Patent Publication Number: US-8120052-B2

Title: Flip chip type LED lighting device manufacturing method

Description:
RELATED APPLICATIONS 
     This application is a Continuation patent application of of pending Ser. No. 11/896,778, filed 6 Sep. 2007, currently pending, which is a Continuation patent application Ser. No. 11/029,387, filed 6 Jan. 2005, now issued as U.S. Pat. No. 7,629,188. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lighting device manufacturing method and more particularly, to a simple method of making flip chip type LED lighting devices without wire bonding. 
     2. Description of the Related Art 
     A lighting device is a requisite in our daily life. It lights up the space when dark. Following fast development of high technology, flip chip LEDs have been intensively used to substitute for conventional incandescent lamps. 
       FIG. 1  is a schematic sectional view of a flip chip type LED lighting device made according to the prior art. According to this design, the flip chip type LED lighting device  1  comprises a submount  12 , bond fingers  16 ,  18  provided at two sides of the submount  12 , and a plurality of flip chip LEDs (light emitting diodes)  10  bonded on the submount  12  and electrically connected to the bond fingers  16 ,  18  by wire bonding. According to this design, a die bonding and a wire bonding procedures must be employed to have the legs of the LEDs  10  connected to the bond fingers  16 ,  18 . This wire bonding procedure is complicated. During wire bonding, the LEDs  10  or submount  12  may be damaged accidentally. 
     Therefore, it is desirable to provide a flip chip type LED lighting device manufacturing method, which eliminates the aforesaid problem. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a flip chip type LED lighting device manufacturing method, which eliminates the application of wire bonding. It is another object of the present invention to provide a flip chip type LED lighting device manufacturing method, which has the bottom wall of the submount exposed to the outside for the bonding of a heat conducting/dissipating member to improve the heat dissipation effect of the lighting device. To achieve these and other objects of the present invention, the flip chip type LED lighting device manufacturing method comprises the steps of a) providing a strip, the strip comprising a plurality of strip elements, the strip elements having a respective metal lead frame respectively electrically connected to one another; b) providing a submount, the submount comprising a submount and a plurality of flip chip LEDs (light emitting diodes) installed in the submount; c) forming a metal bonding layer between the strip bond pad, that has been pre-fixed in the strip, and the submount to form a lighting structure; and d) cutting the lighting structure thus obtained into individual flip chip type LED lighting devices based on each strip element. The method of the invention further comprises the step of bonding a heat conducting/dissipating member to the submount of each individual flip chip type LED lighting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic sectional view of a flip chip type LED lighting device made according to the prior art. 
         FIG. 2  is a block diagram showing the flow of a flip chip type LED lighting device manufacturing method according to the present invention. 
         FIG. 3  is a schematic drawing of a strip for the fabrication of a flip chip type LED lighting device according to the present invention. 
         FIG. 4  is a schematic sectional view of a flip chip type LED lighting device made according to the present invention. 
         FIG. 5  is a schematic sectional view of a light module based on a flip chip type LED lighting device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIG. 2 , a flip chip type LED lighting device manufacturing method in accordance with the present invention includes the steps of: 
     S 10 —providing a strip, as  FIG. 3  shown, wherein the strip is prepared having a plurality of strip elements  20 , each strip element  20  having a metal lead frame  21 , the metal lead frames  21  of the strip elements  20  being respectively electrically connected together; 
     S 12 —providing a submount, for example, silicon or low temperature co-firing ceramic (LTCC) submount is provided, and a plurality of light emitting elements, for example, light emitting diodes are installed on the silicon submount by flip chip; 
     S 14 —formation of metal bonding layer where a metal bonding layer is formed on the bottom wall of the strip or the top wall of the submount with a low temperature solder material for example, tin base alloy, bismuth base alloy, or indium base alloy, or by means of eutectic bonding, or gold to gold ultrasonic bonding to form a lighting structure; 
     S 16 —bonding of sub-mount to strip where the submount is attached to the bottom side of the strip and at the same time the submount is heated to melt the metal bonding layer to fix the submount to the strip and to electrically connect the metal lead frames to the bond pads of the submount, or using a lower bonding temperature by associating with ultrasonic energy; and 
     S 18 —cutting where the structure thus obtained is cut into individual flip chip type LED lighting devices each containing one strip element. 
     After the aforesaid step S 18 , a heat conducting/dissipating member is provided under and fixedly fastened to each individual flip chip type LED lighting device. The heat conducting/dissipating member could be bonded to the flip chip type LED lighting device by means of the application of a conductive adhesive containing silver or copper filler. Alternatively, a low temperature solder material may be directly applied on the bottom wall of the flip chip type LED lighting device and following treated with thermal process (Ex. reflow) to achieve the bonding. It is also constructive to bond a heat conducting/dissipating member to the bottom wall of each individual flip chip type LED lighting device by means of eutectic bonding. 
     After bonding of a heat conducting/dissipating member to the bottom wall of each individual flip chip type LED lighting device, a light condensing element, for example, condenser lens or reflector is used to adjust the light path of the lighting device, enhancing the radiation brightness. 
       FIG. 4  is a sectional view of a flip chip type LED lighting device  2  made according to the present invention. As illustrated, the flip chip type LED lighting device  2  comprises a strip element  20 , a metal lead frame  21  embedded in the strip element  20 , a flip chip embedded submount  22  bonded to the strip element  20 , flip chip LEDs  24  bonded to circuits on the strip element  20 , and a metal, for example, conductive or Ag paste bonding layer  26  between the strip element  20  and the sub-mount  22 . 
       FIG. 5  is a light module based on the aforesaid flip chip type LED lighting device. As illustrated, the light module comprises a flip chip type LED lighting device  2 , a heat conducting/dissipating member  30  bonded to the bottom wall of the submount  22  by means of a thermal interface material (TIM), for example, silver glue, copper glue, low temperature solder material, and a light condensing element  32  covering the top side of the flip chip type LED lighting device  2  to concentrate the light of the flip chip LEDs  24 . 
     As indicated above, The method of the present invention comprises the step of providing a strip, the step of providing a submount, the step of forming a metal bonding layer on the strip or submount, the step of bonding the submount to the strip, and the step of cutting the structure thus obtained into individual flip chip type LED lighting devices. This method eliminates the is procedure of wire bonding as is commonly seen in the prior art designs. Therefore, the invention simplifies the fabrication of flip chip type LED lighting devices. 
     Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention.