1. Field of the Invention
The present invention relates a light emitting device using a semiconductor light emitting element, and a light receiving device used in an optical sensor or the like, and, more particularly, to a low-profile light emitting device used as the backlight of a liquid crystal display.
2. Description of the Related Art
In recent years, the backlight of a liquid crystal display employs a surface-emitting light source comprising a low-profile light emitting device and an optical guide which spreads the light emitted by the light emitting device. One among the light emitting devices used in such applications is a low-profile light emitting device comprising a light emitting diode disposed in a flat housing made of a resin (refer to, for example, Japanese Unexamined Patent Publication (Kokai) No. 2004-363537). The resin housing has such a constitution as a protrusion is provided on an elongated light emitting surface and a recess which receives the protrusion is formed on the end face of the optical guide, so as to improve the precision of positioning with respect to the optical guide.
Japanese Unexamined Patent Publication (Kokai) No. 2004-363537 discloses such a constitution as a hanger lead is provided in a part of a lead frame, so as to support the housing on the lead frame during the process of manufacturing the light emitting device. A method of supporting the housing by using a typical hanger lead will be described below with reference to the accompanying drawing.
FIG. 10(A) shows an example of lead frame 102 having a housing 106. Supported on the lead frame 102 by the hanger lead 100 is the housing 106 which has a flat shape and incorporates a pair of lead electrodes 104. FIG. 10(B) is a partially enlarged view of the structure of supporting the housing 106 by the hanger lead 100. As can be seen from this drawing, a distal end 108 of the hanger lead 100 is embedded in a side surface 110 of the housing 106. The housing 106 is supported on the lead frame 102, by forming the support structure comprising the housing 106 and the hanger lead 100 on the side surfaces 110 on both sides of the housing 106. The housing 106 is supported in such a manner as the principal surface thereof is disposed at right angles to the front surface of the lead frame 102.
FIGS. 11(A) and 11(B) are perspective views of a light emitting device constituted from the lead frame 102 provided with the housing 106 shown in FIGS. 10(A) and 10(B). A method of forming the light emitting device 114 shown in FIG. 11 from the lead frame 102 provided with the housing 106 shown in FIGS. 10(A) and 10(B) will now be described.
First, an LED is mounted in a recess 112 of the housing 106. As distal end portions of a pair of lead electrodes 104 are exposed in the recess 112, electrical continuity is established in advance between the two distal end portions and positive or negative electrode of the LED, respectively, by die bonding or wire bonding. The recess 112 is filled with a translucent resin so as to seal the LED with the resin 116 in the housing 106. Then the lead frame 102 is cut off along dashed line X. The lead electrode 104 which is cut off the lead frame 102 is bent along the bottom surface of the housing 106 and is further bent along the side surface. During the bending operation, the housing 106 is held in a predetermined posture by the hanger lead 100. Last, the hanger lead 100 is bent in the state of supporting the housing 106, and the hanger lead 100 is pulled out of the side surface 110 of the housing 106, thereby obtaining the light emitting device 114. As a result, the depression 118 in which the distal end portions 108 of the hanger lead 100 were embedded is left to remain in the side surfaces 110 of the light emitting device 114 as shown in FIGS. 11(A) and 11(B). The low-profile light emitting device 114 manufactured in this way is mounted with the side of the lead electrode 104 facing downward. The light emitting device 114 is combined with an optical guide with the side of the recess 112 serving as the window for light emission, so as to constitute a surface emitting light source for liquid crystal display of mobile phone or mobile computer.
While the light emitting device disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2004-363537 has a thickness small enough to suit the application to plane light source, recently there is a demand for light emitting device of further smaller thickness. However, decreasing the thickness of the light emitting device having the constitution disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2004-363537 gives rise to some problems.
For example, when a low-profile light emitting device is manufactured by using lead frame provided with hanger lead, it is necessary to decrease the width of the hanger lead which results in a decrease in strength of the hanger lead. This increases the possibility of such troubles to occur as the hanger lead is subjected to torsional deformation when the lead frame provided with hanger lead is transported, thus causing the housing to tilt. Also during the operation to bend the lead electrode 104, stress acting on the housing 106 causes the hanger lead 100 to twist, thus resulting in tilting of the housing 106. Tilting of the housing makes it impossible to die-bond the semiconductor element, thus giving rise to the possibility of faulty products.
The low-profile light emitting device is prone to troubles during positioning also in case it is mounted by a conventional chip mounter. A chip mounter which is commonly used has a suction nozzle for transferring the chip. The light emitting device is held on the top surface thereof by the suction nozzle by means of negative pressure, and is transferred to the mounting position. The light emitting device transferred by the suction nozzle is precisely positioned at the predetermined position of a sub-mount, and is placed at the predetermined position by breaking the vacuum in the suction nozzle. However, in case the semiconductor device is thinner and lighter in weight than the conventional one, position of the semiconductor device may be displaced by a slight movement of air caused by breaking the vacuum, even when the semiconductor device and the sub-mount are aligned precisely before breaking the vacuum of the suction nozzle.