Theory- 9 : - Soldering and Desoldering: Techniques

Mastering Soldering & Desoldering: Engineering Theory & Practical Guide

Soldering is the foundational core of electronics manufacturing and repair, enabling permanent, highly conductive electrical and mechanical joints using melted filler alloy. Desoldering reverses this process, permitting non-destructive component removal, diagnostic repair, and recycling.

Figure 1: Complete Workbench Setup for Electronic Assembly & Rework

1. Selection & Preparation: Materials & Tools

Solder Alloy Specifications

Property	Lead-Based (e.g., 60/40 Sn/Pb)	Lead-Free (e.g., SAC305)
Melting Point	183°C (Eutectic blend)	217°C – 221°C
Working Temp	300°C – 350°C	350°C – 400°C
Workability	Flows easily; smooth, bright joint finish	Slightly higher skill required; duller joint finish
Compliance	Restricted globally (RoHS compliance issues)	Environmentally friendly & globally compliant

Essential Equipment Breakdown

Chemical Flux

Removes oxide layers from component pins and PCB pads during heating to facilitate capillary wetting action.

Soldering Iron

15–30W: Precision SMD & PCB work.
40–60W: General electronics.
80W+: Heavy duty wiring.

Tip Geometries

Conical: Pointed fine work.
Chisel: Flat thermal transfer.
Bevel: Versatile blend for dragging.

Figure 2: Thermal Transfer & Capillary Action During Solder Feeding

2. Step-by-Step Soldering Execution

1

Preparation & Surface Cleaning

Clean component leads and PCB copper pads thoroughly using isopropyl alcohol (IPA) to strip oxidation.

2

Tinning the Tip

Coat the hot tip with fresh solder to enhance thermal conductivity and prevent oxidation.

3

Joint Pre-Heating

Apply the tip to both the pad and component pin simultaneously for 1 to 2 seconds.

4

Applying Solder

Feed solder wire into the opposite side of the joint, allowing capillary action to draw it completely around the connection.

5

Cooling & Inspection

Remove the wire first, then the iron. A high-quality joint should present a smooth, shiny, concave "volcano" shape.

3. Desoldering Tools & Rework Techniques

• Desoldering Pump (Solder Sucker): Mechanical spring-loaded vacuum plunger. Best suited for through-hole component leads.
• Desoldering Wick (Braid): Fine copper braid pre-coated with flux. Absorbs molten solder via natural capillary action.
• Hot Air Rework Station: Delivers controlled streams of heated air. Uniformly melts multiple pins at once, essential for Surface Mount Devices (SMDs).
• Desoldering Gun: Integrated tool combining a hollow heating tip with an electric vacuum pump for single-handed operation.

Figure 3: Desoldering Pump, Wick Braid, and Hot Air Rework Equipment

Engineering Quality Rule

Never attempt to move a newly soldered joint during its cooling phase. Disturbing the cooling alloy leads to a "cold joint"—resulting in high internal resistance, brittle structural integrity, and eventual circuit failure.