SUBSTRATE AND METHOD FOR PRODUCING THE SUBSTRATE

Abstract

In an embodiment a method for producing a substrate includes forming a green sheet stack including first green sheets and second green sheets, wherein each of the first green sheets and the second green sheets contains a ceramic material as a main component, and wherein the second green sheets further contain a sintering aid in addition to the ceramic material.

Claims

1. A method for producing a substrate, the method comprising: forming a green sheet stack comprising first green sheets and second green sheets, wherein each of the first green sheets and the second green sheets contains a ceramic material as a main component, wherein the first green sheets are free from a sintering aid and wherein the second green sheets contain the sintering aid.

2. The method according to claim 1, wherein the green sheet stack is formed such that each terminating layer of the green sheet stack consist of at least one first green sheet forming the outermost layer of the green sheet stack.

3. The method according to claim 2, wherein after sintering and finishing producing the substrate the terminating layer formed from at least one first green sheet remains as part of the substrate.

4. The method according to claim 1, wherein the green sheet stack has integrated redistribution traces.

5. The method according to claim 1, wherein the green sheet stack has one or more first green sheets arranged between two second green sheets.

6. The method according to claim 5, wherein the green sheet stack has an alternating stacking sequence of first and second green sheets.

7. The method according to claim 1, wherein the green sheet stack comprises two terminating layers, each terminating layer comprising at least one first green sheet, and wherein the green sheet stack has, after sintering, a sintering shrinkage that is less than 16% in each spatial direction in at least two of three spatial directions.

8. The method according to claim 1, wherein the ceramic material comprises AlN, Al.sub.2O.sub.3, Si.sub.3N.sub.4, BN, SiC, BeO, or ZTA.

9. The method according to claim 1, wherein a quantitative proportion of the sintering aid in the second green sheets is chosen such that the following applies with respect to 100% by weight of the ceramic material: 2% by weight?a?100% by weight.

10. The method according to claim 1, wherein the sintering aid comprises metal oxides or metal halides.

11. The method according to claim 10, wherein the sintering aid is selected from the group consisting of Y.sub.2O.sub.3, CaO, CaF.sub.2, YF.sub.3 and rare earth oxides.

12. The method according to claim 1, further comprising sintering the green sheet stack at a temperature selected from a range of 1600? C. to 2000? C.

13. The method according to claim 1, further comprising sintering the green sheet stack with a holding time selected from a range of 2 h to 10 h.

14. The method according to claim 1, wherein the ceramic material contained as a main component in the first green sheets and the second green sheets is the same ceramic material.

15. A substrate comprising: a ceramic main body having first volume regions and second volume regions, each of the first volume regions and the second volume regions containing a ceramic material, wherein the first volume regions contains less sintering aid than the second volume regions, and wherein some of the first volume regions terminate the substrate in a stacking direction.

16. The substrate according to claim 15, wherein the first volume regions and the second volume regions form a layered structure.

17. The substrate according to claim 15, wherein the ceramic main body has a thickness that lies in a range of 300 ?m to 400 ?m and has a transverse rupture strength of at least 450 MPa.

18. The substrate according to claim 15, wherein the ceramic main body has contact areas configured to mount components on the substrate, and/or integrated redistribution traces, and/or vias.

19. The substrate according to claim 18, wherein the integrated redistribution traces comprise tungsten.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] A method for producing a substrate is described in more detail below on the basis of schematic representations of a pressed green sheet stack, possible stacking sequences of first and second green sheets in the green sheet stack and a substrate. Furthermore, a scanning electron micrograph (SEM micrograph) of a cross section through a ceramic main body is shown.

[0052] FIG. 1 shows a pressed green sheet stack;

[0053] FIG. 2 shows a first stacking sequence of a green sheet stack in cross section;

[0054] FIG. 3 shows a second stacking sequence of a green sheet stack in cross section;

[0055] FIG. 4 shows a third stacking sequence of a green sheet stack in cross section;

[0056] FIG. 5 shows a substrate in cross section; and

[0057] FIG. 6 shows an SEM micrograph of a detail of a cross section of a ceramic main body.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0058] Elements that are the same, similar or appear to be the same are provided with the same designations in the figures. The figures and the relative sizes of elements in the figures are not drawn to scale.

[0059] FIG. 1 shows a pressed green sheet stack 10. The pressed green sheet stack 10 comprises first and second green sheets (not shown). The spatial extent of the pressed green sheet stack 10 is illustrated by dimensioning arrows x, y and z. Since the dimensioning arrows x, y and z respectively run parallel to an axis of the same name in a Cartesian coordinate system, the dimensioning arrows are also referred to here and hereinafter as the corresponding axis of the coordinate system. In other words, the dimensioning arrow x corresponds to an x axis, the dimensioning arrow y corresponds to a y axis and the dimensioning arrow z corresponds to a z axis in a Cartesian coordinate system. Since the following figures show possible stacking sequences of first and second green sheets (not shown) of the pressed green sheet stack 10, the designation of the axes is used analogously for all stacking sequences in the following figures.

[0060] FIG. 2 shows a first stacking sequence of first green sheets 1 and second green sheets 2 in cross section, in order to form the pressed green sheet stack 10 with altogether fourteen green sheets. The pressed green sheet stack 10 has two terminating layers 3, which contain a first green sheet 1 each. All of the other layers of the pressed green sheet stack 10 consist of second green sheets 2. The cross section runs in a plane through the pressed green sheet stack 10 that runs parallel to a first plane, which is defined by the x axis and the z axis. The first green sheets 1 contain a ceramic material that contains AlN as the main constituent. The second green sheets 2 contain a ceramic material that contains AlN as the main constituent and, with respect to 100% by weight AlN, additionally 3.4% by weight Y.sub.2O.sub.3 as a sintering aid. By stacking the first green sheets 1 and second green sheets 2, a green sheet stack (not shown) is formed. This is pressed in order to obtain the pressed green sheet stack 10. Subsequently, the pressed green sheet stack 10 is first decarburized at 600? C. in air and then sintered at 1810? C. for 4 hours in an atmosphere primarily containing N.sub.2/H.sub.2 under atmospheric pressure, in order to obtain a first ceramic main body (not shown), which is based on the pressed green sheet stack 10 that has the first stacking sequence.

[0061] The first ceramic main body (not shown) has a thickness of about 360 ?m. Furthermore, the first ceramic main body has with respect to the pressed green sheet stack 10 a shrinkage of 15.9% along its x axis and a shrinkage of 15.8% along its y axis. This sintering shrinkage is significantly less than a sintering shrinkage that occurs in conventional methods for producing comparable ceramic main bodies.

[0062] Furthermore, the first ceramic main body (not shown) has a transverse rupture strength of 495 MPa. This value is significantly higher than the value that is achieved for ceramic main bodies of a similar thickness that are produced by means of conventional methods.

[0063] FIG. 3 shows a second stacking sequence of first green sheets 1 and second green sheets 2 in cross section, in order to form the pressed green sheet stack 10 with altogether fourteen green sheets. The cross section runs in a plane through the pressed green sheet stack 10 that runs parallel to a plane which is defined by the x axis and the z axis. On account of the second stacking sequence, the pressed green sheet stack 10 has terminating layers 3, which respectively consist of two first green sheets 1. Furthermore, all of the other layers of the pressed green sheet stack 10 consist of second green sheets 2.

[0064] The composition of the first green sheets 1 and the second green sheets 2 is the same as the composition of the first green sheets 1 and second green sheets 2 as it is specified in the description relating to FIG. 2. The method for producing a second ceramic main body (not shown), which is based on a green sheet stack 10 having the second stacking sequence, is analogous to the method that is specified in the description relating to FIG. 2.

[0065] The second ceramic main body (not shown) has a thickness of about 360 ?m auf. The second ceramic main body (not shown) has with respect to the pressed green sheet stack 10 that has the second stacking sequence a sintering shrinkage of 13.7% along its x axis and 13.8% along its y axis. This shows that a configuration of the terminating layers 3 by means of two first green sheets 1 leads to a further reduction of the sintering shrinkage.

[0066] Furthermore, the second ceramic main body (not shown) has a transverse rupture strength of 516 MPa. This value is once again higher than the value obtained for the first ceramic main body (not shown), as is apparent from the description relating to FIG. 2. This high value of the transverse rupture stress allows the highest requirements for the robustness of the ceramic main body to be satisfied.

[0067] FIG. 4 shows a third stacking sequence of first green sheets 1 and second green sheets 2 in cross section, in order to form the pressed green sheet stack 10 with altogether fourteen green sheets. The cross section runs in a plane through the green sheet stack 10 that runs parallel to a plane which is defined by the x axis and the z axis. On account of the third stacking sequence, the pressed green sheet stack 10 has two terminating layers 3, which respectively consist of a first green sheet 1. Furthermore, the green sheet stack 10 that has the third stacking sequence has first green sheets 1, which are formed between two second green sheets 2. Three stacked second green sheets 2 are arranged between each of the first green sheets 1 forming the terminating layers 3 and the first green sheets 1 formed between the two second green sheets 2. Furthermore, the first green sheets 1 that are formed between two second green sheets 2 are separated from one another by four second green sheets 2 stacked one on top of the other. Such a stacking sequence makes it possible to influence the sintering shrinkage in a specifically selective manner.

[0068] The composition of the first green sheets 1 and the second green sheets 2 is the same as the composition of the first green sheets 1 and second green sheets 2 as it is specified in the description relating to FIG. 2. The method for producing a third ceramic main body (not shown), which is based on a green sheet stack 10 having the third stacking sequence, is analogous to the method that is specified in the description relating to FIG. 2.

[0069] FIG. 5 shows a substrate 20, which comprises a ceramic main body 21, in cross section. The ceramic main body 21 is based on a green sheet stack that has a second stacking sequence. The compositions of the first and second green sheets are the same as the compositions specified in the description relating to FIG. 2. The temperature for sintering and the holding time are also the same as the temperature and holding time referred to in the description relating to FIG. 2.

[0070] The ceramic main body 21 has first volume regions 4 and second volume regions 5. The first volume regions 4 have a smaller concentration of sintering aids than the second volume regions 5. Furthermore, the substrate has integrated redistribution traces 6 and vias 7. The vias 7 allow the substrate to be loaded with components on both sides by way of contact areas 8. Furthermore, the integrated redistribution traces 6 allow more components to be mounted by way of the contact areas 8 on a given surface area of the substrate 20 than without the integrated redistribution traces 6. As a result, further miniaturization can be made possible.

[0071] FIG. 6 shows in an SEM micrograph a detail of a cross section through a ceramic main body 21, which is based on a green sheet stack having the second stacking sequence. The light points in the SEM micrograph represent a secondary phase, which is produced by the sintering aid. It can be clearly seen that the second volume regions 5, which were originally formed by second green sheets, have a greater number of secondary phases than the first volume regions 4, which were originally formed by the first green sheets. The fact that the first volume regions 4 are not entirely free from secondary phases is attributable to a diffusion of the sintering aids from the second green sheets into the first green sheets that is initiated by sintering.

[0072] Nevertheless, the first volume regions 4 have significantly fewer secondary phases. Since these secondary phases preferably crystallize on surfaces, the roughness of these surfaces is greatly increased. The use of terminating layers that consist of first green sheets allows the roughness of the surface to be greatly reduced.

[0073] The invention is not restricted to the exemplary embodiments shown. In particular, the total number of green sheets of the green sheet stack and the stacking sequence of the first and second green sheets may vary.