SMT steel mesh, also known as steel plate, its main function is to help the deposition of solder paste, transfer the exact amount of solder paste to the exact position on the bare board. The steel mesh consists of a mesh frame, a wire mesh and a steel sheet. There are a number of holes in the steel sheet that correspond to the locations on the PCB that need to be printed.

In use, the PCB is placed under the steel mesh, and the solder paste is printed on the PCB through a small hole in a fixed position on the steel mesh.

The less the solder paste is blocked on the steel grid, the more it deposits on the PCB. Therefore, when a bad situation occurs during the printing process, the condition of the steel plate should be checked first.

SMT steel mesh can be divided into seven types: laser template, electropolishing template, electroforming template, step template, bonding template, nickel plating template and etching template. The SMT stencil manufacturing process has three methods: chemical etching, laser cutting and electroforming.

1. Purpose:

Standardize the production of SMT steel mesh, so that SMT steel mesh production has rules to follow; standardize the use and management of steel mesh to improve work efficiency.

Standardize the management and use of SMT scrapers to improve work efficiency.

2. Scope of application:

All engineering personnel, equipment technicians, production line printers, quality department IPQC, PMC department warehouses in the SMT workshop.

General technical requirements

1, stretch net

Use red rubber + aluminum tape method, in the aluminum frame and the glue joint, it must be evenly scraped with a protective paint. At the same time, in order to ensure sufficient tension and good flatness of the stencil, it is recommended that the stainless steel plate retain 25mm-50mm from the inner side of the frame.

2, the frame

The frame size is determined by the requirements of the printing press. For example, the DEK265 and MPM UP 3000 models have a frame size of 29ˊ 29ˊ and are made of aluminum alloy. The frame profile is 1.5ˊ 1.5ˊ.

3. Reference point

According to the size and shape provided by the PCB data, it is opened in a 1:1 manner and is semi-transparent on the reverse side of the printing. At the corresponding coordinates, the entire PCB is opened at least two reference points.

4, opening requirements

(1) Position and size ensure high opening accuracy and open in strict accordance with the prescribed opening method.

(2) The size of the independent opening should not be too large, the width should not be larger than 2mm, and the bridge with a pad size larger than 2mm should be 0.4mm in the middle to avoid affecting the strength of the stencil.

(3) The open area must be centered.

5, characters

For the convenience of production, it is recommended to engrave the following characters in the lower left or lower right corner of the stencil: Model; T; Date; stencil production company name.

6, stencil thickness

In order to ensure the amount of solder paste printed and the quality of soldering, the surface of the stencil is smooth and uniform, and the thickness is uniform. The thickness of the stencil is referred to the above table, and the thickness of the stencil should be based on the premise of the finest pitch QFP BGA.

For example, there are 0.5mm QFP and CHIP 0402 components on the PCB, and the thickness of the stencil is 0.12mm;

For example, there are 0.5mmQFP and CHIP 0603 components on the PCB, and the thickness of the stencil is 0.15mm;