Monolithic Ceramic Component and Production Method

Abstract

A film stack made from compacted green films and capable of being sintered to form a ceramic component with monolithic multi-layer structure is disclosed. The film stack includes a functional layer comprising a green film comprising a functional ceramic and a tension layer comprising a green film comprising a dielectric material. The tension layer is directly adjacent to the functional layer in the multi-layer structure. The multilayer structure also includes a first metallization plane and second metallization plane. The functional layer is between the first metallization plane and the second metallization plane.

Claims

1.-14. (canceled)

15. A method for manufacturing a ceramic component comprising, producing first green films made from a functional ceramic and second green films made from a recrystallizing dielectric material with the aid of a binder, generating via contacts are generated in the green films, the via contacts being filled with an electrically conductive paste, generating electrically conductive structures on the green films, stacking the first and second green films one above the other to form a stack, performing compaction and debinding processes on the stack at a first temperature T1, heating the stack to a second temperature T2>T1, in which the dielectric material is recrystallized, heating the stack to a third temperature T3>T2, in which the material of the functional ceramic is sintered but the recrystallized dielectric material remains solid, and cooling the stack to generate a monolithic ceramic multi-layer structure.

16. The method of claim 15, further comprising providing tension layers as outer layers in the film stack, and after the sintering of the functional ceramic, generating and baking electrically conductive structures or electrical contact surfaces on a top side of the ceramic multi-layer structure.

17. The method of claim 16, further comprising generating at least two contact surfaces electrically insulated from each other or generating conductive structures on the top side of the multi-layer structure, and providing a resistor structure on the ceramic multi-layer structure that connects the two contact surfaces in a high-impedance way.

18. The method of claim 17, wherein providing a resistor structure further comprises printing and baking the resistor structure.

19. The method of claim 17, wherein providing resistor structure further comprises sputtering the resistor structure.

20. The method of claim 17, further comprising generating a passivation layer above the resistor structure.

21. The method of claim 15, wherein producing the second green film comprises using a glass powder with particle sizes in the μm range, the glass powder comprising crystalline particles of a material with a defined crystal lattice.

22. The method of claim 21, wherein the crystalline particles are included in the glass powder in a percentage of 20-60 weight percent.

23. The method of claim 15, wherein heating the stack to the third temperature comprises heating the stack under uniaxial compaction of the films between plane-parallel plates.

24. The method of claim 15, wherein stacking the first and second green films one above the other to form a stack further comprises forming a film stack that includes a plurality of first green films stacked one directly above the other each with electrically conductive structures arranged on the plurality of first green films to form a block; and sintering the block to produce a single functional layer, in which at least one block is stacked in an alternating way with second green films.

25. The method of claim 15, wherein producing first green films comprises a stack with at least two different first green films with different functional ceramics to form a ceramic multi-layer structure and realizing different component functions in the ceramic multi-layer by using electrically conductive structures and/or the electrical contact surfaces.

26. Monolithic sintered component, formed by a process comprising: sintering a stack of green films, the stack comprising: a functional layer comprising a green film comprising a functional ceramic, a tension layer comprising a green film comprising a dielectric, material directly adjacent to the functional layer in the multi-layer structure, a first metallization plane and a second metallization plane, the functional layer being between the first metallization plane and the second metallization plane, electrically conductive structures, which form a component function together with the functional layer, in the first and second metallization planes, and wherein the green film for the tension layer has a phase-change temperature below a sintering temperature of the functional ceramic and at which the green film transitions into a recrystallized phase that remains in a solid phase above the sintering temperature of the functional ceramic.

Description

DESCRIPTIONS OF THE DRAWINGS

[0032] Shown are:

[0033] FIGS. 1A-B, a ceramic monolithic component with an asymmetrical multi-layer structure in schematic cross section,

[0034] FIGS. 2A-C, a monolithic ceramic multi-layer component with an asymmetrical structure in schematic cross section,

[0035] FIGS. 3A-C, a ceramic component constructed as an ESD/EMI filter in schematic cross section,

[0036] FIGS. 4A-C, another ESD/EMI filter in schematic cross section,

[0037] FIGS. 5A-E, different processing steps for the production of the ceramic component with reference to schematic cross sections.

DETAILED DESCRIPTION

[0038] FIG. 1A shows a simple embodiment of the invention. It comprises two monolithic interconnected layers, namely, a functional layer F and a tension layer S. In two metallization planes (not shown in the figure), electrically conductive structures are realized that produce, together with the functional layer F, a component function. The metallization planes can be arranged on both outer surfaces (shown at the top and bottom in the figure) of the two-layer structure. It is also possible to provide the metallization planes on both sides (top and bottom) adjacent to the functional layer F and another optionally on the top side of the two-layer structure. The two-layer structure can be expanded through the alternating arrangement of additional function and tension layers F, S. FIG. 1B shows, for example, another multi-layer structure in which two tension layers S and two functional layers F are arranged in an alternating way one above the other and are connected to each other monolithically. FIGS. 1A and 1B each represent asymmetrical multi-layer superstructures.

[0039] FIGS. 2A-C shows a series of possible symmetrical multi-layer superstructures in which the symmetry specifically relates to the layer sequence in the stack direction and advantageously also to their layer thicknesses. Such multi-layer arrangements are compensated and therefore have low distortion after sintering with respect to possible deformation.

[0040] Both the asymmetrical superstructures according to FIGS. 1A-B and the symmetrical superstructures according to FIGS. 2A-C can also be advantageously arranged alternatingly with single or multiple layers. Here, it is possible that the layers pointing outwardly (up or down) in the stack are each selected from the same type and from functional or tension layers. It is also possible, however, to assign the two layers pointing outward to different types.

[0041] FIGS. 3A-C shows a first concrete embodiment of a ceramic component. Shown is a filter against ESD/EMI interference (electrostatic discharge/electromagnetic interference), which is assembled from R and C elements in a π arrangement.

[0042] FIG. 3C shows an equivalent circuit diagram of this π-filter, which is connected as a protective component between two contacts 1 and 2. The two connections are bridged with a high-impedance resistor R, with which electrostatic charges with low time constants can be harmlessly discharged. Before and after the resistor, the circuit is bridged by a parallel branch with a voltage-dependent resistor connected to ground. The resistor has a purely capacitive action at low voltages. High voltage or high-frequency interference on one of the two terminals 1 or 2 is harmlessly discharged to ground via the varistor. FIG. 3A shows such a filter from the bottom side, on which are arranged the electrical contact surfaces or the solder bumps on these surfaces. The filter can have, for example, 5 terminals as shown here and can be connected in two lines or between two pairs of terminals. The middle terminal is provided for the ground connection.

[0043] FIG. 3B shows the component in schematic cross section. It is built from two tension layers S1, S2, between which there is a functional layer F. The functional layer F in turn comprises several ceramic layers, between which metallization planes are arranged. On the bottom side, the component has contact surfaces KF1. On the top side, corresponding contact surfaces KF2 are arranged. Each via contact connects a pair of contact surfaces KF1 and KF2 arranged on opposite surfaces, wherein the via contacts are advantageously guided vertically through all of the ceramic layers of the component.

[0044] Another via contact shown in the middle in the figure is connected to a bottom contact surface KF1, but reaches only partially through the functional layer F. Conductive structures LS arranged in the metallization planes are connected to each via contact DK. The conductive structures LS connected to a via contact DK are separated galvanically from the conductive structures that are assigned to other via contacts. For example, the conductive structures that are assigned to the via contact DK1 shown on the left in the figure are arranged in different metallization planes than those connected to the middle via contact DK.sub.m. Both conductive structures overlap each other and form a first capacitor C. Likewise, the conductive structures overlap the conductive structures connected to the middle DK.sub.m and the right via contact DK2 and form another capacitor C′. The middle via contact DK.sub.m and the contact surface KF1 assigned to it are provided for the ground connection, while the outer conductive contacts are connected to the electrical terminals 1 and 2, which should each be protected against overvoltages and electromagnetic pulses.

[0045] The resistor R is arranged as a conductive resistive layer WS on the surface of the second tension layer S2 in such a way that it connects the two contact surfaces KF2 and KF2′ to each other with high impedance. Above the resistive layer WS there is a passivation layer P, which forms the uppermost layer of the ceramic component.

[0046] The component shown in FIGS. 3A-C can be realized, for example, with typical dimensions of 1×1×0.5 mm. For the tension layers, glass ceramic layers can be used, while the functional layer F is realized from a varistor ceramic. For this purpose, strontium titanate, silicon carbide, and other varistor materials can be used with bismuth or praseodymium-doped zinc oxides. The passivation layer P can be made from a layer thickness or a CVD oxide or another comparable dielectric thin-film material.

[0047] FIGS. 4A-C shows another embodiment of the invention, which can be similarly used as an ESD/EMI protective filter. FIG. 4C shows the equivalent circuit diagram of such a filter in which two terminals 1 and 2 to be protected are bridged by the series circuit of a first inductor L1, a resistor R and a second inductor L2. Between the first terminal and the first inductor, a transverse branch to ground is connected made up of the parallel circuit of a capacitor C and a varistor V. Between the second inductor L2 and the second terminal 2, another parallel branch is connected to ground comprising the parallel circuit of another capacitor C′ and a varistor V. The C elements here each represent only the parasitic capacitance of the varistor electrodes. The named filter is designed particularly as protection against rapidly rising and therefore high-frequency interference, which is harmlessly compensated via the inductors L. High voltages appearing on the terminals 1 or 2 are harmlessly discharged to ground via the low-impedance varistors at high voltages.

[0048] FIG. 4A shows the bottom side of the component, on which the terminals are arranged as contact surfaces KF provided with solder bumps LK.

[0049] FIG. 4B shows the component in schematic cross section. In contrast to the component shown in FIGS. 3A-C, here, in the multi-layer structure, after the first functional layer F1, another second functional layer F2, in which the inductors L1 and L2 are realized, is in turn provided as the varistor ceramic material layer with a structure similar to that in FIG. 3B. This second functional layer F2 is made advantageously from a material with high susceptibility, for example, a ferrite. Also, in the second functional layer F2 there are several metallization layers, in each of which a winding or a half-winding of a coil is realized in the form of conductive structures LS. Each winding is connected by means of a via contact DK—to the winding above or to the conductive structures of this metallization plane realizing the winding. In FIG. 4B, for the second functional layer F2 four metallization planes are shown, which thus form four windings of each inductor.

[0050] A first via contact DK connects a first contact surface KF1 arranged on the bottom side of the component through the first functional layer F1 to the lowermost metallization plane of the second functional layer F2. The uppermost metallization plane of the second functional layer F2 is connected by means of via contacts to contact surfaces KF2 or KF2′ arranged on the top side of the second functional layer. The two upper contact surfaces KF2, KF2′ are in turn connected by means of a resistive layer WS, which realizes the high-impedance resistor R. By means of the resistive layer WS, as the uppermost layer, a passivation layer P is arranged.

[0051] The ceramic components according to the invention, which are constructed, for example, according to FIG. 3 or 4, can be manufactured with high precision and with minimal lateral distortion. Only in this way is a sufficiently precise relative adjustment of conductive structures realized in different ceramic green films and via contacts possible and thus also an interference-free operation of the component.

[0052] FIGS. 5A-E shows, with reference to schematic cross sections, different processing steps for the manufacture of the multi-layer structure for a ceramic component according to the invention. In the first step, the corresponding green films are manufactured, wherein different known film casting and drawing processes can be used. The functional films F contain particles of the desired functional ceramics in a binder. Advantageously, an average particle diameter is set in the μm range. In contrast, the tension layers S contain the components of a recrystallizing material, for example, a glass ceramic, particularly in the form of suitable oxides of the glass ceramic components.

[0053] The particles of the tension layers S are also distributed homogeneously in a binder, wherein particle diameters in the μm range are preferred. In addition, the tension layers contain crystalline mineral particles, which can be used as crystallization seeds for the glass ceramic in the recrystallization process. Advantageously, the glass components are mixed with the crystalline particles in a weight ratio between 2:1 and 1:2. An example glass ceramic composition comprises four [components] each in weight percent 54% SiO.sub.2, 17% PbO, 7.4% CaO, 6.6% Al.sub.2O.sub.3, 6% B.sub.2O.sub.3, 3.2% MgO, 3% Na.sub.2O.

[0054] In the next step, holes are generated in the green films for the via contacts DK, for example, through punching. Then the via contacts are filled with a conductive material, for example, a paste filled with conductive particles. As the conductive particles, metallic grains or whiskers of the systems Ag, AgPd, AgPt, Pd, Pt are suitable. The filling of the via contacts can be realized, for example, with a doctor blade above a template or by means of screen printing.

[0055] In the next step, conductive structures LS are deposited on the green films, for example, by printing a conductive paste, advantageously of the same system, with a suitable technology, for example, by means of screen printing. FIGS. 5A-E shows different green films provided for a multi-layer structure according to the invention. In the figure, two green films GS1 and GS2 are provided for a first and a second tension layer. For the functional layer, here three green films GF1 to GF3 are shown. In practice, however, the multi-layer structure usually consists of a greater number of green films with functional ceramic material, in order to realize within the functional layer a corresponding number of metallization planes with conductive structures formed in these planes.

[0056] In the next step, the green films GS and GF are stacked one above the other and compacted together in the sequence shown in FIG. 5A. FIG. 5B shows the compacted film stack in schematic cross section.

[0057] A temperature program is then performed, in which in the first step a debinding process takes place on the green film, in that the binder material is transitioned in an oxidizing mainly into gaseous, volatile products. Without prior cooling, the recrystallization process of the tension layer S can follow this debinding process.

[0058] For example, the stacked and compacted green films are heated in several steps to a maximum debinding temperature of ca. 450°. For this purpose, they are heated, for example, at 5 K per minute to 100° Celsius and at 0.2 K to 0.5 K per minute to 450° C. The recrystallization of the tension layer, which is performed in the selected embodiments at, e.g., 880° Celsius, can directly follow debinding. For this process, heating is performed at a rate of ca. 5 K to 10 K per minute to this first recrystallization temperature and held at this temperature for ca. 15 to 60 min. Then the layer structure, which now comprises a recrystallized tension layer, can be cooled back to room temperature.

[0059] In the next step, the second sintering for the compaction and sintering of the functional ceramic is performed. The heating profile for this sintering is selected according to the desired ceramics and equals, in the embodiment, with the varistor ceramic, for example, heating at a rate of 1 K to 4 K per minute to ca. 1000° to 1100° C. It is held at this temperature for ca. 180 to 240 min and then cooled at a cooling rate of −1 K to −4 K to room temperature.

[0060] However, it is also possible to heat directly to the second sintering temperature after the recrystallization of the tension layer without prior cooling.

[0061] As a result, the monolithic ceramic body with a multi-layer structure shown in FIG. 5C is obtained. Compared with FIG. 5B, which represents the stack of green films compacted together, due to the debinding and compaction, the sintering shrinkage leads to a reduction in the thickness of the stack from a value d.sub.u for the green film stack of FIG. 5B to a thickness d.sub.s, reduced by ca. 50% in the sintered state according to FIG. 5C. The tensioning effect that the tension layer exerts on the layer structure during the second sintering process produces practically no changes in the lateral dimensions, so that corresponding lateral diameters 1 remain nearly unchanged. The length is of the sintered multi-layer structure according to FIG. 5C is less than the length l.sub.u, of the unsintered film stack of FIG. 5B by a maximum degree of ca. 2%.

[0062] In the next step, electrical contact surfaces or conductive structures are deposited on the top and bottom sides of the multi-layer structure, for example, similarly again in the form of printed screen printing pastes, which are baked in a third sintering process. FIG. 5D shows the multi-layer structure with lower contact surfaces KF1 and upper contact surfaces KF2.

[0063] In the next step, a resistive layer WS is in turn generated, for example, by printing and baking a resistive material. This include high-impedance but conductive particles, for example, particles made from ruthenium oxide RuO.sub.2, bismuth ruthenium oxide Bi.sub.2Ru.sub.2O.sub.7, made from carbon, titanium nitride, Ti.sub.2N, LaB.sub.6, WO.sub.2, Al.sub.2O.sub.3, or also different lead-oxide compounds. Then a passivation layer is generated, which is also printed or deposited with any other method, in particular, a thin-film method. A printed passivation layer is baked. Then the lower contact surfaces KF1 are provided with solder bumps LK, which allow simple soldering of the component.

[0064] At the stage of FIG. 5D, for example, it is possible to use the monolithic ceramic multi-layer structure as a substrate material for discrete or integrated electric and electronic components. Accordingly, a discrete or integrated component can be mounted on at least one surface of the multi-layer structure and electrically connected to the contact surfaces KF. Possibilities of arrangement are provided in flip-chip or SMD designs. It is also possible to bond the other corresponding component and to form a contact with the contact surfaces KF by means of bonding wires. In this way, additional interconnection with component functions is possible that cannot be realized or not well realized in the ceramic multi-layer structure.

[0065] In another construction, a structured multi-layer structure can be generated, in that green films of different surface area are used. In this way, stepped multi-layer superstructures can be obtained, wherein space for the arrangement of discrete or integrated components can be provided on the stepped surfaces. Instead of a stepped structure, it is also possible, before the stack, to already provide a part of the, e.g., upper green films with a correspondingly spacious recess, which represents a cavity that is open at the top in the finished, sintered monolithic multi-layer structure. A discrete component can also be introduced into such a cavity in a space-saving manner and can be electrically connected to the monolithic component according to the invention.

[0066] The invention is not limited to the structures shown in the embodiment examples. Instead, ceramic components according to the invention can be realized with an arbitrary number of metallization planes and an arbitrary construction of the conductive structures, which are arranged in these planes and which remain separated from each other also galvanically according to the component function. In addition to the component shown in FIGS. 4A-C with two different functional layers, other different functional layers can also be integrated in the component, each connected to the function realized in the component. In all cases, it is possible to realize components with minimal lateral shrinkage during the sintering. In addition, it is possible to use a material with low dielectric constant for the tension layer and to construct conductive structures separated from each other by the tension layer in the component and contact surfaces with low parasitic capacitance. In addition, it is possible to use via contacts for forming inductors that have an inductance corresponding to their total length.

[0067] The manufacture of components according to the invention was shown in FIGS. 5A-E only with reference to the structures required for a single component. Obviously, green films with larger surface areas, on which the structures for a plurality of ceramic components can be produced in parallel, are also used. Separation of these components can then be performed, for example, on the basis of the compacted stack of green films. It is also possible to separate the components only after a first or second sintering process, said method requiring less effort. If the ceramic components are used as carrier substrates for different, additional components, then it is advantageous to perform the placement of these additional components before the separation of the ceramic components.