Patent Publication Number: US-2004045657-A1

Title: Method for forming a multi-layer ceramic electronic device

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the invention  
       [0002] This invention relates to a method for forming a multi-layer ceramic electronic device.  
       [0003] 2. Description of the related art  
       [0004] With the rapid advancement in electronic devices, such as ceramic printed circuit boards, minimization of the profiles of the same has been a major concern of manufacturers. Formation of multi-layer circuits on a ceramic substrate has been developed for reducing the profiles of the electronic devices. FIGS. 1A to  1 E illustrate consecutive steps of a conventional method for forming a multi-layer ceramic electronic device. The method includes the steps of: (a) forming a first circuit layer  22  with a pattern of first contacts (not shown) on a ceramic substrate  21  (see FIG. 1A), which is normally made from aluminum oxide (Al 2 O 3 ) , by printing and patterning a conductive paste on the ceramic substrate, followed by drying and heating to cause sintering of the conductive paste and the ceramic substrate  21 ; (b) printing and patterning a dielectric paste on the first circuit layer  22 , followed by drying and heating to cause sintering of the dielectric paste so as to form a dielectric film  231  on the first circuit layer  22  (see FIG. 1B) ; (c) repeating step (b) so as to form a second dielectric film  232  on the dielectric film  231  (see FIG. 1B), the first and second dielectric films  231 ,  232  being heated and bonded together to form a dielectric layer  23  with a pattern of through-holes  24  that are registered respectively with the first contacts of the first circuit layer  22  (see FIG. 1C); (d) filling the through-holes  24  with the conductive paste, followed by drying and heating to cause sintering of the conductive paste so as to form the conductive paste in the through-holes  24  into connecting vias  25  that are integrally and respectively connected to the first contacts of the first circuit layer  22  (see FIG. 1D); and (e) repeating step (b) to step (d) so as to form a second circuit layer  221  with a pattern of second contacts (not shown) on the dielectric layer  23 , a second dielectric layer  27  on the second circuit layer  221 , a third circuit layer  222  with a pattern of third contacts (not shown) on the second dielectric layer  27 , a third dielectric layer  28  on the third circuit layer  222 , a fourth circuit layer  223  with a pattern of fourth contacts (not shown) on the third dielectric layer  28 , a pattern of second connecting vias  26  integrally and respectively connected to the second contacts of the second circuit layer  221 , and a pattern of third connecting vias  29  integrally and respectively connected to the third contacts of the third circuit layer  222 .  
       [0005] The conventional method is disadvantageous in that formation of the first, second and third dielectric layers  23 ,  27 ,  28  is complex and tedious, and that too many heating and cooling operations are involved in the aforesaid processing steps. Since each heating and cooling operation can result in error in flatness of each layer on the ceramic substrate by virtue of thermal expansion and contraction and by virtue of variation in the amount of solvent contained in the composition of the dielectric paste for each of the resultant dielectric films, the total error in flatness of the electronic device can be considerably increased. Moreover, the production yield of the conventional method is significantly reduced due to a relatively large number of processing steps involved.  
       SUMMARY OF THE INVENTION  
       [0006] Therefore, the object of the present invention is to provide a method for forming a multi-layer ceramic electronic device that is capable of overcoming the aforementioned drawbacks of the prior art.  
       [0007] According to the present invention, there is provided a method for forming a multi-layer ceramic electronic device. The method comprises the steps of: (a) forming a circuit layer with a pattern of contacts on a ceramic substrate; (b) forming at least a dielectric blank sheet with a pattern of throughholes on a supporting film; (c) filling each of the through-holes in the dielectric blank sheet with a conductive paste; (d) drying the dielectric blank sheet and the conductive paste in the through-holes; (e) removing the dielectric blank sheet from the supporting film and subsequently overlaying the dielectric blank sheet on the circuit layer on the ceramic substrate in such a manner that the through-holes are registered respectively with the contacts; and (f) pressing and heating the ceramic substrate and the dielectric blank sheet so as to cause sintering of the contacts and the conductive paste in each of the through-holes and so as to form the conductive paste in each of the through-holes into a connecting via that is integrally connected to a respective one of the contacts. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0008] In the drawings which illustrate an embodiment of the invention, FIGS. 1A to  1 E illustrate consecutive steps of a conventional method for forming a multi-layer ceramic electronic device;  
     [0009]FIG. 2 is a block diagram illustrating consecutive steps of a preferred embodiment of a method of this invention for forming a multi-layer ceramic electronic device;  
     [0010]FIGS. 3A to  3 D are sectional views illustrating the consecutive steps for forming the multi-layer ceramic electronic device with a circuit layer and a dielectric layer according to the method of this invention; and  
     [0011]FIGS. 4A to  4 E are sectional views illustrating the consecutive steps for forming the multi-layer ceramic electronic device with two circuit layers and two dielectric layers according to the method of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0012] For the sake of brevity, like elements are denoted by the same reference numerals throughout the disclosure.  
     [0013]FIG. 2 is a block diagram illustrating consecutive steps of a preferred embodiment of a method of this invention for forming a multi-layer ceramic electronic device.  
     [0014] Referring to FIGS. 3A to  3 D, the method includes the steps of: (a) forming a first circuit layer  41  with a pattern of first contacts  413  on a ceramic substrate  40  (see FIG. 3A); (b) forming at least a dielectric blank sheet  42  with a pattern of through-holes  420  on a supporting film  100  (see FIG. 3B) ; (c) filling each of the through-holes  420  in the dielectric blank sheet  42  with a first conductive paste  421  in a respective one of the through-holes  420  (see FIG. 3B); (d) drying the dielectric blank sheet  42  and the first conductive paste  421  in the through-holes  420 ; (e) removing the dielectric blank sheet  42  from the supporting film  100  and subsequently overlaying the dielectric blank sheet  42  on the first circuit layer  41  on the ceramic substrate  40  in such a manner that the through-holes  420  are registered respectively with the first contacts  413  (see FIG. 3C); and (f) pressing and heating the ceramic substrate  40  and the dielectric blank sheet  42  so as to cause sintering of the first contacts  413  and the first conductive paste  421  in each of the through-holes  420  and so as to form the first conductive paste  421  in each of the through-holes  420  into a connecting via  422  that is integrally connected to a respective one of the first contacts  413  (see FIG. 3D).  
     [0015] The assembly of the dielectric blank sheet  42  and the supporting film  100  is formed by passing the supporting film  100  and dielectric paste through a nip zone defined by a pair of rollers (not shown). The supporting film  100  is preferably made from a plastic material.  
     [0016] The first circuit layer  41  on the ceramic substrate  40  is formed by coating a second conductive paste on the ceramic substrate  40 , drying the second conductive paste on the ceramic substrate  40 , followed by heating the second conductive paste on the ceramic substrate  40  to cause sintering of the ceramic substrate  40  and the second conductive paste on the ceramic substrate  40 .  
     [0017]FIGS. 4A to  4 E illustrate a modified embodiment of the multi-layer ceramic electronic device formed according to the method of this invention. In this modified embodiment, two dielectric blank sheets  42  are processed simultaneously according to step (b) to step (c) . A third conductive paste  43 ′ with a contact pattern  431  is coated on a surface of one of the dielectric blank sheets  42  in step (c) such that the third conductive paste  43 ′ on the surface of said one of the dielectric blank sheets  42  is formed into a second circuit layer  43  with a pattern of second contacts  432  that are integrally and respectively connected to the connecting vias  422  in the through-holes  420  in the dielectric blank sheets  42  after going through step (d) to step (f).  
     [0018] Instead of repeated printing and heating operations during formation of the dielectric layers on the respective circuit layers as disclosed in the prior art, the dielectric blank sheets  42  can be simultaneously prepared according to step (b) to step (c) of the method of this invention, and are pressed and heated together with the first and second circuit layers  41 ,  43  and the ceramic substrate  40  in step (f), thereby eliminating the aforesaid drawbacks as encountered in the prior art.  
     [0019] With the invention thus explained, it is apparent that various modifications and variations can be made without departing from the spirit of the present invention. It is therefore intended that the invention be limited only as recited in the appended claims.