Abstract:
A reflection-type photosensor is formed in a body of U-shape with lenses formed on arms of the U. The optical axes of the lenses intersect at a location outside of the U-shape at a position above the gap between the arms. The surface roughness of facing surfaces of the arms is such as to cause light dispersion. Leads are formed in parallel within the body and exit the bottom surface. The light emitter and light detector may be mounted on thinned parts of first leads such that peripheral portions of the first leads serve as reflective surfaces.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a reflection-type photosensor, and more particularly to a simple resin-molded reflection-type photosensor. 
     In a conventional reflection-type photosensor, utilized as a pattern recognition sensor or a tape-end sensor for a VCR (video cassette recorder), the light emitting portion and the light detecting portion are prepared separately and then assembled into a unit package such that they are spaced from one another and coupled with respect to radiation emitted and detected thereby, via a reflective object. 
     Such conventional reflection-type photosensor has a ceramic substrate with a pir of recesses in one surface thereof, input leads and output leads implanted into the substrate such that the leads extend from the bottoms of the recesses to the other surface of the substrate, and a light emitting pellet and a light detecting pellet which are respectively disposed within the two recesses and mounted on tip ends of respective ones of the input and output leads with the other electrodes electrically connected to tip ends of respective other ones of the input and output leads. The recesses are filled with a transparent silicone resin and covered with a transparent cap. 
     In the conventional reflection-type photosensor, however, the structure becomes bulky, and in addition, the assembly work is complicated. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a reflection-type photosensor with a resin-molded single package which is adaptable to mass productivity at low cost. 
     Another object of the invention is to provide a reflection-type photosensor with a resin-molded structure of a size smaller than the prior art structure. 
     One of the features of the invention resides in that pellet-mounting areas of leads in light emitting and detecting portions are disposed substantially in the same plane within a single molded package with a pair of lenses, and a light emitting pellet and a light detecting pellet are photocoupled in side-by-side relationship so that the structure is made suitable to mass production. 
     In order to attain enhancement of the optocoupling efficiency, it is preferable to provide a reflection portion in the leads for mounting the pellets. That is, the pellet mounting areas are recessed or thinned to form stairs or steps between the pellet mounting areas and the remaining area of the leads. The wall of the stair can be utilized for light reflection. 
     Still further, an air gap is provided between the emitting portion and the detecting portion, and preferably, at least inside surfaces of the air gap are finished with a rough surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing the surface appearance of a reflection-type photosensor according to a first embodiment of the invention. 
     FIG. 2 is a cross-sectional view of FIG. 1. 
     FIG. 3A, FIG. 3B and FIG. 3C are a front view, a top view and a right side view, respectively of a second embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 and FIG. 2, a light emitting portion 12 comprises a light emitting pellet 32 mounted on a mounting area 222 at a tip end of one of the two input leads 22 and electrically connected thereto. The other electrode (not shown) of the emitting pellet 32 is electrically connected to a tip end 224 of the other of the two input leads 22 through a bonding wire 42. Similarly, a light detecting portion 14 comprises light detecting pellet 34 mounted on a pellet mounting area 242 of one of two output leads 24. The other electrode (not shown) of the detecting pellet 34 is electrically connected to a tip end 244 of the other output lead 24. The emitting portion 12 and detecting portion 14 are supported by a bridge portion 16 so as to form an air gap portion 17 therebetween. The emitting portion 12 and detecting portion 14 are further provided with first and second convex lenses 181 and 182 located respectively at corner portions adjacent to the gap portion 17. The optical axis of the first lens 181 is aligned in a plane parallel to a principal surface of the emitting pellet 32 so as to converge the light emitted from the side surfaces of the emitting pellet 32 and direct the light toward the object 100. In the same manner, the optical axis of the second lens 182 is aligned in a plane parallel to a principal surface of the detecting pellet 34 so as to converge reflected light from the object 100 on the side surface of the detecting pellet 34. In other words, the optical axes are arranged so as to cross to each other above the gap portion 17. 
     According to this embodiment, since the air gap portion 17 is provided between the emitting portion 12 and detecting portion 14 and between the lenses 181 and 182, direct optocoupling between the emitting pellet 32 and detecting pellet 34 can be neglected for commercial use. This is because light dispersion occurs at both walls opposing each other through the air gap portion 17, thus the direct optocoupling, which is detected as noise, is decreased while reflected light, detected as a signal, is enhanced by the pair of the lenses 181 and 182. If the air gap portion were omitted, the signal to noise (S/N) ratio would be greatly decreased and the device could not be used in practice. To this end, it has previously been thought that a light shielding portion between the emitting portion and the detecting portion was unavoidable. This thinking has engendered a complicated manufacturing process and high cost. 
     According to the present invention, on the contrary, all of the emitting portion with its lens, the detecting portion with its lens and the bridge portion are commonly housed within a single resin-molded package thereby facilitating the manufacturing process. Furthermore, since all leads 22 and 24 are arranged in the same plate and both the pellet mounting areas 222 and 242 are present also in the same plane, the thickness of the molded package can be decreased. Moreover, all the leads 22, 24 can be derived from the same direction as illustrated, and therefore the width of the reflection-type photosensor or its dimension in the direction of the optical axis can reasonably be minimized. Since all the leads are derived in the same plane and in the same direction, a transfer molding technique using a two-split metal mold which is adaptable to mass production can easily be applied. 
     Where transfer molding is carried out by means of a two-split metal mold, the splice line of the mold must be matched with the lead frame surface. In FIG. 1, the splice line of the metal mold is indicated by a dotted line 60. 
     The single resin to be used for the molding should be transparent to the light emitted from the emitting pellet. 
     When the outside surface of the resin-molded package is made rough, except for the lens portion, the S/N ratio is further improved. Such modification can be easily achieved by finishing the inside surfaces of the two-split metal mold like a frosted glass surface except for the portion corresponding to the convex lenses which should be finished like a mirror surface. 
     The region of the rough surface or ground surface can be limited to only the opposing wall portions 171 exposed to the air gap portion 17. 
     FIG. 3A to FIG. 3C show another embodiment of the invention. Like reference numerals represent like parts in FIG. 1 and FIG. 2. What is different from the foregoing embodiment is that the pellet mounting areas of the leads take another form. As shown in FIG. 3A and FIG. 3B, the respective pellet mounting areas 222 and 242 of the leads are formed thinner than the thickness of the adjacent elongated lead wire portion 22, thereby providing a pair of stair wall portions 225 and 245 at two adjacent side edges of the pellet mounting area. 
     In this embodiment, part of the light coming from the emitting pellet 32 is reflected by the pair of stair wall portions 225, and likewise, part of the light incident on the detecting portion is reflected at a pair of stair wall portions 245 of the output lead 26 toward the detecting pellet 34 to increase the quantity of the incident light, thus contributing to an enhancement of the photocoupling efficiency. 
     The thin portions of the element mounting areas are formed concurrently when forming the lead frames by appropriately designing the lead frame punch cutting die and therefore manufacturing processing will not be increased thereby. It is apparent that the lead frames can be formed not only through punching but also by a known etching process. 
     As a typical example of the invention, a light emitting diode (LED) of gallium arsenide (GaAs) and emitting infrared rays is used as the emitting pellet 32, and a phototransistor of silicon (Si) is used as the detecting pellet 34. Each pellet is mounted on a silver plated iron lead frame with silver paste. The pellets are then subjected to transfer molding after wire bonding by means of gold wire. An infrared ray transmissive, visible light blocking resin or, for example, a product known as NT8513-9700 (manufactured by Nitto Electric Industrial Co., Ltd.) which uses visible light blocking dye-stuff mixed in an epoxy resin, is used as the molding resin. 
     Referring to typical dimensions of each part, the resin-molded package is 11.0 mm in overall width, 2.5 mm in thickness and 8.5 mm in height. Each convex lens 181, 182 is semispherical and 2 mm in diameter. The distance between vertices of the convex lenses 181 and 182 is 3.0 mm. The thickness of the pellet mounting areas of both leads is 0.26 mm, while that of the remaining area of the leads is 0.46 mm. Thus, the height of stair wall portions 225 and 245 is 0.2 mm. Since the thickness of the ordinary emitting and detecting pellets is about 0.2 mm, the stair wall portions may act effectively as reflectors. When the outside surface of the resin-molded package except for lens portions has a roughness of about 5 to 10 μm, noise or leak current is decreased by one half. 
     The reflection-type photosensor according to the present invention is not limited to the aforementioned materials and dimensions. 
     As described above, since the reflection-type photosensor according to the invention can be miniaturized and made thin, it is capable of complying fully with current requirements that electronic parts be designed thin and small. The manufacturing process can be facilitated and the quantity of resin needed can also be decreased according to the invention, to attain a reflection-type photosensor adaptable to mass production at a low cost.