SMT technology started in 70s, rapid growth in 80s, stable development in 90s, so far has gradually matured. Solder paste printing, component placement and reflow process are the three main processes of SMT assembly, solder paste printing is the first step in the whole electronic factory production line of SMT in solder paste printing and reflow furnace is the key link of the production process, the production yield is also guaranteed, it has become the industry the consensus!
In recent years, with the printed circuit board (PCB) packaging density high density solder paste, screen printing process requirements to improve operation quality from grow with each passing day. The printing paste and the quality is a crucial part in SMT production, the paste of the metal powder size, metal content distribution, flux ratio, temperature, time and stirring time of solder paste storage environment, storage time will affect the print quality. Due to solder paste causes poor tin, welding effect is not good, and other quality problems occur.
At present, consumer electronic products are developing towards a short and thin direction, so the demand of solder paste printing is higher and higher.
Since 1985, the introduction of SMT production line, mass production of color TV tuner, China's electronic manufacturing industry has applied SMT technology for nearly 30 years. In the early days, the solder paste printing process was relatively new to the public. But with the development of the consumer electronics market increasingly large scale, product replacement cycle becomes more and more fast, products in the pursuit of high-quality, high stability and portability requirements, the production technology of the increasingly high demand. Solder paste printing is used more and more in many electronic products and various SMT production processes, and the development of solder paste printing technology has also been improved rapidly. The process of solder paste printing is also getting higher and higher. Relative requirements of the stability and precision of the equipment is also increasing.
More than a decade ago, a lot of people might not be familiar with the full automatic solder paste printing industry. But with the smart phones, tablet PCs, automotive electronics, smart home and other consumer electronics in people's daily life has been widely used. In stable quality, convenient portability, high degree of functional integration of consumer demand, also put forward higher requirements on the technical requirements of the production process of these electronic products, it also promoted the application of SMT high precision screen printing technology, automatic high precision printing machine technology has been rapid development.
From a single variety of project, standard production to small batch and multi varieties, customized production, development and change of manufacturing industry has brought new requirements, high precision and high efficiency and high quality, realize the wisdom of the plant through the information and communication technology, intelligent manufacturing has become a new trend of the present industrial manufacturing.
In 1970s the surface mount technology SMT, refers to the printing on the printed circuit board solder coated solder paste, and the pad surface mount components affixed to an accurate filling coated with solder paste on the circuit board heating reflux temperature curve according to the specific, let the molten solder paste, the alloy composition and cooling after solidification between the components and the printed circuit board and solder joints formed connection metallurgy technology.
Solder paste printing machine as the front line equipment of SMT production line, its importance is self-evident, for solder paste printing process technology knowledge, we must first understand the following:
1, steel mesh: its main function is to solder paste accurately coated on the PCB plate pad, and its quality directly affects the quality of printing paste. At present, the production methods of steel mesh include chemical etching, laser cutting, electroforming, nano steel mesh, etc..
2, solder paste: solder paste components, solder paste size is directly related to the lower tin effect, the current solder paste general No. 3-6 powder.
3, scraper pressure: refers to the depth of the scraper drop, is one of the important factors affecting the quality of printing, scraper pressure is too small will make the steel network surface residual layer of solder paste, easy to cause printing, forming, bonding and other printing defects. Consistency of print quality between front and rear squeegee, constancy of pressure in printing process.
4, printing speed: printing speed and scraper pressure there is a certain relationship, the drop speed is equivalent to increase the pressure, reduce the pressure can play the role of improving the printing speed.
5, printing gap: printing gap refers to the distance between the steel mesh and PCB, which affects the amount of printing paste on the PCB board and the thickness of the printed solder paste. Is a major factor directly affecting the quality of printing.
6, scraper and steel mesh angle: the smaller the angle of the scraper and steel mesh, the greater the downward pressure, easy to solder paste into the mesh, but also easy to solder paste is pressed to the bottom of the steel mesh, resulting in paste adhesion. The angle between the blade and the steel mesh is usually 45~60 degrees.
7, scraper thickness: thickness and paste forming plump, with the pressure setting to form a certain relationship, in precision printing machine in a certain key role, especially for the ladder steel mesh, thickness and angle is very important. The thickness is usually between 0.2-0.5mm.