JP2009239100A - Multilayer ceramics substrate and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramics substrate that enhances reliability by preventing the occurrence of cracks, even if thermal stress is applied to a ceramic substrate according to the differences of thermal expansion coefficient among the mounted substrates, in heat cycle test and the like. <P>SOLUTION: A ceramic substrate 11, which is formed by laminating and calcinating ceramic green sheets, includes: a circular recess 12 (12a and 12b) which has the shape of a concentric circle in the bottom of the ceramic substrate and has at least two or more stage differences; electrodes 13a and 13b provided in the bottom of each stage of the recesss 12a and 12b; a solder material 15 with which the recess is filled and which is bonded to the electrodes 13a and 13b; and a metal ball 16 which is bonded to the solder material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laminated ceramic substrate having a wiring pattern on a surface layer and an inner layer formed by laminating and firing a ceramic green sheet having a required via and a metal film wiring pattern, and in particular, a connection terminal for a mounting substrate. The present invention relates to a structure of a laminated ceramic substrate using a metal ball array (BGA) as a part and a manufacturing method thereof.

  Conventionally, a ceramic green sheet is formed from a slurry in which ceramic powder is mixed and dispersed, a required wiring pattern is formed on the ceramic green sheet using vias and conductor paste, and the ceramic green sheet is laminated and fired. A multilayer ceramic substrate having wiring patterns on the surface layer and the inner layer is manufactured. Then, by providing a connection terminal portion such as a metal ball array (BGA) such as a solder ball or a solder bump array on the bottom surface of the fired multilayer ceramic substrate, and connecting the connection terminal portion to a wiring pad of the mounting substrate, the multilayer ceramic substrate The internal wiring and the wiring of the mounting board are connected.

  Since such a multilayer ceramic substrate is made of ceramics, it has excellent heat resistance and moisture resistance, as well as good low-loss characteristics (frequency characteristics) in high-frequency circuits, and wiring patterns can be formed on the surface and inner layers. Multi-layer wiring can be easily formed and is widely used as a substrate for high-frequency modules and LSI packages.

However, the thermal expansion coefficient of the ceramic substrate is 5 to 6 ppm / ° C., whereas the thermal expansion coefficient of the solder ball is 18 to 19 ppm / ° C., and the thermal expansion coefficient of the mounting substrate made of a resin substrate is 20 to 40 ppm / ° C. Because it is as high as ° C, thermal stress is applied to the ceramic substrate in temperature cycle tests, etc., especially cracks are generated from the corners of the recess provided to accommodate balls such as BGA on the ceramic substrate, and the via conductor is disconnected and connected There exists a problem that a defect may arise (refer patent document 1).
Japanese Patent No. 3377866

  The present invention has been made on the basis of the above circumstances, and is provided for accommodating balls such as BGA even in the case of a thermal cycle test or the like even if thermal stress is applied to the ceramic substrate due to the difference in thermal expansion coefficient from the mounting substrate. Another object of the present invention is to provide a multilayer ceramic substrate and a method for manufacturing the same, which can prevent cracks generated at the corners of the recesses and improve reliability.

  The multilayer ceramic substrate of the present invention is a ceramic substrate formed by laminating and firing ceramic green sheets, a circular recess having at least two or more steps concentrically on the bottom surface of the ceramic substrate, and each step of the recess. An electrode provided on the bottom surface, a solder material filled in the recess and bonded to the electrode, and a metal ball bonded to the solder material are provided.

  The method for manufacturing a laminated ceramic substrate according to the present invention includes preparing a first green sheet having a plurality of large openings for accommodating metal balls, and providing the plurality of middle openings for accommodating metal balls and the outer periphery of the middle openings. A second green sheet provided with an annular electrode paste pattern having an outer diameter larger than the outer diameter of the large opening was prepared, and a second electrode sheet provided with a circular electrode paste pattern having an outer diameter larger than the outer diameter of the middle opening was prepared. Prepare three green sheets, stack the first green sheet as the lowermost layer, the second green sheet as the upper layer, the third green sheet as the upper layer, and the other green sheets as the upper layer, followed by firing. And forming a multilayer ceramic substrate having a concentric circular recess on the bottom surface and having a circular recess having at least two steps or more and an electrode exposed on the bottom surface of each recess. A plating layer is formed on each exposed surface of the electrode, and a solder material is filled in the recess. The solder material is joined to the exposed surface of the electrode through the plating layer, and a metal ball is loaded in the recess. Is characterized by being bonded to a solder material.

  According to the multilayer ceramic substrate of the present invention, the number of concave corners is increased by forming a circular concave portion having at least two steps on the bottom surface of the ceramic substrate and having a step structure inside the concave portion. . As a result, the thermal stress concentrated on the corner caused by the difference in thermal expansion coefficient between the mounting substrate and the ceramic substrate can be dispersed in many directions, and the thermal stress applied to one place can be remarkably reduced. Thereby, generation | occurrence | production of the crack in the recessed part of the terminal connection part provided in the ceramic substrate bottom face can be suppressed effectively, the mounting strength of a laminated ceramic substrate can be improved, and reliability can be improved.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a laminated ceramic substrate and a manufacturing method thereof according to the present invention will be described with reference to the accompanying drawings. In the drawings, the same or corresponding members or elements will be described with the same reference numerals.

  FIG. 1 shows a main part of a multilayer ceramic substrate according to a first embodiment of the present invention. The ceramic substrate 11 is made of a ceramic green sheet mainly composed of alumina and borosilicate glass, a required via is formed, a green sheet on which a wiring pattern made of a silver conductor paste is screen-printed is laminated, and an internal wiring conductor is used. It is a low-temperature fired multilayer ceramic (LTCC) substrate fired at a relatively low temperature of 900 ° C. or lower which is lower than the melting point of a certain silver conductor. Therefore, the ceramic substrate 11 includes a portion 11a formed from the lowermost green sheet, a portion 11b formed from the upper green sheet, a portion 11c formed from the upper green sheet, and several layers to Dozens of layers of green sheets are laminated and fired, and the inner layer has a wiring pattern made of a silver conductor, and the wiring patterns of each layer are connected to each other through vias filled with a silver conductor. Yes.

  The ceramic substrate 11 is provided with a circular recess 12 having a concentric shape and having two steps. The concave portion 12 includes a concave portion 12a having a large opening and a shallow annular bottom surface (first step) for accommodating the metal ball 16, and a concave portion 12b having a deep circular bottom surface (second step) in the middle opening. It is concentric and has a step shape. An annular electrode 13a is disposed on the bottom surface of the shallow recess 12a, the inner diameter thereof is equal to the inner diameter of the bottom surface of the recess 12a, and the outer diameter thereof is larger than the outer diameter of the bottom surface of the recess 12a. It is provided beyond. Further, a circular electrode 13b is disposed on the bottom surface of the deep recess 12b, and the outer diameter thereof is larger than the outer diameter of the bottom surface of the recess 12b, and is provided beyond the outer periphery of the bottom surface of the recess 12b. Here, the electrodes 13a and 13b are thick film electrodes made of a silver conductor formed by screen-printing and baking a silver conductor paste, and the film thickness thereof is about 5 to 20 μm. The depths (steps) of the recesses 12a and 12b are about 50 to 200 μm, respectively. This is a thickness of 1-2 sheets.

  On the exposed surface of the electrode 13a disposed on the bottom surface of the recess 12a and on the exposed surface of the electrode 13b disposed on the bottom surface of the recess 12b, a Ni plating layer having a thickness of 3-5 μm and an Au plating having a thickness of 0.1-1 μm are provided. A plated layer 14 made of a layer or the like is formed, and this plated layer 14 prevents soldering of the electrodes 13a and 13b made of a silver conductor or the like. The recess 12 (12a, 12b) is filled with a solder material 15, and the solder material 15 is bonded to the exposed surfaces of the electrodes 13a, 13b via the plating layer. Then, a metal ball 16 such as a solder ball is loaded in the recess 12 and joined to the solder material 15 and fixed. The ceramic substrate 11 c includes a via 17, and the via 17 is filled with a silver conductor and is connected to a wiring pattern on the inner layer of the ceramic substrate 11.

  The metal ball 16 functions as a connection terminal of the ceramic substrate 11 and is fixed to the wiring pad 22 of the mounting substrate 21 such as a resin substrate by soldering or the like. The metal ball 16 is not limited to a solder ball, and a Cu ball or the like can also be used. Further, only the connection terminal portions of the two metal balls are illustrated, but actually, the connection terminal portions of a large number of metal balls are arranged vertically and horizontally on the bottom surface of the ceramic substrate.

  Next, the effect of the above configuration will be described with reference to FIG. FIG. 2A shows a connecting terminal portion of a conventional metal ball. The recess 12 provided on the bottom surface of the ceramic substrate 11 is filled with a solder material, and the metal ball 16 is bonded and fixed to the solder material. On the other hand, the metal ball 16 is bonded to the wiring pad 22 of the mounting substrate 21. And fixed. The recess 12 of the conventional example has two corners a and b in cross section as shown in the figure, and thermal stress due to the difference in thermal expansion coefficient between the mounting substrate 21 and the ceramic substrate 11 in the temperature cycle test or the like is at two corners. Concentrate on parts a and b. For this reason, cracks C are likely to occur at the two corners a and b. When the crack C propagates and reaches the via or the wiring layer, problems such as disconnection or poor wiring connection occur.

  On the other hand, the metal ball mounting structure of the present invention includes a circular recess 12 having a plurality of steps of at least two steps in a concentric shape for housing the metal ball 16. That is, the recess 12 has a total of six corners a, b, c, d, e, and f in cross section. Among them, in the temperature cycle test or the like, the thermal stress due to the difference in thermal expansion coefficient between the mounting substrate 21 and the ceramic substrate 11 is dispersed mainly at the four corners a, c, d, and f which are concave corners. Therefore, it is possible to avoid and reduce the concentration of thermal stress at the corners, thereby preventing the occurrence of cracks, improving the mounting strength, and improving the reliability.

  Furthermore, the concentric circular recess 12 containing the metal ball 16 and having at least two steps is provided with electrodes 13a and 13b made of a silver conductor or the like on each bottom surface. The electrode 13a has an outer diameter larger than the outer diameter 12a of the shallow bottom surface and completely covers the corners a and f, and the electrode 13b has an outer diameter larger than the outer diameter 12b of the deep bottom surface, Cover parts c and d completely. Therefore, the corners a, c, d, and f where cracks are likely to occur are covered by the thick film electrode made of a silver conductor or the like, so that the generation of cracks can be blocked and suppressed.

  FIG. 3 shows a multilayer ceramic substrate according to a modification of the first embodiment. In this embodiment, a concentric circular recess 12 having three steps is provided on the bottom surface of the ceramic substrate 11. That is, the recess 12 that accommodates the metal ball 16 is formed from the shallow recess 12a, the intermediate depth recess 12b, and the deep recess 12c. Thick film silver electrodes 13a, 13b, and 13c having outer diameters larger than the outer diameter of the bottom surface are provided on the bottom surfaces of the recesses, and the electrodes 13a, 13b, and 13c are corners of the recesses where cracks are likely to occur. The parts a, c, e, f, h, and j are respectively covered. A plating layer 14 made of a Ni plating layer, an Au plating layer, or the like is formed on the exposed surfaces inside the recesses of the electrodes 13a, 13b, and 13c, and bonded to the solder material 15 filled in the recesses, and further bonded to the metal balls 16 is doing. A via 17 is provided at the top of the recess 12, and the via 17 is filled with a silver conductor and connected to the wiring pattern on the inner layer of the ceramic substrate 11.

  In the structure of the connection terminal portion of the metal ball having the above-described configuration, the concavity-shaped circular recess 12 having three steps is provided, so that the recess 12 is a, b, c, d, e, It has a total of 10 corners of f, g, h, i, j. For this reason, the thermal stress due to the difference in thermal expansion coefficient between the mounting substrate 21 and the ceramic substrate 11 is dispersed at the six corners a, c, e, f, h, j in a temperature cycle test or the like. Therefore, the concentration of thermal stress can be further reduced and alleviated by the large number of concave corners, thereby preventing the generation of cracks, improving the mounting strength, and improving the reliability.

  Furthermore, concentric circular recesses 12 having electrodes 13a, 13b, and 13c made of silver conductors or the like on the bottom surfaces of the recesses 12 and having concave corners a, c, e, f, h, Since j is covered by a thick film electrode made of a silver conductor or the like, the occurrence of cracks can be blocked and further suppressed.

  FIG. 4 shows a ceramic substrate according to the second embodiment of the present invention. In this embodiment, concentric circular recesses 12 (12a, 12b) having two steps are provided on the bottom surface of the ceramic substrate 11, provided on the bottom surfaces of the recesses, and from the outer diameter of the bottom surface. Is similar to the ceramic substrate of the first embodiment in that it includes electrodes 13a and 13b having large outer diameters, but thick film electrodes 13m made of a silver conductor or the like are further formed on the inner peripheral wall surfaces of the recesses 12, respectively. The difference is that 13n is provided. That is, a thick film electrode 13m made of a silver conductor or the like is provided on the inner peripheral wall surface of the shallow recess 12a, and a thick film electrode 13n made of a silver conductor or the like is provided on the inner peripheral wall surface of the deep recess 12b. The entire inner surface of the recess 12 of the electrodes 13a and 13b provided on the bottom surfaces of the recesses and the electrodes 13m and 13n provided on the inner peripheral wall surfaces of the recesses is composed of a Ni plating layer, an Au plating layer, or the like. A plated layer 14 is formed, connected to the solder material 15 filled in the recess, and further connected to the metal ball 16.

  Therefore, the entire inner surface (bottom surface and inner peripheral wall surface) of the recess 12 provided on the bottom surface of the ceramic substrate is covered with the thick film electrodes 13a, 13b, 13m, and 13n, and further, the Ni plating layer and the Au plating layer are formed on the upper surface. Since the plating layer 14 is coated, the entire inner surface of the recess 12 is bonded to the solder material 15, and the solder material 15 is further bonded to the metal ball 16. The concave portion 12 can be firmly fixed. Similarly to the first embodiment, thermal stress can be dispersed by a plurality of corner portions formed by circular concave portions having steps, and thick film electrodes 13a and 13b made of a silver conductor or the like covering the corner portions. The presence of thick film electrodes 13m and 13n made of silver conductor covering the inner peripheral wall surface of a circular recess having a step, together with the effect of suppressing the occurrence of cracks due to the presence of heat, further receives thermal stress on the entire surface inside the recess. Therefore, it is possible to increase the mounting strength, prevent the occurrence of cracks, and improve the reliability.

  Next, the manufacturing method of the ceramic substrate of 1st Embodiment of this invention is demonstrated with reference to FIG. First, a ceramic green sheet that can be fired at a low temperature, mainly composed of alumina and borosilicate glass, is prepared. An array of large openings 31 for accommodating metal balls is formed on the green sheet 11a, which is the lowest layer, by punching or the like. On the green sheet 11b that is the second layer from the lowest layer, an array of middle openings 32 that accommodates metal balls is formed by punching or the like, and an outer diameter larger than the outer diameter of the large openings 31 is formed on the outer periphery of the middle openings 32. An array of annular silver paste patterns 13a is formed by screen printing. An array of vias 17 is formed on the green sheet 11c that is the third layer from the bottom layer by punching or the like, and an array of circular silver paste patterns 13b having an outer diameter larger than the outer diameter of the middle opening 32 is formed by screen printing. Form.

  Then, these green sheets and a green sheet of the fourth layer or more (not shown) are combined and laminated, and fired at a relatively low temperature of 900 ° C. or lower which is not higher than the melting point of silver. As shown in FIG. 5 (e), a multilayer ceramic substrate having concentric circular recesses 12 (12a, 12b) on the bottom surface and electrodes 13a, 13b on the bottom surfaces of the recesses, respectively. Can be formed. Then, a plating layer 14 made of an Ni plating layer, an Au plating layer, or the like is formed on each exposed surface of the electrodes 13a and 13b, and the concave portion 12 is filled with a solder material 15. The solder material 15 is connected to the electrode via the plating layer 14. The laminated ceramic substrate of the present invention can be manufactured by joining the exposed surfaces of 13a and 13b, loading metal balls 16 into the recesses 12 and joining the metal balls 16 to the solder material 15.

  Next, the manufacturing method of the ceramic substrate of 2nd Embodiment of this invention shown in FIG. 4 is demonstrated with reference to FIG. First, similarly, a ceramic green sheet that can be fired at a low temperature, mainly composed of alumina and borosilicate glass, is prepared (see (a)). An array of large openings 31 for accommodating metal balls is formed on the green sheet 11a, which is the lowest layer, by punching or the like. On the green sheet 11b, which is the second layer from the bottom layer, an array of inner openings 32 that accommodates metal balls is formed by punching or the like. An array of vias 17 is formed by punching or the like on the green sheet 11c that is the third layer from the bottom layer. (See (b))

  Next, a silver paste is filled into the large opening 31 of the green sheet 11a by screen printing to form a silver conductor filler 31a, and the silver paste is filled into the middle opening 32 of the green sheet 11b by screen printing. The filler 32a is formed, and the silver electrode pattern 13b that covers the via 17 of the green sheet 11c is formed by screen printing (see (c)). Then, by so-called castellation, the central portion of the silver conductor filler 31a on the inner peripheral wall surface of the large opening 31 of the green sheet 11a is removed by punching to form a coating of the cylindrical silver conductor 13m on the inner peripheral wall surface of 31a. To do. Subsequently, the central portion of the silver conductor filler 32a on the inner peripheral wall surface of the middle opening 32 of the green sheet 11b is removed by punching to form a coating of the cylindrical silver conductor 13n on the inner peripheral wall surface of 32a ((d)). (See (e)). Further, an array of annular silver paste patterns 13a having an outer diameter larger than the outer diameter of the large opening 31 is formed on the outer periphery of the middle opening 32 on the green sheet 11b by screen printing (see (d)). A circular silver electrode pattern is screen-printed on the green sheet 11b, and then the inner opening 32 is casted to form a coating of a cylindrical silver conductor 13n on the inner peripheral wall surface of the inner opening 32. You may make it remove the center part of the filler 32a of the silver conductor of a surrounding wall surface by punching.

  And these green sheets and the green sheet of the 4th layer or more which are not illustrated are laminated | stacked, and it bakes at the comparatively low temperature of 900 degrees C or less below melting | fusing point of silver. By laminating the green sheets 11a, 11b, and 11c, as shown in FIG. 6 (e), a circular recess 12 (12a, 12b) having a concentric shape on the bottom surface and having two steps, and each of the recesses A laminated ceramic substrate having electrodes 13a and 13b on the bottom surface thereof and electrodes 13m and 13n on the inner peripheral wall surfaces of the recesses 12a and 12b can be formed. Then, the entire inner surface of the recess 12 is covered with electrodes, a plating layer 14 made of an Ni plating layer and an Au plating layer is formed on the exposed surface of each electrode, and the solder material 15 is filled in the recess 12. 15 is bonded to the exposed surface, which is the entire surface of the recesses of the electrodes 13 a, 13 b, 13 m, 13 n, through the plating layer 14, and the metal balls 16 are loaded into the recesses 12, and the metal balls 16 are bonded to the solder material 15. Thus, the multilayer ceramic substrate of the present invention can be manufactured.

  The manufacturing method described above is for a method of forming a concentric recess having two steps on the bottom surface. However, the inner opening 32 and the electrode of the green sheet 11b are also applied to a recess having three or more steps. This can be dealt with by providing a plurality of green sheets with the size of 13a changed. The electrode printing on the inner peripheral wall surface of the recess 12 may be formed by screen printing without using the castellation method.

  The above embodiment relates to a so-called low-temperature fired laminated ceramic substrate using a green sheet and a silver electrode that can be fired at a low temperature mainly composed of alumina and borosilicate glass. Of course, the gist of the present invention can be similarly applied to ceramic substrates. Further, not only silver electrodes but also electrodes such as Ag / Pd, Ag / Pt, Pt / Pd, and Au may be used, and the plating layer 14 is a three or more plating layer composed of a combination of Ni / Pd / Au plating layers. Also good.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

The principal part of the laminated ceramic substrate of 1st Embodiment of this invention is shown, (a) is sectional drawing, (b) is a bottom view of a recessed part. (A) is sectional drawing which shows the mounting structure of the metal ball of a prior art example, (b) is sectional drawing which shows the mounting structure of the metal ball of this invention. It is sectional drawing which shows the principal part of the laminated ceramic substrate provided with the recessed part which has a three-step level | step difference concentrically. It is sectional drawing which shows the principal part of the laminated ceramic substrate of 2nd Embodiment of this invention. It is a figure which shows the manufacturing process of the laminated ceramic substrate of 1st Embodiment of this invention, (a) (b) shows the array on a green sheet, (c) is an enlarged plan view for one of (b) (D) is a sectional view thereof, and (e) is an enlarged sectional view showing a state in which green sheets 11a, 11b, and 11c are laminated. It is a figure which shows the manufacturing process of the laminated ceramic substrate of 2nd Embodiment of this invention, (a)-(d) shows the array on a green sheet, (e) laminated | stacked green sheet 11a, 11b, 11c. It is an expanded sectional view showing a state.

Explanation of symbols

11 Ceramic substrate 12, 12a, 12b, 12c Recessed portion 13a, 13b, 13c, 13m, 13n Thick film electrode 14 made of silver conductor Plating layer 15 made of Ni plating layer and Au plating layer 15 Solder material 16 Metal ball 21 Mounting substrate 22 Wiring pad 31 Large opening 32 Middle opening

Claims (4)

In ceramic substrates formed by laminating and firing ceramic green sheets,
A circular concavity that is concentric on the bottom surface of the ceramic substrate and has at least two steps, and
An electrode provided on the bottom surface of each step of the recess;
A solder material filled in the recess and bonded to the electrode;
A laminated ceramic substrate comprising a metal ball bonded to the solder material.   The multilayer ceramic substrate according to claim 1, wherein the electrode provided on the bottom surface of each step of the recess has an outer diameter larger than the outer diameter of the bottom surface.   The multilayer ceramic substrate according to claim 1, further comprising an electrode on each inner peripheral wall surface of the recess. Preparing a first green sheet having a plurality of large openings to accommodate metal balls;
Preparing a second green sheet provided with a plurality of middle openings for accommodating the metal balls and an annular electrode paste pattern having an outer diameter larger than the outer diameter of the large openings provided on the outer periphery of the middle openings;
Preparing a third green sheet provided with a circular electrode paste pattern having an outer diameter larger than the outer diameter of the middle opening;
The first green sheet is laminated on the bottom layer, the second green sheet is laminated on the upper layer, the third green sheet is further laminated on the upper layer, and other green sheets are further laminated on the upper layer. Forming a multilayer ceramic substrate provided with concentric circular recesses having at least two steps and electrodes exposed on the bottom surfaces of the recesses;
Forming a plating layer on each exposed surface of the electrode;
Filling the recess with solder material, the solder material is bonded to the exposed surface of the electrode through the plating layer;
A method of manufacturing a laminated ceramic substrate, wherein a metal ball is loaded into the recess, and the metal ball is bonded to the solder material.

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