AT12321U1 - MULTILAYER PCB LAYER ELEMENT WITH AT LEAST ONE LASER BEAM STOPPING ELEMENT AND METHOD FOR ATTACHING SUCH A LASER BEAM STOPPER IN A MULTILAYER PCB ELEMENT - Google Patents

Description

Austrian Patent Office AT 12 321 U1 2012-03-15

Description: The invention relates to a printed circuit board element, in particular a multilayer printed circuit board element, with a plurality of dielectric layers and conductor layers, and with at least one laser beam stop element in the interior of the printed circuit board element, around a laser beam used for drilling or cutting at a deeper penetration into the Prevent PCB element.

Furthermore, the invention relates to a method for attaching a laser beam stop element in such a printed circuit board element.

Circuit board elements are generally constructed of different layers which are adhesively bonded together, wherein a thermal pressing process can be used. In the case of multilayer printed circuit board elements, so-called multilayer printed circuit board elements, a plurality of dielectric layers (insulating layers) and metallizations (conductor layers) are stacked on one another, so as to produce conductive connections between electronic components at several levels. Usually, such printed circuit board elements are made of resin layers, e.g. Epoxy resin layers, and copper layers constructed, wherein at least two layers are provided.

For the production of conductive connections to internal components holes are to be mounted in such PCB elements to predetermined depths. If there is to be an electrical connection between conductive planes, the holes thus created can then be e.g. be galvanically coppered. In general, it is often necessary to cut or drill these printed circuit board elements with control of the depth of cut or drilling, and for this cutting or drilling, a laser, such as a laser, is typically required. a C02 laser is used. Although it is also possible to use a general depth control method, this is of limited use. For cutting and drilling with laser beams, for example, a copper layer inside the structure of the printed circuit board element serves to prevent the laser beam from penetrating deeper into the printed circuit board element, ie to stop the cutting or drilling process. Here, this stopping effect is based on the fact that copper layers or generally metal layers reflect very well in the visible or infrared light range; For example, a C02 laser beam is well reflected on a copper layer. In contrast, a laser beam would cut copper in the UV range.

However, now arises in printed circuit board elements with already structured inner layers, the problem that the conductor layer (eg, a copper layer) by structuring only locally available, but at other locations, the metallization is etched away, so that, for example, two resin layers directly connected are; Similarly, a solder mask can connect directly to an epoxy resin layer. In such places, where resin layers adjoin one another or a solder mask adjoins a resin layer, the above-described laser stop function is no longer present since the metallization required for this purpose is lacking. In these cases, it is difficult to determine the depth of cut or depth of the laser beam, i. its penetration into the structure of the printed circuit board element to control.

It is an object of the present invention to provide a printed circuit board element or a method as stated above, with which it is possible, even in the case of an already made structuring of inner layers an efficient and reliable control of the depth of cut or depth of a laser beam inside to ensure a printed circuit board element.

To achieve this object, the invention provides a printed circuit board element as in claim 1 and a method as defined in claim 9 before. Advantageous embodiments and further developments are specified in the dependent claims.

In the present technique, a separate " additional " Stop element for the laser beam introduced, at least in those places where the restriction of the 1/11 Austrian Patent Office AT12 321 U1 2012-03-15

Depth of cut or depth of the laser beam is desired. Of course, this own stop element can also be attached flat over the entire surface of the underlying layer; In particular, it can also be structured in a conventional manner. For structuring, for example, a printing technique for local application can be used, such as ink jet printing, screen printing or the like. However, a structuring is also possible if the material of the additional stop layer in a conventional manner photosensitized, so that then using a conventional Photoprocesses structuring can be performed. Also for this purpose, printing techniques, as indicated above, or other coating methods, for example: spraying, etc., can be used. In all these cases, however, the stop element is a separate, additional element which can be attached separately and which can be specially adapted for the desired purposes. This additional stop element contains small particles, in particular in the nm to pm range. These particles consist in particular of a suitable metal, for example of gold, silver, copper, aluminum, tin and / or lead; however, other suitable reflowing or fusible materials, e.g. Ceramic particles, are used. The particles, e.g. be spherical or platelet-shaped, are so small that the laser beam can not easily penetrate through the material of the layer, for example due to multiple reflection on the particles, if they are larger, or if the particles are not round, but platelet-shaped, or if a large proportion of particle binder is present to connect the large particles together, then this binder can not be reflected and penetrated by the laser beam. Even with such larger particles in the stop element, the reflection may be poor. In this way, it would be conceivable that enough energy can be introduced into the stop element with the laser beam in order to penetrate it, instead of stopping the laser beam. For small particles, however, on the one hand, the binder content can be very low, and on the other hand, the energy of the laser beam can be used to melt the material, or can be higher due to the higher proportion of particles, the reflection.

For the size of the particles can be taken as a measure that the particles have a "nano-character". should be, i. the particles should have a size at which the melting point of the nanoparticles deviates from the melting point of the general printed circuit board material. For particles of silver, for example, a particle size of about 100 nm has been found to be advantageous.

Thus, in the mechanism according to the present technology, the energy of the laser beam can also be used to completely or partially melt the particles, thereby stopping the laser beam at that point, except that the laser beam is similar to the conventional copper layer , completely or at least largely reflected. By the thermal contact of the particles in the laser beam impingement area, by the way, a cooling effect, a heat dissipation, is effected.

The present stop element is preferably provided as an additional layer part, in particular in the form of a paste, and used up, e.g. printed, this paste containing the small particles and the binder.

It is also also conceivable to attach the stop element for stopping a laser beam in a layer above or below a removable separating layer or between two removable separating layers. For example, such release liners are used to prevent overlying and underlying resin layers from sticking together. This is provided, for example, when a portion of a substrate, i. a rigid resin layer, to be subsequently removed, so as to obtain a so-called rigid-flex circuit board, cf. For example WO 2008/098269 A, WO 2008/098270 A, WO 2008/098271 A and WO 2008/098272 A. The attachment of the stop element to or between the separating layers also has the advantage that it can be removed together with the separating layers.

On the other hand, the laser stop element 14 can also be present as a separate, prefabricated film (tape) and, for example, laminated onto a resin layer or inserted into a resin layer. Also in this case, there is a layered, separate, independently of the conductor layers mounted laser stop element, which is attached as an additional layer.

A often particularly favorable embodiment is further characterized by the fact that the present particles are incorporated directly as a filler in one of the layers of the printed circuit board element or are. For example, the particles may be introduced into a respective resin layer of the circuit board member, but they may be incorporated in or contained in the aforementioned separation layers, in which case the separation layer additionally functions as a stopper member; Similarly, in the aforementioned case of incorporation of filler nano-particles into a resin layer, the latter serves as a laser stop pest.

Incidentally, a plurality of such stop elements will be present as a rule in addition to conductor layers attached to a circuit board element stop elements.

The invention will be described below with reference to preferred embodiments, to which it should not be limited, and with reference to the accompanying drawings even further. 1 shows a known multilayer printed circuit board element in a very schemati's cross section, wherein also only very schematically a laser beam for cutting or drilling a contacting hole for a conductor layer in the interior of the conductor element is shown wherein the laser beam is stopped at the inner conductor layer in a conventional manner (by reflection); Fig. 2 is a similar schematic cross-sectional view, but now compared to Fig. 1, the inner conductor layer is patterned so that the laser beam, when directed to a location where the inner conductor layer has no metal due to the patterning, at a deeper penetration is not hindered; Fig. 3 is a similar schematic cross section through a printed circuit board element, but now a separate stop element for stopping the laser beam is provided according to an embodiment of the invention; Fig. 4 is a similar cross section, but here with only two PCB layers, again with an additional stop element is provided for the laser beam, but now between two removable separating layers; Fig. 4A is a cross-sectional view similar to Fig. 4, but now with only a removable one

Separating layer, on which an additional stop element is mounted; Fig. 5 shows a single layer with a resin layer and an attached, already structured conductor layer, as well as with a layer provided above with small particles, which is used to form an additional layer for the production of a separate element for stopping a laser beam during cutting or Drilling the finished printed circuit board element is provided; and [0023] FIG. 6 shows a multilayer structure with three layers still shown separately for the multilayer structure, the middle layer corresponding to that according to FIG. 5, after the additional layer has been patterned, according to the additional stop elements according to FIG to form the invention, and wherein also schematically the pressing of the individual layers to the multilayer printed circuit board element is illustrated.

In Fig. 1 is a very schematic and not to scale a conventional structure of a multilayer printed circuit board element 1 is shown, wherein by way of example three layers 2, 3 and 4 are shown, but without the printed circuit board element structure should be limited thereto. Specifically, there are three resin layers 5, 6 and 7 made of, for example, epoxy resin as known per se, and may contain glass fibers for reinforcement. Further, in the example shown, there are four conductor layers (metal layers, usually copper layers) 8, 9, 10 and 11, two of which are 8, 11 on the outside of the structure, whereas the copper layers 9 and 10 are inside. 3/11 Austrian Patent Office AT 12 321 U1 2012-03-15

Very schematically, a laser beam 12 is indicated in Fig. 1, wherein this laser beam for drilling contact holes or for applying cuts, such as for removing parts of printed circuit board layers, is used. Such removal of printed circuit board parts is e.g. then provided when flexible parts of the printed circuit board element are desired, so a so-called. Rigid-flex circuit board is to produce. The penetration depth of the laser beam 12 is limited as shown in FIG. 1 by the inner copper layer 9, since this copper layer or metallization 9 the laser beam, e.g. a C02 laser beam, well reflected. Due to this reflection on the copper layer 9, therefore, the laser beam 12 can not penetrate further into the interior of the structure of the printed circuit board element 1.

It should be noted here that in general metals, as used for the conductor layers 8, 9, 10 and 11, laser light in the visible or infrared region reflect well; However, a laser beam in the UV range would cut a copper layer, for example. For such UV lasers, therefore, the penetration depth when drilling or cutting circuit board elements is controlled differently, wherein special, non-metallic spacer material parts are embedded in the layer structure, whose function is to provide a space or distance for the UV laser, and in the Drilling or cutting can be destroyed with the UV laser. This method with the well-known "Distanzelmenten " However, it is only suitable for relatively slow cutting or drilling and requires the insertion of the spacer material in the interior of about the resin layers.

If, when cutting a printed circuit board element 1 with a laser beam 12 in the visible light range or in the infrared range, the situation is that the inner conductor layer, e.g. the copper layer 9, already structured, cf. Fig. 2, wherein regions 13 are present in this conductor layer 9 without metal, so there is no reflection of the laser beam 12 on a metal surface, and the laser beam 12 penetrates deeper than intended in the circuit board element 1, as shown in Fig. 2. Although it would be conceivable to regulate the penetration depth of the laser beam 12 due to the control of the turn-on of the laser beam 12, but this method is too inaccurate and also depends u.a. from the thicknesses and materials of the respective layers, in particular the resin layers 5, etc., which may well vary.

If at the point of the conductor layer 9 (or even the conductor layer 10, if there should be a structuring) already a solder mask be attached, nevertheless, at the points 13 still lacking a metallization, so that then the penetration depth of the laser beam 12 can not be easily controlled or limited.

According to the present technique is now in the required places, namely where later by means of the laser beam 12, a cut or a hole to be attached, and where already the conductor layer, e.g. the copper layer 9 is patterned, having its own independent additional stop element - also referred to herein as auxiliary stop element 14 - attached, this additional stop element 14 being independent of (in addition to) the conductor layers, e.g. 9, is mounted and acts as a laser beam stop member by the laser beam 12 is reflected at this additional stop element 14 and / or its energy is used to melt particles in this additional stop element 14. In FIG. 3, by way of example, such a local additional stop element 14 is shown in a metallization-free region 13 in an already structured conductor layer 9 of a printed circuit board element 1, which is otherwise constructed as shown in FIGS. 1 and 2. This additive stopper 14 contains small particles connected by a binder, which particles are so small that they melt earlier than the entire material complex. For example, silver particles and gold particles were tested for these "nano" particles, and it has been found that good results can be obtained with silver particles and gold particles having a particle size of about 100 nm.

These small particles, whose size can extend into the pm range, are so small that in the stop member 14 and little binder is needed, which is advantageous because this binder is not useful for the stop function and under certain circumstances prevents reflection of the laser beam 12 on the nano-particles. In the case of particles which are too large, furthermore, due to the geometry of the particles, a multiple reflection (or a relatively high proportion of binder due to a relatively high proportion of binder) may occur, in which case penetration of the laser light through the region or the layer of stubble 14 would be possible therethrough, so that the laser beam nonetheless penetrates too deeply. Of importance for the present stop element 14 and its stop function are therefore the "smallness". the particle in conjunction with the low binder content, or the reflection and absorption properties, in which case the energy of the laser beam 12 is also used to possibly melt the nano-particles, except that the reflection at the stop element 14 comparable to that at a In any case, copper layer 9 (see FIG. 1) can be high.

Other materials for the nanoparticles would be, for example, copper, tin, lead, aluminum, generally metals that can be processed into the "nano" particles, but also ceramic materials.

For example, epoxy resins have proved suitable as binders; Solvents based on α-terpin oil can be used for the additional layer mass.

With such or similar binders and such nano-particles as indicated, e.g. a layer mass can be produced in the form of a paste, which can easily be applied in the course of the production of the printed circuit board element 1 as an addition to the other components. In particular, to apply this paste to the stop member 14, a variety of printing techniques, including screen printing or ink jet printing, and other coating techniques, e.g. also spray coating. One possibility is also to first apply the paste in the form of a surface layer and then to structure this surface layer, which can be done by means of known photo-exposure techniques (with subsequent development processes) if photosensitive properties are provided for the paste. This will be explained in more detail below with reference to FIGS. 5 and 6.

In operation, the energy of the laser beam 12 is absorbed by the small particles, wherein the energy is used to partially or completely melt the particles. Furthermore, the laser beam 12 is partially or completely reflected. An advantage is further that, due to the thermal contact of the particles, the area where the laser beam 12 impinges is cooled, since heat is transported away by the particles.

The present laser beam stop element 14 is particularly suitable for applications where 12 cuts are made in the printed circuit board element 1 by means of the laser beam, for example around a part of a layer, e.g. Layer 2 (see Fig. 1) so as to provide by removing the rigid resin part at this point a possible flexible printed circuit board area, as is known in the art.

When removing parts of layers of a printed circuit board element, it is also known, as mentioned above, to incorporate removable separating layers, so as to prevent sticking of layers at this point. However, these separation layers do not act as such as stop elements for the laser beam 12. The provision of such separation layers, such as the separation layers 15, 16 in Fig. 4 or the individual separation layer 16 in Fig. 4A, can now with the attachment of a laser beam stop element 14 such be explained in principle explained with reference to FIG. 3, cf. 4 and 4A. In this case, it is possible to attach the additional or own stop element 14 between two separating layers 15, 16 (see FIG. 4), or to mount them on a separating layer 16 (see FIG. 4A). Of course, it would also be possible, depending on the circumstances, to provide the stop element 14 also underneath such a separating layer (for example, 15 in Fig. 4) without attaching another separating layer 16 underneath.

In the case of FIGS. 4 and 4A, for example, a part 17 of the upper layer 5 with 8 could be removed from the rest of the printed circuit board element 1. This part 17 can be self-contained, e.g. be rectangular, with its boundary is formed by at least one separating layer 15, 16 and the stop member 14, and wherein the cut by means of the laser beam 12 is mounted around this part 17 to finally remove the part 17 can. This is not shown in detail in FIGS. 4 and 4A, but in itself, apart from the present stop element 14, conventional technology is inherent in the patent application AT12 321 U1 2012-03-15.

In Fig. 5 is schematically shown in a cross section a layer, e.g. the layer 3 of the printed circuit board element 1 according to FIG. 1, with a resin layer 6 and an already structured conductor layer 9 applied thereon. As a result of the structuring, regions 13 are present in the conductor layer 9, where there is no more metallization. This situation according to FIG. 5 is provided for an inner layer of a multilayer printed circuit board element 1 approximately according to FIGS. 1 to 3.

For the attachment of the own stop elements 14 in the regions 13, a particle surface layer 14 'is now provided on the layer 3 in this example, which is e.g. by spreading the paste and knife coating, by spraying (spray-coating), printing or a similar known method can be done. This surface layer 14 'of the paste with the nano-particles and the binder is additionally coated with a photosensitive element, e.g. a commercially available photoinitiator together with a binder to be crosslinked. As a result, by appropriate exposure through a mask, the surface layer 14 'partially cured and partially attackable for an etchant (or photographically developable) are designed so that in a subsequent etching (or development step), much as in the structuring of Conductor layers, eg 9, a structured additional layer is obtained as a stop element 14, cf. Fig. 6.

The inner layer 3 is then stacked as shown in FIG. 6 together with the outer layers 2, 4 (and optionally with other inner layers, which are not shown) in a conventional manner and - usually in conjunction with other such Layer packages in the manner of a "book", as is known per se - arranged in a press and then with heating to connect the layers 2, 3 and 4 are adhesively bonded, pressed, see. the press parts 18, 19 shown in Fig. 6. (It should be noted here that, of course, there are also non-thermal connection possibilities which can also be used when the present additional stop elements 14 are installed.) [0040] FIGS Such pressing can of course also take place if the additional stop elements 14 have been attached in a different manner, for example by screen printing, at the desired locations (ie "structured").

Another way to achieve the present stop elements 14 independently of the conductor layers 8, 9, 10, 11, for example, is to incorporate the aforementioned particles directly as a filler in a suitable manner in the appropriate layers or layers. The particles are thus in this case directly, as a "filler" in the resin system of a resin layer of the circuit board element or else optionally in a release layer 15 or 16 (in which case only one such release layer will be present) may be included, and the resin layer or Separation layer then acts as a laser stop layer or layer, ie as a laser stop element 14, again independently of the conductor layers 8, 9, 10, 11th

Another possibility for providing a Stoppelements 14 may consist in that prefabricated stop elements 14 are present as a film (tape), these stopper films are laminated on a (resin) layer or inserted in the layer structure.

With the present additional stop elements 14 for the laser beam 12, the stop properties can be influenced via the reflection or absorption properties for which the particles and their size or shape are responsible in particular. The advantage here is that these additional stop elements 14 can be mounted anywhere in the multilayer structure, namely where later limiting the penetration depth of the laser beam when cutting or drilling of the printed circuit board element 1 is desired. These variable application sites, as well as the flexible application methods, are of particular advantage. It has also proved to be favorable that a paste in layer form, with the nano-particles, can be printed or added in another form to the printed circuit board element, after which the conductor layers have been patterned and etched, without a copper layer in the sense of FIG

Claims (20)

Austrian Patent Office AT 12 321 U1 2012-03-15 basis is able to stop a laser beam. Upon impact of the laser beam 12 on the auxiliary stop element 14, the small particles are reflected as mentioned, or possibly partially or completely melted and sintered to prevent the laser beam from further penetration into the printed circuit board element. If the invention has been explained above with reference to particularly preferred embodiments, so of course changes and modifications are possible within the scope of the invention. Thus, in the drawing, as far as described so far, the laser stop element 14 is always shown (approximately) in a plane with the already structured conductor layer 9. However, it is equally conceivable and possible to use the additional stop element 14 within a resin layer, e.g. 6; to attach, as indicated for simplicity in Fig. 3 additionally dashed lines. This is easily possible, in particular, if the resin layers are made of e.g. two layers, as in the case of resin systems, e.g. Epoxy resin layers, which are formed from so-called prepregs, which are originally in film form and can be simply superimposed for pressing, about to achieve an increased insulation layer. In the case of a photosensitive paste paste, technologies are also applicable, whereby only a single-stage development process is used as a photo process. As far as the additional layer mass is concerned, there are, for example, pastes or inks filled with aluminum particles, wherein the aluminum particles are of the order of a few micrometers (eg approx. 4) and are approximately platelet-shaped, so as to provide a layered arrangement during application (printing). to achieve. Claims 1. Circuit board element (1), in particular multilayer printed circuit board element, with a plurality of dielectric layers (5, 6, 7) and conductor layers (8, 9, 10, 11), and with at least one own one of the conductor layers (8, 9, 10, 11) different laser beam stop element (14) in the interior of the printed circuit board element in order to prevent a laser beam (12) used for drilling or cutting from deep penetration into the printed circuit board element, characterized in that the laser beam stop element (14) with laser beam Energy absorbing and / or reflecting small particles is formed. 2. Printed circuit board element according to claim 1, characterized in that the particles are coated with a binder, e.g. a resin, in particular epoxy resin, are bonded to a layer part. 3. printed circuit board element according to claim 1 or 2, characterized in that the particles have a size in the nm to pm range. 4. printed circuit board element according to one of claims 1 to 3, characterized in that the particles have a spherical shape. 5. printed circuit board element according to one of claims 1 to 3, characterized in that the particles have a platelet shape. A circuit board element according to any one of claims 1 to 5, characterized in that at least some particles of metal, e.g. Silver and / or gold. 7. printed circuit board element according to one of claims 1 to 6, characterized in that at least some particles of ceramic material. 8. printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) is an imprinted layer part. 9. printed circuit board element according to one of claims 1 to 8, characterized in that the stop element (14) is photolithographically structured. 10. printed circuit board element according to one of claims 1 to 9, characterized in that the stop element (14) on or in a removable separating layer (15, 16) or between two removable separating layers (15, 16) is mounted. 7/11 Austrian Patent Office AT 12 321 U1 2012-03-15 11. Printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) is formed by an inserted or laminated film. 12. printed circuit board element according to one of claims 1 to 7, characterized in that the stop element (14) by the locally in a layer (6) or layer (15, 16) is incorporated as a filler particles. 13. A method for producing a printed circuit board element (1) according to any one of claims 1 to 12, wherein prior to connecting layers (2, 3, 4) of the printed circuit board element own, of the conductor layers (8, 9, 10, 11) different stop element (14) is mounted at the desired location, after which the layers are pressed with the inclusion of the additional stop element (14), characterized in that the laser beam stop element (14) is formed with laser beam energy absorbing and / or reflecting particles. 14. The method according to claim 13, characterized in that the stop element (14) on or in a removable separating layer (15, 16) or between two removable separating layers (15, 16) is attached. A method according to claim 13 or 14, characterized in that particles of metal, e.g. Silver and / or gold, are used. A method according to any one of claims 13 to 15, characterized in that the stop element (14) is used in a printing process, e.g. Screen printing, ink jet printing or the like, or layered in a spray coating process. 17. The method according to any one of claims 13 to 15, characterized in that the layer-shaped stopper (14) light-sensitively equipped and structured in a Photoätzte-chik or photodevelopment process before the other (n) layer (s) attached and the layers (2, 3, 4) are pressed. A method according to any one of claims 13 to 17, characterized in that the stop element (14) is a paste, e.g. with a resin, such as epoxy resin, as a binder, is applied. 19. The method according to any one of claims 13 to 15, characterized in that the stop element (14) is mounted as a prefabricated film, which is inserted between layers (2, 3, 15, 16) or laminated to a layer (3, 16) , 20. The method according to any one of claims 13 to 15, characterized in that the particles are incorporated as a filler locally in a layer (15, 16) or layer (6). For this 3 sheets drawings 8/11