Patent Publication Number: US-2012031651-A1

Title: Circuit board

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Taiwan Patent Application No. 099215014, filed on Aug. 5, 2010, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a circuit board, and more particularly, to a circuit board that can accelerate the thermal energy transfer rate. 
     2. Related Art 
     The current electronic devices, such as mobile phones and computers, and the household appliances, such as televisions and refrigerators, include a plurality of electronic components, for example, active components or passive components. Most of the electronic components are mounted on a circuit substrate, and the electronic components output and receive electrical signals by using the circuitry of the circuit substrate. Thus, the electrical signals can be transmitted among the electronic components. 
     However, the electronic components will generate some thermal energy during the operation, and some electronic components, such as light-emitting diodes (LEDs) and power components, even generate a large amount of thermal energy during the operation. Therefore, how to accelerate the thermal energy transfer rate of the electronic components is a subject worth studying. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a circuit board enabling to accelerate the thermal energy transfer rate of electronic components. 
     The present invention provides a circuit board including a circuit layer, a thermally conductive substrate, an insulation layer, and at least one thermally conductive material. The thermally conductive substrate has a plane. The insulation layer is disposed between the circuit layer and the plane, and partially covers the plane. The thermally conductive material covers the plane without covered by the insulation layer and is in contact with the thermally conductive substrate. The insulation layer exposes the thermally conductive material. 
     Based on the above, since the thermally conductive material covers the plane without covered by the insulation layer and is in contact with the thermally conductive substrate, the thermally conductive material and the thermally conductive substrate enable to accelerate the thermal energy transfer rate when operating electronic components generate thermal energy. 
     To make the features and advantages of the present invention more clear and understandable, the present invention will be described below in great detail through the embodiments in combination with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the present invention, and wherein: 
         FIG. 1  is a cross-sectional schematic view of a circuit board according to an embodiment of the present invention; and 
         FIG. 2  is a cross-sectional schematic view of a circuit board according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a cross-sectional schematic view of a circuit board according to an embodiment of the present invention. Referring to  FIG. 1 , a circuit board  100  includes a circuit layer  110 , a thermally conductive substrate  120 , an insulation layer  130 , and a thermally conductive material  140 . The thermally conductive substrate  120  has a plane  122 , and both the insulation layer  130  and the thermally conductive material  140  are disposed between the circuit layer  110  and the plane  122 . 
     The insulation layer  130  partially covers the plane  122 , that is, the insulation layer  130  does not completely cover the plane  122 . In other words, a part of the plane  122  is not covered by the insulation layer  130 . The thermally conductive material  140  covers the plane  122  without covered by the insulation layer  130 , and the insulation layer  130  exposes the thermally conductive material  140 . The thermally conductive material  140  is in contact with the thermally conductive substrate  120 , thereby thermally coupled to the thermally conductive substrate  120 . Therefore, thermal energy can be transferred between the thermally conductive material  140  and the thermally conductive substrate  120  in the manner of thermal conduction. 
     The thermally conductive substrate  120  has a high thermal conductivity, for example, higher than 1 W/MK. The thermally conductive substrate  120  may be a metal plate or a carbon-material plate. The carbon-material plate generally refers to a plate made of carbon, such as a carbon fiber plate or a graphite plate. The metal plate may be an alloy plate, such as an aluminum magnesium alloy plate, or a plate substantially made of a single kind of metal, such as, aluminum plate or copper plate. 
     The thermally conductive material  140  may be an insulator and may be a ceramic layer, thermal pad, or thermal glue layer, in which the thermal pad is a solid. The thermal glue layer generally refers to a film layer formed of an adhesive having a high thermal conductivity, such as a thermal adhesive, in which the thermal adhesive may be in liquid state or colloidal state. In addition, both the thermal pad and the thermal adhesive may include a plurality of particles having high thermal conductivity, such as a metal particle, carbon powder, or silicon carbide (SiC) powder. 
     Although  FIG. 1  only shows one thermally conductive material  140 , the circuit board  100  may include a plurality of thermally conductive materials  140  in other embodiments. In other words, the number of the conductive materials  140  included by the circuit board  100  is one or more. Therefore, the number of the thermally conductive material  140  shown in  FIG. 1  is only for an example and does not limit the present invention. 
     The thermal conductivity of the insulation layer  130  is lower than that of the thermally conductive substrate  120 , and may be lower than 1 W/MK. For example, the thermal conductivity of the insulation layer  130  may be between 0.3 W/MK and 0.5 W/MK. In addition, the insulation layer  130  and the thermally conductive substrate  120  may be formed in the manner of lamination or printing. 
     When the insulation layer  130  and the thermally conductive substrate  120  are formed in the manner of lamination, the insulation layer  130  may be a prepreg, and the thermally conductive substrate  120  may be a thermal pad, that is, both the insulation layer  130  and the thermally conductive substrate  120  may be formed by laminating the prepreg and the thermal pad. In addition, before laminating the prepreg, the prepreg may be punched, routed, or laser ablated, so as to form an opening H 1  in the insulation layer  130  and to enable the thermal pad to be disposed inside the opening H 1 . 
     When the insulation layer  130  and the thermally conductive substrate  120  are formed in the manner of printing, the thermally conductive material  140  may be a ceramic layer or thermal glue layer, and both the insulation layer  130  and the thermally conductive substrate  120  may be formed by applying a coating in liquid state, colloidal state, or is paste-like. For example, the coating may be resin or a coating containing resin. In addition, when the insulation layer  130  and the thermally conductive substrate  120  are formed in the manner of printing, after the coating is applied, the coating may be baked or illuminated by light, thereby curing the coating, in which the light may be ultraviolet light. 
     The circuit board  100  may further include an electronic component  150 , such as a light-emitting diode, power component, chip package, or die. The electronic component  150  includes a component main body  152  and a plurality of pads  154   d  and  154   w.  The component main body  152  has a bottom surface B 1 , and the pads  154   d  and  154   w  are disposed on the bottom surface B 1 . The pad  154   d  may be a dummy pad, and the pad  154   w  may be a working pad. Thus, when the electronic component  150  is in operation, a current can only pass through the pad  154   w  without passing through the pad  154   d.    
     It should be noted that, although  FIG. 1  shows only one electronic component  150 , the circuit board  100  may include a plurality of electronic components  150  in other embodiments. That is, the number of the electronic component  150  included by the circuit board  100  may be one or more. Therefore, the number of the electronic component  150  shown in  FIG. 1  is only for an example and does not limit the present invention. 
     The electronic component  150  may be electrically connected to the circuit layer  110  in a manner of flip chip, as shown in  FIG. 1 . Particularly, the circuit board  100  may further include a plurality of solder bumps  160  connecting to the electronic component  150  and the thermally conductive substrate  120 . Each solder bump  160  is connected to one of the pads  154   w  or  154   d,  and the solder bumps  160  are in contact with the pads  154   w,    154   d  and the circuit layer  110 . Therefore, the pads  154   w  and  154   d  may be electrically connected to the circuit layer  110  through the solder bumps  160 , and may further be thermally coupled to the thermally conductive material  140  through the solder bumps  160  and the circuit layer  110 . 
     In the embodiment in  FIG. 1 , the pads  154   w  and  154   d  are thermally coupled to the thermally conductive material  140  through the solder bumps  160  and the circuit layer  110 . However, in other embodiments, when the pad  154   d  is a dummy pad, the pad  154   d  may be thermally coupled to the thermally conductive material  140  through the solder bumps  160  without through the circuit layer  110 . Even the pad  154   d  may be in direct contact with the thermally conductive material  140  and may not need the solder bumps  160  to thermally coupled to the thermally conductive material  140 . Therefore, even if the solder bumps  160  do not exist, the pad  154   d  also may be directly thermally coupled to the thermally conductive material  140 . 
     Based on the above, since the pads  154   w  and  154   d  are thermally coupled to the thermally conductive material  140 , and the thermally conductive material  140  is thermally coupled to the thermally conductive substrate  120 , the thermally conductive material  140  and the thermally conductive substrate  120  can accelerate the thermal energy transfer rate when the operating electronic component  150  generates thermal energy, so as to reduce a probability that the electronic component  150  is overheating. 
     In addition, the thermally conductive material  140  covers the plane  122  without covered by the insulation layer  130  and is exposed by the insulation layer  130 , so that the thermally conductive material  140  does not completely cover the plane  122  of the thermally conductive substrate  120 , thereby capable of limiting the use of the thermally conductive material  140  of the circuit board  100 . Moreover, the material cost of the thermally conductive material  140  is usually higher than that of the insulation layer  130 , so that the overall manufacturing cost of the circuit board  100  in this embodiment can be reduced because the use of the thermally conductive material  140  can be limited. 
     It should be noted that, in addition to the manner of flip chip, the electronic component  150  also may be electrically connected to the circuit layer  110  in other manners, For example, the electronic component  150  may be electrically connected to the circuit layer  110  in the manner of wire bonding. Therefore, the manner of electrical connection between the electronic component  150  and the circuit layer  110  shown in  FIG. 1  is only for an example and does not limit the present invention. 
     In addition, the component main body  152  further has a side surface Si connecting to the bottom surface B 1 . The thermally conductive material  140  has a contact surface  142  in contact with the thermally conductive substrate  120  and a side edge  144  connecting to the contact surface  142 . The area of the bottom surface B 1  may be smaller than that of the plane  122  covered by the thermally conductive material  140 , that is, the area of the bottom surface B 1  is smaller than that of the contact surface  142 . 
     Further, in this embodiment, the thermally conductive material  140  may protrude from the side surface S  1 , and the component main body  152  may not protrude from the side edge  144 , so that the component main body  152  may be completely located inside the contact surface  142 . Therefore, most of the thermal energy from the electronic component  150  is transferred by the thermally conductive material  140 , so as to reduce a probability that the electronic component  150  is overheating. 
       FIG. 2  is a cross-sectional schematic view of a circuit board according to another embodiment of the present invention. Referring to  FIG. 2 , a circuit board  200  in this embodiment is similar to the circuit board  100  in the above embodiment. For example, circuit board  100 ,  200  both include some identical components. The difference between the circuit board  100 ,  200  only refers to a thermally conductive substrate  220  and an electronic component  250  included by the circuit board  200 . 
     Particularly, the thermally conductive substrate  220  has a multiple-layer structure, and a component main body  252  included by the electronic component  250  has a bottom surface B 2  and a side surface S 2  connecting to the bottom surface B 2 . The area of the bottom surface B 2  is larger than that of the plane  122  covered by the thermally conductive material  140 . That is, the area of the bottom surface B 2  is larger than that of the contact surface  142 . In addition, the thermally conductive material  140  does not protrude from the side surface S 2  of the component main body  252 . 
     The thermally conductive substrate  220  has a multiple-layer structure and includes a thermally conductive layer  222  and a main body layer  224 , and the thermally conductive layer  222  is located between the main body layer  224  and the insulation layer  130 . The thermally conductive layer  222  has a high thermal conductivity, for example, higher than 1 W/MK. The thermally conductive layer  222  may be a metal layer or carbon-material layer. 
     The carbon-material layer generally refers to a film layer mainly formed by carbon, such as a carbon fiber layer, a graphite layer, or a diamond film. Therefore, the thermally conductive substrate  220  also can accelerate the thermal energy transfer rate, so as to reduce a probability that the electronic component  250  is overheating. 
     It should be noted that, the electronic component  250  further includes a plurality of pads  154   d  and  154   w,  and only one pad  154   d  is thermally coupled to the thermally conductive material  140 , as shown in  FIG. 2 . However, both the pads  154   w  and  154   d  also can be thermally coupled to the thermally conductive material  140 . In addition, in the circuit board  200  shown in  FIG. 2 , the thermally conductive substrate  220  may be replaced with the thermally conductive substrate  120  in  FIG. 1 . Therefore, the pads  154   d,    154   w  and the thermally conductive substrate  220  shown in  FIG. 2  are only for an example and do not limit the present invention. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.