EP2797853A1

EP2797853A1 - Process for producing dcb substrates

Info

Publication number: EP2797853A1
Application number: EP12821253.7A
Authority: EP
Inventors: Jürgen SCHULZ-HARDER; Karsten Schmidt; Karl Exel
Original assignee: Curamik Electronics GmbH
Current assignee: Rogers Germany GmbH
Priority date: 2011-12-27
Filing date: 2012-12-27
Publication date: 2014-11-05
Also published as: KR20140119047A; JP2015503500A; WO2013097845A1; US20140338162A1; DE102012101057A1; CN104105678A

Abstract

Process for producing DCB substrates having in each case at least one ceramic layer which consists essentially of aluminium nitride (AlN) and is provided on at least one surface side with an intermediate layer consisting essentially of aluminium oxide and also has at least one metallization formed by a metal layer or metal foil on the intermediate layer.

Description

Process for the preparation of DCB substrates

The invention relates to a method for the manufacture len of DCB substrates, in particular in the form of printed circuit boards for electrical circuits and / or modules, according to the preamble of claim 1. Methods of this kind are known.

Known is the so-called "DCB process" (Direct Copper Bond Technology)

For example, for connecting metal lschichten or sheets (eg copper sheets or - fol ies) with each other and / or with ceramic or ceramic layers, using metal sheets or films, especially those of copper or copper alloys, on their surface sides a layer or coating of a chemical

Compound of the metal l and a reactive gas, preferably oxygen. In this method, for example, in US-PS 37 44 120 or in DE-PS 23 1 9 854 described method, this layer or coating forms together with the adjacent metal l a eutectic (reflow) with a melting temperature below the melting temperature of the metal ls ( For example, copper), so that by placing the film on the ceramic and heating all ichl layers can be connected to each other, through

Melting of the metal or copper essentially only in the area of the melting layer or oxide layer.

This DCB method then indicates e.g. the following process steps:

Oxidizing a metal foil, e.g. Kupferfol ie such that there is a uniform metal or copper oxide layer;

Placing the metal foil, for example copper foil, on the ceramic layer;

Heating the composite to a process temperature between about 1025 to 1083 ° C, e.g. to about 1071 ° C;

• Cool to room temperature. Substrates prepared by this method (hereinafter also referred to as "DCB bonding") are hereinafter referred to as "DCB substrates", regardless of the metal I used for the metal layers or foils. When using aluminum nitride (AIN) ceramic layers, it is also known to produce an intermediate layer of aluminum oxide (Al 2 O 3) on at least one surface side of the respective ceramic layer, first by thermal oxidation in air or in an oxygen-containing atmosphere. Only via this intermediate layer is it then possible to connect the metallization forming the corresponding metal foil, for example copper foil, by DCB bonding with the ceramic.

The object of the invention is to provide a method by which DCB substrates with at least one ceramic layer consisting essentially of aluminum nitride with improved quality, in particular with improved mechanical and / or electrical and / or thermal properties, can be produced. To solve this problem, a method according to claim 1 is formed.

An essential feature of the method according to the invention is that the particular ceramic layer used, which consists essentially of aluminum nitride (AIN), for example, with an aluminum nitride content of at least 90%, preferably with an aluminum nitride content of at least 96%, with further constituents including sintering aids such as yttria Y203), calcium oxide (CaO), magnesium oxide (MgO) and release agents such as boron nitride (BN) and reaction products such as garnet (Y203 ^" Al203), and boron oxide (B203), prior to producing the at least one intermediate layer of alumina (AI203) is mechanically and / or chemically cleaned on the relevant surface side, ie a surface layer existing therefrom which results from the sintering process and contains, inter alia, reaction processes from the sintering process is developed in a further development of the invention.

the removal of the surface layer, in particular also of the surface layer containing an oxidic ceramic, takes place mechanically, for example by brushing, grinding, lapping, sandblasting, pressure blasting,

and or

the removal of the surface layer takes place by chemical treatment, for example by treatment with an alkaline solution, preferably with an aqueous solution having a pH greater than 10, preferably with a pH greater than 12,

and or the removal of the surface layer takes place at a treatment temperature in the range between 20 ° C and 100 ° C, preferably at a temperature greater than 50 ° C,

and or

that the removal of the surface layer by treatment with sodium hydroxide solution, preferably with 5% sodium hydroxide solution and / or by a treatment with

Potassium hydroxide (KOH) and / or sodium carbonate (Na2C03),

and or

the removal of the surface layer takes place thermally in liquid and / or vapor, for example by treatment under pressure in an autoclave

Temperatures up to 300 ° C,

and or

a thin layer of copper or copper oxide or of at least one other copper-containing compound is applied to the ceramic layer on at least one surface side prior to the production of the at least one intermediate layer, and that subsequently the at least one intermediate layer is produced by thermal oxidation,

and or

the thermal oxidation takes place until a layer thickness in the range between 0.5 // m and 10 // m has been established for the at least one intermediate layer (3),

and or

that the mechanical and chemical processing for removing the at least one surface layer are performed at least partially overlapping in time or in succession,

and or

the application of the thin layer of copper or copper oxide or of the at least one copper-containing compound is effected by immersing the ceramic layer in an aqueous copper ion-containing solution, for example in an aqueous solution with 0.005 to 2.0 mol / ICu + + ion content,

and or

the application of the thin layer of copper or of copper oxide or of the at least one other copper-containing compound takes place by sputtering and / or by CVD deposition and / or by chemical deposition, and or

that the at least one intermediate layer by thermal oxidation, i. by heating the ceramic layer to a temperature in the range between 800 ° C and 1 450 ° C in air or in an oxygen-containing atmosphere with an oxygen content between 10% and 90%,

and or

the method comprises the following method steps:

Applying at least one oxidized metal foil made of copper or a

Copper alloy on at least one surface side of the cleaned

Ceramic layer of AIN,

Heating the at least one metal foil and the ceramic layer to a temperature of 400 ° C - 1083 ° C,

Removing the at least one metal foil, preferably after cooling the metal foil and the ceramic layer,

Oxidizing the ceramic layer at a temperature of 850 ° C - 1450 ° C in an oxygen-containing atmosphere to form the intermediate layer on at least one surface side of the ceramic layer, and.

DCB bonding at least one metal foil to at least one surface side of the ceramic layer,

and or

the method comprises the following method steps:

Oxidizing the cleaned ceramic layer of AIN at a temperature of 800 ° C -1450 ° C,

DCB bonding at least one metal foil of copper or a copper alloy to at least one surface side of the oxidized ceramic layer,

Removing the at least one metal foil, preferably by etching,

Re-oxidizing the ceramic layer (2) at a temperature of 800 ° C - 1450 ° C, and

and or

that the method comprises the following method steps,

in that by casting and / or calendering and / or pressing a crumb of aluminum nitride and sintering aids produced and from this by sintering a Are made of a ceramic layer, that on at least one surface side of the ceramic layer, the intermediate layer is produced and then the pre-oxidized metal layer or metal foil is connected by DCB bonding, that before generating the at least one intermediate layer on the respective surface side of the ceramic layer there existing, from the Sintering process resulting surface layer is removed, and then that the intermediate layer is generated,

wherein the aforementioned features can be used individually or in any combination.

The expression "essentially" or "approximately" in the sense of the invention means deviations from the exact value by +/- 10%, preferably by +/- 5% and / or deviations in the form of changes that are insignificant for the function. Further developments, advantages and applications of the invention will become apparent from the following description of exemplary embodiments and from the figures. In this case, all described and / or illustrated features alone or in any combination are fundamentally the subject of the invention, regardless of their summary in the claims or their dependency. Also, the content of the claims is made an integral part of the description.

The invention will be explained in more detail with reference to the figures of embodiments. Show it:

Figure 1 is a DCB substrate with an insulating or ceramic layer of aluminum nitride (AIN) in section.

2 in positions a) -f) different method steps for producing the DCB

Substrate of Figure 1;

3 shows an enlarged view of the ceramic layer of aluminum nitride together with an intermediate layer applied to this ceramic layer essentially consisting of aluminum oxide (Al 2 O 3) in the method of FIG

2;

4 in positions a) -f) different method steps for producing the DCB

Substrates of Figure 1 in a further embodiment of the invention; 5 shows an enlarged view of the ceramic layer of aluminum nitride together with an intermediate layer applied to this ceramic layer essentially consisting of aluminum oxide (Al 2 O 3) in the method of FIG. 4.

In FIG. 1, 1 is a metal-ceramic substrate or a DCB substrate which is in the

Substantially consists of a ceramic layer 2 of protective or intermediate layers 3, each of which is located on a surface side of the ceramic layer 2, as well as metallizations 4 and 5, which are each applied to one of the intermediate layers 3 and of which the metal isation 3 for forming of metal areas 3.1, for example in the form of

Conductor tracks, contact surfaces, mounting surfaces, etc. is structured.

In detail, the ceramic layer 2 is one made of aluminum nitride (AIN), for example, with a content of aluminum nitride (AIN) of at least 90% by weight, preferably with a content of aluminum nitride (AIN) of about 96% by weight, the remainder each being further additives or substantially other additives, in particular sintering aids, such as

For example, yttria (Y203), ceria (CaO), barium oxide (B203), barium nitride (BN), calcium oxide (CaO), etc. are. The intermediate layers 3 are also ceramic layers and consist of aluminum oxide (AI302) with a small proportion of other constituents, in particular

Sintering aids, for example with a small proportion of yttrium oxide (Y203),

Barium nitride (BN), barium oxide (B203), calcium oxide (CaO). The metallizations 4 and 5 are layers or foils of copper, of a copper alloy, or of aluminum or an aluminum alloy.

The basic process steps for producing the substrate 1 are shown in FIG. 2 in the local positions a) -f). According to the position a), the ceramic layer 2 of aluminum nitride is first provided, by casting and / or calendering and / or pressing a crumb foil 2.1 made of aluminum nitride (AIN) with the sintering aids and by subsequent sintering of the respective green sheet 2.1, also in the stack with further Crünfolien at the required sintering temperature, for example at a temperature in the range between 1 600 ° C and 1 900 ° C. After sintering, the green ceramic layer 2.2 (ceramic layer as-fired) is obtained according to the position b). During sintering in the stack, release agents such as boron nitride (BN) are used. This raw ceramic layer 2.2 has, in particular, surface layers 6 originating from the sintering process, for example with a thickness in the range between 0.05 mm and 0.3 mm. The surface layers 6 consist essentially of

Impurities and components or compounds of the sintering aids and release agents, such. Boron oxide (B203), boron nitride (BN), yttrium oxide (Y203), garnet

(Y203 ^{^} AI203, calcium oxide (CaO), etc. According to the position c) are in a next step, the

Surface layer 6 is removed, so that the ceramic layer 2 is obtained with cleaned or clean surface sides.

In a next method step, according to the position d), the application of the intermediate layers 3, e.g. by thermal oxidation. For this purpose, the ceramic layer 2 in air or in an oxygen-containing atmosphere, for example in an atmosphere containing inert gas, for example nitrogen, argon, etc., and oxygen in a proportion of 10% - 90%, to a temperature in the range between 800 ° C heated to 1450 ° C. The intermediate layers 3 likewise contain constituents (3.1) or reaction products of the sintering aids, for example Y 2 O 3, BN, B 2 O 3 etc. (FIGS. 3 and 5)

In a further method step takes place according to the position e), the DCB bonding or the surface bonding of the metallizations 4 and 5 forming metal layers or metal foils of copper, a copper alloy, aluminum or from a

Aluminum alloy. For this purpose, the pre-oxidized metal layers or metal foils are respectively placed on an intermediate layer 3 and then subsequently connected by DCB bonding with the intermediate layers 3 and via the with the ceramic layer 2. The DCB bonding is performed by heating the assembly formed by the metal foils or layers and the ceramic layer 2 with the intermediate layers 3 to the DCB temperature in the range between

1 025 ° C and 1 083 ° C in a protective gas or inert gas atmosphere with a low oxygen content and then cooling to ambient temperature. Here, the respective copper or aluminum oxide with the adjacent copper or aluminum forms a eutectic melt on the after cooling under DCB temperature which the respective Metallization 4 or 5 forming metal layer or metal foil with the adjacent

Intermediate layer 3 and connected via this with the ceramic layer 2. With the intermediate layers 3, the wetting of the ceramic with the liquid eutectic necessary for this connection is achieved, whereby the DCB bonding of the metallizations 4 and 5 or of the metal layers or metal foils forming this metallization becomes possible in the first place.

In a further method step, the structuring of at least the metallization 4 takes place in accordance with the position f) to form the metal regions 4.1, which are also electrically separated from one another, using a suitable and known masking and etching method. This structuring can be omitted if the metallizations 4 and 5 and in particular the metallization 4 already pre-structured on with the

Intermediate layer 3 provided ceramic layer 2 are applied by DCB bonding.

Various methods are possible for removing the surface layers 6, in particular a mechanical and / or material-removing treatment and / or a chemical treatment, for example a chemical treatment with a suitable aqueous solution or alkali, preferably with an aqueous alkaline solution having a pH greater oil or preferably greater than 12, for example by immersing the

Raw ceramic layer 2.2 in this aqueous solution or alkali.

In particular, sodium hydroxide solution (NaOH) and in particular a 5% sodium hydroxide solution are suitable as the treatment solution. However, other alkaline treatment solutions, for example KOH, Na 2 CO 3, are also suitable for the treatment. The treatment is preferably carried out at a temperature in the range between 20 ° C and 100 ° C, preferably at a temperature greater than 50 ° C. Another possibility is a treatment with the solutions mentioned under pressure in an autoclave to 300 ° C. Hereby, the

Treatment times are significantly reduced.

In addition to or instead of the chemical treatment, a mechanical treatment removing the material of the surface layers 6 is also possible, for example removal of the surface layers 6 by brushing and / or grinding and / or lapping, sand blasting, pressure blasting, etc.

In one embodiment of the method according to the invention, the mechanical

Treatment before the chemical treatment or following the chemical treatment. In a preferred embodiment of the method according to the invention are mechanical treatment and chemical treatment carried out at least partially overlapping in time.

It has also been found that particularly good results with the method according to the invention, especially with regard to the mechanical strength and quality of

Connection of the metallizations 4 and 5 with the ceramic and in terms of electrical properties can be achieved when in the intermediate layer 3 copper or copper oxide or copper ions are incorporated. It has been shown that 3 discontinuities 7 form without incorporation of copper or copper oxide or copper ions in the intermediate layers, in which the respective intermediate layer 3 is not completely formed or interrupted.

These discontinuities 7, i. in particular the pores and interruptions, lead to the fact that in the region of discontinuities 7 no DCB connection between the ceramic and the respective metallization 4 or 5 comes about, ie below the respective

Metallization 4 and 5 bubbles or cavities form. Through these bubbles or voids u.a. not only the mechanical strength of the connection between the metallizations 4 and 5 and the ceramic, but in particular the dielectric strength of the substrate 1 between the metallizations 4 and 5 significantly affected. By incorporating copper or copper oxide or copper ions into the intermediate layers 3, the discontinuities 7 and the associated disadvantages are effectively avoided (FIG. 5).

The incorporation of copper, copper oxide or copper ions can take place in different ways. FIG. 4 shows in the positions a-f the essential steps a method in which, after the provision of the ceramic ceramics 2.1 (position a), after the sintering and cleaning of the raw ceramics 2.2 (Positions b and c) on both surface sides of the cleaned, ie freed from the surface layers 6 ceramic layer 2 is applied in each case a thin layer 8 of copper or a copper-containing compound, as shown in Figure 4 in the position c) subsequent Position c) 'is indicated. Following this, in turn, according to position d), the two intermediate layers 3 having the desired thicknesses are produced by thermal oxidation in an oxygen-containing atmosphere. Also in these methods, the intermediate layers 3 are set to a layer thickness between about 0.5 // m and 10 ym. The further method steps (positions e) and f)) correspond to the method as described in connection with FIG. The layers 8 for example, with a thickness in the range between 1, 5 x 10 ^"4 // m and 1 200 x ^{10" 4} // m. The layers 8 can be obtained, for example, by immersing the cleaned ceramic layer 2 in an aqueous solution containing copper ions, for example in an aqueous solution with 0.005 to 2.0 mol / ICu + + ion content and / or by sputtering and / or by CVD deposition and / or chemical deposition can be applied. The layers 8 can also be produced by the use of brushes with bristles containing copper in the case of mechanical removal of the surface layers 6.

Another method for doping the Al 2 O 3 intermediate layers 3 with copper during the thermal oxidation can be carried out by the following method steps:

Cleaning the ceramic or ceramic layer 2 with the methods described above,

Placing oxidized copper foils on the ceramic layer 2,

Heating the ceramic layer 2 and the copper foils in a DCB process atmosphere to a temperature of 400 ° C - 1083 ° C,

Cooling the ceramic layer 2 and the copper foils to room temperature, and

Oxidation of the ceramic layer 2 by the above method at temperatures of 850 ° C - 1450 ° C to produce the intermediate layers 3, preferably the

used copper foils are removed before this oxidation.

Another method for doping the Al 2 O 3 intermediate layers 3 with copper can be carried out by the following method steps:

Cleaning the ceramic or ceramic layer 2 with the methods described above,

Oxidizing the ceramic layer 2 without copper doping at a temperature of 800 ° C - 1450 ° C to produce a still flaws 7 containing AI203 intermediate layer 3, DCB bonding of oxidized copper foils on the intermediate layers 3,

Removal of the copper foils, for example by chemical etching,

re-oxidation of the ceramic layer 2 at temperatures of 800 ° C - 1450 ° to produce the intermediate layers. 3

With the two aforementioned methods, copper / copper oxide is likewise incorporated into the Al 2 O 3 intermediate layers 3. Due to the intercalation 9 of copper / copper oxide resulting from defects and interruptions free continuous intermediate layers 3, as indicated in Figure 5. The invention has been described above by means of exemplary embodiments. It is understood that numerous changes and modifications are possible without thereby departing from the inventive concept underlying the invention.

LIST OF REFERENCE NUMBERS

substratum

ceramic layer

Ceramic foil made of ceramic material

burned raw ceramics

interlayer

metallization

metal sector

surface layer

Defect or interruption

Layer of copper, copper oxide or copper ions copper-containing deposits

Claims

claims

Process for the preparation of DCB substrates each having at least one im

Substantially made of aluminum nitride (AIN) ceramic layer (2), on at least one surface side, preferably on both surfaces with an intermediate layer (3) consisting essentially of alumina (AI203) is provided, and with at least one of a metal lschicht or metal lfolie formed metal lation on the respective intermediate layer (3), wherein by casting and / or calendering and / or pressing a Crünfol ie (2.1) of aluminum nitride and

Produced sintering aids and from this by sintering a Rohkeramikschicht (2.2) Hergestel be, and wherein on at least one surface side, preferably on both surface sides of the ceramic layer (2), the intermediate layer (3) generated and with this then the pre-oxidized metal lschicht or metal lfol ie connected by DCB bonding,

characterized,

that prior to the generation of the at least one intermediate layer (3) on the respective surface side of the ceramic layer (2) there is removed a surface layer (6) resulting from the sintering process and in particular containing impurities and / or reaction products from the sintering process.

2. The method according to claim 1, characterized in that the removal of

Surface layer (6) takes place mechanically, for example by brushing, grinding, lapping, sandblasting, pressure blasting.

3. The method according to claim 1 or 2, characterized in that the removal of the surface layer (6) by chemical treatment, for example by treatment with an alkaline solution, preferably with an aqueous solution having a pH greater than 10, preferably with a PH value greater than 1 2.

4. The method according to claim 3, characterized in that the removal of

Surface layer (6) at a treatment temperature in the range between 20 ° C and 100 ° C, preferably at a temperature greater than 50 ° C.

5. The method according to claim 3 or 4, characterized in that the removal of the surface layer (6) by treatment with sodium hydroxide solution, preferably with 5% sodium hydroxide solution and / or by treatment with potassium hydroxide (KOH) and / or sodium carbonate (Na2C03).

6. The method according to any one of the preceding claims, characterized in that the removal of the surface layer (6) takes place thermally in liquid and / or vapor, for example by treatment under pressure in an autoclave at temperatures up to 300 ° C.

7. The method according to any one of the preceding claims, characterized in that prior to generating the at least one intermediate layer (3) on the ceramic layer (2) on at least one surface side, a thin layer of copper or copper oxide or at least one other copper-containing compound is applied, and that subsequently the at least one intermediate layer (3) is produced by thermal oxidation.

8. The method according to any one of the preceding claims, characterized in that the thermal oxidation takes place until the at least one

Intermediate layer (3) has set a layer thickness in the range between 0.5 // m and 10 // m.

9. The method according to any one of the preceding claims, characterized in that the mechanical and chemical processing for removing the at least one surface layer (6) are performed at least partially overlapping in time or successively in time.

10. The method according to any one of claims 6 - 8, characterized in that the

Applying the thin layer of copper or copper oxide or of the at least one copper-containing compound by immersing the ceramic layer in an aqueous solution containing copper ions, for example, in an aqueous solution with 0.005 to 2.0 mol / ICu + + ion content. Method according to one of claims 6 - 9, characterized in that the

Applying the thin layer of copper or copper oxide or at least one other copper-containing compound by sputtering and / or carried out by CVD deposition and / or by chemical deposition.

Method according to one of the preceding claims, characterized in that the at least one intermediate layer (3) is obtained by thermal oxidation, i. by heating the ceramic layer (2) to a temperature in the range between 800 ° C and 1 450 ° C in air or in an oxygen-containing atmosphere with an oxygen content between 10% and 90%.

Method according to one of the preceding claims, characterized by the following method steps:

Placing at least one oxidized metal foil of copper or a copper alloy on at least one surface side of the cleaned ceramic layer (2) of AIN, heating the at least one metal foil and the ceramic layer (2) onto one

Temperature of 400 ° C - 1083 ° C,

Removing the at least one metal foil, preferably after cooling the metal foil and the ceramic layer (2),

Oxidizing the ceramic layer (2) at a temperature of 850 ° C - 1450 ° C in an oxygen-containing atmosphere to produce the intermediate layer (3) on at least one surface side of the ceramic layer (2), and.

DCB bonding at least one metal foil to at least one surface side of the ceramic layer (2).

Oxidizing the cleaned ceramic layer (2) of AIN at a temperature of 800 ° C 1450 ° C,

DCB bonding at least one metal foil of copper or a copper alloy to at least one surface side of the oxidized ceramic layer (2),

Removing the at least one metal foil, preferably by etching,

Re-oxidizing the ceramic layer (2) at a temperature of 800 ° C - 1450 ° C, and DCB bonding at least one metal foil to at least one surface side of the ceramic layer (2).