad fully covered - No exposed copper on pad
Lead well-coated - Solder flows partway up component lead

Visual Inspection Checklist

Examine each joint under magnification if possible:

☐ Shiny, not dull - Indicates proper temperature and flow
☐ Concave fillet - Not ball-shaped or flat
☐ No cracks - Joint wasn't disturbed while cooling
☐ No bridges - Adjacent pads not connected by solder
☐ Pad visible - Can see solder flowed onto pad
☐ Lead visible - Can see solder flowed up lead

Bad Joint Examples

Cold joint:

Dull, grainy, crystalline appearance
Solder didn't flow properly at temperature
Poor electrical connection, may fail intermittently
Fix: Re-heat until solder melts and flows smoothly

Insufficient solder:

Pad or lead not fully wetted
May look like solder "balled up" instead of flowing
Poor mechanical strength
Fix: Add more solder while heating

Excess solder:

Large blob, can't see pad or lead
Wastes solder, may hide defects underneath
Fix: Remove excess with solder wick

Solder bridge:

Unwanted solder connection between adjacent pads
Causes short circuit
Fix: Remove with solder wick or carefully with iron

Part 6: Wire Soldering

Robots need soldered wire connections for motors, batteries, and sensors.

Soldering Stranded Wire to Terminal

Stranded wire (multiple thin strands) is flexible but requires tinning:

Strip insulation - Remove 3-4mm (just enough to fit in terminal)
Twist strands together - All strands aligned, no fraying
Tin the wire - Heat wire end, apply solder until solder wicks into strands
Position in terminal - Insert tinned wire into terminal hole or pad
Solder joint - Heat terminal and wire, add solder if needed (wire may have enough)
Hold steady - Wait 2-3 seconds for solder to solidify
Tug test - Gently pull wire - should not come loose

Why Tinning Matters

Untinned stranded wire:

Individual strands don't all make contact
Strands can fray and short to adjacent terminals
Difficult to insert into terminal holes

Tinned stranded wire:

Behaves like solid wire (all strands bonded)
Easy to insert into holes
All strands make electrical contact

Soldering Solid Wire

Solid core wire (single thick strand) doesn't require tinning:

Strip 3-4mm insulation
Insert wire into terminal or wrap around post
Heat wire and terminal together
Apply solder - flows onto wire and terminal
Hold steady while cooling

Part 7: Desoldering Basics

Mistakes happen. You need to remove solder or components sometimes.

Desoldering with Solder Wick (Braid)

Solder wick is braided copper wire that absorbs molten solder:

Place wick on top of unwanted solder
Press hot iron tip onto wick (heats solder through wick)
Solder melts and wicks into braid by capillary action
Remove iron and wick together (solder solidifies in wick)
Cut off used section of wick, repeat if needed

Tips:

Apply flux to wick for better solder absorption
Press firmly - good contact needed for heat transfer
Fresh wick works better than saturated wick

Desoldering with Solder Sucker (Pump)

Solder sucker is spring-loaded vacuum pump:

Heat solder joint until molten
Position sucker tip near molten solder
Press sucker button - creates vacuum, sucks up solder
Clean sucker tip before next use

Tips:

Position sucker before pressing button (solder solidifies quickly)
May need multiple attempts for large joints
Works best on through-hole joints

Removing Through-Hole Components

Heat one lead, pull component gently (don't force!)
Heat other lead, pull gently
Alternate heating leads until component releases
Alternative: Use solder wick or sucker to remove all solder first, then pull component

Warning: Excessive force can lift pads (damage PCB). Heat sufficiently before pulling.

Part 8: Practice Exercises

Before attempting SimpleBot PCB assembly, practice these exercises:

Exercise 1: Basic Through-Hole (20-30 joints)

Materials: Perfboard, 10-15 resistors, solder

Insert resistors in perfboard (space them out)
Solder one lead of each resistor
Inspect each joint - shiny? Concave fillet?
Solder second lead of each resistor
Inspect all joints

Goal: Consistent, shiny joints with proper fillet shape.

Exercise 2: Wire Soldering (5-10 wires)

Materials: Stranded wire, terminal blocks or pads

Cut 5 wire pieces (5cm each)
Strip and tin each wire
Solder wires to terminals or pads
Tug test each wire

Goal: Secure wire connections that don't pull loose.

Exercise 3: Close-Pitched Joints (IC Socket)

Materials: Perfboard, IC socket (14-pin or 16-pin)

Insert IC socket in perfboard
Solder all pins (pay attention to spacing)
Inspect for solder bridges between adjacent pins
Use wick to remove any bridges

Goal: All pins soldered without bridges.

Exercise 4: Desoldering Practice

Materials: Previously soldered perfboard, solder wick or sucker

Remove 5 resistors using solder wick
Remove 5 resistors using solder sucker (if available)
Inspect pads - should be clean and intact

Goal: Remove components without damaging pads.

Part 9: SimpleBot PCB Assembly

You're now ready to assemble the SimpleBot PCB!

Component Order (Solder Shortest First)

Resistors - Flat against board, solder from bottom
Capacitors - Watch polarity on electrolytic capacitors
IC sockets - Notch indicates pin 1 direction
Headers - Hold straight while soldering first pin
Terminal blocks - Large joints, may need more heat
Inspect - Check every joint before continuing

SimpleBot-Specific Tips

Motor terminals - Large joints require higher heat and more solder
Power connector - Double-check polarity before soldering
Pin headers - Tack one pin first, adjust if crooked, then solder rest
IC orientation - Notch or dot indicates pin 1

Full assembly guide: SimpleBot:PCB Assembly

Part 10: Troubleshooting

Problem: Solder Won't Melt

Cause: Temperature too low
Fix: Increase iron temperature 10-20°C

Problem: Solder Balls Up Instead of Flowing

Cause: Oxidized surfaces or insufficient flux
Fix: Clean surfaces with brass wool, apply flux, increase heat

Problem: Iron Tip is Black/Brown

Cause: Oxidized tip (not tinned properly)
Fix: Clean with brass wool, immediately tin with fresh solder

Problem: Joint Looks Good But Fails Electrically

Cause: Cold joint - solder didn't bond despite appearance
Fix: Re-heat joint until solder melts and flows smoothly

Problem: Component Gets Too Hot

Cause: Taking too long to solder (heat soaking component)
Fix: Work faster (2-3 seconds per joint), use higher temperature for faster heat transfer

Problem: Lifted Pad

Cause: Excessive force or heat damaged adhesive between pad and PCB
Fix: Solder component lead directly to trace (requires scraping soldermask), or use jumper wire

Part 11: Skills Checklist

By now, you should be able to:

☐ Set up soldering iron and set appropriate temperature
☐ Tin the iron tip before and during work
☐ Make shiny through-hole solder joints
☐ Recognize good joints vs cold joints
☐ Solder stranded wire (strip, tin, solder)
☐ Identify and remove solder bridges
☐ Remove components with solder wick or sucker
☐ Trim component leads flush with joint
☐ Inspect joints with magnification
☐ Work safely (glasses, ventilation, iron stand)

If you can check all these boxes, you're ready to assemble SimpleBot!

Next Steps

Build SimpleBot

Apply your soldering skills:

SimpleBot - Full robot build guide
SimpleBot:PCB Assembly - Detailed soldering instructions for SimpleBot PCB

Learn Advanced Techniques

Soldering Techniques - SMD soldering, hot air rework, desoldering
Soldering - Full competency overview with intermediate and advanced topics

Continue Practicing

Electronics kits from SparkFun, Adafruit, or Digikey
Solder practice boards (IC trainer boards, SMD practice boards)
Dead electronics for desoldering practice

Common Beginner Mistakes

Not tinning the tip - Single biggest cause of poor results; tin frequently!
Temperature too low - Solder doesn't flow; increase 10-20°C
Not cleaning tip - Wipe on brass wool before every joint
Applying solder to iron instead of joint - Prevents proper wetting
Pulling on component before solder solidifies - Creates disturbed joint
Using too much solder - More is not better; use just enough for fillet
Insufficient heat time - Solder needs time to flow; don't rush
Working without ventilation - Flux fumes are irritating; open window or use fan

Tips for Success

Practice first - 20-30 practice joints before real PCB
Good lighting - See what you're doing (magnification helps too)
Comfortable position - Steady hands require comfortable posture
Take breaks - Hand fatigue leads to mistakes
Inspect as you go - Catch problems early
Don't rush - Speed comes with practice; focus on quality first
Ask for help - Show your joints to experienced solderers for feedback

Tools and Resources

Recommended Purchases for Beginners

Soldering iron - Pinecil ($30) or Hakko FX-888D ($90)
Solder - 0.8mm lead-free SAC305 ($10-15 for 50g)
Safety glasses - Any ANSI-rated glasses ($5-10)
Brass wool - Hakko 599B tip cleaner ($5)
Practice kit - Through-hole soldering practice board ($10-20)

Total budget: $60-150