JP2006140538A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board where a metallic member is firmly brazed on a wiring layer formed on the surface of an insulating substrate, corrosion such as gap corrosion is less likely generated in a material for brazing or in a wiring layer, the attenuation of a signal transmitted between the wiring layers is reduced, and a semiconductor device is operated more accurately and more stably. <P>SOLUTION: The wiring board 6 includes the first wiring layer 2 and the second wiring layer 3 with the metallic member 8 brazed on the surface of the insulating substrate 1. A copper-plated layer 7a coats the surface of the first wiring layer, and a nickel-plated layer 7b coats the surface of the second wiring layer 3. The first wiring layer 2 and the second wiring layer 3 are electrically connected by an inner wiring layer 4 formed in the insulating substrate 1. The inner wiring layer 4 is electrically connected to the first wiring layer 2 and the second wiring layer 3 by a through hole conductor 4a with the through hole conductor 4a penetrating only a ceramic green sheet that is a topmost layer of the insulating substrate 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wiring board formed by electrically connecting a first wiring layer formed on the surface of an insulating substrate and a second wiring layer to which a metal member is brazed.

  2. Description of the Related Art Conventionally, wiring boards used for mounting electronic components such as semiconductor elements, capacitive elements, resistors, etc. are generally made of an electrically insulating material such as an aluminum oxide sintered body as shown in FIG. An insulating substrate 21 on which electronic components are mounted, a wiring layer 22 formed on the upper surface of the insulating substrate 21 from the region where the electronic components are mounted to the outer periphery, and a brazing material such as silver solder on the wiring layer 22. The electronic component such as the semiconductor element 24 is mounted on the upper surface of the insulating base 21 and the electrode of the electronic component is bonded to the wiring layer 22 with the bonding wire 25. Then, an electronic device is obtained by sealing the electronic component with a lid, a sealing resin, or the like as necessary.

  In such an electronic device, the external lead terminal is connected to the wiring conductor of the external electric circuit board via a conductive bonding material such as solder, whereby each electrode of the electronic component is electrically connected to the external electric circuit via the wiring layer. Will be.

It should be noted that the wiring layer usually has corrosion resistance and bonding properties such as nickel, copper, gold, etc. in order to prevent the participation corrosion and to improve the bonding property of the bonding wire and the wettability (reactivity) of the brazing material. A plating layer with good brazing material wettability is applied.
JP 2000-77805 A

  However, since the wiring board is continuously formed on the upper surface of the insulating substrate from the region where the metal member of the wiring layer is brazed to the region where the bonding wire is connected, the metal member is brazed to the wiring layer. In this case, the brazing material flows out from the brazing region of the wiring layer, and the amount of brazing material for brazing the metal member is insufficient, so that the metal member cannot be firmly brazed to the wiring layer. .

  In order to solve the above drawbacks, for example, a region of the wiring layer where a metal member such as a lead terminal is brazed is partitioned by a ceramic insulating layer to prevent the brazing material from flowing out to an unnecessary region of the wiring layer. It is possible to do.

  However, when the region of the wiring layer where the metal member is brazed is partitioned with a ceramic insulating layer or the like, the brazing material such as silver brazing does not react with the ceramic insulating layer. A minute gap is formed in the gap, and moisture in the outside air enters the gap, causing gap corrosion in the brazing material and the wiring layer, resulting in deterioration of the bonding strength of the metal member and adjacent wiring layers due to the eluted metal component. Cause problems such as electrical short circuit.

  In particular, such crevice corrosion is caused by the exposure of the lead terminal after the lead terminal is brazed to the wiring layer in order to improve the wettability of the solder to the lead terminal and to effectively prevent the oxidative corrosion of the lead terminal. When coating a plating layer such as nickel, copper, or gold on the surface, the entire wiring board is usually immersed in a corrosive solution such as a plating solution or various processing solutions. There was also a problem of becoming.

  The present invention has been devised in view of the above problems, and its purpose is to be able to firmly braze a metal member to a wiring layer formed on the surface of an insulating substrate, and to a brazing material or a wiring layer. An object of the present invention is to provide a wiring board that is less susceptible to crevice corrosion and the like.

  It is another object of the present invention to provide a wiring board capable of reducing the attenuation of signals propagated between the wiring layers and stabilizing and operating the semiconductor element more accurately.

  The wiring board of the present invention is a wiring board formed by forming a first wiring layer and a second wiring layer to which a metal member is brazed on the surface of an insulating base, and the first wiring layer is formed on the surface. The copper plating layer, the second wiring layer is coated with a nickel plating layer, and the first wiring layer and the second wiring layer are interposed through an internal wiring layer formed inside the insulating substrate. It is characterized by being electrically connected.

  In the wiring board of the present invention, the internal wiring layer is electrically connected to the first wiring layer and the second wiring layer by a through-hole conductor, and the through-hole conductor is connected to the outermost part of the insulating substrate. Only the upper ceramic green sheet is penetrated.

  The semiconductor device according to the present invention is characterized in that a semiconductor element is mounted on the upper surface of the wiring board described above and each electrode of the wiring conductor is connected to the first wiring layer.

  According to the wiring board of the present invention, the second wiring layer to which the metal member is brazed is electrically connected via the first wiring layer and the internal wiring layer, and is not in direct contact with the second wiring layer. When the metal member is brazed, the brazing material does not flow out to the first wiring layer, the second wiring layer and the metal member can be brazed with a sufficient amount of brazing material, and the metal member is The wiring layer can be firmly brazed. At the same time, it is not necessary to form a coating material for preventing the brazing material from flowing out on the surface of the wiring layer, and there is no gap that induces crevice corrosion, so that corrosion of the wiring layer can be effectively prevented. .

  According to the wiring board of the present invention, the first wiring layer has a copper plating layer on its surface, the second wiring layer has a nickel plating layer on its surface, and the first wiring layer and the second wiring layer. Is electrically connected via an internal wiring layer formed inside the insulating substrate, so that attenuation of signals propagated between the wiring layers is reduced, and the semiconductor element is made more accurate. It can be stabilized and operated.

  Furthermore, according to the wiring board of the present invention, the internal wiring layer is electrically connected to the first wiring layer and the second wiring layer through the through-hole conductor, and the through-hole conductor is connected to the uppermost layer of the insulating base. Since it penetrates only the ceramic green sheet that becomes, by reducing the length of the internal wiring layer as much as possible, the attenuation of the signal propagated between the first wiring layer and the second wiring layer is reduced, The semiconductor element can be stabilized and operated more accurately.

  According to the semiconductor device of the present invention, it is possible to provide a semiconductor device in which a semiconductor element is mounted on the upper surface of the wiring board described above and each electrode of the wiring conductor is connected to the first wiring layer. It is possible to provide a semiconductor device that can be stabilized and operated more accurately.

  Next, an embodiment of a wiring board according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an embodiment in which the wiring board of the present invention is used as a wiring board for mounting a semiconductor element. 1 is an insulating substrate, 2 is a first wiring layer, 3 is a second wiring layer, and 4 is an internal part. A wiring substrate 6 on which the semiconductor element 5 is mounted is formed by the insulating base 1, the first wiring layer 2, the second wiring layer 3, and the internal wiring layer 4.

  Further, as shown in FIG. 2, a plating layer 7 a is applied to the surface of the first wiring layer 2, and a plating layer 7 b is applied to the surface of the second wiring layer 3, and the second wiring layer 3 is plated. Lead terminals 8 are brazed with the layer 7b interposed therebetween.

  The insulating substrate 1 functions as a substrate on which the semiconductor element 5 and the like are mounted and supported, and the semiconductor element 5 is bonded and fixed to the upper surface of the insulating substrate 1 via an adhesive such as brazing material, glass, or organic resin.

  The insulating substrate 1 is formed of an electrically insulating material such as an aluminum oxide sintered body, an aluminum nitride sintered body, or a mullite sintered body. Add appropriate organic binder, solvent, etc. to raw material powders such as silicon oxide, magnesium oxide, calcium oxide, etc. to make mud and mold it into a sheet by doctor blade method or calender roll method etc. A ceramic green sheet is obtained, and thereafter, the ceramic green sheet is appropriately punched and punched, and a plurality of these are laminated and fired at a high temperature.

  Further, the electrodes of the semiconductor element 5 are connected to the first wiring layer 2 formed on the upper surface of the insulating substrate 1 via bonding wires 10, and the external lead terminals 8 are connected to the second wiring layer 3 via the brazing material 9. It is brazed. The first wiring layer 2 and the second wiring layer 3 are electrically connected via an internal wiring layer 4 to be described later, and a semiconductor is obtained by connecting an external lead terminal 8 to an external electric circuit board via solder or the like. The electrode of the element 5 is electrically connected to an external electric circuit.

  The first wiring layer 2 and the second wiring layer 3 on the upper surface of the insulating base 1 are made of a metal material such as tungsten, molybdenum, manganese, copper, silver, or an alloy containing these as a main component. For example, one kind of these metals Alternatively, a conductive paste obtained by adding an appropriate organic solvent and binder to the metal powder containing two kinds of main components is printed on a ceramic green sheet serving as the insulating substrate 1 in a predetermined pattern by screen printing or the like. It is formed.

  The plating layer 7a applied to the first wiring layer 2 prevents the oxidative corrosion of the first wiring layer 2 and improves the bonding property of the bonding wire 10 to the first wiring layer. 2 The plating layer 7b deposited on the wiring layer 3 prevents the oxidative corrosion of the second wiring layer 3 and improves the wettability of the brazing material when the external lead terminals 8 are brazed. It is made of a metal having good corrosion resistance such as gold, bonding property, and wettability of brazing material.

  Such plating layers 7a and 7b are, for example, in an electroless plating solution mainly composed of a metal to be deposited, such as nickel, copper, or gold, and a reducing agent such as boron or phosphorus. By immersing the first wiring layer 2 and the second wiring layer 3 for a predetermined time, the first wiring layer 2 and the second wiring layer 3 can be deposited to a predetermined thickness.

  In the wiring board 6 of the present invention, it is important to make electrical connection between the first wiring layer 2 and the second wiring layer 3 through the internal wiring layer 4 formed inside the insulating substrate 1.

  By performing electrical connection between the first wiring layer 2 and the second wiring layer 3 via the internal wiring layer 4, the first wiring layer 2 and the second wiring layer 3 are not in direct contact with each other. When the external lead terminal 8 is brazed to the wiring layer 3 via the brazing material 9, the brazing material 9 does not flow to the first wiring layer 2, thereby brazing the external lead terminal 8. 9 can be secured sufficiently, and the external lead terminal 8 can be firmly brazed to the second wiring layer 3.

  The internal wiring layer 4 includes, for example, a through-hole conductor 4a formed from the first wiring layer 2 and the second wiring layer 3 directly into the insulating base 1 and a through-hole conductor 4a formed inside the insulating base 1. It is composed of an inner layer conductor 4b that conducts between them, and a through hole is formed at a predetermined position of a ceramic green sheet to be an insulating base 1, and the same as the formation of the first wiring layer 2 or the second wiring layer 3 A conductive paste is printed, applied, and filled in the surface of the ceramic green sheet and in the through holes, and formed inside the insulating substrate 1.

  The internal wiring layer 4 is preferably made as short as possible by providing the through-hole conductors 4a only on the ceramic green sheet that is the uppermost layer of the insulating base 1, and the like. By making the length as short as possible, the attenuation of the signal propagated between the first wiring layer 2 and the second wiring layer 3 becomes extremely small, and the semiconductor element 5 mounted on the wiring board 6 is made more accurate. In addition, it can be operated stably.

The internal wiring layer 4 is formed so that the contact area with respect to the first wiring layer 2 and the second wiring layer 3 is about 0.002 mm ² or more in order to reduce the resistance of the entire wiring layer. For example, considering that the inner diameter of the through-hole conductor 4a is 50 μm or more, and the processing accuracy and downsizing of the wiring board are taken into consideration, it is preferable to form a columnar shape having an inner diameter of about 75 μm to 100 μm. In this case, the through-hole conductor 4a usually has a circular cross section, but may be an ellipse, a polygon such as a quadrangle or a hexagon.

  The lead terminal 8 functions as an external connection terminal of the wiring board 6 and is made of a metal material such as copper, an alloy mainly composed of copper, an iron-nickel alloy, or an iron-nickel-cobalt alloy. It is formed by subjecting the material to known metal processing such as rolling and punching. The lead terminal 8 is brazed to the second wiring layer 3 via a brazing material 9 such as silver brazing. For example, the lead terminal 8 is placed on the second wiring layer 3 and a silver-copper eutectic brazing material is interposed therebetween. In addition, it is brazed on the second wiring layer 3 by heat treatment at a temperature of about 800 ° C.

  The lead terminal 8 is preferably brazed onto the second wiring layer 3 and then its exposed surface is preferably covered with a plating layer (not shown) such as nickel, copper, or gold. Covering with a plating layer may prevent oxidative corrosion of the lead terminal 8 and improve solder wettability when the lead terminal 8 is connected to the wiring conductor of the external electric circuit board via solder or the like. In addition, the electrical resistance of the lead terminal 8 can be further reduced. Such a plating layer is formed by the same method as the plating layers 7a and 7b of the first wiring layer 2 and the second wiring layer 3, more specifically, a metal containing a metal to be deposited and a reducing agent as main components. It can be formed by immersing the lead terminal 8 (usually, in fact, the entire wiring board 6) in the electrolytic plating solution.

  In this case, according to the wiring board of the present invention, since the first wiring layer 2 and the second wiring layer 3 are connected via the internal wiring layer 4 as described above, the wiring layer 3 is connected to the second wiring layer 3. There is no need to form a ceramic insulation layer to prevent the material from flowing out, and no gaps are created. Even if the entire wiring board is immersed in the plating solution, it does not induce or promote crevice corrosion, and leads It is possible to effectively prevent deterioration of the bonding strength of the terminal 8 (metal member) and electrical short circuit between adjacent wiring layers, particularly the second wiring layer 3 due to the eluted metal component.

  In the wiring substrate 6 of the present invention, the first wiring layer 2 is preferably formed of a metal material containing copper as one of the main components, and the first wiring layer 2 is made of the main component. For example, if a metal material containing copper is used, the electrical resistance of the entire wiring layer is lowered, and the attenuation of the propagated signal is further reduced, so that the semiconductor element 5 mounted on the wiring board 6 is further increased. It can be operated accurately and stably.

  In this case, the first wiring layer 2 is made of a metal material such as tungsten-copper or molybdenum-copper, and in particular, a ratio of 10 to 70% by volume of copper and 30 to 90% by volume of tungsten and / or molybdenum. It is preferable that it is contained.

This achieves a reduction in resistance of the first wiring layer 2 and simultaneous sintering with the insulating base 1 made of an aluminum oxide sintered body and the like, and also preserves the first wiring layer 2 during simultaneous firing. This is because the electrical resistance of the conductor forming the first wiring layer 2 is about 5.5 × 10 ^{− when the} copper content is less than 10% by volume and the tungsten or molybdenum content is more than 90% by volume. ⁶ Ω · cm or higher. On the other hand, if the amount of copper is more than 70% by volume and the amount of tungsten or molybdenum is less than 30% by volume, the retention of the first wiring layer 2 during co-firing is reduced, and bleeding occurs in the first wiring layer 2. This is because the first wiring layer 2 aggregates due to the molten copper and disconnection occurs, and peeling of the first wiring layer 2 occurs due to a difference in the thermal expansion system between the insulating substrate 1 and the first wiring layer 2. The optimum composition range is 40-60% by volume of copper and 60-40% by volume of tungsten and / or molybdenum.

  Further, in the present invention, tungsten and / or molybdenum in the first wiring layer 2 is dispersed and contained in a matrix made of copper as sintered particles of spherical or several particles having an average particle diameter of 1 to 10 μm. It is desirable. This is because when the average particle size is smaller than 1 μm, the shape retention of the first wiring layer 2 is deteriorated and the structure becomes porous and the resistance of the first wiring layer 2 is increased. This is because the matrix is divided by particles of tungsten or molybdenum and the resistance of the first wiring layer 2 is increased, or the copper component is separated and bleeding occurs. Most preferably, tungsten and / or molybdenum is dispersed with an average particle size of 1.3 to 5 μm, particularly 1.3 to 3 μm.

  The first wiring layer 2 may contain aluminum oxide or the same component as that of the insulating substrate 1 at a ratio of 0.05 to 2% by volume in order to improve adhesion to the insulating substrate 1. Is possible.

  Furthermore, in the wiring substrate 6 of the present invention, the first wiring layer 2 containing copper is co-fired with the insulating substrate 1 at a temperature exceeding the melting point of copper, whereby the copper component in the first wiring layer 2 is insulated. However, according to the present invention, the diffusion distance of copper to the insulating substrate 1 around the first wiring layer 2 containing at least copper is preferably 20 μm or less, particularly preferably 10 μm or less. . This is because if the diffusion distance of copper into the insulating substrate 1 exceeds 20 μm, the insulation between the first wiring layers 2 is lowered when the electric circuit is formed, and the reliability of the electric circuit is lowered.

  By setting the copper diffusion distance to 20 μm or less, the minimum distance between the first wiring layers 2 formed in the same plane in the first wiring layer 2 is increased to 100 μm or less, particularly 90 μm or less. Can be achieved.

  In the wiring board 6 of the present invention, the plating layer 7a to be deposited on the surface of the first wiring layer 2 is preferably composed mainly of a low resistance metal such as copper. Can be further reduced in resistance.

  If a low resistance metal such as copper is used as the plating layer 7a of the first wiring layer 2, the frequency of the signal propagating through the first wiring layer 2 is increased, and the consumption of the semiconductor element 5 mounted on the wiring substrate 6 is reduced. The first wiring layer 2 can be made to have a very low resistance in response to the demand for lower resistance of the entire wiring layer, such as electric power, and the loss of signals propagating in the first wiring layer 2 can be reduced to a very small one. Thus, the semiconductor element 5 can be normally operated more reliably.

  When the plating layer 7a of the first wiring layer 2 is made of copper, if the thickness thereof is less than 2 μm, the resistance of the first wiring layer 2 tends to be insufficient for the high frequency of the propagated signal, etc. If it exceeds 15 μm, the adhesiveness to the first wiring layer 2 is lowered due to internal stress, and there is a risk of causing problems such as blistering and peeling. Accordingly, when the plating layer 7a of the first wiring layer 2 is made of copper, the thickness is preferably in the range of 2 μm to 15 μm, and more preferably in the range of 3 μm to 6 μm.

  When the plating layer 7a of the first wiring layer 2 is made of copper, for example, a copper compound serving as a copper supply source such as copper sulfate and a reducing agent such as formalin and sodium hypophosphite are the main components. By immersing the first wiring layer 2 in the electroless copper plating solution for a predetermined time, the first wiring layer 2 is deposited on the first wiring layer 2 to a predetermined thickness.

  In this case, in the copper plating layer to be deposited, the eutectoid component contained in the plating layer varies depending on the type of the reducing agent used. For example, in the case of formalin, the copper content is 99.9. A high-purity copper layer of not less than wt% is formed, and a copper layer containing several wt% of phosphorus is formed in the case of sodium hypophosphite. Since it is preferable that the copper plating layer has high purity in order to reduce resistance, it is preferable to use a reducing agent that does not contain a eutectoid component in the plating layer such as formalin.

  Further, when the first wiring layer 2 is formed of tungsten and / or molybdenum and copper and a plating layer made of copper is deposited on the surface thereof, it is exposed on the surface of the first wiring layer 2 as a pretreatment for plating. It is preferable to remove the refractory metal of tungsten and / or molybdenum as much as possible by etching, and to increase the ratio of the exposed copper component of the surface of the first wiring layer 2 to, for example, 80% or more. If the exposed ratio of the copper component in the surface of the first wiring layer 2 is set to 80% or more, the ratio of bonding of copper, which are the same metal, between the first wiring layer 2 and the plating layer increases. The adhesion strength of the copper plating layer to the layer 2 can be further improved.

  Further, since the second wiring layer 3 acts as a connection pad for brazing a metal member such as the lead terminal 8 or the like, the second wiring layer 3 has an adhesive strength to the insulating substrate 1 in order to ensure the connection reliability of the metal member to the wiring board. For example, it is necessary to increase it to 3 kgf (29.4 N) or more, and it is preferable to form with a metal material such as tungsten, molybdenum, tungsten and / or an alloy containing molybdenum as a main component.

  The second wiring layer 3 is preferably made of a material composed of tungsten and / or molybdenum and an iron group metal, and the second wiring layer 3 having the above composition gives high adhesion strength to the insulating substrate 1. Can do.

  When the second wiring layer 3 is formed by simultaneous firing with the first wiring layer 2 containing a large amount of low melting point copper as a conductor component, the firing temperature must be fired at a low temperature of 1200 to 1500 ° C. Therefore, a conductor made of only tungsten or molybdenum cannot be sufficiently sintered during low-temperature firing.

  Therefore, as described above, the sinterability at a low temperature can be enhanced by containing an iron group metal in an amount of 0.1 to 5% by volume in terms of oxide in addition to tungsten and molybdenum.

  When the amount of the iron group metal is less than 0.1% by volume, the second wiring layer 3 is not densified, resulting in poor sintering, and the adhesive strength with the insulating substrate 1 is reduced. On the other hand, when the amount of iron group metal exceeds 5% by volume, tungsten and molybdenum particles grow abnormally and the adhesive strength decreases. The amount of the iron group metal is particularly preferably 0.5 to 2% by volume in terms of oxide.

  In addition, it is also effective to add the same kind of component powder as that of the insulating substrate 1 such as aluminum oxide in the second wiring layer 3 in order to increase the adhesive strength with the insulating substrate 1 mainly composed of aluminum oxide or the like. It is. However, if the content is more than 45% by volume, sintering failure is caused, and plating defects (plating does not adhere) occur in the plating process described later. This lack of plating may cause a reduction in the bonding reliability of metal members such as the lead terminals 8. For example, in the case of aluminum oxide, its content is particularly preferably 2 to 35% by volume.

Examples of the iron group metal in the second wiring layer 3 include iron, nickel, and cobalt. Among these, nickel is most desirable. Further, the oxide equivalent amount is an amount converted in the form of Fe ₂ O _{3 for} iron (Fe), NiO for nickel (Ni), and Co ₃ O ₄ for cobalt (Co).

  Further, when the second wiring layer 3 is made of tungsten and / or molybdenum and an iron group metal, the plating layer 7b to be deposited on the surface is a metal material mainly composed of tungsten or molybdenum, such as nickel or nickel alloy. It is preferable that the adhesive material is made of a metal having good wettability of the brazing material 9.

  The plating layer 7b of the second wiring layer 3 can be formed by, for example, an electroless plating method using a reducing agent such as sodium hypophosphite, dimethylamine borane, hydrazine, etc. It is formed as a nickel-phosphorus alloy plating layer, a nickel-boron alloy plating layer, a high-purity nickel plating layer having a nickel purity of 99.9% by weight or more, and the like.

  Such a plating layer made of nickel or a nickel alloy has good adhesion to the second wiring layer 3 made of molybdenum and / or tungsten and an iron group metal, and also has good wettability and bondability of the brazing material 9. Therefore, the lead terminal 8 can be firmly brazed to the second wiring layer 3 via the brazing material 9.

  In particular, if the plating layer 7b of the second wiring layer 3 is made of a nickel-boron alloy and has a thickness of 0.8 μm or more, the second wiring layer 3 can be made dense with a plating layer with few pinholes and the like. In addition, the wettability of the brazing material 9 with respect to the second wiring layer 3 can be further improved. Therefore, the plating layer 7b of the second wiring layer 3 is preferably made of a nickel-boron alloy and has a thickness of 0.8 μm or more, such as a decrease in deposition strength accompanying an increase in internal stress of the plating layer. In consideration of preventing this problem, the range of 0.8 to 4 μm is even more preferable.

  In this case, if the boron content in the plating layer made of the nickel boron alloy is less than 0.05% by weight, the corrosion resistance of the plating layer tends to deteriorate, and if it exceeds 3% by weight, the electric resistance of the plating layer is reduced. There is a tendency for the loss of the propagated signal to increase. Therefore, when the plating layer 7b of the second wiring layer 3 is a nickel-boron alloy, the boron content is preferably in the range of 0.05 to 3% by weight.

  Further, when the plating layer 7b of the second wiring layer 3 is made of a nickel-boron alloy, if the content of sulfur as a trace component is less than 0.005% by weight, fine cracks are likely to occur in the plating layer 7b. If it exceeds 0.08% by weight, the corrosion resistance of the plating layer 7b tends to deteriorate. Therefore, when the plating layer 7b of the second wiring layer 3 is made of a nickel-boron alloy, it is preferable that the content of sulfur as a trace component is 0.005 to 0.08% by weight.

  Further, the plating layers 7a and 7b deposited on the first wiring layer 2 and the second wiring layer 3 further cover the exposed surfaces with a gold plating layer (not shown) having a thickness of 0.03 to 3 μm. By doing so, the oxidative corrosion can be prevented more effectively, and the bonding property of the bonding wire 10 can be further improved. Accordingly, the plating layers 7a and 7b of the first wiring layer 2 and the second wiring layer 3 are preferably covered with a gold plating layer having a thickness of 0.03 to 3 μm.

  Further, the internal wiring layer 4 is preferably a low-resistance conductor similar to the first wiring layer 2. For this purpose, the inner wiring layer 4 is made of tungsten and / or molybdenum and copper, specifically, the first wiring layer described above. It is preferable to form the same conductive material as that of the wiring layer 2.

  Furthermore, in order to improve the thermal conductivity and mechanical strength of the insulating substrate 1, it is desirable that the insulating substrate 1 is composed of a highly dense body having a relative density of 95% or more.

  When the insulating base 1 further contains copper in order to reduce the resistance of the first wiring layer 2 as described above, 1200 is required to achieve shape retention by simultaneous firing with the first wiring layer 2. Although it is necessary to perform baking at a low temperature of 1 to 1500 ° C., according to the present invention, it is desirable to make the relative density 95% or higher even in such low temperature baking.

From this point of view, the insulating base 1 in the present invention is preferably, for example, one having aluminum oxide as a main component, specifically, one containing aluminum oxide in a proportion of 90% by weight or more. And containing a Mn (manganese) compound in a proportion of 2.0 to 6.0% by weight in terms of MnO ₂ . That is, if the manganese compound is less than 2.0% by weight, densification at 1200 ° C. to 1500 ° C. is difficult to achieve, and if it exceeds 6.0% by weight, the insulating property of the insulating substrate 1 is lowered. The optimum range of the manganese compound is 3 to 7% by weight in terms of MnO ₂ .

Further, in this insulating substrate 1, a total of 0.4 to 8% by weight of SiO ₂ and alkaline earth element oxides such as MgO, CaO and SrO are added as a third component in order to improve the low temperature sinterability. It is desirable to make it contain in the ratio.

  Further, the insulating substrate 1 may contain a metal such as W, Mo and Cr as a coloring component in a proportion of 2% by weight or less in order to improve the dielectric properties such as the coloring component and the dielectric constant.

  Components other than the above-mentioned aluminum oxide exist as an amorphous phase or a crystalline phase at the grain boundary of the aluminum oxide main crystal phase, but a crystal phase containing an auxiliary component is formed in the grain boundary in order to improve thermal conductivity. It is desirable that

  When the insulating substrate 1 is formed mainly of aluminum oxide, the aluminum oxide main crystal phase exists as a granular or columnar crystal, and the average crystal grain size of these main crystal phases is 1.5 to 5.0 μm. It is desirable that In addition, when the main crystal phase is composed of columnar crystals, the average crystal grain size is based on the minor axis diameter. When the average crystal grain size of the main crystal phase is smaller than 1.5 μm, it is difficult to achieve high thermal conductivity, and when the average grain size is larger than 5.0 μm, sufficient strength required for use as a substrate material can be obtained. This is because it becomes difficult.

  (Method for Forming Wiring Substrate) Next, an example of a method for manufacturing the wiring substrate 6 of the present invention will be specifically described in the case where the insulating substrate 1 is made of an aluminum oxide sintered body.

  First, in order to form the insulating substrate 1, a powder having an average particle diameter of 0.5 μm to 2.5 μm, particularly 0.5 μm to 2.0 μm is prepared as an aluminum oxide raw material powder as a main component. This is because if the average particle size is smaller than 0.5 μm, it is difficult to handle the powder, and the cost of the powder becomes high. If it is larger than 2.5 μm, it is difficult to fire at a temperature of 1500 ° C. or less. It is.

Then, MnO ₂ is added to the aluminum oxide powder at a ratio of 2.0 to 8.0% by weight, particularly 3.0 to 7.0% by weight as the second component. As appropriate, as the third component, SiO ₂ . 0.4 to 8% by weight of MgO, CaO, SrO ₂ powder, etc., and 4% by weight or less in terms of metal using a metal powder or oxide powder of a transition metal such as W, Mo, Cr or the like as a color component as a fourth component Add at a rate of

  In addition to the oxide powder, the oxide may be added as carbonate, nitrate, acetate, or the like that can form an oxide by firing.

  Next, a plurality of ceramic green sheets for forming the insulating substrate 1 are produced using this mixed powder. The ceramic green sheet can be produced by a known forming method. For example, after preparing a slurry by adding an organic binder or solvent to the above mixed powder, it is formed by a doctor blade method, or an organic binder is added to the mixed powder, and a ceramic green sheet having a predetermined thickness is formed by press molding, rolling molding, etc. Can be produced.

  In the ceramic green sheet, a through hole that becomes the through hole conductor 4a of the internal wiring layer 4 is formed by a laser processing method, a mechanical punching method, or the like.

  The ceramic green sheet thus produced is first made of tungsten and / or molybdenum powder and copper powder, and the conductor paste that becomes the first wiring layer 2 is screened on the surface of the ceramic green sheet and in the through hole. Print and fill by printing method.

  The conductor paste is, for example, 10 to 70% by volume of copper powder having an average particle diameter of 1 to 10 μm, particularly 40 to 60% by volume, and 30 to 90 volume of tungsten and / or molybdenum powder having an average particle diameter of 1 to 10 μm. %, Particularly 40 to 60% by volume, and can be prepared by adding and mixing an organic binder or solvent to the solid component.

  In the conductor paste used as the first wiring layer 2 and the internal wiring layer 4, the same composition as the aluminum oxide powder or the component forming the insulating substrate 1 is used in order to improve the adhesion to the insulating substrate 1. It is also possible to add the powder in a proportion of 0.05 to 2% by volume.

  Next, a conductive paste which is made of tungsten and / or molybdenum and an iron group metal and becomes the second wiring layer 3 is printed and applied in a predetermined pattern, for example, a plurality of quadrangular shapes, on the outer periphery of the surface of the ceramic green sheet. To do.

  The conductor paste to be the second wiring layer 3 is, for example, 0.1-5% by volume of an iron group metal oxide powder such as nickel oxide in tungsten and / or molybdenum having an average particle size of 0.5-5 μm. It is produced by adding and mixing an organic binder and a solvent with respect to the solid component contained in the ratio.

  In the conductor paste used as the second wiring layer 3, alumina powder can be contained in the solid component at a ratio of 45% by volume or less in order to improve the adhesion to the insulating substrate 1.

  Finally, after the ceramic green sheets printed with the respective conductive pastes to be the first wiring layer 2, the second wiring layer 3, and the internal wiring layer 4 are aligned and pressure-bonded to each other, the laminate is made non-oxidizing. Baking is performed in the atmosphere under conditions where the maximum baking temperature is 1200 to 1500 ° C.

  If the firing temperature at this time is lower than 1200 ° C., when an ordinary raw material is used, the insulating base made of the aluminum oxide sintered body cannot be densified to a relative density of 95% or more, and the thermal conductivity and strength are low. If the temperature is higher than 1500 ° C., the sintering of tungsten or molybdenum itself proceeds in the first wiring layer 2, and a uniform structure with copper cannot be maintained, and as a result, it is difficult to maintain a low resistance. The resistance will be high. At the same time, the grain size of the aluminum oxide main crystal phase is increased and abnormal grain growth occurs, or the grain boundary length, which is a path when copper diffuses into the ceramic, is shortened and the diffusion rate is also increased. It becomes difficult to control the diffusion distance to 30 μm or less. Accordingly, the firing temperature of the ceramic green sheet is in the range of 1200 to 1500 ° C, preferably in the range of 1350 to 1450 ° C.

In addition, the non-oxidizing atmosphere at the time of firing is preferably nitrogen or a mixed atmosphere of nitrogen and hydrogen. In particular, in order to suppress diffusion of copper in the wiring layer, hydrogen and nitrogen are included. A non-oxidizing atmosphere with a dew point of + 10 ° C. or lower, particularly −10 ° C. or lower is desirable. In addition, you may mix inert gas, such as argon gas, in this atmosphere if desired. When the dew point at the time of firing is higher than + 10 ° C., oxide ceramic such as aluminum oxide, MnO ₂ , SiO ₂ , MgO, and CaO reacts with moisture in the atmosphere during firing to form an oxide film. This is because copper in the copper-containing conductor reacts, which not only prevents the resistance of the conductor from being lowered, but also promotes copper diffusion.

  Furthermore, by controlling the baking temperature and atmosphere as described above, baking can be performed with an arithmetic average roughness Ra of the surface of the insulating substrate 1 of 1 μm or less, particularly 0.7 μm or less. .

  Thus, according to the wiring board 6 of the present invention, the semiconductor element 5 is mounted on the upper surface of the insulating base 1 and each electrode of the semiconductor element 5 is electrically connected to the first wiring layer 2 via the bonding wires 10. Thereafter, if necessary, the semiconductor element 5 is hermetically sealed with a bowl-shaped lid made of metal or ceramic, sealing resin (not shown), or the like, thereby completing a semiconductor device as a product.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiments, the wiring board of the present invention is replaced with a semiconductor element. Although the case where it is applied to a wiring board for mounting has been described, this may be applied to a hybrid integrated circuit board or the like.

It is sectional drawing which shows one Example of the wiring board of this invention. It is a principal part enlarged view of the wiring board shown in FIG. It is sectional drawing which shows an example of the conventional wiring board.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... 1st wiring layer 3 ... 2nd wiring layer 4 ... Internal wiring layer 4a ... Through-hole conductor 4b ... Inner layer conductor 5 ... Semiconductor element 6... Wiring substrate 7 a... First plating layer plating layer 7 b... Second wiring layer plating layer 8... Lead terminal 9. Bonding wire

Claims (3)

A wiring board formed by forming a first wiring layer and a second wiring layer to which a metal member is brazed on the surface of an insulating substrate, wherein the first wiring layer has a copper plating layer on the surface, and a second wiring layer. The wiring layer has a nickel plating layer deposited on the surface, and the first wiring layer and the second wiring layer are electrically connected via an internal wiring layer formed inside the insulating substrate. A wiring board characterized by that. The internal wiring layer is electrically connected to the first wiring layer and the second wiring layer by a through-hole conductor, and the through-hole conductor is formed only of a ceramic green sheet that is the uppermost layer of the insulating base. The wiring board according to claim 1, wherein the wiring board penetrates. 3. A semiconductor device comprising a semiconductor element mounted on the upper surface of the wiring board according to claim 1 or 2, and each electrode of a wiring conductor connected to a first wiring layer.

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