Solder and Flux Selection 210

This class describes various types of solder and flux and discusses how to select them for particular applications.

  • Difficulty Intermediate

  • Format Online

  • Number of Lessons 14

  • Language English


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Course Outline
  • Objectives
  • What Is Solder?
  • Common Solder Metals
  • Other Common Solder Metals
  • Solder Wire
  • Solder Wire Composition
  • Solder Paste
  • Lead-Free Solder
  • What Is Flux?
  • Rosin-Based Flux
  • Water-Soluble Flux
  • No-Clean Flux
  • Solder and Flux Selection
  • Summary
  • Describe characteristics of solder.
  • Match common solder metals with their properties.
  • Match less common solder metals used as alloys with their properties.
  • Describe characteristics of solder wire.
  • Distinguish between common solder wire compositions.
  • Describe characteristics of solder paste.
  • Describe characteristics of lead-free solder.
  • Explain how flux is used in soldering.
  • Describe characteristics of rosin-based flux.
  • Describe characteristics of water-soluble flux.
  • Describe characteristics of no-clean flux.
  • List criteria involved in solder and flux selection.
Vocabulary Term

60/40 solder

Solder that is made of 60% tin and 40% lead. 60/40 is the most commonly used type of solder for hand soldering.

63/37 solder

Solder that is made of 63% tin and 37% lead. 63/37 solder is also known as eutectic solder and is often preferred because it goes directly from a solid to liquid state when melted.


The measure of flux cleaning strength. The more active the flux, the more effectively it cleans.


A metal consisting of two or more materials. One of these materials must be a metal.


A brittle, silvery white metal used as an alternative to tin in soldering alloys. Antimony is less expensive than tin, but its wetting capability is poorer.

base metal

The primary metal used in an alloy. Tin is commonly used as a base metal for soldering alloys.


A white, brittle metal with a pinkish tinge that is used in soldering alloys to increase a solder's wetting ability and lower its melting point.


An alloy of copper and zinc. Brass is difficult to solder.


A material's ability to act as a path for the movement of electricity.


A reddish metal that is very ductile, thermally and electrically conductive, and corrosive resistant. Copper is often used in soldering alloys.


The distance from one edge of a circle to the opposite edge that passes through the center. Diameter is a factor in solder wire selection.

dispensable solder paste

A type of solder that is used with soldering irons that have specially designed tips to distribute the solder. Dispensable solder paste is applied to components in very small amounts.


Able to be drawn, stretched, or formed without breaking.

eutectic solder

Solder that is made of 63% tin and 37% lead. Eutectic solder is also known as 63/37 solder and is often preferred because it goes directly from a solid to liquid state when melted.


A substance that facilitates soldering, brazing, and welding by chemically cleaning the metals to be joined. Common varieties of flux include water-soluble flux and rosin-based flux.

flux core solder

A type of solder wire that is manufactured with flux in the center. During the soldering process, the flux cleans component surfaces as the solder melts.


A silvery gray, soft and ductile metal that can be used in soldering alloys to lower the melting point of solder. Indium has low strength and is expensive.


A material not containing carbon, derived from nonliving substances such as minerals. Inorganic water-soluble fluxes are primarily used with materials that are difficult to solder.


The point at which two metals are joined together by hot liquid solder. The solder then cools and solidifies to form the finished joint.


A heavy gray metal that is very soft and ductile and is a poor conductor of electricity. Lead is often used in soldering alloys, though it presents certain health hazards.

lead-free solder

Solder that contains less than 0.2% lead. The use of lead-free solder is becoming more common due to the health hazards of prolonged lead exposure.

melting point

The temperature at which a solid becomes a liquid. A solder's melting point is a factor in solder selection.


A silvery white metal that is fairly hard and malleable, with properties similar to iron and steel. Nickel is difficult to solder.

no-clean flux

A type of flux that does not require cleaning after soldering. However, it is less active than other types of flux and should be used only with materials that are easy to solder.


A material containing carbon and derived from living organisms. Organic water-soluble fluxes have high activity.


A material's chemical reaction with oxygen. Oxidation causes rust and tarnish to form on metal surfaces, and prevents solder from bonding.

periodic table

The table containing all the elements arranged according to their atomic numbers. Vertical columns in the table contain elements with similar properties.

plastic phase

The stage at which melted solder is neither liquid nor solid, but has a pasty consistency. During the plastic phase, a joint must be held completely still to avoid defects.

printable solder paste

A type of solder that is applied to components through a screen or a stencil. Printable solder pastes are used to apply more solder in less time than with dispensable solder pastes.


The characteristics of a material that distinguish it from other materials. A material's melting point is an example of a property.


A substance deposited or left behind. Flux residue must often be removed from components because it can be corrosive.

rosin-based flux

A type of flux made from purified pine sap and available in three activity levels. Rosin-based fluxes have lower activity than water-soluble fluxes.


A type of lead-free solder made from tin, silver, and copper. SAC is often preferred for its low melting point.


A soft metal that has the highest electrical conductivity of all metals. Silver is used in soldering alloys and creates strong joints.


A type of lead-free solder made from tin and copper. SnCu is a commonly used type of lead-free solder.


A metal alloy, with a melting point or melting range below 840°F (450°C), which is melted to join metallic surfaces.

solder paste

Powdered solder alloy formed into small spheres and coated with a layer of flux. Solder paste is available in both dispensable and printable forms.

solder wire

A form of solder that is most often sold in one-pound spools. Solder wire is the most common form of solder used for hand soldering.


A process in which a filler metal is melted at temperatures below 840°F (450°C) to form a joint between two base metals. Soldering is often used for delicate projects such as jewelry and electronics.

stainless steel

An alloy steel that is designed to resist corrosion. Stainless steel is difficult to solder.


A silvery white metal that is very soft and has poor strength. Tin is generally used as the base metal in soldering alloys.

tin pest

A phenomenon occurring in pure tin in which the crystal structure of the metal changes form, causing the tin to become brittle. Antimony is often used in solder alloys to avoid tin pest.

tin whiskers

A condition in which tiny hair-like protrusions develop in the crystal structure of tin. Tin whiskers can cause short circuits or other damage to electronic components.

water-soluble flux

A type of flux that leaves residue that can be removed with water rather than a cleaning solvent. Water-soluble fluxes have higher activity than rosin-based fluxes.


The contact between a fluid and a surface. A fluid with good wetting ability will spread out over a greater area.