How to control the pcb manufacturing solder paste printing machine process parameters
The main control parameters of pcb manufacturing automatic printing machine are: scraper pressure, printing thickness, printing speed, separation speed of PCB and steel stencil, printing gap between PCB and steel stencil, cleaning frequency and steel stencil cleaning methods
Too small pressure causes insufficient solder paste on the printed board. If too much pressure causes the solder paste to be printed too thin, it is easy to form solder balls and bridges. Generally, the pressure of the squeegee is set to a pressure of 1 kg per 50 mm of the squeegee length, and an acceptable range of 1 to 2 kg.
The effect of the squeegee pressure on the printing thickness is related to the hardness of the squeegee, which is generally determined by the squeegee pressure when the squeegee is scraped through the stencil and there is no residual solder paste on the stencil.
The thickness of the printed solder paste is determined by the thickness of the pcb manufacturing template, and has a certain relationship with the machine setting and the characteristics of the solder paste. A slight adjustment of the printing thickness is often achieved by adjusting the speed of the squeegee and the pressure of the squeegee.
The speed at which the squeegee scrapes the paste on the stencil is also an important factor influencing the thickness of the solder paste. In general, the slower the speed of the squeegee, the greater the viscosity of the solder paste: the faster the squeegee, the lower the viscosity of the solder paste. There is also a certain conversion relationship between the squeegee speed and the squeegee pressure, that is, reducing the squeegee speed is equal to increasing the squeegee pressure, and increasing the squeegee speed is equal to reducing the squeegee pressure. The printing effect is the result of a combination of multiple printing parameters. Usually, the printing speed is low, and the printing result is good. For high speed, the result is feedback by testing.
After solder paste printing, the instantaneous speed of the template leaving PCB, that is, the separation speed, is a parameter related to the printing quality of PCB manufacturing, which is especially important in precision printing machines.Early printing machine were constant speed separations, and advanced printing machine had a tiny hold on the plate as it left the solder paste pattern to ensure the best print pattern.
5.Width of scraper
If the scraper is too wide relative to the PCB, the solder paste printing process requires more pressure and more solder paste, which may lead to the waste of solder paste.Generally, the width of the scraper is preferred about 50mm plus PCB length (printing direction), and the scraper head should fall on the metal template.
Printing gap is the distance between the template and PCB, which is related to the amount of PCB left after printing. As the distance increases, the amount of solder paste in PCB manufacturing increases, which is generally controlled as 0~0.07mm.
The Angle of the scraper affects the vertical force of the scraper on the solder paste. The smaller the Angle is, the larger the vertical force is. The pressure generated can be changed by changing the Angle of the scraper
8.Quality of steel stenciland scraper
Because the steel stencil in the scraper pressure and thrust under long-term usage will change the flatness and tension of the steel stencil, when the flatness of the stencil itself is not good, will cause the printing paste thickness consistency is poor.
Scraper is generally plated with a layer of smooth wear resistant nickel alloy, the coating should be replaced if it fall off, otherwise it will accelerate the wear of steel stencil.In addition, it should be noted that the scraper can not be in a long-term working state of great pressure.
9.Cleaning of steel stencil
During solder paste printing process, the solder paste penetrate into stencil hole, when the stencil clean effect is poor, PCB manufacturing production for a period of time will be left a circle solder paste residue in the surface of the steel stencil hole, which will affect the thickness of the solder paste during printing process, make corresponding solder paste thickness increase, at the same time easy to cause the tin connection, tin slag and tin beads after welding.Therefore, strengthen the maintenance of steel stencil cleaning device and state inspection, focus on checking the steel stencil cleaning rack plastic cleaning scraper and vacuum nozzle plug, to ensure that the steel stencil cleaning device can work normally, to ensure the cleaning effect.Clean the steel mesh at regular intervals.
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