JPH02149485A - Production of ceramic substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a ceramic substrate having excellent thermal conductivity and having a conductor provided on its surface, and the conductor being bonded with high bonding strength. Relating to a manufacturing method.

(Prior art) Aluminum nitride (A j N) ceramic has good thermal conductivity, excellent heat dissipation, and excellent electrical properties such as electrical insulation, so it is attracting attention as a substrate material for semiconductors. There is.

When this AIN is used as a semiconductor substrate, it is usually manufactured as follows. That is, AIN raw material powder is prepared, a predetermined amount of sintering aids (rare earth elements, alkaline earth compounds, etc.) are blended into this raw material powder, and a binder (alkaline resin, etc.) is added to the powder to make the entire material sufficiently. mix,
The obtained mixture is formed into a green sheet by, for example, a doctor blade method, and then sintered in a nitrogen atmosphere. Then, a conductive surface layer is formed on a predetermined surface of the sintered body. As a method for forming a conductive surface layer, a method of applying a thick film method to provide a conductive metallized layer of gold, silver-platinum 1, silver-palladium, etc. has been practiced.

As mentioned above, AIN requires sintering aids such as yttrium oxide and calcium oxide during sintering in order to sinter densely. These sintering aids enter a liquid phase during the AIN sintering process, exist at the grain boundaries of AIN crystal grains, form a grain boundary phase, and firmly bind the AIN crystal grains, thereby making the sintered body dense. It is thought that it will change.

On the other hand, the liquid phase component mentioned above precipitates on the surface of the sintered body during the sintering process to form a liquid phase portion.

In addition, when considering thermal conductivity as a semiconductor substrate, oxygen contained in the sintering aid and present in the grain boundary phase is one of the factors that reduces thermal conductivity. Attempts have also been made to improve thermal conductivity by moving the liquid phase inside the sintered body to the surface of the sintered body and making the liquid phase unevenly distributed on the surface.

In this way, in order to sinter the AIN sintered body densely, it is necessary to contain a certain amount or more of a sintering aid.
The sintering aid makes the sintered body dense and causes a liquid phase portion to exist on the surface of the sintered body.

(Problems to be Solved by the Invention) However, when an AIN sintered body having a liquid phase portion on the surface of the sintered body as described above is used for a semiconductor substrate, there are several problems. For example, because the liquid phase part is precipitated on the surface, the surface of the sintered body is not smooth and has slight irregularities, and if a conductor is formed on this, the bonding strength with the conductor is not sufficient. In addition, the heat generated in the conductive portion cannot be efficiently conducted to the AIN sintered body.

In addition, since the liquid phase part itself has poor thermal conductivity, AIN
This impairs the good thermal conductivity of the sintered body, and furthermore, since the liquid phase portion tends to peel off from the sintered body, it deteriorates the bonding strength with the conductor and the like.

Therefore, in order to use the AIN sintered body as a semiconductor substrate, it is important to remove the liquid phase portion existing on the surface of the sintered body uniformly and in the necessary amount.

In particular, when a plurality of substrates are laminated to form a semiconductor substrate, it is necessary to provide through holes for interlayer connection of the substrates, and a liquid phase portion also exists on the inner surface of these through holes. In such a multilayer substrate, it is necessary to uniformly remove the liquid phase portion present on the surface of the sintered body including through holes.

The present invention was made to deal with such problems, and it forms a bonding surface with a conductor by uniformly and removing the necessary amount of unnecessary liquid phase portion existing on the surface of the AIN sintered body. An object of the present invention is to provide a method for manufacturing a ceramic substrate that has good thermal conductivity and a highly reliable bonded state with the conductor by bonding a desired conductor to this bonding surface.

[Structure of the invention]

(Means for Solving the Problems) The present invention includes a step of obtaining a bonding surface of a conductor by removing a liquid phase portion existing on the surface of a ceramic substrate containing aluminum nitride as a main component using a liquid medium; The method of manufacturing a ceramic substrate is characterized by comprising the step of forming a conductor on the bonding surface.

The AIN sintered body used in the present invention is made by adding compounds such as oxides and fluorides of rare earth elements and alkaline earth metal elements as sintering aids to aluminum nitride powder, and sintering it in a reducing atmosphere. The one tied together is used. Incidentally, the sintering aid component may be added in an amount necessary to sufficiently densify the sintered body, and if the amount is too large, an excessive liquid phase portion will be formed. The amount of the sintering aid component in the total mixture is preferably 15% by weight or less, preferably 10% by weight or less.

As a means for removing the liquid phase portion present on the surface of the ceramic substrate, the present invention employs a step of removing it using a liquid medium. As a means of removing the surface layer, polishing with a tool such as a grindstone may be considered, but this method is inefficient. Further, although honing is a highly efficient and preferable method, it may be difficult to sufficiently remove the liquid phase to the inside of the through hole. In the present invention, there is an etching method as a step of removing a liquid phase using a liquid medium. In this method, for example, the liquid phase portion on the surface of the sintered body can be uniformly removed each time the sintered body is immersed in a predetermined etching solution. Since the etching liquid can easily enter the inside of the through-hole of the substrate, the liquid phase portion existing on the inner surface of the through-hole can be removed in the same way as other surfaces. Etching solutions used in the present invention include H3PO4, H2SO4, NO3, HCI, IP
Examples include acid-based ones such as. Also, NaOH, KOH
, I, IOH, etc. can also be applied.

Note that depending on the etching conditions, the ceramic surface may become m after etching, but in this case, it is preferable to perform a surface smoothing process such as honing after that.

A conductor is formed on the surface of the substrate thus obtained.

For example, a silver thread conductive paste is printed in a predetermined pattern by screen printing and then baked. Further, a terminal pin is inserted into the through hole and connected via the conductor.

(Function) According to the method for manufacturing a ceramic substrate of the present invention, the bonding surface of the conductor is obtained by removing the liquid phase portion existing on the surface of the ceramic substrate mainly composed of aluminum nitride using a liquid medium. Narrow parts such as through-holes can also be obtained in the same condition as other flat parts. Therefore, the bonding state of the conductors formed on the surface of the ceramic substrate including the conductors formed in the through holes can be made uniform and highly reliable.

(Example) Next, examples of the present invention will be described.

FIG. 1 is a partial cross-sectional view showing an embodiment of an aluminum nitride substrate according to the present invention. The liquid phase portion of the surface of the aluminum nitride substrate 1 (including the inner surface of the through hole 3) is removed by etching, and a conductor 2 is formed on the surface. A terminal pin 4 is inserted into the through hole 3 and the conductor 2 is inserted into the through hole 3.
conductively connected to.

Such a ceramic substrate was manufactured as follows.

A slurry made by adding 3% by weight of yttrium oxide as a sintering aid to aluminum nitride powder, adding an organic binder, etc., was made into a 0.5 m thick slurry using a doctor blade method.
It was molded into a sheet of m.

A plurality of through holes (diameter 0.4 mm) were formed in the obtained sheet at predetermined positions by punching.

After degreasing the sheet thus obtained in a nitrogen atmosphere,
Sintering was performed at approximately 1800°C in a nitrogen atmosphere. A liquid phase portion precipitated and existed on the surface of the obtained aluminum nitride sintered body.

Then, the aluminum nitride sintered body was immersed at 70° C. for 20 minutes using a 35% solution of 11CI as an etching solution to remove the etching process (the liquid phase on the surface).

Furthermore, in order to increase the smoothness of the surface, honing was performed to remove the outermost layer. Gold paste for a conductor was printed in a predetermined pattern on the surface of the obtained sintered body by screen printing, and then fired at about 850°C. After that, terminal pins were inserted into the through holes and connected using silver brazing.

The bonding strength of the conductor formed on the surface of the aluminum nitride substrate thus obtained was as high as 0.8 to 1.2 kg/mj, and its variation was small. On the other hand, when no etching treatment is applied, the etching process is 0.2 to 1.
The weight was 0 kg/-, which was smaller than that of the above example, and the variation was large.

In addition, the bonding strength of the terminal pin provided in the through hole is 3.5 to 4 kg/mj in the above example, and 1.5 to 3 kg/mj in the case without machining or notching.
si was small and there were many variations.

As described above, in the ceramic substrate of this embodiment, the bonding strength between the ceramic sintered body and the conductor formed on the surface thereof is large, and a highly reliable bonding state can be obtained with little variation.

[Effects of the Invention] As explained above, according to the method for manufacturing a ceramic substrate of the present invention, the liquid phase portion on the surface of the ceramic sintered body, including the through holes, can be removed, and it is possible to remove the liquid phase portion on the surface of the ceramic sintered body. By uniformly obtaining a suitable surface condition, a ceramic substrate with significantly improved bonding strength to a conductor can be obtained. Furthermore, by using a liquid medium to remove the liquid phase portion, a uniform surface condition can be obtained and a highly reliable bonded condition can be obtained. Furthermore, since the surface condition of the outer surface of the sintered body and the through-hole portion is uniform, the wettability of the conductor paste during conductor printing becomes uniform, making it possible to form fine circuit patterns with minute pitches.
The printing conditions for the outer surface of the sintered body and the through-hole portion can be made the same. Therefore, it is no longer necessary to change the printing conditions of through-hole portions with poor wettability with conductive paste, unlike in the conventional method.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing an embodiment of aluminum nitride Mt according to the present invention. l......Aluminum nitride substrate 2...
...Conductor 3...Through hole 4...Terminal pin

Claims (1)

[Claims] The method includes the steps of: obtaining a bonding surface of a conductor by removing a liquid phase portion existing on the surface of a ceramic substrate containing aluminum nitride as a main component using a liquid medium; and forming a conductor on the bonding surface. A method for manufacturing a ceramic substrate, characterized in that: