Soldering and Brazing: Soft Solder, Hard Solder, Application ~ MECHTECH GURU

Soldering and Brazing: Soft Solder, Hard Solder, Application

Soldering and Brazing


Soldering involves the heating a joint to a suitable temperature and using filler metal (solder) which melts below 4500 C. solder gets distributed between the properly fitted surfaces of the joint by capillary attraction. Heat is required to melt the solder, promotes fluxing action on metal surface which permits the molten solder to wet and flow into the joint. Successful soldering requires:

top 500 Gate guide

  1. Proper fit-up (close together)
  2. Cleaning the surfaces to be joined
  3. Applying flux, assembling parts, and applying heat and solder.
  4.  Remove flux residues after joint is cooled

Soldering Methods

1.      Dip soldering                               5. Induction soldering
2.      Iron soldering                               6. Furnace soldering
3.      Resistance soldering                    7. Infrared soldering
4.      Torch soldering                            8. Ultrasonic soldering

Solders can be classified as:

 Soft Solder

 Soft solder melts at temperature below 350̊ C and operation is known as soft soldering. Soft soldier is an alloy of lead and tin with the following composition 

  1. Tin 50%, Lead 50%
  2. Tin 67%, Lead 33%
  3. Tin 33%, Lead 67%

 Hard Solder

is an alloy of Copper and Zinc that melts above 600 C the operation is performed with hand solder is called hand soldering. To prevent the oxidation of joint surfaces, fluxes are used. Flux should be light in weight so it could be displaced by molten metal
Example of flux- Zinc chloride, rosin and rosin plus alcohol based flux, mixture of zinc chloride and ammonium chloride

Skill is needed for manual soldering operation especially for critical electronic equipment/components. Automated soldering requires less operator skill as the process variable are set before the soldering operation, machine setting, process control and inspection determine joint quality. Lap joint is most commonly used while special types of joints are used to solder electronic component.


Soldering Cable
Soldering Cable


  1. Process is used to join a wide range of metal thickness from thin film to quite heavy components like bus bars and piping.
  2. Expensive automated equipment produces many high quality joints at a time, thus reducing the cost per joint.
  3.  Manual soldering is although slow, but still economical when production needs are low or joint design is complex.


Brazing is a group of welding processes in which the parts are heated to suitable temperature and the filler metal used has a melting temperature above 4500 C and below the solidus of the base metal. The filler metal flows between the closely fitted joints by capillary attraction.
In Braze welding, the filler metal is deposited in a groove exactly at the point where it is to be used capillary action is not a factor. Brazing differ from soldering by the filler metal melting temperature being below 4500 C. 

In brazing melting point temperature of filler material should be greater than 4500C.

The basic elements to be considered for brazing are:
  1.  Joint design
  2.  Filler metal
  3.  Uniform heat
  4.  Protective (or reactive) cover

Processes used for brazing are classified on the basis of methods of heating.

  1.    Torch brazing (oxy-fuel gas torch: for welding thin section 0.25 mm to 6 mm) making lap joint
  2.  Furnace brazing (flux and braze filler is preplaced.
  3.    Induction brazing (3 mm normal up 25 mm)
  4.    Resistance brazing (0.1-12.00 mm sheets)
  5.   Dip brazing (molten salt or molten metal bath)
  6.   Infrared brazing
  7.    Diffusion brazing

Next Post »