Successful Soft Soldering Process

Method of Soft Soldering

To carry out successful soft soldering, the following process is to be adopted:

(a)          Clean the parts thoroughly.

(b)          Tin the parts to be joined, if necessary.

(c)          Assemble the job in proper position.

(d)          Apply flux slightly.

(e)          Melt the solder between the joints with a hot, clean and tinned soldering iron.

(f)           Allow the solder to get completely cooled.

(g)          When it is cooled, wash it properly with clean water (normally warm soapy water).

(h)          Remove all the traces of the flux, which will make the metal corrosive if left in contact with metal.


(a)       Use the minimum amount of solder, this makes the strongest joint.

(b)       Always keep the iron tinned to facilitate the flow of solder.

(c)        Excessive heating of the tinned iron will cause oxidation and requires ‘re-tinning’.

Causes of Faulty Soldering

Causes of faulty soldering are as follows:

(a)          Surface not cleaned thoroughly.

(b)          Surface not assembled properly.

(c)          Using wrong type of solder.

(d)          Using wrong type of flux.

(e)          Soldering iron not heated enough.

(f)           Soldering iron over heated.

(g)          Soldering iron not tinned properly.

Safety at Soldering Bench

Following safety precautions should be observed on soldering bench:

(a)          Use hand gloves and aprons so that molten metal spatter do not harm the body.

(b)          Use a close furnace for heating the irons so that flame spatters do not fall on the body.

(c)          Use tongs while taking out the soldering irons out of the furnace.

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(d)          The metal parts should be properly held.

(e)          Use a good wooden handle for soldering irons.

(f)   While using electrical soldering irons, stand on wooden base to avoid current shocks.

Strength of Soldering Joint

Soldering joints are normally lightly stressed in practice, but there are certain applications where tensile strength and hardness are important as for instance the joining of the end connectors.

Winding in electrical machinery is subjected to shear stress due to centrifugal force. There are two considerations, which affect the strength of the solder. The soundness of the joint will depend largely upon the ease with which the solder tins the joint members and upon the fluidity of the molten solder. These two properties are secured in a greater degree with solder rich in tin.

Soldered End Connectors

Apart from the composition of the solder, the factors explained in the succeeding paragraphs also affect the strength of soldered joint.

(a)       Amount of Solder Used.        The joint should be sound. A heavy fillet outside a joint is not always a sign of strength.

(b)       Soldering Temperature.      If the soldering temperature is too low, solder does not flow readily and penetration into the joint is incomplete. Overheating on the other hand causes the formation of brittle compound        in the joint, which reduces the strength.

(c)        Soldering Time.     If the soldering heat is applied for a prolonged period, the effect is similar to that of overheating.

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