WO2014094022A1

WO2014094022A1 - Semi-finished product for the production of a printed circuit board

Info

Publication number: WO2014094022A1
Application number: PCT/AT2013/050252
Authority: WO
Inventors: Gerhard Schmid; Ljubomir Mareljic
Original assignee: AT&S Austria Technologie und Systemtechnik AG
Current assignee: AT&S Austria Technologie und Systemtechnik AG
Priority date: 2012-12-18
Filing date: 2013-12-16
Publication date: 2014-06-26
Anticipated expiration: 2015-06-18
Also published as: CN203072247U

Abstract

In a semi-finished product (1) for the production of printed circuit boards, the semifinished product (1) comprising a carrier layer (2) and a plurality of conductive layers (4) and insulating layers (5) alternately applied on both sides of the carrier layer (2) and forming printed circuit boards, a release layer (3) is arranged on both sides of the carrier layer (2) between the carrier layer and the plurality of conductive layers (4) and insulating layers (5) and the carrier layer (2) is made of a prepreg-material. The inventive method comprises the steps of providing a carrier layer (2) made of a prepreg-material, coating the carrier layer (2) on both sides with a release layer (3) alternately bonding conductive layers (4) and insulating layers (5) on the release layer (3) on both sides of the carrier layer (2) and separating composites (7) of conductive layers (4) and at least one insulating layer (5) from both sides of the carrier layer (2).

Description

SEMI-FINISHED PRODUCT FOR THE PRODUCTION OF A

PRINTED CIRCUIT BOARD

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a semi-finished product for the production of a printed circuit boards and a method for producing a printed circuit board.

Description of the Related Art

Printed circuit boards, also referred to as printed wire boards are panels carrying and electrically connecting electronic components such as transistors and the like and, hence, form vital parts of electronic products. Printed Circuit boards have a more or less complex structure depending on the specific application. In general a printed circuit board has a plurality of alternating conductive layers and insulating layers bonded together by hardening panels of glass fibres impregnated with organic resin, said panels forming the insulating layers. Such panels for use in the production of printed circuit boards are widely known in the industries as "prepregs" (preimpregnated fibres), which are delivered and processed in an uncured, hence viscous state of the organic resin. The actual insulating layer results when the organic resin has cured. The insulating layers carry conductive layers, for example formed of copper foil, the conductive layers being appropriately processed to form wirings to electrically connect the electronic components. Modern printed circuit boards allow for a high degree of integration of electronic components and their appropriate wiring.

There is, however, a constant need for further miniaturization in the electronic industry in order to provide consumers and professionals with ever smaller yet more capable electronic devices and installations which require more electronic components to be packaged in a smaller space. Many electronic components, nowadays, are produced in nanometer-scale so that very often the printed circuit boards carrying and connecting the electronic components are the limiting parts in terms of miniaturization of electronics. The conductive layers and insulating layers making up a printed circuit board cannot easily be made thinner, since the bonding of the layers, which is often carried out by laminating layer after layer requires a certain mechanical stability in order to avoid the bonded layers to undulate or even tear under the mechanical stresses that arise during lamination. Moreover, when thickness of the layers falls below a certain limit, the handling of the very thin material becomes increasingly critical due to buckling of the materials.

SUMMARY

To be able to produce even thinner printed circuit boards the invention is thus directed to a semi-finished product for the production of printed circuit boards and a method for producing a printed circuit board that avoid the above laid-out limitations and drawbacks.

DETAILED DESCRIPTION

In particular the invention provides for a semi-finished product for the production of printed circuit boards, the semi-finished product comprising a carrier layer and a plurality of conductive layers and insulating layers alternately applied on both sides of the carrier layer and forming printed circuit boards, wherein a release layer is arranged on both sides of the carrier layer between the carrier layer and the plurality of conductive layers and insulating layers. This semi-finished product allows for the production of extremely thin printed circuit boards by supporting the conductive layers and the insulating layers that make up the finished printed circuit board on a central carrier layer providing the necessary mechanical stability. The central carrier layer is at the very center of the semifinished product and the build-up of the conductive layers and insulating layers is arranged symmetrically with the carrier layer as the centre of symmetry. Hence, the conductive and insulating layers can be made thinner than it would be possible without the provision of the carrier layer as none of the described handling problems and problems with buckling or warping of the printed circuit board during lamination arise. Moreover the carrier layer contributes importantly to the overall thickness of the semifinished product so that standard machines for lamination can be used to produce ultra- thin printed circuit boards. After initial binding- or lamination steps have been carried out, usually symmetrically on both sides of the carrier layer, the printed circuit boards or the composites that can then be further processed to give printed circuit boards can be easily separated from the carrier layer owing to the release layer that is arranged between the carrier layer and the plurality of conductive layers and insulating layers that are bonded together. Thus, a release layer, in the sense of this invention, is a layer that can be printed or otherwise applied on a layer and that will not bond or stick to the neighboring layers when lamination- or bonding procedures for forming composites of conductive layers and insulating layers are carried out. The release layer, thus, allows for the easy removal of the plurality of conductive layers and insulating layers and in particular for the easy removal of composites of such layers from another layer even when all those layers have been subjected to bonding and lamination procedures as known in the field of electronic engineering. A release layer in the sense of the present invention is fully disclosed in applicant's US 2011/0272177 Al, in which it is referred to as a„material preventing adhesion". Moreover the carrier layer is made of a prepreg-material. Prepreg (preimpregnated fibres) is a material widely used in the electronic industry to build printed circuit boards. Prepreg is a semi-finished product of composite fibres with an epoxy resin. The fibres usually take the form of a weave or are uni-directional. They contain an amount of the resin material used to bond them together and to other components during manufacture. This material is readily available in the electronic industry and allows for a cheap production of the inventive semi-finished product.

Preferably the release layer is formed by a material selected from the group comprised of metal soaps of Al, Mg, Ca, Na and Zn, combined with a binding agent and a solvent. With these materials, the plurality of conductive layers and insulating layers, the plurality being commonly bonded to form a composite of conductive layers and insulating layers, can easily be separated from the carrier layer.

The resin of prepreg is only partially cured to allow easy handling. The curing of the resin is carried out to the so-called B-Stage and requires cold storage to prevent complete curing. However, also cooled prepreg is subjected to a gradual deterioration process. As a consequence, there is a certain point at which the prepreg is no longer suitable for regular lamination processes. This aged, and hence, partly aged prepreg material has to be discarded and properly disposed of. According to a preferred embodiment of the present invention, however, the prepreg-material of the carrier layer is expired or partly hardened prepreg-material. For the carrier layer it is irrelevant whether the prepreg is expired or not since the carrier layer is not destined to be bonded to the conductive layers and insulating layers of the future printed circuit boards so that the inferior of the quality of this lost prepreg is not detrimental but rather beneficial for the semi-finished product according to the present invention.

As explained above, the carrier layer, besides providing mechanical stability for laminating exceptionally thin composites of conductive layers and insulating layers, contribute to the overall thickness of the semi-finished product to be processed by standard machines for lamination. In this context it is preferred when the carrier layer has a thickness between 200 μιη and 50 μιη, preferably between 150 μιη and 100 μιη, these thicknesses being common in the industry for prepreg-lamination.

The minimum configuration of a printed circuit board is an insulating layer carrying a conductive layer on both sides. To achieve this in as few lamination steps as possible, the semi-finished product according to the present invention is devised such that the release layer on either side of the carrier layer is followed by a conductive layer.

As stated above, buckling and bending of printed circuit boards during lamination or bonding is a common problem that always has to be taken into account during design and production of such boards. As a general rule, printed circuit boards have to be produced by symmetrical lamination processes, meaning that conductive layers and insulating layers are applied or laminated symmetrically on both sides of the printed circuit board leading to printed circuit boards having only even numbers of conductive layers. The production of printed circuit boards with uneven numbers of conductive layers is practically inadvisable due to the described problems with buckling and bending. Obviously, these phenomena will occur more readily when producing ultra-thin printed circuit boards as it is envisaged by the present invention. The provision of a central carrier layer in the inventive semi-finished product allows for the production of printed circuit boards having uneven numbers of conductive layers, when, in conformity with a preferred embodiment of the invention an uneven number of conductive layers, in particular three conductive layers, separated by insulating layers are arranged on either side of the carrier layer. Once a composite having an uneven number of conductive layers is obtained and subsequently separated from the inventive semi-finished product, further lamination processes adding two layers in every symmetrical lamination step will always give an uneven number of conductive layers. _c

5

Preferably at least one of the conductive layers is structured for wiring of electronic components. The printed circuit board separated from the semi-finished product can, however, be further processed according to any known process such as, etching, printing, drilling and the like.

The inventive method for producing a printed circuit board by laminating conductive layers and insulating layers is characterized by the steps of providing a carrier layer coating the carrier layer on both sides with a release layer alternately bonding conductive layers and insulating layers on the release layer on both sides of the carrier layer and separating composites of conductive layers and at least one insulating layer from both sides of the carrier layer.

The above described inventive semi-finished product is obtained after steps a) to c) of the inventive method. After step d) and, if necessary, further processing steps, a printed circuit board is obtained that affords the advantages described with respect to the semifinished product according to the invention.

In particular, the inventive method allows for the production of extremely thin printed circuit boards by supporting the conductive layers and the insulating layers that make up the finished printed circuit board on a carrier layer providing the necessary mechanical stability. Hence, the conductive and insulating layers can be made thinner than it would be possible without the provision of the carrier layer as none of the described handling problems and problems with buckling of the printed circuit board during lamination arise. Moreover the carrier layer contributes importantly to the overall thickness of the semifinished product obtained after steps a) to c) so that standard machines for lamination can be used to produce ultra-thin printed circuit boards. After initial binding- or lamination steps have been carried out, usually symmetrically on both sides of the carrier layer, the printed circuit boards or the composites that can then be further processed to give printed circuit boards can be easily separated from the carrier layer owing to the release layer that is arranged between the carrier layer and the plurality of conductive layers and insulating layers that are bonded together. Thus, a release layer, in the sense of this invention, is a layer that can be printed or otherwise applied on a layer and that will not bond or stick to the neighboring layers when lamination- or bonding procedures for forming composites of conductive layers and insulating layers are carried out. The release layer, thus, allows for the easy removal of the plurality of conductive layers and insulating layers and in particular for the easy removal of composites of such layers from another layer even when all those layers have been subjected to bonding and lamination procedures as known in the field of electronic engineering.

Preferably the release layer is formed by a material selected from the group comprised of With these materials, the plurality of conductive layers and insulating layers, the plurality being commonly bonded to form a composite of conductive layers and insulating layers, can easily be separated from the carrier layer.

Preferably the carrier layer is made of a prepreg-material. Prepreg (pre-impregnated fibres) is a material widely used in the electronic industry to build printed circuit boards. Prepreg is a semi-finished product of composite fibres with an epoxy resin. The fibres usually take the form of a weave or are uni-directional. They contain an amount of the resin material used to bond them together and to other components during manufacture. This material is readily available in the electronic industry and allows for a cheaply carrying out the inventive method.

The resin of the prepreg is only partially cured to allow easy handling. The curing of the resin is carried out to the so-called „B-Stage" and requires cold storage to prevent complete curing. However, also cooled prepreg is subjected to a gradual deterioration process. As a consequence, there is a certain point at which the prepreg is no longer suitable for regular lamination processes. This aged, and hence, partly cured prepreg material has to be discarded and properly disposed of. According to a preferred embodiment of the present invention, however, the prepreg-material of the carrier layer is expired or partly hardened prepreg-material. For the carrier layer it is irrelevant whether the prepreg is expired or not since the carrier layer is not destined to be bonded to the conductive layers and insulating layers of the future printed circuit boards so that the inferior quality of this lost prepreg is not detrimental but rather beneficial for carrying out the method according to the present invention. _,

As explained above, the carrier layer, besides providing mechanical stability for laminating exceptionally thin composites of conductive layers and insulating layers, contribute to the overall thickness of said semi-finished product to be processed by standard machines for lamination. In this context it is preferred when the carrier layer has a thickness between 200 μιη and 50 μιη, preferably between 150 μιη and 100 μιη, these thicknesses being common in the industry for prepreg-lamination.

The minimum configuration of a printed circuit board is an insulating layer carrying a conductive layer on both sides. To achieve this in as few lamination steps as possible, the method according to the present invention is devised such that the release layer on either side of the carrier layer is followed by a conductive layer.

As stated above, buckling and bending of printed circuit boards during lamination or bonding is a common problem that always has to be taken into account during design and production of such boards. As a general rule, printed circuit boards have to be produced by symmetrical lamination processes, meaning that conductive layers and insulating layers are applied or laminated symmetrically on both sides of the printed circuit board leading to printed circuit boards having only even numbers of conductive layers. The production of printed circuit boards with uneven numbers of conductive layers is practically inadvisable due to the described problems with buckling or warping and bending. Obviously, these phenomena will occur more readily when producing ultra-thin printed circuit boards as it is envisaged by the present invention. The provision of a central carrier layer in the inventive method allows for the production of printed circuit boards having uneven numbers of conductive layers, when, in conformity with a preferred embodiment of the invention an uneven number of conductive layers, in particular three conductive layers separated by insulating layers are arranged on either side of the carrier layer prior to the step of separating composites of conductive layers and at least one insulating layer from both sides of the carrier layer. Once a composite having an uneven number of conductive layers is obtained and subsequently separated from said semi-finished product obtained after steps a) to d) of the inventive method, further lamination processes adding two layers in every symmetrical lamination step will always give an uneven number of conductive layers. Preferably at least one of the conductive layers is structured for wiring of electronic components. The printed circuit board can, however, be further processed according to any known process such as, etching, printing, drilling and the like.

Brief Description of the Drawings

The invention will be described in more detail by way of an exemplary embodiment and with reference to the accompanying drawings in which

Fig. 1 shows a sectional view of a semi-finished product,

Fig. 2 shows a sectional view of step d) of the inventive method and

Fig. 3 shows a sectional view of a specific embodiment of the inventive semi-finished product.

Detailed Description of the Drawings

In Fig. 1, the inventive semi-finished product is denoted by 1 and is generally comprised of a central carrier layer 2 and a plurality of conductive layers 4 and insulating layers 5. The conductive layers 4 and the insulating layers 5 are separated by a release layer 3 as specified above to allow the plurality of conductive layers 4 and insulating layers 5 to be easily removed from the carrier layer 2. Owing to the mechanical stability provided for by the relatively thick carrier layer 2, the insulating layers 5 can be very thin. For example the carrier layer 2 has a thickness in the range of about 200 μιη whereas the insulating layers have a thickness of 50 μιη and less. Insulating layers this thin would be extremely difficult to handle without the stabilizing effect of the carrier layer 2.

Fig. 2 shows that the release layers denoted with reference numeral 3 in Fig. 1 allow for separation in the direction of the arrows 6 of the plurality of conductive layers 4 and insulating layers 5 that have been laminated and bonded to give composites 7 of conductive layers 4 and insulating layers 5.

In Fig. 3 it can be seen that according to a particular embodiment of the present invention the composites 7 can be built up to have an uneven number of conductive layers 4. In this case on both sides of the carrier layer 2, a composite 7 comprised of three conductive layers 4 is built up. After separation of the composites 7 from the carrier layer 2 and when the build-up or further processing of the composites 7 to even more complex printed circuit boards is carried out symmetrically on both sides of each composite 7, there will always be an uneven number of conductive layers in the printed circuit board.

Claims

Claims:

1. Semi-finished product for the production of printed circuit boards, the semifinished product (1) comprising a carrier layer (2) and a plurality of conductive layers (4) and insulating layers (5) alternately applied on both sides of the carrier layer (2) and forming printed circuit boards, wherein a release layer (3) is arranged on both sides of the carrier layer (2) between the carrier layer (2) and the plurality of conductive layers (4) and insulating layers (3) and wherein the carrier layer (2) is made of a prepreg-material.

2. Semi-finished product, according to claim 1, characterized in that the release layer (3) is formed by a material selected from the group comprised of metal soaps of Al, Mg, Ca, Na and Zn, combined with a binding agent and a solvent.

3. Semi-finished product according to claim 1 or 2, characterized in that the prepreg- material of the carrier layer (2) is expired or partly hardened prepreg-material.

4. Semi-finished product according to one of claims 1 to 3, characterized in that the carrier layer (2) has a thickness between 200 μιη and 50 μιη, preferably between 150 μιη

5. Semi-finished product according to one of claims 1 to 4, characterized in that the insulating layers (5) have a thickness between 10 μιη and 80 μιη, preferably between 30

6. Semi-finished product according to one of claim 1 to 5, characterized in that the release layer (3) on either side of the carrier layer (2) is followed by a conductive layer.

7. Semi-finished product according to one of claims 1 to 6, characterized in that an uneven number of conductive layers (4), in particular three conductive layers (4) separated by insulating layers (5) are arranged on either side of the carrier layer (2).

8. Semi-finished product according to one of claims 1 to 7, characterized in that at least one of the conductive layers (4) is structured for wiring of electronic components.

9. Method for producing a printed circuit board by laminating conductive layers (4) and insulating layers (5), characterized by the steps of a) providing a carrier layer (2) made of a prepreg-material b) coating the carrier layer (2) on both sides with a release layer (3) c) alternately bonding conductive layers (4) and insulating layers (5) on the release layer (3) on both sides of the carrier layer (2) and d) separating composites (7) of conductive layers (4) and at least one insulating layer (5) from both sides of the carrier layer (2).

10. Method according to claim 9, characterized in that the release layer (3) is formed by a material selected from the group comprised of metal soaps of Al, Mg, Ca, Na and Zn, combined with a binding agent and a solvent.

11. Method according to claim 9 or 10, characterized in that the prepreg-material of the carrier layer (2) is expired or partly hardened prepreg-material.

12. Method according to one of claim 9 to 11, characterized in that the carrier layer (2) has a thickness between 200 μιη and 50 μιη, preferably between 150 μιη and 100 μιη.

13. Method according to one of claims 9 to 12, characterized in that the insulating layers (5) have a thickness between 10 μιη and 80 μιη, preferably between 30 μιη and 40 μπι.

14. Method according to one of claims 9 to 13, characterized in that the release layer (3) on either side of the carrier layer (2) is followed by a conductive layer.

15. Method according to one of claims 9 to 14, characterized in that an uneven number of conductive layers (4), in particular three conductive layers (4) separated by insulating layers (5) are arranged on either side of the carrier layer (2) prior to the step of separating composites (7) of conductive layers (4) and at least one insulating layer (5) from both sides of the carrier layer (2).

16. Method according to one of claims 9 to 15, characterized in that at least one of the conductive layers (4) is structured for wiring of electronic components.