An Overview of Solder Paste

Posted by Alphaassembly on May 29th, 2018

Printed circuit board (PCB) manufacturing requires a bonding agent to connect the surface mount components to the board’s pads. This bonding agent is known as ‘solder paste’, a material that is not just an adhesive, but a component that can form the mechanical bond and electrical connection between the PCB and the components. It is formulated with a mixture of solder alloy in powdered form suspended in flux, and it works by initially holding the components in place before the soldering process, which heats the paste and the entire board to establish the connection. Solder paste is applied to a PCB via stencil printing, and the components are placed by hand or via special equipment or machinery. 

In solder paste, it is the flux that serves as the temporary adhesive to hold the components until the solder is melted in the soldering process to fuse them together. The material is typically putty-like and gray in color, with a composition that varies depending on the purpose. For instance, if you are soldering plastic components to a circuit board made of FR-4 glass epoxy, then you will need the eutectic Sn-Pb (64 percent tin and 37 percent lead) or SAC (Sn/Ag/Cu or tin/silver/copper) alloy. If the results need to be high in shear and tensile strength, you may consider Sn/Sb (tin-antimony) alloys for the board. 

Solder paste is typically composed of tin-lead alloys, with a third metal possibly involved. However, legislation for environmental protection continues to encourage electronics manufacturing companies to consider lead-free solders for safety reasons. Solder paste’s viscosity may change down the line depending on the shear force. Technologically advanced products are versatile and helpful in achieving high yield and throughput, while ensuring lower cost of ownership for different applications. 

Established manufacturers of solder pastes have developed different kinds, including no-clean, lead-free, and halogen-free for a wide array of applications like low-temperature processing and feature printing. Some products are offered in solder bars, spheres, wires, and preforms, with assured stronger solder joints and alloy compatibility. High-quality solder pastes are used in the manufacture of many consumer electronic products, military and medical equipment, automotive systems, computer motherboards, network servers, and much more. Rest assured, the pastes will conform to your unique processes and the environmental regulations you need to follow. 

About the Author:

Alpha Assembly Solutions, Inc. is the global leader in the development, manufacturing and sales of innovative specialty materials used in a wide range of industry segments, including electronics assembly, power electronics, die attach, LED lighting, photovoltaics, semiconductor packaging, automotive and others. Since its founding in 1872, Alpha has been committed to developing and manufacturing the highest quality specialty materials.