Abstract:
The invention relates to a side view LED package in use with an LCD backlight unit. The side view LED package comprises: an LED chip; and a strip-shaped lead frame having a toothed structure formed in a lateral edge thereof. The LED chip is mounted on a surface of the lead frame. An integral package body is made of resin, and includes a hollow front half having a cavity for housing the LED chip and a solid rear half divided from the front half by the lead frame. The toothed structure of the lead frame structure can improve resin flow in order to ensure stability even if the LED package is made extremely thin.

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of Korean Patent Application No. 2005-8218 filed on Jan. 28, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a side view Light Emitting Diode (LED) package in use with an LCD backlight unit. More particularly, the invention relates to a side view LED package having a lead frame structure designed to improve resin flow in order to ensure stability even if the LED package is made extremely thin. 
     2. Description of the Related Art 
     Side view LEDs are widely used as a light source of a backlight unit of a small-sized LCD in a mobile phone, a Personal Digital Assistant (PDA) and so on. The side view LEDs are used in a package, in which their mounting height is getting gradually reduced and it is expected that a dimension of 0.5 mm or less will be required. Furthermore, the LED package should ensure high reliability while realizing high brightness by minimizing light loss and so on. 
     At present, in order to reduce the thickness of the side view LED package, endeavors have been made to reduce the thickness of upper and lower wall parts around an LED window. However, reducing the wall part thickness is extremely difficult task. This task also potentially weakens wall strength thereby failing to ensure reliability. 
     This will be described in more detail with reference to  FIGS. 1 to 4 , in which  FIG. 1  is a front elevation view of a general side view LED package,  FIG. 2  is a cross-sectional view illustrating resin flow on a plane taken along the line II—II in  FIG. 1 ,  FIG. 3  is front elevation view of a side view LED package having lead frames of the prior art, and  FIG. 4  is a cross-sectional view illustrating resin flow on a plane taken along the line IV—IV in  FIG. 3 . 
     First, strip-shaped lead frames  40  are disposed in a mold as shown in  FIG. 2 , and resin is injected into the mold, such that resin forms a body  12  and a wall  14  surrounding a cavity C of an LED package  10  during the flow along the direction of arrow A. Resin spreads laterally in a rear half  12   b  of the body  12  about lead frames  40 , and then directs toward a front half  12   a  of the body  12 . In the meantime, upper and lower wall parts of the front half  12   a  of the body  12  are formed of resin that flows over the lead frame  40  as indicated with arrow B. 
     As shown in  FIGS. 2 and 3 , the lead frames  40  are placed along substantially the entire length of the LED package  10 , with a width larger than that of the bottom  16  of the cavity C. That is, as shown in  FIG. 4 , the lead frames  40  are spaced from the outside surface of the body  12  at a small gap  20 , which acts as a bottleneck. Therefore, it is apparent that resin does not smoothly flow along the direction of arrow B. 
     Then, resin insufficiently feeds to central leading ends of the upper and lower wall parts  18 , thereby creating molding defects such as V-shaped voids. 
     In particular, since the LED package is getting longer in reverse proportion to its thickness reduction, the central leading ends of the wall parts  18  become more susceptible to molding defects. 
     In the meantime, heat generated from the operation of the LED chip  30  expands the lead frames  40  inside the LED package  10  along the length of the package  10 . However, the lead frames  40  having different expansion coefficient from the package body  12  and an encapsulant inside the cavity C causes stress to the whole LED package  10  including the lead frames  40 . 
     Such stress if repeated or continued may cause the lead frames  40  to get loose or separated from the package body  12  to such an extent that a disconnection A takes place between a wire W and a lead frame  40  or between the wire W and an LED chip  30  as shown in  FIG. 5 . 
     These problems are getting more serious according to the reduced thickness of the LED package  10  accompanied with its increased length. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the foregoing problems of the prior art and it is therefore an object of the present invention to provide a side view LED package having a lead frame structure designed to improve resin flow in order to ensure stability even if the LED package is made extremely thin. 
     It is another object of the invention to provide a side view LED package having a lead frame structure designed to ensure stability for internal electrical connection under high temperature-induced stress. 
     According to an aspect of the invention for realizing the object, there is provided a side view LED package comprising: an LED chip; a strip-shaped lead frame having a toothed structure formed in a lateral edge thereof, the LED chip mounted on a surface of the lead frame; and an integral package body made of resin, and including a hollow front half having a cavity for housing the LED chip and a solid rear half divided from the front half by the lead frame. 
     Preferably, the toothed structure of the lead frame forms a resin flow passage promoting resin to flow from the rear half to the front half of the package body. In this case, the resin flow passage may be configured to promote resin flow along a wall of the cavity from both lateral edges of the lead frame to the front half of the package body. 
     Preferably, the toothed structure of the lead frame may comprise a groove formed in the lateral edge of the lead frame to expose a bottom of the cavity. 
     In this case, the groove in the lateral edge of the lead frame may be formed to such an extent that the bottom of the cavity does not directly contact the LED chip. Also, the groove in the lateral edge of the lead frame may be formed along a major part of the lead frame edge in the cavity to such an extent that a portion of the lead frame edge inserted into a wall of the cavity stably supports the lead frame. Then, a remaining part of the lead frame in the cavity may have a width of at least 80% of the thickness of the lead frame. 
     Preferably, the toothed structure of the lead frame as described above may further comprise a groove or hole that is fully buried in the package body. 
     Furthermore, the toothed structure of the lead frame may be preferably formed by punching. 
     Preferably, the toothed structure of the lead frame may comprise a groove or hole that is fully buried in the package body. In this case, the toothed structure of the lead frame may comprise a groove caved into the lateral edge of the lead frame from an inside wall of the cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front elevation view of a general side view LED package; 
         FIG. 2  is a cross-sectional view illustrating resin flow on a plane taken along the line II—II in  FIG. 1 ; 
         FIG. 3  is front elevation view of a side view LED package having lead frames of the prior art; 
         FIG. 4  is a cross-sectional view illustrating resin flow on a plane taken along the line IV—IV in  FIG. 3 ; 
         FIG. 5  is a photograph illustrating disconnection in a bonding area of a lead frame of the prior art; 
         FIG. 6  is a plan view illustrating lead frames according to an embodiment of the invention, which are not mounted on an LED package; 
         FIG. 7  is a front elevation view illustrating a side view LED package mounted with lead frames according to an embodiment of the invention; 
         FIG. 8  is a cross-sectional view illustrating resin flow on a plane taken along the line VIII—VIII in  FIG. 7 ; 
         FIG. 9  is a cross-sectional view illustrating resin flow on a plane taken along the line IX—IX in  FIG. 7 ; 
         FIG. 10  is a cross-sectional view illustrating resin flow on a plane taken along the line X—X in  FIG. 7 ; and 
         FIG. 11  is a front elevation view illustrating a side view LED package mounted with lead frames according to another embodiment of the invention; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 6  is a plan view illustrating lead frames of the invention, which are not mounted on an LED package. 
     Referring to  FIG. 6 , a pair of lead frames  140   a  and  140   b  according to a preferred embodiment of the invention shown in a plan view. The lead frames  140   a  and  140   b  are spread before being inserted into a mold to produce an LED package. When the lead frames  140   a  and  140   b  are inserted into the mold, external terminals  144  are folded about internal terminals  142 . 
     The first and second lead frames  140   a  and  140   b  have a toothed configuration. That is, first resin flowing grooves  146  in the shape of semicircle are formed at both lateral edges of the strip-shaped internal terminal  142  of the first lead frame  140   a , and a first resin flowing groove  146  in the same shape is formed at one lateral edge of the strip-shaped internal terminal  142  of the second lead frame  140   b . The first resin flowing grooves  146  may have various shapes such as square, rectangle, triangle, semi-ellipse and slit. 
     The first resin flowing grooves  146  have a width corresponding to at least 80% of the thickness of the lead frames  140   a  and  140   b . More preferably, the width of the first resin flowing grooves  146  is the same as or larger than the thickness of the lead frames  140   a  and  140   b . The spacing S between the adjacent first resin flowing grooves  146  is preferably at least 80% of the thickness of the lead frames  140   a  and  140   b , and more preferably the same as or longer than the thickness of the lead frames  140   a  and  140   b.    
     When the first resin flowing grooves  146  are shaped as a slit (refer to  FIG. 11 ), the width of the remaining internal terminal  142  is at least 80% of the thickness of the lead frames  140   a  and  140   b , and preferably the same as or larger than the thickness of the lead frames  140  and  140   b.    
     Furthermore, second resin flowing grooves  148  are formed in the shape of semicircle at joints of the internal terminals  142  to the external terminals  144 . The second resin flowing grooves  148  may also have various shapes such as square, rectangle, triangle, semicircle, semi-ellipse and slit. The second resin flowing grooves  148  are preferably sized larger than the first resin flowing grooves  146 . Alternatively, the second resin flowing groove  148  may be substituted with a hole. The hole may also have various shapes such as circle, rectangle, square and ellipse. 
     The width of the second resin flowing grooves  148  is preferably at least 80% of the thickness of the lead frames  140   a  and  140   b , and more preferably the same as or larger than the thickness of the lead frames  140   a  and  140   b.    
     The first and second resin flowing grooves  146  and  148  may be formed by various processes. For example, the resin flowing grooves  146  and  148  may be formed via punching while the lead frames  140   a  and  140   b  are fabricated. Alternatively, the grooves  146  and  148  may be formed by punching lead frames which have been prepared beforehand. 
     The lead frame  140   a  is spaced from the lead frame  140   b  at a predetermined gap G, which is maintained also inside an LED package  100  as shown in  FIG. 7 . 
     Now the side view LED package having the lead frames  140   a  and  140   b  of  FIG. 6  according to the invention will be described with reference to  FIGS. 7 to 10 , in which 
       FIG. 7  is a front elevation view illustrating a side view LED package mounted with lead frames of the invention,  FIG. 8  is a cross-sectional view illustrating resin flow on a plane taken along the line VIII—VIII in  FIG. 7 ,  FIG. 9  is a cross-sectional view illustrating resin flow on a plane taken along the line IX—IX in  FIG. 7 , and  FIG. 10  is a cross-sectional view illustrating resin flow on a plane taken along the line X—X in  FIG. 7 . 
     Referring to the LED package  100  of the invention, a body  102  of resin includes a front half  102   a  and a rear half  102 , which are divided from each other about the lead frames  140   a  and  140   b . A wall  104  is formed at the periphery of the front half  102   a , and a cavity C is formed surrounded by the wall  104 . The cavity C is shaped to provide a space for mounting an LED chip  130  therein, and functions as an LED window for directing light generated by the LED chip  130  to the outside. 
     A plurality of LED chips may be mounted inside the cavity C. In this case, the reference sign  130  may indicate an LED chip mounting area. 
     Internal terminals (refer to  142  in  FIG. 6 ) of the lead frames  140   a  and  140   b  are placed on the bottom  106  inside the cavity C, with the bottom  106  partially exposed as covered with the lead frames  140   a  and  140   b.    
     The LED chip  130  can be mounted by flip chip bonding or wire boding. In case of flip chip bonding, the LED chip  130  is fixed and electrically connected to the lead frames  140   a  and  140   b  by solder bumps (not shown). In case of wire bonding, the LED chip  130  is bonded to the lead frames  140   a  and  140   b  by for example adhesive, and electrically connected thereto by wires (not shown). 
     Although not shown, transparent encasulant is filled in the cavity C to seal the LED chip  130 , the lead frames  140   a  and  140   b  and electric-connector means such as solder bumps and wires as well as to protect these components from the external environment. 
     After being sealed, the lead frames  140   a  and  140   b  are fixed inside the body  102  with the predetermined gap G from each other. The first resin flow grooves  146  partially expose the bottom  106  adjacent to the wall  104  while the second resin flow grooves  148  are completely buried in lateral portions of the package body  102 . 
     Such an LED package  100  is formed by mounting the lead frames  140   a  and  140   b  as in  FIG. 6  into a mold and injecting resin into the mold in the direction of arrow A as shown in  FIGS. 8 and 10 . 
     In an upper part of the LED package  10 , injected resin flows as shown in  FIG. 8  in which components in a lower part are shown in dotted lines for the sake of convenience. 
     First, resin generally flows toward both lateral ends of the body  102  in the rear half  102  of the body  102  about lead frames  140   a  and  140   b . In the meantime, unlike the prior art as shown in  FIG. 2 , resin also flows as indicated by arrow A 146  through the first resin flow grooves  146  of the lead frames  140   a  and  140   b  from the rear half  102   b  to the front half  102 . 
     Resin flow A 146  is formed by the first resin flow grooves  146 . Comparing this with  FIGS. 9 and 10 , bottlenecks  110   a  are formed in a lower part of the lead frame  140  of  FIG. 9  and in upper and lower parts of the lead frame  140  of  FIG. 10 . The bottlenecks  110   a  are formed since lateral edges of the lead frame are inserted into the body  102 . However, the upper part of the lead frame  140  in  FIG. 9  has the first resin flow groove  146 , which forms a resin flow passage  10   b  allowing resin to flow through. 
     Thus, resin flows from the rear part  102   b  to the front part  102   a  of the body along the direction of arrow A 146  to the end of the front part  102   a . This as a result can overcome disadvantages of the prior art, in which resin fails to reach the central leading end of the upper or lower wall part  18 , forming molding defects such as void. 
     In addition, resin flow in the direction of arrow A 146  can create subsidiary resin flows or resin flow branches in the direction of arrow A′ 146 . This can ensure efficient resin feeding across the entire upper and lower areas around the cavity C of the front half  102   a.    
     On the other hand, the second resin flow grooves  148  are positioned at both lateral ends of the package body  102  so as to form resin flow passages as the first resin flow grooves  148  as above. Thus, the flow of resin from the body rear half  102   b  to the body front half  102   a . This enables resin to flow more actively from the body rear part  102   b  to the body front part  102   a , thereby ensuring more efficient resin flow across the entire area of the body  102   a.    
     In the meantime, if the first resin flow holes  146  are sized too large, the LED chip  130  may directly contact the bottom  106  of the package body  102 , which in turn may lower heat dissipation from the LED chip  130 . This is not preferable particularly in case that the LED chip  130  generates large quantity of heat. Therefore, it is preferable that the first resin flow grooves  146  do not directly contact the LED chip  130 . Furthermore, the lead frames  140  also function as a reflector that radiates light generated from the LED chip  130  to the outside through the cavity C. Too large holes in the lead frames  140  inside the cavity C may degrade the performance of the lead frames  140  as a reflector, potentially worsening light emitting efficiency of the LED package  100 . 
     The resin flow grooves  146  and  148  in the lead frames  140  have advantages as follows: 
     Heat generated in response to the actuation of the LED chip  130  causes the lead frames  140  inside the LED package  100  along the length of the LED package  100 . In this case, the lead frames  140  have an expansion coefficient different from those of the package body  102  and the encapsulant in the cavity C, such that the LED package  100  including the lead frames  140  may suffer from stress caused by the different expansion coefficients. 
     However, the lead frames  140  of the invention are configured to have a toothed structure with the resin flow grooves  146  and  148  so as to potentially absorb heat-induced expansion. Then, stress can be removed or at least minimized, and thus the lead frames  140  of the invention do no get loose or separate from the package body  102 . This can advantageously prevent disconnections between the wires or the solder bumps and the lead frames or between the wires or the solder bumps and the LED chip as described above with reference to  FIG. 5 . 
     This advantage is available in particular considering that stress applied to the lead frames  140  under the heat increases gradually in proportion to the length of the lead frames  140  and the total length also increases gradually in proportion to the thickness reduction of the LED package  100 . 
     With reference to  FIG. 11 , another embodiment having expanded first resin flow grooves will be explained. An LED package  200  shown in  FIG. 11  has components substantially the same as those of the LED package  100  afore-described with reference to  FIGS. 6 to 11  except for internal terminals  242  of lead frames  240   a  and  240   b . Thus, corresponding components will be designated with reference signs by  200   s , and will not be repeatedly described. 
     In  FIG. 11 , each of the lead frames  240   a  and  240   b  has a T-shaped internal terminal  242 , with slit shaped openings  246  formed along both lateral sides of the internal terminal  242 . The internal terminal  242  has fixed ends  246   a  inserted into a wall  204  to fix the internal terminal  242 . 
     Preferably, the width of the internal terminal  242  is at least 80% of the thickness of the lead frames  240   a  and  240   b . Besides, at least two pairs of fixed ends  246   a  may be formed if necessary. 
     This as a result can ensure larger resin flow passages with the openings  246 , thereby achieving more efficient resin flow across upper and lower areas of the wall  204 . This arrangement is necessary especially where resin has high viscosity. It is also preferable where resin has relatively large heat conductivity. 
     As described hereinbefore, the LED package of the invention has the lead frame structure designed to improve resin flow, and thus can ensure stability in the upper and lower wall parts around the cavity even if shaped@ extremely thin. 
     Furthermore, the LED package of the invention can ensure stability in internal electrical connection even under high temperature stress owing to the actuation of the LED. 
     While the present invention has been shown and described in connection with the preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.