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1. What is Stencil (Steel Mesh)?

The mounting components themselves have no binding effect. How to mount the mounting components on the PCB?  This requires to print a layer of solder paste on the PCB board, through the solder paste to bond the mounting components and PCB, to achieve this purpose, we need a tool, we call it a stencil. The stencil is also be defined as SMT Stencil, which is a special SMT mold. Its main function is to help deposit the solder paste; the purpose is to transfer the exact amount of solder paste to the exact location on the empty PCB.

2. Evolution of Stencil (Steel Mesh)

The Stencil was originally made of wire mesh, so it was called a mask at that time. It was nylon(polyester)mesh at first. But later because of the durability, there were wire mesh and copper wire mesh appeared. With the development of SMT, the requirements for stencil are getting higher, so the stainless stencil has been produced, which is replaced the previous other material stencils.

3. Classification of stencil

According to the manufacturing process of SMT stencil, it can be divided into laser template, electropolishing template, electroforming template, ladder template, bonding template, nickel plating template, etching template.

4. Specifications of stencil

Conventional stencil specifications are 30*40 cm, 37*47 cm, 42*52 cm, 42*52 cm, 45*55 cm, 55*65 cm, 58.4*58.4 cm and 73.6*73.6 cm. Which type of stencil is required, the processing factory will decide according to the type of SMT machine and PCBA processing. The customer only needs to provide the jointed board solder paste layer Gerber file to the processing factory.

The stencil is divided into two types: solder paste stencil and red rubber stencil. The processing factory will decide to use different processing techniques according to different process requirements, and then make different types of the stencil.

5. Stencil manufacturing process

The manufacturing process of the stencil includes chemical etching, laser cutting, and electroformed.

6. Opening design of the stencil

The design of the stencil should take into account the demolding properties of the solder paste, which is determined by the opening of the width-to-thickness ratio, area ratio, and the geometry of the open sidewall and the smoothness of the hole wall. The thickness, size, and shape of the stencil ensure the yield and reduce the defect rate.

7. Post-processing

Since after laser cutting will produce the metal slag adheres to the hole wall and the opening, the surface is generally polished; of course, polishing is not only to remove the slag (burr) but also to roughen the surface of the steel sheet. Increase the surface friction to facilitate the rolling of the solder paste to achieve a good tinning effect.

8. Cleaning

In order to keep good of the demolding performance of the stencil, the bottom of the stencil should be wiped regularly during the use process, and cleaned in time after use, so that it can get a better mold release effect next time. The cleaning method of the steel mesh is generally wiping and ultrasonic cleaning.