JP3645744B2 - Ceramic wiring board - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ceramic wiring board used for a semiconductor element housing package for housing a semiconductor element, a hybrid integrated circuit board, and the like, and more particularly to a ceramic wiring board on which a semiconductor element is mounted and connected by a flip chip method. is there.
[0002]
[Prior art]
In recent years, a method for mounting a semiconductor element on a ceramic wiring board used for a package for housing a semiconductor element, a hybrid integrated circuit board, or the like is as follows. So-called flip chip bonding, in which an electrode of a semiconductor element is directly connected to a through conductor layer exposed on the surface via an electrical connection means such as solder, is being used frequently.
[0003]
A ceramic wiring board used for a semiconductor element storage package or a hybrid integrated circuit board that employs this flip-chip bonding is generally formed of an insulating base made of an aluminum oxide sintered body, and the insulating base. An electrode of an electronic component such as a semiconductor element is formed on the exposed surface of the penetrating conductor layer exposed on the surface of the insulating substrate. The penetrating conductor layer is made of a refractory metal such as tungsten or molybdenum that has one end exposed on the surface of the insulating substrate. Are connected to each other through an electrical connection means made of solder balls or the like, so that an electronic component such as a semiconductor element is mounted on the ceramic wiring board and each electrode of the electronic component is connected to the through conductor layer.
[0004]
The exposed surface of the through conductor layer is usually excellent in corrosion resistance of nickel, gold, etc. in order to prevent its oxidative corrosion and to improve the wettability with respect to the electrical connection means composed of solder balls or the like. In addition, a metal layer having good wettability with respect to a brazing material such as solder is applied by a plating method.
[0005]
Further, such a ceramic wiring board is generally manufactured by employing a ceramic layering technique and a thick film forming technique such as screen printing. Specifically, the ceramic wiring board is manufactured by the following method.
[0006]
That is,
(1) First, an organic solvent and a solvent are added to a ceramic raw material powder composed of aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), calcium oxide (CaO), etc. Next, this is formed into a sheet shape by a conventionally known doctor blade method or calendar roll method to form a plurality of ceramic green sheets (ceramic green sheets) and through holes are formed at predetermined positions by punching or the like To do.
[0007]
(2) Next, a conductive paste obtained by adding and mixing an organic solvent and a solvent into a metal powder such as tungsten or molybdenum is printed and filled in the through hole by a screen printing method or the like.
[0008]
(3) Finally, these ceramic green sheets are stacked one above the other so that one end of the conductive paste printed and filled in the through holes is exposed, and fired at a temperature of about 1600 ° C. in a reducing atmosphere. A ceramic wiring board is completed by sintering and integrating the ceramic green sheet and the conductive paste.
[0009]
In this case, if the sintering start temperatures of the ceramic green sheet and the conductive paste are different, the contraction start time associated with the sintering is different between the ceramic green sheet and the conductive paste, and the insulation substrate and the through conductor layer are between. As a result, stress is generated and cracks and the like are generated in the insulating substrate, and therefore, a conductive paste whose sintering start temperature approximates the sintering start temperature of the ceramic green sheet is usually used.
[0010]
However, recently, the increase in the size of the semiconductor element and the increase in the signal propagation speed have rapidly advanced, and when the semiconductor element is mounted on the above-described conventional ceramic wiring board, it has the following drawbacks.
[0011]
That is,
(1) thermal expansion coefficient of the sintered aluminum oxide contained in the silicon and the insulating substrate of the semiconductor device, each 3.0 × 10 ^-6 /℃~3.5×10 ^-6 /℃,6.0 × a 10 ^-6 /℃~7.5×10 ^-6 / ℃, a large thermal stress between them when the heat generated is applied to the like when operated a semiconductor element on both since it differs greatly Due to the thermal stress, the electrical connection means such as solder balls and the semiconductor element are damaged or peeled off from the insulating substrate, thereby losing the function as the semiconductor device.
[0012]
(2) Since the dielectric constant of the aluminum oxide sintered body constituting the insulating base is as high as 9 to 10 (room temperature 1 MHz), the propagation speed of the signal transmitted through the through conductor layer provided on the insulating base is slow, and therefore the signal A semiconductor element requiring high-speed propagation cannot be mounted.
[0013]
Therefore in order to solve the above drawbacks, the thermal expansion coefficient of the silicon constituting the semiconductor device instead of the insulating substrate to the sintered aluminum oxide (3.0 × 10 ^-6 /℃~3.5×10 ^-6 / ° C.) and having a thermal expansion coefficient of 4.0 × 10 ^-6 /℃~4.5×10 ^-6 / ℃ approximated, and dielectric constant can be formed at a 6.3 low mullite sintered body Conceivable.
[0014]
[Problems to be solved by the invention]
However, when the insulating substrate is formed of a mullite sintered body, the conductive paste serving as the through conductor layer contains molybdenum as a main component in order to approximate the sintering start temperature of the ceramic green sheet serving as the mullite sintered body. When the through conductor layer is formed of this molybdenum, the molybdenum is a metal that is easily oxidized, and an oxide is very easily formed on the exposed surface. If an oxide is formed on the surface of the through conductor layer, a plated layer of nickel or the like cannot be formed on the exposed surface of the through conductor layer with good adhesion. As a result, each electrode of the electronic component is formed on the through conductor layer with solder balls or the like. There is a disadvantage that it cannot be firmly and electrically connected via the mechanical connection means.
[0015]
The present invention has been devised in view of the above problems, and an object of the present invention is to form an insulating substrate with a mullite sintered body and to form a plating layer on the exposed surface of the through conductor layer with good adhesion. It is to provide a ceramic wiring board.
[0016]
[Means for Solving the Problems]
The present invention comprises an insulating substrate, and a through conductor layer formed in the insulating substrate, one end of which is exposed on the surface of the insulating substrate, and an electrode of a semiconductor element is connected to the exposed surface via an electrical connection means. a ceramic wiring substrate, the insulating substrate is made of mullite sintered body, and together with the through conductor layer is formed of a metal material mainly composed of molybdenum, the exposed surface is made of tungsten, the cross-sectional shape The central part is thick and the peripheral part is covered with a thin coating layer.
[0017]
According to the ceramic wiring board of the present invention, since the exposed surface of the through conductor layer is coated with a coating layer made of tungsten that is difficult to oxidize, the exposed surface of the through conductor layer has good wettability with respect to a brazing material such as solder. A plated layer of nickel or the like can be reliably and firmly applied, and as a result, each electrode of the electronic component can be firmly and electrically connected to the through conductor layer via an electrical connection means such as a solder ball. Can do.
[0018]
Further, according to the ceramic wiring board of the present invention, the entire region of the through conductor layer is formed of a metal material whose main component is molybdenum whose sintering start temperature approximates the sintering start temperature of the ceramic green sheet serving as the insulating base. Therefore, no great stress is generated between the insulating base and the through conductor layer, and no crack or the like is generated in the insulating base due to the stress.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will now be described in detail with reference to the accompanying drawings.
1 and 2 show an embodiment in which the ceramic wiring board of the present invention is applied to an insulating base of a package for housing a semiconductor element. In the figure, 1 is an insulating base made of a ceramic wiring board, and 2 is a lid. is there. The insulating substrate 1 and the lid body 2 constitute a container 4 for housing a semiconductor element.
[0020]
The insulating substrate 1 acts as a support member for supporting the semiconductor element 3, and the semiconductor element 3 is mounted and mounted at a substantially central portion of the upper surface.
[0021]
The insulating substrate 1 is made of mullite sintered body, it said mullite sintered material is the thermal expansion coefficient of ^{4.0 × 10 -6 /℃~4.5×10 -6 / ℃} , the semiconductor device 3 since that approximates the thermal expansion coefficient of silicon constituting ^{(3.0 × 10 -6 /℃~3.5×10 -6 /} ℃), after mounting a semiconductor element mounted 3 on an insulating substrate 1, to both Even if heat generated when the semiconductor element 3 is operated or the like is applied, no large thermal stress is generated between the two, and the semiconductor element 3 is damaged by the thermal stress or the semiconductor element 3 is insulated. There is no peeling from the substrate 1.
[0022]
The insulating substrate 1 made of the mullite sintered body is made of, for example, an appropriate organic binder, a solvent and the like added to a raw material powder such as mullite, calcium oxide, and magnesium oxide to form a slurry, and the slurry is a doctor blade. The ceramic green sheet (ceramic green sheet) is formed by adopting the method and the calender roll method. After that, the ceramic green sheet is appropriately punched and laminated, and the temperature is about 1600 ° C. Manufactured by firing.
[0023]
The insulating base 1 has a plurality of through conductor layers 5 formed on the upper surface thereof from the region where the semiconductor element 3 is mounted and mounted to the bottom surface through the inside and side surfaces. Each electrode of the semiconductor element 3 is connected to the exposed area via an electrical connection means 8 such as a solder ball, and the external lead terminal 7 is connected to a solder lead or the like on the lower surface of the insulating substrate 1. It is brazed through the material.
[0024]
The through conductor layer 5 acts as a conductive path for connecting each electrode of the semiconductor element 3 to an external lead terminal 7 connected to an external electric circuit, and exposes each electrode of the semiconductor element 3 on the upper surface of the insulating substrate 1. Each electrode of the semiconductor element 3 is connected to the through conductor layer 5 on the lower surface of the insulating substrate 1 through the through conductor layer 5 if it is connected to the exposed surface of the through conductor layer 5 through the electrical connection means 8 such as a solder ball. When the external lead terminal 7 is electrically connected to the attached external lead terminal 7 and the external lead terminal 7 is connected to the external electrical circuit, each electrode of the semiconductor element 3 is connected to the external electrical circuit via the through conductor layer 5 and the external lead terminal 7. It will be electrically connected.
[0025]
In addition, since the through conductor layer 5 has a low dielectric constant of 6.3 (room temperature 1 MHz) of the mullite sintered body forming the insulating substrate 1, the propagation speed of the electric signal in the through conductor layer 5 is increased. As a result, an electric signal can be input / output between the semiconductor element 3 and the external electric circuit through the through conductor layer 5 at a high speed.
[0026]
The through conductor layer 5 is formed of a metal material mainly composed of molybdenum, and the exposed surface is covered with a coating layer 5a made of tungsten. The through conductor layer 5 and the coating layer 5a are, for example, Preparing a plurality of ceramic green sheets to be the insulating base 1 by firing with through holes formed at the same position, and then, in each through hole of the plurality of ceramic green sheets, with molybdenum powder as a main component, Printed and filled with conductive paste mainly composed of molybdenum obtained by adding powder and organic solvent and solvent such as aluminum oxide and magnesium oxide, and laminating these ceramic green sheets up and down, and finally into the through hole Add organic solvent and solvent to tungsten powder and mix on the exposed surface of the conductive paste mainly composed of printed molybdenum. With resulting conductive paste is coated by printing applied by screen printing is produced by firing the high temperature.
[0027]
The through conductor layer 5 is also formed of a metal material mainly composed of molybdenum, and the exposed surface is covered with a coating layer 5a made of tungsten, which is difficult to oxidize. Therefore, the exposed surface of the through conductor layer 5 and the coating layer 5a No oxide is formed on the surface of the coating layer 5a, and a plated layer such as nickel or gold having good wettability with respect to a brazing material such as solder, which will be described later, can be reliably and firmly deposited on the surface of the coating layer 5a.
[0028]
Further, the through conductor layer 5 is entirely formed of a metal material mainly composed of molybdenum having a sintering start temperature approximate to the sintering start temperature of the ceramic green sheet to be the insulating base 1. A large stress is not generated between the insulating substrate 1 and the through conductor layer 5, and a crack or the like is not generated in the insulating substrate 1 due to the stress.
[0029]
If the thickness of the coating layer 5a is greater than 1000 μm, the tungsten powder sintered body is hard and brittle and tends to cause defects such as chipping and peeling, and is thin and less than 50 μm. Then, the exposed surface of the through conductor layer 5 tends to be oxidized through the pinhole (hole) in the coating layer 5a. Therefore, the coating layer 5a preferably has a thickness in the range of 50 μm to 1000 μm.
[0030]
Further, the coating layer 5a, the cross-sectional shape is thin peripheral portion thicker center portion, so-called Ri it as semicylindrical shape, stress periphery of such thermal stress, without having to particularly concentrate on the outer peripheral edge, through conductors The bonding strength to the layer 5 can be made even stronger. Therefore, the coating layer 5a, it is assumed that to keep the cross-sectional shape as the hog-backed shape.
[0031]
As shown in FIG. 2, the covering layer 5a covering the exposed surface of the through conductor layer 5 is further coated with a nickel plating layer 9 or a gold plating layer 10 on the exposed surface. The metal plating layer 10 improves the wettability of the electrical connection means 8 made of solder balls or the like with respect to the through conductor layer 5 and firmly attaches the electrical connection means 8 made of solder balls or the like to the through conductor layer 5. Make.
[0032]
The nickel plating layer 9 is formed by, for example, an electroless plating method. Specifically, nickel sulfate 20 to 40 g / liter, sodium succinate 40 to 60 g / liter, boric acid 25 to 35 g / liter, After preparing an electroless nickel plating solution composed of ammonium chloride 25-35 g / liter, dimethylamine borane 2.5-4.5 g / liter, and the like, the exposed surface of the through conductor layer 5 is degreased and acid-treated, By immersing in a solution containing a catalyst agent to perform an activation treatment, and then immersing the exposed surface of the through conductor layer 5 in the electroless nickel plating solution set at 60 to 65 ° C. for 30 to 60 minutes. The exposed surface of the through conductor layer 5 is deposited to a predetermined thickness (2 μm to 8 μm), and the gold plating layer 10 is, for example, 20 to 40 g potassium hydroxide. From ram / liter, ethylenediaminetetraacetic acid 30-50 gram / liter, potassium dihydrogen phosphate 15-45 gram / liter, potassium cyanide 0.01-0.1 gram / liter, potassium gold cyanide 1-4 gram / liter, etc. A gold plating solution (liquid temperature: 85 to 95 ° C.) is prepared, and nickel plating is performed by immersing the exposed surface of the through conductor layer 5 on which the nickel plating layer 9 is deposited on the surface for 5 to 15 minutes. A predetermined thickness (0.02 μm to 0.3 μm) is deposited on the layer 9.
[0033]
When the thickness of the nickel plating layer 9 is less than 2 μm, it tends to be difficult to firmly adhere the gold plating layer 10 to the exposed surface of the through conductor layer 5, and when the thickness exceeds 8 μm, the nickel plating layer 9 is formed. There is a risk that a large stress is generated during the formation and this is inherent in the nickel plating layer 9, and the reliability of the adhesion between the exposed surface of the through conductor layer 5 and the nickel plating layer 9 decreases due to the internal stress. There is. Therefore, the nickel plating layer 9 preferably has a thickness in the range of 2 μm to 8 μm.
[0034]
Further, when the thickness of the gold plating layer 10 is less than 0.02 μm, the underlying nickel plating layer 9 cannot be completely covered, and the bonding strength of the electrical connection means 8 made of solder balls or the like to the through conductor layer 5. Further, when the thickness exceeds 0.3 μm, a part of the gold plating layer 10 diffuses into the electrical connection means 8 made of solder balls or the like, and the mechanical strength of the electrical connection means 8 is increased. There is a risk of lowering. Therefore, it is preferable that the gold plating layer 10 has a thickness in the range of 0.02 μm to 0.3 μm.
[0035]
Furthermore, the nickel plating layer 9 has a surface roughness in the range of 0.5 μm ≦ Ra ≦ 1.5 μm in terms of centerline average roughness (Ra). Since the adhesion area with the plating layer 10 is wide, the adhesion strength between them can be made extremely strong. Therefore, it is preferable that the surface of the nickel plating layer 9 is roughened in the range of 0.5 μm ≦ Ra ≦ 1.5 μm in terms of centerline average roughness (Ra).
[0036]
As a method of roughening the surface of the nickel plating layer 9 in the range of 0.5 μm ≦ Ra ≦ 1.5 μm in terms of center line average roughness (Ra), a medium of about # 1500 is applied to the surface of the nickel plating layer 9. to spray at a pressure of ^{0kg / cm 2 ~4.0kg / cm 2} , it is carried out by so-called blasting performed.
[0037]
On the other hand, an external lead terminal 7 is attached to the through conductor layer 5 led out on the lower surface of the insulating base 1 via a brazing material such as silver solder, and the external lead terminal 7 is connected to the semiconductor element 3. Each electrode is electrically connected to an external electric circuit.
[0038]
The external lead terminal 7 is made of a metal material such as iron-nickel-cobalt alloy or iron-nickel alloy. For example, an ingot (lumb) such as iron-nickel-cobalt alloy or iron-nickel alloy is rolled or punched. It is formed in a predetermined shape by applying a conventionally known metal processing method such as a method.
[0039]
The external lead terminal 7 is oxidized when the exposed surface is coated with a metal such as nickel or gold having good conductivity and corrosion resistance to a thickness of 1 μm to 20 μm by plating. Corrosion can be effectively prevented and connection with an external electric circuit can be made good. Therefore, it is preferable that nickel, gold or the like is deposited on the exposed surface of the external lead terminal 7 to a thickness of 1 μm to 20 μm by plating.
[0040]
Further, the insulating base 1 to which the external lead terminals 7 are attached is joined with a lid 2 having a bowl shape on the outer periphery of the upper surface via a sealing material made of glass, resin, brazing material, etc. The semiconductor element 3 is hermetically sealed inside the container 4 composed of 1 and the lid 2.
[0041]
The lid 2 has a function of hermetically housing the semiconductor element 3 in the container 4, and is made of a metal material such as copper, iron-nickel-cobalt alloy, iron-nickel-alloy, or an aluminum oxide sintered body. It is formed of a ceramic sintered body.
[0042]
Thus, according to the package for housing a semiconductor element described above, the semiconductor element 3 is connected to the upper surface of the insulating base 1, and each electrode of the semiconductor element 3 is connected to the surface of the coating layer 5a via the electrical connection means 8 made of solder balls or the like. After that, a lid-like lid 2 is joined to the upper surface of the insulating base 1 via a sealing material made of glass, resin, brazing material, etc., and the insulating base 1 and the lid 2 A semiconductor device as a final product is obtained by airtightly housing the semiconductor element 3 in the container 4 made of
[0043]
The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. For example, in the above-described embodiments, the ceramic wiring board of the present invention can be changed. Although the case where the present invention is applied to a semiconductor element housing package for housing semiconductor elements has been described as an example, it may be applied to a hybrid integrated circuit board on which semiconductor elements are mounted.
[0044]
【The invention's effect】
According to the ceramic wiring board of the present invention, since the insulating base is formed of a mullite sintered body, the thermal expansion coefficients of the semiconductor element and the insulating base approximate to each other, and the thermal stress caused by the difference between the thermal expansion coefficients of the two. It is possible to maintain the function as a semiconductor device for a long period of time while keeping the dielectric constant small, and it is possible to mount a semiconductor element that requires high-speed signal propagation as the dielectric constant of the insulating base is as low as about 6.3. It was.
[0045]
In addition, according to the ceramic wiring board of the present invention, the through conductor layer is formed of a metal material mainly composed of molybdenum, and the exposed surface is covered with a coating layer made of tungsten that is difficult to oxidize. On the surface of the coating layer to be applied, a plating layer of nickel or the like having good wettability with respect to the soldering material such as solder can be reliably and firmly applied. As a result, each electrode of the electronic component is soldered to the through conductor layer. It has become possible to make a strong electrical connection through electrical connection means such as balls.
[0046]
Furthermore, according to the ceramic wiring board of the present invention, the entire region of the through conductor layer is made of a metal material mainly composed of molybdenum whose sintering start temperature approximates the sintering start temperature of the ceramic green sheet serving as the insulating base. Since it is formed, a large stress is not generated between the insulating base and the through conductor layer, and a crack or the like is not generated in the insulating base due to the stress.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment in which the ceramic wiring board of the present invention is applied to an insulating substrate of a package for housing semiconductor elements.
FIG. 2 is an enlarged cross-sectional view of a main part of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulation base | substrate 2 ... Cover body 3 ... Semiconductor element 5 ... Penetration conductor layer 5a ... Cover layer 7 ... External lead terminal 8 ... Electrical connection means 9 ... Nickel Plating layer 10 ・ ・ Gold plating layer

Claims (1)

A ceramic wiring board comprising an insulating base, a through conductor layer formed in the insulating base, one end of which is exposed on the surface of the insulating base, and an electrode of the semiconductor element is connected to the exposed surface through an electrical connection means. there, the insulating substrate is made of mullite sintered body, and together with the through conductor layer is formed of a metal material mainly composed of molybdenum, the exposed surface is made of tungsten, the cross-sectional shape thicker central portion A ceramic wiring board characterized in that a peripheral portion is covered with a thin covering layer.

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