JP2003069217A - Method for manufacturing circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a circuit board capable of simultaneously baking a plurality of moldings while the moldings remain superposed without using a spreading powder between the moldings. SOLUTION: The method for manufacturing the circuit board comprises (a) a step of manufacturing the molding having a roughness control surface controlled to a surface roughness of 2 to 5 μm at least on the surface containing a silicon nitride as a main body, (b) a step of baking the plurality of the moldings obtained in the step (a) in a stacked state so that at least one surface of all the superposed surfaces becomes the roughness control surface, (c) a step of separating the baked laminate obtained in the step (b) into individual sintered materials from the roughness control surface, and (d) a step of forming the conductor layer on the surface including at least the roughness control surface of the respective sintered materials obtained in the step (c).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a circuit board excellent in mass productivity for manufacturing at low cost a circuit board that can be suitably used for various insulating substrate materials and semiconductor element housing package materials. Regarding

[0002]

2. Description of the Related Art In recent years, the heat generated from a semiconductor device has been increasing with the high integration of semiconductor elements. In order to prevent malfunction of the semiconductor device, a substrate that quickly releases such heat to the outside of the device. Is needed.

However, conventionally used alumina materials for various insulating substrates and packages for accommodating semiconductor elements have a low thermal conductivity of about 20 W / mK, and as a substitute, a high thermal conductivity of 150 W / mK or more. Aluminum nitride with index began to be noticed.

However, it has been found that aluminum nitride has low strength and fracture toughness value and cannot be applied to parts to which high stress is applied and fields requiring high reliability. Therefore, silicon nitride has recently been attracting attention as a material that meets the requirements for high thermal conductivity, high strength, and high reliability.

Silicon nitride was predicted to have high thermal conductivity from the constituent elements and crystal structure, but recently, a silicon nitride sintered body having a thermal conductivity of 120 W / mK comparable to that of aluminum nitride was finally developed. The application of high thermal conductivity silicon nitride has been studied.

In general, a silicon nitride sintered body is formed by molding a mixed powder obtained by adding a sintering aid to a silicon nitride powder, and then molding the obtained molded body in a non-oxidizing atmosphere from 1700 to 1900.
It is produced by firing in a firing furnace at a high temperature of about ℃ for a predetermined time, but since silicon nitride is oxidized in an oxidizing atmosphere,
It was necessary to shut off the inside of the firing furnace from the outside and use a nitrogen gas, an inert gas, or the like to create a non-oxidizing atmosphere. as a result,
A circuit board made of a silicon nitride sintered material has a higher cost than a circuit board made of an oxide, and it is necessary to reduce the cost.

Therefore, many molded bodies are fired at once,
To improve productivity, a molded product is produced without adding a sintering additive that causes adhesion when the molded products are stacked, and the molded products are stacked, and spread powder is sandwiched between the molded products and baked. Japanese Patent Laid-Open No. 5-17234 and Japanese Patent Laid-Open No.
-330927 is proposed.

[0008]

However, in the method described in Japanese Patent Application Laid-Open No. 5-17234 and Japanese Patent Application Laid-Open No. 5-330927, since the spread powder is sandwiched between the molded bodies, the substrate after firing Since the spread powder adheres to the surface of the substrate, the surface of the substrate is roughened unevenly, so that there is a problem that the bonding strength of the metal plate or the like decreases.

Therefore, it is an object of the present invention to provide a method for manufacturing a circuit board, which is capable of firing a plurality of molded bodies at once without stacking the spread powder between the molded bodies.

[0010]

According to the method of manufacturing a circuit board of the present invention, the surface roughness R _max of at least one surface is 2 to 5.
Even if there is no spreading powder or a ceramic sheet between the compacts by directly stacking the compacts adjusted to μm and firing,
This is based on the finding that a large number of molded bodies can be fired in a single firing without the molded bodies adhering to each other, and as a result, low cost can be achieved.

That is, (a) a step of producing a molded body having a roughness control surface whose main surface is silicon nitride and at least one surface of which is controlled to have a surface roughness of 2 to 5 μm; ) A step of firing a plurality of molded bodies obtained in the step of stacking such that at least one surface of all overlapping surfaces is the roughness control surface, and (c) the step (b) A step of separating the obtained fired laminate from the roughness control surface into individual sintered bodies, and (d) a surface including at least the roughness control surface of each sintered body obtained in the step (d). It is characterized in that a conductor layer is formed.

In particular, in the step (b), the plurality of molded bodies are placed in a non-oxidizing atmosphere at 1650 ° C. to 1800 ° C.
It is preferable to bake at ° C. This makes it possible to obtain a sintered body that is dense, has high strength, and has high thermal conductivity.

In the step (d), a paste containing an active metal is applied to the surface of the sintered body, and the paste is placed in vacuum 8
It is preferable to perform the heat treatment at 00 ° C. to 1000 ° C. to form the conductor layer. This can increase the bonding strength between the conductor layer and the silicon nitride sintered body.

Further, in the step (d), a brazing material containing an active metal is applied to the surface of the sintered body, a metal foil and / or a metal plate is placed on the brazing material, and the brazing material is placed in vacuum 800
It is preferable that the conductor layer is formed by performing heat treatment at a temperature of from 1000 to 1000 ° C. This can increase the bonding strength between the conductor layer and the silicon nitride sintered body.

Furthermore, it is preferable to etch the metal foil and / or the metal plate bonded to the surface of the sintered body. Thereby, a complicated and fine circuit pattern can be easily manufactured.

[0016]

DETAILED DESCRIPTION OF THE INVENTION A method of manufacturing a circuit board according to the present invention will be described.

First, a molded body is produced in step (a). First, a raw material powder is prepared for that purpose. The silicon nitride powder has a purity of 94 to 98% and an average particle size of 0.1 to 1.5 μm.
m, α ratio of 80% or more, impurity oxygen amount of 0.5 to 3.0
Weight% is desirable. Impurity oxygen content is 3.0% by weight
If it is more than 0.5% by weight, the surface of the sintered body is likely to be roughened and the strength may be deteriorated. If it is less than 0.5% by weight, the sinterability is deteriorated.

It is preferable to add a desired sintering aid to the silicon nitride powder. As the sintering aid, known compounds such as rare earth element compounds, Mg compounds, Si compounds and Al compounds can be used. These compounds are
In addition to oxides, carbonates or acetates that can form oxides by firing may be used.

If the amount of the sintering aid added is too small, the sintering will be inferior and the thermal conductivity and strength will decrease, and if it is too large, the liquid phase will exude during firing, and the molded products that have been superposed will overlap each other. Is easily attached, it is preferable to add an appropriate amount depending on the auxiliary agent to be added. Specifically, if it is a rare earth element compound, it is 3 to 20% by weight, especially 10 in terms of oxide.
~ 15 wt%, 0.5 for Mg compounds in terms of oxides
˜5% by weight, especially 1 to 3% by weight, and if it is a Si compound, it is 0.1 to 7% by weight in terms of oxide, especially 0.1 to 4% by weight
If it is an Al compound, it is preferably 0.1 to 2% by weight, particularly 0.1 to 1% by weight in terms of oxide. Further, if a desired composition of all the above-mentioned sintering aids is combined to obtain an appropriate composition, the addition amount of each may be changed from the above range.

Next, an organic binder and a solvent are added to the above powder, and the mixture is mixed and then molded. The molding can be carried out by a known method such as a press molding method, an extrusion molding method, an injection molding method, a tape molding method, etc. However, since the circuit board is thin and the surface is smooth, it is preferable to use the doctor blade method.

In the doctor blade method, a slurry is prepared, a tape is prepared, and the tape is cut to prepare a sheet-shaped molded body. At that time, the surface roughness of at least one surface of the green sheet is 2 to 5 μm.
It is important that the thickness is 3 to 4.5 μm, more preferably 3.5 to 4 μm. The surface roughness in the present invention indicates the maximum surface roughness represented by R _max , and may be simply referred to as R _max . Further, the surface roughness R _max of the present invention can be measured by a contact-type surface roughness measuring device.

This is because if R _max of at least one surface is less than 3 μm when superposed, the compacts adhere to each other during firing, resulting in a high defect rate.
_{This is because when the maximum value} exceeds 5 μm, the surface of the sintered body becomes rough, and the bonding strength of the metal plate or the like decreases.

In order to prepare the roughness control surface whose surface roughness is controlled to 2 to 5 μm, it is effective to adjust the conditions for drying the slurry, the surface roughness of the carrier tape and the like. For example, the drying temperature of the tape is set to 50 ° C. and the surface roughness of the carrier tape is set to 3 μm. Also, the surface roughness is 3
It is also possible to transfer the roughness by pressing a PET film controlled to μm onto the molded body.

If one surface of the molded body is the roughness control surface, the surface roughness of the other surface is not limited,
To prevent the adhesion of plating after the circuit is formed on the substrate surface,
It is preferably from 5 to 1.5 μm, and particularly preferably from 0.7 to 1.2 μm, and the roughness control surface is most preferable in order to further reduce the adhesion between the molded bodies during firing.

This sheet-shaped molded product may be used as a molded product as it is as a single layer, or a thin green sheet may be laminated to form a molded product. It goes without saying that one surface needs to form the roughness control surface.

Next, in step (b), a sintered body is produced. Therefore, first, a plurality of molded bodies produced in the step (a) are prepared. At least one surface of each of these molded bodies has the roughness control surface, that is, the surface roughness R _max is 2 to 5 μm.
Since it is m, at least one surface of all superposed surfaces is stacked so as to be the roughness control surface.

In other words, if the roughness control surfaces of the molded bodies are stacked at the same position, for example, the roughness control surfaces of all the molded bodies are the upper surfaces, the stacked surfaces formed by the two molded bodies will have the same surface. The surface of the molded body located below serves as a roughness control surface, and it is possible to prevent the molded bodies from adhering to each other by firing. Further, the same effect can be obtained by stacking all the molded bodies so that the roughness control surface is the lower surface.

After stacking a plurality of molded bodies in this way,
While keeping this state, it is placed in a firing furnace and fired. The firing is preferably performed in a non-oxidizing atmosphere, and specifically, an oxygen partial pressure of 1 × 10 ⁻⁵ atm or less is preferable in order to prevent the oxidation of the molded body and the inhibition of sintering. . That is, the inside of the firing furnace may be filled with an inert gas such as nitrogen gas or Ar, but a part thereof may be replaced with a reducing gas such as hydrogen gas or ammonia gas.
Nitrogen gas is particularly preferable for suppressing decomposition of silicon nitride.

The firing temperature varies depending on the type of sintering aid and the amount added, but it is 1650 to 1800 ° C., especially 1 ° C.
It is preferably 680 to 1750 ° C, more preferably 1700 to 1720 ° C. This is because the sintering is insufficient at a temperature lower than 1650 ° C, and the silicon nitride is decomposed at a temperature higher than 1800 ° C to lower the strength. The firing time is not particularly limited as long as the relative density of the sintered body is 95% or more, but it is sufficient to hold the firing temperature, that is, the maximum holding temperature for 3 to 12 hours.

In order to crystallize the glass phase and increase the strength and thermal conductivity, the temperature is lowered to 1500 ° C. at a rate of 60 ° C./hour or less after completion of firing, after which heating is stopped and natural cooling is performed. It is preferable.

If desired, a degreasing treatment may be performed at 900 ° C. in a weakly oxidizing atmosphere to remove the binder before firing.

Thirdly, in step (c), the fired laminate obtained by firing in step (b) is separated into individual sintered bodies. In other words, it is important that the sintered bodies are fired in the stacked state in the step (b), and that they are taken out and all the sintered bodies are easily separated from the roughness control surface.

According to the present invention, since at least one surface of the superposed surfaces is the roughness control surface, the roughness control surface does not adhere even after firing. Therefore, the roughness control surface can be easily formed. The body can be separated.

Finally, in step (d), a conductor layer is formed on the surface of the sintered body. That is, a circuit board can be obtained by forming a conductor layer on the roughness control surface and, if desired, another surface. The conductor layer is formed on the roughness control surface because the surface roughness is relatively large, so that the conductor layer having high adhesion can be formed.

For forming the conductor layer, known methods such as a thick film method, a metal brazing method, a vapor deposition method and an active metal method can be used. In particular, the metal brazing method and the active metal method are low in cost. , To obtain good adhesion.

For example, a paste containing an active metal is applied to the surface of the sintered body including the roughness control surface and baked. Here, the active metal means at least one metal selected from Ti, Zr, and Hf, and the viscosity is adjusted by adding a solvent and optionally a dispersant.

Printing is preferable as a coating method, and it is particularly preferable to use a printing method using a screen because of low cost and mass production. Then, in order to prevent the oxidation of the silicon nitride and the paste, it is preferable to perform heat treatment at 800 ° C. to 1000 ° C., particularly 850 to 950 ° C. in a non-oxidizing atmosphere, particularly in vacuum. By setting this temperature range, a sufficient adhesion strength between the conductor layer and the sintered body can be secured, and a circuit board without conductor spreading can be manufactured.

Alternatively, a brazing material containing an active metal may be applied to the surface of the sintered body, a metal foil and / or a metal plate may be placed on the brazing material, and heat treatment may be performed for bonding. .
Here, the active metal means at least one metal selected from Ti, Zr, and Hf, and a brazing material containing this is used. Specific brazing materials include Cu-Ag-Ti and Cu.
A brazing material such as -Au-Ti can be exemplified.

The metal foil and / or the metal plate are made of Cu,
It is preferable to contain at least one low resistance metal of Al and Au, and the thickness thereof is preferably 0.1 mm or more, and particularly 0.2 mm or more. As a result, heat generation can be suppressed, and in particular, when a large current flows, the metal heat is generated and it is possible to prevent the circuit from breaking.

It is preferable to perform heat treatment at 800 to 1000 ° C. for joining the metal foil and / or the metal plate and the sintered body. Bonding in this temperature range makes it possible to secure a sufficient bonding strength between the metal plate or the like and the sintered body and to obtain a circuit board in which the brazing material does not spread.

Further, in order to obtain a uniform joined body, it is preferable that pressure is applied during the heat treatment to join.

When the conductor layer is a circuit pattern, a metal foil or a metal plate on which a circuit pattern is formed may be used, but when handling is difficult, a metal foil or a metal plate on which a circuit pattern is not formed is used. After joining, it is preferable to form a desired circuit pattern by etching. Specifically, it is preferable to form a predetermined circuit pattern on the surface of the metal foil or the metal plate by using steps such as resist application, exposure, development, etching treatment, and resist stripping. By using this method, a complicated circuit pattern can be easily manufactured.

[0043]

EXAMPLE A silicon nitride powder produced by a direct nitriding method having an average particle size of 1 μm, an α ratio of 87% and an impurity oxygen content of 1% by weight, and Er ₂ O having an average particle size of 1 μm and a purity of 99.9%. ₃ powder, Y ₂ O ₃ powder, Yb ₂ O ₃ powder, MgO powder, MgCO
₃ powders, AlN powders and Al ₂ O ₃ powders were mixed in the proportions shown in Table 1, acrylic resin binder and toluene were added to the mixed powders as a solvent, and after kneading, a thickness of 0.4 mm was obtained by a doctor blade method. A green sheet was molded.

In the production of this green sheet, the drying temperature and the carrier tape surface roughness were changed as shown in Table 1 to adjust the surface roughness of the lower surface of the green sheet, which was used as the roughness control surface.

The green sheets thus obtained are laminated so that the roughness control surface faces downward, and cut to a length of 80 m.
m, width 115 mm, thickness 0.8 mm molded body for substrate,
For each sample, 100 disc-shaped moldings for evaluation having a diameter of 12 mm and a thickness of 5 mm were prepared.

These substrate compacts were stacked in a stack of 20 compacts each so that the roughness control face was on the lower side, that is, the roughness control face was always on the overlapping face. By firing under the firing conditions shown in Table 1 to produce a sintered body for a substrate,
After firing, each sintered body was separated for each stage, and the number of the sintered bodies that could not be attached was measured. The oxygen partial pressure in the firing atmosphere was 1 × 10 ⁻⁵ atm or less.

Next, an insulating substrate having a length of 60 mm, a width of 90 mm, and a thickness of 0.6 mm is prepared as a substrate for bonding and evaluating a sample for a substrate, and Cu-Ag-Ti active metal solder is formed in a circuit pattern on one surface of the substrate. A Cu plate was applied by printing and printed with a solder resist in a circuit pattern of 0.5 mm. Further, the back surface thereof is coated with a Cu-Ag-Ti paste by screen printing, and is put in a reducing atmosphere at 900
The paste was baked while the Cu plates were joined by heat treatment at ℃.

The Cu plate of the obtained joined body was subjected to an etching treatment to form a circuit pattern, and the surface of the circuit pattern was subjected to electroless Ni plating to produce a circuit board. Among 100 samples, defective products were measured as circuit boards, and defective rates in all steps were measured.

[0049]

[Table 1]

Sample No. of the present invention. In Nos. 3 to 21, the firing failure was 10 or less, and the total failure rate was 10% or less.

On the other hand, the sample No. having a roughness control surface as large as 6 μm, which is out of the range of the present invention, was used. No. 1 had two or less defective firings, but the total defective rate was as high as 90%.

Further, the surface roughness control surface is as small as 2 μm or less, which is outside the range of the present invention. In No. 2, the number of defective firing was 90, and the total defective rate was 100%, which were all very high.

[0053]

According to the present invention, one surface of a molded article is
By adjusting the roughness to 5 μm and using it as a roughness control surface, the sintered bodies do not adhere to each other even when a plurality of molded bodies are stacked and fired so that the roughness control surface comes to the overlapping surface.

That is, when the method of the present invention is used, a large amount of a sintered body can be obtained by one-time firing without using spread powder, and the defect rate can be reduced, so that the cost of the circuit board can be reduced. You can

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 23/12 C04B 35/64 K H05K 3/06 G 3/12 610 35/58 102D H01L 23/12 D F term ( Reference) 4G001 BA06 BA08 BA09 BA32 BA36 BB06 BB08 BB09 BB32 BB36 BC17 BC22 BD23 BE32 BE35 4G026 BA17 BB22 BB27 BF31 BG02 BG21 BH07 5E339 AB06 AD01 BC02 BD06 BD11 BE13 EE23 DD23 BB23 BB23 BB23 BB24 BB67

Claims (5)

[Claims] 1. A step of: (a) producing a molded article having a roughness control surface whose main surface is silicon nitride and whose surface roughness is controlled to 2 to 5 μm; and (b) the step (a) above. ) A step of firing a plurality of molded bodies obtained in the step of stacking such that at least one surface of all overlapping surfaces is the roughness control surface, and (c) the step (b) A step of separating the obtained fired laminate from the roughness control surface into individual sintered bodies, and (d) a surface including at least the roughness control surface of each sintered body obtained in the step (c). A method of manufacturing a circuit board, comprising forming a conductor layer. 2. The method for manufacturing a circuit board according to claim 1, wherein in the step (b), the plurality of molded bodies are fired at 1650 ° C. to 1800 ° C. in a non-oxidizing atmosphere. 3. In the step (d), a paste containing an active metal is applied to the surface of the sintered body, and the temperature is 800 ° C. in vacuum.
The method for manufacturing a circuit board according to claim 1 or 2, wherein the conductor layer is formed by performing a heat treatment at 1000 ° C. 4. In the step (d), a brazing material containing an active metal is applied to the surface of the sintered body, a metal foil and / or a metal plate is placed on the brazing material, and the brazing material is placed in vacuum 800 ℃ ~ 10
The method for manufacturing a circuit board according to claim 1, wherein the conductor layer is formed by performing heat treatment at 00 ° C. 5. The method of manufacturing a circuit board according to claim 4, wherein the metal foil and / or the metal plate bonded to the surface of the sintered body is etched.