By | September 12, 2015
Soldering

SOLDERING METHODS

There is a lot of similarity between soldering and brazing processes. The major difference between them is less heat and lower temperature is required in case of soldering. The different processes (methods) used in soldering are touch soldering, furnace soldering, resistance soldering, dip soldering and infrared soldering. All the above methods are common to both soldering and brazing processes. There are some more methods used in case of soldering only, these are hand soldering; wave soldering and reflow soldering. These methods are described below.

Hand Soldering

Hand soldering is done manually using solder iron. Small joints are made by this way in very short duration approximately in one second.

Wave Soldering

Wave soldering is a mechanical and technique that allows multiple lead wires to be soldered to a Printed Circuit Board (PCB) as it passes over a wave of molten solder. In this process a PCB on which electronic components have been placed with their lead wires extending through the through the holes in the board, is loaded onto a conveyor for transport through the wave soldering equipment. The conveyor supports the PCB on its sides, so its underside is exposed to the processing steps, which consists of the following:

  • flux is applied through foaming, spraying, brushing, and
  • wave soldering is used pump liquid solder from a molten both on to the bottom of board to make soldering connections between lead wire and metal circuit on the

Reflow Soldering

This process is also widely used in electronics to assemble surface mount components to print circuit boards. In this process a solder paste consisting of solder powders in a flux binder is applied to spots on the board where electrical contacts are to be made between surface mount components and the copper circuit. The components are placed on the paste spots, and the board is heated to melt the solder, forming mechanical and electrical bonds between the component leads and the copper on the circuit board.

SOLDERING TOOLS

The main tool used for soldering is the soldering iron. In addition to soldering some consumable are also used in the process of soldering like fluxes, solder wire or stick and

Resistance Welding

spelter. These are described below.

Soldering Iron

It consists of a copper bit attached to iron rod at its one end, and a wooden handle at the other end. It is used to melt the filler metal and paste it to make the joint. A soldering iron can be a forge soldering iron which is heated in a furnace to have sufficient temperature to melt the filler metal or it can be electric solder iron.

Electric solder iron is heated by passing electric current through it. Use of electric solder iron is popular and cost effective. It is used in making very precise joints in electronic and electrical equipment.

Spelter

Spelter is an alloy of zinc and copper in equal proportion. This is one of the filler metal with low melting point with other desirable properties to make good quality solder joint.

Different types of solders and fluxes, which are common consumables used in soldering have already been described. Some precautions are to be followed to keep the soldering tools as described below.

  • Selection of correct tool according to the A defective tool should not be used.
  • Electrically heated solder iron should have proper
  • Hot solder iron, when idle, should be placed on its proper
  • Tip of the solder iron should be cleaned before, its
  • Solder iron should be gripped at its handle while in

SOLDERING PROCEDURE

Following sequential steps should be carried out as soldering procedure.

Work Preparation

Workpieces which are to be joined together should be perfectly clean. There should not be any dirt, dust, rust, paint or grease. This is so that the solder or spelter can stick to the joint with proper strength. Cleaning is done with the help   of a file or sandpaper. In case of joining of conducting wires, insulation of portion to be joined should be perfectly removed. Sometimes chemicals are used to clean the workpieces. De-scaling (removal of scaling) is done by dipping the workpieces into dilute HCl.

Brazing Joints and Surface Preparation

Preparation of Joint

After cleaning workpieces should be kept together in correct position to make the final joint. Workpieces should be clamped to avoid any relative movement between them that may disturb the joint making. At the joint smaller grooves are made on the workpieces to facilitate better flow of molten solder and so good strength of the joint. There may be the two objectives of joint :

  • to bear load, and
  • to make electrical

In case of load bearing joints lap joint or butt joints are preferred. It is important to note down that strength of a soldered joint cannot be compared with welded joint. If electrical contact is to be made the solder should be so selected that resistance   of joint should match with the resistance of the conductor.

Fluxing

Fluxing includes selection of appropriate flux and its application to the joint. Selection of flux depends on the material of workpiece keeping its purpose in view. It is applied to the joint with the help of a brush before soldering. It avoids oxidation of molten metal, helps in flow of molten solder into the joint and so maintains strength of the joint.

Tinning

In this step of soldering procedure, the bit of solder iron is cleaned, application of flux is done over it. It is brought in contact of solder wire so the bit carries sufficient amount of molten solder over it. After that it is used to make tags of solder at various process through out the joint. If soldering is done to make electrical contacts of conductivity wires the complete joint is made by tagging few times. In case of long joint, after tagging the molten solder is filled to the joint by bringing hot bit of solder iron and solder wire together in contact with the joint.

Filling the joint with molten solder and allowing to solidify is the last step of the procedure called soldering.

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