WO1997027051A1

WO1997027051A1 - Method for manufacturing laminates

Info

Publication number: WO1997027051A1
Application number: PCT/JP1997/000167
Authority: WO
Inventors: Takeshi Okamoto; Kazushi Kawamura; Toru Kuwata; Hidekazu Takano; Takeshi Tomisaki
Original assignee: Matsushita Electric Works, Ltd.
Priority date: 1996-01-26
Filing date: 1997-01-24
Publication date: 1997-07-31
Also published as: JP3332315B2; JPH09201899A

Abstract

A method for manufacturing laminates by forming combined stacks of synthetic resin sheets (1) with continuous sheets (3b, 3c) of metal foil, a laminated block (6) is formed with a plurality of the combined stacks stacked and with insulating interlayers (5) interposed by forming a plurality of the combined stacks in the longitudinal direction of the continuous sheets while folding back the continuous sheets betweent adjacent ones of the combined stacks, and the laminated block (6) is molded under a pressure while suplying an electric current to the continuous metal foil sheets, whereby the respective laminates can be mutually separated without being injured, the separation of the laminates being made quick and easily automated.

Description

SPECIFICATION "Method for Manufacturing Laminates" Technical Background of the Invention This invention relates to a method for manufacturing laminates and, more specifically, to a method for manufacturing a plurality of laminates through a thermoforming of stacked synthetic resin sheets with metal foils interposed, while supplying an electric current to the metal foils. Disclosure of Prior Art

The laminate having on its surfaces the metal foils has been obtained by integrally molding the metal foils and synthetic resin sheets, and the laminate manufactured with such metal foils as a copper foil and such synthetic resin sheets as prepregs employed has been utilized as processed to be a printed circuit board.

Such laminates have been manufactured by stacking the metal foils and prepregs along with internal layer members or internal and external layer members added into a combined stack, molding this combined stack under a heat and a pressure to melt the synthetic resin which constituting the prepregs, and subjecting the molded stack to a thermosetting or cold-setting. The heating under the pressure in molding the combined stack is generally performed through a hot press with such heat source as steam or electric heating, or through a vacuum press.

The hot press in this case is to heat and pressurize the combined stack of the metal foils, prepregs and so on from both of top and bottom sides by means of heating plates. The vacuum press, on the other hand, is to heat and pressurize the combined stack of the metal foils, prepregs and so on by hermetically covering the stack by means of a packing member, drawing a vacuum in the interior of the packing member, and leading a hot and pressurized gas to the exterior of the packing member. In performing the molding with such hot. press or vacuum press, a plurality of the combined stacks are stacked into multiple layers with interlayers interposed respectively between adjacent ones of the combined stacks, so as to be a laminated block, and such laminated block is heated and pressurized, so that a plurality of laminates can be simultaneously obtained. The interlayers are employed for ensuring the surface flatness of the respective laminates, and plates of such metal as stainless steel are generally employed.

Now, when the laminated block of the combined stacks stacked into the multiple layers is heated and pressurized by means of the hot press, the laminated block is to be heated from both of the top and bottom sides with the heating plates, so that there arises a risk that the heating temperature differs between top side or bottom side combined stack of the laminated block which is closer to the heating plates and intermediate one of the combined stacks remote from the heating plates, due to a delay in the heat transfer and a heat radiation from side surfaces of the laminated block, resulting in a fluctuation of the quality of the laminates obtained due to non-uniform heating temperature. Accordingly, the number of the combined stacks allowed to be stacked for the hot press is limited.

In the vacuum press, on the other hand, the heat is applied to the laminated block from its periphery, and the heating temperature of the respective combined stacks of the laminated block is to be substantially uniformly raised, but there still arises a temperature difference between outer peripheral parts and core part of the laminated block also due to the delay in the heat transfer. For this reason, there has been a problem that the molding of the laminate having large area has been uneasy. As one of measures for eliminating these drawbacks, there has been provided a method for performing the heating by means of a generated heat with a supply of electric current to a metal foil connected to an electric power source, an example of which is disclosed in U.K. Patent No. 1,321,305. The metal foil is formed as a continuous sheet, for example, one set of the combined stack is formed with such synthetic resin sheets as the prepregs or internal layer members stacked between two of the continuous sheets, a plurality of the combined stacks are formed with the continuous sheets repeatedly folded back in respect of longitudinal direction, and the laminated block is formed by stacking the plurality of the combined stacks in multiple layers with insulating interlayers interposed. The laminated block is set between pressure plates, an electric power source of an electric heating device is connected to both ends of the continuous sheets of the metal foils, an electric current is supplied to the continuous sheets of the metal foils while subjecting the laminated block to a cold pressing with the pressure plates, and the continuous sheets generate a heat due to the Joule heat, so that the respective combined stacks can be heated with this generated heat while being molded. According to this method, further, the respective combined stacks can be heated directly and in its entirety, so that the respective combined stacks can be heated uniformly in their stacking direction and planar direction, and a larger number of the laminates can be simultaneously molded without any fluctuation in the quality.

Further, since the laminates molded by electrically heating and pressing the laminated block are in an integrally continued state by the continuous sheets of the metal foil, the respective laminates are required to be separated after being molded. Thus, the upper laminate is separated by opening it upward and thereafter cutting folded part of the continuous sheets with such cutlery as a cutter knife inserted between the upper and lower laminates, and the respective laminates are sequentially separated by repeating the cutting work of the continuous sheets with the cutlery in similar manner as in the above, after releasing the interlayers.

However, due to that the continuous sheets are to be cut. by the cutlery after opening the respective laminates upward, there remain problems that the cutlery involves a risk . of injuring the laminates, the cutting to be curried out by opening every laminate one by one renders the cutting and separating work to be time-consuming and the workability - A -

to be deteriorated, and the separation can hardly be automated.

Description of the Invention It is an object of the present invention to provide a method for manufacturing the laminates, which method is capable of overcoming the foregoing problems, separating the respective laminates without injuring them, yet performing quickly the separating work of the respective laminates, and automating easily the separating work. According to a first feature of the present invention, the method for manufacturing the laminates in which the combined stacks are formed by stacking the synthetic resin sheets with the metal foils formed as the continuous sheets, the laminated block is formed with a plurality of the combined stacks stacked and with the insulating interlayers interposed by forming the plurality of the combined stacks in the longitudinal direction of the continuous sheets and folding back the continuous sheets between adjacent ones of the combined stacks, and the laminated block is molded under a pressure while supplying an electric current to the continuous sheets of the metal foil, is charcterized in that a movable cutting means is provided preliminarily at folded parts of the continuous sheets at the above stacking step, and the folded parts of the continuous sheets are cut by the cutting means after the molding step in a state where the laminates are stacked.

Another feature of the invention resides in a formation of the cutting means independently of the interlayers. Still another feature of the invention resides in a formation of the cutting means at an end part of the interlayers. Further another feature of the invention resides in forming of the cutting means with a wire and cutting of the folded parts of the continuous sheets by moving the wire kept in tension. Still another feature of the invention is to cut the continuous sheets at the folded parts while rolling up the wire. Another feature of the present invention is to form the cutting means with a piece of plate in a cutlery shape. Another feature of the present invention is that the continuous sheets are cut at the folded parts by means of the interlayers moved to slide. Another feature of the present invention is that the interlayers are formed in a double structure to have a cutter projected out of the interior of the respective interlayers for cutting the folded parts of the continuous sheets. Still another feature of the present invention is that the continuous sheets are cut while applying an ultrasonic vibration to the cutting means.

Brief Explanation of the Drawings FIGURE 1 is a perspective view showing an embodiment of the present invention;

FIG. 2 is a perspective view showing an interlayer in another embodiment of the present invention;

FIG. 3 is a perspective view of another embodiment of the present invention;

FIG. 4 is a perspective view of another embodiment of the present invention; FIG. 5 is a perspective view of another embodiment of the present invention;

FIGS. 6(a) to 6(c) are schematic explanatory views of the interlayer in other embodiments of the present invention; FIGS. 7(a) and 7(b) show in sectioned views the interlayer in another embodiment of the present, invention; and

FIG. 8 is a schematic sectioned view showing the molding of the laminates in another embodiment of the present invention.

Best Mode for Working the Invention The respective embodiment of the present invention shall be described in the followings with reference to the drawings. FIG. 8 shows a working aspect of an apparatus for manufacturing the laminates in which they are molded while supplying an electric current to metal foils 2 to generate a heat, and the apparatus is formed with a molding press device including pressure plates 21 and an electric heating device combined. The metal foils 2 employed here are formed as continuous sheets 3, and two sheets 3b and 3c are employed so as to form a laminated block 6. That is, such synthetic resin sheets 1 as prepregs la and inner layer member lb are stacked on one sheet 3b of the two continuous metal foil sheets 3b and 3c, the other sheet 3c is stacked over the synthetic resin sheets 1, and a set of combined stack 4 of the continuous sheets 3b and 3c and synthetic resin sheets 1 is formed. Next, an interlayer 5 is stacked on the sheet 3c, then the sheet 3c is folded back to be stacked on the top side of the interlayer 5, further synthetic resin sheets 1 of the prepregs la and inner layer member lb are stacked on the sheet 3c, the other sheet 3b is then folded back to be stacked on the synthetic resin sheets 1, and another set of the combined stack 4 of the sheets 3b and 3c and synthetic resin sheets 1 is formed thereby. Repeating these steps, a plurality of sets of the combined stacks 4 are formed in longitudinal direction of the continuous sheets 3b and 3c as being sequentially stacked with the interlayers 5 interposed, and the laminated block 6 is formed by alternately stacking in multiple layers the plurality of interlayers 5 and combined stacks 4. The

—-~- interlayers 5 are made to be electrically insulating and formed to be smooth at their surfaces. While in the working aspect of FIG. 8 two of the continuous metal foil sheets 3b and 3c are shown to be employed, the same laminated block 6 can be formed by means of a single continuous sheet 3 of the metal foil. The foregoing laminated block 6 is set between the pressure plates 21 of the molding press device, an electric power source 22 of the electric heating device is connected to both ends of the continuous sheets 3, the respective combined stacks 4 are molded as heated under a pressure by generating a heat with a switch of the power source 22 made ON to supply an electric current to the continuous sheets 3 of the metal foils 2 while pressurizing the laminated block 6 with the pressure plates 21, and laminates 7 in respective which the synthetic resin sheets 1 of the prepregs la and inner layer member lb are stacked to be integral are made obtainable. In the working aspect of FIG. 8, six of the laminates 7 can be simultaneously manufactured, and any larger number of the laminates 7 can be simultaneously manufactured by increasing stacking number of the combined stacks 4. Further, as shown by an imaginary line in FIG. 8, the molding press device may also be constituted as a vacuum laminating press device by enclosing the molding press device in a vacuum chamber 24.

Referring next concretely to materials and molding conditions of the constitution of the foregoing laminate 1 , the prepregs la made of a glass cloth impregnated with epoxy resin and the inner layer member lb prepared by forming inner layer circuits on both surfaces of inner layer plate of epoxy resin with a glass cloth substrate are employed as the synthetic resin sheets 1, as made in a set with the prepregs la arranged on both sides of the inner layer member lb. For the metal foil 2 constituting the continuous sheets 3, a copper foil of a thickness 18μm is employed. Further, as the interlayers 5, an aluminum plate on the entire surfaces of which an electrically insulating coat of a thickness 30-60μm is formed by processing the surfaces for forming a hard corrosion-resistant coating and impregnating tetrafluoroethylene in the coating.

Also, the laminated block 6 is formed by vertically stacking the plurality of the combined stacks 4 with the continuous sheets 3 folded back into a meandering shape, disposing the respective folded parts 3a alternately on opposite side, and this laminated block 6 is set in the vacuum laminating press device, as seen in FIG. 8. In this state, the interior of the vacuum chamber 24 is drawn to a vacuum of a pressure of 10 Torr, the laminated block 6 is pressed from top and bottom sides with the pressing plates

2 21 under a pressure of lOkgf/cm and, at the same time, a DC current is supplied to the continuous metal foil sheets 3 with the power source 22 of the electric heating device made

ON to have a heat generated by the metal foils 2 forming the continuous sheets 3 and functioning as an electric resistor for heating the block. At this time, the temperature of the combined stacks 4 being heated is measured by means of a thermocouple, and the molding of the block while heating and pressing is carried out for 100 minutes while attaining a feedback control of the supplied current value so as to keep the heating temperature at 180°C.

With such molding as in the above carried out, the plurality of the laminates 7 of such synthetic resin sheets 1 as the prepregs la and inner layer member lb and such continuous sheets 3 as the continuous metal foils 2 mutually integrally stacked can be simultaneously manufactured, while the laminates 7 are in a state of being integrally joined by the continuous sheets 3. Here, the laminated block 6 after being molded is released from the device, and the continuous sheets 3 are cut to separate the respective laminates 7 from each other. In cutting the continuous sheets 3 for separating the respective laminates 7, there may be employed arrangements, in one of which a cutting means 8 independent of the interlayers 5 is employed, and in the other of which a cutting means 8 is provided at an end part of the interlayers 5. References shall be made first to the arrangement employing the cutting means 8 independent of the interlayers 5. In an embodiment of FIG. 1, wires 9 are used as the cutting means 8, as inserted on inner side of the folded parts 3a of the continuous sheets 3, and the respective laminates 7 are mutually separated by cutting the sheets 3 such that the wires 9 fixed at their one end are pulled at the other end outward of the sheets 3 while keeping +^■ , wires 9 in tension, as shown by an arrow in FIG. 1, to h the wires 9 moved while cutting the folded parts 3a. this time, the wires 9 may be pulled one by one to cut sequentially each one of the folded parts 3a, or collectively in a plurality to cut a plurality of the folded parts 3a simultaneously. For the wires 9, it is possible to employ, other than thread or string like wires, ones of strip shape, and the material is not required to be specifically limited so long as they are durable at molding temperature of about 180 °C, including such metals as iron, stainless steel and copper, such natural material thread as woolen thread, and such heat-resisting synthetic resin fiber thread as aramid resin fiber thread.

The wires 9 constituting the cutting means 8 are inserted inside the folded parts 3a preliminarily at the stacking step in which the combined stacks 4 are stacked to form the laminated block 6, and the laminates 7 can be mutually separated only by pulling the wires 9 to cut the continuous sheets 3, after releasing the laminated block 6 the molding of which has been completed. The risk of injuring the laminates 7 as in the case of cutting the continuous sheets 3 of the laminated block 6 with the cutlery inserted therein is eliminated.

The cutting of the continuous sheets 3 by means of the wires 9 forming the cutting means 8 can be performed by pulling the wires 9 in the state where the laminates 7 are kept in the stacked state just after being molded, as shown in FIG. 1. In this way, such labor as cutting the sheets with the upper positioned laminate 7 opened one by one, as has been so far required, is rendered unnecessary so that the separating work can be performed quickly, and the cutting and separating can be easily automated. Further, the arrangement can be so made that the wires 9 forming the cutting means 8 are preliminarily inserted inside the folded parts 3a of the continuous sheets 3 at the stacking step, and the folded parts 3a of the continuous sheets 3 are cut by pulling the wires 9 while maintaining the state in which the laminates 7 molded are stacked after termination of the molding.

An embodiment of FIG. 2 is arranged to fix an end of the wire 9 to the interlayer 5, in which the folded parts 3a of the continuous sheets 3 can be cut only by pulling the other end part of the wire 9 secured at one end to the interlayer 5.

In another embodiment of FIG. 3, a continuous one of the wire 9 wound on a reel 25 is provided as passed through the respective folded parts 3a in meandering shape sequentially from the lowest one of the plurality of the folded parts 3a disposed vertically on each side of the laminated block 6. That is, one set of the combined stack 4 consisting of the two continuous sheets 3b and 3c and the synthetic resin sheets 1 is formed by stacking the synthetic resin sheets 1 of the prepregs la and inner layer member lb on one end portion of the one sheet 3b of the two continuous sheets 3b and 3c, and further stacking the other sheet 3c on this synthetic resin sheets 1. Next, the interlayer 5 is stacked on the sheet 3c, the sheet 3c is then folded back over the interlayer 5 with the wire 9 placed on a corresponding part of the sheet 3c to the folded part 3a, further synthetic resin sheets 1 of the prepregs la and inner layer member lb are stacked on this folded sheet 3c, the other sheet 3b is folded back and stacked on the synthetic resin sheets 1, and another set of the combined stack 4 consisting of the continuous sheets 3b and 3c and synthetic resin sheets 1 is formed. Repeating these steps, the laminated block 6 is formed with the plurality of sets of the combined stacks 4 as stacked through the interlayers 5 while inserting the wire 9 in meandering manner inside the folded parts 3a of the sheets 3. For the wire 9, the thread-shaped aramid fibers may be employed, while one of the strip shape may also be used. Further, the wire 9 may be passed of course through inside the respective folded parts 3a sequentially from the topmost one.

Further, after termination of the foregoing molding, the folded parts 3a can be cut by releasing the laminated block 6, fixing one end part 9a of the wire 9, and rolling up the wire 9 on the reel 25 rotated, so as to pull the wire 9 outward of the sheets 3, keeping the wire 9 in tension, while the plurality of the folded parts 3a disposed vertically on each side of the laminated block 6 can be cut sequentially from the topmost one. In this manner, the respective laminates 7 after being molded can be mutually separated by cutting the continuous sheets 3 with the wire 9, while keeping the laminates 7 in the stacked state, so that the separating work can be quickly carried out and the cutting and separation can be easily automated. When the wire 9 is passed through inside the respective folded parts 3a in the meandering manner sequentially from the topmost one, the folded parts 3a are to be cut sequentially from the topmost one.

In cutting the continuous sheets 3 with the wire 9 being rolled up on the reel 25, the cutting of the sheets 3 at the time when the heating and pressing duration terminates in the molding step allows the current supply from the source 22 to be made OFF at the cut part of the sheets 3, so that the current supply to the sheets 3 can be stopped simultaneously with the cutting of the sheets 3 to stop the heat generation of the sheets 3. In another embodiment of FIG. 4, cutlery plate strips 10 are inserted as the cutting means 8 inside the respective folded parts 3a of the continuous sheets 3 in the laminated block 6. That is, one set of the combined stack 4 consisting of the sheets 3b and 3c and synthetic resin sheets 1 is formed, by stacking such synthetic resin sheets 1 as the prepregs la and inner layer member lb on an end portion of one sheet 3b of the two sheets 3b and 3c, and further stacking the other sheet 3c. Repeating these steps, a plurality of sets of the combined stacks 4 are stacked through the interlayers 5 while inserting the cutlery plate strips 10 inside the folded parts 3a of the sheets 3, and the laminated block 6 can be formed. For the cutlery plate strips 10, one of such optional material as the stainless steel may be employed. After termination of the foregoing molding, the laminated block 6 is released, and the folded parts 3a of the sheets 3 can be cut by moving the respective cutlery plate strips 10 outward of the sheets 3. In this manner, the respective laminated 7 can be mutually separated by cutting the sheets 3 with the cutlery plate strips 10, keeping the laminates 7 after being molded just in the stacked state, so that the separating work can be quickly performed and the cutting and separation can be easily adapted to the automation.

Next, references shall be made to the arrangement in which the continuous sheets 3 are cut by the cutting means 8 provided to the end portion of the interlayers 5.

In another embodiment of FIG. 5, the cutting means 8 is provided to the interlayers 5 by forming a blade edge 5a at one side edge of each interlayer 5 on the side facing the folded part 3a of the continuous sheets 3. The laminated block 6 is formed in the same manner as in FIG. 8 but with the interlayers 5 each having the blade edge 5a employed, the block is molded in the same manner as in the aspect of FIG. 8, and thereafter the laminated block 6 is released. Then, in the state where the laminate 7 is opened upward, the interlayer 5 is slid in horizontal direction towards the folded part 3a, so that the continuous sheets 3 can be cut at the folded parts 3a by the blade edge 5a to have the respective laminates 7 separated. In this manner, the laminates 7 can be mutually separated by cutting the sheets 3 with the interlayers 5 utilized, and it is enabled to separate the laminates 7 without injuring them.

The blade edge 5a of the interlayer 5 may be formed in any of such shapes of square type as in FIG. 6(a), diagonally slanted type as in FIG. 6(b), and triangularly projecting type as in FIG. 6(c). In another embodiment of FIG. 7, the interlayers 5 are formed in a double structure with the interior made hollow, and a cutter 11 forming the cutting means 8 is inserted in the hollow interior of the interlayer 7 to be retracted and projected as shown in FIG. 7(a) . This cutter i_s provided for being projected out of a side edge opening of the interlayer 5. With the interlayers 5 having the cutters 11 inserted therein, the laminated block 6 is formed in the same manner as in FIG. 8, and therafter the laminated block 6 is released. Then the interlayer 5 is moved as slid towards the folded part 3a with the cutter 11 projected from the interlayer 5, the folded part 3a of the continuous sheets 3 is cut by the cutter 11, and the respective laminates 7 can be mutually separated. It is thus enabled to separate the laminates 7 by cutting the continuous metal foil sheets 3 by utilizing the interlayers 5, and the separation of the laminates 7 can be performed through the cutting of the continuous sheets 3 by the cutter 11 in the state where the laminates 7 after being molded are kept as stacked, so that the separation can be quickly executed and the automation of the cutting and separation is made easier. Since the cutters 11 are slid inside the interlayers 5, further, the laminates 7 are not to be injured by the cutters 11.

In the respective foregoing embodiments of FIGS. 1 to 7, it will be possible to apply an ultrasonic vibration to the wire or wires 9, cutlery plate stips 10, interlayers 5 or cutters 11 forming the cutting means 8, during the cutting. When the continuous sheets 3 are cut while applying to the cutting means 8 the ultrasonic vibration, the cutting is enabled not to cause any cutting fins or shavings to occur.

It should be also appreciated that the foregoing arrangement for the stopping of heat generation by means of the cutting of the continuous metal foil sheets 3 to turn the current supply to the sheets 3 OFF is applicable as it is to the arrangements of FIGS. 1 to 7.

Claims

1. A method for manufacturing laminates in which combined stacks are formed by stacking synthetic resin sheets with metal foils formed as continuous sheets, a laminated block is formed with a plurality of the combined stacks stacked and with insulating interlayers interposed by forming a plurality of the combined stacks in the longitudinal direction of the continuous sheets and folding back the continuous sheets between adjacent ones of the combined stacks, and the laminated block is molded under a pressure while supplying an electric current to the continuous sheets of the metal foil, characterized in that a movable cutting means is provided preliminarily at folded parts of the continuous sheets at said stacking step, and the folded parts of the continuous sheets are cut by the cutting means after said molding step in a state where the laminates are stacked.

2. The method according to claim 1, characterized in that the cutting means is formed independently of the interlayers.

3. The method according to claim 1, characterized in that the cutting means is provided at an end part of the respective interlayers.

4. The method according to claim 2, characterized in that the cutting means comprises a wire, the folded parts of the continuous metal foil sheets are cut by moving the wire while keeping the wire in tension.

5. The method according to claim 4, characterized in that the folded parts of the continuous metal foil sheets are cut by rolling up the wire.

6. The method according to claim 2, characterized in that the cutting means comprises cutlery plate strips.

7. The method according to claim 3, characterized in that the folded parts of the continuous metal foil sheets are cut by sliding the interlayers.

8. The method according to claim 3, characterized in that the interlayers are respectively formed in a double structure, and the cutting means comprises a cutter slidably inserted in the respective interlayers for being projected out of said end part of the interlayers.