Soldering

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Soldering
The hands-on technique of joining electronic components to circuit boards
Difficulty Range Beginner to Advanced
Time to Basic 1-2 days
Essential Tools Soldering iron ($20-50), lead-free solder, safety glasses, ventilation
Optional Tools Helping hands, solder wick, flux pen, hot air station
Get Started Soldering Guide
Unlocks (Basic) SimpleBot PCB assembly, basic electronics repair
Unlocks (Advanced) SMD assembly, PCB rework, custom sensor modules

Soldering is the competency of physically joining electronic components to circuit boards using molten metal. In robotics, soldering is essential for assembling PCBs, connecting sensors and motors, and creating permanent electrical connections that withstand vibration and movement.

Soldering is distinct from Electronics (understanding circuits and components) and PCB Design (creating circuit board layouts). This competency focuses on the hands-on fabrication technique: heating the iron, forming good joints, avoiding cold solder and bridges, and safely working with molten metal.

Why Soldering Matters for Robotics

Robots need permanent electrical connections:

  • PCB assembly - Attach components to circuit boards (SimpleBot PCB, motor driver boards)
  • Wire connections - Secure wires to connectors and components
  • Sensor modules - Build custom sensors and breakout boards
  • Repair - Fix broken connections, replace damaged components

Without soldering skills, you're limited to breadboards and pre-assembled modules. Soldering unlocks:

  • Building robots with custom PCBs
  • Creating robust connections that survive robot movement
  • Repairing damaged electronics
  • Designing and fabricating your own sensor modules

Skill Progression

Beginner (SimpleBot Level)

Skills you need to assemble SimpleBot PCB:

  • Safety fundamentals - Eye protection, ventilation, burn prevention
  • Iron temperature control - Set appropriate temperature (300-350°C for lead-free)
  • Tinning the tip - Keep the tip coated with fresh solder
  • Through-hole soldering - Insert component leads, solder from bottom
  • Solder joint inspection - Recognize good joints vs cold joints vs bridges
  • Wire soldering - Strip insulation, tin wire, solder to terminal
  • Basic desoldering - Remove excess solder with solder sucker or wick

Unlocks:

  • SimpleBot PCB assembly (resistors, capacitors, headers, motor terminals)
  • Basic sensor module assembly
  • Wire-to-board connections for motors and batteries

Tutorials: Soldering Guide

At this level you can:

  • Assemble through-hole PCB kits
  • Solder headers and terminals to breakout boards
  • Create secure wire connections
  • Troubleshoot basic soldering issues

Intermediate (SMD and Rework)

Skills for advanced PCB assembly and repair:

  • SMD hand soldering - 0805/0603 resistors and capacitors with iron and tweezers
  • Hot air rework - Remove and replace SMD components with hot air
  • Flux usage - Apply flux for better solder flow and heat transfer
  • Desoldering techniques - Solder wick, solder sucker, hot air removal
  • Component rework - Replace damaged ICs and connectors
  • Drag soldering - Efficiently solder multi-pin ICs
  • Solder paste application - Apply paste for reflow or hot air soldering

Unlocks:

  • Hand-assembly of SMD PCBs (motor drivers, sensor boards)
  • Repair of existing electronics (broken traces, lifted pads, damaged components)
  • Custom sensor modules with SMD components
  • Prototype boards with mixed through-hole and SMD

Tutorials: Soldering Techniques

At this level you can:

  • Hand-solder SMD components down to 0603 size
  • Rework and repair PCBs with hot air and desoldering tools
  • Replace damaged connectors and ICs
  • Assemble custom sensor modules

Advanced (Fine-Pitch and Production)

Skills for complex assemblies and production-quality work:

  • Fine-pitch SMD - 0402 components, TQFP, QFN packages (0.5mm pitch or finer)
  • Reflow soldering - Use reflow oven or hot plate for solder paste assembly
  • BGA rework - Ball grid array component removal and replacement
  • Microscope work - Solder under magnification for fine-pitch components
  • Thermal management - Preheat boards, manage heat-sensitive components
  • Quality control - Inspect joints with microscope, identify defects
  • Production techniques - Efficient workflows, jigs, and fixtures

Unlocks:

  • Complete PCB assembly for complex robots
  • Reflow soldering for production quantities
  • Repair of laptop/phone electronics (fine-pitch work)
  • Custom high-density sensor arrays

Tutorials: Advanced soldering resources (external)

At this level you can:

  • Assemble any PCB design, regardless of component density
  • Rework complex multi-layer boards
  • Set up production soldering workflows
  • Troubleshoot and repair professional electronics

Learning Paths

Path 1: SimpleBot Builder (Beginner)

  1. Read Soldering Guide - Learn safety, technique, and practice on scrap
  2. Practice on perfboard or practice kit (20-30 joints to build muscle memory)
  3. Assemble SimpleBot PCB - Through-hole components only
  4. Inspect joints and fix any cold solder or bridges

Result: You can confidently assemble through-hole PCBs for robotics projects.

Path 2: SMD Assembler (Intermediate)

  1. Complete Path 1 (SimpleBot Builder)
  2. Study Soldering Techniques - SMD soldering and hot air rework
  3. Practice SMD soldering on breakout boards (start with 0805, work down to 0603)
  4. Assemble an SMD motor driver or sensor board
  5. Learn desoldering with solder wick and hot air

Result: You can hand-assemble SMD boards and perform PCB rework.

Path 3: Production Assembly (Advanced)

  1. Complete Path 2 (SMD Assembler)
  2. Learn reflow soldering (hot plate or reflow oven)
  3. Practice fine-pitch soldering (TQFP, QFN) under microscope
  4. Set up efficient workflows with jigs and fixtures
  5. Study IPC-A-610 soldering standards

Result: You can assemble production-quality PCBs and manage complex assemblies.

Essential Concepts

Good Solder Joint Characteristics

A proper solder joint has:

  • Shiny appearance - Smooth, reflective surface (not dull or grainy)
  • Concave fillet - Solder flows up the lead in a smooth curve (volcano shape)
  • Complete wetting - Solder adheres to both pad and component lead
  • No excess solder - Just enough to form a fillet (not a blob)
  • No cold joint - Solder flowed properly at temperature (not crystalline)

Temperature Control

  • Lead solder (60/40 Sn/Pb) - Melts at 183°C, work at 300-330°C
  • Lead-free solder (SAC305, 96.5/3.0/0.5 Sn/Ag/Cu) - Melts at 217°C, work at 320-370°C
  • Too cold - Solder doesn't flow, forms cold joints
  • Too hot - Damages components, lifts pads, oxidizes tip faster

Heat Transfer

Good solder joints require heating both the pad and the component lead:

  1. Touch iron tip to pad and lead simultaneously
  2. Apply solder to the joint (not the iron tip)
  3. Solder flows toward heat - if it balls up, increase heat or clean surfaces
  4. Remove iron after solder flows smoothly around joint (1-3 seconds)

Flux

Flux is the "secret ingredient" that makes soldering work:

  • Removes oxidation - Cleans metal surfaces for better wetting
  • Improves heat transfer - Helps solder flow smoothly
  • Prevents oxidation - Protects joint while hot
  • Types: Rosin (mildly corrosive, common), No-clean (low residue), Water-soluble (requires cleaning)

Most solder has a flux core, but additional flux improves results on difficult joints.

Common Soldering Defects

  • Cold joint - Dull, grainy appearance; solder didn't flow properly (re-heat to fix)
  • Solder bridge - Unwanted connection between adjacent pads (remove with solder wick)
  • Insufficient solder - Joint doesn't fully wet pad or lead (add more solder)
  • Excess solder - Large blob that may hide defects (remove excess with wick)
  • Lifted pad - Pad separated from PCB due to excessive heat or force (difficult repair)
  • Tombstoning - SMD component stands on end (one side heated before the other)

Tools and Equipment

Essential Tools (Start Here)

  • Soldering iron ($20-50) - Temperature-controlled preferred (Hakko FX-888D, Pinecil, TS100)
  • Solder ($10-15) - 0.8mm diameter lead-free (SAC305) or 60/40 leaded for practice
  • Safety glasses ($5-10) - Protect eyes from solder spatter
  • Solder stand ($5-10) - Safe place to rest hot iron
  • Brass wool or sponge ($5) - Clean iron tip
  • Wire cutters ($10-15) - Trim component leads after soldering
  • Ventilation (free-$50) - Work near open window or use fume extractor fan

Total beginner budget: $50-100

Intermediate Tools

  • Helping hands ($10-30) - Third hand to hold PCBs and wires
  • Solder wick ($5-10) - Braided copper removes excess solder
  • Desoldering pump ($5-15) - Suck up molten solder
  • Flux pen ($5-10) - Apply extra flux for difficult joints
  • Tip cleaner ($5-10) - Brass wool more effective than wet sponge
  • Magnifying lamp ($20-50) - Inspect joints and work with small components
  • Tweezers ($5-15) - Place and hold SMD components

Total intermediate budget: $50-150 (plus beginner tools)

Advanced Tools

  • Hot air rework station ($50-150) - Remove and replace SMD components
  • Soldering microscope ($100-400) - 10-20× magnification for fine-pitch work
  • Reflow oven or hot plate ($50-300) - Solder paste assembly
  • Chip Quik or low-temp solder ($10-20) - Ease removal of multi-pin ICs
  • PCB vise ($20-50) - Secure PCBs for rework
  • Temperature-controlled preheater ($50-200) - Preheat boards for large components

Total advanced budget: $300-1000+ (plus beginner and intermediate tools)

Safety Considerations

Soldering involves high temperatures and fumes:

  • Burns - Soldering irons reach 300-400°C; tip can cause instant injury
  • Eye protection - Solder spatter and clipped component leads can fly
  • Fumes - Flux produces irritating smoke; work with ventilation
  • Lead exposure - Use lead-free solder or wash hands after handling leaded solder
  • Fire hazard - Iron can ignite paper, plastic, fabric; use metal stand

Safety rules:

  1. Always wear safety glasses
  2. Work in ventilated area (fume extractor or open window)
  3. Never leave hot iron unattended
  4. Use soldering iron stand when not actively soldering
  5. Keep flammable materials away from work area
  6. Wash hands after soldering (especially with leaded solder)

Component-Specific Techniques

Through-Hole Components (Resistors, Capacitors, Headers)

  1. Insert component leads through holes from top side
  2. Bend leads slightly on bottom to hold component in place
  3. Solder from bottom side: heat pad and lead together, apply solder
  4. Trim excess lead flush with solder joint

SimpleBot PCB assembly uses through-hole components throughout.

Wire Soldering

  1. Strip 2-3mm of insulation from wire
  2. Tin the wire: heat wire, apply small amount of solder
  3. Position tinned wire in terminal or pad
  4. Heat wire and terminal together, add solder if needed
  5. Hold steady until solder solidifies (1-2 seconds)

SMD Resistors and Capacitors

  1. Apply flux to pads
  2. Tin one pad with small amount of solder
  3. Place component on pads with tweezers, heat tinned pad to tack in place
  4. Solder opposite end: heat pad and component, apply solder
  5. Re-flow first side if needed to ensure good joint

IC Chips (Through-Hole)

  1. Use IC socket if possible (avoids heat damage, allows replacement)
  2. If soldering directly: insert IC, tack opposite corners first
  3. Solder all pins quickly (avoid prolonged heating)
  4. Inspect for bridges between adjacent pins

IC Chips (SMD)

  1. Align IC with pads, tack one corner pin
  2. Apply flux generously to all pins
  3. Use drag soldering: draw iron tip across pins with small amount of solder on tip
  4. Solder bridges across pins, then draw iron to separate
  5. Alternative: Solder each pin individually with fine-tip iron

Common Pitfalls

  • Not tinning the tip - Oxidized tip won't transfer heat; tin tip before every few joints
  • Too much solder - Obscures defects and wastes material; use just enough to form fillet
  • Moving joint before solidification - Creates cold joint; hold steady 1-2 seconds
  • Heating component instead of joint - Apply heat to pad and lead, not component body
  • Dirty or oxidized surfaces - Clean with flux or abrasive before soldering
  • Wrong temperature - Too cold = cold joints, too hot = lifted pads and damaged components
  • Poor ventilation - Flux fumes are irritating; always work with airflow

Practice Recommendations

Before attempting SimpleBot PCB assembly:

Beginner Practice (1-2 hours)

  1. Practice on perfboard or scrap PCB: solder 20-30 through-hole resistor leads
  2. Inspect each joint: shiny? Concave fillet? No cold joints?
  3. Practice wire soldering: solder stranded wire to terminal blocks
  4. Desolder practice: remove components with solder wick or sucker

Intermediate Practice (2-4 hours)

  1. Hand-solder 0805 SMD resistors/capacitors (practice kit or breakout board)
  2. Practice hot air rework: remove and replace SMD components
  3. Work down to 0603 components once comfortable with 0805
  4. Practice drag soldering on SOIC or TQFP chips

Quality Check

Use magnifying glass to inspect joints:

  • No cold joints (dull, grainy appearance)
  • No bridges between adjacent pins
  • Complete wetting on pad and lead
  • Shiny, smooth surface

Tutorials and Resources

BRS Tutorials

Implementation Pages

External Resources

Related Competencies

  • Electronics - Understand circuits and components before soldering them
  • PCB Design - Design circuit boards that you'll assemble with soldering
  • Mechanics - Mechanical assembly often requires soldered wire connections
  • 3D Printing - Print jigs and fixtures for holding PCBs during soldering

See Also

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