Introduction to Soldering

lesson 2:Introduction to Soldering

Soldering is the process of joining two or more electronic parts together by melting solder around the connection. Solder is a metal alloy made of tin and lead, which is melted using a hot iron, and when it cools, it creates a strong, permanent electrical bond between the parts. A soldering iron is used for this and can be defined as a hand tool that is plugged into a standard 120v AC outlet and heats up to melt solder around electrical connections.

Soft soldering
This is a quick method of joining most metals such as steel, brass and copper. The process is the best for light fabrications where the joints are not subjected to vibrations and heat and so do not need to be strong. The soft solder alloy is made from varying proportions of tin and lead with antimony. The melting point varies according to the composition ranging from 183 to 250℃.
Hard soldering
This is used where strong a joint is needed or where the parts will be used in greater heat than the melting points of soft solder thus the lowest melting point for hard solders is 625℃. The most widely used hard solders are silver alloys. Hard soldering is often used in jewelry and metal work art for joining copper, silver and gold. Heat for hard soldering is applied directly with the flame of a torch.
This type of soldering uses a metal with a much higher melting point than those used in hard and soft soldering. However, similarly to hard soldering, the metal being bonded is heated as opposed to being melted. Once both the materials are heated sufficiently, you can then place the soldering metal between them which melts and acts as a bonding agent.


Mount the Component

Begin by inserting the leads of the LED into the holes of the circuit board. Flip the board over and bend the leads outward at a 45′ angle. This will help the component make a better connection with the copper pad and prevent it from falling out while soldering.

Heat the Joint

Turn your soldering iron on and if it has an adjustable heat control, set it to 400℃. At this point, touch the tip of the iron to the copper pad and the resistor lead at the same time. You need to hold the soldering iron in place for 3-4 seconds in order to heat the pad and the lead.

Apply Solder to Joint

Continue holding the soldering iron on the copper pad and the lead and touch your solder to the joint.
NOTE: -Don’t touch the solder directly to the tip of the iron. You want the joint to be hot enough to melt the solder when it’s touched. If the joint is too cold, it will form a bad connection.

Snip the Leads

Remove the soldering iron and let the solder cool down naturally as shown below. Don’t blow on the solder as this will cause a bad joint. Once cool, you can snip the extra wire from leads.
A proper solder joint is smooth, shiny and looks like a volcano or cone shape. You want just enough solder to cover the entire joint but not too much so it becomes a ball or spills to a nearby lead or joint.


A well-done solder joint resembles the diagram below.

A good solder joint has very few things to look for compared to a poor one. A good solder joint shows the following characteristics:
• Smooth.
• Bright.
• Shiny.
• Clean.
• Concave solder fillet.
• Good wetting.
• The end of the wire or lead is covered with solder.


Cold Joint

For this, the solder did not melt completely. It is often characterized by a rough or lumpy surface. Cold joints are unreliable. The solder bond will be poor and the cracks may develop in the joint over time.

Repair: Cold joints can usually be repaired by simply re-heating the joint with a hot iron until the solder flows. Many cold joints also suffer from too much solder. The excess solder can usually be drawn-off with the tip of the iron.
Prevention: A properly pre-heated soldering iron with sufficient power will help prevent cold joints.

Disturbed joint

A Disturbed joint is one that has been subjected to movement as the solder was solidifying. The surface of the joint may appear frosted, crystalline or rough.

Repair: This joint can be repaired by reheating and allowing it to cool undisturbed.
Prevention: Proper preparation, including immobilizing the joint and stabilizing the work in a vise can prevent disturbed joints.

Overheated Joint

At the other extreme, we have the overheated joint. The solder has not yet flowed well and the residue of burnt flux will make fixing this joint difficult.

Repair: An overheated joint can usually be repaired after cleaning. Careful scraping with the tip of a knife, or little isopropyl alcohol & a toothbrush will remove the burnt flux.
Prevention: A clean, hot soldering iron, proper preparation and cleaning of the joint will help prevent overheated joints.

Too Much Solder

If you get too enthusiastic and apply too much solder onto a pin, excess buildup is what you’ll get, characterized by its rounded and raised shape. The direct reason is that the solder withdrawal is too late.
Repair: It is usually possible to draw off some of the excess solder with the tip of a hot iron. In extreme cases, a solder-sucker or some solder wick can be helpful as well.


Solder Bridge

This happens when two solder joints have melted together, forming an unintended connection between the two.

Repair: Sometimes the excess solder can be drawn off by dragging the tip of a hot iron between the two solder joints. If there is too much solder, a solder sucker or solder wick can help get rid of the excess.
Prevention: Solder bridges most often happen between joints with too much solder to begin with. Use only enough solder to make a good joint.

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