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Solder Paste Stencils – What You Need To Know

Author: Laurie Kneller
by Laurie Kneller
Posted: Jul 27, 2017
Creating a circuit board requires multiple phases and steps, the most important one of them being the application of solder paste to the board surface. Accurate placement of the correct amount of paste to the right parts of the pad will ensure that there are no defects in the resultant circuit assembly. And considering the commercial mass production parameters pertaining to the electronics industry, this accuracy and precision will have to be maintained time after time, on each circuit board being assembled in your facility. The way to achieve this is through the use of solder paste stencils. This article will tell you everything you need to know about solder paste stencils and the role they play in the SMT assembly process.

Solder paste stencils – their role in SMT assembly

The most common method of applying solder paste to circuit pads in an SMT assembly process is through a stencil printer. The solder stencil is pre-designed with apertures and dimensions that match your resultant circuit parameters. Before beginning the assembly process, the stencil needs to be cleaned and dried so as to prevent oxidation of the substrate surface and avoid the formation of solder balls. Once the optimum surface state is achieved, the stencil is carefully placed on the circuit pad and the solder paste is applied with the help of a squeegee blade. The squeegee uses force to ensure the paste moves across the stencil and properly reaches the SMT circuit surface. The squeegee is also used to spread the solder paste evenly across the stencil to ensure accurate application. Once the process is complete, the stencil is carefully separated from the substrate and other circuit components are put in place to complete the circuit design before the paste cools off and forms a bond with the surfaces.

Solder paste stencils – their composition and types

Solder paste stencils are generally manufactured using a thin sheet material, usually metal, with your pre-designed circuit pattern already cut into the surface. The process used to cut this pattern into the stencil usually forms the basis of its classification. Originally, this task was carried out through chemical etching, but today, with the increasing demand for miniaturized circuitry, precise design and accurate rendition is becoming ever more important. Hence, processes like laser cutting and electroplating are used to create increasingly smooth, well-defined, intricate and ultra-fine stencils that help ensure accurate solder paste deposition. When designing solder paste stencils, the size, shape, thickness, finish, material and aperture aspect ratio are all important factors that will eventually determine the quality and electrical reliability of the circuit being produced.

Solder paste stencils – the difference they have created

The solder paste stencil has two key roles to play in the SMT assembly process – ensuring precise and accurate placement of the paste or flux on the substrate and ensuring formation of properly sized and shaped deposits on the circuit board. A properly fabricated solder paste stencil can help you streamline your assembly process, helping you replicate the circuit design again, and again, and again – all the while maintaining its accuracy, precision and electrical reliability.

The exponential growth of the electronics industry can therefore, be credited to solder paste stencils – the tool responsible for maintaining SMT assembly quality at any scale of production.

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.

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Author: Laurie Kneller

Laurie Kneller

Member since: Jul 28, 2016
Published articles: 35

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