Things to Consider While Choosing Lead-Bearing Solder Paste

Posted by Alphaassembly on May 19th, 2017

PCB (printed circuit board) manufacturing cannot be completed without solder paste, the material used to connect the surface mount parts to the board’s pads. There are various types of solder pastes available, but those that contain lead are widely preferred. Lead-bearing solder paste is manufactured to meet the unique requirements of tin-lead soldering processes to ensure excellent and reliable print volume repeatability.

Here are some things to keep in mind before deciding to buy lead-bearing solder paste:

Types of lead-bearing solder pastes

Lead-bearing solder paste can be made in different alloys. Sn63/Pb37 is the most common form of tin-lead alloy used for a variety of applications. This means the paste is composed of 63% tin and 37%  lead. Solder paste is essentially powder metal suspended in flux, which is added to serve as a temporary adhesive to hold the components until the solder is melted during the soldering process to create a stronger physical bond.

Sn63/Pb37 lead solder paste is preferred when soldering plastic components to a FR-4 glass epoxy PCB. Another alternative to tin-lead alloys is the SAC alloy, which is composed of tin, silver, and copper (Sn/Ag/Cu). Lead-bearing solder paste may also come with a third alloyed metal.

Properties of the lead-bearing solder paste

When using lead-bearing solder paste to assembly circuitry, be sure to test and determine its various rheological properties to make sure that it is suitable for intended application. Take note of its viscosity, which is the degree to which the paste can resist the tendency to flow. The viscosity of solder paste may vary depending on the desired level of shearing force. The supplier or manufacturer of the paste should be able to state about the viscosity of the paste. Otherwise, it is recommended to test a sample of the paste.

Slump, the tendency of the material to spread after being applied, is another factor that must be considered when choosing a lead solder paste. Slump must be minimal, as it can increase the risk of forming a solder bridge between two adjacent lands, which can lead to soldering defects. Consider the working life of the lead-bearing solder paste, which pertains to the how long it can stay on the circuit board without affecting the printing properties.

About the Author:

Alpha Assembly Solutions Inc. is a premier company engaged in the development and manufacture of high quality electronics assembly materials. Since the year of its inception, way back in 1872, the company has played its role on the frontline of innovation, bringing many first-to-market products to the fore thereby, creating a premier niche for itself in the market.

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