Multi-layer printed circuit board comprising a through connection for high frequency applications

A high frequency multi-layer printed circuit board, according to the present invention, comprises a through connection having an impedance adapting structure surrounding the through connection and enabling an adjustment of the characteristic impedance of the through connection to a desired value. Thus, high frequency signals may be led through the printed circuit board with reduced signal deformation. The high frequency multi-layer printed circuit board is applicable for high frequency signals up to the GHz-range.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of connecting techniques for high frequency devices, and, more particularly, to a through connection for multi-layer printed circuit boards for high frequency applications.

2. Description of the Related Art

As semiconductor manufacturers continue to scale down on-chip features, the on-chip operating frequencies of those reduced size features may be accordingly increased, due substantially to reduced parasitic device capacitances. While, some applications, for example, state of the art microprocessors, may be driven with an on-chip operating frequency (clock rate) that may be higher than the input/output frequency, other applications, for example, high frequency transmitter and receiver devices, e.g., for wireless local area networks (WLANs) or mobile phones, may need to input/output high frequency signals in the GHz-range. For example, a WLAN transceiver may supply/receive a 2.4 GHz-signal to/from a connected antenna that may, for instance, be printed on a common substrate. Typically, integrated circuit die are mounted on a substrate and connected to other devices by conduction lines formed on an elaborate multi-layer substrate. In particular, connections for high frequency signals of more than 300 MHz are subjected to certain constraints with respect to the employed substrate materials and the line design and may be formed, for example, by microstrip lines to provide connection lines with a controlled impedance. Conventional through connections, however, may cause signal reflection and attenuation of high frequency signals, in particular in the GHz range.

On the other hand, as a general rule, scaled features enable increased functionality at a maintained die size, or a reduced die size at a maintained functionality. In both cases, however, the density of inputs and outputs (I/Os) on the die is increased. For a conventional peripheral bond pad arrangement, the resulting bond pad pitch (the distance between the centers of two adjacent bond pads) is accordingly reduced. Thus, bonding of die of advanced integrated circuits, in particular for high frequency integrated circuits, is a challenge for manufacturers of electronic components. Typically, integrated circuit devices are mounted on a substrate and the contact pads of the device are connected to corresponding pads on the substrate by wire bonding, tape automated bonding (TAB) or flip chip bonding techniques.

Contrary to wire bonding and TAB, flip chip bonding is not restricted to the employment of peripheral bond pads. The flip chip technology, however, requires an equal bump pitch on the die and on the substrate to which the die is to be bonded. The minimal bump pitch achievable on a substrate depends on the carrier material and on the corresponding available technology. In general, bond pad redistribution is required to provide reliable and cost-efficient components. Consequently, semiconductor manufacturers arrange the bond pads in two or more rows disposed in the peripheral region of the chip area (peripheral array), or redistribute the peripheral bond pads over the entire chip area (area array) to allow for a higher bond pad pitch. For high frequency integrated circuits, die with on-die redistribution of bump pads and chip carriers providing the required functionality are, in general, not available.

As a high frequency chip carrier material may be employed, for example, ceramic, polyimide or flame-retardant fiberglass epoxy laminate (FR4). In large-scale production, FR4 is, in spite of the poor material properties (high dielectric constant, high loss angle), even for high frequency applications, a widely used material for its economical benefits. Through connections formed with conventional FR4 printed circuit board (PCB) technologies, however, may cause undue high frequency signal deformation.

In view of the above-mentioned problems, there exists a need for an improved connection technique for devices in high frequency applications.

SUMMARY OF THE INVENTION

According to one illustrative embodiment of the present invention, a high frequency multi-layer printed circuit board is provided. The printed circuit board comprises a layer stack comprising a first metal-comprising layer, a second metal-comprising layer and at least one dielectric layer separating the first and second metal-comprising layers. The printed circuit board further comprises a transition structure comprising a through connection extending from the first metal-comprising layer through the at least one dielectric layer to the second metal-comprising layer, and an impedance adapting structure surrounding the through connection at least partially and providing a characteristic impedance of the transition structure, the characteristic impedance being adapted to a desired impedance value.

In accordance with another illustrative embodiment of the present invention, a high frequency multi-layer printed circuit board comprising a layer stack comprising a first metal-comprising layer, a second metal-comprising layer and at least one dielectric layer separating the first and second metal-comprising layers is provided. The printed circuit board further comprises a transition structure comprising a through connection extending from the first metal-comprising layer through the at least one dielectric layer to the second metal-comprising layer and an impedance adapting structure formed in the first and second metal-comprising layers, wherein the first and second metal-comprising layers comprise substantially concentric metal-free regions surrounded by metal-containing regions, the metal-free regions being substantially coaxially aligned to the through connection and having a diameter being adapted to a desired value of the characteristic impedance of the transition structure.

In accordance with yet another illustrative embodiment of the present invention, a high frequency multi-layer printed circuit board comprising a layer stack comprising a first metal-comprising layer and a second metal-comprising layer, at least one metal-comprising inner layer disposed between the first and second metal-comprising layers, and at least two dielectric layers separating the metal-comprising layers is provided. The printed circuit board further comprises a transition structure comprising a through connection extending from the first metal-comprising layer through the at least one metal-comprising inner layer and the at least two dielectric layers to the second metal-comprising layer, and an impedance adapting structure formed in the inner metal-comprising layer, wherein the inner metal-comprising layer comprises a substantially concentric metal-free region surrounded by a metal-containing region, the metal-free region being substantially coaxially aligned to the through connection and having a diameter being adapted to a desired value of the characteristic impedance of the transition structure.

In accordance with still another illustrative embodiment of the present invention, a high frequency multi-layer printed circuit board comprising a layer stack comprising a first metal-comprising layer and a second metal-comprising layer, at least two metal-comprising inner layers disposed between the first and second metal-comprising layers, and at least three dielectric layers separating the metal-comprising layers is provided. The printed circuit board further comprises a transition structure comprising a through connection extending from the first metal-comprising layer through the at least two metal-comprising inner layers and the at least three dielectric layers to the second metal-comprising layer, and an impedance adapting structure connecting at least two of the at least two metal-comprising inner layers conductively by a plurality of coaxial vias arranged on a substantially circular line substantially coaxially aligned with the through connection.

In accordance with a further illustrative embodiment of the present invention, a high frequency device is provided. The device comprises an integrated high frequency circuit die comprising a high frequency terminal and a high frequency multi-layer printed circuit board comprising a transition structure, wherein the integrated high frequency circuit die is mounted on the high frequency multi-layer printed circuit board and the high frequency terminal is connected to the transition structure, wherein the transition structure comprises a through connection and an impedance adapting structure.

In accordance with still a further illustrative embodiment of the present invention, a method of manufacturing a high frequency multi-layer printed circuit board is provided. The method comprises choosing a desired impedance value and forming a layer stack comprising at least a first metal-comprising layer and a second metal-comprising layer and at least one dielectric layer separating the first and second metal-comprising layers. The method further comprises forming a through connection extending from the first metal-comprising layer through the at least one dielectric layer to the second metal-comprising layer, and forming an impedance adapting structure surrounding the through connection at least partially and adapting therewith the characteristic impedance of a transition structure to the desired impedance value, wherein the transition structure is comprised of the through connection and the impedance adapting structure.

DETAILED DESCRIPTION OF THE INVENTION

Furthermore, the used geometric terms such as concentric, circular and coaxial relate to features which may not necessarily exhibit a precise geometric accuracy. The actual shape of the corresponding features may diverge from the precise geometric shape unless the functionality of the features is not unduly affected, for example, due to manufacturing tolerances.

With reference toFIGS. 1a,1b,2,3a,3b,4,5a,5b,6a,6b,7aand7b, further illustrative embodiments of the present invention will now be described in more detail, wherein similar or identical components are denoted by the same reference numeral except for the first digit, which is selected in correspondence with the number of the respective figure.

FIG. 1aschematically represents a plan view andFIG. 1bdepicts a sectional view of an embodiment of a high frequency multi-layer printed circuit board100comprising a layer stack110and a transition structure108. The layer stack110comprises a first metal-comprising layer103, a second metal-comprising layer105and at least one dielectric layer102. The transition structure108is comprised of an impedance adapting structure106, a through connection104, a dielectric material region132and pads109.

The high frequency multi-layer printed circuit board100may be formed by laminating a layer stack110by conventional multi-layer PCB techniques. The first and second metal-comprising layers103,105may, for example, comprise copper, gold or aluminum, and may have a thickness in the range of approximately 5-200 μm. The copper-comprising layer may be coated by a passivation layer (not shown) comprising, for example, gold, nickel, tin, lead, or a combination thereof. The thickness of the passivation layer may be in the range of approximately 50 nm to 20 μm. The at least one dielectric layer102may comprise any dielectric material appropriate for high frequency applications, such as, for example, FR4, polymers, such as, e.g., liquid crystal polymer (LCP), polytetrafluorethylen (PTFE), or polyimide and ceramics, such as alumna (Al2O3) or aluminum nitride (AlN). The thickness of the dielectric layer102is in the range of approximately 0.1-2 mm. The dielectric constant (∈r) of the employed dielectric materials, determining the velocity of propagation of an electromagnetic wave in the dielectric material, is in the range of approximately 2-10, wherein a lower dielectric constant corresponds to a higher velocity of propagation and, hence, to a greater wavelength. The loss angle of the used dielectric materials, influencing the attenuation of a high frequency wave propagating in the dielectric material, is in the range of approximately 0.001-0.1.

The transition structure108is formed in the multi-layer printed circuit board100. A hole112is formed in the layer stack110, for example, by well-known mechanical or laser-based techniques or by etching. Subsequently, the walls of the hole are plated by well-established plating technologies to form the impedance adapting structure106. The total thickness of the plated layer is in the range of approximately 5-50 μm. It is to be noted that at high frequencies, due to the skin effect, the current may be concentrated to a surface sub-layer (not shown) with a thickness of only several Em. Thus, a thin plated layer may be sufficient for the transition structure108in high frequency applications. As a next step, the hole comprising the plated layer forming the impedance adapting structure106is filled by a dielectric material132. The material132may by the same as the dielectric material102or may comprise an alternative material with an appropriate electrical characteristic. Subsequently, an inner hole116is formed that is substantially coaxially aligned with the impedance adapting structure106, by mechanical or laser-based techniques or by etching to form the through connection104therein. The plating technologies employed to form the impedance adapting structure106may also be applied to form a plated layer at the wall of the inner hole116forming the through connection104. Since, due to the skin effect, the current in the through connection104is concentrated to a thin outer sub-layer (not shown), an inner portion (not shown) of the through connection104may be filled by a dielectric material, if desired, without a substantial increase of an electrical resistance exerted to high frequency signals.

The diameters113,111of the impedance adapting structure106and of the through connection104are adapted to a desired impedance value, for example, to the input/output impedance of a connected transceiver and/or a connected microstrip line. The desired impedance value is in the range of approximately 10-300Ω and in a specific embodiment approximately 50Ω. The characteristic impedance of a substantially coaxial structure depends on the dielectric constant (∈r) of the material132and on the ratio of an outer diameter111(d2) of the through connection104and an inner diameter113(d1) of the impedance adapting structure106(Z0≈60/∈r1/2×ln(d1/d2)). Thus, the impedance of the transition structure108may be adapted to a desired impedance value by choosing the material132and/or by choosing the ratio of the diameters111and113. For a dielectric constant (∈r) of 4 (e.g., FR4 material) and a characteristic impedance in the range of 10-300Ω, the ratio of the diameters111and113is in the range of approximately 1.5 to 22,000. For the impedance value of 50Ω and a dielectric constant (∈r) in the range of 2-10, the ratio of the diameters111and113is in the range of approximately 3.2 to 14. In a specific embodiment, the dielectric constant (∈r) is approximately 4 and the characteristic impedance is approximately 50Ω, and the resulting ratio of the diameters111and113is approximately 8.8. In a further embodiment, the geometrical parameters of the transition structure108may be determined by well-known 3D-electromagnetic-field-simulation techniques, for example, by finite element methods, to account for additional effects of connected structures, for example, of a bump structure (not shown) or of a transition (not shown) to a microstrip line.

FIG. 2schematically represents a sectional view of a high frequency device250in accordance with an illustrative embodiment of the present invention. A high frequency integrated circuit die220comprising bond pads226is bonded onto a high frequency multi-layer printed circuit board200by bonds222. The multi-layer printed circuit board200comprises first and second metal-comprising layers203,205, a dielectric layer202, bond pads224, conductive connection lines214, and a transition structure208. The transition structure208comprises a through connection204and an impedance adapting structure206.

The multi-layer printed circuit board200and the transition structure208may be formed as set forth with respect toFIGS. 1aand1b. The bond pads224,209are formed in the first and second metal-comprising layers203,205of the multi-layer printed circuit board200by well-established multi-layer PCB technologies. The through connection204of the transition structure208is in contact with the bond pads209so that a high frequency signal from the integrated circuit die220may be conducted through the respective bond222and the through connection204to a component (not shown) disposed on the opposite side of the multi-layer printed circuit board200. The bonds222depicted inFIG. 2show bump bonds but may, in another embodiment, comprise TAB-bonds or wire bonds. In a further embodiment, the multi-layer printed circuit board200may be employed as a chip carrier for one or more die including at least one high frequency integrated circuit. In particular, for flip chip bonded die, the chip carrier may serve to redistribute, for example, a dense peripheral bond pad arrangement to a wider spread array bond pad arrangement even when high frequency terminals are involved. Thus, small chip carriers comprising an elaborate fine-pitch layout may be mounted on large PCBs (not shown) to mitigate the layout requirements of large main boards (not shown) to reduce the overall manufacturing costs of electronic components. On the main board may be mounted additional components requiring only a coarse-pitch layout, for example, key pads, passive devices, antennas, etc. Thus, in corresponding applications, low cost FR4 PCBs may be employed for the main boards. In one embodiment utilizing the transition structure208, even the high frequency chip carrier may be manufactured of FR4 material providing a cost-effective high frequency chip carrier for large-scale production. The chip carrier may be mounted on the main board by a bump bond process or by a readily unlockable plug and socket connection.

FIG. 3arepresents a plan view andFIG. 3ba sectional view of a multi-layer printed circuit board300comprising a further embodiment of a transition structure308according to the present invention. The multi-layer printed circuit board300comprises a layer stack310comprising a first metal-comprising layer303and a second metal-comprising layer305, two metal-comprising inner layers307disposed between the first and second metal-comprising layers303,305, and three dielectric layers302separating the metal-comprising layers303,305,307. The transition structure308comprises a through connection304, and a impedance adapting structure306. The impedance adapting structure306comprises eight coaxial vias344, and metal-containing regions342,346substantially coaxially aligned to the through connection304.

The multi-layer printed circuit board300is formed by well-established multi-layer PCB techniques, wherein, as a first step, the two metal-comprising inner layers307are patterned to form the metal-containing regions346. The ratio of an inner diameter313of the metal-containing regions346and an outer diameter311of the through connection304may be determined as set forth with respect to the transition structure108ofFIG. 1in analogy to the described coaxial embodiment or by calculations based on electromagnet field simulations. The coaxial vias344are arranged on a substantially circular line318which is substantially coaxially aligned with the through connection304to be formed subsequently. The diameter317of the circular line318is also determined with respect to the impedance of the transition structure308. In one embodiment, the coaxial vias344may be disposed on the substantially circular line so that the innermost portions of the vias344are tangent to a circle with the diameter313. The two metal-containing regions346are conductively connected by the coaxial vias344. After the layer stack comprising the two metal-comprising inner layers307is completed, the first and second metal-comprising layers303,305are laminated on the opposite sides of the inner layer stack each separated by one of the dielectric layers302, respectively. The first and second metal-comprising layers are patterned by well-known PCB patterning processes. In these layers303,305, the metal-containing regions342are provided corresponding to the metal-containing regions346to form a part of the impedance adapting structure306. The outer boundaries (not shown) of the metal-containing regions346,342do not substantially affect the impedance of the transition structure308and may, for instance, be arbitrarily defined as long as the shape is in accordance with the design rules of the employed PCB technology. The metal-containing regions342,346and coaxial vias344of the impedance adapting structure306commonly provide impedance adjusting functionality comparable to the impedance adapting structure106described with respect toFIGS. 1aand1b.

The through connection304extending from the first metal-comprising layer303through the two metal-comprising inner layers307and the three dielectric layers302to the second metal-comprising layer305is formed by well-known multi-layer PCB technologies. Pads309may be formed on the first and second metal-comprising layers303,305to allow for a reliable connection of the through connection304. The through connection304may be connected directly by die bonds such as, for example, bump bonds370or wire bonds (not shown). In another embodiment, the through connection304may be connected by conduction lines having a defined impedance, such as, for instance, microstrip lines (not shown). The connection may further comprise balun transformers (not shown) to meet symmetry requirements.

In the depicted embodiment, eight coaxial vias344are approximately equidistantly arranged on the substantially circular line318. In another embodiment, a different number of coaxial vias344, for example, six or twelve coaxial vias344may be arranged on the circular line318. In a further embodiment, the impedance adapting structure306may be connected to the ground potential.

FIG. 4represents a sectional view of a specific embodiment of a multi-layer high frequency PCB400comprising a high frequency transition structure408as is indicated as structure308inFIGS. 3aand3b, wherein the layout is adapted to currently achievable FR4-PCB design rules. The multi-layer high frequency PCB400comprises, in addition to the transition structure408, a first metal-containing outer layer448and a second metal-containing outer layer449, each separated by an outer dielectric layer423, two outer vias464, two microstrip lines462and bond pads458.FIG. 4further depicts bump bonds470,452and a main board456and a part of a die420bonded to the PCB400.

The through connection404of the transition structure408is at one side connected to a bond pad459of a high frequency terminal of the die420and at the opposite side to a bond pad455of the main board456. The connection is effected by the outer vias464and the microstrip lines462. The microstrip lines462are designed by well-known design rules taking into account the width and thickness of the line and its distance to the adjacent ground layer. In a further embodiment, the bump bonds452connecting the main board456and/or the bump bonds470connecting the die420may be directly formed on bond pads460disposed on the outer vias464and the microstrip lines may be omitted. The impedance adjustment may be performed as set forth with respect to the impedance adapting structure306ofFIGS. 3aand3bby using the coaxial line approach or by electromagnetic field simulation. The simulation may further take the influence of the outer vias464and/or of the bump bonds450,452into account.

In one embodiment of the multi-layer PCB400, the metal-comprising layers403,405,407,448and449comprise copper and a thickness445of the first and second metal-comprising outer layers448,449is approximately 40 μm, a thickness447of the first and second metal-comprising layers403,405is approximately 20 μm, and a thickness449of the metal-comprising inner layers407is approximately 30 μm. The dielectric layers402,423comprise flame-retardant fiberglass epoxy laminate (FR4) having a dielectric constant of approximately 4.4 at a frequency of 1 GHz. A thickness441of the dielectric layers402is approximately 100 μm and a thickness443of the dielectric outer layers423is approximately 63 μm. An outer diameter411of the through connection404is approximately 240 μm and a diameter435of the pads409is approximately 500 μm. An inner diameter413of the metal-comprising regions442,446formed in the first and second metal-comprising layers403,405,407is approximately 1090 μm. A diameter419of the substantially circular line defining the position of the eight coaxial vias444is approximately 1400 μm. A diameter466of the pads468of the coaxial vias444is approximately 500 μm and a diameter465of the through connection of the coaxial vias444is approximately 200 μm. A diameter461of the pads460of the outer vias464is approximately 250 μm and a diameter463of the through connection of the outer vias464is approximately 100 μm. A distance433between the axis of the through connection404and the axis of the outer vias464is approximately 300 μm so that the pads409of the through connection404and the pads460of the outer vias464partially overlap. A diameter453of the bump pads458is approximately 600 μm and the distance451between the centers of adjacent bump pads458is approximately 1270 μm.

The measured insertion loss of the transition structure including the outer vias464(without the attenuation caused by the microstrip lines) is approximately −0.29 dB at a signal frequency of 2.4 GHz. Calculated scattering parameters (or S-parameters) confirm the measurement results. The calculations were performed based on the material parameters κCu=5.8 S/m as the electrical conductivity of copper and tan δ=0.04 as the loss angle of FR4. The resulting input reflectance factors S11are: 0.003/−94° at 0.1 GHz; 0.050/−170° at 2.4 GHz and 0.092/64° at 6.0 GHz and a corresponding reflectance damping of approximately −52 db, −26 db and −21 db, respectively. The results for the transmission loss S12are: −0.01 db at 0.1 GHz; −0.17 db at 2.4 GHz and −0.54 db at 6.0 GHz and for the output reflectance factor S22: 0.003/−93° at 0.1 GHz; 0.047/−155° at 2.4 GHz and 0.095/83° at 6.0 GHz. The obtained results demonstrate that a multi-layer transition structure formed in an FR4 PCB by employing merely currently available standard structures may provide an appropriate impedance adaptation to transmit signals in the GHz frequency range.

For some applications, the impedance adapting structure may be simplified to increase the cost-effectiveness of the PCB manufacturing process while still providing sufficient impedance adaptability. With respect toFIGS. 5a,5b,6a,6c,7aand7b, corresponding embodiments of impedance adapting structures for high frequency multi-layer PCBs are described in the following. The simplified impedance adapting structures are designed to reduce the number of required layers of the multi-layer stack and/or to reduce the required PCB area. Combinations of the features of the different embodiments of the invention may be employed to obtain further impedance adapting structures.

FIG. 5arepresents a plan view andFIG. 5ba sectional view of a further embodiment of a high frequency printed circuit board500comprising a transition structure508. The high frequency circuit board500is comprised of a multi-layer stack510comprising a first metal-comprising layer503and a second metal-comprising layer505. The transition structure508comprises a through connection including pads509and an impedance adapting structure506.

The high frequency printed circuit board500comprises only standard components and may, thus, be manufactured by well-established conventional PCB technologies.

The inner diameter513of the impedance adapting structure506may be adapted to reduce an impedance mismatch of the through connection504and connected structures. The appropriate diameter may be determined by reflectance measurements carried out with corresponding test structures or by calculation. The calculation may be based, as described above, on the coaxial line approximation taking on the ratio of diameters513and511into account, or on well-established electromagnetic field simulations. The simulations may also take the influence of connected structures into account. In one embodiment, the ratio of the diameters513and511is in the range of approximately 2 to 10.

FIG. 6arepresents a plan view andFIG. 6ba sectional view of a further embodiment of a high frequency printed circuit board600similar to the embodiment shown inFIGS. 5aand5b. Contrary thereto, the embodiment ofFIGS. 6aand6bcomprises at least one additional metal-comprising inner layer607disposed between the first and second metal-comprising layers603,605, and at least two dielectric layers602separated by the at least one metal-comprising inner layer607. The through connection604extends from the first metal-comprising layer603through the at least two dielectric layers602and the at least one metal-comprising inner layer607to the second metal-comprising layer605. Contrary to the embodiment ofFIGS. 5aand5b, the impedance adapting structure606of the transition structure608is formed in the metal-comprising inner layer607. The impedance of the transition structure608may be adapted to a desired value by adjusting the ratio of the diameter617of the impedance adapting structure606and the diameter611of the through connection604. In one embodiment, the ratio of the diameters617and611is in the range of approximately 2 to 10.

FIG. 7arepresents a plan view andFIG. 7ba sectional view of a further embodiment of a high frequency printed circuit board700similar toFIGS. 6aand6b. Contrary thereto, the embodiment ofFIGS. 7aand7bcomprises at least two metal-comprising inner layers707, and at least three dielectric layers702separated by the at least two metal-comprising inner layers707. The through connection704extends from the first metal-comprising layer703through the at least three dielectric layers702and the at least two metal-comprising inner layers707to the second metal-comprising layer705. Contrary to the embodiment ofFIGS. 6aand6b, the impedance adapting structure706is formed by coaxial vias744disposed on a circular line718between at least two metal-comprising inner layers707as described above, with respect toFIGS. 3aand3b. The impedance of the transition structure708may be adapted to a desired value by adjusting the ratio of the diameter719of the circular line718and the diameter711of the through connection704. In one embodiment, the ratio of the diameters719and711is in the range of approximately 3 to 20.

As a result, the present invention provides a multi-layer printed circuit board for high frequency applications. The multi-layer printed circuit board comprises a transition structure allowing adaptation of its impedance to a desired value, for example, to the output/input impedance of a transceiver device so that a high frequency signal from/to the transceiver may be led to the opposite side of the multi-layer printed circuit board, for instance, to feed the signal to an antenna printed on the multi-layer printed circuit board. Furthermore, the proposed transition structure may be used to manufacture high frequency chip carriers, for example, for flip chip applications, that allow redistribution of a fine-pitch bond pad arrangement of a die into a coarse-pitch bond pad arrangement, even when high frequency die terminals are involved. The achieved impedance adaptability is sufficient to achieve the required transmission behavior even when FR4 material is used as the substrate material so that cost-efficient multi-layer printed circuit boards and chip carriers may be provided.