Hard-Soft Soldering

Solderability - Learn More From a Real Expert

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Hard And Soft Soldering

There’s so much to learn regarding the efficient use of a soldering iron. The main, perhaps the only difference between hard and soft soldering is the melting point of the filler metal. In hard soldering, the filler metal has a point exceeding420 degrees Celsius while in sift soldering, the filler metal’s melting point is below 420 degrees Celsius. Most alloys used in hard soldering are silver-based while those used in soft soldering are lead-based. Hard soldering is also known as silver soldering. The solder used in the process is usually an alloy of silver and thus the term silver soldering. The melting point of the solder in this process is often above 430 degrees centigrade. In its most basic, silver soldering includes melting the solder and allowing it to flow to the joints of the metal pieces being bonded together. The high temperature and the type of alloy used in hard soldering produces to strongest joints possible with a soldering process.

Silver soldering produces results close to those of other high-temperature methods such as welding and brazing. In fact, some people classify silver soldering as a form of brazing. The basic process involved in silver soldering include making the joint, ensuring it is clean, applying flux, applying heat and the required solder, cleaning the workspace and cleaning off any necessary areas. This is pretty similar to the process followed in soft soldering.

Soft soldering on the other uses lead-based or tin-based alloys but follows the exact same process as hard soldering. The joints produced by soft soldering are however much weaker as compared to those of hard soldering. The two methods each have advantages and shortcomings. Soft soldering can be used for operations on PCBs without much risk of component while hard soldering cannot. On the other hand, the structural strength of hard soldering joint is far better than that of soft-soldered joints.

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Factors affecting your soldering results: Surface condition

For this description, the surface condition refers to the surface of the printed circuit board. However, you will not always be working on PCBs. Most of the steps though are applicable to all types of surfaces. A working surface may influence the outcome of soldering results in various ways through its resist flow, cleanliness and spacing of components.

Resist flow

This is the attribute of a soldering surface that prevents the flow of solder to unintended areas. Surfaces with good resist flow are able to maintain solder at the point of contact until it cools. If a surface has poor resist flow, the solder will flow and cool into solder balls which are some of the defects associated with incorrect soldering. The material making up a surface is the main factor determining the resist flow of the board.

Cleanliness

Metals, metal oxides, solder and flux attach very poorly to dirty surfaces. This implies that for you to achieve the best results, it is important to clean the surface and rid it of many impurities as possible. Dirty surfaces cause insufficient wetting and therefore produce poor and weak joints that develop cracks with time.

Component spacing

The distance between components on a PCB determines the possibility of formation of solder beads. Solder beads are related to solder balls. However a solder bead refers to a group of solder balls that form closely together and thus resemble a bead. Solder beads often occur close to the components that were being soldered. Just how to solder beads form? The formation of solder beads is usually supported by the application of too much solder paste or the limited distance across two components. A well-spaced surface allows for good flow of solder paste and flux without forming solder bridges.

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Fiber-focus infrared soldering

This is perhaps the most advanced and the most complicated soldering technique. Basically, it involves passing infrared rays from various sources through a fiber elements and then focusing all these rays onto a single spot where the solder is applied and the materials bond. Infrared waves a reused in heating in many industries such as aviation, kitchen appliances and spas. The working of infrared soldering equipment would basically include;

Opaque objects

From an infrared heat source, the waves only heat opaque objects on their paths and will leave the surrounding air at its normal temperature. This implies that the technique can be used to solder very small components that would normally be unsolderable using conventional techniques such as a soldering iron.

Wave focusing

Once the waves travel through the fiber tubes, they are eventually focused to a single point where the intended solder joint is located. The focusing of rays caused the surface to heat up thus creating a good environment for the application of solder. The attributes of infrared rays on opaque objects caused gradual but very consistent heating of the components.

Soldering

Once the surface is heated up, solder is applied as happens with every other soldering technique. The solder melts and flows to the intended joint where it cools forming a very strong joint. The process is very neat, clean and precise. However, the normal soldering points to observe areas important in this technique as in any other. The board must be clean, correct temperatures must be used, solder must be of the right amount, the joint must be fluxed and the components must not be moved before the solder dries up since this will cause the common disturbed joint problem.