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Lab 04 - Soldering

Lab 04 — Intro to Soldering

Overview

The focus of this lab is to practice soldering, become familiar with lab equipment and become familiar with safety procedures for safe soldering.

Soldering is the process of using a metal alloy with a low melting temperature to fuse together two other pieces of metal. This is used in all electronics for two reasons: 1. It ensures a strong mechanical connection (i.e. the wires in your computer don’t fall off the circuit board in transit) and 2. Provides a highly conductive electrical connection.

To enhance the “stickiness” of the solder, we use rosin. This is most commonly found within the solder itself but can be applied separately as needed.

This week I practiced Lap Joint (wire–wire) and Through-hole (component–PCB) soldering to verify fundamentals and quality criteria. I organized process photos and key notes in my e-portfolio.

Lab & Environment

Course: Purdue AT 209 – Lab 04

Station: Electronics soldering station (iron, holder, wet/brass sponge, wick)

PPE: Safety glasses, closed-toe shoes

Materials: 24 AWG wire, ¼-inch strip length, resistor, single-sided PCB, Sn-Pb (or lead-free) solder, flux-cored solder

Tools and Equipment

In addition to the safety equipment listed above, be sure that you have the following:

A soldering station including

Base station

Soldering iron

Sponge

Solder

Wire cutters (flush cuts)

Wire strippers

Wire

Helping hands

PCB

Resistors

Solder wick

Soldering Safety

Solder composition: Tin–lead alloy with rosin flux (pine-derived; distinctive odor; may cause minor eye/respiratory irritation).

Iron tip is very hot—use caution.

Basic precautions:

Wear safety glasses

Wear long pants

Wear closed-toe shoes

Optional: wear a mask

Do not eat or touch your face without washing hands

Wash hands with soap before leaving the lab

Tips for successful soldering

Clean leads: Better wetting and conductivity; repairs may require extra cleaning.

Mechanical connection: Solder alone isn’t strong—ensure mechanical fixation plus the electrical joint.

Sufficient heat: Heat the leads and pad so solder melts and flows around the joint.

Clean, shiny tip: Transfers heat faster and reduces contamination, improving joint quality.

Methods / Procedure

Common: Preheat iron → clean tip (brass/wet sponge) → light tinning → secure work

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Lap Joint

Strip wire ¼ in → tin each conductor (heat the metal, feed solder to the heated metal)

Overlap 1–2 cm and heat the overlap simultaneously → feed a small amount of solder to induce capillary flow → allow to cool naturally

Through-hole

Insert leads and slightly splay to hold position

Heat pad + lead together (~1 s) → add a small amount of solder → confirm a concave fillet → trim the lead

Rework (if needed): Place solder wick on the pad and heat from above with the tip → once solder is wicked up, lift wick and tip straight up together → reheat and re-solder.

Quality Criteria

Lap Joint: Smooth, shiny wetting across the entire overlap; no exposed copper or blobs; insulation close to the joint for strain relief

Through-hole: Smooth concave fillet, good hole fill (no voids when viewed at an angle), no bridges or cold joints, clean lead trim

Common Defects & Quick Fix

Excess solder (blob) → wick removal → reheat and apply a small amount of solder

Cold joint (dull, grainy) → add flux → heat sufficiently → re-solder

Bridge (short between adjacent pads) → remove with wick + flux, then re-form the joint

Poor wetting → re-clean/tin the tip; add 0.5–1 s of heating time