Patent Publication Number: US-7723829-B2

Title: Embedded metal heat sink for semiconductor

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   The present application is a divisional of U.S. application Ser. No. 11/470,279 filed Sep. 6, 2006, which in turn is based on, and claims priority from, Taiwan Application No. 95123020, filed Jun. 26, 2006, the disclosures of which are hereby incorporated by reference herein in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a metal heat sink and a method for manufacturing the same, and more particularly, to an embedded metal heat sink for an opto-electrical device and a method for manufacturing the same. 
   BACKGROUND OF THE INVENTION 
   When small solid state opto-electrical devices, such as light-emitting diodes (LEDs) or laser diodes (LDs), are applied in a large or small backlight module or illumination module, many opto-electrical devices are needed to generate sufficient brightness or illumination for the modules. However, when the opto-electrical devices are operated at high power, the temperature of the module composed of the opto-electrical devices increases, thereby degrading the operational quality of the module and ultimately burning out the opto-electrical devices. 
   To resolve this high temperature issue, the module composed of the opto-electrical devices is typically cooled by fans set in the module or by increasing the heat dissipation area. However, regarding setting fans in the module, the vibration caused by the operation of the fans results in the lights flickering, and the fans consume additional power. Regarding increasing the heat dissipation area, although the heat sinks can be composed of metal with high thermal conductivity, glue mixed with metal is used to connect the opto-electrical device and the heat sinks, and the thermal conductivity of the glue is much lower than that of the pure metal. As a result, the heat generated during the operation of the opto-electrical device mostly accumulates at the connection interface, so that the heat sinks cannot transfer heat well, thereby making the heat sinks less effective, and easily damaging the opto-electrical devices during long-term operation or ultimately making the opto-electrical devices being operated with larger input power usage. 
   In addition, the heat sinks are typically connected to a circuit board with glue for electrically connecting the opto-electrical device and an outer circuit. Accordingly, the heat generated during the operation of the device accumulates at the glue, and the thermal conductivity of the circuit board composed of the plastic material is low, so the heat conductivity rate is low and greatly decreases the heat dissipation efficiency of the heat sinks. 
   Therefore, with the increasing demand for opto-electrical devices, such as light-emitting diodes and laser diodes, for backlight modules and illumination modules, a technique for manufacturing an opto-electrical device with high heat-sinking efficiency is required. 
   SUMMARY OF THE INVENTION 
   One aspect of the present invention is to provide an embedded metal heat sink for a semiconductor device, in which the embedded metal heat sink includes at least one bonding pad used as a transition electrode for electrically connecting a positive electrode or a negative electrode of the semiconductor device and an outer circuit, so that the semiconductor device embedded on the metal heat sink can be successfully connected to the outer circuit. 
   Another aspect of the present invention is to provide an embedded metal heat sink for a semiconductor device, in which the metal heat sink can be directly deposited on a bottom surface of the semiconductor device with the assistant of an adhesive tape and without the use of glue or a pasting technique. In addition, bonding pads are deposed on the metal heat sink surrounding the semiconductor device for the electrical transition between electrodes of the semiconductor device and an outer circuit. Therefore, the temperature of the operating device can be rapidly and effectively lowered for improving the operational quality of the device and prolonging the life of the device, and the positive electrode and the negative electrode of the semiconductor device can be successfully connected to the outer circuit, thereby saving the using of a circuit board. 
   According to the aforementioned aspects, the present invention provides an embedded metal heat sink for a semiconductor device, comprising: a metal thin layer including a first surface and a second surface on opposite sides, wherein at least one semiconductor device is embedded in the first surface of the metal thin layer, and the semiconductor device has two electrodes with different conductivity types; a metal heat sink deposited on the second surface of the metal thin layer; and two bonding pads deposed on the first surface of the metal thin layer around the semiconductor device and respectively corresponding to the electrodes, wherein the electrodes are electrically and respectively connected to the corresponding bonding pads by at least two wires, and the bonding pads are electrically connected to an outer circuit. 
   According to a preferred embodiment of the present invention, a material of the metal heat sink may be Fe/Ni alloy, Cu, Ni, Al, W or an alloy thereof, and each bonding pad includes an insulating layer and a conductive layer deposed on the insulating layer, wherein the insulating layer is adhered to the first surface of the thin metal layer. 
   A semiconductor device is directly embedded into a metal heat sink by directly forming the metal heat sink on the semiconductor device. Then, bonding pads are deposed on the metal heat sink around the semiconductor device for the transition of the electrical connection between the electrodes of the semiconductor device and an outer circuit. As a result, the metal heat sink cannot be additionally deposed on a circuit board, thereby greatly increasing the heat-sinking efficiency, enhancing the operation stability of the device and effectively prolonging the life of the device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and many of the attendant advantages of this invention are more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein: 
       FIGS. 1A through 8  are schematic flow diagrams showing the process for manufacturing an embedded metal heat sink for a semiconductor device in accordance with a preferred embodiment of the present invention, wherein the schematic flow diagrams includes cross-sectional views and the corresponding top views. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The present invention discloses an embedded metal heat sink for a semiconductor device, in which electrodes of the semiconductor device are in contact with an outer circuit, and the heat-sinking efficiency of the metal heat sink is increased to improve the heat-dissipating problem of the semiconductor device. In order to make the illustration of the present invention more explicit, the following description is stated with reference to  FIGS. 1A through 8 . 
     FIGS. 1A through 8  are schematic flow diagrams showing the process for manufacturing an embedded metal heat sink for a semiconductor device in accordance with a preferred embodiment of the present invention, wherein the schematic flow diagrams includes cross-sectional views and the corresponding top views. In the manufacturing of an embedded metal heat sink of a semiconductor device of the present invention, a temporary substrate  100  and an adhesive tape  102  are initially provided, and the adhesive tape  102  is adhered to the temporary substrate  100  to make a surface  104  of the adhesive tape  102  contact with a surface of the temporary substrate  100 , such as shown in  FIGS. 1A and 1B , of which  FIG. 1A  is the top view and  FIG. 1B  is the corresponding cross-sectional view. The adhesive tape  102  includes another surface  106  opposite the surfaces  104 . The adhesive tape  102  is preferably composed of an acid-proof and alkali-proof material, and the adhesive tape  102  has a thickness greater than about 10 μm. In a preferred embodiment of the present invention, the adhesive tape  102  preferably has a thickness of about 100 μm and is a double-sided adhesive tape, that is, surface  104  and surface  106  of the adhesive tape  102  are both adhesive. However, in the present invention, if the adhesive tape  102  is composed of a soft plastic material, only the surface  104  might be adhesive while the surface  106  is not adhesive. 
   Then, one or more semiconductor devices are provided, wherein the semiconductor devices are composed of compound semiconductor materials, such as GaN-based materials, AlGaInP-based materials, PbS-based materials or SiC-based materials, and the semiconductor devices are, for example, transistors, monolithic ICs, or opto-electrical devices, such as light-emitting diodes or laser diodes. Each semiconductor device includes two electrodes of different conductivity types, wherein the electrodes are deposed on the same side or on different sides of the semiconductor device, such as opto-electrical devices  108   a  and  108   b  shown in  FIG. 2C . In the exemplary embodiment, two electrodes  110  and  112  of the opto-electrical device  108   a  are deposed on the same side of the opto-electrical device  108   a ; and two electrodes  110  and  112  of the opto-electrical device  108   b  are deposed on two opposite sides of the opto-electrical device  108   b . While the electrode  110  is N-type, the electrode  112  is P-type; and while the electrode  110  is P-type, the electrode  112  is N-type. In the exemplary embodiment, the opto-electrical device  108   a  is adapted for the semiconductor device. A side of the opto-electrical device  108   a  is pressed downward on the surface  106  of the adhesive tape  102  to make the opto-electrical device  108   a  adhere to or embedded into the surface  106  of the adhesive tape  102  and to expose the side of opto-electrical device  108   a  opposite to the adhered side, wherein the side of the opto-electrical device  108   a  pressed into the adhesive tape  102  are set with two electrodes  110  and  112 , such as shown in  FIGS. 2A and 2B , wherein  FIG. 2A  is the top view and  FIG. 2B  is the corresponding cross-sectional view. In the present invention, the adhered side of the opto-electrical device  108   a  is pressed into the adhesive tape  102  has to be set with at least one electrode to prevent the two electrodes from electrically connecting. When many opto-electrical devices  108   a  are processed at the same time, these opto-electrical devices  108   a  can be arranged according to the process requirements. 
   In the present invention, the opto-electrical devices  108   a  may be GaN-based light-emitting diodes, AlGaInP-based light-emitting diodes, PbS-based light-emitting diodes or SiC-based light-emitting diodes. In another embodiment, the opto-electrical devices  108   a  may be GaN-based laser diodes, AlGaInP-based laser diodes, PbS-based laser diodes or SiC-based laser diodes. 
   After the opto-electrical device  108   a  is fixed in the adhesive tape  102 , a thin metal layer  114  is directly formed to cover the exposed surface of the opto-electrical device  108   a  and the exposed region in the surface  106  of the adhesive tape  102  by, for example, an evaporation deposition method, a sputtering deposition method or an electroless plating deposition method, such as shown in  FIGS. 3A and 3B , in which  FIG. 3A  is the top view and  FIG. 3B  is the corresponding cross-sectional view. In the present invention, the thin metal layer  114  is preferably composed of a metal material with good adhesion, such as Ni, Cr, Ti, or an alloy thereof, to facilitate the deposition of the metal material. Besides, the thin metal layer  114  may be composed of a metal material of high reflectivity, such as Ag, Pt, Al, Au, Ni, Ti, or an alloy thereof. In the present invention, the thin metal layer  114  may be composed of a single-layered metal structure, or may be composed of a multi-layered metal structure. A thickness of the thin metal layer  114  is preferably less than about 10 μm. In an exemplary embodiment, the thickness of the thin metal layer  114  is about 10 nm. 
   After the thin metal layer  120  is formed, a heat sink of the semiconductor device may be formed directly, or a light-reflecting structure is selectively formed on the semiconductor device according to the product needs, such as the semiconductor device is an opto-electrical device, for increasing the light extraction of the opto-electrical device. In the embodiment, a reflective layer  120  is formed to cover the thin metal layer  114  on the opto-electrical device  108   a  by, for example, an evaporation deposition method, a sputtering deposition method, an electroless plating deposition method or an electro plating deposition method, wherein the reflective layer  120  is preferably composed of a metal material of good reflectivity, such as Ag, Pt, Al, Au, Ni, Ti, or an alloy thereof, and the reflective layer  120  may be composed of a single-layered metal structure or a multi-layered metal structure. As shown in FIGS.  4 A and  4 B, in the preferred embodiment, the reflective layer  120  is composed of a silver film  116  and a gold film  118  stacked on the thin metal layer  114  in sequence, wherein a thickness of the silver film  116  is about 300 nm, and a thickness of the gold film  118  is about 150 nm. In the present invention, a thickness of the reflective layer  120  is preferably less than about 10 μm. However, when the thin metal layer  114  is composed of a metal material of high reflectivity, the thin metal layer  114  can provide light-reflecting function, and a reflective layer may not be additionally formed. 
   Then, a metal heat sink  122  is formed to cover the reflective layer  120  by, for example, a plating method or an electroless plating method, wherein the metal heat sink  122  is composed of a thicker metal layer for providing larger heat conduction, such as shown in  FIGS. 5A and 5B , in which  FIG. 5A  is the top view and  FIG. 5B  is the corresponding cross-sectional view. Because the metal heat sink  122  is formed by a plating method or an electroless plating method in the present invention, the metal heat sink  122  is substantially grown on the reflective layer  120 . The metal heat sink  122  is preferred composed of a metal of good thermal conductivity, such as Fe/Ni alloy, Cu, Ni, Al, W, or an alloy thereof. The metal heat sink  122  is generally thicker and preferably has a thickness greater than about 10 μm for larger heat conduction. In an embodiment of the present invention, a thickness of the metal heat sink  122  is preferably about 3 mm. 
   One feature of the present invention is that the thin metal layer is initially formed by an evaporation deposition method, a sputtering deposition method or an electroless plating deposition method and is used as the base for plating or electroless plating the metal heat sink, and a reflective layer is selectively formed according to the needs of the semiconductor device for increasing the light extraction efficiency of the opto-electrical device. With only one single adhesive tape used, the metal heat sink can be formed on the bottom surface of the semiconductor device. As a result, the present process is very simple, and the standard process equipment can still be used, thereby preventing increasing the process cost. Furthermore, the semiconductor device is embedded in the surface of the metal heat sink, with no glue between the semiconductor device and the metal heat sink, thereby greatly increasing the heat-transmitting area and the heat-transmitting speed of the semiconductor device. 
   After the metal heat sink  122  is formed, the adhesive tape  102  and the temporary substrate  100  are removed to expose a side of the opto-electrical device  108   a , the electrodes  110  and  112  deposed on the side of the opto-electrical device  108   a , and the surface at the side of the thin metal layer  114  where the opto-electrical device  108   a  located, such as shown in  FIG. 6 . Because the thin metal layer  114  and the opto-electrical device  108   a  are adhered to the temporary substrate  100  by the adhesive tape  102 , the metal heat sink  122 , the thin metal layer  114  and the opto-electrical device  108   a  can be separated from the temporary substrate  100  easily. 
   Next, a plurality of bonding pads  128  and  134  are adhered to the exposed surface of the thin metal layer  114  around the opto-electrical device  108   a  through the glue  140  by an adhesive method, such as shown in  FIG. 7 . The bonding pad  128  mainly includes an insulating layer  124  and a conductive layer  126 , wherein the insulating layer  124  is adhered to the surface of the thin metal layer  114  through the adhesive glue  140 , and the conductive layer  126  is deposed on the insulating layer  124 . Similarly, the bonding pad  134  mainly includes an insulating layer  130  and a conductive layer  132 , wherein the insulating layer  130  is adhered to the surface of the thin metal layer  114  through the adhesive glue  140 , and the conductive layer  132  is deposed on the insulating layer  130 . In the present invention, each semiconductor device at least includes two electrodes of different conductivity types, so that each semiconductor device preferably correspond to two bonding pads, that is, each electrode corresponds to one bonding pad. 
   Subsequently, at least two wires  136  and  138  are formed to respectively connect the electrode  110  of the opto-electrical device  108   a  and the conductive layer  126  of the bonding pad  128 , and the electrode  112  and the conductive layer  132  of the bonding pad  134 , for electrically connecting the electrode  110  and the bonding pad  128 , and the electrode  112  and the bonding pad  134  respectively, such as shown in  FIG. 8 . In the present invention, the electrode and the bonding pad of the same conductivity types may be connected by one or more wires. For example, the positive electrode may be connected to the positive bonding pad by four wires, and the negative electrode may be connected to the negative bonding pad by three wires. Therefore, at least one wire must be set between each conductivity type electrode and the bonding pad of the same conductivity type, and the number of connection wires between the electrode and the bonding pad of the same conductivity type can be modified according to the requirements of the device design. Because wires of an outer circuit (not shown) are bigger, and the sizes of the electrodes  110  and  112  of the semiconductor device, such as the opto-electric device  108   a , are smaller, so that it is unfavorable for the outer circuit being directly connected to the electrodes  110  and  112 . Therefore, with the installation of the bonding pads  128  and  134 , which are much larger than the electrodes  110  and  112  in size, the outer circuit can be easily connected to the electrodes  110  and  112 . By deposing the transitive bonding pads  128  and  134  on the surface of the thin metal layer  114  around the opto-electrical device  108   a  and using a wire bonding technique, the electrodes  110  and  112  of the opto-electrical device  108   a  can be successfully and electrically connected to the outer circuit, which is connected to the bonding pads  128  and  134 , respectively through the wire  136  and the bonding pad  128 , and the wire  138  and the bonding pad  134  without using a circuit board. 
   Another feature of the present invention is that the bonding pads are deposed on the metal heat sink for transition, so that it is beneficial for the electrical connection between the electrodes of the semiconductor device and the outer circuit, so that a circuit board is unnecessary. Furthermore, the heat dissipating function of the metal heat sink can be completely elaborated since the metal heat sink does not need to be deposed on the circuit board. 
   According to the aforementioned description, one advantage of the present invention is that the embedded metal heat sink for the semiconductor device of the present invention includes at least one bonding pad, and the at least one bonding pad can be used as a transition electrode for electrically connecting a positive electrode or a negative electrode of the semiconductor device and an outer circuit, so that the semiconductor device embedded on the metal heat sink can be successfully connected to the outer circuit, and an circuit can be omitted. 
   According to the aforementioned description, another advantage of the present invention is that the semiconductor device of the present invention can be electrically connected to an outer circuit successfully without pasting the embedded metal heat sink for the semiconductor device to a circuit board, so that the heat sinking efficiency of the metal heat sink can effectively work out. 
   According to the aforementioned description, still another advantage of the present invention is the metal heat sink can be directly deposited on a bottom surface of the semiconductor device with the assistant of an adhesive tape and without the use of glue or a pasting technique, so that the temperature of the operating device can be rapidly and effectively lowered to enhance the operational quality of the device and prolonging the life of the device. 
   As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrated of the present invention rather than limiting of the present invention. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.