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Real Physics & Gaming Learning - Soldering Factors

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Factors Affecting Your Soldering Results: Heat

Soldering makes use of heat, at least in most of the techniques. The amount, timing and type of heat applied determine to a great extent the outcome of your soldering efforts. The first aspect is the amount of heat. First, it is important to determine whether what you intend to do is hard or soft soldering and whether your materials will support hard soldering. Hard or silver soldering usually operates with temperatures higher than 420 degrees and may thus melt some workspaces. For PCBs, soft soldering is the most commonly used. After deciding on this, it is important to set the thermostat to the required degree prior to preheating. This eliminates the chances of overheating before you have the time to adjust the control. These two steps will ensure that you have the right temperature to do your soldering.

Next is the exposure time. You may have the correct heat level and control but if you expose your workspace to this heat for longer than necessary, it may get damaged or cause some of the elements to melt. This required observation skills to be able to decide when the solder has flown to the joint sufficiently and ensure there are no overheated or cold joints in the PCB. The last important aspect in heating is the type of heat. Depending on the soldering iron you use, this could be a contact flame, open flame or a glowing source of heat. Open flames, often found in outdated butane soldering torches are highly uncontrollable thus rendering them almost useless for use in printed circuit boards. It is advisable to use controllable heat such as in a temperature-controlled soldering iron.

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Factors affecting your soldering results: Thermal mass and linkage

Each joint with a soldering pad has its own thermal mass. This is its unique ability to absorb and to store heat energy. The thermal mass of an element determines how much heat is needed to solder it and for how long the item will be exposed to that level of heat. Thermal linkage on the other hand refers to the surface area forming the points of contact between the soldering iron tip and the lead. A very small thermal linkage causes insufficient flow of solder and thus structurally-weak joints.

The above-mentioned factors determine to a great extent the outcome of a soldering task. If excess heat is applies to material with low thermal mass, it almost certainly melts the item and causes an overheated joint. On the other hand, if less than sufficient heat is applied to material with high thermal mass, the end result will be a solder-starved joint or a cold joint. It is therefore important to understand the thermal mass of the solder and the workspace.

Thermal linkage on the other hand has a direct effect on the amount of solder that will flow to the joint. A very wide linkage will cause an excessively soldered joint while a very small linkage will cause a solder-starved joint. The balance therefore lies in having just the right surface contact of thermal linkage to ensure sufficient flow of solder. Thermal linkage is influenced by factors such as the size of the tip, size of the component lead, iron handling technique and the skill of the artist. For very small or very large components however, it becomes very difficult to have sufficient linkage with an average soldering iron.

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Factors affecting your soldering results: Solder paste and flux

In PCBs, solder paste is used to make links between components mounted on the board and the copper traces on the board. Flux on the other hand is the material used to clean and prevent metal from oxidization due to heating in soldering. These two can greatly influence the quality of soldering achieved using a soldering iron on a printed circuit board. Excessive solder paste causes solder beads to form on the surface of the board. From the description of the formation of soldering beads, the formation of solder beads is usually supported by the application of too much solder paste or the limited distance across two components. Once the pad is heated during soldering, the solder paste melts and flows to adjacent components. Depending on the amount of solder paste, it eventually crosses the gap between components and thus forms bridges of solder paste. However, once solder filler metal is heated and applied to the surface, it pulls back some of the excess solder paste towards the component. Due to the excessive amount though, some of the solder paste remains as a small ball between the components. The formation of this and many other balls of solder paste eventually form a solder bead.

Flux on the other hand is primarily used in soldering as a reducing agent and ensures that metals to turn into their respective oxides as a result of heating. Flux is usually rosin coated. Rosin, in its natural state is non-corrosive and does not exhibit acidic or alkaline characteristics. However, once heated, the coating in flux becomes relatively acidic and acts as a reducing agent to undo any oxidization within the process. It is therefore important to choose good quality solder paste and flux if the results are to be as good. Brands from reputable manufacturers are always safe bets.