Today, let’s learn about the definition of PCB SMT Stencil.
The SMT Stencil, professionally known as an "SMT template," is most commonly made of stainless steel, colloquially referred to as a steel stencil. It is the template used in the first process of SMT surface mounting to print solder paste onto the PCB circuit board.
Before SMT placement, screen printing is required. The stencil used when printing solder paste (a semi-liquid, semi-solid tin paste) or red glue onto the bare PCB is the SMT steel stencil.
The PCB steel stencil is a thin sheet of steel with many pad holes. The positions of these holes exactly match the positions of the PCB pads. This is used for automatic or semi-automatic chip placement. The stencil is placed over the board, and then solder paste (a viscous solder) is spread, so that the circuit board pads have solder on them (the stencil only has holes where the pads are, so other positions do not have solder); then the components are placed on top. After that, they are placed in the reflow oven to be soldered.
The PCB steel stencil is used when there are a large number of surface-mounted ICs, resistors, and capacitors on the PCB board. During soldering, a reflow oven is used for machine soldering. Before soldering, solder paste needs to be applied to the pads of the surface-mounted components, which requires the creation of a steel stencil. The stencil has holes opened at the positions of each surface-mount pad, so when the machine spreads the solder paste, solder paste will leak through all the holes onto the PCB board, then the components are placed, and finally, they are put into the reflow oven.
The so-called steel stencil opening refers to the process of creating a steel stencil based on the Gerber files, which are generally the Top Paste layer and Bottom Paste layer of the PCB circuit board file.
SMT steel stencils are generally made from 0.12mm thick steel sheets, with additional laser polishing, and the price is around 500 yuan per sheet.
Next we will learn about the different ways of categorizing of SMT stencils.
