The main appearance requirements of the prepreg used in the multilayer board are: the cloth surface should be flat, free of oil, stains, foreign matter or other defects, no cracks and excessive resin powder, but microcracks are allowed. The main performance indicators of prepreg include Resin conent, Resin flow, Gel TIme, and VolaTile content. In addition, there is an indicator of the control of dicyandiamide crystallization in the US military standard. MIL_I)_13949. (1) The resin content refers to the mass fraction of the resin in the prepreg, and the general resin content is 45% to 65%, and the content thereof decreases as the thickness of the fiberglass cloth increases. For the prepreg of the same system, the content directly affects the electrical properties and dimensional stability of the prepreg, such as dielectric constant and breakdown voltage. Generally, the content is high, the dielectric constant is low, the breakdown voltage is high, but the dimensional stability is poor, and the volatile matter content is high. (2) Resin flow refers to the fraction of the resin that can flow in the resin as a percentage of the total resin. The fluidity of the resin is generally between 25 9/6 and 40%, and the content decreases as the thickness of the fiberglass cloth increases. The fluidity is high, and the resin is lost in the laminating process, and the lack of glue or gel-poor phenomenon is easy to occur; the fluidity is low, and it is easy to cause difficulty in filling the pattern gap, and bubbles and voids are generated. Therefore, in the production process of the multi-layer board, it is preferable to select a pre-solidified sheet of medium fluidity. However, current semi-curing manufacturers usually provide proportional fluidity instead of fluidity and gel time. Proportional fluidity data can better predict the final thickness of the finished board, which is one of the important parameters in the production process of multi-layer boards. (3) Gel time refers to the total time that the resin is in a liquid state under heating. The gel time is generally from 140 to 190 s. The gel has a long time, the resin has sufficient time to wet the pattern, and can effectively fill the pattern, which is beneficial to the control of the pressing parameters. (4) Volatile content refers to the residue of some small molecular solvents used in the resin when impregnated with fiberglass cloth. The volatile matter accounts for the percentage of volatiles in the prepreg. The general volatile content is less than or equal to 0.3%. . The volatile matter is high, and bubbles are easily formed in the lamination, causing the resin foam to flow. Although the use of vacuum pressing can greatly reduce the formation of bubbles, generally the prepreg manufacturers should strictly control their content. Sewing Machine Motor,Dc Motor Sewing Machine,Industrial Sewing Machine,Brushless Servo Motor LISHUI SHUANGZHENG MOTOR CO.,LTD. , https://www.szservomotor.com