Abstract:
A method of making a package substrate includes steps of forming a plurality of trenches on a first surface of a metal plate, placing insulation material in the trenches, removing metal plate material under the second surface of the metal plate, and exposing the insulation material in the trenches from substrate. The resulting substrate body includes a conductive portion made of the metal plate, and an insulation portion made of the insulation material. The bonding layers on the opposite sides of the substrate are conducted by the conductive portion for heat dissipation, and are separated from one another by the insulation portion.

Description:
This application is a division of copending application Ser. No. 13/111,009, filed May 19, 2011. 
    
    
     FIELD OF INVENTION 
     The present invention relates to a method for forming a package substrate for increasing heat dissipation. 
     BACKGROUND OF THE INVENTION 
     In the development trend of electronic industry, electronic products get thinner and lighter with high performance, function and speed. In addition, it is a trend to enhance beat dissipation to meet requirement of electronic devices with long life. 
     A conventional package substrate for attaching a light emitting diode (LED)  14  is shown in  FIG. 1A  and  FIG. 1B . A ceramic substrate  10  having a surface  10   a  and a surface  10   b , a bonding layer  13  is formed on the surfaces  10   a  and  10   b  of the ceramic substrate  10 , and conductive holes  100  are formed through the ceramic substrate  10  for electrically connecting the bonding layer  13  on the surfaces  10   a  and  10   b  of the ceramic substrate  10 . A light emitting diode  14  is mounted on the bonding layer  13  on the surface  10   a  of the ceramic substrate  10 . 
     As shown in  FIG. 1A , the P electrode and the N electrode of the LED  14  are disposed on the same surface of the LED  14 , such that the P electrode and the N electrode of the LED  14  are connected to the bonding layer  13  via wirings  15 . Alternatively, as shown in  FIG. 1B , the P electrode and the N electrode of the LED  14 ′ are disposed on different surfaces of the LED  14 ′, and thus one electrode is connected to the bonding layer  13  via a wiring  15 , and the other electrode is directly and electrically connected to the bonding layer  13 . 
     Heat generates during the operation of the LED  14 ,  14 ′, and the heat is introduced to the surface  10   b  of the ceramic substrate  10  is conductive holes  100 . In addition the material of the ceramic substrate  10  also facilitates heat dissipation. 
     However, the conventional ceramic substrate  10  has the coefficient of thermal conductivity as 17-170 w/m·k, which is significantly smaller than that (250 w/m·k) of aluminum material and also smaller than that (400 w/m·k) of copper material. The ceramic substrate  10  has worse thermal conductivity and heat dissipation than metal material. The bonding layer  13  and the conductive holes  100  facilitate heat dissipation, but the volume of the conductive holes  100  is much smaller than that of the ceramic substrate  10 . Therefore, the heat dissipation efficiency of the ceramic substrate  10  is not compatible with metal materials. 
     Accordingly, there is an urgent need to enhance the effect of heat dissipation in the art. 
     SUMMARY OF THE INVENTION 
     The present invention involves making a package substrate, including a substrate body having a conductive portion, an insulation portion, and two surfaces opposing to each other; and a plurality of bonding layers formed on the two surfaces of the substrate body, conducted via the conductive portion for heat dissipation, and separated from one another by the insulation portion. 
     In the package substrate of the present invention, the conductive portion is made of metal material, and the insulation portion is made of polymer or ceramics. 
     Further, the insulation portions of the present invention may be arranged alternately for dividing the substrate body into a plurality of regions. 
     In addition, the bonding layer may have a pad for attaching a light emitting diode. 
     The present invention provides a method for forming a package substrate, including the steps of: providing a metal plate having a first surface and a second surface opposing to the first surface; forming a plurality of trenches on the first surface of the metal plate; providing insulation material in the trenches; removing metal plate material under the second surface of the metal plate, and exposing the insulation material in the trenches from the first and second surfaces of the substrate body to form a substrate body having two surfaces opposing to each other, wherein the substrate body includes a conductive portion made of the metal plate, and an insulation portion made of the insulation material; and forming as plurality of bonding layers on the two surfaces of the substrate body, wherein the bonding layers are conducted via the conductive portion for heat dissipation, and separated from one another by the insulation portion. 
     In the method of the present invention, the trenches are arranged alternately for dividing the first surface of the metal plate into a plurality of regions. 
     The method of the present invention further includes the steps of forming the insulation material on the first surface of the metal plate and in the trenches; and removing a portion of the insulation material on the first surface of the metal plate and remaining the insulation material in the trenches. 
     The present invention further provides a method for forming a package substrate, including the steps of: providing an insulation plate; forming a plurality hollow regions through the insulation plate; providing metal material in the hollow regions to form a substrate body with two surfaces opposing to each other, wherein the substrate body includes a conductive portion made of the metal material, and an insulation portion made of the insulation plate with hollow regions; and forming a plurality of bonding layers on the two surfaces of the substrate body, wherein the bonding layers are conducted via the conductive portion for heat dissipation, and separated from one another by the insulation portion. 
     In the method of present invention, the hollow regions are arranged alternately to form a plurality of isolated regions. 
     In the method of the present invention, the metal plate or the metal material is copper (Cu) or aluminum (Al). 
     In the method of the present invention, the insulation portion is made of polymer or ceramics. 
     In addition, in the method of the present invention, the bonding layer may have a pad for attaching a light emitting diode. 
     In the package, the substrate body includes a conductive portion and an insulation portion, and there is a significant ratio of the volume of the conductive portion to the volume of the insulation portion. The volume of the conductive holes in the conventional ceramic plate is extremely small. In contrast, the heat dissipation effect of the substrate body in the present invention is significantly increased to prevent the bonding layer from burn out owing to overheating and to enhance heat dissipation of a light emitting diode. 
     Moreover, the conductive holes are used as conductive paths in the prior art. In contrast, the conductive portion is the conductive path for the upper and lower bonding layers in the present invention to increase electrical conductivity, and the insulation portion of the present invention prevents the bonding layers from a short circuit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  (PRIOR ART) are respectively a cross-sectional schematic view of a light emitting diode (LED) mounted on a package substrate according to different embodiments of the prior art; 
         FIGS. 2A to 2E  are cross-sectional views showing a method for fabricating a package substrate according to an embodiment of the present invention, wherein FIG.  2 A′ is a top view of a metal plate; 
       FIGS.  2 F and  2 F′ are respectively a cross-sectional schematic view of an LED mounted on a package substrate according to different embodiments of the present invention; 
         FIGS. 3A to 3C  are schematic cross-sectional diagrams showing a process of a substrate body of a package substrate according to another embodiment of the present invention, wherein FIG.  3 B′ is a top view of an insulation plate; and 
         FIG. 4  is a top view of another insulation plate in the process of  FIGS. 3A to 3C , wherein FIG.  4 ′ is a partially enlarged view of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following specific examples are used for illustrating the present invention. A person skilled in the art can easily conceive the other advantages and effects of the present invention. 
     According to the embodiments shown in  FIG. 2A  to  FIG. 2F  and FIG.  2 A′, the terms “above” and “under” are used for illustrating relative direction of the features rather than limiting the scope of the present invention. 
       FIG. 2A  to  FIG. 2E  show the method for forming a package substrate of the present invention. 
     As shown in  FIG. 2A  and FIG.  2 A′, a metal plate  20  having a first surface  20   a  and a second surface  20   b  opposing to the first surface  20   a  is provided. The metal plate  20  is made of a thermal conductive material such as copper (Cu) or aluminum (Al). A plurality of trenches  200  are formed on the first surface  20   a  of the metal plate  20 , and the trenches  200  are arranged alternately in high density for dividing the first surface  20   a  of the metal plate  20  into a plurality of regions as shown in FIG.  2 A′. 
     As shown in  FIG. 2B , an insulation material  21  is formed on the first surface  20   a  of the metal plate  20  and in the trenches  200 . The insulation material may be polymer such as an epoxy resin, or a ceramic material such as Al 2 O 3  or AlN. 
     As shown in  FIG. 2C , the insulation material  21  on the first surface  20   a  of the metal plate  20  is removed, and only the insulation material  21  in the trenches is remained. 
     As shown in  FIG. 2D , the portion of the metal plate  20  under the second surface  20   b  of the metal plate  20  is removed, and the remaining metal plate  20  is a conductive portion  221  to form a substrate body  22  having an upper surface  22   a  and a lower surface  22   b . The insulation material  21  in the trenches  200  is exposed from the two surfaces  22   a ,  22   b  of the substrate body  22  to form an insulation portion  220 . The volume of the conductive portion  221  is larger than the volume of the insulation portion  220 . 
     As shown  FIG. 2E , bonding layers  23   a ,  23   b  are formed on the upper surface  22   a  and the lower surface  22   b  of the substrate body  22 , and conducted via the conductive portion  221 . The bonding layers  23   a ,  23   b  are separated by the insulation portions  220  to effectively prevent the bonding layers  23   a ,  23   b  from a short circuit. 
       FIG. 2F  and FIG.  2 F′ show an embodiment using the above package substrate. As shown in  FIG. 2F , the bonding layer  23   a  on the surface  22   a  of the substrate body  22  has electrical connection pads  230  and a pad  231 . In the following process, the P electrode and the N electrode are disposed on the same surface of a light emitting diode (LED)  24 , which is attached on the pad  231 . The P and N electrodes of the light emitting diode  24  are electrically connected to the electrical connection pad  230  by the wiring  25 , and the heat dissipation of the LED  24  is performed via the conductive portion  221 . 
     Alternatively, as shown in FIG.  2 F′, the P electrode and the N electrode are disposed on different surfaces, such as top surface and bottom surface, of a light emitting diode (LED)  24 ′. The electrode on the top surface of the LED  24 ′ is electrically connected to the electrical connection pad  230  by the wiring  25 , and the electrode on the bottom surface of the LED  24 ′ is directly and electrically connected to the bonding layer  23 . The heat dissipation of the LED  24 ′ is performed via the conductive portion  221 . 
     The most volume of the substrate body  22  is made of the conductive portion  221  in the present invention. The coefficient of thermal conductivity of metal material is higher than the common material. For example, the coefficient of thermal conductivity of aluminum material is 250 w/m·k, and the coefficient of thermal conductivity of copper material is 400 w/m·k. In comparison with the conventional ceramic substrate, the substrate body  22  of the present invention has much better thermal conductivity and heat dissipation, and thus significantly enhances performance and extends life of the light emitting diodes  24 ,  24 ′. 
     Further, the conductive portion  221  of the present invention is used as a conductive path for the bonding layers  23   a ,  23   b  on the upper and lower surfaces. Therefore, the present invention increases electrical conductivity by using only the insulation portion  220 , so as to prevent the bonding layers  23   a ,  23   b  from a short circuit. 
       FIG. 3A  to  FIG. 3C  show another embodiment of the method for forming a package substrate in the present invention. This embodiment is similar to the above embodiment except the procedure for forming the substrate body  32 . The similar procedure is not described in this embodiment. 
     As shown in  FIG. 3A , an insulation plate  30  is provided. 
     As shown in  FIG. 3B  and FIG.  3 B′, a plurality of hollow regions  300  are formed through the insulation plate  30 . The volume of the hollow regions is larger than the volume of the remaining insulation plate  30 . 
     As shown in  FIG. 3C , the metal material is formed in the hollow regions  300 . For example, the metal material is filled in the hollow regions  300  to form a substrate body  32  having an upper surface  32   a  and a lower surface  32   b . The substrate body  32  includes a conductive portion  321  made of the metal material and an insulation portion  320  through the insulation plate  30 . The volume of the conductive portion  321  is larger than the volume of the insulation portion  320 . 
     Referring to  FIG. 4  and FIG.  4 ′, an insulation plate  40  has a plurality of hollow regions  400  for receiving the metal material. A hollow region  400  includes a rectangular hole  400   a  and two circular holes  400   b  disposed at the same side and outside the angle of the rectangular hole  400   a . The hollow regions  400  are aligned in an array. In the following procedure, the conductive potion in the rectangular hole  400   a  is used for carrying a chip and providing a path for heat dissipation of the chip, and the conductive portion in the circular hole  400   b  is used for electrical connection of the bonding layers on the upper and lower surfaces of the substrate. 
     As shown in FIGS.  2 F and  2 F′, the present invention further provides a package substrate, including a substrate body  22  having two surfaces  22   a ,  22   b  opposing to each other; and bonding layers  23   a ,  23   b  respective formed on the surfaces  22   a ,  22   b  of the substrate body  22 . 
     The substrate body  22  includes conductive portions  221  and insulation portions  220 , and the volume of the conductive portions is larger than the volume of the insulation portions  220 . The conductive portion  221  is made of copper or aluminum for heat dissipation. The insulation portions  220  are formed through the surfaces  22   a ,  22   b  of the substrate body  22 . The insulation portions  220  are arranged alternately for dividing the substrate body  22  into a plurality of regions, wherein the conductive portion  221  is formed in the region. The insulation region  220  is made of polymer or ceramic material. 
     The bonding layers  23   a ,  23   b  are conducted via the conductive portion  221 , and separated by the insulation portions  220 . Further, the bonding layer  23   a  has pads  231  for attaching light emitting diodes  24 ,  24 ′. The light emitting diodes  24 ,  24 ′ are electrically connected to the bonding layer  23   a , and the heat dissipation of the light emitting diodes  24 ,  24 ′ is performed via the conductive portion  221 . 
     In the present invention, the volume of the conductive portion of the substrate body is significantly larger than that in the prior art, so as to significantly increase heat dissipation, to prevent the bonding layer from burn out owing to overheating and to extend life of the light emitting diode. 
     In addition, the conductive portion of the substrate body is the conductive path for the upper and lower bonding layers in the present invention to increase electrical conductivity, and the insulation portion of the present invention prevents the bonding layers from a short circuit. 
     The invention has been described using exemplary preferred embodiments. However, it is to be understood that the scope of the invention is not limited to the disclosed arrangements. The scope of the claims, therefore, should be accorded the broadest interpretation, so as to encompass all such modifications and similar arrangements.