Six different fabrication processes for SMT stencils

Classification of SMT stencils:

From the production process, about can be divided into laser stencil, electropolished stencil, nano stencil, electrocasting stencil, etching stencil, step stencil and so on.

Laser stencil is cut and shaped by laser, which is the most commonly used stencil in the industry at present. It is made directly by using data files, which reduces the production error link and has high precision, but it needs to be cut one by one, which is not fast.
Electropolishing stencil is to polish and polish the hole wall of the stencil by electrolytic polishing after laser cutting to improve the opening hole wall. Its hole wall is smooth and it is especially suitable for ultra-fine pitch QFN/BGA.
Nano stencil is based on electropolished stencil with some nano rare metals added to its surface, and by changing the metal structure to make a good combination, the hardness of the stencil is greatly improved and the rare metals have a repulsive effect on the flux in the solder paste, which greatly reduces the number of times of washing the stencil and improves the production efficiency and printing quality. Nano stencil has all the advantages of electropolished stencil, the advantages of its non-stick solder paste so that its printing is more difficult to pull the tip, suitable for more sophisticated components of the solder paste printing.
Electroforming stencil is the most complex kind of stencil manufacturing technology, is through the deposition of nickel metal in the base plate or template and metal layer of a metal molding process. Electroforming stencil aperture wall smooth, inverted trapezoidal structure, the best release of solder paste, for micro BGA, ultra-fine pitch QFP and small chip components such as 0201, 01005, has good printing performance. And because of the characteristics of the electroforming process itself, the formation of the edge of the hole slightly higher than the thickness of the ring-like protrusions of the steel sheet, solder paste printing is quite a “sealing ring” in the printing of this sealing ring is conducive to the stencil and the pad or solder mask close to the pad to prevent the leakage of solder paste to the outside of the pad. Of course, the cost of this process stencil is also the highest.
Etching stencil is through the chemical etching process, a molding, faster, in the laser stencil is not popular when the mainstream stencil, with the development of technology and environmental protection requirements are increasingly high, etching stencils have been replaced by laser stencils, but the etching process as still irreplaceable.
Step stencil: Step stencil is made of two or more thicknesses on the same stencil to achieve precise control of the amount of tin for the purpose of STEP-UP local thickening can be overcome in some parts of the foot position is not uniform, and STEP-DOWN local thinning stencil can be effectively controlled FINE PICTH parts foot short-circuiting problems.

There are so many types of stencils just from the production process, and we haven’t even talked about the material of the stencil yet. As a PCB board or stencil does not have a lot of research procurement staff, how to buy stencils?

Actually, ordinary laser stencils are suitable for most products. If you need a special stencil, SMT processing plant will be the first time to communicate with you, because the printing effect of the stencil directly affects the yield of the patch. In order to produce high yield products, the mounter will use the most qualified stencil.

Even for the most common laser stencils, the price varies from tens to hundreds. From the material, to the design, manufacturing process, all affect the quality of the stencil. A good stencil will have a good effect on the tin, so that the mounting is more accurate and beautiful.