Process for preparing multi-material laminates

Abstract

To provide a system and apparatus for preparing multilayer plastic laminates for printed circuit boards capable of minimizing the number of laminates to be discarded.SOLUTION: The present invention provides: a process for preparing multi-material laminates for printed circuit boards that envisages the formation of a stack of plastic laminates, indicated below as "packages 1" below, separated by plates 3 of electrically insulating material, and the heating of the stack in the presence of at least two temperature detectors that allow the uniformity of the temperature to be obtained along the whole stack; and a system for producing the laminates.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a process for making a multi-material laminate for printed circuit boards, comprising the formation of a stack of plastic laminates, hereinafter referred to as the "package", separated by plates of electrically insulating material, and heating of the stack in the presence of at least two temperature detectors making it possible to obtain a uniformity of temperature along the entire stack, and a system for realizing said laminate. [Background technology]

[0002] Printed circuit boards for electronic components are generally manufactured starting from a plastic laminate which contains at least one thin metal layer.

[0003] Within the context of this invention, the individual packages are composed of alternating sheets of variously metallized dielectric materials ("inner layers") and sheets of pre-impregnated and partially polymerized plastic material (prepreg). The first and last layers of every package are composed of strip sections of copper or similar metallic material capable of conducting electricity.

[0004] Italian patent 0001255128 relates to a method for the production of plastic laminates with metal plates, in particular for printed circuit boards, carried out by means of a descending column hydraulic press, the support and pressure surfaces of which are not heated. The method described in the above mentioned patent consists in the formation of a stack of packs, each of which comprises a group of support sheets ("prepregs") impregnated with a partially polymerized plastic material and containing a metal plate on one or both sides, characterized in that the metal plate is obtained from a continuous strip which, starting from the bottom, is placed on the underside of the first group of sheets, then folded 180° and placed on the upper side of such group, after the sandwiching of the metal plate, suitably insulated by the sandwiching of a sheet of kraft paper, is folded a second time 180° in a direction opposite to the first direction, then folded a third time 180° in a direction opposite to the second folding direction, then placed on the upper side of the second group of sheets, and so on until it reaches the upper side of the last group of sheets. After completing the formation of the stack of packs, the two ends of the strip are connected to a current generator with appropriate power so that the electrical circuit of the generator is closed by generating an appropriate pressure on the stack of packs and the various parts of the strip mating with the faces behave like electrical resistors, generating the heat necessary to bring about the melting of the plastic material impregnating the support sheet, obtaining an intimate connection (i.e. an almost irreversible weld) between the various elements and the formation of a plastic laminate.

[0005] As non-limiting examples, the strips may be made of copper, the metal plates interposed between the various packs may be made of stainless steel, and each pack may be constructed of a sheet of woven glass fabric impregnated with epoxy resin. A stack of packs, including the copper strips folded into a coil around a separator plate, is placed between two containment plates, in contact with the lower and upper surfaces respectively, and maintained in alignment by, for example, two vertical cylindrical rods.

[0006] The use of copper strip wound as a coil through which a heating current circulates, as described above, generates heat directly within the stack of material, allowing a more even heat distribution than that permitted by a multi-surface press, where only the pucks at the two ends of the stack come into contact with the heated surface.

[0007] The process of using copper strips to heat the packs has a drawback: the packs at the ends of the stack are cooler than the packs located in the middle of the stack, and this difference This increases with the overall height of the stack itself, resulting in the need to discard packs at the ends of the stack. The lower peripheral heating is due to the fact that the packs at the ends do not benefit much from the thermal mass generated around the packs located in the center of the stack.

[0008] A further drawback is the use of kraft paper sheets to insulate the separator sheets, which increases the time to make a stack of packs. The systematic use of kraft paper sheets also slows down the temperature rise of the stack. Summary of the Invention [Problem to be solved by the invention]

[0009] It is therefore an object of the present invention to provide a method for producing multi-layer plastic laminates for printed circuit boards which is substantially free of the drawbacks of the methods mentioned above and in particular makes it possible to produce laminates adapted to uniformly realise printed circuit boards and which makes it possible to minimise the number of discarded laminates. [Means for solving the problem]

[0010] The subject of the present invention is a process for producing a plastic laminate comprising at least two thin metal layers suitable for the realization of a printed circuit board, said process comprising the steps of: Forming at least one stack of two or more packages (1), each package (1) comprising one or more support sheets, each sheet comprising, if present, independently of the others, a dielectric material (S) impregnated with at least one polymeric material (MP) and two thin layers of metallic conductive material (M), one on each side of the package, the metallic thin layers being obtained starting from a continuous strip (2), one end of which is placed under a first support sheet or group of support sheets (11) at the bottom of the stack, the strip being folded by 180° so that the strip is placed on the upper side of said sheet or group of sheets (11). and after placing the plate (3) between the first package (11) and the package above it (12), the strip is folded 180° in a direction opposite to the first fold to be placed in contact with the underside of the sheet or group of sheets (12), then the strip is folded again 180° in a direction opposite to the previous fold to be placed on the top side of the second sheet or group of sheets of the package (12), and the folding of the strip as described above is repeated until the other end of the strip is placed on the top side of the sheet or group of sheets of the package (13) at the top of the stack, and the two ends of the strip are connected to the main generator (4); heating the strip (2) at a temperature T such that, as a result of the effect of the current circulating in the strip, when the electric circuit of the generator (4) is closed, the polymer material (MP) is cross-linked, and after applying a pressure on the stack suitable to cause the mutual adhesion of the packages (1) separated by the plate (3), the layers are joined to each other and to the parts of the metal strip placed in close proximity to them, to obtain a package (1) in the form of a stack, the plate (3) being a plate made of metal or of another material, which conducts heat without warping at the maximum temperature obtained during the heating of the stack as described above, two heating plates (51) and (52) are placed respectively below the lower layer and above the upper layer of the stack, providing heat to the ends of the stack by connection to two secondary generators, which are respectively (61) and (62), The temperature in the stack is sensed via two or more probes (7) positioned away from the heating plates (61 and (62) by at least one package (1); The two or more probes (7) determine the primary generator (4) and / or secondary generators (61) and (62) to obtain cross-linking of the polymeric material (MP), so that the laminate is formed in a uniform manner in all layers of the stack.

[0011] The subject of the present invention is also a method for producing a printed circuit board comprising at least two thin metal layers. A system for making a plastic laminate comprising at least one stack of two or more packages (1), each package (1) comprising one or more support sheets, if present, independently of the others, a dielectric material (S) impregnated with at least one polymeric material (MP) and two thin layers of metallic conductive material (M), one on each side of the package, the metallic thin layers being obtained starting from a continuous strip (2), one end of which is connected to a first support at the bottom of the stack. A sheet or a group of supporting sheets (11) is placed under the strip, the strip is folded 180° so that the strip is placed on the top side of said sheet or group of sheets, after which the plate (3) is placed between the first package (11) and the package above it (12), the strip is folded 180° in the opposite direction to the first fold so that it is placed in contact with the underside of the sheet or group of sheets (12), the strip is then folded again 180° in the opposite direction to the previous fold so that the second sheet or group of sheets is placed on the top side of the second sheet or group of sheets (12). the two strips are connected to a main generator (4) which, when the electric circuit of the generator (4) is closed, is capable of supplying a power suitable for heating the strips at a temperature T such as to cross-link the polymeric material (MP), thereby obtaining a package (1) in the form of a stack, after applying a pressure on the stack suitable for causing the mutual adhesion of the packages (1) separated by the plate (3), the layers being joined to each other and to the parts of the metal strip placed in close proximity to them, the plate (3) being a plate made of metal or of another material, which conducts heat without warping at the maximum temperature obtained during the heating of the stack as described above, the two heating plates (51) and (52) being placed respectively below the lower layer and above the upper layer of the stack, providing heat to the ends of the stack by connection to two secondary generators, which are respectively (61) and (62), Within the stack are two or more internal temperature probes (7) positioned so as to be spaced apart from the heating plates (61 and (62) by at least one package (1); a control unit (9) connected to the probe (7) and suitable for controlling, preferably by on and off, the main generator (4) and / or the secondary generators (61 and 62), in order to obtain cross-linking of the polymer material (MP) and to result in the formation of the package (1) in a uniform manner in all layers of the stack; and means (8) for applying pressure to said stack of two or more packages (1) selected from a two-layer press, optionally under vacuum, and an airbag.

[0012] Further features and advantages of the present invention will become more apparent from the following description of some preferred embodiments thereof, with reference to the accompanying drawings. [Brief description of the drawings]

[0013] [Figure 1] A "package" is shown that includes a layer of dielectric material (S) impregnated with a polymeric material (MP) and two thin layers of metallic conductive material (M), one on each side of the package. [Diagram 2] 1 shows a system for producing a multi-layer plastic laminate comprising at least two thin metal layers adapted for the manufacture of printed circuit boards, including a temperature probe according to the invention, and is numbered as follows: [Diagram 3] 1 shows a graph of the temperature detected along a stack according to the present invention (with four probes positioned as above) when there is no peripheral heating and only two heaters and two probes positioned at the ends of the stack, with the arrows indicating the location of the probes present. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The term "airbag" in the context of this invention refers to synthetic rubber, based on chlorosulfonated polyethylene (Hypalon®) or another polymeric material, and silicone. It refers to a device in which pressure is applied to an air cushion created by a diaphragm. The diaphragm exerts pressure on a pressure piston, which in turn transmits the force to the package of laminate being pressed. A tank for supplying air is connected to the press through an electronically controlled servo valve. A computer calculates the amount of air to be applied to reach the programmed pressure in the press cycle.

[0015] Unless otherwise indicated, within the context of the present invention, the percentages and amounts of components in a mixture relate to the weight of such component relative to the total weight of the mixture.

[0016] Unless otherwise specified, within the context of the present invention, a designation that a composition "comprises" one or more ingredients or substances means that other ingredients or substances may be present in addition to the ingredient or ingredients specifically named.

[0017] Unless otherwise specified, within the context of the present invention, ranges of values ​​given for dimensions, e.g., the content by weight of a component, include the lower and upper limits of the range. For example, if the content by weight or volume of component A is given as "X to Y", X and Y are numerical values ​​and A can be X or Y or any one of the intermediate values.

[0018] The inventors have surprisingly found that thanks to the temperature control within the stack obtained via at least two or more probes (7) positioned within the stack at a position such that they are at least one packet (1) or more away from the heating plates (61) and (62), it is possible to obtain essentially uniform packages, thus minimizing the number of discarded multi-layer plastic laminates.

[0019] In the method according to the invention, after the initial heat transfer, the combined action of the main generator and the two auxiliary heaters ensures that the temperature measured in the stack via the probe is essentially uniform from the start of polymerization of the resin in the prepregs, thereby obtaining polymerization and subsequently allowing uniform cross-linking of the resin in all packages of the stack.

[0020] In the method according to the invention, the upper and lower heating plates (51) and (52) are operated in synergy with the main generator to obtain the most uniform temperature among the probes placed in the stack of packages, regardless of the effective temperature reached by the auxiliary heaters. The temperature of the upper heating plate (52) and the lower heating plate (51) are not controlled.

[0021] The method is applicable to the manufacture of individual laminates, i.e., laminates containing only one layer of dielectric material metallized on both sides, and also to the manufacture of laminates containing one or more layers of dielectric material.

[0022] In a preferred embodiment, the polymeric material (MP) is an epoxy resin or a mixture comprising at least one epoxy resin.

[0023] In a preferred embodiment, the dielectric material (S) comprises or consists of one or more layers of fiberglass, FR4, PFTE (Teflon®), polyimide (Kapton®), glass or mixtures thereof. More preferably, the dielectric material (S) comprises or consists of one or more layers of fiberglass. Optionally, other layers of dielectric materials different from fiberglass may be present, such as, by way of non-limiting example, rubber, glass or ceramic materials.

[0024] The metallized multi-layer plastic laminate obtained by the method according to the invention can be directly or after suitable processing, followed by drilling of the circuit layout, masking and photolithographic processing, removal of excess copper, etc. , as well as for through-hole metallization.

[0025] In a preferred embodiment of the invention, the method further comprises the steps of returning to the initial pressure and temperature conditions once the heating step under pressure is completed and cross-linking of the polymeric material is obtained, cutting the metal strip flush with the opposite side of the stack from which it exits, and dismantling the stack itself into single packages thus metallized.

[0026] In a preferred embodiment of the invention, the probes (7) are 3 to 6, preferably 4, distributed along the entire height, at least two of them being arranged in the stack in such a position that they are separated by at least one package (1) or more by the heating plates (61) and (62), and their temperature detection, via the control unit (9), determines the operation of the main generator (4) and the two auxiliary heaters (51) and (52).

[0027] In a preferred embodiment of the invention, pressure is applied to the stack via a press, optionally under vacuum, or via placing the stack in an autoclave or air bag.

[0028] Typically, but not by way of limitation, pressure is applied to the top or bottom heater by an air chamber (also known as an "air bag") and transmitted from there to the stack. The pressure during the work cycle is varied in discrete steps until a predetermined temperature value is reached.

[0029] In a preferred embodiment of the invention, the crosslinking is carried out at 80-150°C and / or the laminate is formed at a pressure of 1-3 MPa. As a non-limiting example, a cycle for the formation of the laminate can be envisaged for an interval of 80°C-150°C, the temperature being increased to a rate of 2-6° / min at a pressure of 10-30 kg / cm2, and a second interval of the same pressure and 180°C.

[0030] In a preferred embodiment of the invention, the metal material of the strip (2) is selected between copper and aluminum and / or the material of the plate (3) is one of aluminum, titanium and steel, optionally coated with a layer of an electrically insulating material.

[0031] Preferably, the separator plate (3) is aluminum and is suitably anodized to obtain a surface layer of electrically insulating black oxide.

[0032] In an embodiment provided as a non-limiting example, the current provided by the main generator traverses the metal casing of each auxiliary heater.

[0033] In an embodiment provided as a non-limiting example, a portion of the coiled strip at the base of the stack is placed on an extractable metal tray, which is crossed by the current supplied by the main generator and heated by an auxiliary electric heater mounted thereon.

[0034] As a non-limiting example, a loop of copper strip formed at an end of a stack can include, in order from the copper strip, an amortized buffer layer and a separator plate.

[0035] In a preferred embodiment of the invention, the temperature is controlled via a control unit (9), i.e. a programmable logic controller (PLC) via a computer, which provides a substantially uniform temperature throughout all stacks, and optionally heats the stacks gradually according to a pre-set mode by suitable control laws.

[0036] In a preferred embodiment of the present invention, in this process, the current administered by the primary generator (4) has an intensity of 250-4000 A and the voltage generated by the secondary generators (61) and (62) is 110-220 V.

[0037] Preferably, the process of the invention envisages the further step in which the formed package (1) is subjected to cutting of the excess metal parts and then, optionally, manual cutting and separation of the individual packages which are sent to a subsequent trimming step.

[0038] A further aspect of the invention is a system for producing a plastic laminate comprising at least two metal thin layers suitable for the manufacture of printed circuit boards, the plastic laminate comprising at least one stack of two or more packages (1), each package (1) comprising one or more support sheets, if present, independently of the others, a dielectric material (S) impregnated with at least one polymeric material (MP) and two thin layers of metallic conductive material (M), one on each side of the package, the metal thin layers being obtained starting from a continuous strip (2) and being continuous One end of the strip (2) is placed under a first support sheet or group of support sheets (11) at the bottom of the stack, the strip is folded 180° so that after it is folded, the strip is placed on the top side of said sheet or group of sheets, after placing the plate (3) between the first package (11) and the package above it (12), the strip is folded 180° in the opposite direction to the first fold so that it is placed in contact with the underside of the sheet or group of sheets (12), then the strip is folded again 180° in the opposite direction to the previous fold. the first strip is folded and placed on top of a second sheet or group of sheets, the folding of the strip being repeated until the other end of the strip is placed on top of the sheet or group of sheets of the package (13) at the top of the stack, the two strips being connected to a main generator (4) which, when the electric circuit of the generator (4) is closed, is capable of supplying a power suitable for heating the strip at a temperature T such as to cross-link the polymeric material (MP), thereby obtaining a package (1) in the form of a stack, after applying a pressure on the stack suitable for causing the mutual adhesion of the packages (1) separated by a plate (3), the layers being joined to each other and to the parts of the metal strip placed in close proximity to them, the plate (3) being a plate made of metal or of another material, which conducts heat without warping at the maximum temperature obtained during the heating of the stack as described above, the two heating plates (51) and (52) being placed respectively below the lower layer and above the upper layer of the stack, providing heat to the ends of the stack by connection to two secondary generators, which are respectively (61) and (62); Within the stack are two or more internal temperature probes (7) positioned so as to be spaced apart from the heating plates (61 and (62) by at least one package (1); there is a control unit (9) connected to the probe (7) and suitable for controlling, preferably by on and off, the main generator (4) and / or the secondary generators (61 and 62) in order to obtain cross-linking of the polymer material (MP) and to result in the formation of the package (1) in a uniform manner in all layers of the stack, It is characterised by the presence of means (8) for applying pressure to said stack of two or more packages (1), preferably selected from a two-layer press, optionally under vacuum, and an airbag.

[0039] In one aspect, the present invention relates to an apparatus for producing a multi-layer plastic laminate for a printed circuit board, the apparatus comprising: first and second means adapted to cooperate to apply pressure to a stack of packages, each of which is comprised of a layer of conductive material and a layer of insulating material, when the stack is placed therebetween; a first electric heating plate and a second electric heating plate associated with said first and second means, respectively; a main generator configured to be connected to conductive strips extending within the stack; two secondary generators connected to the heating plate; two or more temperature probes adapted to be inserted inside the stack and outside the electric heating plate and positioned at least one package away from the electric heating plate, and adapted to detect an internal temperature of the stack; and a control unit configured to drive the primary and secondary generators as a function of signals received from the two or more probes to obtain a substantially uniform temperature throughout the stack (i.e. substantially the same temperature in all areas of the stack regardless of their location). "Substantially uniform" typically and reasonably means that the temperature difference from one point to the other relative to the average temperature varies by an interval of ±5°C.

[0040] Preferably, the control unit is adapted to drive said primary and secondary generators as a function of signals received from the two or more probes so as to heat the stack gradually and uniformly, i.e. the temperature within the stack is preferably uniform from moment to moment during heating of the stack, and possibly from moment to moment during cooling of the stack, as well as during "cooking" or "curing" of the stack.

[0041] Typically, the control unit implements (e.g., via its own internal pre-sets or its own internal software or firmware, if it is a programmed control unit) at least one drive law as a function of one or more of all temperatures detected in the region inside the stack, which can be applied to the drive of the conductive strips. In particular, the control unit can implement two or three drive laws, each implemented as a function of one or more or all of the temperatures detected in the region inside the stack, which can be applied to the drive of the conductive strips and the two electric heating plates.

[0042] Preferably, the device comprises three, or four, or five temperature probes, more preferably four temperature probes.

[0043] In the following example, which is provided to illustrate one embodiment of the present invention, without limiting its purpose, four probes are arranged to detect the temperature uniformly distributed over the extension of the stack, at least two of which are positioned within the stack in such a position that they are separated by at least one package (1) or more by heating plates (61) and (62), and the temperature detection determines, via a control unit (9), the operation of the main generator (4) and two auxiliary heaters (51) and (52).

[0044] Thanks to their insulation to the heat generated and to the cold surface of the press, the two additional heaters form a barrier to the dispersion of the heat generated within the stack. The packages closest to the two ends of the stack mainly benefit from the additional heat, which compensates for the lower heating they would have due to their position. In addition to this, the positioning of the probe within the stack of packages thus determines a better and more precise management of the thermal conditions, without directly detecting the temperature of the auxiliary heaters.

[0045] In the absence of a probe positioned according to the invention, the presence of two auxiliary heaters controlled to achieve the same thermal profile managed by the central probe would not guarantee temperature uniformity along the entire stack, an aspect that becomes more evident as the overall height of the stack itself increases.

[0046] The positioning of the probes in the stack and the addition of a second probe in the central region is more Determine accurate temperature control: even if in the central and peripheral regions the temperature is slightly higher than that set and controlled by the probe, the overall temperature variation along the stack is moderate, and the end result is a substantially uniform package after crosslinking.

[0047] Figure 3 shows a comparison of temperatures detected along a stack according to the invention (with four probes positioned as above) when there is no peripheral heating and only two heaters and two probes positioned at the ends of the stack. The arrows indicate the location of the probes present.

[0048] The dashed line shows the temperature profile obtained without the heating plate.

[0049] The temperature profile shown by the dashed and dotted line is obtained in the presence of two heating plates placed at the top and bottom of the stack with two probes placed on the plates and a central probe.

[0050] The solid line shows the temperature profile obtained with a stack having four probes arranged according to the invention.

[0051] It can be seen how in the configuration according to the invention (solid line) the temperature trend is substantially uniform over the entire extension of the stack, whereas in the other two configurations without an intermediate probe the temperature varies significantly along the stack, destroying the uniformity of the multi-layer plastic laminate obtained at different points of the stack.

Claims

1. 1. A process for making a plastic laminate suitable for the manufacture of printed circuit boards, comprising: Forming at least one stack of two or more plastic laminates (hereinafter packages (1)), each package (1) comprising a number of sheets, each package (1) comprising, independently of the others, a dielectric material (S) impregnated with at least one polymeric material (MP) and two thin metal layers of conductive material (M), one on each side of the package (1), said thin metal layers being produced from a continuous strip (2) of metal, said strip (2) being produced such that one end of said strip (2) is placed under a first set of sheets (11) at the bottom of said stack, said strip (2) being folded by 180° before said strip (2) is placed over said first set of sheets (11). after placing a plate (3) between the first set of sheets (11) and a second set of sheets (12) thereon, the strip (2) is folded 180° in a direction opposite to the first fold and placed in contact with the underside of the second set of sheets (12), then the strip (2) is folded again 180° in a direction opposite to the previous fold and placed on the upper side of the second set of sheets (12), the folding of the strip (2) is repeated until the other end of the strip (2) is placed on the upper side of the topmost set of sheets (13) of the stack, the two ends of the strip (2) being connected to a main generator (4); heating said strip (2) at a temperature such that, as a result of the electric current circulating through it, when the electric circuit of the main generator (4) is closed, it cross-links the polymer material (MP), thereby allowing the sheets and the parts of the strip (2) arranged adjacent to each other to be joined together to obtain a package (1) in the form of a stack, after applying to the stack a pressure suitable for causing the mutual adhesion of the packages (1) separated by the plates (3), said plates (3) being plates made of metal or of another material, which conduct heat without warping at the maximum temperature obtained during the heating of the stack as described above, and two heating plates (51) and (52) arranged respectively below the lower layer and above the upper layer of the stack, providing heat to the ends of the stack by means of connections to two secondary generators (61, 62), the temperature of the stack is detected via two or more probes (7) each arranged inside the stack such that only the package (1) is spaced from the heating plates (51 and 52); wherein said main generator (4) and said two secondary generators (61, 62) are controlled to be turned on and off based on said temperature detected via each of said two or more probes (7) in order to obtain crosslinking of said polymeric material (MP), thereby resulting in said formation of said laminate.

2. The process of claim 1 , wherein the pressure is applied to the stack via a press (8).

3. The process of claim 1 or claim 2, wherein the crosslinking is carried out at 80-150° C. and / or the laminate is formed at a pressure of 1-3 MPa.

4. 4. The process according to any one of claims 1 to 3, wherein the metal material of the strip (2) is selected between copper and aluminum and / or the material of the plate (3) is one of aluminum, titanium and steel.

5. The process according to any one of claims 1 to 4, wherein the thickness of the single laminate package (1) obtained by said process is between 1 mm and 10 mm.

6. The process according to any one of claims 1 to 5, wherein the temperature of the stack is detected via three to five probes (7).

7. 7. The process according to any one of claims 1 to 6, wherein the temperature is controlled via a control unit (9), i.e. a programmable logic controller (PLC), thereby obtaining a substantially uniform temperature throughout all the stacks.

8. A system for producing plastic laminates suitable for the manufacture of printed circuit boards, comprising at least one stack of two or more plastic laminates (hereinafter packages (1)), each package (1) comprising a number of sheets, each package (1) comprising, independently of the others, a dielectric material (S) impregnated with at least one polymeric material (MP) and two thin metal layers of conductive material (M), one on each side of the package (1), said thin metal layers being produced from a continuous strip (2) of metal, said production being carried out by means of a process comprising the steps of: The first end of the strip (2) is placed under a first group of sheets (11) at the bottom of the stack, the strip (2) is folded 180° and then folded so that the strip (2) is placed on the top side of the first group of sheets (11), a plate (3) is placed between the first group of sheets (11) and a second group of sheets (12) above it, the strip (2) is then folded 180° in the opposite direction to the first fold and placed in contact with the underside of the second group of sheets (12), the strip (2) is then folded 180° in the opposite direction to the previous fold and placed in contact with the underside of the second group of sheets (12), and is then folded again by 180° to be placed on the top side of the second set of sheets (12), the folding of the strip (2) being repeated until the other end of the strip (2) is placed on the top side of the topmost set of sheets (13) of the stack, the two ends of the strip (2) being connected to a main generator (4) which, when the electrical circuit of the main generator (4) is closed, is capable of supplying an electrical power suitable for heating the strip (2) at a temperature such as to cross-link the polymer material (MP), thereby forming the preform (10). The sheets and the portions of the strips (2) arranged adjacent to each other can be joined to obtain a package (1) in the form of a stack, after applying a pressure to the stack suitable for causing mutual adhesion of the packages (1) separated by plates (3), the plates (3) being plates made of metal or of another material, conducting heat without warping at the maximum temperature obtained during heating of the stack as described above, two heating plates (51) and (52) being respectively arranged below the lower layer and above the upper layer of the stack, two secondary generators (61,62) to provide heat to the ends of the stack; The stack has two or more internal temperature probes (7), each of the two or more internal temperature probes (7) being each positioned within the stack so as to be spaced from the heating plates (51) and (52) by one or more packages (1); there is a control unit (9) connected to said two or more internal temperature probes (7) and suitable for controlling said main generator (4) and said two secondary generators (61, 62) to be turned on / off based on the temperature detected via each of said two or more internal temperature probes (7) to obtain crosslinking of said polymer material (MP) and to result in the formation of said laminate, The system is characterized by a means (8) for applying pressure to said stack of two or more packages (1), which is one of a two-ply press and an airbag.

9. 1. An apparatus for producing multi-layer plastic laminates for printed circuit boards, comprising: first and second means adapted to cooperate to apply pressure to a stack of packages (1) when said stack is placed therebetween, said stack being composed of layers of conductive and insulating material respectively; a first electric heating plate and a second electric heating plate respectively superimposed on said first and second means; a main generator configured to be connected to conductive strips (2) extending across the stack; two secondary generators connected to the electric heating plate; two or more temperature probes, each positioned inside the stack so as to be spaced from the electric heating plate by at least one package (1), and adapted to detect a temperature of the stack; and a control unit configured to drive the main generator and the two secondary generators based on inputs regarding the temperatures received from the two or more temperature probes to obtain a substantially uniform temperature throughout the stack.

10. 10. The apparatus of claim 9, comprising three, four, or five temperature probes.

11. 11. Apparatus according to claim 9 or claim 10, wherein the control unit is adapted to drive the main generator and the two secondary generators as a function of signals received from the two or more probes so as to gradually and uniformly heat the stack.

12. 12. Apparatus according to claim 9 or claim 10 or claim 11, wherein the control unit implements at least one drive law as a function of one or more or all of the temperatures detected in the region within the stack.

13. 13. The apparatus of claim 12, wherein the control unit implements two or three drive laws, each as a function of one or more or all of the temperatures sensed in the region within the stack.

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