WO2014037871A1

WO2014037871A1 - Multilayer stack forming apparatus

Info

Publication number: WO2014037871A1
Application number: PCT/IB2013/058245
Authority: WO
Inventors: Bruno Ceraso
Original assignee: Cedal Equipment S.R.L.
Priority date: 2012-09-04
Filing date: 2013-09-03
Publication date: 2014-03-13
Also published as: TWI707617B; ITGE20120087A1; CN104661820A; JP2015533746A; TW201417665A; KR20150054890A; JP6265996B2

Abstract

The invention concerns an apparatus for forming stacks of multilayers (L) of printed circuits and the like, wherein a film unrolled from a coil (31) is applied between stacked layers (L). The apparatus is provided with system of fixed and movable divertring rolls (40, 41) that allows to control the tension of the film unrolled from the coil (31), thereby preventing possible breaking thereof.

Description

Title: "Multilayer stack forming apparatus "

The present invention concerns, according to a general aspect thereof, thmanufacturing process of printed circuits.

As it is known, the manufacturing process of printed circuits is a rather complex cycle which is carried out through several phases, starting from electrically conductive sheets bearing the tracks of the printed circuit in accordance with its designed drawing or topography, until their assembling in the so called "multi layers" (commonly called "multilayer" by the persons skilled in the art), which are foils obtained from the stacking of electrically conductive and insulating layers.

The insulating layers are formed by the so called "pre-preg", that is to say a synthetic fabric impregnated with hot curing epoxy resins that are electrically insulating, thereby forming a homogeneous laminated foil with the conductive layers stacked after a hot pressing phase.

Printed circuits obtained with this technology can be either of rigid type like those of the usual electronic boards, or of flexible type like for example those used for the wire connection of computer components (PC or the similar), printers, copiers, or other machines in general; the thickness of the printed circuits may vary from few tenth of millimeter to some millimiters.

With the development of the consumer elctronicics technologies and apparatuses (internet, mobile phones, laptops, tablets, navigators etc.), especially the last generation devices, the complexity of the functions carried out by the electronic circuits is steadily growing. This requires increasingly high level performances, without penalising the lightness and manageability of the devices which, on the other hand, evolve following the trend of having smaller dimensions and thickness.

This challenging situation compels the device manufacturers to reduce spaces and in the supply chain this implies that the pieces must be lightest and thinnest.

The printed circuit suppliers have thus been brought to evolve towards providing a greater number of layers stacked in the "multilayer" and, as a matter of consequence, with a reduced thickness so as to keep unchanged the overall dimensions of the circuits.

In order to have an order of magnitude, a finished multilayer foil has a thickness of about one millimetre and therefore the layers forming it, range from a few tenth of millimetre to a few hundredth of microns.

It comes out that the multilayer foils manufacturing is nowadays fairly tough and difficult: indeed it should be observed that the larger is the number of layers to be stacked, the higher must be the precision for applying them one upon the other, because otherwise the resulting circuit is faulty.

On the other side, since the thickness of the single layers is around few tenth of microns, stacking precision tolerances must comply therewith and thus they will be of the same order of magnitude (i.e. microns).

The present invention belongs to such a technological background.

Indeed the applicant has developed in the past a manufacturing process for stacks of multlayers, which provides for a final step of pressing and thermowelding in a specific heating press.

On the latter there are loaded multilayer foils to form stacks with a height of about 20-30 centimetres; in order to transfer heat necessary for the termowelding, between the multilayer foils there is inserted a copper film, twisting it with folds spaced with a preset pitch.

By supplying electrical current to the copper film, it warms up because of the Joule effect and then it transfers heat to the stacked multilayers, which are squeezed at the same time by the pressure exerted on them by the press.

With this process it is pssible to obtain a uniform distribution of the temperature throghout the whole multilayer stack, which can be 30 cm high or more, without incurring the risk of having zones with a higher temperature in connection with the ends and cooler zones in the middle of the stack.

In order to apply the copper film with twisted folds, an apparatus is used which has been purposely developed in the past: the present invention concerns in a more specific aspect, to an improvement to this type of apparatus.

Indeed, following to the aforesaid technological evolution in the printed circuit field, also the thickness of the conductive copper film used in their manufacturing process must be kept as lower as possible.

It comes out that the use in the apparatus designed by the present applicant and described in international patent application WO 94/23948, is made difficult by the frequent breakings that the film may be subjected to, if the speed of application is not kept sufficiently low.

However, as it can be easily understood, keeping low application speed of the copper film is negative for the overall efficiency of the productive cycle, since it is an operating phase from which others depend downstream, such as especially the hot pressing. The present invention aims therefore at overcoming these drawbacks of the known apparatuses.

In other words, the technical problem underlying the invention is that of providing an apparatus for forming stacks of multilayer foils suitable for the production of printed circuits, that allows the application of the copper film twisted in folds without the risk of breaking thereof even in the case of reduced thickness.

The idea for solving this problem is that of making an apparatus wherein the stress exerted on the copper film, is kept under the breaking limit during the various application phases of the twisted folds.

The technical problem above is solved by an apparatus whose features are set forth in the claims appended to this descritipon.

These and other features of the invention, as well as the effects deriving therefrom and the advantages achieved by the apparatus according to the invention, will better result from the description of a preferred and non-limiting example thereof, provided hereinafter with reference to the appended drawings wherein:

- fig. 1 shows an assonometric view of an apparatus for forming stacks of layers, in accordance with the invention;

- fig. 2 and 3 show respective front and lateral views of the apparatus of fig. 1;

- fig. 4 is a front view of a detail of the apparatus of the preceding figures;

- figs. 5, 6, 7 and 8 are respective sections along lines A-A, B-B, C-C, and D-D of fig. 4;

- fig. 9 shows a view fromabove of the detail of fig. 4.

With reference to the figures just listed, therein reference 1 indicates as a whole an apparatus for stacking multilayer foils, in accomdance with the invention; for sake of simpoicity and brevity, hereinafter in the description there will be emphasised the structural and functional aspects that serve to understand the invention, whereas for further particulars reference should be made to the explanations provided in international application WO 94/23948 already referred to above, whose content is herein incorporated by reference.

Therefore, apparatus 1 comprises a base with a rectangular layout, substantially formed by four upright posts 3 set on the ground, connected each other by respective beams 4 and cross bars 5; the base 2 supports a frame 20 comprising four columns 23 arranged at the angles of the base 2 above the posts 3, joined together by a pair of beams 24.

For the reasons that will become more apparent afterwards, frame 20 does not have cross bars extending transversely to the apparatus between the columns 23, while for such purpose the stiffening is provided by a canopy 25 located at the upper end of the columns 23.

In the inside part of the beams 4 of the base 2 and of those 24 of the frame 20 there are provided guides 16, 26 for sliding two coil carrier stands 30, shown in detail in fig. 4-9; the stands 30 are movable back and forth along guides 16, 26 during the various stacking phases of the multilayer foils that will be dealt with later; to this purpose, in the apparatus there are provided respective electric motors, not shown in the drawings because known per se.

The stands 30 are alike and therefore in the following only one of them will be considered, for sake of simplicity.

On each stand 30 there is a copper film coil 31 mounted on a shaft 32 rotatably supported in connection with two lateral shoulders 33, 34, by bearings 35, 36; unwinding of the coil 31 is carried out in a controlled manner by means of a driving motor 38 of the shaft, as it will be better explained later.

In the cage 30 there are further present, above the coil 31, fixed rolls 40 and movable rolls 41, that divert the film unrolled from the coil; similar diverrting fixed rolls 42 are arranged below the coil 31.

The movable rolls 41 cane be moved to and from the coil by means of the end supports 43, 44, slidingly guided along the shoulders 33, 34 of the stand; the latter include to this purpose respective pairs of guiding rails 45, 46.

In addition, in the shoulder 33 (i.e. the one where there is not the motor 38) there is arranged a groove 48 centrally located with respect to pair of rails 45, and in connection therewith on the outer side of the shoulder 33 there is provided an actuator 50.

The latter may be of any appropriate type, electromechanical, pneumatic, or hydraulic, and is connected to a mobile suport 43 of the diverting rolls 41; according to a preferred embodiment of the of the invention, actuator 50 iscontrolled by the general control system of the apparatus, so as to apply a preset force to the support 43 as it will result better afterward.

For loading the multilayer foils to be stacked, appartus 1 comprises a robotized system, comprising two loaders 52 respectively solid with the coil-carrier stands 30. Each loader comprises a tiltable panel 54, which can be moved from a lowered condition to a raised condition as shown in fig. 2, on which there are provided grasping means of the multilayer foils, such as sucking pads 55.

For moving it the panel 54 is attached to the end of a telescopic arm 57 tilting with respect to the stand 30, moved by a hydraulic (or pneumatic) cylinder 58; in particular, the telescopic arm 57 is attached to a plate 59 solid with a rotating pin 60, mounted cantilever transversely upward with respect to the stand 30, by means of a couple of support brackets 61.

Likewise, the hydraulic cylinder 58 is attached to a cross bar 63 supported above the stand 30 by two spacers 64; in this manner each loader 52 picks up the multilayer foils L that are laid on buffer trolleys 65 provided at the ends of the apparatus and, moving solid with the respective stand 30, load them on a platform 17 shown in fig. 1 of the drawings and similar to that described in WO 94/23948 already referred to before. This platform, as far as the height of the stack increases, is lowered so that each new multilayer foil is laid by the loader 52 on the stack, always at the same level.

From what has been set forth heretofore it is possible to understand the functioning of the apparatus 1 according to the invention and the manner in which it solves the technical problem underlying it.

Indeed, as explained above, for manufacturing thin printed circuits the copper film unwound from the coils 31 and used for the formation of the stacks of multilayer foils, has a thickness in the order of few tenth of microns and it is thus subject to the risk of tears.

For avoiding this, in the apparatus 1 the stress applied to the film is kept below a set safety level; this is achieved by the presence of the diverting movable rolls 41 and of the actuator 50 which operates on the support 43 of said rolls 41.

Indeed, the effect arising from these features provides for the film unwound from the coil 31 to be kept tensioned in a controlled manner during the various working phases of the apparatus, during which each coil-carrier stand 30 makes an alternate motion to and from the centre of the apparatus, along the guides 16 and 26. This alternate movement of the stands 30 with the coils 31 (similar to that occurring in the prior art WO 94/23948) generates unavoidably variations in the stress applied to the unwinding film, thereby reaching maximum values that might produce the breaking of the film.

On the contrary, in the present invention when the unwound film reaches a set level of stress the movable diverting rolls 41 move upwards because of the action of the actuator 50, so as to be close to the fixed diverting rolls 40 and to reduce the length of the film portion twisted between them, as shown in fig. 8 with dotted line, thereby reducing the tension thereof.

In this connection it should be observed that the functioning of the actuator 50 is regulated by the control system of the apparatus 1 , in accordance with the torque applied by the motor 38 driving the unwinding of the coil 31.

In particular, the latter is an electric motor and the control system of the apparatus 1 operates on its electrical working parameters (voltage and current in particular), thereby regulating the functioning of the actuator 50 as a matter of consequence.

In practice, when the resisting torque applied to the motor 38 exceeds a determined level, this means that that the stress in the film unwound from the coil 31 reaches a corresponding level: the control system imposes then the actuator 50 to modify the position of the support 43 as well as that of the rolls 41 that are solid therewith, so as to change accordingly the copper film stress and to prevent any braking risk.

The twisting phase of the film folds can therefore be carried out likewis it is known in the art, that is to say with the coil-carrier stands 30 moving alternately from a reared position toward the end of the frame 20 of the apparatus (shown in fig. 1 and 3), and a forth position in connection with the stacking zone of the multilayer foils L. On this subject it should be observed that the loading devices 52 solid with the stands 30, allow to increase the multlayer stacks forming speed since in practice there is no time off, from the application of the copper film unwound from coils 30 to the stacking of a new multilayer foil.

Indeed, when a first stand makes a forth stroke, it moves from an end of the apparatus toward almost the opposite end of the apparatus 1 , where there is located the other stand 30 which is stopped in a waiting condition; during this stroke the copper film unwinds from the respective coil 31, thereby forming a fold on the stack of multilayer foils present in the middle of the apparatus.

The loader 52 lays thus a new multilayer foil L on the fold, which is thus covered by the copper film during the bacward stroke of the stand 30.

During the backward stroke of the first stand, the stroke of the other stand 30 can start, in the same manner as it has been just explained: it derives that there are no dead moments between the stacking of a new multilayer foil L and the application of the copper film, so that the apparatus working cycle affords a high production yield.

The functioning of the apparatus 1 can be further fully automated by supplying the multilayer foils L to the trolleys 65, without the intervention of workers responsible for this task.

Obviously changes to the invention are possible with respect to what has been set forth hitherto.

Indeed, although the embodiment considered above is advantageous because it is either structurally and functionally reliable, it could be thought to modify the system of fixed and movable diverting rolls 40, 41 by reducing their number or changing the layout. However it must be emphasised that the embodiment considered above has the advantage of being rather flexible, because the path of the copper film must not develop necessarily throughout all the rolls 40, 41 but only few of them can be sufficient.

It must be taken into account that the requirements may change as far as the multilayer foils L stacking process goes on, because the diametre of the coil 31 diminishes as well as its weight and the relating inertia.

All of these variants fall within the following claims.

Claims

1. Apparatus for forming stacks of multilayer foils (L) for printed circuits and the like, wherein a film unwound from a coil (31) is applied between stacked foils (L), characterized in that it comprises control means (40,41 , 42, 43, 44, 45, 46, 50) to control the stress of the film unwound from the coil (31), thereby preventing breaking thereof.

2. Apparatus according to claim 1, wherein said control means comprise a plurality of rolls (40, 41, 42) around which the film passes following a forward path, having a variable distance thereby varying the film stress.

3. Apparatus according to claims 1 or 2, wherein the diverting rolls (40, 41, 42) and the coil (31) are mounted on the same stand (30) movable back and forth the stacking zone of the multilayer foils (L).

4. Apparatus according to claim 3, wherein the movable diverting rolls (41) are arranged on supports (43, 44) sliding along the coil-carrier stand (30).

5. Apparatus according to claim 4, comprising an actuator (50) operating on at least one support (43) of the movable diverting rolls (41).

6. Apparatus according to any of the preceding claims, comprising a motor (38) associated to the coil (31) for unwinding the film.

7. Apparatus according to any of the preceding claims, comprising a loading device (52) for loading the multilayer foils (L) to be stacked, solid with the coil-carrier stand (30) and provided with grasping means (54, 55) for grasping the foils (L).

8. Apparatus according to claim 7, wherein the loading device (52) is arranged behind the coil (31) with reference to the forward stroke of the coil-carrier stand (30) towards the inside of the apparatus, thereby stacking a multilayer foil (L) on the film unwound from the coil (31).

9. Apparatus according to claims 6 or 7, wherein the loading device (52) comprises a telescopic arm (57) tilting about the coil carrier stand (30), which carries grasping means (54, 55) for grasping the foils (L) thereby allowing to move foils (L) at several heights.

10. Apparatus according to claim 9, wherein the grasping means (54, 55) comprise sucking pads (55) supported by a panel (54) attached to the telescopic arm (57).

11. Apparatus according to any of the preceding claims, comprising a bearing structure (2, 20) in which at least one coil (31) carrying stand (30) is movable, characterized in that it comprises at least one trolley (65) for leaning the multilayer foils (L) to be stacked, arranged in connection with the end of the structure (2, 20) where there is the finish of the stroke of the coil-carrier stand (30).