Patent Publication Number: US-2022240389-A1

Title: Ceramic substrate manufacturing method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a ceramic substrate manufacturing method, and more specifically, to a ceramic substrate manufacturing method, which manufactures a ceramic substrate with a circuit formed on a surface of a ceramic substrate. 
     BACKGROUND ART 
     A ceramic substrate is formed by integrally attaching a metal foil such as a copper foil on a ceramic substrate. The ceramic substrate is generated by a manufacturing process such as active metal brazing (AMB) or direct bond copper (DBC), and can also be classified into a ceramic AMB substrate, a ceramic DBC substrate, etc. depending on a difference between the manufacturing processes. 
     The ceramic AMB substrate is manufactured in the active metal brazing (AMB) method for directly brazing a metal on a surface of the ceramic substrate without performing metallization (or metal wiring) on the surface of the ceramic substrate. 
     The ceramic AMB substrate is applied to the applications such as a vehicle, a wind turbine, and high-voltage DC transmission because it has high heat-dissipation property and reliability. 
     However, there is a problem in that the ceramic substrate has an increased etching time in an etching process and a distance (interval) between circuits when an electrode circuit is formed of a copper of 0.8 T or more. 
     In addition, the ceramic AMB substrate can be manufactured only by electroless plating using photolithography after the copper circuit is formed during partial plating. Therefore, there is a problem in that it is necessary to perform the electroless plating process after performing a treatment to prevent the side surface of the copper circuit from being plated. 
     In addition, if the ceramic AMB substrate is manufactured by dual side cooling (DSC), a spacer is interposed between two substrates, and the two substrates and the spacer are bonded by soldering. At this time, the ceramic AMB substrate contains many problems after manufacturing because the coefficient of thermal expansion and thermal conductivity of the spacer conflict with the ceramic AMB substrate. 
     In addition, the ceramic AMB substrate has a problem in that a bonding force is reduced because the substrate and the spacer are bonded by soldering. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is proposed to solve the conventional problems, and an object of the present disclosure is to provide a ceramic substrate manufacturing method, which etches and bonds a copper sheet on a ceramic substrate, thereby shortening the entire process time of the ceramic substrate and improving the reliability and lifespan of a product. 
     Another object of the present disclosure is to provide a ceramic substrate manufacturing method, which etches and then partially plates a copper sheet, thereby improving a closely contacting force between a circuit pattern and a copper sheet and removing smearing due to an electroless plating. 
     Still another object of the present disclosure is to provide a ceramic substrate manufacturing method, which bonds a ceramic substrate in a brazing method using a spacer with the thermal conductivity and coefficient of thermal expansion matched with those of the ceramic substrate, thereby securing reliability of the ceramic substrate. 
     Technical Solution 
     To achieve the objects, a ceramic substrate manufacturing method according to a first exemplary embodiment of the present disclosure includes preparing a metal substrate by etching a copper sheet, preparing a unit ceramic substrate by etching a ceramic substrate, assembling the metal substrate and the unit ceramic substrate, forming a stack by bonding the metal substrate and the unit ceramic substrate, partially printing a metal paste on a surface of the stack, and sintering the metal paste. 
     The assembling may include assembling the metal substrates and the unit ceramic substrate such that the metal substrates are disposed on both surfaces of the unit ceramic substrate using a brazing jig, and the metal paste may be an Ag paste. 
     To achieve the objects, a ceramic substrate manufacturing method according to a second exemplary embodiment of the present disclosure includes forming a plating substrate by plating a part of a copper sheet with a metal, preparing a metal substrate by etching the plating substrate, preparing a unit ceramic substrate by etching a ceramic substrate, and assembling the metal substrate and the unit ceramic substrate. The forming of the plating substrate may include forming a metal plating by partially electroplating the copper sheet with Ni and Ag, and the assembling may include assembling the metal substrates and the unit ceramic substrate such that the metal substrates are disposed on both surfaces of the unit ceramic substrate using a brazing jig. 
     To achieve the objects, a ceramic substrate manufacturing method according to a third exemplary embodiment of the present disclosure includes disposing a spacer between ceramic substrates and brazing and bonding the spacer and the ceramic substrates, in which the disposing includes disposing a spacer with a thermal conductivity and a coefficient of thermal expansion each equal to or greater than a reference value. At this time, the reference value of the thermal conductivity of the spacer can be 240 W/m·K, and the reference value of the coefficient of thermal expansion of the spacer can be 6.8 ppm/K. 
     Advantageous Effects 
     According to the ceramic manufacturing method according to the exemplary embodiment of the present disclosure, it is possible to etch and then bond the copper sheet on the ceramic substrate, thereby shortening the entire process time of the ceramic substrate. 
     According to the ceramic manufacturing method according to the exemplary embodiment of the present disclosure, it is possible to etch and then bond the copper sheet on the ceramic substrate to form a stress relief edge structure, thereby improving the reliability and lifespan of a product. 
     According to the ceramic manufacturing method according to the exemplary embodiment of the present disclosure, it is possible to etch and then partially plate the copper sheet, thereby improving the bonding force between the circuit pattern and the copper sheet and removing the smearing due to the electroless plating. 
     According to the ceramic manufacturing method according to the exemplary embodiment of the present disclosure, it is possible to etch and then partially plate the copper sheet. Therefore, the method can be applied even when the circuit pattern is formed of a thick copper. 
     According to the ceramic manufacturing method according to the exemplary embodiment of the present disclosure, it is possible to bond the ceramic substrates in the brazing method using the spacer with the excellent thermal properties of the coefficient of thermal expansion of 6.8 ppm/K and the thermal conductivity of 240 W/m·K. It is possible to secure the very excellent the bonding force and the high reliability and high thermal properties of the ceramic substrate. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for explaining a general ceramic substrate manufacturing process. 
         FIG. 2  is a diagram for explaining a ceramic substrate manufacturing method according to a first exemplary embodiment of the present disclosure. 
         FIGS. 3 and 4  are diagrams for explaining a ceramic substrate manufacturing method according to a second exemplary embodiment of the present disclosure. 
         FIGS. 5 to 7  are diagrams for explaining a ceramic substrate manufacturing method according to a third exemplary embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, the most preferred exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings in order to specifically describe the present disclosure such that those skilled in the art to which the present disclosure pertains may easily carry out the technical spirit of the present disclosure. First, in adding reference numerals to the components of each drawing, it should be noted that the same components have the same reference numerals, if possible, even if they are illustrated in different drawings. In addition, in describing the present disclosure, when it is determined that the detailed description of the related publicly-known configuration or function may obscure the subject matter of the present disclosure, the detailed description thereof will be omitted. 
     Referring to  FIG. 1 , in a general ceramic substrate manufacturing method, a ceramic AMB substrate  10  is manufactured through a raw material preparation process, a brazing process, a photolithography process, a plating process, a CU etching process, a seed etching process, a TiN etching process, a laser scribing process, and a breaking process. 
     In the raw material preparation process, a copper sheet  11  and a ceramic substrate  12  are prepared as raw materials. In the raw material preparation process, the copper sheets  11  are stacked on upper and lower surfaces of the ceramic substrate  12 , respectively. 
     In the brazing process, the cooper sheets  11  and the ceramic substrate  12  stacked in the raw material preparation process are bonded by applying a constant temperature thereto. In the brazing process, a stack  13  in which the copper sheets  11  are stacked and bonded on both surfaces of the ceramic substrate  12  is formed by bonding the copper sheets  11  and the ceramic substrate  12 . 
     A circuit pattern having a predetermined shape is formed on the stack  13  through the photolithography process, the plating process, the copper etching process, the seed etching process, the TiN etching process, and the laser scribing process. 
     In the breaking process, a final ceramic AMB substrate  10  is generated by breaking the stack  13  with the circuit pattern formed thereon in a unit size. 
     However, the general ceramic substrate manufacturing method has a problem of an increased etching time in the etching process and a distance (interval) between circuits if an electrode circuit is formed of a copper of 0.8 T or more. 
     Therefore, a ceramic substrate manufacturing method according to a first exemplary embodiment of the present disclosure solves the aforementioned problem by manufacturing a ceramic AMB substrate by etching a copper sheet and then bonding it to a ceramic substrate. 
     Referring to  FIG. 2 , in the ceramic substrate manufacturing method according to the first exemplary embodiment of the present disclosure, a ceramic AMB substrate is manufactured through a raw material preparation process, an assembly process, a brazing process, a partial Ag print process, and a paste sintering process. 
     In the raw material preparation process, a metal substrate  112  is prepared by etching a copper sheet  110  in a predetermined size and shape. In the raw material preparation process, a unit ceramic substrate  122  is prepared by etching a ceramic substrate  120  with a pattern formed thereon in a predetermined size and shape. At this time, in the raw material preparation process, the metal substrates  112  disposed on upper and lower surfaces of the unit ceramic substrate  122  may be etched in different sizes or shapes. 
     In the assembly process, the metal substrates  112  and the unit ceramic substrate  122  are assembled. At this time, in the assembly process, the metal substrates  112  are disposed on both surfaces of the unit ceramic substrate  122  using a brazing jig. 
     In the brazing process, the metal substrates  112  and the unit ceramic substrate  122  are bonded by applying a constant temperature thereto in a state where the metal substrates  112  are assembled on both surfaces of the unit ceramic substrate  122 . In the brazing process, a stack  130  in which the metal substrates  112  are bonded on both surfaces of the unit ceramic substrate  122  is formed by bonding the metal substrates  112  and the unit ceramic substrate  122 . At this time, in the brazing process, the metal substrates  112  and the unit ceramic substrate  122  are bonded using a filler metal. Here, the filler metal has, for example, a multilayer structure formed through plating with Cu and Ag. 
     In the partial print process, an Ag paste  140  is partially printed on a surface of the stack  130 . In the paste sintering process, a ceramic AMB substrate  100  in a final state is manufactured by sintering the Ag paste  140  through an N2 Reflow method. 
     As described above, the ceramic substrate manufacturing method according to the first exemplary embodiment of the present disclosure is a method for etching and then bonding a copper electrode on the ceramic like a mold punching method. According to the ceramic substrate manufacturing method, it is possible to manufacture a ceramic AMB substrate, which shortens the entire process time (processes such as seed etching and TiN etching are omitted), and improves the reliability and lifespan of a product by forming a stress relief edge structure. 
     Meanwhile, the general ceramic substrate manufacturing method has a problem in that it is necessary to perform the electroless plating process after performing a treatment to prevent the side surface of the copper circuit from being plated because the ceramic substrate is manufactured only by the electroless plating using photolithography after the copper circuit is formed upon partial plating. 
     Therefore, a ceramic substrate manufacturing method according to a second exemplary embodiment of the present disclosure solves the aforementioned problem by manufacturing a ceramic AMB substrate by etching and then partially plating a copper sheet. 
     Referring to  FIGS. 3 and 4 , in ceramic substrate manufacturing method according to the second exemplary embodiment of the present disclosure, a ceramic AMB substrate is manufactured through a partial Ni—Ag plating process, a raw material preparation process, and an assembly process. 
     The partial Ni—Ag plating process includes partially plating a copper sheet with Ni and Ag. At this time, in the partial Ni—Ag plating process, a plating substrate  210  with the copper sheet partially plated with Ni and Ag is generated through a partial electroplating. 
     In the raw material preparation process, a metal substrate  212  is prepared by etching the plating substrate  210  in a predetermined size and shape. In the raw material preparation process, a unit ceramic substrate  222  is prepared by etching a ceramic substrate  220  with a pattern formed thereon in a predetermined size and shape. 
     In the assembly process, the metal substrates  212  and the unit ceramic substrate  222  are assembled. At this time, in the assembly process, a final ceramic AMB substrate  200  is manufactured by assembling the metal substrates  212  and the unit ceramic substrate  222  such that the metal substrates  212  are disposed on upper and lower surfaces of the unit ceramic substrate  222  using a brazing jig. 
     The ceramic substrate manufacturing method according to the second exemplary embodiment of the present disclosure is a method for etching a copper electrode in advance to bond it to the ceramic like a mold punching method. According to the ceramic substrate manufacturing method, it is possible to manufacture the ceramic AMB substrate  200 , which shortens the entire process time (processes such as seed etching and TiN etching are omitted), and improves the reliability and lifespan of a product by forming a stress relief edge structure (A of  FIG. 4 ). 
     In addition, according to the ceramic substrate manufacturing method according to the second exemplary embodiment of the present disclosure, the ceramic AMB substrate is manufactured by forming each of the raw materials in advance through the mold punching, and bonding the copper electrode etched by the etching on the ceramic with the pattern already formed at once. Therefore, it is possible to manufacture a thick copper electrode product that cannot be manufactured by the manufacturing method for forming the copper electrode using the conventional etching method, and provide many effects, such as implementing a structure of alleviating stress and removing void defects on the bonded surface. 
     Meanwhile, in the general ceramic substrate manufacturing method, the ceramic AMB substrate for dual side cooling (DSC) has many problems because the coefficient of thermal expansion and thermal conductivity of the spacer conflict with the ceramic AMB substrate, and has a problem of a reduced bonding force because the substrate and the spacer are bonded by soldering. 
     Therefore, a ceramic substrate manufacturing method according to a third exemplary embodiment of the present disclosure solves the aforementioned problem by manufacturing a ceramic AMB substrate for DSC by bonding ceramic substrates in a brazing method using a spacer with the coefficient of thermal expansion and the thermal conductivity matched with those of the ceramic AMB substrate. 
     Referring to  FIG. 5 , in the ceramic substrate manufacturing method according to the third exemplary embodiment of the present disclosure, a ceramic AMB substrate  500  for DSC is manufactured by bonding ceramic substrates  400  in a brazing method using a spacer  300  with excellent thermal properties of a coefficient of thermal expansion of 6.8 ppm/K and a thermal conductivity of 240 W/m·K. Here, the ceramic substrate  500  is, for example, the ceramic AMB substrate manufactured in the aforementioned ceramic substrate manufacturing method according to the first or second exemplary embodiment. Of course, the ceramic substrate  500  can also be a ceramic DBC substrate manufactured in another ceramic substrate manufacturing method. 
     Since the coefficient of thermal expansion and thermal conductivity of copper are 17 ppm/K and 390 W/m·K, respectively, when the ceramic substrates are bonded in the soldering process using the conventional spacer made of a Cu or CuMo material, there occurs a problem in which the ceramic substrates (DBC or AMB) are not bonded by a difference in the coefficient of thermal expansion. 
     Therefore, referring to  FIGS. 6 and 7 , in the ceramic substrate manufacturing method according to the third exemplary embodiment of the present disclosure, the ceramic AMB substrate  500  for DSC with the excellent bonding force and the high reliability and high thermal properties may be manufactured by bonding the ceramic substrates  400  through the brazing process using the spacer  300  with the thermal properties of the coefficient of thermal expansion of 6.8 ppm/K and the thermal conductivity of 240 W/m·K. 
     Although the preferred exemplary embodiments of the present disclosure have been described above, it is understood that the present disclosure may be modified in various forms, and those skilled in the art may carry out various modified examples and changed examples without departing from the scope of the claims of the present disclosure.