sales@ipcb.com
The first process in the PCB assembly line is to print solder paste on the PCB,and printing solder paste requires a tool, which is a PCB stencil. Its main function is to help the deposition of solder paste, the purpose is to transfer the exact amount of solder paste to the exact position on the PCB board. Steel mesh plays an important role in SMD processing, and the quality of steel mesh even directly affects the quality of the whole PCB.
First,the stencil production requirements of PCB processing plant
1 - Into the board direction and paste machine to be unified.
2 - Mark the product model, thickness, production date.
3 - The frame size according to the structure of the printing machine and product specifications.
4 - Request the supplier to make the stencil according to the relevant documents and data of the SMT small batch SMD factory.
5 - The size of the opening pipe and the opening should be determined according to the type of each component.
6 -Thickness of the scraping glue is generally 0.18MM-0.2MM,and the scraping tin is 0.1MM-0.15MM.
PCB stencil
Second,PCB processing plant stencil acceptance requirements
1 - Whether the tension is good.
2 - Whether the marking is complete.
3 - Whether the flatness is level or not.
4 - Whether the frame size is correct.
5 - Whether the thickness is in accordance with the product requirements.
6 -Is the piping and size of the openings in accordance with the requirements.
7 -Is the location and number of openings consistent with the GERBER file.
PCB stencil
Third,the choice of PCB stencil
In terms of production process, it can be divided into laser stencils,electro-polished stencils,nanometer stencils,electro-cast stencils, etched stencils and ladder stencils.
1 -Laser mesh is formed by laser cutting,which is the most commonly used mesh in the industry nowadays.It is made directly by using data files,which reduces the number of production errors and has high precision,but it needs to be cut one by one and is not fast enough.
2 - Electro-polished steel mesh is made by polishing the hole wall of the mesh with electro-polishing tube after laser cutting to improve the hole wall of the opening.It is particularly suitable for ultra-fine pitch QFN/BGA.
3 - Nano stencil is based on the electropolished stencil with some rare metals added to its surface,and by changing the structure of the metals to make a good combination,so that the hardness of the stencil is greatly improved and the rare metals have a repulsive effect on the flux in the solder paste, thus greatly reducing the number of washing times,improving production efficiency and printing quality.Nano stencil has all the advantages of electro-polished stencil, and its non-stick solder paste advantage makes its printing more difficult to pull the tip, which is suitable for the solder paste printing of more precise components.
4 - Electroformed stencils are the most complex type of stencil manufacturing technology,a metal forming process that involves depositing nickel metal on a substrate or specimen to form a metal layer. Electroforming stencils have smooth aperture walls, an inverted trapezoidal structure,and the best solder paste release for micro BGAs,ultra fine pitch QFPs,and small chip components such as 0201 - 01005,which have good printing performance. Moreover, due to the characteristics of the electroforming process,a ring-like protrusion is formed at the edge of the hole slightly above the thickness of the stencil,which is equivalent to a sealing ring when solder paste is printed. This sealing ring facilitates the stencil to fit tightly with the pads or solder masks during printing,and prevents the leakage of solder paste to the outside of the pads.Of course,the cost of stencils in this process is also the highest.
5 - Etched stencil is through the chemical etching process, one-time forming, faster, in the laser stencil is not popular when the mainstream stencil,with the development of science and technology as well as environmental protection requirements are becoming more and more demanding, etching stencil has been replaced by laser stencils, but etching as a process is still irreplaceable.
6 - Stepped stencil is made into two or more thicknesses on the same stencil to achieve the purpose of precise control of the amount of tin,STEP-UP partially thickened to overcome the problem of uneven foot bit of some parts, and STEP-DOWN partially thinned stencil can effectively control the problem of short-circuiting of the feet of FINE PICTH parts.
PCB stencil
The price of even the most common laser stencils can vary from tens to hundreds of dollars. The quality of the stencil is influenced by the data, design, and manufacturing technology. A good PCB stencil will have a good tinning effect and make the mounting more accurate and beautiful.
The quality of PCB stencil will directly determine whether the tin on the pad is uniform and full PCB stencil quality is good or bad,determines whether the tin on the pad is uniform and full, and even directly affects the reliability of the soldering of the PCB board products, the entire processing will have a great impact, so it must be strictly in accordance with the needs of the production of stencils to ensure the quality of each step in order to do a good job of the overall quality of the processing of the PCB hit parts.