Patent DE-102006016400-A1 (DE)
Title: Base material for making printed circuit boards, produced by pressing layers of glass fabric vacuum-impregnated with solvent-free epoxy resin, has defined properties
Inventor: SCHAEFER HANS-JUERGEN
IPC: H05K3/46
Filed: 2006-04-07
Abstract: Base material for making printed circuit boards, produced by pressing layers of glass fabric vacuum-impregnated with solvent-free epoxy resin, has a weight loss of no more than 0.25% after 3 hours at 120[deg]C and exhibits no delamination after ten reflow soldering operations at 260[deg]C. Independent claims are also included for: (1) prepreg for making a base material as above, produced by impregnating rolls of glass fabric with solvent-free epoxy resin, either in an autoclave or under vacuum on a perforated winding cylinder, and precuring the product by radiant heating; (2) base material as above, in strip or roll form, laminated on both sides with copper foil; (3) producing a prepreg as above by heating a roll of glass fabric to 50-100[deg]C in an oven, placing the roll upright in an autoclave equipped with a casing having a closed base and a headpiece, generating a vacuum of 5-10 mbar, filling the autoclave from the bottom with solvent-free epoxy resin at the same temperature, draining off the resin, feeding the prepreg into a discharge trough equipped with a metering roller, impregnating the prepreg further in an impregnation bath upstream of a meander radiant compact dryer or treater and precuring the prepreg upstream of a double belt press for continuous curing; (4) producing a prepreg as above by winding a roll of glass fabric onto a winding cylinder having central bores, sealing both sides of the cylinder with a pneumatic closure device, hermetically sealing the cylinder with a pneumatic rubber cover applied on an arbor, using a winding mechanism to immerse the fabric in a bath of solvent-free resin with a temperature of 50-100[deg]C and a viscosity of 100-500 mPas, evacuating the cylinder down to 10-500 mbar with a vacuum pump through a pipe that is located in the arbor and is equipped with a float valve to prevent resin ingress, removing excess resin in a stripper unit or a pair of metering rollers, installing a meander radiant compact dryer or treater upstream of a double belt press and, before this, passing the fabric over a guide roll through a glueing press and a web storage station and over another guide roll into an impregnation bath, adjusting the resin content with a pair of metering rollers, and preferably precuring the product for 30-40 seconds in a radiant dryer; (5) producing a base material as above in roll form by laminating the prepreg with copper foil in a treater comprising two laminating rollers at 20-60[deg]C, two laminating rollers at 180-220[deg]C and two rolls of copper foil, curing the product in a descending drying channel, and cooling the product to 20-50[deg]C by means of an air cooler and cooling rollers before forming it into a roll with a winding mechanism; (6) producing a base material as above in strip form by producing prepregsas above from a solvent-free epoxy resin, preferably with a gel time of 50-70 seconds at 170[deg]C, precuring the prepregs with an infrared lamp to a residual gel time of 20-30 seconds, passing the prepregs through a pressure-free zone with a length of 50-75 cm in 10-15 seconds, precuring the prepregs for 3-5 second in an isochoric press zone, preferably with a length of 50-100 cm, comprising a press plate with a PTFE cover having a fishbone pattern of channels with discharge holes, and curing the product in an isobaric press zone at 5-20 bar and 180-190[deg]C for 60-120 second; (7) device for applying a vacuum to the inside of a roll of glass fabric, comprising a pneumatic arbor with an inner tube that extends to the middle of the arbor and ends there in an opening that can be closed with a float valve, through which a vacuum can be applied to the fabric through holes in a metal cylinder; (8) meander radiant compact dryer for producing prepregs as above, comprising a drying oven, preferably 4-8 m high and 1.5-2 m wide, that can be divided into 2-meter segments and is equipped with vertical infrared lamps on both sides and in the middle and with coolable guide rollers in the middle.