JP5489701B2 - Multilayer wiring board and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer wiring board used for an in-vivo embedded device embedded in a living body and a method for manufacturing the same.

  It is known that a multilayer wiring board provided with an insulating substrate made of ceramics is used for an in-vivo embedded device to be embedded in a living body, and the demand thereof has been increasing in recent years.

  This multilayer wiring board for use in an in-vivo embedded device has the same basic structure as a multilayer wiring board used in the field of mobile communication, etc., and is formed inside an insulating substrate in which a plurality of ceramic insulating layers are laminated. Wiring layers formed therein, through conductors penetrating the ceramic insulating layer, and connection pads formed on one main surface and the other main surface of the insulating base.

  By the way, since the multilayer wiring board for use in an in-vivo embedded device is required to have biocompatibility, an alumina sintered body is used as a material for forming a ceramic insulating layer, and platinum is used as a material for forming a through conductor and a connection pad. It is known (see Patent Document 1).

  However, platinum is an expensive material. Therefore, in order to reduce costs, it is conceivable that the internal wiring layer and the through conductor that do not directly contact the living body are made of cheaper tungsten or molybdenum instead of platinum, and only the connection pad forming material is platinum.

  Here, in order to manufacture such a multilayer wiring board, a ceramic green sheet mainly composed of alumina powder is prepared, a through hole is formed in the ceramic green sheet, and a conductive paste for a through conductor is formed in the through hole. And a method of firing a ceramic green sheet laminate by laminating a plurality of ceramic green sheets and applying a conductive paste for a wiring layer to one main surface of the ceramic green sheet. .

  However, in order to fire a conductor paste for through conductors or wiring layers mainly composed of tungsten or molybdenum, it is necessary to fire in a hydrogen-nitrogen mixed atmosphere to prevent oxidation. If the conductive paste for connection pads mainly composed of platinum is fired at the same time, the oxide formed on the outermost surface of the conductive paste for connection pads mainly composed of platinum will be reduced by hydrogen. The wettability between the pad conductor paste and the ceramic insulating layer is lowered, resulting in a problem that the bonding strength is lowered.

  Therefore, an insulating base in which a plurality of ceramic insulating layers made of an alumina-based sintered body are laminated, a wiring layer mainly composed of tungsten or molybdenum formed inside the insulating base, and tungsten penetrating the ceramic insulating layer or After preparing a multilayer wiring board precursor comprising a through conductor mainly composed of molybdenum, a conductor paste for connection pads mainly composed of platinum is applied to the main surface of the insulating substrate, and then fired again in a vacuum. A way to do this is conceivable.

JP-T-2005-502403

  Here, when a connection pad conductor paste containing platinum as a main component is baked at, for example, 1280 ° C. to form a connection pad, tungsten or molybdenum, which is a through conductor forming material, and platinum forming the connection pad When the intermetallic compound is formed and the intermetallic compound reaches the surface of the connection pad, the biocompatibility may be lowered.

  On the other hand, when a connection pad conductor paste mainly composed of platinum is baked at, for example, 850 to 1000 ° C. to form a connection pad, the formation of the intermetallic compound as described above can be eliminated. Therefore, the density of platinum forming the connection pad is insufficient. For this reason, when using a multilayer wiring board in a living body, there is a possibility that the biocompatibility may be lowered by passing through the connection pad and the body fluid reaching the surface of the through conductor.

  Therefore, the connection pad needs to be densely formed without forming an intermetallic compound with the through conductor forming material.

  The present invention has been made in view of the above circumstances, and provides a multilayer wiring board having a dense connection pad mainly composed of platinum, which can be manufactured at a lower cost and has excellent biocompatibility, and a method for manufacturing the same. For the purpose.

A multilayer wiring board according to the present invention includes an insulating substrate in which a plurality of ceramic insulating layers made of an alumina sintered body are laminated, a wiring layer mainly composed of tungsten or molybdenum formed inside the insulating substrate, The connection formed at least on the one main surface, comprising a through conductor mainly composed of tungsten or molybdenum penetrating the ceramic insulating layer, and a connection pad formed on one main surface and the other main surface of the insulating base. The surface of the pad is composed of only 71 to 88% by mass of platinum and the remaining gold, and the gold is dispersed in the platinum substantially uniformly without being connected to each other , and has biocompatibility. It is a feature.

A method for manufacturing a multilayer wiring board according to the present invention is a method for manufacturing a multilayer wiring board according to the present invention having the above-described configuration, wherein a ceramic green sheet mainly composed of alumina powder is produced, and a through hole is formed in the ceramic green sheet. The through hole is filled with a conductive paste for a through conductor mainly composed of tungsten or molybdenum, and a conductive paste for a wiring layer mainly composed of tungsten or molybdenum is applied to one main surface of the ceramic green sheet. A ceramic green sheet laminate is prepared by laminating a plurality of the ceramic green sheets in which the through holes are filled with a conductor paste for through conductors and one of the main surfaces is coated with a conductor paste for wiring layers. After firing the body at 1350-1700 ° C. in a mixed atmosphere of nitrogen and hydrogen, At least one main surface of the resulting insulating base by firing La Mick green sheet laminate, a 71-88 wt% of the platinum powder and the balance of gold powder and only mixed connection pads conductor paste as inorganic component coating And firing at 850 to 1000 ° C. in a vacuum.

According to the multilayer wiring board of the present invention, at least one surface of the connection pads formed on the main surface of the insulating substrate consists of 71 to 88 wt% of platinum and the remainder gold and only gold in platinum, together By being distributed almost uniformly without being connected, it is possible to realize a biocompatible multilayer wiring board having a dense connection pad mainly composed of platinum having excellent biocompatibility .

Further, according to the method for manufacturing a multilayer wiring board of the present invention, an insulating base in which a plurality of ceramic insulating layers made of an alumina sintered body are laminated, and tungsten or molybdenum formed inside the insulating base as a main component. A multilayer wiring board precursor comprising a wiring layer to be formed and a through conductor mainly composed of tungsten or molybdenum penetrating the ceramic insulating layer, 71 to 88% by mass of platinum powder and the remaining gold as inorganic components By applying the connection pad conductor paste mixed only with the powder and firing at 850 to 1000 ° C. in vacuum, platinum and gold contained in the connection pad conductor paste do not become an alloy (platinum crystal lattice). Gold is dispersed almost uniformly in platinum while maintaining its function as a sintering aid for gold (adhesive effect of gold) without any gold atoms being taken in. Dense connection pads state can be formed. In addition, since the gold and gold contained in the connection pad conductor paste are not connected to form a continuous phase, it is possible to prevent the through conductor from being exposed even when the gold is eluted into the living body during use of the multilayer wiring board. And a multilayer wiring board having excellent biocompatibility can be obtained.

It is a schematic sectional drawing which shows an example of embodiment of the multilayer wiring board of this invention.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an example of an embodiment of a multilayer wiring board according to the present invention. The multilayer wiring board shown in FIG. 1 has a plurality of ceramic insulating layers 11, 12, 13, 14 made of an alumina sintered body. , Laminated wiring layer 2 mainly composed of tungsten or molybdenum formed inside insulating substrate 1, and tungsten or molybdenum penetrating ceramic insulating layers 11, 12, 13, and 14 as main components. And the connection pads 41 and 42 formed on one main surface and the other main surface of the insulating base 1, and the surface of the connection pad 41 formed on at least one main surface is 71 to 88% by mass. And the remaining gold, and the gold is almost uniformly dispersed in the platinum.

The insulating base 1 is composed of a plurality of ceramic insulating layers 11, 12, 13, and 14 made of an alumina sintered body, and each ceramic insulating layer 11, 12, 13, and 14 is 88 to 96 mass% alumina. And the remaining glass (sintering aid component). The alumina content is determined by Rietveld analysis from the diffraction main peak intensity of X-ray diffraction. The average crystal grain size of alumina is, for example, about 1 to 5 μm. The average crystal grain size is obtained by mirror-polishing the surface of the measurement sample (alumina sintered body) and performing etching using phosphoric acid, for example. Then, after melting the grain boundaries, a plurality of lines are drawn for a predetermined region of, for example, a 1000 times image by a scanning electron microscope (SEM), and the number of intersections with the grain boundaries of each line is counted. it can. As the glass _rest, include those containing SiO 2, MgO and CaO.

  The thickness of the plurality of ceramic insulating layers 11, 12, 13, and 14 is usually about 50 to 200 μm, the thickness of the insulating base 1 is usually about 0.2 to 0.8 mm, and the length and width are about 1 to 30 mm each. The insulating substrate 1 (the plurality of ceramic insulating layers 11, 12, 13, and 14) is made of such an alumina sintered body, so that the insulating substrate is formed. The biocompatibility of 1 is good.

  A wiring layer 2 mainly composed of tungsten or molybdenum is provided inside the insulating substrate 1, and a through conductor mainly composed of tungsten or molybdenum penetrating the ceramic insulating layers 11, 12, 13, and 14, respectively. 3 is provided. The wiring layer 2 is formed by sintering a wiring layer conductor paste mainly composed of tungsten powder or molybdenum powder, and the through conductor 3 is sintered from a through conductor conductor paste mainly composed of tungsten powder or molybdenum powder. Are formed to a diameter of about 50 to 200 μm. The wiring layer 2 and the through conductor 3 may contain the same type of material as the material for forming the ceramic insulating layers 11, 12, 13, and 14 by addition of a trace amount or diffusion.

  Connection pads 41 and 42 are formed on one main surface and the other main surface of the insulating substrate 1. And the surface of the connection pad 41 formed in at least one main surface consists of 71-88 mass% platinum and the remainder gold | metal | money, and gold is disperse | distributing substantially uniformly in platinum.

  Here, the surface of the connection pad may be composed of 71 to 88% by mass of platinum and the remaining gold only by the connection pad 41 formed on one main surface, and both main surfaces of one main surface and the other main surface. The connection pads 41 and 42 formed on the body may be used, and which form is determined as appropriate in consideration of biocompatibility when embedded in a living body. For example, the multilayer wiring board of the present invention constitutes a part of a package for housing semiconductor elements, and the connection pads 42 formed on the other main surface face the internal space of the package for housing semiconductor elements, When there is no possibility of contact, only the surface of the connection pad 41 on one main surface is composed of 71 to 88% by mass of platinum and the remaining gold, and the gold is dispersed almost uniformly in the platinum. It only has to be like this.

  Further, at least the surface of the connection pads 41 and 42 is composed of 71 to 88% by mass of platinum and the remaining gold, and it is sufficient that the gold is dispersed almost uniformly in the platinum. The entirety of 42 may be formed in this way. The first layer mainly composed of tungsten or molybdenum electrically connected to the through conductor 3 and platinum and gold so as to cover the first layer. It means that it may be composed of the formed second layer on the surface side.

  Specifically, when the entire connection pads 41 and 42 are formed of platinum and gold as described above and are directly electrically connected to the through conductor 3, the thickness of the connection pads 41 and 42 is about 3 to 50 μm. The diameters of the connection pads 41 and 42 are formed to be about 10 to 400 μm larger than the diameter of the through conductor 3.

  In addition, the connection pads 41 and 42 are a first layer mainly composed of tungsten or molybdenum electrically connected to the through conductor 3, and a second layer formed of platinum and gold so as to cover the first layer. The first layer is about 3 to 15 μm in diameter and 75 to 300 μm in diameter, and the second layer is about 3 to 50 μm in diameter and about 100 to 400 μm in diameter. It is formed.

  In the multilayer wiring board of the present invention, it is important that the surfaces of the connection pads 41 and 42 are composed of 71 to 88% by mass of platinum and the remaining gold. Since platinum and gold are in such a ratio and gold is almost uniformly dispersed in platinum, they do not become alloys during production (when firing at 850 to 1000 ° C. in a vacuum described later). The connection pads 41 and 42 are sintered closely (without the incorporation of gold atoms in the platinum crystal lattice) while maintaining the function of gold as a sintering aid (adhesive effect of gold). It is formed. When the proportion of platinum is less than 71 mass%, gold and gold are connected to form a continuous phase under the firing conditions described later, and when the gold is eluted into the living body while using the multilayer wiring board, the through conductor 3 May be exposed, and the biocompatibility of the connection pads 41 and 42 may be reduced. On the other hand, if the proportion of platinum exceeds 88% by mass, platinum and gold form an alloy under the firing conditions described later, and gold atoms are taken into the platinum crystal lattice. The function as an auxiliary agent (adhesion effect by gold) may be reduced, and the denseness of the connection pads 41 and 42 may be reduced.

  In addition, it can measure that the ratio of platinum is 71-88 mass% from the main peak intensity ratio of platinum in the diffraction peak of the X-ray diffraction of the connection pads 41 and 42.

  Whether or not gold and gold are connected to form a continuous phase is determined by cutting the connection pads 41 and 42 and polishing the cross section, and analyzing the cross section by wavelength dispersive X-ray microanalyzer analysis (EPMA). It can be measured by element mapping at a magnification of 1000 times.

  Further, the denseness of the connection pads 41 and 42 is binary by cutting the connection pads 41 and 42 and polishing the cross section, and processing the image of the cross section with a scanning electron microscope (SEM) 1000 times. And can be measured. The void ratio can be calculated by quantifying the ratio of the void portion among the binarized values.

  As described above, according to the multilayer wiring board of the present invention, it is possible to realize a multilayer wiring board having a dense connection pad mainly composed of platinum having excellent biocompatibility. It is possible to suppress the elution of the tungsten or molybdenum conductor component that forms the through-conductor through the living body during use.

  Next, a manufacturing method for manufacturing the multilayer wiring board having the above configuration will be described.

  In the method for producing a multilayer wiring board according to the present invention, first, a ceramic green sheet mainly composed of alumina powder is produced.

For example, alumina powder having an average particle diameter of 1 to 5 μm is added to 88 to 96% by mass, 2 to 8% by mass of SiO ₂ powder, 0.5 to 2% by mass of MgO powder, and 0.1 to 2% by mass of CaO powder. After mixing the mixed powder, for example, an organic binder such as acrylic or cellulose, an organic solvent such as toluene or alcohol, and adjusting the slurry, press method, doctor blade method, rolling method, injection method, etc. A ceramic green sheet is produced by a forming method. The thickness of the ceramic green sheet is, for example, about 60 to 230 μm.

  Next, a through-hole is formed in the ceramic green sheet, and the through-hole is filled with a conductive paste for a through conductor mainly composed of tungsten or molybdenum, and one main surface of the ceramic green sheet is mainly composed of tungsten or molybdenum. Apply wiring layer conductor paste.

  The through hole is formed with a diameter of about 60 to 230 μm by a micro drill, a laser, or the like. Then, a through-hole is filled with a conductive paste for through conductor formed by adding the above organic binder, organic solvent or the like to tungsten powder or molybdenum powder. On the other hand, a conductor paste for wiring layer formed by adding an organic binder, an organic solvent, or the like as described above to tungsten powder or molybdenum powder is applied to one main surface of the ceramic green sheet by a method such as screen printing or gravure printing.

  Next, a plurality of ceramic green sheets each having a through-hole filled with a conductive paste for through conductors and coated with a conductor paste for wiring layers on one main surface are laminated to produce a ceramic green sheet laminate.

  The method of laminating is a method of applying heat and pressure to the stacked ceramic green sheet laminates and thermocompression bonding, or a method of applying an adhesive composed of an organic binder, plasticizer, solvent, etc. between the ceramic green sheets and thermocompression bonding. Etc. can be adopted. In addition, the conditions of the heating and pressing at the time of lamination | stacking change with kinds and quantity of organic binders etc. to be used, for example, set to 30-100 degreeC and 2-20 MPa.

  Next, the ceramic green sheet laminate is fired at 1350-1700 ° C. in a mixed atmosphere of nitrogen and hydrogen.

  Here, the mixed atmosphere of nitrogen and hydrogen is, for example, an atmosphere of about 80 to 95% nitrogen and 5 to 20% hydrogen, and is fired at 1350 to 1700 ° C. in such an atmosphere to obtain an alumina sintered body. An insulating substrate 1 in which a plurality of ceramic insulating layers 11, 12, 13, and 14 are stacked, a wiring layer 2 mainly composed of tungsten or molybdenum formed inside the insulating substrate 1, a ceramic insulating layer 11, A precursor of a multilayer wiring board including a through conductor mainly composed of tungsten or molybdenum penetrating 12, 13, and 14 is produced.

  Finally, a connection pad conductor paste in which 71 to 88% by mass of platinum powder and the remaining gold powder was mixed was applied to at least one main surface of the insulating base 1 in the obtained precursor, and 850 to 850 in vacuum. Bake at 1000 ° C.

  The conductive paste for connection pads is a mixed powder of 71 to 88% by mass of platinum powder and the balance (12 to 29% by mass) of gold powder, for example, an organic binder such as acrylic or cellulose, organic such as toluene or alcohol. A solvent is added. For example, a mixture obtained by adding 5 to 30 parts by mass of an organic binder and 0.1 to 5 parts by mass of an organic solvent is added to 100 parts by mass of the mixed powder.

  When the entire connection pads 41 and 42 to be manufactured are formed of platinum and gold as described above and are directly electrically connected to the through conductor 3, the thickness of the connection pad conductor paste is about 5 to 60 μm. The diameter of the formed conductive paste for connection pad is formed to be about 10 to 400 μm larger than the diameter of the through hole.

  The connection pads 41 and 42 to be manufactured are formed of a first layer mainly composed of tungsten or molybdenum electrically connected to the through conductor 3 and platinum and gold so as to cover the first layer. When the second layer is formed, the thickness of the first layer is about 5 to 20 μm, the diameter is about 85 to 350 μm, the thickness of the second layer is about 5 to 60 μm, and the diameter is 100 to 400 μm. Formed to a degree.

  Here, it is important to fire again at 850 to 1000 ° C. in vacuum. By firing in vacuum, oxidation of the previously formed through conductor and wiring layer mainly composed of tungsten or molybdenum can be prevented, and platinum and hydrogen can be fired without reacting. is there. Moreover, since the firing temperature is 850 ° C. or higher, the minimum temperature necessary for sintering of the connection pad conductor paste can be secured, and when the firing temperature is 1000 ° C. or lower, this connection pad conductor paste. This is because it is possible to suppress the formation of an intermetallic compound between the conductive paste for through conductors.

  And in the mixed powder of platinum powder and gold powder, it is important that the content of platinum powder is 71 to 88 mass%.

  In the case of only platinum powder, since the melting point of platinum is as high as 1700 ° C. or higher, the movement (diffusion) of the substance hardly occurs at a temperature of about 1000 ° C. or lower, and the sintering is difficult to proceed. Here, when gold is dispersed in platinum and each exists independently, since gold has a melting point of about 1080 ° C., the substance actively moves even at a temperature of about 1000 ° C. Taking advantage of this active mass transfer of gold, an “interdiffusion” phenomenon occurs between gold and platinum, and platinum, which has a low mobility in single platinum, starts mass transfer. This is because gold and platinum are close to each other in crystal structure so that mutual diffusion is likely to occur. This mass transfer is used to promote the sintering of platinum.

  In the present invention, the firing temperature for sintering the connection pad conductor paste is set to 850 to 1000 ° C. According to the binary phase diagram of platinum and gold, platinum and gold are sintered at this temperature. In order to exist independently without becoming an alloy, the proportion of platinum powder needs to be 32 to 88 mass%. In the connection pads 41 and 42 to be formed, when an alloy of platinum and gold is formed and gold atoms are taken into the crystal lattice of platinum, the function as a gold sintering aid is reduced, and the connection There is a possibility that the denseness of the pads 41 and 42 may be lowered. When platinum and gold form an alloy phase, platinum and gold exist from the beginning after interdiffusion, so there is the potential to bother the further diffusion phenomenon. This is because the sintering does not work and the effect of promoting sintering is not born.

  However, according to the calculation result of the site percolation of the simple cubic lattice, when the ratio of the platinum powder is less than 71% by mass, the gold powder and the gold powder are connected to form a continuous phase, and the multilayer wiring board is being used. When gold is eluted in the living body, the through conductor may be exposed, and the biocompatibility of the connection pads 41 and 42 may be reduced.

  Therefore, in the mixed powder of platinum powder and gold powder, it is important that the content of platinum powder is 71 to 88% by mass. This ratio is the same even after sintering.

  As described above, according to the method for manufacturing a multilayer wiring board of the present invention, platinum and gold contained in the connection pad conductor paste are not alloyed, and the gold and gold contained in the connection pad conductor paste are not. A dense connection pad in which gold is dispersed almost uniformly in platinum in a state in which the continuous phase is not formed and the function as a sintering aid component by gold (adhesion effect by gold) is maintained. A multilayer wiring board that can be formed and has excellent biocompatibility can be obtained.

92% by mass of alumina powder having an average particle diameter of 2 μm is mixed with 6% by mass of SiO ₂ powder, 1% by mass of MgO powder and 1% by mass of CaO powder, and an acrylic organic binder and toluene are added to the mixed powder. Then, after adjusting the slurry, a ceramic green sheet is prepared by a doctor blade method. The thickness of the ceramic green sheet was 180 μm.

  Next, a through-hole having a diameter of 235 μm is formed in the ceramic green sheet, and the through-hole is filled with a conductor paste for a through conductor containing molybdenum powder as a main component by a screen printing method. The layer conductor paste was applied to one main surface of the ceramic green sheet by screen printing.

  Next, a ceramic green sheet laminate is prepared by laminating three layers of ceramic green sheets in which through holes are filled with a conductor paste for through conductors or coated with the conductor paste for connection pads. Was fired at 1600 ° C. for 1 hour in a mixed atmosphere of nitrogen and hydrogen to prepare a precursor of a multilayer wiring board.

  In this precursor, 100 parts by mass of a mixed powder of platinum powder and gold powder mixed at a ratio of platinum shown in Table 1 on one main surface and the other main surface of the insulating substrate 1 is added 12 parts of an acrylic organic binder by external addition. The conductor paste for connection pads added with 1 part by mass of 1 part by mass and terpineol was applied to a thickness of 40 μm.

  And it baked over 1 hour in the temperature shown in Table 1 in the vacuum, and produced the multilayer wiring board.

About the obtained multilayer wiring board, the presence or absence of the gold | metal | money connection in a connection pad was measured by the wavelength dispersion type | mold X-ray microanalyzer analysis (EPMA) method.
Further, the denseness of the connection pads was binarized by image processing of a 1000-fold image by scanning electron microscope (SEM), and the void ratio was obtained. These results are shown in Table 1.

  According to Table 1, sample No. which is a sample within the scope of the present invention. In Nos. 2 to 3 and 6 to 7, there is no connection of gold, the void ratio is less than 32% by volume, and the through conductor is not exposed.

  On the other hand, sample No. which is a sample outside the scope of the present invention. In 1, 4 to 5, and 8, a connection of gold is observed, or a void ratio of 32% by volume or more is observed, and there is a high risk for biocompatibility.

1: Insulating substrate 11, 12, 13, 14: Ceramic insulating layer 2: Wiring layer 3: Through conductor 41, 42: Connection pad

Claims (2)

An insulating base in which a plurality of ceramic insulating layers made of an alumina sintered body are laminated, a wiring layer mainly composed of tungsten or molybdenum formed inside the insulating base, and tungsten or the penetrating through the ceramic insulating layer A through conductor mainly composed of molybdenum and a connection pad formed on one main surface and the other main surface of the insulating base, and at least a surface of the connection pad formed on the one main surface is 71 to 88 mass % of made of platinum and the remainder gold and only, the multilayer wiring substrate on which the gold in the platinum, biocompatible, characterized in that it is substantially uniformly dispersed not connected to each other. A ceramic green sheet having alumina powder as a main component is produced, a through hole is formed in the ceramic green sheet, and the through hole is filled with a conductive paste for a through conductor mainly containing tungsten or molybdenum, and the ceramic green sheet The wiring layer conductor paste containing tungsten or molybdenum as a main component is applied to one main surface, the through hole is filled with the conductor paste for through conductor, and the wiring layer conductor paste is applied to the one main surface. A ceramic green sheet laminate is produced by laminating a plurality of ceramic green sheets, and the ceramic green sheet laminate is fired at 1350-1700 ° C. in a mixed atmosphere of nitrogen and hydrogen, and then the ceramic green sheet laminate is fired. at least one main surface of the resulting insulating base Te, inorganic components Characterized in that a 71 to 88% by weight of the platinum powder and the balance of gold powder and only mixed connection pads conductor paste is applied, baked in vacuum 850 to 1000 ° C. and, biocompatible A method for manufacturing a multilayer wiring board.

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