Abstract:
There are provided a method of manufacturing a ceramic sintered body. A method of manufacturing a ceramic sintered body according to one aspect of the invention may include: preparing at least one ceramic sheet having first ceramic particles and glass particles; preparing at least one constraining sheet having second ceramic particles having a smaller particle size than the glass particles and the first ceramic particles; forming a ceramic laminate by alternating the ceramic sheet and the constraining sheet while the ceramic sheet and the constraining sheet are in contact with each other; and sintering the ceramic laminate so that components, which do not react with the first ceramic particles, from the glass particle are moved into the constraining sheet to sinter the constraining sheet when the ceramic sheet is sintered.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. application Ser. No. 12/510,162, filed on Jul. 27, 2009, which claims the priority of Korean Patent Application No. 10-2008-0104468, filed on Oct. 23, 2008, and Korean Patent Application No. 10-2009-0045995, filed on May 26, 2009, in the Korean Intellectual Property Office, the disclosure of all of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a ceramic laminate and a method of manufacturing a ceramic sintered body. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, multilayer ceramic substrates have been used as components on which active elements, such as semiconductor IC chips, and passive elements, such as capacitors, inductors and resistors, are mounted. Also, multilayer ceramic substrates have simply been used in semiconductor IC packages. Specifically, these multilayer ceramic substrates have been widely used to construct various electronic components including PA module substrates, RF diode switches, filters, chip antennas, various package components and complex devices. 
         [0006]    In order to manufacture the above-described multilayer ceramic substrates, dielectric sheets having wiring conductors formed thereon are laminated, and the sintering process is necessarily performed on the laminate to achieve optimum characteristics. However, after this sintering process is performed, the multilayer ceramic substrates shrink because ceramics are sintered. Since multilayer ceramic substrates do not shrink evenly in all directions, dimensional changes occur in the planar direction of ceramic layers. The shrinkage of the ceramic substrate in the planar direction also causes undesirable deformations or distortions. Specifically, the accuracy of external electrodes for connections with chip components, which are mounted onto multilayer ceramic substrates, may be reduced or wiring conductors may be disconnected. 
         [0007]    The shrinkage of the ceramic substrate in the planar direction causes a misalignment between conductor patterns and the ceramic substrate when mounting components. As a result, it may be impossible to mount semiconductor chips, such as chip size packages (CSPs) and MCM (multi-chip modules), with high accuracy. Therefore, there has been proposed a so-called non-shrinking method in order to remove shrinkage in the planar direction in a sintering process when multilayer ceramic substrates are manufactured. 
         [0008]    According to a general non-shrinking method, constraining sheets are formed using alumina powder, which is a ceramic that is not sintered at 900° C. or less, the formed constraining sheets are laminated on the top and bottom of low temperature co-fired ceramic (LTCC) dielectric sheets to form a ceramic substrate, a predetermined weight is applied to the ceramic substrate to perform plasticizing and sintering, and then the constraining sheets are removed therefrom, thereby obtaining a ceramic substrate.  FIG. 1  is a cross-sectional view illustrating one process of a general non-shrinking method of manufacturing a ceramic substrate. Constraining layers  11  are disposed on the top and bottom of a ceramic laminate  10  that has a plurality of ceramic sheets laminated onto one another. Here, each of the constraining layers  11  is not sintered at a sintering temperature of the ceramic laminate  10 . The constraining layers  11  can prevent shrinkage in the planar direction of the ceramic laminate  10  during the sintering process. 
         [0009]    However, in the non-shrinking method, illustrated in  FIG. 1 , a large constraining force is applied to ceramic sheets adjacent to the constraining sheets  11 , but a relatively small constraining force is applied to the inner part of the ceramic laminate  10 . Since the constraining force is unevenly applied to the ceramic laminate  10 , a stress imbalance occurs in the inner part of the ceramic laminate  10 . As a result, the reliability of the ceramic substrate may be deteriorated. This problem may be worsened when the ceramic laminate  10  is thick. 
       SUMMARY OF THE INVENTION 
       [0010]    An aspect of the present invention provides a ceramic laminate having constraining layers that can evenly exert a constraining force onto a ceramic laminate during sintering. 
         [0011]    Another aspect of the present invention provides a method of manufacturing a ceramic sintered body that is obtained by sintering the ceramic laminate. 
         [0012]    According to an aspect of the present invention, there is provided a ceramic laminate including: at least one ceramic sheet having first ceramic particles and glass particles; and at least one constraining sheet having second ceramic particles and alternating with the ceramic sheet while the constraining sheet and the ceramic sheet are in contact with each other, wherein the glass particles and the first ceramic particles each have a larger particle size than the second ceramic particles, and the first ceramic particles have a particle size of 1 μm or more, the glass particles have a particle size within the range of 1 μm to 10 μm, and the second ceramic particles have a particle size of 1 μm or less. 
         [0013]    The ceramic sheet and the constraining sheet may each include a conductive pattern and a conductive via. 
         [0014]    The ceramic sheet may have a thickness within the range of 20 μm to 200 μm. 
         [0015]    The constraining sheet may have a thickness of 20 μm or less. 
         [0016]    The ceramic sheet may be thicker than the constraining sheet. 
         [0017]    The first and second ceramic particles may be formed of the same material. 
         [0018]    The constraining sheet may include the second ceramic particles and organic binders. 
         [0019]    The glass particles may include a composition represented by (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2 —ZnO—B 2 O 3 . 
         [0020]    The first ceramic particles may include Al 2 O 3 . 
         [0021]    The ceramic sheet may include 40 to 80 wt % of the glass particles and 20 to 60 wt % of the first ceramic particles. 
         [0022]    The glass particles include 2 to 10 wt % of ZnO. 
         [0023]    According to another aspect of the present invention, there is provided a method of manufacturing a ceramic sintered body, the method including: preparing at least one ceramic sheet having first ceramic particles and glass particles; preparing at least one constraining sheet having second ceramic particles having a smaller particle size than the glass particles and the first ceramic particles; forming a ceramic laminate by alternating the ceramic sheet and the constraining sheet while the ceramic sheet and the constraining sheet are in contact with each other; and sintering the ceramic laminate so that components, which do not react with the first ceramic particles, from the glass particle are moved into the constraining sheet to sinter the constraining sheet when the ceramic sheet is sintered. 
         [0024]    The constraining sheet may be sintered after the ceramic sheet is sintered. 
         [0025]    The constraining sheet may be sintered at the sintering temperature of the ceramic sheet. 
         [0026]    The glass particles may include a composition represented by (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2 —ZnO—B 2 O 3 . 
         [0027]    The first ceramic particles may include Al 2 O 3 . 
         [0028]    The ceramic sheet may include 40 to 80 wt % of the glass particles and 20 to 60 wt % of the first ceramic particles. 
         [0029]    The glass particles may include 2 to 10 wt % of ZnO. 
         [0030]    Components, which do not react with the first ceramic particles, may include ZnO. 
         [0031]    The first ceramic particles may have a particle size of 1 μm or more, the glass particles may have a particle size within the range of 1 μm to 10 μM, and the second ceramic particles may have a particle size of 1 μm or less. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0033]      FIG. 1  is a cross-sectional view illustrating one process of a general non-shrinking method of manufacturing a ceramic substrate; 
           [0034]      FIG. 2  is a cross-sectional view illustrating a ceramic laminate according to an exemplary embodiment of the invention; 
           [0035]      FIG. 3  is a detailed view illustrating a ceramic sheet and a constraining sheet of the ceramic laminate, shown in  FIG. 2 ; 
           [0036]      FIG. 4  is an enlarged view illustrating particles constituting a ceramic sheet and a constraining sheet; and 
           [0037]      FIG. 5  is an enlarged view illustrating particles constituting a ceramic sheet and a constraining sheet. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0038]    Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The invention may however be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like components. 
         [0039]      FIG. 2  is a cross-sectional view illustrating a ceramic laminate according to an exemplary embodiment of the invention.  FIG. 3  is a detailed view illustrating a ceramic sheet and a constraining sheet of the ceramic laminate, shown in  FIG. 2 . First, referring to  FIG. 2 , a ceramic laminate  100  according to this embodiment includes ceramic sheets  101  and constraining sheets  102 . The ceramic sheets  101  and the constraining sheets  102  alternate with each other while they are bonded to each other. The ceramic sheets  101  may be formed using glass, ceramic fillers and organic binders by the doctor blade method known in the related art. The constraining sheets  102  include glass ceramic fillers and organic binders and a very small amount of glass so that the constraining sheets  102  cannot be sintered at the sintering temperature of the ceramic sheets  101 . These constraining sheets  102  can exert a constraining force onto the ceramic sheets  101  during sintering. 
         [0040]    As described above, unlike the related art, in the ceramic laminate  100 , each of the constraining sheets  102  is disposed between the ceramic sheets  101 . The constraining sheets  102  remain in the final device, that is, a ceramic sintered body. To this end, as shown in  FIG. 3 , conductive patterns  103  and conductive vias  104  may be provided in the ceramic sheets  101  and the constraining sheets  102 . 
         [0041]    As the constraining sheets  102  are in contact with the top and bottom of each of the ceramic sheets  101 , the constraining force can be evenly exerted onto the ceramic sheets  101  to thereby prevent a stress imbalance. Furthermore, since the constraining sheets  102  do not need to be removed after the sintering process, processing convenience can be significantly increased. As it will be described below, even though glass particles are moved within the constraining sheets  102  during the sintering process, an excessive volume of the constraining sheets  102  having a high proportion of ceramic fillers may deteriorate properties of a ceramic sintered body after the sintering process, that is, a ceramic substrate. Therefore, the above-described constraining sheet may have a thickness t 2  of 20 μm or less, preferably, 10 μm or less. The ceramic sheet  101  has a thickness t 1  within the range of 20 μm to 200 μm. 
         [0042]    As described above, the constraining sheets  102  include ceramic fillers that are not sintered at the sintering temperature of the ceramic sheets  101 . However, as the ceramic sheets  101  start to be sintered, the constraining sheets  102  may also be sintered at a relatively low temperature. This will be described with reference to  FIGS. 4 and 5 .  FIGS. 4 and 5  are views enlarging particles constituting a ceramic sheet and a constraining sheet. Here, in  FIG. 4 , the ceramic laminate  100 , shown in  FIG. 2 , is kept at a temperature less than the sintering temperature, and in  FIG. 5 , glass particles are being moved during the sintering process. During the sintering process of the ceramic sheets  101 , when the constraining sheets  102  are not sintered, and then start to be sintered at a temperature much higher than the sintering temperature of the ceramic sheets  101 , the sintering state of the ceramic sheets  101 , which have already been sintered, may be deteriorated. Considering this, in this embodiment, glass particles are moved into the constraining sheets  102  while the ceramic sheets  101  are sintered. 
         [0043]    If glass particles G, partially constituting the ceramic sheets  101 , are moved into the constraining sheets  102  during the sintering process, the sintering temperature of the constraining sheets  102  is gradually reduced, and thus the constraining sheets  102  may be sintered at a temperature close to the sintering temperature of the ceramic sheets  101 . Therefore, the ceramic sintered body can be obtained in which the ceramic laminate  100  is evenly sintered. To this end, a diameter D 1  of each of the glass particles G and a diameter D 3  of each of the ceramic particles (first ceramic particles C 1 ) constituting the ceramic fillers that are included in the ceramic sheets  101  need to be larger than a diameter D 2  of each of the ceramic particles (second ceramic particles C 2 ) that are included in the constraining sheets  102 . As shown in  FIG. 5 , this helps to promote the movement of the glass particles G by capillary action. Specifically, the particle diameter D 1  of each of the glass particles G may be within the range of 1 μm to 10 μm, preferably, around 2.5 μm. The first ceramic particles C 1  may be of similar size to the glass particles G in terms of sintering characteristics. Preferably, the particle diameter D 3  of the ceramic particle may be 1 μm or more. Considering this, the particle diameter D 2  of the second ceramic particle C 2  may be 1 μm. Here, since the plurality of glass particles G and the first and second ceramic particles C 1  and C 2  exist, the particle diameter can be defined as a mean particle diameter. 
         [0044]    Since the glass penetrates into the constraining sheets  102  during the sintering process, the second ceramic particles C 2 , included in the constraining sheets  102 , are preferably formed of a material that has relatively higher wettability with respect to the glass of the ceramic sheets  101 . The same applies to the first ceramic particles C 1 . When unreacted glass materials remain among the glass particles G during the sintering process, these unreacted glass materials may be easily moved into the constraining sheets  102 . Considering these factors, the glass particles G may be formed of a composition represented by (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2 —ZnO—B 2 O 3 , and the first ceramic particles C 1  may be formed of Al 2 O 3 . Here, the glass particles G and the first ceramic particles C 1  are mixed while the glass particles G are added at a ratio of 40 to 80 wt % of (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2  and the first ceramic particles C 1  are added at a ratio of 20 to 60 wt % of Al 2 O 3  with respect to the ceramic sheets  101 . 
         [0045]    During the sintering process, glass, containing large amounts of Zn and B, is introduced into the constraining sheets  102  from the ceramic sheets  101 . Here, as described, the glass, introduced into the constraining sheets  102 , is left without making a reaction to the first ceramic particles C 1 . The glass, introduced into the constraining sheets  102 , results in a pore-free interface between the ceramic sheets  101  and the constraining sheets  102 . Specifically, during the sintering process, when (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2 -based glass reacts with Al 2 O 3 , (Ca, Sr, Ba)Al 2 Si 2 O 8 , unreacted glass components are obtained. In the above reaction, ZnO mostly becomes unreacted glass components. Here, a crystal of (Ca, Sr, Ba)Al 2 Si 2 O 8  rarely contains ZnO. Crystallographically, since an ionic radius of each of the elements, such as Ca, Sr and Ba, is much larger than that of Zn, Zn is difficult to substitute for the elements. Therefore, the glass components containing large amounts of Zn are moved into the constraining sheets  102  during the sinter process of the ceramic sheets  101 . That is, glass particles G′, having moved to the constraining sheets  102 , shown in  FIG. 5 , are different from the glass particles G that have existed in the ceramic sheets  101 . 
         [0046]    The glass components containing the large amounts of Zn, having moved into the constraining sheet  102 , react with the second ceramic particles C 2 , for example, Al 2 O 3 , a crystalline phase, such as ZnAl 2 O 4 , is precipitated. As this reaction occurs, the unreacted glass in the ceramic sheet  101  is introduced into the constraining sheet  102  at a higher rate. Herein, the constraining sheets  102  are sintered. When ZnO is added to the (Ca, Sr, Ba)O—Al 2 O 3 —SiO 2 -based glass, the content of ZnO needs to be appropriately controlled. For example, SiO 2  is added at a ratio of 40 to 70 wt %, Al 2 O 3  is added at a ratio of 5 to 20 wt %, (Ca, Sr, Ba)O is added at a ratio of 10 to 35 wt %, Ba 2 O 3  is added at a ratio of 5 to 15 wt %, ZnO is added at a ratio of 2 to 10 wt % by weight of the glass particles G. When the ZnO content is 2 wt % or higher, this ensures high fluidity of the glass of the ceramic sheet  101 , and thus, the remaining space of the ceramic sheets  101  after glass is introduced into the constraining sheets  102  can be filled with the glass. However, when the amount of ZnO increases considerably, basic properties of the LTCC materials, including strength, chemical resistance and insulation, may be adversely affected. Therefore, the content of ZnO does not preferably exceed 10 wt %. 
         [0047]    The inventors of this invention have carried out experiments under various conditions to find out the effects of the invention. That is, the inventors sintered ceramic laminates and measured contraction ratios, and the results are shown in Table 1 as follows. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                   
                 Constraining 
                   
               
               
                   
                 Ceramic sheet 
                 layer 
               
             
          
           
               
                   
                   
                 Particle 
                 Particle 
                 Fraction 
                   
                 Particle 
                 Sintering 
                 Contraction 
               
               
                   
                 thickness 
                 size (G) 
                 size (C1) 
                 size (C1) 
                 thickness 
                 (C2) 
                 temperature 
                 ratio 
               
               
                   
                   
               
             
          
           
               
                 1 
                 50 μm 
                 2.5 μm 
                 1.7 μm 
                 35 wt % 
                 6.5 μm 
                 600 nm 
                 850° C. 
                 0.342 
               
               
                 2 
                 50 μm 
                 2.5 μm 
                 1.7 μm 
                 35 wt % 
                 6.5 μm 
                 600 nm 
                 870° C. 
                 0.258 
               
               
                 3 
                 50 μm 
                 2.5 μm 
                 1.7 μm 
                 35 wt % 
                 6.5 μm 
                 600 nm 
                 900° C. 
                 0.183 
               
               
                 4 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 50 wt % 
                 6.5 μm 
                 600 nm 
                 850° C. 
                 0.500 
               
               
                 5 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 50 wt % 
                 6.5 μm 
                 600 nm 
                 870° C. 
                 0.458 
               
               
                 6 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 50 wt % 
                 6.5 μm 
                 600 nm 
                 900° C. 
                 0.183 
               
               
                 7 
                  50 μm 
                 2.5 μm 
                 2.5 μm 
                 40 wt % 
                 6.5 μm 
                 600 nm 
                 850° C. 
                 0.658 
               
               
                 8 
                  50 μm 
                 2.5 μm 
                 2.5 μm 
                 40 wt % 
                 6.5 μm 
                 600 nm 
                 870° C. 
                 0.483 
               
               
                 9 
                  50 μm 
                 2.5 μm 
                 2.5 μm 
                 40 wt % 
                 6.5 μm 
                 600 nm 
                 900° C. 
                 0.617 
               
               
                 10 
                  50 μm 
                 4.5 μm 
                 1.7 μm 
                 30 wt % 
                 4.5 μm 
                 600 nm 
                 870° C. 
                 0.370 
               
               
                 11 
                  50 μm 
                 2.5 μm 
                 1.7 μm 
                 50 wt % 
                 4.5 μm 
                 600 nm 
                 870° C. 
                 0.605 
               
               
                 12 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 50 wt % 
                 4.5 μm 
                 600 nm 
                 870° C. 
                 0.674 
               
               
                 13 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 40 wt % 
                 4.5 μm 
                 600 nm 
                 870° C. 
                 0.277 
               
               
                 14 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 30 wt % 
                 4.5 μm 
                 600 nm 
                 870° C. 
                 0.342 
               
               
                 15 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 40 wt % 
                 5.5 μm 
                 500 nm 
                 870° C. 
                 0.340 
               
               
                 16 
                 100 μm 
                 2.5 μm 
                 1.7 μm 
                 30 wt % 
                 5.5 μm 
                 500 nm 
                 870° C. 
                 0.407 
               
               
                   
               
             
          
         
       
     
         [0048]    Sample Nos. 1 to 3 are glass for ceramic sheets, which is formed of Ca—Al—Si—O glass. Sample Nos. 4 to 6 and 11 to 16 are formed of Ca—Al—Si—Zn—O glass. Sample Nos. 7 to 9 are formed of Mg—Ca—Si—O glass. Sample No. 10 is formed of Ca—Al—Si—B glass. 
         [0049]    As described above, when a non-shrinking method according to the embodiments of the invention is used, a constraining force is evenly exerted onto a ceramic laminate, and constraining sheets are naturally sintered at a temperature around the sintering temperature of ceramic sheets because of the transferral of glass particles to thereby increase sintering characteristics. 
         [0050]    As set forth above, according to exemplary embodiments of the invention, a ceramic laminate having constraining sheets that can evenly exert a constraining force onto a ceramic substrate during sintering can be provided. Further, a non-shrinking method according to exemplary embodiments of the invention allows constraining sheets to be naturally sintered at a temperature around the sintering temperature of ceramic sheets because of the transferral of glass particles to thereby increase sintering characteristics. Furthermore, since there is no need to remove constraining sheets after sintering, processing convenience can be significantly increased. 
         [0051]    While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.