JP3779306B2 - Ceramic substrate and method of forming thin film on roughened surface of ceramic substrate - Google Patents

Description

  The present invention relates to a ceramic substrate and a method for forming a thin film on a roughened surface of a ceramic substrate.

Conventionally, various ceramic substrates have been manufactured as substrates for mounting electronic components and the like that generate a large amount of heat.
Such a ceramic substrate is generally known as having a metal conductor layer such as a wiring pattern formed on the surface of an insulating base made of a ceramic sintered body.

  FIG. 4 illustrates a conventional ceramic substrate 10. The insulating base material 11 constituting the ceramic substrate 10 is formed with a through hole forming hole 13 constituting a through hole 12 for conducting conduction between the front and back sides. A through-hole conductor layer 14 is formed in the through-hole forming hole 13 by filling with a conductive metal paste. A conductor pattern 15 is formed on the surface of the ceramic substrate 10. In addition, the conductor pattern 15 and the end surface of the through-hole conductor layer 14 exposed from the opening of the through-hole forming hole 13 are electrically connected by surface contact.

  The ceramic substrate 10 is manufactured through a procedure in which, for example, a conductive metal paste 14 is printed on a green sheet to form the through-hole conductor layer 14 and then fired. Further, the insulating base material (sintered body) 11 obtained through firing is subjected to a surface polishing process such as lapping, and the thickness and surface roughness are adjusted by this process. And the ceramic substrate 10 provided with the conductor pattern 15 as the final product is obtained by forming a metal film on the surface of the insulating base material 11 according to a predetermined method (a thin film method, a thick film method, a plating method, etc.).

  By the way, in the case of the ceramic substrate 10, it is mentioned as a feature that different substances, that is, a metal part with good wettability and a ceramic part with poor wettability are mixed in the same plane.

  In other words, even if the conductor pattern 15 is formed by each of the film forming methods, it means that sufficient adhesion force due to a chemical bonding force cannot be expected between the ceramic and the metal.

  Therefore, in the case of such a conductor pattern 15, the adhesion between the ceramic and the metal mainly depends on the surface roughness of the insulating base material 11, that is, the physical anchor effect due to the unevenness of the surface of the insulating base material 11. become.

  Therefore, in order to obtain the conductor pattern 15 having excellent adhesion, the surface roughness of the insulating base material 11 is set within a range that can bring about a suitable anchor effect, for example, by surface polishing performed in the final process. It becomes effective. And when the above countermeasures are not taken, the conductor pattern 15 will be easily peeled off due to insufficient adhesion.

  However, when the surface polishing treatment is performed by a conventional general method, not only the surface of the insulating base material 11 but also the exposed portion of the through-hole conductor layer 14 is attacked by abrasive grains. In this case, the metal of the said part is scraped off more than a ceramic part, and the malfunction that the void 16 etc. will be made in an end surface arises. For this reason, the connection state between the conductor pattern 15 and the end face is deteriorated, and the connection reliability is lowered (see FIG. 5).

  The present invention has been made in view of the above circumstances, and the first object thereof is to provide adhesion to such a surface even when a ceramic portion and a metal portion are mixed in the same surface. An object of the present invention is to provide a ceramic substrate capable of forming an excellent thin film.

  A second object of the present invention is to provide a method for forming a thin film on a roughened surface of a ceramic substrate, which can easily and reliably form a thin film having excellent adhesion to the roughened surface. .

In order to solve the above problems, in the first invention according to claim 1, in the ceramic substrate comprising an insulating base made of aluminum nitride, a metal through-hole conductor layer and a metal thin film , the insulating group The surface roughness of the material is in the range of 0.01 μm to 5 μm, the surface roughness of the conductor layer in the through hole is in the range of 0.002 μm to 2 μm, and the surface roughness of the insulating substrate is The gist of the ceramic substrate is that it is larger than the surface roughness of the conductor layer in the through hole.

In this case, it is desirable that the ceramic constituting the insulating substrate is aluminum nitride (AlN). In addition, the metal constituting the through-hole conductor layer may be at least one selected from tungsten (W), molybdenum (Mo), and copper (Cu).

According to a second aspect of the present invention, the metallizing method, the sputtering method, the plating method, the vapor deposition method, the ion plating method, the active metal method, and the CVD method are used. 2. A roughened surface of a ceramic substrate according to claim 1, wherein a metal thin film or a non-metallic thin film is formed on the roughened surface of the ceramic substrate comprising a ceramic insulating base and a metal through-hole conductor layer. The gist of the thin film forming method is as follows.

Furthermore, in the third invention according to claim 4, the ceramic comprising the ceramic insulating substrate and the metal through-hole conductor layer by using at least one selected from a dry film and a liquid resist. The gist of the method for forming a thin film on a roughened surface of a ceramic substrate according to claim 1, wherein a nonmetallic thin film is formed on the roughened surface of the substrate.

Hereinafter, the ceramic substrate of the present invention and the procedures for manufacturing such a ceramic substrate will be described.
The ceramic substrate of the present invention is characterized in that an insulating base made of aluminum nitride and a metal through-hole conductor layer are mixed at least in the same plane. In this substrate, the surface roughness of the insulating base and the surface roughness of the conductor layer in the through hole must be in the range of 0.01 μm to 5 μm and 0.002 μm to 2 μm, respectively.

  This is because if the surface roughness of the insulating base material is less than 0.01 μm, a predetermined anchor effect cannot be obtained, and the thin film formed on the ceramic substrate surface is easily peeled off. On the other hand, if the surface roughness of the insulating substrate exceeds 5 μm, the anchor effect can be improved, but the smoothness of the substrate surface is impaired, which is not preferable.

In addition, when the surface roughness of the conductor layer in the through hole exceeds 2 μm, the connection state between the conductor layer in the through hole and the thin film formed thereon deteriorates, especially when both are conductor layers. An electrical connection failure or the like is likely to occur between them.

In the ceramic substrate of the present invention, the surface roughness of the insulating base and the through-hole conductor layer is set within the above range, and the surface roughness of the insulating base is larger than the surface roughness of the through-hole conductor layer. It is preferable to keep it.

In this case, the surface roughness of the insulating substrate and the surface roughness of the conductor layer in the through hole are about 0.1 μm to 0.5 μm and 0.02 μm to 0.2 μm, respectively (that is, the latter surface roughness of the former is The value is preferably a fraction of a value).

  In the present invention, the ceramic constituting the insulating substrate is preferably AlN. This is because not only has high thermal conductivity required for a substrate for mounting electronic components and the like, but also can be easily adjusted to a suitable range of surface roughness by various methods described later.

The metal constituting the through-hole conductor layer is preferably at least one selected from W, Mo, and Cu, and is particularly preferably W. The reason is that the conductor layer in the through hole can be easily formed on the insulating base material by printing them in a paste form. Moreover, it is because it can adjust to the suitable range of surface roughness easily by various methods mentioned later. In addition to the metals listed here, metals such as niobium (Nb), tantalum (Ta), gold (Au), and silver (Ag) may be used.

  When producing the ceramic substrate as described above, first, a raw material slurry is produced by adding and kneading a binder, a sintering aid and the like to the ceramic powder of AlN. Then, by performing sheet molding or press molding using the slurry as a raw material, a flat green sheet is produced.

The green sheet thus obtained is provided with a structure for forming a through-hole conductor layer such as a through hole by a conventionally known processing method. Then, for example, a conductive metal paste containing W, Ta, Cu or the like as a main component is prepared, and printed on a green sheet, thereby forming a metal through-hole conductor layer in the through-hole or the like. . Thereafter, the green sheet becomes a dense ceramic sintered body through degreasing, temporary firing, and main firing.

Next, the physical method (wrapping) or chemical method (etching) is used to adjust the surface roughness and overall thickness of the ceramic sintered body (insulating base material / conductor layer in the through-hole ) to a predetermined range. ) Surface treatment is performed. In this case, the physical method and the chemical method may be performed alone or in combination. Then, by applying at least one of these surface treatment methods, the ceramic sintered body has a predetermined roughened surface (the surface roughness of the insulating substrate is 0.01 μm to 5 μm, the surface roughness of the conductor layer in the through hole). 0.002 μm to 2 μm) is formed.

  Lapping is a kind of processing method using loose abrasive grains. More specifically, a workpiece is obtained by performing relative motion in a state where abrasive grains are interposed between a tool called a lap and the workpiece. It is a method of processing.

  And in this invention, lapping is performed using the abrasive grain for grinding | polishing which contains at least any one selected from ceramic oxide, ceramic carbide, ceramic nitride, and diamond as a main component. This is because it is necessary to use abrasive grains having a hardness equal to or higher than that of the workpiece in order to polish hard ceramics to obtain a predetermined roughened surface.

Examples of the abrasive grains for polishing, for example, GC abrasive grains mainly composed of SiC, _Al 2 _{O 3} WA abrasive grains mainly composed of, _Al 2 _{O 3} and ZrO ₂ and FO abrasive grains mainly composed of, Examples include final finishing diamond abrasive grains such as FQ abrasive grains mainly composed of SiO ₂ .

  When GC abrasive grains are used, the grain size of the abrasive grains is preferably about 1200 to 3000 mesh. When WA abrasive grains are used, the grain size of the abrasive grains is preferably about 700 μm to 1200 μm. When FO abrasive grains are used, the grain size of the abrasive grains is preferably about 400 to 800 mesh. When FQ abrasive grains are used, the grain size of the abrasive grains is preferably about 400 mesh to 800 mesh. When diamond abrasive grains are used, the average grain diameter of the abrasive grains is preferably about 0.5 μm to 4.0 μm.

In addition to the abrasive grains listed here, for example, other ceramic oxides (Fe ₂ O ₃ , TiO ₂ , MgO, CeO ₂ , Cr ₂ O ₃ , CrO _3, etc.), ceramic carbides (ZrC, B ₄ C, etc.) , TiC, etc.), abrasive grains containing ceramic nitride (BN, Si ₃ N ₄ , TiN, etc.) as main components may be used. Thereafter, polishing using diamond abrasive grains is performed as a finish.

In the present invention, etching refers to dissolving the surface of a workpiece using a strong alkaline solution in which NaOH, KOH or the like is dissolved, or a weak alkaline solution in which Na ₂ CO ₃ , K ₂ CO ₃ , NH ₃ or the like is dissolved. This is the method.

  On the roughened surface obtained by carrying out any of the surface treatment methods described above, a metal thin film or a non-metal thin film is formed which becomes a conductor layer or an insulating layer on the ceramic substrate.

  The metal thin film is formed by at least one film forming method selected from metallizing method, sputtering method, plating method, vapor deposition method, ion plating method, active metal method, and CVD method. This is because these methods are suitable as means for forming a metal thin film having excellent adhesion on the roughened surface of the ceramic sintered body.

  Examples of the metal thin film obtained by the various film forming methods described above include thin films such as Au, Ag, Ni, Co, Al, Fe, Ti, and Cr in addition to Cu generally used as a material for forming a conductor pattern. It is done. The thickness of the metal thin film is preferably about 0.05 μm to 5 μm.

  The nonmetallic thin film is formed by using at least one selected from a dry film and a liquid resist. This is because these materials are suitable as materials for forming a non-metallic thin film (for example, a resin insulating layer such as various resists) on the roughened surface. Note that the thickness of the non-metallic thin film in the case of using the above materials is preferably about 5 μm to 50 μm.

  And when forming a resin insulation layer as a nonmetallic thin film, it is suitable to use photosensitive polyimide resin, photosensitive epoxy resin, photosensitive alkali resin, etc., for example.

  In addition, such a non-metallic thin film is formed by at least one film forming method selected from the metallizing method, the sputtering method, the plating method, the vapor deposition method, the ion plating method, the active metal method, and the CVD method mentioned above. Can also be formed.

  As described above, the ceramic substrate of the present invention has a roughened surface set to a surface roughness that can provide a suitable anchor effect. Therefore, even when the ceramic portion and the metal portion are mixed in the same plane, the thin film formed on the roughened surface has excellent adhesion.

  Further, according to the thin film forming method of the present invention, it is possible to easily and reliably form a thin film having excellent adhesion to the roughened surface.

  As described above in detail, according to the ceramic substrate of the present invention, even when a ceramic portion and a metal portion are mixed in the same plane, a thin film having excellent adhesion to such a surface is formed. There is an excellent effect of being able to.

  In addition, according to the method of forming a thin film on the roughened surface of the ceramic substrate of the ceramic substrate of the present invention, an excellent effect that a thin film having excellent adhesion to the roughened surface can be easily and reliably formed. Play.

Hereinafter, an embodiment in which the present invention is embodied in an AlN substrate will be described in detail with reference to FIGS.
In this example, 1000 g of AlN powder having an average particle size of 1.1 μm, 50 g of Y ₂ O ₃ powder as a sintering aid, 120 g of an acrylic binder, and a predetermined amount of plasticizer, dispersant, and solvent A raw material slurry for obtaining the green sheet 7 was prepared by uniformly kneading the ethanol added.

  Further, 120 g of an acrylic binder is added to 5000 g of W powder having an average particle size of 1.3 μm, and a mixture of a solvent and a dispersant is uniformly kneaded and adjusted to a predetermined viscosity, whereby a conductor layer in a through hole is obtained. W paste 9 for obtaining 3 was prepared.

  Next, a flat green sheet 7 was produced from the raw slurry in accordance with the sheet forming procedure of the doctor blade method. And the through-hole formation hole 8 was formed by punching the predetermined part of the obtained green sheet 7 by punching (refer Fig.1 (a)). By printing the W paste 9 with the green sheet 7 set on a screen printing machine, the W paste 9 was completely filled into the through-hole forming holes 8 (see FIG. 1B).

Next, the green sheet 7 was degreased at 700 ° C. and calcined at 1600 ° C., and then hot pressed under an inert atmosphere for 3 hours at 1830 ° C. and 200 kg / cm ² . The green sheet 7 and the W paste 9 were sintered at the same time by the above-described treatment, so that an AlN substrate 1a was obtained (see FIG. 1C).

  The AlN substrate 1a obtained through firing is in a state where the end face of the through-hole in-conductor layer 3 is exposed from the opening of the through-hole forming hole 8, as shown in FIG. Therefore, in the AlN substrate 1a, it can be said that the ceramic portion and the metal portion are mixed in substantially the same plane. Further, since the AlN substrate 1a is not subjected to the surface treatment, both the surface roughness Ra1 of the AlN substrate 2 and the surface roughness Ra2 of the through-hole in-conductor layer 3 are still large.

  Here, surface treatment by a physical or chemical method is performed on both the front and back surfaces of the AlN substrate 1a to obtain a thinned AlN substrate 1 having a roughened surface 6 (FIG. 1 ( d)).

  In this example, a total of 13 test samples were prepared by performing two types of surface treatments as described below. First, as a first surface treatment method, lapping was performed with a small double-sided lapping machine (manufactured by Nippon Engis). As processing conditions at this time, the rotation speed was set to 900 rpm and the processing time was set to 10 minutes.

  Moreover, 10 types of abrasive grains as shown in Table 1 were selected as lapping abrasive grains, and a lapping solution having a predetermined concentration (350 g / liter) was prepared using each abrasive grain. And after lapping on said conditions, the test samples 1-10 were obtained by finishing with a diamond abrasive grain.

また、第２の表面処理方法として、上記のラッピング処理を施した各サンプル１〜１０に対し、３種のアルカリ性エッチング液（表２参照）によるエッチングを行った。そして、表２に示されるような条件に従って処理を行うことにより、試験サンプル１１〜１３を得た。

In addition, as a second surface treatment method, each sample 1 to 10 subjected to the above lapping treatment was etched with three types of alkaline etching solutions (see Table 2). And the test samples 11-13 were obtained by processing according to conditions as shown in Table 2.

前記各種表面処理によって得られたサンプル１〜１３について、接触式表面粗さ計による、ＡｌＮ基材２及びスルーホール内導体層３の表面粗さ（中心線平均粗さ）Ｒa1，Ｒa2の測定を行った。それらの測定結果を表３にまとめて示す。

For samples 1 to 13 obtained by the above various surface treatments, the surface roughness (centerline average roughness) Ra1 and Ra2 of the AlN substrate 2 and the through-hole conductor layer 3 are measured by a contact-type surface roughness meter. went. The measurement results are summarized in Table 3.

その結果、表３から明らかなように、いずれの試験サンプルについても、表面粗さＲa1，Ｒa2の値がいずれも所定範囲内（Ｒa1＝０．０１μｍ〜５μｍ，Ｒa2＝０．００２μｍ〜２μｍ）となることが確認された。また、ＡｌＮ基材２の表面粗さＲa1と、スルーホール内導体層３の表面粗さＲa2とを比較すると、後者が前者の約数分の１以下となることも確認された（図２参照）。

As a result, as is apparent from Table 3, the surface roughness Ra1 and Ra2 are both within a predetermined range (Ra1 = 0.01 μm to 5 μm, Ra2 = 0.002 μm to 2 μm) for any test sample. It was confirmed that In addition, when the surface roughness Ra1 of the AlN substrate 2 and the surface roughness Ra2 of the through-hole conductor layer 3 were compared, it was also confirmed that the latter was less than a fraction of the former (see FIG. 2). ).

  Subsequently, the formation of the metal / nonmetal thin film on the roughened surface 6 of each test sample 1 to 13 was performed by the following method. First, the AlN substrate 1 was washed and dried, and then a catalyst nucleus for depositing electroless copper plating on the roughened surface 6 was applied. Next, a photosensitive epoxy resin was applied to the AlN substrate 1 and exposed and developed to form a plating resist 5 having a thickness of 20 μm on the roughened surface 6. Next, after activating the catalyst nucleus, electroless copper plating was performed using an electroless copper plating bath. As a result, a conductor pattern 4 having a thickness of 20 μm was formed in a portion where the plating resist 5 was not formed (see FIG. 3).

  When each thin film obtained by such a procedure was observed, no peeling or the like was observed on the thin film for any of the test samples, and it was confirmed that the formation state was extremely good (see Table 3). . Further, no voids or the like were generated at the portion where the conductor pattern 4 and the end face of the through-hole conductor layer 3 were in contact with each other, and the connection between them was extremely good (see FIG. 3).

In addition, this invention is not limited only to the said Example, It can change as follows. For example,
(A) Instead of the embodiment in which the present invention is embodied in a ceramic double-sided plate, it is of course possible to embody a ceramic multilayer plate formed by laminating and firing sheet-formed green sheets. In this case, it is preferable to form a conductive pattern in the inner layer in advance using a conductive metal paste or the like before the sheet lamination step.

(B) Moreover, it is good also as performing surface grinding | polishing and formation of a thin film only about the single side | surface of a ceramic substrate.
(C) Instead of the surface treatment method as in the embodiment, so-called mechanochemical wrapping using, for example, an etching solution as a wrapping solution can also be performed. According to such a surface treatment method, the process can be simplified and made more efficient than when etching and lapping are performed alone.

  The mechanochemical wrapping is not only a process in which the solid-liquid reaction between the lapping liquid and the non-processed product is dominant, but also a process in which the solid-phase reaction between the abrasive grains and the non-processed product is dominant. Those which are are also effective.

  (D) The metal conductor layer provided on the ceramic insulating substrate is not limited to the through-hole conductor layer as in the embodiment. For example, the insulating substrate may be provided with a recess, and a conductor layer may be provided on the inner surface of the recess.

  (E) The non-metallic thin film formed on the roughened surface is not limited to resin, and may be ceramics, for example.

(A)-(d) is a partial schematic sectional drawing which shows the manufacturing process of the AlN board | substrate in an Example. It is a partial schematic sectional drawing which shows the state which formed the roughening surface by the surface treatment with respect to an AlN board | substrate. It is a partial schematic sectional drawing which shows the state which formed the conductor pattern and the plating resist in the AlN board | substrate. It is a partial schematic sectional drawing which shows the conventional ceramic substrate. It is a partial schematic sectional drawing for demonstrating the problem in the conventional ceramic substrate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1a ... AlN board | substrate as a ceramic substrate, 2 ... AlN base material as an insulating base material, 3 ... Conductor layer in through-hole as a metal conductor layer, 4 ... Conductor pattern as a metal thin film, 5 ... Nonmetal Plating resist as thin film, 6 ... roughened surface, Ra1 ... surface roughness of insulating substrate, Ra2 ... surface roughness of conductor layer.

Claims (4)

In a ceramic substrate (1) comprising an insulating base (2) made of aluminum nitride, a metal through-hole conductor layer (3) and a metal thin film (4), the surface roughness (2) of the insulating base (2) ( Ra1) is in the range of 0.01 μm to 5 μm, the surface roughness (Ra2) of the conductor layer (3) in the through hole is in the range of 0.002 μm to 2 μm, and the insulating substrate (2) The surface roughness (Ra1) of the ceramic substrate is larger than the surface roughness (Ra2) of the through-hole conductor layer (3). The ceramic substrate according to claim 1, wherein the metal constituting the through-hole conductor layer (3) is at least one selected from tungsten, molybdenum, and copper. By using at least one film forming method selected from metallizing method, sputtering method, plating method, vapor deposition method, ion plating method, active metal method and CVD method, ceramic insulating substrate (2) and metal 2. A ceramic substrate according to claim 1, wherein a metal thin film (4) or a non-metal thin film (5) is formed on the roughened surface (6) of the ceramic substrate (1) comprising the conductor layer (3) in the through hole. A method for forming a thin film on the roughened surface. By using at least one selected from a dry film and a liquid resist, a roughened surface of a ceramic substrate (1) comprising a ceramic insulating substrate (2) and a metal through-hole conductor layer (3) The method of forming a thin film on a roughened surface of a ceramic substrate according to claim 1, wherein the nonmetallic thin film (5) is formed on (6).

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