Multilayer PCB boards with major appearance prepreg requires: Oil should be smooth, no oil, no stains, no foreign matter or other defects, no rupture and excessive resin powder, but allow microcracks.
Prepreg key performance indicators gel content (Resin conent), Fluidity (Resin flow), gel time (Gel time), volatile matter content (Volatile content) four. In addition, the U.S. military standard. MIL_I) _13949 control indicators there dicyandiamide crystals.
(1) means a resin content in the prepreg resin is occupied by the mass fraction of the resin content is generally 45% to 65%, the content of glass fiber cloth with a thickness increases. For the same prepreg system, the direct effect on the content of the prepreg dielectric constant, breakdown voltage and other electrical properties and dimensional stability. In general: content, low dielectric constant, high breakdown voltage, but poor dimensional stability, high volatile matter content.
(2) means a resin flow of the resin to flow resin comprises fraction of the total resin flow of the resin is generally between 259/6 to 40%, the content of glass fiber cloth with a thickness increases. Liquidity is high, the loss of resin during lamination and more prone to lack of plastic or plastic-poor phenomenon; low fluidity, is likely to cause difficulties in filling gaps graphics, bubbles, voids and so on. Therefore, in multi-layer PCB board manufacturing process, selection of appropriate flow prepreg degrees. However, the current prepreg manufacturers usually provide the ratio of fluidity and fluidity instead of gel time, the proportion of the flow of the data can be used to predict the final thickness of the finished board, multilayer PCB board manufacturing process is one of the important parameters.
(3) Gel time means the total time for the resin under heating, in a liquid flow. Gel time is generally 140 ~ 190s. Long gel time, the resin has sufficient time to wet the graphics, and can effectively fill the graphics control parameters conducive to suppress.
(4) represents the content of volatiles small molecule resin impregnated glass fiber cloth used in the solvent the residue was pre-cured at the time of the volatiles the percentage representing the quality of the prepreg, said volatile content is generally less volatile content O.3% . The volatiles were high, bubbles easily formed in the lamination, resulting in a resin foam flow. Although the use of a vacuum press can be greatly reduced bubble formation, but generally prepreg manufacturers should strictly control their content.
