How to Choose the Right Solder
Solder is an alloy, generally consisting of a composition of tin and lead or some other metals. It’s usually available in the form of a wire and wounded as spools. In a soldering task, solder is the primary accessory used for creating solder joints or connections. There is a wide variety of solders available in different mixtures and sizes.
For good soldering and precise outcomes, it’s important to have the right type of solder suitable for your work-piece and components. While many already know which is best for their work, others might be in dilemma. To make it easier, you can consider these factors that I have noted down.
Type of solder
As solder is a form of alloy with different metal mixtures, there is wide range of solders. However, solders can be classified into three basic types.
Lead-based solder is the most commonly used solder. It’s made of tin and lead mixed in certain proportion. This type of solder is prohibited for commercial applications such as plumbing due to the risk of lead poisoning. Lead-based solders are popular because they have lower melting points. Generally there are three types of lead-tin solders:
This is a composition of 60% tin and 40% lead. With melting point of 190°C, it also has a high pasty or working range. It tends to stay liquid for longer period after heating, which forms rounder and higher solder seams, making this the ultimate choice for copper foil projects. Also, the 60/40 solder spools are comparatively the most inexpensive ones.
60/40 solder wires are also called non-eutectic solders as they have a semi-solid state between liquid and solid. If a joint made from this solder is moved during the semi-solid stage, it can result in cold solder joint or bad connection.
It’s made of 50% tin and 50% lead. This solder was traditionally used for lead came soldering tasks where a flatter solder joint was desired. It’s never recommended to use for electronics except for some particular brands. 50/50 solder wires were earlier used in plumbing until lead poison became an issue.
63/37 solder is a mixture of 63% tin and 37% lead. This type of solder has lower melting point of around 180°C. It’s mostly preferred for electronics because of its eutectic property. 63/37 solder is also known as eutectic solder as they don’t have semi-solid condition. Due to this the solder is considered easier to work with as there is very less chances of cold joint formation. However, this type of solder is more expensive than other lead-based solders.
Solder containing lead is being phased out slowly under some new EU directives such as the RoHS and WEEE. It’s now being replaced with tin-antimony alloys. Earlier, only a few years back lead-based solders were the most popular ones and considered the best, but now some shops have even stopped selling these solders.
Lead-free solder has a greater melting point than lead-based solder and requires more aggressive fluxes, which means that the soldering unit must be designed for lead-free solder and able to deliver the right temperature. Lead-free solder generally melts at around 230°C. The iron tips will also need a different and precise coating to withstand the flux. If you use a soldering iron constructed for lead solders to solder lead-free, then it may result in dry joints and reduce tip life.
One of the most commonly used lead-free solders is a 96.5/3/0.5 alloy. It is made of a mixture of 0.5% copper, 3% silver and 96.5% tin. Unfortunately lead free solder is the most expensive one. It creates strong, but more brittle connections. If you are concerned about the long-term effects of using lead solder then you can switch to lead-free, but before that you must be proficient in working with lead-based.
Solder with Flux Core
Flux is a compound, usually used along with solder while soldering in order to improve the quality of solder joints. Some solders are designed with flux in their core for user convenience. By using a solder with flux core, you won’t have to invest on or work with separate flux. There are two basic types of flux core solders:
Rosin Flux Core
The solder with rosin core has channels filled with rosin flux. Both lead-based and lead-free solders can have rosin core. This type of solder is recommended for all types of soldering jobs including electronics. Rosin flux is great for all joints as it becomes inert and harmless once the joint has cooled.
Acid Flux Core
Solder with acid core has acid flux in its channels. This is recommended only for plumbing and sheet metal soldering. Never use solder with acid core for electronics. As acid remains active at room temperature, it’ll corrode and damage the electrical joints.
Solders come in variety of sizes, with variable thickness. It’s important to choose the right size suitable for your work-piece. Solders are usually determined by their diameters. 0.02″, 0.063″ and 0.04″ are the most commonly used. Larger diameters are great for larger joints and components. For fine soldering works like though-hole components and fine electronics, 0.02″ and 0.04″ are preferred. Solder having 0.04″ diameter can be used in almost all soldering tasks.
While choosing the solder, you must always consider your experience with soldering. If you are a novice, you should first work with lead-based. While working, make sure that your work area is always well ventilated. Health is also an important factor so don’t put it at risk.