Soldering - Types and techniques

What is soldering?

Soldering is a welding method to connect solid metal or alloy parts by means of a metal or intermediate alloy called a solder. During the welding process, the metal (or intermediate alloy) is fired to the flow state, while the welding metal only needs to be heated to a certain temperature at which brazing metal and solder can diffuse into each other.

Welding scales are widely used in engineering: electrical engineering, electronics and other fields; welding of metal cutting tools, thermal tools ...

The typical characteristics of soldering are:

Because there is no change in the chemical composition of the solder metal and the heat-sensitive region does not exist, the weld is not distorted.

It is possible to weld complex structures that other welding methods are difficult to implement.

Ability to weld different materials.

High productivity and does not require high skill level.

High economic efficiency.

What is the solder?

Solders are metals or alloys capable of bonding metallic or alloyed materials together to form a strong welded joint that satisfies the welding work requirements.

Requirements for solders

Solders need to be met the following requirements:

Hot melting solders need to be able to diffuse well into the metal to form a strong weld.

The melting temperature of the solders must be lower than the melting point of the solder metal.

At melting temperatures, the welds must be highly dilute to fill the entire weld.

The thermal conductivity of the weld metal and weld need to be approximately the same.

Welds need to ensure ductility, durability, no crispy hot or cold coil.

Easy to manufacture, low cost.

Classification of solders:

Based on the melting temperature, people split into two groups.

- Easy melting group is called soft solders. This group has a melting temperature of less than 450 ° C.

- Hard-melting group is also known as hard solders. This group has a melting temperature greater than 450 ° C.

Types of solders:

- Soft solders

Soft solders are Sn, Pb, Cd, Bi alloy and have a working temperature of (190 ÷ 350) ºC.

Soft solders are used to weld workpiece at low temperatures, with small force.

Soft solders including: welding tin and special welding material.

+ Tin solder

Tin solder is tin-lead alloy. It is composed of: tin solder 25-30-33-40-50-60-90 (90% Sn, 30% Pb). Welding grade 25 to 50 is mainly used for soldering iron. Tin solder 60 is used for welding electric meter, tin solder 90 used for welding food containers.

+ Special soft solder

Based on tin-lead alloys, Cu, Zn, Bi, Cd are added to create a low melting point welding material to weld structures to ensure special requirements: welding thin zinc plates, thermal insulators ...

Special soft solders commonly used are:


SN - Pb - Bi alloy

The composition of the alloy consists of: 15.5% Sn + 32.5% Pb + 52% Bi. This alloy has a melting point of about 96ºC.

Sn - Pb - Cd - Bi alloy.

The composition of the alloy is: 13.3% Sn + 26.7% Pb + 10% Cd + 50Bi. This alloy has a melting point of about 60 ° C.

- Hard soldering

Hard solders have a relatively high hardness and mechanical properties, so hard solders are often used to weld links that require high mechanical strength and heat resistance.

Hard soldering screeds commonly used include: Brass, silver, hot-dip welding materials ...

+ Brass (Cu-Zn alloy)

Used to weld links made of ferrous and nonferrous metals with melting temperatures above 1000ºC.

+ Silver

Silver scales used for soldering scales usually contain additional elements: copper and zinc.

This welding material can weld all ferrous and nonferrous metals (except metals with lower melting temperature than the melting point of welds such as aluminum, magnesium, zinc ...).

The advantages of silver scabs are:


High ductility and durability

Good anti-rust properties

Works well under bending conditions and shock loads

+ Heat resistant welding

Hot-dip fusion is the alloy containing: (50 ÷ 90)% Cu; (20 ÷ 40)% Zn; (3 ÷ 8)% Ni; (2 ÷ 5)% Mn and less than 2% Fe.

Hot-dip galvanized welds are widely used to weld workpieces at high temperatures and heat-resistant alloys.

Requirements for solders

Solder wipes clean the oxide and other contaminants in the weld and metal welds.

Welding need to meet the following requirements:

Create good conditions for solder scatter diffusion into solder metal

Surface protection of welded metal and welded non-oxidized welding flux during welding.

Dissolve the oxide on the surface of the weld metal and weld.

Do not change the composition and properties of solder metals and welds when heated.

Does not cause metal erosion and does not generate toxic gases when welding.

The welding is cheap, easy to manufacture.

Welding fluxes

Depending on the weld metal components and technical requirements of the weld, we can use the appropriate welding fluxes.