CIE 25
Steve O'Toole

SOLDERING LAB
Soldering is the process of joining two metals without melting either metal to be in the 
joining process.   What is melted and what fuses to the two metals molecularly is the 
solder.  Solder is an alloy, generally composed of tin and lead, with a melting point lower 
than that of the metals to be joined.
When heat is applied to a solder connection and solder is applied, the solder flows 
around the joint and mixes with the molecules on the surface of the metals.  Once cool 
the joint becomes one continuous metal surface.  One could take two copper wires and 
wrap them together to make an electrical connection; however, they are still just two 
wires subject to a variable resistance at the connection point due to vibration and/or 
corrosion (oxidation), when wires or connections are made with a solder both a 
chemical and metallurgical reaction takes place.  The solder causes a small amount of 
the copper to dissolve at temperatures well below the melting point of the copper, 
causing the formation of a new alloy that is neither solder or copper.  Upon cooling, a 
continuous metallic connection is formed fusing the two metals together.  This new 
connection is not subject to a high or variable resistance.
Rules for Soldering
1.	Inspect the terminals and wires to be soldered.  Clean as required with solvent, 
lead cleaner, or abrasive cloth.
2.	Apply solder with flux to the clean tip the moment it is hot enough to liquefy 
solder.  This is called tinning.
3.	Clean the tip of the heated soldering iron by wiping it lightly on a sponge that has 
been moistened with water.
4.	Place the soldering iron tip on the terminal (more heat massive contact) 
immediately melt a small amount of solder at the point of contact.  This provides 
a solder bridge over which heat can flow.
5.	When the terminal reaches the melting temperature of the solder, apply more 
solder to the terminal (not the soldering iron) melting only as much as is needed 
quickly.
6.	As soon as enough solder is applied, remove the solder iron to prevent excessive 
heat from damaging the terminal, PCB pad, and/or components.
7.	Allow the connection to cool without movement until the solder fully solidifies.
8.	After all soldering is completed, the flux residue may be removed with a suitable 
solvent cleaner.
Lab Procedure
Obtain a single sided PCB and correctly attach the related components as per the above 
soldering instructions.  Have an instructor or lab assistant check your work.