JP5612558B2 - Semiconductor package substrate and manufacturing method thereof - Google Patents

Description

  The present invention relates to a substrate for a semiconductor package on which a semiconductor element is mounted and a method for manufacturing the same.

  Ceramic substrates are known as substrates for mounting so-called power semiconductors that perform power control and semiconductor elements that become high temperature during operation, such as light emitting elements such as LEDs. The ceramic substrate has higher heat resistance and thermal conductivity than a resin substrate such as a paper phenol substrate. Since it has high heat resistance, it is difficult to be deformed even when heated with the operation of the semiconductor element. Moreover, since it has high thermal conductivity, heat generated from the semiconductor element can be quickly radiated to the outside.

  In order to promote heat dissipation of the ceramic substrate, a heat sink may be provided on the ceramic substrate. For example, in Patent Document 1, a heat sink made of a metal material is bonded to an LTCC (Low-temperature Co-fired Ceramics) substrate.

  As a means for joining the LTCC substrate and the heat sink, in Patent Document 1, a mixed paste in which glass particles and metal particles are kneaded into an organic binder is used. A laminated body in which the mixed paste is sandwiched between the LTCC substrate and the heat sink is formed and fired. The LTCC substrate is made of so-called glass ceramics in which a glass-based material is added to alumina. At the time of firing, the glass component in the LTCC substrate and the glass component in the mixed paste at the interface between the LTCC substrate and the mixed paste. And melt and mix. The LTCC substrate and the mixed paste are joined by the mixed glass component. In addition, at the interface between the mixed paste and the heat sink, the metal in the mixed paste and the metal in the heat sink are melted and mixed to form an alloy. In this way, the heat sink and the LTCC substrate are bonded via the mixed paste.

Further, as a heat sink material, glass ceramics such as 96% alumina (Al ₂ O ₃ ) may be used instead of a metal material. In this case, an inorganic adhesive containing a glass component may be used for joining the LTCC substrate and the heat sink. When the inorganic adhesive is sandwiched between the LTCC substrate and the heat sink, the glass component in the LTCC substrate and the glass component in the inorganic adhesive are melted and mixed. Similarly, the glass component of the heat sink and the glass component in the inorganic adhesive are melted and mixed. As a result, the LTCC substrate and the heat sink are joined.

JP 2010-516051 A

  By the way, it is preferable that the material of the heat sink is a material having high thermal conductivity because of the property of promoting the heat dissipation of the substrate. Examples of such a high thermal conductivity material include high-purity (for example, a purity of 99% or higher) alumina, aluminum nitride, silicon carbide, and other insulating ceramic materials. These ceramic materials contain little or no glass component. Therefore, even if an inorganic adhesive is used, the mixing of the glass components as described above does not occur sufficiently. Moreover, even when mixed paste is used, these ceramic materials do not contain metal materials, or even if they are contained, the melting point and decomposition temperature of the ceramic materials are high, so that it is difficult for metals to dissolve and almost all alloys are used. Not generated. Thus, when trying to use a material with high thermal conductivity as a heat sink, there has been a problem that it becomes difficult to join by the conventional joining method.

  One aspect of the present invention relates to a semiconductor package substrate. The substrate includes a laminate including a heat sink, a bonding material layer stacked on the heat sink, and a substrate formed on the bonding material layer and provided with a wiring connected to a semiconductor element. Furthermore, each layer of the laminate is bonded by firing in an air atmosphere.

  In the above invention, it is preferable that the bonding material layer includes a metal layer in contact with the heat sink.

  Moreover, in the said invention, it is suitable for the said metal layer to be formed so that the thickness of the said metal layer may become thinner than the thickness of the said heat sink and the said board | substrate.

  In the above invention, it is preferable that the substrate is an LTCC substrate, and the heat sink is made of silicon carbide, aluminum nitride, or beryllia.

  In the above invention, it is preferable that the bonding material layer includes an inorganic adhesive layer sandwiched between the metal layer and the substrate. Further, the substrate is fired alone in advance, the heat sink, the metal layer, the inorganic adhesive layer, and the fired substrate are sequentially laminated, and the laminated body laminated in that order is pressure-bonded, and the pressure-bonding is performed. It is preferable that the laminated body is fired in an air atmosphere.

  Another embodiment of the present invention relates to a method for manufacturing a semiconductor package substrate. In this method, a bonding material layer is stacked on a heat sink, and a substrate on which wiring connected to a semiconductor element is formed is stacked on the bonding material layer. Furthermore, each layer of the laminated body in which the heat sink, the bonding material layer, and the substrate are laminated is bonded by firing in an air atmosphere.

  In the above invention, it is preferable that the bonding material layer includes a metal layer in contact with the heat sink.

  Moreover, in the said invention, it is suitable to form the said metal layer so that the thickness of the said metal layer may become thinner than the thickness of the said heat sink and the said board | substrate.

  In the above invention, it is preferable that the substrate is an LTCC substrate, and the heat sink is made of silicon carbide, aluminum nitride, or beryllia.

  In the above invention, it is preferable that the bonding material layer includes an inorganic adhesive layer sandwiched between the metal layer and the substrate. Further, the substrate is fired alone in advance, the heat sink, the metal layer, the inorganic adhesive layer, and the fired substrate are sequentially laminated, and the laminated body laminated in the order is pressure-bonded and the pressure-bonded. It is preferable to fire the laminated body in an air atmosphere.

  According to the present invention, it is possible to bond materials that were conventionally difficult to bond to a substrate.

It is a perspective view which illustrates the composition of the substrate for semiconductor packages concerning this embodiment. It is sectional drawing which illustrates the structure of the substrate for semiconductor packages which concerns on this Embodiment. It is sectional drawing which illustrates the structure of another example of the substrate for semiconductor packages which concerns on this Embodiment. It is sectional drawing which illustrates the structure of another example of the substrate for semiconductor packages which concerns on this Embodiment.

  A semiconductor package substrate according to the present embodiment is illustrated in FIG. The semiconductor package substrate 10 includes a heat sink 12, a bonding material layer 14, and a wiring substrate 16.

  The wiring board 16 is a board for mounting the semiconductor element 18 (see FIG. 2). In order to quickly release the heat generated from the semiconductor element 18, it is preferable that the wiring substrate 16 is made of a material having high heat dissipation. In order to prevent deformation due to heat, the wiring board 16 is preferably formed of a material having high heat resistance. For example, the wiring board 16 is preferably composed of a ceramic substrate. In addition, among the ceramic substrates, LTCC (Low-temperature Co-fired Ceramics), which can use metal materials such as silver (Ag) and copper (Cu) with low conductor resistance as wiring, is used. It is more preferable to use it as the wiring board 16.

  On the wiring board 16, wiring 20 connected to the semiconductor element 18 is formed. For example, in FIGS. 1 and 2, the surface layer wiring 22 exposed from the wiring substrate 16 and the inner layer wiring 24 provided in the wiring substrate 16 are formed. In order to form such a multilayer wiring structure, the wiring substrate 16 may be configured by laminating sheets on which wiring patterns are printed. For example, in FIG. 2, the wiring board 16 is composed of three layers of sheets 26A, 26B, and 26C.

  In addition, the wiring board 16 preferably has a predetermined thickness in order to function as a package that protects the semiconductor element 18 from external impacts. For example, it is preferable to provide a thickness of 12.5 μm or more and 200 μm or less per sheet constituting the wiring board 16.

  Further, as illustrated in FIG. 2, a cavity 28 in which the semiconductor element 18 can be disposed may be formed in the upper sheet 26 </ b> C and the intermediate sheet 26 </ b> B of the wiring substrate 16. After the semiconductor element 18 is disposed in the cavity 28, the semiconductor element 18 can be sealed by filling with resin or the like.

  Further, a thermal via 32 for releasing the heat of the semiconductor element 18 to the outside may be formed on the arrangement surface 30 on which the semiconductor element 18 is arranged. In FIG. 2, the thermal via 32 is formed so as to penetrate the sheet 26A under the wiring board 16 in the thickness direction (Z-axis direction).

  Further, as shown in FIG. 3, the lower layer sheet 26 </ b> A may be omitted, and the semiconductor element 18 may be directly disposed on the bonding material layer 14. Since the lower layer sheet is omitted, the heat of the semiconductor element 18 can be quickly released to the outside.

  Returning to FIG. 2, the heat sink 12 is a member for radiating the heat generated in the semiconductor element 18 to the outside. For that purpose, the heat sink 12 is preferably made of a material having higher thermal conductivity than the wiring board 16. In addition, if the thermal expansion coefficients of the wiring board 16 and the heat sink 12 are different, the joined body of both may be deformed (warped) when the temperature rises. Therefore, it is more preferable that the thermal expansion coefficients of the wiring board 16 and the heat sink 12 are substantially equal.

  That is, it is preferable that the heat sink 12 is made of a material having higher thermal conductivity than the wiring board 16 and a thermal expansion coefficient substantially equal to that of the wiring board 16. For example, when the wiring board 16 is LTCC, it is made of a so-called insulating ceramic material that does not contain a glass component, such as 99% alumina, 99% beryllia (BeO), aluminum nitride (AlN), silicon carbide (SiC), or the like. It is preferable to configure the heat sink 12. In addition, the case where it does not contain a glass component here also corresponds to the case where it hardly contains (it contains in a trace amount). Specifically, it refers to a ceramic having a glass component content of 1% or less.

The thermal conductivity of LTCC is 2.5 [Wm ^-1 K ^-1 ] or more and 3.5 [Wm ^-1 K ^-1 ] or less, whereas 99% alumina, 99% beryllia, aluminum nitride, silicon carbide The thermal conductivities of each are 31 [Wm ⁻¹ K ⁻¹ ], 240 [Wm ⁻¹ K ⁻¹ ], 100 [Wm ⁻¹ K ⁻¹ ] or more and 260 [Wm ⁻¹ K ⁻¹ ] or less, 270, respectively. It is about [Wm ⁻¹ K ⁻¹ ]. Both have higher thermal conductivity than LTCC.

The thermal expansion coefficient of LTCC is 4.5 [10 ⁻⁶ K ⁻¹ ] or more and 12.0 [10 ⁻⁶ K ⁻¹ ] or less at around 25 ° C., whereas 99% alumina and 99% beryllia. The thermal expansion coefficients of aluminum nitride and silicon carbide are 6.8 [10 ⁻⁶ K ⁻¹ ], 6.8 [10 ⁻⁶ K ⁻¹ ], and 4.5 [10 ⁻⁶ K at around 25 ° C., respectively. ^-1 ] and about 3.7 [10 ^-6 K ^-1 ]. All have a thermal expansion coefficient substantially equal to LTCC.

  Further, the heat sink 12 may have a role as a bottom plate of the semiconductor package substrate 10, and for example, has a screw hole 34 (see FIG. 1) for fixing the semiconductor package substrate 10 to a casing or the like. It may be. At this time, it is preferable that the heat sink 12 has a predetermined rigidity in order to securely fix the semiconductor package substrate 10 and the casing against an external impact. For example, the heat sink 12 preferably has a thickness of 50 μm or more and 200 μm or less.

  The bonding material layer 14 is a member that bonds the wiring board 16 and the heat sink 12 together. The bonding material layer 14 may be any material that can be oxidized (covalently bonded through oxygen) to the wiring board 16 and the heat sink 12, and includes a material that can form an interface with the wiring board 16 and the heat sink 12 during firing. It only has to be. For example, the bonding material layer 14 preferably includes glass or a metal material. Furthermore, when the thermal expansion coefficients of the heat sink 12 and the wiring board 16 are different, a material that can follow the tensile stress generated at the interface when the temperature rises is preferable. For example, it is preferable to use a metal material having malleability and ductility as a member in contact with the interface between the heat sink 12 and the wiring board 16. For example, silver (Ag), an alloy of silver and palladium (Pd), or an alloy of silver and platinum (Pt) may be used as such a member.

  Further, even when the thermal expansion coefficients of the heat sink 12 and the wiring board 16 are substantially equal, if the thermal expansion coefficients of these members and the bonding material layer 14 are different, these semiconductor package substrates 10 are subject to a rise in temperature. There is a risk of deformation (warping). Therefore, it is preferable to form the bonding material layer 14 thinner than the heat sink 12 and the wiring substrate 16. For example, it is preferable to determine the thickness of the bonding material layer 14 so that the thickness of the thinner one of the heat sink 12 and the wiring substrate 16 is less than half. For example, it is preferable to configure the bonding material layer 14 so that the thickness after firing is 10 μm or more and 30 μm or less.

  Next, a method for manufacturing the semiconductor package substrate 10 according to the present embodiment will be described. First, a pattern is formed on the green sheet. The green sheet is a sheet-like member in which the raw material of the wiring board 16 is kneaded into an organic binder. For example, when the wiring board 16 is made of LTCC, a sheet in which glass and a ceramic material are kneaded into an organic binder is used. The green sheet is subjected to a process of opening a position serving as a cavity or printing a wiring pattern. Further, green sheets on which patterns are formed are stacked. For example, when the wiring substrate 16 of FIG. 2 is manufactured, three layers of green sheets are laminated.

  Next, a metal paste is applied on the heat sink 12. The metal paste is a paste in which a metal material that is a raw material of the bonding material layer 14 is kneaded into an organic binder. Here, the applied metal paste may be dried at a predetermined temperature (for example, 70 ° C. or higher). Furthermore, the green sheet laminated | stacked on the metal paste is arrange | positioned.

  Furthermore, the heat sink 12, the paste of the metal paste, and the green sheet are placed in the furnace in a pressure-bonded state. For example, a weight is placed on a green sheet in a state where the laminate is placed on a setter (bottom plate).

  Further, the laminate is fired in an air atmosphere (oxidizing atmosphere). In addition, in order to promote the oxidative bond of each adjacent layer, baking may be performed in a state where the oxygen partial pressure is increased as compared with the atmosphere. Firing is performed over a temperature and time at which the organic material in the metal paste and the green sheet can be sufficiently decomposed by heat decomposition. For example, while maintaining the peak temperature of 850 ° C. for 10 minutes, the entire baking time is 60 minutes.

  In the firing in the air atmosphere, the heat sink 12 and the bonding material layer 14 and the bonding material layer 14 and the wiring board 16 are bonded. According to the inventor's hypothesis, it is considered that the heat sink 12 and the bonding material layer 14 and the bonding material layer 14 and the wiring board 16 are bonded by an oxidative bond, and as a result, the respective layers are bonded. That is, a covalent bond via oxygen is performed at the interface between adjacent layers. For example, when the heat sink 12 is silicon carbide, the bonding material layer 14 is silver, and the wiring substrate 16 is LTCC, a bond of Si—O—Ag is generated between the heat sink 12 and the bonding material layer 14. In addition, bonding with Ag—O—Si occurs between the bonding material layer 14 and the wiring substrate 16. These oxidative bonds are formed on the interface where the layers face each other, and adjacent layers are joined.

  Note that some warping may occur in the wiring board 16 after the green sheet is fired. If the wiring board 16 is warped with respect to the bonding material layer 14, the bonding material layer 14 and the wiring board 16 may be peeled off. Therefore, as shown in FIG. 4, a bonding material layer 14-1 composed of a metal layer 40 and a glass layer 42 may be used.

  In the method for manufacturing the semiconductor package substrate 10 shown in FIG. 4, a metal paste containing a metal that becomes the material of the metal layer 40 and an inorganic adhesive containing glass powder that becomes the material of the glass layer 42 are used. Here, for example, lead borosilicate glass is used as the glass powder.

  First, the wiring sheet 16 is obtained by firing the green sheet alone in advance. Further, the heat sink 12, the metal paste, the inorganic adhesive, and the wiring board 16 are laminated in this order. Next, each layer of the laminate is pressure-bonded by a hot water isostatic press or the like. At this time, due to the fluidity of the inorganic adhesive, the inorganic adhesive layer is deformed into a shape that follows the warp of the wiring board 16.

  Next, the laminated body after the pressure bonding is pressure bonded and fired in an air atmosphere. For example, similarly to the above, the state of the peak temperature of 850 ° C. is maintained for 10 minutes, and the entire baking time is set to 60 minutes. At this time, the glass component in the wiring board 16 and the glass component in the inorganic adhesive are melted and mixed. Further, silicon in the inorganic adhesive and metal in the metal paste bind oxygen through an oxidative bond. That is, when the metal in the metal paste is Ag, a covalent bond with Ag—O—Si is performed. Similarly, the heat sink 12 and the metal in the metal paste are bonded by an oxidative bond. As a result, adjacent layers are joined.

  A silicon carbide substrate was used as the heat sink 12, and a two-layer LTCC substrate was used as the wiring substrate 16. Further, silver was used as the metal layer 40 of the bonding material layer 14 and lead borosilicate glass was used as the inorganic adhesive. First, two layers of LTCC green sheets on which wiring patterns were formed were stacked and baked.

  A silver paste in which silver was kneaded into an organic binder was applied on the heat sink 12. A silver paste having a silver content of 85 wt% was used. When applying the silver paste, a 200 mesh screen having a wire diameter of 23 μm was used. The coating thickness of the silver paste was about 35 μm. The applied silver paste was dried under a drying condition of 80 ° C. The film thickness after drying was 28 μm.

  Next, an inorganic adhesive obtained by kneading a powder of lead borosilicate glass in an organic binder was applied to the bottom surface of the fired wiring board 16 (the surface facing the surface wiring 22). Furthermore, the heat sink 12, the silver paste, the inorganic adhesive, and the wiring board 16 were laminated in this order, and this laminate was vacuum packed with a vinyl pack. Further, the stacked laminate was placed in a warm water chamber of a warm water isostatic press. Further, after preheating at a temperature condition of 90 ° C., a pressure of 20 MPa to 35 MPa was applied. By being preheated at 90 ° C., fluidity was generated in the inorganic adhesive, and the inorganic adhesive was filled following the warping of the wiring board.

  Next, the laminated body packed from the warm water chamber was taken out, and the laminated body was taken out from the vinyl pack. This laminate was fired in the air under conditions of a peak temperature of 850 ° C. and a total firing time of about 60 minutes. As a result, all the layers of the laminate were securely bonded, and no peeling or the like was observed.

  DESCRIPTION OF SYMBOLS 10 Semiconductor package substrate, 12 Heat sink, 14 Bonding material layer, 16 Wiring board, 18 Semiconductor element, 20 Wiring, 22 Surface wiring, 24 Inner layer wiring, 26 Wiring board sheet, 28 Cavity, 30 Arrangement surface, 32 Thermal via, 34 screw holes, 40 metal layers, 42 glass layers.

Claims (6)

A heat sink,
A bonding material layer laminated on the heat sink;
A substrate on which the wiring connected to the semiconductor element is formed and laminated on the bonding material layer;
Comprising a laminate including
The bonding material layer includes a metal layer in contact with the heat sink, and an inorganic adhesive layer sandwiched between the metal layer and the substrate,
The substrate is baked alone in advance in the state of a laminate in which green sheets are laminated ,
The heat sink, the metal layer, the inorganic adhesive layer, and the fired substrate are sequentially laminated,
Each layer of the laminated body laminated in that order is pressure-bonded by an isotropic pressure press , and the inorganic adhesive layer is transformed into a shape that follows the warpage of the substrate after firing,
A substrate for a semiconductor package, wherein the layers of the laminate are joined by firing the pressure-bonded laminate in an air atmosphere. The semiconductor package substrate according to claim 1,
The semiconductor package substrate, wherein the metal layer is formed so that the thickness of the metal layer is thinner than the thickness of the heat sink and the substrate. The semiconductor package substrate according to claim 2,
The substrate is an LTCC substrate,
The substrate for a semiconductor package, wherein the heat sink is made of silicon carbide, aluminum nitride, or beryllia. Laminate the bonding material layer on the heat sink,
In the bonding material layer, a substrate on which wiring connected to a semiconductor element is formed is laminated,
A method for manufacturing a substrate for a semiconductor package, wherein each layer of the laminate in which the heat sink, the bonding material layer, and the substrate are laminated is bonded by firing in an air atmosphere,
The bonding material layer includes a metal layer in contact with the heat sink, and an inorganic adhesive layer sandwiched between the metal layer and the substrate,
The substrate is baked alone in advance in the state of a laminate in which green sheets are laminated ,
Laminating the heat sink, the metal layer, the inorganic adhesive layer, and the fired substrate in order,
By crimping each layer of the laminate laminated in the order by an isotropic pressure press , the inorganic adhesive layer is transformed into a shape that follows the warpage of the substrate after firing ,
A method of manufacturing a substrate for a semiconductor package, comprising bonding the layers of the laminate by firing the pressure-bonded laminate in an air atmosphere. A method of manufacturing a semiconductor package substrate according to claim 4,
The method for manufacturing a substrate for a semiconductor package, wherein the metal layer is formed so that the thickness of the metal layer is thinner than the thickness of the heat sink and the substrate. A method of manufacturing a substrate for a semiconductor package according to claim 5,
The substrate is an LTCC substrate,
The method of manufacturing a substrate for a semiconductor package, wherein the heat sink is made of silicon carbide, aluminum nitride, or beryllia.

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