Patent Description:
In the context of growing product functionalities of component carriers equipped with one or more electronic components and increasing miniaturization of such components as well as a rising number of components to be mounted on or embedded in the component carriers such as printed circuit boards, increasingly more powerful array-like components or packages having several components are being employed, which have a plurality of contacts or connections, with ever smaller spacing between these contacts. Removal of heat generated by such components and the component carrier itself during operation becomes an increasing issue. At the same time, component carriers shall be mechanically robust and electrically reliable so as to be operable even under harsh conditions.

Document <CIT> describes a method of manufacturing a circuit board element comprising a plurality of electrically conductive layers and electrically insulating layers arranged to form a stack; during the lamination step, cylindrical copper wires and an electronic component are arranged between the electrically insulating layers, to be stably embedded in the stack due to the lamination pressing step.

Document <CIT> discloses a sacrificial material for the production of internal cavities in laminated structures made of ceramic material; due to an increase of the temperature during the lamination step, the sacrificial material is burned out and then removed from the laminated structures.

Document <CIT> describes a method for forming a ceramic circuit board where rods are embedded in ceramic green sheets, subsequently pulled out after the sintering of said sheets.

There may be a need to extend the functionality of a component carrier.

According to an exemplary embodiment of the invention, a method of manufacturing a component carrier according to claim <NUM> is provided.

In the context of the present application, the term "stack" may particularly denote an arrangement of multiple planar layer structures which are mounted in parallel on top of one another.

In the context of the present application, the term "layer structure" may particularly denote a continuous layer, a patterned layer or a plurality of nonconsecutive islands within a common plane.

In the context of the present application, the term "filament" may particularly denote any wire, fiber, thread, string or yarn or any other oblong structure which is sufficiently flexible to be bendable (in particular elastically or plastically) for forming any desired shape. A filament may also be denoted as a very thin rope. Such a filament may be an oblong structure, for instance an essentially cylindrical structure, having a very small diameter (for instance of less than <NUM>, particularly less than <NUM>) and a very long length (for instance longer than <NUM>, particularly longer than <NUM>). Thus, a filament may be a small dimensioned fiber having a large aspect ratio, for instance larger than <NUM>. For instance, filaments used for embedding in a component carrier may be flat filaments (which may have an oval or rectangular cross-section, for instance to form a ribbon) or may have a circular or square cross-section.

A component carrier resulting from an embodiment of the invention is provided, in which one or more filaments are embedded. The filament is removed after its embedding in the stack so as to leave a hollow channel in an interior of the component carrier at a position where the embedded filament had been located. By taking this measure, it may be possible with simple means to improve the functionality of the obtained component carrier. The hollow channel obtained within the stack can be used for example for cooling purposes (in particular for guiding cooling fluid through the component carrier), as access for acoustic waves (for instance in the event of an embedded microphone or loudspeaker), or which may be filled with appropriate material (such as thermally conductive and/or electrically conductive material) to promote or adjust a corresponding function of the component carrier. In view of the small dimensions of a filament in the two dimensions being orthogonal to the main extension direction of the filament, embedding such a filament in component carrier material may be very simple.

In a component carrier resulting from an embodiment of the invention, one or more cavities may be created in the plane of a component carrier (such as a printed circuit board, PCB) in any format, preferably but not necessarily without using any cutting technique, but merely by embedding a filament in the component carrier material and subsequently removing at least part of the filament from the component carrier. The possibility of building channels and cavities in the component carrier in any possible format is highly advantageous. It is also advantageous that such a channel (configured as a negative or inverse form to the embedded filament) can be formed at any production stage of the component carrier. The described concept is also compatible with any two-dimensional or three-dimensional geometry of the cavity or filament. The filament or string can be optionally coated, for instance by an electrically conductive material (for example copper), to leave an electrically conductive wall in the cavity when pulling the filament out of the component carrier. As other possible materials of the component carrier, is also possible to use a plastic material such as nylon or a metal such as steel, i.e. material allowing to pull out at least a core of the filament without tearing or leaving undesired rests of the filament behind, i.e. an interior of the component carrier. In other words, the filament may be configured so that, when pulled out of the component carrier, the filament or string does not leave any rests in the cavity. The cavity can be formed in the component carrier at any production stage, even after assembly. One single filament or string can produce the cavity for many different cards or component carriers of a panel. Another possibility is to use extremely fine strings to produce microscopic channels in the component carrier. For instance, it may be possible to apply electric contacts to the cavity and to use it in applications such as gas sensors, microphones, antennas, etc..

Exemplary applications resulting from an embodiment of the invention are active cooling via one or more micro-channels, the formation of an acoustic channel, medical applications implementing microfluidic channels, sensor applications, RF (radio frequency) applications (which may also implement an air gap in an interior of the component carrier), optical applications (where an optical signal may propagate through an air gap maintained after removing the filament from the component carrier, or a waveguide embedded in the component carrier in the form of a filament. Exemplary embodiments resulting from an embodiment of the invention may enable active cooling directly in the component carrier via the construction of one or more cooling channels through which a coolant (such as water or air) can flow to remove heat (for instance generated by an embedded component during operation) from an interior of the component carrier. The filament concept can also be used for high-frequency antennas to form air channels for wave propagations. Exemplary embodiments of the invention may also allow the construction of sensor platforms in which the embedded component or a hollow channel formed by subsequently removing an embedded filament from a component carrier may contribute to the sensor function.

For instance, a material of the filament may be capable of withstanding higher temperatures than applied during processing or manufacturing (in particularly pressing or laminating).

According to the invention, the method comprises removing the embedded filament - partially or entirely - out of the stack. By taking this measure, an embedded cavity can be formed in the stack with low effort.

In an embodiment of the invention, at least one material of the filament and a material of at least one of the at least one electrically insulating layer structure and/or of at least one of the at least one electrically conductive layer structure are identical. For instance, when the filament is removed partially out of the stack, the remaining filament material of the component carrier may be the same as a material of an electrically conductive layer structure and/or an electrically insulating layer structure of the stack.

According to the invention, the method comprises removing the filament from the stack by pulling the filament out of the stack. For this purpose, an end portion of the filament should extend out of the component carrier material after the embedding, so that a pulling end remains accessible.

In an embodiment of the invention, the method comprises embedding the filament in the stack so as to form a two-dimensional trajectory within a plane perpendicular to a stacking direction of the layer structures of the stack. Thus, the filament may extend along a path so as to lie within a two-dimensional area being coplanar with the layer structures of the stack. In particular when the filament is made of a flexible, bendable or elastic material, it is possible that the filament is placed in a two-dimensionally bent shape in an interior of the component carrier in the plane corresponding to the stacked layer structures of the component carrier.

In an embodiment of the invention, the method comprises embedding the filament in the stack so that the filament is arranged along a three-dimensional trajectory having at least a section within and at least one other section perpendicular to a stacking plane of the layer structures of the stack. Such an embodiment is shown, for instance, in <FIG>. It is also possible that the embedded filament is not only arranged along a path within a plane arranged vertical to the stacking direction of the layer structures, but that the trajectory of the filament has contributions within the mentioned plane and perpendicular to the mentioned plane. In the latter embodiment, a three-dimensionally curved filament embedded in the component carrier, or (for instance after pulling the filament out of the component carrier) a three-dimensionally curved cavity can be formed.

In an embodiment of the invention, the method comprises covering at least part of an interior wall of the stack, delimited by a channel remaining after removing the filament, by a coating. For instance, at least a part of the channel may be lined with a coating, in particular a coating selected from the group consisting of an electrically conductive coating, a thermally conductive coating, a reflective coating, and a waterproof coating. Such a lining of the cavity wall can be accomplished by coating the filament, prior to inserting the same into the stack, with a material which remains in the cavity after having pulled a core of the filament out of the component carrier. For instance, such a coating may be a solid hollow tube (for instance made of copper material when the coating shall be electrically conductive and thermally conductive) surrounding the core of the filament with low mutual adhesion. It is also possible that the coating is a paste or the like applied to the filament and configured for remaining adhered to the component carrier material when the core of the filament is removed out of the component carrier. A release layer of the filament between the core and the coating may promote separation of the coating from the core, when the release layer is made of a poorly adhesive material (relative to the core and the coating).

In an embodiment of the invention, the method comprises partially or completely filling a channel, remaining in the stack after removing the filament, with electrically conductive material. This can be accomplished, for instance, by pressing a - for instance paste like - electrically conductive material (for instance copper paste) into the cavity (for instance using a syringe or the like).

Additionally or alternatively, the method may comprise filling a channel, remaining in the stack after removing the filament, partially or completely with a highly thermally conductive material (for instance having a value of the thermal conductivity of at least <NUM> W/mK) to thereby form a heat removal structure for removing heat generated during operation of the component carrier. This can be accomplished, for instance, by pressing a - for instance paste like - thermally conductive material (for instance copper paste) into the cavity (for instance using a syringe or the like).

In an embodiment of the invention, the method comprises guiding a cooling fluid (such as a cooling liquid, for instance water, or a cooling gas, for instance air) through a channel remaining in the stack after removing the filament for removing heat generated during operation of the component carrier. This can be highly advantageous in particular when a component (such as a semiconductor chip) is embedded in the component carrier and generates considerable amount of heat during operation. The component can then be surrounded for instance by the filament already during embedding so that the heat removal function is provided spatially very close to the component when the filament has been removed and the cooling fluid is guided through the channel.

In an embodiment of the invention, the method comprises configuring a channel remaining in the stack after removing the filament for guiding one of acoustic waves (such as sound), electromagnetic high-frequency waves (for instance microwaves), and visible electromagnetic waves (i.e. visible light) along the channel. For instance, the interior end of the channel may then be connected with a movable membrane of an acoustic element (such as a microphone or a loudspeaker). Also high-frequency components (for instance for microwave applications) may be connected to an acoustic hollow space which may be formed with the filament based channel. Also light may propagate through the channel, for instance in terms of an optoelectronic application.

In an embodiment of the invention, a surface of the filament in contact with the stack is non-adhesive with regard to the material of the stack. For instance, the filament may comprise a core covered with a coating made of a material having poorly adhesive properties with regard to surrounding material of the stack. For instance, this may be accomplished by forming a surface of the filament of a non-adhesive material such as a waxy material. It is also possible that the entire filament consists of material having poor adhesion properties with regard to surrounding material of the stack. For instance, this may be accomplished by manufacturing the filament of a non-adhesive material such as polytetrafluoroethylene. By taking this measure, it may be simplified to remove the filament out of the component carrier without the risk of tearing.

In an embodiment of the invention, the method comprises promoting removal of the filament out of the stack by at least one of the group consisting of ultrasonic vibrations, and temperature increase. Providing ultrasonic waves in the surrounding of the component carrier with embedded filament and/or heating the mentioned arrangement to an elevated temperature has turned out to promote the removal of the filament out of the component carrier. Also by taking this measure, the risk of tearing of the filament during pulling it out from the component carrier may be strongly reduced.

In an embodiment of the invention, the method comprises forming at least one recess in at least one of the layer structures of the stack, placing the filament in the recess, and connecting the layer structures, in particular by lamination, to thereby embed the filament in the stack. When a recess is formed in the component carrier material prior to inserting the filaments therein, the trajectory of the filament may be defined with particularly high precision. Forming a cavity in the stack prior to embedding the filament therein may also be advantageous when the filament has a relatively large cross-section.

In another embodiment of the invention, the method comprises embedding the filament between opposing planar surfaces of two adjacent layer structures of the stack, in particular without previously forming a cavity in any of these two layer structures. In such a preferred embodiment, there is no need of forming a cavity in a layer structure in which the filament is embedded by lamination. Thus, the mentioned embodiment allows manufacturing a component carrier with embedded filament or with an interior hollow channel after having removed an embedded filament out of the component carrier with particularly low effort. In particular when the filament has a relatively small cross-section, such a manufacture is easily possible.

According to one embodiment of the invention, the method comprises embedding a filament in the stack, which filament comprises a core covered with a release layer being covered, in turn, by a coating. According to the claimed method, it is then possible to remove the core (optionally with the release layer) out of the stack while keeping the coating inside of the stack for lining a remaining channel in the stack. In such an embodiment, the filament comprises three distinguishable layers in a cross-section. In an interior, a core made of a material (such as steel) with high mechanical integrity and strength is provided allowing to pull out the filament without the risk of breakage. An intermediate layer may be made of release material (such as a waxy material) allowing for a mutual low frictional sliding of the interior core relative to the exterior sleeve. The exterior sleeve may be made of a material having a poor adhesion with regard to surrounding component carrier material and may include a functionality (for instance an electric, an optical, and/or a thermal function). For instance, this exterior sleeve may be made of copper (for instance to provide an electrically conductive and/or thermally conductive connection between an interior and exterior of the component carrier) or an optically highly reflective material (promoting a low loss propagation of electromagnetic radiation such as light between an interior and an exterior of the component carrier).

According to the invention, the filament is configured so as to be removable from the stack. Removal of the filament is accomplished by pulling the filament out of the stack. The material of the filament should then have a sufficient mechanical strength so as to be reliably prevented from tearing during the pulling operation.

In an embodiment of the invention, a cross-section of the filament has a shape of the group consisting of a round shape (in particular a circular shape or an elliptic shape) and a polygonal shape (in particular a triangular shape, a rectangular shape, a cross shape or a star shape). Correspondingly, a cross-section of a channel obtained by removing the filament from the component carrier may have the same shape as the assigned filament. Substantially any cross-sectional shape of the filament and of the channel is possible. However, it may be advantageous that the filament is configured so as to have a constant cross-section at least in a portion of the filament being embedded in the interior of the component carrier.

A component carrier resulting from an embodiment of the invention, the component carrier comprises an embedded sensor component in direct contact with the filament so that the sensor component is exposable towards an environment of the component carrier upon removing the filament out of the stack. Correspondingly, the embedded sensor component may be in direct contact with a channel (after having removed the filament out of the stack) so that the sensor component is exposed towards an environment of the component carrier via the channel. Examples for sensors which can be implemented according to exemplary embodiments of the invention are gas sensors, liquid sensors, humidity sensors, chemical sensors, acoustic sensors, etc. It is also possible that the filament forms part of a sensor.

In an embodiment of the invention, a thickness of the filament (and correspondingly of the channel) is in a range between <NUM> and <NUM>. For instance, the thickness of the filament or the channel may be <NUM>. Additionally or alternatively, a length of the filament (and correspondingly of the channel) in an interior of the component carrier may be in a range between0. <NUM> and <NUM>. However, other dimensions are of course possible.

In an embodiment resulting from the invention, the component carrier comprises a stack of at least one electrically insulating layer structure and at least one electrically conductive layer structure. For example, the component carrier may be a laminate of the mentioned electrically insulating layer structure(s) and electrically conductive layer structure(s), in particular formed by applying mechanical pressure, if desired supported by thermal energy. The mentioned stack may provide a plate-shaped component carrier capable of providing a large mounting surface for further components and being nevertheless very thin and compact.

In an embodiment resulting from the invention, the component carrier is shaped as a plate.

In an embodiment resulting from the present invention, the component carrier is configured as one of the group consisting of a printed circuit board, and a substrate (in particular an IC substrate).

In the context of the present application, the term "printed circuit board" (PCB) may particularly denote a component carrier (which may be plate-shaped (i.e. planar), three-dimensionally curved (for instance when manufactured using 3D printing) or which may have any other shape) which is formed by laminating several electrically conductive layer structures with several electrically insulating layer structures, for instance by applying pressure, if desired accompanied by the supply of thermal energy. As preferred materials for PCB technology, the electrically conductive layer structures are made of copper, whereas the electrically insulating layer structures may comprise resin and/or glass fibers, so-called prepreg or FR4 material. The various electrically conductive layer structures may be connected to one another in a desired way by forming through-holes through the laminate, for instance by laser drilling or mechanical drilling, and by filling them with electrically conductive material (in particular copper), thereby forming vias as through-hole connections. Apart from one or more components which may be embedded in a printed circuit board, a printed circuit board is usually configured for accommodating one or more components on one or both opposing surfaces of the plate-shaped printed circuit board. They may be connected to the respective main surface by soldering. A dielectric part of a PCB may be composed of resin with reinforcing fibers (such as glass fibers).

In the context of the present application, the term "substrate" may particularly denote a small component carrier having substantially the same size as a component (in particular an electronic component) to be mounted thereon. More specifically, a substrate can be understood as a carrier for electrical connections or electrical networks as well as component carrier comparable to a printed circuit board (PCB), however with a considerably higher density of laterally and/or vertically arranged connections. Lateral connections are for example conductive paths, whereas vertical connections may be for example drill holes. These lateral and/or vertical connections are arranged within the substrate and can be used to provide electrical and/or mechanical connections of housed components or unhoused components (such as bare dies), particularly of IC chips, with a printed circuit board or intermediate printed circuit board. Thus, the term "substrate" also includes "IC substrates". A dielectric part of a substrate may be composed of resin with reinforcing spheres (such as glass spheres).

A substrate or interposer may comprises or consist of at least a layer of glass, silicon, ceramic and/or organic material (like resin). A substrate or interposer may also comprises a photoimageable or dry-etchable organic material like epoxy-based Build-Up films or polymer compounds like Polyimide, Polybenzoxazole, or Benzocyclobutene.

In an embodiment resulting from the invention, the at least one electrically insulating layer structure comprises at least one of the group consisting of resin (such as reinforced or non-reinforced resins, for instance epoxy resin or Bismaleimide-Triazine resin, more specifically FR-<NUM> or FR-<NUM>), cyanate ester, polyphenylene derivate, glass (in particular glass fibers, glass-spheres, multilayer glass, glass-like materials), prepreg material, photoimageable dielectric material, polyimide, polyamide, liquid crystal polymer (LCP), epoxy-based Build-Up Film, polytetrafluoroethylene (Teflon), a ceramic, and a metal oxide. Reinforcing materials such as webs, fibers or spheres, for example made of glass (multilayer glass) may be used as well. Although prepreg, FR4, or epoxy-based Build-Up Film or photoimageable dielectrics are usually preferred, other materials may be used as well. For high frequency applications, high-frequency materials such as polytetrafluoroethylene, liquid crystal polymer and/or cyanate ester resins may be implemented in the component carrier as electrically insulating layer structure.

In an embodiment of the invention, the at least one electrically conductive layer structure comprises at least one of the group consisting of copper, aluminum, nickel, silver, gold, palladium, and tungsten. Although copper is usually preferred, other materials or coated versions thereof are possible as well, in particular coated with supra-conductive material such as graphene.

In an embodiment of the invention, the component carrier comprises a component embedded in the stack.

The at least one component can be selected from a group consisting of an electrically non-conductive inlay, an electrically conductive inlay (such as a metal inlay, preferably comprising copper or aluminum), a heat transfer unit (for example a heat pipe), a light guiding element (for example an optical waveguide or a light conductor connection), an electronic component, or combinations thereof. For example, the component can be an active electronic component, a passive electronic component, an electronic chip, a storage device (for instance a DRAM or another data memory), a filter, an integrated circuit, a signal processing component, a power management component, an optoelectronic interface element, a voltage converter (for example a DC/DC converter or an AC/DC converter), a cryptographic component, a transmitter and/or receiver, an electromechanical transducer, a sensor, an actuator, a microelectromechanical system (MEMS), a microprocessor, a capacitor, a resistor, an inductance, a battery, a switch, a camera, an antenna, a logic chip, and an energy harvesting unit. However, other components may be embedded in the component carrier. For example, a magnetic element can be used as a component. Such a magnetic element may be a permanent magnetic element (such as a ferromagnetic element, an antiferromagnetic element, a multiferroic element or a ferrimagnetic element, for instance a ferrite core) or may be a paramagnetic element. However, the component may also be a further component carrier (for example a printed circuit board, a substrate, or an interposer) in a board-in-board configuration. The component may be surface mounted on the component carrier and/or may be embedded in an interior thereof. Moreover, also other components, in particular those which generate and emit electromagnetic radiation and/or are sensitive with regard to electromagnetic radiation propagating from an environment, may be used as component.

In an embodiment resulting from the invention, the component carrier is a laminate-type component carrier. In such an embodiment, the component carrier is a compound of multiple layer structures which are stacked and connected together by applying a pressing force, if desired accompanied by heat.

According to an embodiment of the invention, one or more filaments are embedded in a stack of component carrier material. Subsequently removing the filament(s) by pulling it/them out from the stack may allow the formation of one or more channels or cavities in the component carrier (in particular a printed circuit board, PCB). These channels or cavities can be used for many different applications such as sensors, thermal management, antennas, etc..

By the described manufacturing architecture, it may be possible to form one or more tunnels or channels in a PCB structure in a similar way as an earthworm forms cavities in the earth. According to an embodiment of the invention, a filament or string may be used for this construction. For example, the string or filament can be made of materials such as polytetrafluoroethylene, metals, nylon, wires, etc. If the filament or string material is selected to have good adhesion to the surrounding component carrier material (in particular PCB epoxy material), then this core material of the filament can be advantageously coated with a further material (which may be denoted as release material) which does not have good or which does not have any adhesion to the epoxy material (for instance polytetrafluoroethylene, graphite (such as DLC, diamond like carbon), wax, silicon, etc.). Descriptively speaking, the filament or string then works as a temporary embedded structure in the component carrier. The filament can have substantially any cross-sectional format (for instance triangular, circular, quadrangular, or any other).

For instance after a lamination process (which may be accomplished by the supply of mechanical pressure and/or heat), the string can be pulled out of the component carrier leaving behind its cavity as in the above biomimetic example of the wormhole. For example, in order to make the release process more efficient and reliable, ultrasound vibrations and temperature increase can be applied. This can help to break the binding forces between the release layer and the epoxy material. The release process can be carried out at any time of the production of the component carrier, when the component carrier is readily manufactured or after assembly of one or more components on the component carrier.

The tunnel left behind can be formed to extend in two or three dimensions depending on how the filament or string is placed in the stack up. The tunnel can also be connected to plated through holes and/or laser drilled vias. The filament or string can also be pulled off from holes made on the surface of the component carrier.

In addition, tunnels and/or a cavity formed by the filament or string can be metallized (for instance can have copper added to its walls), for example via a galvanic copper process forming a sealed structure.

In one embodiment, the one or more cavities made in the component carrier may extend straight or linear. Techniques with wax may be applied where the hole is formed in the component carrier. A releasing procedure and the freeing of the cavity can be done at the final stage where the component carriers are already cut out of the production panel format.

Thus, exemplary embodiments of the invention may make it possible to build channels and cavities in the component carrier in any possible format. Advantageously, such a channel can be formed at any production stage of the component carrier. When pulled, the string or filament does not leave any rests in the cavity. To further reduce the effort, one single string or filament can produce the cavity for many different component carriers of a panel.

In an embodiment, the string or filament can be made of extremely resistant material such as nylon. Another possibility is to use extremely fine strings to produce microscopic channels.

Exemplary embodiments may also enable active cooling directly in the component carrier via the construction of one or more channels. Other exemplary embodiments of the invention may also allow the construction of sensor platforms in an interior of the component carrier. The cavity formed using such an embedded filament may contribute to the sensor function.

<FIG> illustrates a cross-sectional view of a pre-form of a component carrier <NUM> having a filament <NUM> to be embedded in a cavity or recess <NUM> according to an intermediate stage of an embodiment of the invention. The cross-sectional view of <FIG> illustrates the pre-form of the component carrier <NUM> before lamination.

In the shown embodiment, the component carrier <NUM> is embodied as printed circuit board (PCB). The component carrier <NUM> according to <FIG> comprises a layer stack <NUM> - which is to be connected by lamination - composed of multiple electrically conductive layer structures <NUM> and multiple electrically insulating layer structures <NUM>.

The electrically conductive layer structures <NUM> may comprise patterned metal layers (such as plated copper and/or patterned copper foils, etc.) and metallic vertical interconnects (not shown in <FIG>). The vertical interconnects may be formed, for example, by mechanically drilling and/or laser drilling. Correspondingly formed drill holes may then be at least partially filled with electrically conductive material (for instance copper), for instance by a combination of electroless plating and subsequently galvanic plating. In particular, the vertical interconnects are formed by forming holes by laser drilling and subsequently electrically conducting the holes by copper plating.

The electrically insulating layer structures <NUM> may comprise laminated layers which may be made of resin (in particular of epoxy resin), optionally additionally comprising reinforcing particles (such as glass fibers or glass spheres). For instance, the electrically insulating layer structures <NUM> may be made of prepreg or resin based build-up material. The electrically insulating layer structures <NUM> also comprise a central base structure <NUM> with a cavity or recess <NUM>. The base structure <NUM> may for instance be made of a fully cured dielectric material such as FR4. The layer structures <NUM>, <NUM> may be connected by lamination to thereby embed the filament <NUM> in the stack <NUM>. Descriptively speaking, <FIG> illustrates a PCB build-up before lamination.

As shown in <FIG>, the filament <NUM> (extending in a direction perpendicular to the paper plane of <FIG>) with a circular cross-section is embedded in the stack <NUM>. The filament <NUM> may be made of material having poor adhesion properties with regard to surrounding material of the stack <NUM>. For instance, the filament <NUM> may be made of steel so that the filament <NUM> is mechanically strong enabling to be subsequently pulled out of the rest of the component carrier <NUM>. In a corresponding embodiment, a cavity shall be formed at the position of the filament <NUM> by removing the latter from the stack <NUM>. In the shown embodiment, a cross-section of the filament <NUM> has a circular shape. A thickness or diameter, D, of the filament <NUM> may be for example <NUM>. A length of the filament <NUM> in a direction perpendicular to the paper plane of <FIG> may be for example <NUM>. Although not shown in <FIG>, an end of the filament <NUM> may extend beyond or out of the stack <NUM> so as to allow pulling out the filament <NUM> after its embedding out of the stack <NUM>.

As shown in <FIG>, the filament <NUM> may be sandwiched between upper and lower continuous planar sheets of the electrically insulating layer structures <NUM> (for instance made of an uncured material such as prepreg) and may be accommodated in a central through hole of the central base structure <NUM> (for instance made of a cured material such as FR4). Such a procedure may be advantageous when the filament <NUM> has a high thickness or diameter D.

<FIG> illustrates a cross-sectional view of a component carrier <NUM> having a filament <NUM> embedded between planar layers <NUM>, <NUM> according to an intermediate stage of an embodiment of the invention.

In the embodiment of <FIG>, it may be possible to sandwich the filament <NUM> directly between two opposing planar surfaces (not shown) of two adjacent layer structures <NUM> (for instance made of an uncured material such as prepreg) of the stack <NUM> without previously forming a recess <NUM> in any of these two layer structures <NUM>. In other words, the central base structure <NUM> shown in <FIG> may be omitted according to <FIG>. Such an approach allows to particularly simplify manufacture of the component carrier <NUM> without the need of forming through holes prior to embedding the filament <NUM>, and may be particularly appropriate when the filament <NUM> has a relatively small thickness or diameter D.

In the shown embodiment, the filament <NUM> comprises a cylindrical core <NUM> (for instance made of steel) covered with a hollow cylindrical coating <NUM> made of a material (for instance polytetrafluoroethylene) having poorly adhesive properties with regard to surrounding material of the stack <NUM>. By taking this measure, the filament <NUM> is properly configured so as to be removable from the stack <NUM> by pulling the filament <NUM> out of the stack <NUM> without the risk of tearing of the core <NUM>. A channel <NUM> (not shown in <FIG>, see however <FIG>) may then be formed in the stack <NUM>.

Hence, <FIG> shows a PCB build-up after lamination.

In an example not belonging to the invention, the filament <NUM> may be directly adjacent to one or both of the layers <NUM>. This may allow to directly remove heat on copper layers, so that the filament <NUM> may be used for example for water cooling.

<FIG> illustrates a three dimensionally curved filament <NUM> embedded in a component carrier <NUM> according to an intermediate stage of an embodiment of the invention. According to <FIG>, the filament <NUM> has been embedded in the stack <NUM> so as to form a two-dimensional trajectory within a plane perpendicular to a stacking direction of layer structures <NUM>, <NUM> of the stack <NUM>. Since ends <NUM> of the filament <NUM> extend beyond side walls of the component carrier <NUM>, it is possible to pull (in particular manually or machine supported) the filament <NUM> out of the component carrier <NUM> so as to form a correspondingly shaped planar channel <NUM> (see <FIG>) in an interior of the component carrier <NUM>.

<FIG> illustrates a cross-sectional image of a component carrier <NUM> having a channel <NUM> formed by embedding and subsequently removing a filament <NUM> (not shown in <FIG>) in the component carrier <NUM> resulting from an embodiment of the invention.

More precisely, <FIG> shows an image of an actually manufactured printed circuit board (PCB) with an approximately <NUM> diameter thick and approximately <NUM> long hollow channel <NUM>. Thus, <FIG> shows the picture of a real prototype manufactured in the laboratory. A slot or recess <NUM> was built in a thick PCB core as base structure <NUM>. A wire for microelectronics purposes coated with silicon spray was placed as a filament <NUM> in the cavity or recess <NUM> to build the tunnel. In a subsequent procedure, the slot was filled with epoxy material. The structure was placed in an oven at <NUM> for <NUM> minutes for curing. After curing, the filament <NUM> was pulled from the rest of the component carrier <NUM>, and the hollow channel <NUM> was obtained. If desired or required, removal of the filament <NUM> out of the stack <NUM> may be promoted by ultrasonic vibrations and/or temperature increase.

<FIG> illustrates a cross-sectional image of a component carrier <NUM> having a channel <NUM> lined with a tubular coating <NUM> resulting from an embodiment of the invention. The channel <NUM> with the coating <NUM> is embodied as a copper coated tunnel.

Thus, the shown component carrier <NUM> has a (in particular hollow) channel <NUM> with constant circular cross-section in the stack <NUM>. A sidewall of the channel <NUM> is lined with an electrically conductive and thermally conductive copper coating <NUM>. Descriptively speaking, the coating <NUM> delimiting channel <NUM> may form an in-plane plated through hole.

After embedding a filament <NUM> with the coating <NUM> in the stack <NUM> (in particular using a construction of the filament <NUM> as shown in <FIG> as described below), the component carrier <NUM> shown in <FIG> may be formed by removing a core <NUM> of the filament <NUM> from the stack <NUM> by pulling the core <NUM> of the filament <NUM> out of the stack <NUM>. When the core <NUM> of the filament <NUM> is removed out of the channel <NUM>, the coating <NUM> may remain inside the channel <NUM> and may delimit the channel <NUM>. As an alternative manufacturing method, it may be also possible to remove the entire filament <NUM> after embedding the same in the stack <NUM> and to subsequently cover exposed walls of the channel <NUM> by the copper coating <NUM>.

<FIG> illustrates a cross-sectional image of a component carrier <NUM> having a channel <NUM> lined with a tubular coating <NUM> and composed of multiple connected channel sections (see reference numeral <NUM>) extending horizontally and vertically through the component carrier <NUM> resulting from an embodiment of the invention.

<FIG> shows an example of ducts for water cooling of the component carrier <NUM>. As indicated by arrows <NUM>, water or any other liquid or gaseous cooling medium may be guided through the channel <NUM> for removing heat out of an interior of the component carrier <NUM> during operation.

<FIG> illustrates a component carrier <NUM> of the type shown in <FIG> and being usable as ducts for high-frequency or acoustic applications. One or more components <NUM> may be embedded in the component carrier <NUM> and/or may be externally connected to the component carrier <NUM>. The components <NUM> may be for instance sensor components and/or actuator components for applications such as LIFI (light fidelity), WIFI/WLAN (wireless local area network), acoustic applications (for instance for a microphone function or a loudspeaker function), etc. For instance, the channel <NUM> may be used for the propagation of high-frequency signals, acoustic signals or a resonator function. In particular, the channel <NUM> formed in the stack <NUM> by removing the filament <NUM> may be configured as an acoustic resonator recess.

<FIG> illustrates a component carrier <NUM> of the type shown in <FIG> and being usable for a gas sensor application.

An embedded sensor component <NUM> is provided in direct contact with the channel <NUM> defined by the meanwhile removed filament <NUM> so that the sensor component <NUM> is exposed towards an environment of the component carrier <NUM> via the channel <NUM> upon removing the filament <NUM> out of the stack <NUM>. <FIG> relates to the example of a duct (in form of channel <NUM>) for gas sensing by gas sensor component <NUM>.

<FIG> illustrate cross-sectional views of component carriers <NUM> with channels <NUM> formed by removing previously embedded filaments <NUM> according to embodiments of the invention. In the embodiment of <FIG>, a copper-lined (see coating <NUM>) channel <NUM> with plus-shape is shown. In the embodiment of <FIG>, a copper-lined (see coating <NUM>) channel <NUM> with arc-shape is shown. In the embodiment of <FIG>, a copper-lined (see coating <NUM>) channel <NUM> with cross-shape is shown. In the embodiment of <FIG>, a copper-lined (see coating <NUM>) channel <NUM> with trapezoid-shape is shown. In the embodiment of <FIG>, a channel <NUM> with star-shape is shown. In the embodiment of <FIG>, a channel <NUM> with oval shape is shown. Many other cross-sectional shapes (for instance a triangular shape) are possible, wherein the respective cross-sectional shape may be selected in accordance with a certain application or function of the component carrier <NUM>. For instance, when the filament <NUM> forms an embedded heat pipe, a triangular cross-section may be advantageous so that evaporated medium may flow along one or more corners of the triangle.

<FIG> illustrate cross-sectional views of component carriers <NUM> resulting from embodiments of the invention with embedded component(s) <NUM> and a channel <NUM> (formed by removing a previously embedded filament <NUM> from the component carrier <NUM>) based water or air cooling of such components <NUM>. A skilled person will understand that water or air cooling may be substituted by cooling using another cooling medium, for instance a liquid gas.

In the embodiment of <FIG>, component <NUM> (for instance a semiconductor die such as a microprocessor) may be embedded in the stack <NUM> or placed on the surface of the build-up. According to <FIG>, two components <NUM> (for instance two semiconductor dies such as a microprocessor and a memory) are embedded in the stack <NUM> or placed on the surface of the build-up. During operation of the respective component carrier <NUM>, a substantial amount of heat may be generated by the component(s) <NUM>. By the coiled (see <FIG>) or meandrous (see <FIG>) configuration of the channel <NUM> in the region of the respective components(s) <NUM>, a cooling medium guided through the channel <NUM> may efficiently cooling the respective component(s) <NUM>.

As an alternative to the configuration of <FIG>, it is also possible to produce the filament <NUM> of a thermally highly conductive material (such as copper or aluminum) and to dimension the filament <NUM> sufficiently large so that the thermal coupling of the respective filament <NUM> with the component(s) <NUM> allows removing heat generated during operation of the component carrier <NUM> away from the component(s) <NUM>. In such an embodiment, the filament <NUM> itself serves as heat removing structure for cooling the components <NUM>.

<FIG> illustrates a cross-sectional view of a component carrier <NUM> with filament <NUM>-based wiring structure forming an inductor for a wireless charging application according to an example not belonging to the invention, in particular the filament <NUM> made of an electrically conductive material such as copper. In view of the wound configuration of the filament <NUM> according to <FIG>, the filament <NUM> fulfils an inductor function. Although not shown in <FIG>, the coiled type inductor formed by the filament <NUM> may be accompanied with a magnetic core (for instance made of a ferrite), which can be embedded in the component carrier <NUM> as an embedded component <NUM>. Alternatively, a filament <NUM>-based antenna structure embedded in a component carrier <NUM> may be formed in a corresponding way as shown in <FIG>.

Alternatively, according to an embodiment of the present invention, it is possible to remove a dummy filament <NUM> out of the component carrier <NUM> to thereby maintain a channel <NUM> with coiled shape. It may then be possible to subsequently filling such a channel <NUM> remaining in the stack <NUM> after removing the filament <NUM> with electrically conductive material to thereby form an inductor structure or an antenna structure.

<FIG> illustrates a cross-sectional view of a component carrier <NUM> with horizontal channel <NUM> resulting from an embodiment of the invention.

The (in particular hollow) channel <NUM> is coated with an electrically conductive coating <NUM>, for instance made of copper. The channel <NUM> is formed by embedding a filament <NUM> in the component carrier <NUM> and subsequently removing the filament <NUM>.

As can be taken from <FIG>, the coating <NUM> may be connected to one or more electrically conductive layer structures <NUM> of the (for instance PCB-type) component carrier <NUM>. <FIG> in particular shows, as electrically conductive layer structures <NUM>, vertical interconnect structures (in particular copper filled mechanically drilled through holes and copper filled laser drilled through holes) and patterned copper foils. The electrically conductive layer structures <NUM> configured as (in particular laser and/or mechanically drilled) vias may function to electrically and/or thermally connect the PCB-type component carrier <NUM>.

<FIG> illustrates a cross-sectional view of a component carrier <NUM> with a channel <NUM> having multiple section extending horizontally (see reference numeral <NUM>), vertically (see reference numeral <NUM>) and slanted (see reference numeral <NUM>) resulting from an embodiment of the invention.

The structure according to <FIG> shows an embedded filament <NUM> in the stack <NUM> which is bent along a three-dimensional trajectory in the stack <NUM>. Different sections of the filament <NUM> have different angles Φ, φ, etc. with regard to a vertical direction (in other words, Φ, φ may denote the respective cavity angle towards the surface normal). Referring to <FIG>, the orientation of the filament <NUM> may be selected to reach one or more predefined constraints such as Φ≠φ, <NUM>≤Φ≤π, etc. After having removed the filament <NUM> out of the component carrier <NUM>, a three-dimensionally curved cavity or channel <NUM> maintains.

<FIG> illustrates a cross-sectional view (parallel to an extension direction of a filament <NUM>) of a component carrier <NUM> with a shielded channel <NUM> resulting from an embodiment of the invention. <FIG> illustrates a cross-sectional view of a filament <NUM> (wherein an extension direction of the filament <NUM> is perpendicular to the paper plane of <FIG>) used in an embodiment of the invention, which can be used advantageously for the embodiment of <FIG>.

<FIG> shows a filament <NUM> used an embodiment of the invention, in which a longitudinally central portion of the filament <NUM> has a coating <NUM> of copper. Between a core <NUM> and the coating <NUM> of the filament <NUM>, a release layer <NUM> is sandwiched which is non-adhesive. Thus, the core <NUM> of the filament <NUM> is covered with the release layer <NUM> being covered, in turn, by the copper coating <NUM>. As a result, when removing the core <NUM> with the release layer <NUM> out of the stack <NUM> by pulling along pulling direction <NUM>, the coating <NUM> maintains inside of the stack <NUM> for lining the remaining channel <NUM> in the stack <NUM>. By such a procedure, a shielded cavity may be formed by channel <NUM> surrounded by the copper coating <NUM>.

<FIG> illustrates a cross-sectional view of an electrically conductive filament <NUM> electrically and mechanically connected to one or more pads <NUM> of a component <NUM> according to an example not belonging to the present invention. As shown, the component <NUM> and the filament <NUM> are preassembled before embedding them in a stack <NUM> of the component carrier <NUM>.

According to <FIG>, the electrically conductive filament <NUM> is electrically coupled with one or more pads <NUM> of the component <NUM> so as to transfer electric signals and/or electric energy between the component <NUM> and an exterior of the component carrier <NUM>. When the component <NUM> with already electrically connected filament <NUM> is embedded in the stack <NUM> (without previous cavity formation according to <FIG> or with previous cavity formation, see recess <NUM> in <FIG>), a complicated subsequent electric contacting of the component <NUM> may be omitted.

Claim 1:
A method of manufacturing a component carrier (<NUM>), wherein the method comprises:
forming a stack (<NUM>) comprising at least one electrically insulating layer structure (<NUM>) and at least one electrically conductive layer structure (<NUM>), wherein the at least one electrically insulating layer structure (<NUM>) comprises a reinforced resin or a non-reinforced resin, in particular epoxy resin;
embedding a filament (<NUM>) in the stack (<NUM>); and
removing at least part of the filament (<NUM>) from the stack (<NUM>) by pulling the filament (<NUM>) out of the stack (<NUM>) comprising the cured reinforced or non-reinforced resin; wherein
the filament (<NUM>) is made or is coated with a material having a low adhesion to the epoxy material; or
the filament (<NUM>) comprises a core (<NUM>) covered with a release layer (<NUM>) being covered, in turn, by a coating (<NUM>), so that while removing the core (<NUM>) out of the stack (<NUM>) the coating (<NUM>) is kept inside of the stack (<NUM>) for lining a remaining channel (<NUM>) in the stack (<NUM>) with the coating (<NUM>).