The black glass fiber cloth is pressed and cured in three stages, namely, preheating, hot pressing and cooling. Sp...
The black glass fiber cloth is pressed and cured in three stages, namely, preheating, hot pressing and cooling. Special epoxy plates must also undergo heat treatment after hot pressing, i.e. supplementary curing.
(1) The preheating stage. Put the billet box into the pressing and heating room. Close the hot plate, and then press 1~3MPa, keep the temperature to 100~120℃ for 25~45min, so that the resin in the pre-impregnated material can penetrate into the gap of the fiberglass cloth which is the material of FR4 laminate sheet, and further make the volatile overflow. If the preheating temperature is too high, it is easy to flow glue and even run material (billet slides out of the heating room). And the hemp hole will appear on the surface of laminate sheet; If the preheating temperature is too low and the time is insufficient, heating and pressurizing too fast in the hot pressing stage will cause the fiberglass cloth to slip out.
(2) The hot-pressing stage. Setting of temperature, pressure and time plays a key role in the performance of epoxy fiberglass cloth laminated sheet. It is set according to the curing conditions of epoxy adhesives. For example, the epoxy phenolic glass cloth laminate sheet is set to cure at 170~175℃, while the epoxy silicone glass cloth laminate sheet is set to cure at (210±10)℃. Because the thin plate is very easy to transfer heat, the hot pressing temperature can be reduced by 5~10℃ when pressing thin plate, so that the plate has a certain elasticity, which is used for punching and shearing insulation parts and insulation liner.
(3) After cooling and stripping, the hot plate should be cooled with cold water, which should be cooled slowly to prevent internal stress from causing laminated sheet warping and deformation. The general cooling time is 30~60min. Then release the pressure, open the hot plate and take out the product.
(4) Finally, the laminated sheet is put into an oven at 100~140℃ for heat treatment to eliminate the internal stress of the laminate sheet and the residual low molecular substances in the sheet, so as to further improve the mechanical and electrical characteristics of the epoxy laminate sheet.
The final step is machining. Cut off the rough edges of the laminate sheet. Generally, the epoxy board supplier will use a plate shearing machine to cut sheets below 3 mm to reduce waste. Cutting machine is recommended for epoxy boards above 3 mm.