Safety Glasses
Lab Activity

Soldering &
Measuring Resistance

Through-Hole Soldering & Multimeter Skills

Introduction

What is Soldering?

  • Soldering is one of the most fundamental skills in electronics. The two go together like peas and carrots.
  • A whole new world opens up once you can pick up a soldering iron: you can build, repair, and customize electronic circuits at the component level.
  • In this lab we cover through-hole (PTH) soldering: components go through holes in the PCB and are soldered on the back side.
  • We will solder 10 resistors to a Resistor Check PCB, then measure each one with a multimeter and record the results.
Resistor Check PCB with a resistor next to it Today's project: Resistor Check PCB
Materials

What is Solder?

// Solder — the noun
An alloy of two or more metals, sold as thin wire on spools or tubes. Available leaded and lead-free.
// Solder — the verb
To join two pieces of metal at a solder joint. "We solder with solder!"
// Leaded (Pb + Sn)
Lower melting point, excellent flow. Still preferred by many hobbyists — handle with care.
// Lead-Free (RoHS)
Higher melting point, uses a flux core to aid flow. Industry standard for commercial products.
Solder wire spool and tube Spool (left) & tube (right) — leaded and lead-free varieties
Equipment

Soldering Iron — Types

// Simple Wand Iron
Plugs directly into the wall. No temperature control — the heating element is built into the wand. Affordable and portable.
Simple plug-in soldering iron Simple wand — no base
// Soldering Station
A base + wand setup. The base controls temperature. Analog bases use a dial; digital bases show the exact temperature. Some offer heat profiles for different components.
Digital and analog soldering stations Digital station (left) & analog station (right)

// All irons have the same key parts: tip, wand, and some form of heat source. The station just adds control.

Equipment

Iron Anatomy — Tips, Stand & Cleaning

// Tip
Heats up and allows solder to flow. The tip transfers heat — not solder. Solder melts because the joint is hot enough, not because solder touches the tip.
Four different soldering iron tip shapes Common tip shapes — chisel, conical, bevel, fine point
// Stand / Cradle
Always rest the iron here when not actively soldering. Prevents burns and fire hazards. Premium stands add auto-shutoff when the wand is cradled.
Three iron stand types: plastic with sponge, metal coil, brass wool Stand types — sponge cradle, coil stand, brass wool stand
// Brass Sponge (not wet sponge!)
Tips oxidize over time — turning black and rejecting solder. Wipe on a brass sponge: it strips build-up without temperature shock. A wet sponge causes rapid expansion/contraction that eventually holes the tip.
Soldering iron tip being cleaned in brass sponge Brass sponge in use
Technique

Soldering Tutorial

Technique

Dave's Rules

// 01
Be cautious when handling hot irons.
// 02
Use third hands or vices to hold boards while you solder.
// 03
Set your iron at a good medium heat: 325–375°C (600-700°F).
// 04
If you see smoke from your solder, turn down the heat.
// 05
Tin your tip with solder before each connection.
// 06
Use the side of the tip (the sweet spot), not the very tip.
// 07
Heat both the pad and the part evenly and at the same time.
// 08
Pull the solder away, then the iron.
// 09
A good joint looks like a volcano or Hershey kiss, not a ball or clump.
// 10
When finished, tin the tip to extend its life before turning the iron off.
Technique

What is wrong with this stock photo?

Stock photo of soldering — spot the mistakes
Technique

Soldering Technique

Technique diagram showing correct iron position, feeding solder, and joint quality grades A through E
  • Be cautious with hot irons.
  • Set to 325–375°C (600-700°F). Smoke = too hot.
  • Tin your tip before each joint.
  • Use the side of the tip, not the point.
  • Heat pad AND part together.
  • Pull solder first, then iron. Good joint = volcano shape.
Quality Check

Solder Joint Quality

Good Joint
  • Shiny, smooth surface
  • Volcano / Hershey kiss profile
  • Solder wets fully up the pin and across the pad
Cold Solder Joint
Macro photo of a cold solder joint showing a dull, balled joint on a green PCB
  • Dull, grainy or balled-up surface
  • Tiny gap between solder and pin — no real connection
  • Cause: not enough heat applied to the joint
Lab Procedure

Soldering the Resistor Check Board

  1. Get 10 resistors from your instructor along with your Resistor Check PCB.
  2. Bend the leads so they fit through the inner pair of holes on the board. Closer is better, but doesn't need to be exact.
  3. Place a resistor on the top side of the PCB (the side with the puma logo), leads going through the inner pair of holes.
  4. On the back side, pull the leads outward to hold the resistor tightly against the board.
Bare Resistor Check PCB with a loose resistor next to it The Resistor Check PCB
Completed Resistor Check board — the goal Step 2: Bend the leads
Resistor placed on the top side of the PCB through the holes Step 3: Place on top side
Pulling resistor leads outward on the back of the board Step 4: Pull leads outward
Lab Procedure

Soldering the Resistor Check Board

  1. Flip the board leads-up. Solder both leads to their pads.
  2. Trim the leads with flush cutters so they barely protrude past the solder joint.
  3. Repeat for all 10 resistors. When the board is full, show your instructor before measuring.
Soldering iron tip touching leads on the PCB Step 5: Soldering
Flush cutters trimming resistor leads on the back of the board Step 6: Trimming leads
All 10 resistors mounted on the Resistor Check board Step 7: All 10 mounted
Reading Resistors

Resistor Color Code

Band 16Blue
Band 22Red
Band 3×10⁰Black
Band 4±5%Gold
  • Find Band 1: gold or silver = Band 4. The other end is Band 1.
  • Band 1 + Band 2 give the first two digits.
  • Band 3 is the multiplier: 10n. Black = ×1, Yellow = ×10,000.
  • Band 4 = tolerance. Gold = ±5%.
Blue, Red, Black, Gold
62 × 1 = 62 Ω
±5% → 58.9 Ω to 65.1 Ω
Full resistor color code reference table showing all digit, multiplier and tolerance colors
Measurement

Measuring Resistance

  1. Set your multimeter to Resistance (Ω) mode.
  2. Set the range to the closest value ABOVE the nominal resistance. (For 62 Ω, use the 200 Ω range.)
  3. Touch the probes to the two leads of the resistor. Be careful not to bridge adjacent pads.
  4. Read the display. Units match the range you set. (200 Ω range = Ohms; 2 KΩ range = kΩ; 2 MΩ range = MΩ.)
62.4
Good reading. Within tolerance. Record it.
1
"1" on left side — range too low. Increase your range.
.000
".000" shown — range too high. Decrease your range.

// Always set the range ABOVE the expected value first, then work down if needed.

Lab Data

Record Your Results

Board #
Name
Date
Period
Resistor Nominal Value Measured Value
R1 _______ Ω_______ Ω
R2 _______ Ω_______ Ω
R3 _______ Ω_______ Ω
R4 _______ Ω_______ Ω
R5 _______ Ω_______ Ω
R6 _______ Ω_______ Ω
R7 _______ Ω_______ Ω
R8 _______ Ω_______ Ω
R9 _______ Ω_______ Ω
R10_______ Ω_______ Ω