DE10145364A1 - Production of a ceramic substrate comprises preparing a base body having a stack of layers containing non-sintered ceramic material, arranging and fixing a rigid constrained layer to the uppermost layer of the stack, and removing - Google Patents

Abstract

Production of a ceramic substrate comprises: (a) preparing a base body (2) having a stack (2a) of layers (3) containing non-sintered ceramic material; (b) arranging a rigid constrained layer (4) on the upper surface (6) of the uppermost layer (7) of the stack; (c) fixing the constrained layer to the uppermost layer of the stack and sintering the stack; and (d) removing the constrained layer. Preferably sintering is carried out without using external forces. The constrained layer contains pores into which a sintering agent penetrates during sintering. The constrained layer is made from Al2O3. The sintering agent is made from glass.

Description

The invention relates to a method for producing a ceramic substrate, wherein a base body is provided that is a stack of superimposed layers having. The layers of the stack contain one green ceramic material. In a subsequent step the stack sintered.

Methods of the type mentioned are used for Manufacture of multilayer ceramic substrates in which passive components can be integrated. On the Surface of the substrate can be such as SMD, wire bonding or flip-chip assembly active Components are assembled. This creates from the ceramic substrates multifunctional modules that in particular are suitable to save space.

Due to the small space requirement, the above mentioned Modules, in particular, applications in the field of terminal equipment Mobile sector. The method mentioned at the beginning has the Disadvantage that the unsintered ceramic material containing Layers parallel to the layer plane during sintering shrink. In addition, the effect of shrinking occurs Direction of the layer thickness. The shrinking of the layers has the disadvantage that the component after sintering Has final dimensions that are only very limited by the Initial dimensions of the stack provided can be. This results in a relatively large spread the dimensions of the ceramic substrates.

The goal is pursued, for the layers of the stack too to use different ceramic materials. There different ceramic materials are generally different shrinking strongly during sintering, this results in the problem that with different shrinkage of the layers one mechanical instability of the ceramic substrate occur can. Analogous to the bimetal effect, for example happen that the ceramic substrate bends. Furthermore it is possible that with very different Shrinkage behavior separate the individual layers from each other (Delamination). Because the dimensional stability of the ceramic Substrate or the mechanical stability of the ceramic substrate suffers greatly from this, is one Behavior undesirable.

From the publication DE 691 06 830 T2 is a method of known type, with the help of which Shrink the layers of the stack in the lateral direction should be reduced. To do this, one is used before sintering the stack flexible constraint on the surface of the stack applied, with the flexible constraint finely divided Includes particles of inorganic solids, which in one evaporable polymeric binders are dispersed. The Layers of that used in the citation Layer stacks also contain a polymeric binder and additionally an inorganic binder. From the top one Layer of the layer stack penetrates the inorganic Binder into the constraint layer. Due to the flexibility of the Compulsory shift should be achieved that the Compulsory layer of the respective topology of the top one Adapts layer of the stack well. However, this succeeds in Area of depressions (cavities) only imperfectly, so that at these points a significant change in the geometric dimensions of the ceramic substrate during the Sintering occurs. By penetrating the inorganic Binder from the top layer of the layer stack in the constraint is taken care that a sufficient mechanical adhesion of the constraint layer on the top one Layer of the layer stack is guaranteed. Since the Compulsory layer to form their flexibility a polymer Contains binder during sintering or before the sintering of the ceramic substrate must be evaporated, will also volatilize the in the layers of the Layer stack existing polymeric binder hindered. Around any volatilization of the polymeric binder that is present in the layer stack, the Forced layer formed as a porous layer. The Penetration of the constraint layer with the inorganic binder of ceramic body must not be more than 50 µm, because otherwise removing the constraint layer after that Sintering of the base body is made very difficult. One too low penetration of the constraint layer with the inorganic Binder is not desirable either, because otherwise the constraint layer is not sufficiently firm on the surface of the layer stack is liable. For the compulsory shift, a Material used during the sintering of the Layer stack not sintered and therefore no shrinkage, especially in the lateral direction. This missing The shrinking of the compulsory layer is immediately transferred the top layer of the layer stack, which is due to the relatively firm connection to the constraint layer on shrinking is prevented. Through the top layer of the layer stack are also below the top one Layer of the layer stack arranged layers on Shrinkage prevented, to the extent that the layer thickness of the individual layers and the strength of their mechanical Allow connection to each other. The stronger the is mechanical coupling between the layers of the layer stack, the smaller the lateral shrinkage of the individual Layers.

The known method has the disadvantage that the Compulsory layer due to its content of a polymer Binder the volatilization of the polymeric binder from the Layers of the layer stack hindered. It also has the known method has the disadvantage that the constraint is flexible, which is why a certain minimum shrinkage during sintering cannot be prevented. Furthermore can be bent or bent by the flexible constraint layer Warps of the layer stack during sintering only be badly controlled.

The aim of the present invention is therefore a method to provide for the production of a ceramic substrate, with its help a good control of the shrinkage of the Layer stack is made possible during the sintering. In particular, a method is to be provided with which Help warping and warping the layer stack can be controlled during sintering.

This goal is achieved according to the invention by a method Claim 1 reached. Advantageous embodiments of the Invention can be found in the further claims.

The invention provides a method for producing a ceramic substrate, in which in a first step Base body is provided, which is a stack of contains superimposed layers. The Overlying layers contain an unsintered ceramic material. In a subsequent step becomes a rigid constraint on the surface of the top layer of the stack arranged. In a further step, the constraint layer on the top layer attached and the stack sintered. Finally, the constraint layer is removed from the stack.

A layer is closed under a rigid compulsory layer understand that does not shrink when sintering the stack. A a suitable rigid constraint layer would be, for example Ceramic plate containing alumina, which is essential has been sintered at temperatures higher than that Sintering temperature of the stack.

The method has the advantage that due to the rigid constraint layer, the lateral shrinkage of the Layer stack during sintering as well as bends and Warpage of the layer stack can be controlled well can.

Because the rigid constraint layer on the surface of the top one Layer of the stack is attached and therefore to this adheres, the sintering of the layer stack in one advantageous embodiment of the invention take place without forces. It must therefore not with one force the constraint or another rigid plate or a rigid frame on the surface of the layer stack are pressed. This simplifies the mechanical device for sintering the layer stack, because standard sintering devices that make the simple Push the body to be sintered into the sintering furnace provide, can be used.

The top layer of the layer stack can be a Contain sintering aids that become fluid during sintering. This allows the attachment of the Forced shift on the top layer.

In an advantageous embodiment of the invention, the constraining layer can have pores into which the sintering aid penetrates during the sintering. Since the sintering aid becomes fluid during sintering, it can penetrate into the pores of the constraint layer. Suitable pores of the constraining layer would have an expansion of 5 to 10 μm, a suitable expansion of the pores also being dependent on the viscosity of the sintering aid during sintering. In an exemplary embodiment of the invention, a glass which contains SiO ₂ and calcium can be used as the sintering aid.

In a further advantageous embodiment of the invention the constraint layer and the sintering aid are chosen so that the sintering aid with during the sintering Components of the compulsory layer react chemically.

For such a chemical reaction, a ceramic plate containing Al ₂ O ₃ can be used, for example, as a rigid constraint layer. A glass which contains SiO ₂ and calcium can be used as the sintering aid in the uppermost layer of the layer stack. Such a glass can form a chemical compound called anorthite (CaAl ₂ Si ₂ O ₈ ) at a temperature of 900 ° C with the Al ₂ O _{3 of} the constraint layer. This creates a reaction layer between the top layer of the layer stack and the constraint layer, which brings about a firm connection of the constraint layer to the top layer of the layer stack.

In particular, a ceramic plate which contains Al ₂ O ₃ and which is free of sintering aids can be used as the constraining layer. Such a ceramic plate can be produced by sintering at temperatures of 1500 ° C. This high sintering temperature ensures that the forced layer is no longer subject to shrinkage during the sintering of the layer stack at temperatures> 1000 ° C.

In addition, it is advantageous if the penetration of the Sintering aids in the pores of the constraint layer and the chemical Reaction of the sintering aid with components of the Compulsory layer through appropriate material selection with each other is combined. This ensures a particularly firm connection to the Forced layer to the top layer of the layer stack accomplished.

In an advantageous embodiment of the invention a constraint layer can be used that has a thickness between 0.5 mm and 1.5 mm. The constraint must be one have certain minimum thickness, in particular for Large-scale sintered bodies have sufficient mechanical stability exhibit. Beyond that, the compulsory shift must not be too thick, otherwise the removal of the constraint layer too becomes complex.

The constraining layer can contain grains of Al ₂ O ₃ , for example, which are sintered together.

The layers of the layer stack can contain barium titanate, calcium titanate, strontium titanate, lead titanate, CaZrO ₃ , BaZrO ₃ , BaSnO ₃ , metal carbides such as silicon carbide, metal nitrides such as aluminum nitride, minerals such as molite and kyanite, zirconium dioxide or also various types of silicon dioxide as a ceramic solid component. Even glasses with a high softening point can be used as the ceramic component, provided that they have sufficiently high softening points. Mixtures of such materials can also be used for the ceramic solid component of the layers of the layer stack.

The use of the inventive method for The production of ceramic substrates enables in particular the Using layered stacks that are shaped like a plate have, the plate has a base of at least 18 cm × 18 cm and a height of 0.5 to 3 mm. through such a plate can be in a single Manufacturing step a large area, or by subsequent cutting of the large-area substrate, a variety of small Substrates are produced.

It is also particularly advantageous if the sintering of the layer stack at a temperature of less than 1000 ° C, because in this case an LTCC sintering process is present, the use of silver compounds for Conductor structures inside the substrate allow what to leads to lower losses within the component. The The use of silver also has the advantage that it is used in Contrary to those required at higher sintering temperatures Platinum is available lighter and cheaper.

Removing the constraint layer after sintering the stack can, for example, by sputtering or Sandblasting is done.

It is also advantageous if in addition to the top of the layer stack also on the underside of the layer stack a constraint layer on the surface of the bottom layer of the layer stack is arranged. This can do that Shrinking the layers of the layer stack from two sides can be reduced, resulting in an even lower shrinkage has the consequence.

It is particularly useful as a stack Layer stack to use where between two layers Conductor tracks are arranged. These traces can be used are used to make wiring between on the Surface of the ceramic substrate arranged active Components and arranged in the interior of the ceramic substrate passive components. The conductor tracks respectively electrically conductive surfaces between two layers of the Layer stacks can also be used passive Realize components, such as capacitors or coils.

Around the conductor tracks arranged between the layers to contact each other, it is advantageous if a Layer in the stack contains a feedthrough that is electrical is conductive and on two different sides of the Layer interconnects interconnects.

In the following the invention based on Exemplary embodiments and the associated figures explained in more detail.

Fig. 1 shows an example of a ceramic substrate during its production process of the invention in a schematic cross-section.

Figs. 2 and 3 show a ceramic substrate produced by the process of the invention after sintering, one with two constraint layers, each one of them on the bottom and on the top (Fig. 2), and once with only a constraining layer on the top of the substrate ( Fig. 3).

Fig. 4 shows a LTCC substrate, in a schematic cross-section, produced using the inventive method.

Fig. 1 shows a basic body 2 with a pile 2 a of superposed layers 3. The layers 3 contain an unsintered ceramic material. In general, the layers 3 contain the layer stack 2 a in addition to the ceramic material and the sintering aid or a binder 5 that the layers 3, which are usually green sheets (English: Green tapes) imparts present, the time necessary for processing flexibility. The surface 13 of the bottom layer 14 of the stack 2 a lies directly on the second rigid layer 12 . On the surface 6 of the top layer 7 of the stack 2a is located directly on the constraining layer. 4 The constraining layers 4 , 12 contain grains 8 made of Al ₂ O ₃ and have pores 9 . These pores 9 form cavities into which the sintering aid 5 , which originates from the top layer 7 or from the bottom layer 14 of the layer stack 2 a, can penetrate. Adhesion of the respective constraining layer to the layer stack 2 a is imparted by the sintering aid 5 penetrating into the pores 9 . The application of the forced layers 4 , 12 to the layer stack 2 a can take place before or after the debinding of the layer stack 2 a. In the direction of expansion of the layers 3 in the lateral direction of the stack 2 can thus a shrinkage be effectively reduced during sintering. Holding the layer stack 2 a in the lateral direction causes the shrinking to take place almost exclusively in the vertical direction, that is to say perpendicular to the flat sides of the layers 3 . This so-called "shrinkage in the z direction" is all the stronger.

Figs. 2 and 3 each show a stack 2 of a superposed layers 3, wherein the ceramic substrate 1 has already been completed by sintering of the stack 2 a chamfered. The shrinkage of the individual layers 3 that occurs during sintering produces the curved outer contour of the ceramic substrate 1 shown in FIG. 2. As is shown in FIG. 2 on the upper side of a forced layer 4 and on the bottom a second constraining layer 12, the maximum shrinkage has occurred in the production of the substrate 1 in the region of the middle layers 3. In contrast, according to FIG. 3, the biggest change of the outer contour or the maximum shrinkage of the substrate 1 forming layer 3 in the region of the lower layers occurred because a constraining layer 4 is disposed in this case only on the surface of the uppermost layer 7.

Figs. 2 and 3 show that it is advantageous, both on the top and on the bottom of the stack 2 a each having a constraining layer 4 to provide 12, as this of the product to the substrate decreases a change in geometric dimensions during the sintering most can be.

Fig. 4 shows a ready-made with the inventive process ceramic substrate 1 in which the constraining layers have already been removed. The substrate 1 is made from a stack 2 a of layers 3 , one on top of the other, which contain an unsintered ceramic material, the unsintered ceramic material having been converted into a sintered ceramic material by sintering. Components 18 , 19 are arranged on the upper side of the uppermost layer 3 of the ceramic substrate 1 , the first component 18 being attached to the surface of the ceramic substrate by wire bonding and subsequent potting and the second component 19 by flip-chip mounting. The two components 18 , 19 can be ceramic microwave filters, for example. Metallizations 20 are arranged on the underside of the ceramic substrate 1 , on which the substrate 1 can be soldered to a printed circuit board and can thus be brought into electrical contact with further electronic components. Metallizations 20 are also arranged on the upper side of the substrate 1 , on which the components 18 , 19 can be attached. The substrate 1 has a height H of 1 mm. The number of layers 3 is six.

In the interior of the substrate 1 there are wiring levels which are implemented by conductor tracks 10 . A wiring level is always at the interface between two layers 3 . The conductor tracks 10 can be formed, for example, by a screen printing paste containing silver. In addition, a layer 3 also has leadthroughs 11 which make contact with interconnects 10 on two opposite sides of layer 3 . In the through holes 11 are arranged electrically conductive materials that advantageously the bushings 11 fill.

In the upper region of the substrate 1 , two of the layers 3 are formed as layers 15 with a high ∈. Such a ∈ can be, for example, ∈ = 20. Passive components such as capacitors 17 can be integrated into the substrate 1 by means of appropriately designed conductor tracks 10 or electrically conductive surfaces 24 in the wiring levels. According to Fig. 4 conductive surfaces 24 are arranged at the boundary layers between two layers 3 and so connected by bushings 11 to each other, that interlocking comb structures as they are known from multilayer capacitors arise. By printing a resistance paste 25 before the layers 3 are stacked at the interfaces between the layers 3 , integrated resistors can also be produced as passive components in the substrate 1 . Integrated coils 16 can also be produced in the substrate 1 by forming conductor tracks 10 in the form of spiral tracks and by stringing together spiral tracks stacked one above the other.

The illustrated invention is preferably used for stacks 2 a, which are made of layers 3 running essentially along planes. However, it is also conceivable to apply the invention to curved substrates, the layers 3 then not running along a plane but along curved curves.

Claims (15)

1. A method for producing a ceramic substrate ( 1 ) with the following steps: a) providing a base body ( 2 ) with a stack ( 2 a) of layers ( 3 ) lying one above the other, which contain an unsintered ceramic material b) arranging a rigid constraining layer ( 4 ) on the surface ( 6 ) of the uppermost layer ( 7 ) of the stack ( 2 a) c) attaching the constraining layer ( 4 ) to the top layer ( 7 ) and sintering the stack ( 2 a) d) removing the constraint layer ( 4 ). 2. The method according to claim 1, the sintering takes place without the action of external forces. 3. The method according to any one of claims 1 or 2, wherein the top layer ( 7 ) contains a sintering aid ( 5 ) which becomes fluid during the sintering. 4. The method according to claim 3, wherein the constraining layer ( 4 ) has pores ( 9 ) into which the sintering aid ( 5 ) penetrates during the sintering. 5. The method according to any one of claims 3 or 4, wherein the sintering aid ( 5 ) reacts chemically with components of the constraining layer ( 4 ) during sintering. 6. The method according to any one of claims 1 to 5, wherein the constraining layer ( 4 ) contains Al ₂ O ₃ . 7. The method according to any one of claims 1 to 6, wherein the constraining layer ( 4 ) before sintering is free of a sintering aid ( 5 ). 8. The method according to any one of claims 1 to 7, wherein the constraining layer ( 4 ) has a thickness which is between 0.2 mm and 1.5 mm. 9. The method according to any one of claims 1 to 8, wherein the sintering aid ( 5 ) contains glass. 10. The method according to any one of claims 1 to 9, wherein layers ( 3 ) are used to form the stack ( 2 a), which contain Al ₂ O ₃ as the ceramic material and glass as the sintering aid. 11. The method according to any one of claims 1 to 10, wherein a stack ( 2 a) is used which has the shape of a plate, the plate having a base area of at least 18 cm × 18 cm and a height (H) of 0.5 up to 3 mm. 12. The method according to any one of claims 1 to 11, wherein the removal of the constraining layer ( 4 ) is carried out by sputtering or sandblasting. 13. The method according to any one of claims 1 to 12, wherein a stack ( 2 a) is used in which conductor tracks ( 10 ) are arranged between two layers ( 3 ). 14. The method according to any one of claims 1 to 13, wherein a layer ( 3 ) contains an electrically conductive feedthrough ( 11 ) which connects two interconnects ( 10 ) arranged on different sides of the layer ( 3 ). 15. The method according to any one of claims 1 to 14, wherein a second rigid constraining layer ( 12 ) on the surface ( 13 ) of the lowermost layer ( 14 ) of the stack ( 2 a) is arranged.