THICK-FILM PASTE MEDIATED CERAMICS BONDED WITH METAL OR METAL HYBRID FOILS

Abstract

Described is a process for preparing a ceramic substrate bonded with a metal foil. Moreover, described is a metal-ceramic-substrate provided with a thick-film layer and the use of a thick-film paste for bonding a metal foil onto a ceramic substrate.

Claims

1.-15. (canceled)

16. A process for preparing a structured metal-ceramic substrate, comprising: applying a thick-film paste onto a ceramic substrate; applying a metal foil onto the thick-film layer of the ceramic substrate; and bonding the metal foil with the ceramic substrate via the thick-film layer.

17. The process according to claim 16, wherein one of the thick-film paste and the metal foil is applied either continuously or discontinuously.

18. The process according to claim 16, wherein the thick-film paste is coated onto the ceramic substrate by one of screen printing and multilayer printing.

19. The process according to claim 16, wherein the metal foil and/or the thick-film layer is oxidized before bonding to the ceramic substrate.

20. The process according to claim 16, wherein the thick-film paste is applied onto the substrate by multilayer coating and a first coating of this multilayer coating is provided with lines for contacts.

21. The process according to claim 16, wherein the thick-film paste comprises at least one of copper, Bi.sub.2O.sub.3, a glass material, and copper in an amount of one of from 40 to 92 wt.-%, 70 to 92 wt.-%, and 75 to 90 wt.-%, each based on the total weight of the thick-film paste.

22. A process for preparing a structured metal-ceramic substrate, comprising: applying a thick-film paste onto a metal foil; applying a ceramic substrate onto the thick-film layer of the metal foil; and bonding the metal foil with the ceramic substrate via the thick-film layer.

23. The process according to claim 22, wherein one of the thick-film paste and the metal foil is applied either continuously or discontinuously.

24. The process according to claim 22, wherein the thick-film paste is coated onto the metal foil by one of screen printing and multilayer printing.

25. The process according to claim 22, wherein the metal foil and/or the thick-film layer is oxidized before bonding to the ceramic substrate.

26. The process according to claim 22, wherein the thick-film paste comprises at least one of copper, Bi.sub.2O.sub.3, a glass material, and copper in an amount of one of from 40 to 92 wt.-%, 70 to 92 wt.-%, and 75 to 90 wt.-%, each based on the total weight of the thick-film paste.

27. A metal-ceramic substrate, comprising a ceramic substrate and, provided thereon, a metal-containing thick-film layer, and, provided thereon; a metal foil.

28. The metal-ceramic substrate according to claim 27, wherein the thick-film layer and/or the metal foil is structured.

29. Use of a thick-film paste for preparing a metal-ceramic substrate as intermediate layer between a ceramic substrate and a metal foil.

30. The use according to claim 29, characterized in that the thick-film paste comprises copper as a metal and optionally Bi.sub.2O.sub.3.

Description

FIRST EMBODIMENT OF THE CLAIMED PROCESS

[0015] In the process according to the first embodiment of the present invention, the thick-film paste is applied onto the ceramic substrate in the first process step.

[0016] First Aspect: Discontinuous Application of the Thick-Film Paste

[0017] In a first aspect of the claimed process, the thick-film paste can be applied onto the ceramic substrate discontinuously such that the thick-film paste is only applied on those parts of the ceramic substrate, which correspond to an intended electronic circuit of the final metal-ceramic substrate.

[0018] In this first aspect, the metal foil may be applied, thereafter, continuously over the whole thick-film layer of the ceramic substrate. After that, the metal foil is bonded with the ceramic substrate and then structured, for example by etching.

[0019] In this first aspect, the metal foil may also be applied discontinuously over the thick-film layer only on those parts of the ceramic substrate on which the thick-film paste is applied.

[0020] Second Aspect: Continuous Application of the Thick-Film Paste

[0021] In a further second aspect of the process according to the present invention, the thick-film paste is applied continuously onto the ceramic substrate.

[0022] In this second aspect, the metal foil may be applied continuously over the whole thick-film layer of the ceramic substrate and the metal foil and the thick-film layer are structured, for example, by etching after bonding.

[0023] In this second aspect, the metal foil may also be applied discontinuously only on those parts of the ceramic substrate which correspond to an intended electronic circuit of the final metal-ceramic substrate. In this case, the thick-film layer is structured, for example, by etching after bonding.

[0024] After applying the thick-film paste onto the ceramic substrate, the thick-film paste may be air-dried prior to applying the metal foil onto the thick-film layer.

[0025] After applying the thick-film paste onto the ceramic substrate, the thick-film paste may also be sintered prior to applying the metal foil. Such a sintering process can be carried out by a temperature of below 1025 C. Preferably, the sintering process is carried out by a temperature in the range of from 300 to 1025 C., more preferably in the range of from 600 to 1025 C., more preferably in the range of from 900 to 1025 C., more preferably in the range of from 900 to less then 1025 C., more preferably in the range of from 900 to 1000 C. This temperature for the sintering process does in particular not provide a bonding of the thick-film paste and the substrate via a DCB process, but provides almost a continuously coating on the ceramic substrate by the known thick-film technology. Accordingly, this process step of sintering distinguishes the process according to the present invention from, for example, the process described in DE 10 2010 025 313 A in which the mixture of the metal and the oxide of the metal is bonded to the ceramic substrate at a higher temperature and under DCB conditions. Such DCB conditions (in particular the required temperature) are not applied doing the sintering process in the process according to the present invention. After applying the thick-film paste onto the ceramic substrate, the thick-film paste may also be air-dried and sintered prior to applying the metal foil onto the thick-film layer. The sintering conditions are as described above.

[0026] The sintering process of the applied thick-film paste is usually carried out under an inert atmosphere, such as a nitrogen atmosphere.

SECOND EMBODIMENT OF THE CLAIMED PROCESS

[0027] In a further modified process for preparing a structured metal-ceramic substrate according to the second embodiment of the present invention, the modified claimed process comprises the following process steps:

[0028] (2.1) applying of a thick-film paste onto a metal foil;

[0029] (2.2) applying of a ceramic substrate onto the thick-film layer of the metal foil; and

[0030] (2.3) bonding the metal foil with the ceramic substrate via the thick-film layer.

[0031] In this modified process, the thick-film paste may be coated onto the metal foil substrate by screen printing.

[0032] After applying the thick-film paste onto the metal foil, the thick-film paste may be air-dried prior to applying the metal foil onto the ceramic.

[0033] In the modified process according to the present invention, the metal foil and the thick-film paste are structured by etching before or after bonding the metal foil onto the ceramic substrate via the thick-film layer.

[0034] The Following Explanations are Given for Both Embodiments of the Claimed Process:

[0035] The thick-film paste may be applied onto the substrate or the metal foil by multilayer printing. If a process step of multilayer coating is applied and the thick-film paste is applied onto a substrate, the first coating of the multilayer coating may be provided with lines for contacts.

[0036] In both processes for preparing a structured metal-ceramic substrate, i.e. the normal process and the modified process, the bonding steps (1.3) and/or (2.3) are carried out by firing. Usually, the firing is carried out at a temperature of between 750 and 1100 C., more preferably of between 800 and 1085 C. In these bonding steps the metal foil is bonded via the thick-film paste to the substrate basically not by applying the DCB process since the metal foil is in contact with the layer provided by the thick-film paste and not with the substrate.

[0037] The metal foil may be oxidized before bonding to the ceramic substrate via the thick-film layer in both embodiments of the processes according to the present invention. In another embodiment of the present invention the metal foil is not oxidized before bonding to the ceramic substrate via the thick-film layer.

[0038] In a further modification of the claimed processes according to both embodiments, the thick-film layer may be oxidized before bonding of the metal foil onto the ceramic substrate. In another embodiment of the present invention the thick-film layer is not oxidized before bonding of the metal foil onto the ceramic substrate.

[0039] The process steps (1.3) and/or (2.3) of bonding the metal foil onto the ceramic substrate provided with the thick-film layer may be carried out under pressure.

[0040] In both embodiments according to the present invention, the metal foil is preferably a copper foil.

[0041] In a further aspect of the present invention, the ceramic may be selected from the group consisting of an Al.sub.2O.sub.3 ceramic, an AlN ceramic and a Si.sub.3N.sub.4 ceramic.

[0042] Thick-Film Paste

[0043] In the following, the thick-film paste, which can be used in the process according to both embodiments of the present invention, is described in more detail:

[0044] The thick-film paste used in the process according to the present invention (either in the normal process or in the modified process) may comprise copper as a metal and optionally Bi.sub.2O.sub.3.

[0045] The thick-film paste comprises preferably 40 to 92 wt.-% copper, more preferably 40 to less than 92 wt.-% copper, more preferably 70 to less than 92 wt.-% copper, most preferably 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0046] The thick-film paste comprises preferably 0 to 50 wt.-% Bi.sub.2O.sub.3, more preferably 1 to 20 wt.-% Bi.sub.2O.sub.3, most preferably 2 to 15 wt.-% Bi.sub.2O.sub.3, each based on the total weight of the thick-film paste.

[0047] The copper particles used in the thick-film paste have a median diameter (d.sub.50) preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0048] The Bi.sub.2O.sub.3 particles used optionally in the thick-film paste have a median diameter (d.sub.50) preferably of less than 100 m, more preferably of less than 20 m, most preferably of less than 10 m.

[0049] In a further embodiment of the present invention, the metal-containing thick-film paste may comprise copper and a glass component.

[0050] The amount of copper in the thick-film paste in case of a simultaneous use of a glass component might be as defined above, i.e. preferably in an amount of from 40 to 92 wt.-%, more preferably 40 to less than 92 wt.-% copper, more preferably in an amount of from 70 to less than 92 wt.-% copper, most preferably in an amount of from 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0051] In the case of use of a glass component in the thick-film paste, the thick-film paste comprises preferably of from 0 to 50 wt.-%, more preferably 1 to 20 wt.-%, most preferably 2 to 15 wt.-%, of the glass component, each based on the total weight of the thick-film paste.

[0052] In the case of use of a glass component in the thick-film paste, the copper particles may have the same median diameter (d.sub.50) as already mentioned above, i.e. preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0053] In the case of use of a glass component in the thick-film paste, the glass component particles may have a median diameter (d.sub.50) of less than 100 m, more preferably less than 20 m, most preferably less than 10 m.

[0054] The metal-containing thick-film paste, preferably on the basis of copper, may comprisebesides the glass component and Bi.sub.2O.sub.3further components, selected from the group consisting of PbO, TeO.sub.2, Bi.sub.2O.sub.3, ZnO, B.sub.2O.sub.3, Al.sub.2O.sub.3, TiO.sub.2, CaO, K.sub.2O, MgO, Na.sub.2O, ZrO.sub.2, and Li.sub.2O.

[0055] After applying the thick-film paste either onto the ceramic substrate or onto the metal foil, the layer thickness is preferably of from 5 to 150 m, more preferably of from 20 to 125 m, most preferably of from 30 to 100 m.

[0056] In a preferred embodiment of the present invention, the amount of copper oxide in the thick-film paste is less than 2 wt.-%, more preferably less than 1.9 wt.-%, more preferably less than 1.8 wt.-%, more preferably less than 1.5 wt.-%.

[0057] Metal-Ceramic Substrate

[0058] In a further aspect, the present invention relates to a metal-ceramic substrate, comprising

[0059] (a) a ceramic substrate and, provided thereon,

[0060] (b) a metal-containing thick-film layer, and, provided thereon,

[0061] (c) a metal foil.

[0062] The metal foil and/or the metal-containing thick-film layer may be structured.

[0063] The thick-film layer, provided onto the ceramic substrate, comprises preferably copper as a metal and optionally Bi.sub.2O.sub.3.

[0064] The thick-film paste comprises preferably 40 to 92 wt.-% copper, more preferably 40 to less than 92 wt.-% copper, more preferably 70 to less than 92 wt.-% copper, most preferably 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0065] The thick-film paste comprises preferably 0 to 50 wt.-% Bi.sub.2O.sub.3, more preferably 1 to 20 wt.-% Bi.sub.2O.sub.3, most preferably 2 to 15 wt.-% Bi.sub.2O.sub.3, each based on the total weight of the thick-film paste.

[0066] The copper particles used in the thick-film paste have a median diameter (d.sub.50) preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0067] The Bi.sub.2O.sub.3 particles used optionally in the thick-film paste have a median diameter (d.sub.50) preferably of less than 100 m, more preferably of less than 20 m, most preferably of less than 10 m.

[0068] In a further embodiment of the present invention, the metal-containing thick-film paste may comprise copper and a glass component.

[0069] The amount of copper in the thick-film paste in case of a simultaneous use of a glass component might be as defined above, i.e. preferably in an amount of from 40 to 92 wt.-%, more preferably in an amount of from 70 to 92 wt.-% copper, most preferably in an amount of from 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0070] In the case of use of a glass component in the thick-film paste, the thick-film paste comprises preferably of from 0 to 50 wt.-%, more preferably 1 to 20 wt.-%, most preferably 2 to 15 wt.-%, of the glass component, each based on the total weight of the thick-film paste.

[0071] In the case of use of a glass component in the thick-film paste, the copper particles may have the same median diameter (d.sub.50) as already mentioned above, i.e. preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0072] In the case of use of a glass component in the thick-film paste, the glass component particles have may have a median diameter (d.sub.50) of less than 100 m, more preferably less than 20 m, most preferably less than 10 m.

[0073] The metal-containing thick-film paste may comprisebesides the glass component and Bi.sub.2O.sub.3further components, selected from the group consisting of PbO, TeO.sub.2, Bi.sub.2O.sub.3, ZnO, B.sub.2O.sub.3, Al.sub.2O.sub.3, TiO.sub.2, CaO, K.sub.2O, MgO, Na.sub.2O, ZrO.sub.2, and Li.sub.2O.

[0074] The layer thickness of the thick-film paste is preferably 10 to 150 m, more preferably 20 to 125 m, most preferably 30 to 100 m.

[0075] The metal foil is preferably a copper foil.

[0076] In a further aspect of the present invention, the ceramic may be selected from the group consisting of an Al.sub.2O.sub.3 ceramic, an AlN ceramic and a Si.sub.3N.sub.4 ceramic.

[0077] The metal-ceramic substrate according to the present invention may preferably be prepared according to the above-mentioned process.

[0078] In a further aspect, the present invention relates to the use of the above-mentioned thick-film paste for preparing a metal-ceramic substrate as intermediate layer between a ceramic substrate and a metal foil. The above-mentioned thick-film is used in order to avoid the delamination of the resulting system of a substrate and a metal foil during operation by thermal cycles.

[0079] The thick-film layer, provided onto the ceramic substrate, comprises preferably copper as a metal and optionally Bi.sub.2O.sub.3.

[0080] The thick-film paste comprises preferably 40 to 92 wt.-% copper, more preferably 40 to less than 92 wt.-% copper, more preferably 70 to less than 92 wt.-% copper, most preferably 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0081] The thick-film paste comprises preferably 0 to 50 wt.-% Bi.sub.2O.sub.3, more preferably 1 to 20 wt.-% Bi.sub.2O.sub.3, most preferably 2 to 15 wt.-% Bi.sub.2O.sub.3, each based on the total weight of the thick-film paste.

[0082] The copper particles used in the thick-film paste have a median diameter (d.sub.50) preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0083] The Bi.sub.2O.sub.3 particles used optionally in the thick-film paste have a median diameter (d.sub.50) preferably of less than 100 m, more preferably of less than 20 m, most preferably of less than 10 m.

[0084] In a further embodiment of the present invention, the metal-containing thick-film paste may comprise copper and a glass component.

[0085] The amount of copper in the thick-film paste in case of a simultaneous use of a glass component might be as defined above, i.e. preferably in an amount of from 40 to 92 wt.-%, more preferably in an amount of from 70 to 92 wt.-% copper, most preferably in an amount of from 75 to 90 wt.-% copper, each based on the total weight of the thick-film paste.

[0086] In the case of use of a glass component in the thick-film paste, the thick-film paste comprises preferably of from 0 to 50 wt.-%, more preferably 1 to 20 wt.-%, most preferably 2 to 15 wt.-%, of the glass component, each based on the total weight of the thick-film paste.

[0087] In the case of use of a glass component in the thick-film paste, the copper particles may have the same median diameter (d.sub.50) as already mentioned above, i.e. preferably of between 0.1 to 20 m, more preferably of between 1 and 10 m, most preferably of between 2 and 7 m.

[0088] In the case of use of a glass component in the thick-film paste, the glass component particles have may have a median diameter (d.sub.50) of less than 100 m, more preferably less than 20 m, most preferably less than 10 m.

[0089] The metal-containing thick-film paste may comprisebesides the glass component and Bi.sub.2O.sub.3further components, selected from the group consisting of PbO, TeO.sub.2, Bi.sub.2O.sub.3, ZnO, B.sub.2O.sub.3, Al.sub.2O.sub.3, TiO.sub.2, CaO, K.sub.2O, MgO, Na.sub.2O, ZrO.sub.2, and Li.sub.2O.

[0090] The layer thickness of the thick-film paste is preferably 10 to 150 m, more preferably 20 to 125 m, most preferably 30 to 100 m.

[0091] The metal foil is preferably a copper foil.

[0092] The present invention is described in more detail with regard to the following examples:

[0093] A thick-film paste material is prepared starting from the following glass composition (in wt.-%):

TABLE-US-00001 Tg d.sub.50 (DSC, Glass (m) C.) SiO.sub.2 ZnO B.sub.2O.sub.3 Al.sub.2O.sub.3 TiO.sub.2 CaO K.sub.2O MgO Na.sub.2O ZrO.sub.2 Li.sub.2O A 2.6 744 38 0.2 3.9 19.5 2.4 35.9 0.1 0 0 0.1 0 B 3.6 677 27.3 3.9 10.5 24.7 3.5 25.9 0 3.21 0.8 0 0 C 2.8 584.6 61.2 0.5 9.0 3.3 6.4 8.8 6.5 0.5 2.8 0 0.6

Vehicle Formulation

[0094]

TABLE-US-00002 Texanol Butyl [wt %] diglyme Acrylic resin 43 23 34

Paste Formulation

[0095]

TABLE-US-00003 Glass Cu powder type; Vehicle Bi.sub.2O.sub.3 [wt %] Paste [wt %] (d.sub.50 of 4.7 m) [wt %] [wt %] (d.sub.50 of 4.3 m) A 86 A; 3 11 B 86 B; 3 11 C 86 C; 3 11 D 86 11 3

[0096] Starting from these paste formulations, a ceramic metal substrate was prepared by printing the pastes on a Al.sub.2O.sub.3 ceramic substrate in a thickness of 40 m. The pastes were dried in an oven at 110 C. for 10 min and sintered at 950 C. for 10 minutes before a Cu foil with a thickness of 300 m was applied onto the dried pastes and the composite was fired in an oven at 1040 C. for 150 min.

[0097] For comparison, a ceramic metal substrate was prepared starting from the same ceramic substrate and the same Cu foil as for the examples with pastes, but using a standard DCB process with a bonding temperature of 1063 C. for 240 min.

[0098] The finished metal ceramic substrates have been subject to thermal cycles (15 min at 40 C., 15 sec. transfer time, 15 min at +150 C.). The test results can be seen in the following table.

TABLE-US-00004 Metal # of thermal cycles before ceramic substrate Paste delamination 1 A 1550 2 B 2470 3 C 3040 4 D 2850 5 No paste, standard DCB 100 process