The printing industry is the first and most important part of SMT assembly technology.The quality of printing will directly affect the penetration rate of SMT welding. In the actual production process, we found that 60-70% of the welding defects are related to the printing quality.Therefore, it is necessary to study all aspects of the printing process.The design of the plate plays an important role in all aspects of printing process.
General technical requirements:
1. Net frame: the frame size depends on the requirements of the printing press. Take DEK265 and MPM UP 3000 models as examples.
2. Tension network: use red rubber and aluminum adhesive tape, and scrape a layer of protective paint evenly at the joint of aluminum frame and adhesive.At the same time, in order to ensure sufficient tension and good flatness of the mesh, it is recommended that the stainless steel plate is reserved 25mm-50mm from the inner side of the mesh frame.
3. Datum point: open the hole in 1:1 mode according to the size and shape provided by PCB data, and carve half through on the printed reverse side.At the corresponding coordinates, open at least two reference points for the whole PCB.
4. Opening requirements: 1.41.Position and dimension ensure high opening accuracy and open in strict accordance with the specified opening method.1.42.The independent opening size cannot be too large, the width cannot be greater than 2mm, and the bridge of 0.4mm needs to be built in the middle of the welding plate size greater than 2mm, so as not to affect the strength of the plate.1.43.The open area must be centered.
5. Characters: for the convenience of production, it is suggested to carve the characters above or below in the lower left or right corner of the screen: Model;T;The Date;Board production company name.
6. Mesh thickness: in order to guarantee the printing amount and welding quality of solder paste, the surface of the mesh should be smooth and uniform, and the thickness of the mesh should refer to the above table. The thickness of the mesh should be based on the premise of meeting the minimum spacing QFP BGA.If there are 0.5mmQFP and CHIP 0402 components on the PCB, the thickness of the mesh is 0.12mm.If there are more than 0.5mmqfp and CHIP 0603 components on the PCB, the thickness of the mesh is 0.15mm.