Abstract:
An optoelectronic module including a transparent substrate that carries a conductor track, an optoelectronic chip having an optoelectronic sensor and/or emitter for light disposed on the substrate, and via a contacting element the chip is connected to the conductor track and kept spaced apart from the transparent substrate. An opaque light blocking element, disposed between the substrate and the chip, that shields the sensor from lateral incident light and/or lateral light opposite the emitter.

Description:
Applicants claim, under 35 U.S.C. §119, the benefit of priority of the filing date of Mar. 25, 1998 of a German patent application, copy attached, Ser. No. 298 05 392.6, filed on the aforementioned date, the entire contents of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an optoelectronic module, which can be employed in particular in optoelectronic travel, angle and rotational measuring instruments or other optoelectronic devices. 
     2. Description of the Related Art 
     In the journal “F&amp;M”, No. 10 (1996), Vol. 104, pages 752-756, an emitter-receiver module is disclosed. An LED is disposed on a photodiode array chip, which is connected via gold bumps to conductor tracks on a transparent glass plate in what is known as flip-chip technology. The intermediate space between the chip and the glass substrate is filled with an underfiller for the sake of mechanical stabilization. This arrangement is intended to project light onto a scale by means of the LED and to detect the reflected light by the photodiodes. It is disadvantageous, however, that the underfiller is a very good light guide, which guides a large portion of the light in the underfiller, which has been projected by the LED, to the photodiodes. Portions of the light are diverted to the photodiodes by scattering in the underfiller and reflection at the boundary faces of the underfiller and the glass substrate, and further portions are projected directly at the edges of the LED onto the receiver surfaces of the optic chip. As a consequence, the proportion of useful light to parasitic or unwanted light striking the photodiodes is unfavorable. 
     From German Patent Disclosure DE 197 20 300 A, a chip- in-chip implantation of a gallium arsenide LED chip in a silicon-PIN-diode receiver matrix is known. Once again, there can be a considerable proportion of scattered light, which strikes the diode receiver matrix directly without taking the desired course, for instance to a scale having an optical graduation. As a result, on the one hand the useful signal proportion is reduced considerably, and on the other the photodiodes are already modulated with a considerable proportion of direct light. In such flip-chip assemblies, it is also conventional and for applications indispensable, for the sake of mechanical stability and surface passivation, that an optical underfiller be placed between the chip surfaces and the glass substrate plate. The underfiller does provide high mechanical strength and chemical resistance, but it causes an even larger proportion of light to be coupled directly to the photodiode surfaces. Once again, the optoelectronic efficiency is markedly worse as a result. 
     SUMMARY OF THE INVENTION 
     With this as the point of departure, an object and advantage of the present invention is to create an optoelectronic module in which the proportion of useful light to parasitic or unwanted light is improved. 
     The above object and advantage is attained by an optoelectronic module including a transparent substrate that carries a conductor track, an optoelectronic chip having an optoelectronic sensor and/or emitter for light disposed on the substrate and via a contacting element the chip is connected to the conductor track and kept spaced apart from the transparent substrate. An opaque light blocking element, disposed between the substrate and the chip, that shields the sensor from lateral incident light and/or lateral light opposite the emitter. 
     The optoelectronic module of the present invention has a transparent substrate that carries conductor tracks. This substrate may be in platelike form. Glass and/or plastic can be considered in particular as the material for the substrate. 
     An optoelectronic chip with at least one sensor and/or emitter for light is also present, which is disposed with the sensor and/or emitter oriented toward the substrate on the substrate. The sensor and/or emitter can be embodied in one face of the chip. However, it can also be an additional component that is mounted on the chip. 
     The chip is connected to the conductor tracks and kept at a distance from the transparent substrate via contacting elements. The contacting elements serve the purpose of both mechanical and electrical connection of the chip to the substrate or to the conductor tracks disposed on it. Gold bumps or similar contacting elements can be considered in particular as the contacting elements. The known flip-chip technology can be employed. 
     In the optoelectronic module, an underfiller is preferably disposed between the chip and the transparent substrate. The underfiller can be transparent, especially if it covers an optoelectronic sensor and/or emitter. The underfiller may involve an epoxy resin, silicone, or a similar hardening plastic material. An underfiller is indeed preferred but is not obligatory. 
     Finally, in the intermediate space between the chip and the transparent substrate, an opaque light blocking element is disposed, which more or less shields off the sensor from lateral incident light and/or lateral light projected by the emitter. Lateral denotes means an incidence of light or projection of light from or in a direction that is inclined to a vertical axis or line through the chip. This means, for instance, an incident light that does not originate directly at a specific external object but instead is due to scattering or reflection, or it can also be direct radiation from some other object. This parasitic or unwanted light can also originate in a light emitter integrated with the module. It can also be a light projection that is not aimed directly at a different object. As a consequence, in the module of the present invention, the proportion of parasitic or unwanted light striking the sensor or transmitted by the emitter is at least reduced considerably, and on the other hand, the proportion of useful light is increased. 
     The present invention also encompasses an only partial suppression of parasitic or unwanted light by the light blocking element. It is also within the scope of the present invention that the light blocking element is not ideally opaque, and the substrate and optionally the underfiller are not ideally transparent. Within the scope of the present invention, an opacity or transparency may exist with regard to only certain light wavelengths or light length ranges of a light source with which the optoelectronic module cooperates. The decisive factor is that a considerable suppression of parasitic or unwanted light in favor of the useful light is attained for at least a certain light wavelength. 
     The module may be purely a receiver module that cooperates with an external artificial or natural light source. In that case, the light blocking element especially suppresses the interfering influence of scattered and extraneous light. However, it can also be purely an emitter module that especially effectively transmits light to some external object. It can also be an emitter-receiver module, in which an emitter is disposed on the chip, and the light blocking element is disposed between the emitter and the sensor. The emitter can in particular be an LED. The light blocking element prevents both optical crosstalk from the emitter to the sensor and the incidence of extraneous light onto the sensor. 
     Especially if underfillers or some similar optically transparent potting compound is employed, the parasitic or unwanted light due to scattering and reflection is minimized in the module, and thermomechanical stresses in the overall structure can also be kept very low. Such stresses can be due in particular to the different coefficients of thermal expansion of the materials. To adapt the coefficients of expansion toward that of gold bumps, underfillers are often filled with finely ground quartz, but this in turn increases the proportion of scattered light. The present invention makes it easier to use such underfillers and ,thus, to reduce thermomechanical stresses. 
     The light blocking element is preferably of a conformable material that conforms to the chip and/or to the transparent substrate. This counteracts a passage of light between the light blocking element and the chip or substrate. For production reasons, however, the light blocking element can be solidly joined to the chip and/or the transparent substrate for this purpose. Thus, the light blocking element can include a commercially available silicone rubber or some other injection moldable material. For economic production, this material can already be applied to the wafer of the chip with a dispenser before the wafer is sawn apart. Another economical method uses a printable material, which is applied as a light blocking element by screen printing, for instance. In this way, light blocking elements can also be printed on in the wafer grouping. Naturally, it is also conceivable to apply the light blocking element to the transparent substrate and then to mount the chip. 
     The light blocking element is preferably elastically deformable. To that end, it can comprise silicone or some other elastically deformable material. It can be disposed, elastically prestressed, between the transparent substrate and the chip. The elastic light blocking element is capable of compensating for tolerances in the spacing between the transparent substrate and the optoelectronic chip that are due in particular to the technology of the connecting elements. In gold bumps, for instance, differences in spacing of approximately 20% are entirely normal. The elasticity assures a good lightproof contact with both the transparent substrate and the chip that prevents a passage of parasitic or unwanted light through them. 
     Precisely in the case of an elastic light blocking element, the bonding wires and/or leads needed can be passed between contacting faces of the light blocking element on the chip and/or on the transparent substrate. These bonding wires and/or conductor tracks can lead to an emitter and/or to a sensor. The bonding wires of an emitter can, however, also be passed through the light blocking element. The elastic light blocking element can also compensate for tolerances in the amount of underfiller employed, if the underfiller is positively displaced laterally in the bonding of the chip and the substrate. 
     The light blocking element can have various shapes. The suppression of parasitic or unwanted light is especially advantageous if the light blocking element surrounds the sensor and/or the emitter. In the case of an emitter-receiver module with a central light emitter and sensors distributed around it, for instance, the light blocking element can be disposed around the emitter. Especially in this case, it can be circular-annular in shape. It can also be embodied in matrix form in accordance with the disposition of a plurality of sensors on one chip and can surround a plurality of sensors. 
     The light blocking element can be; manufactured as a micromolded part. It can have specially designed channels that enable the underfiller to be introduced after the chip has been mounted on the substrate. Special laminations disposed in meandering fashion in the channels allow the underfiller to flow through, on the hand, and on the other they assure maximum lightproofness. 
     The inside face of the light blocking element can also be embodied such that it contributes to a better light yield from the light source. To that end, it can have a spherical, a spherical or planar form. As a result, an otherwise ineffective edge radiation from an LED can be utilized by targeted reflection from the inside face of the light blocking element. 
     The module can be used in particular in an optoelectronic instrument for measuring travel, angle or rotation. To that end, the emitter can be disposed either on the module or outside the module. The transparent substrate can then have a scanning grating for scanning of a scale. 
     The invention will be described in further detail below in terms of exemplary embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic longitudinal section through a first embodiment of a emitter-receiver module and an optical position measuring instrument; according to the present invention 
     FIG. 2, in an enlarged detail of FIG. 1, shows the development of the emitter-receiver module and optical position measuring instrument of, scattered light in the underfiller; 
     FIG. 3 is a schematic longitudinal section of a first embodiment of a light blocking element embodied as a molded part; according to the present invention 
     FIG. 4 is a schematic longitudinal section through a second embodiment of a emitter-receiver module with the light blocking element of FIG. 3 and a depth-structured chip; according to the present invention 
     FIG. 5 is a detail of a third embodiment of a emitter-receiver module with a further light blocking element; according to the present invention 
     FIG. 6 is a detail of a fourth embodiment of a module according to the present invention; 
     FIG. 7 is a detail of a fifth embodiment of a module according to the present invention; 
     FIG. 8 is a detail of a sixth embodiment of a module according to the present invention; 
     FIG. 9 is a detail of a seventh embodiment of a module according to the present invention; and 
     FIG. 10 is a schematic longitudinal section through an eighth embodiment of a module according to the present invention; in an angle measuring instrument operating by the transmitted light principle according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Elements in the various exemplary embodiments that match one another are identified by the same reference numerals in the ensuing description. In this sense, the description has validity for all the exemplary embodiments involved. When the terms “top” and “bottom” are used, they pertain how the elements are disposed in the drawings. 
     In FIG. 1, an emitter-receiver module  1  has a transparent substrate  2 , which in this example is platelike and is of glass. On its surface, it has conductor tracks  3 ,  4 . On the underside, it is provided with a matrix structure  5 —also known as a scanning grating—including a succession of transparent and opaque regions each of constant length, which by way of example can be printed on or scratched in. 
     A chip  6  (semiconductor substrate) is disposed on the upper side of the substrate  2  and is fixed via gold bumps  7 ,  8  to the conductor tracks  3 ,  4  of the substrate  2  and electrically conductively joined to them. On the side toward the substrate  2 , the chip  6  has a plurality of sensor surfaces  9 ,  10 , which belong to integrated optoelectronic sensors. 
     Also on the side of the chip  6  toward the substrate  2 , an optoelectronic emitter  11  is provided. It is located in the center of the chip  6  between the sensors  9 ,  10 . In this example, it is a gallium arsenide light emitting diode  1   1  which is mounted in an indentation  12  in the underside of the chip and is contacted via bonding wires  13 ,  14  to conductor tracks on the underside of the chip  6 . 
     For passivation and to improve the mechanical stability, an underfiller  16  is disposed in this flip-chip structure in the intermediate space between the substrate  2  and the chip  6 . The underfiller is transparent at least for the wavelength or wavelength range of the light transmitted by the emitter  11  and received by the sensors  9 ,  10 . Such underfillers  16  as a rule include hardening plastic material, such as epoxy resin or silicone, which has a coefficient of thermal expansion that leads to strains in the emitter-receiver module  1 . To adapt this coefficient of expansion to that of the gold bumps  7 ,  8 , the underfiller  16  can be filled with quartz powder or quartz beads  17 , as shown in FIG.  2 . FIG. 2 also shows that of the light  18  projected by the LED  11 , only a portion  18 . 1  (useful portion) directly passes through the transparent substrate  2  to reach the sensors  9 ,  10 . Another portion is projected as edge radiation  18 . 2  directly from the side of the LED  11 . A further portion  18 . 3  is reflected once or multiple times by the quartz particles  17 . There are also portions  18 . 4  and  18 . 5  that are reflected from the surfaces of the substrate  2 . 
     To keep the parasitic or unwanted light  18 . 2 - 18 . 5  in the underfiller  16  away from the sensor surfaces  9 ,  10 , an annular, opaque light blocking element  19  is disposed between the chip  6  and the substrate  2  in FIG.  1 . This light blocking element  19  can in particular include commercially available silicone rubber. For the sake of economical production, the light blocking element  19  can already be applied with a dispenser to a wafer that has not yet been sawn apart and that includes the chip  6 . Another economical method for applying the light blocking element  19  that can be considered is screen printing. By it, light blocking elements  19  can also be printed on in the wafer grouping. It is also conceivable to apply the light blocking element  19  to the substrate  2  and then to put the chip  6  in place and fix it. 
     One advantage of an elastic light blocking element  19  is that it can compensate for tolerances in the height of the gold bumps  7 ,  8  and can have a good lightproof contact with the substrate  2  and the chip  6 . It can also compensate for tolerances in the quantity of underfiller  16  inside and outside the light blocking element  19  that are caused by expansion. The bonding wires  13 ,  14  can also be passed through as needed, without having to provide special openings, since the material of the elastic light blocking element  19  is positively displaced at the locations where the bonding wires are. 
     Thus the light  18 . 1  emerging from the glass substrate  2  after passing through the matrix structure  5  preferentially reaches the sensors  9 ,  10 . To that end, a scale  200  is associated with the underside of the emitter-receiver module  1 ; it has a surface, oriented parallel to the substrate  2 , with a reflective matrix structure  20 —also known as a measuring graduation. This structure or division can be applied or printed on or scratched in in a known manner by lithographic processes. 
     The light is reflected by the reflecting fields of the scale  200  and passes through the transparent regions of the scanning grating  5  of the substrate  2  to reach the sensors  9 ,  10 . The light  18 . 1  is at best reflected weakly by the nonreflective fields of the scale  200 , and these reflections are also kept away from the sensors  9 ,  10  by associated dark fields of the scanning grating  5  of the substrate  2 . As a consequence, a very highly modulated light signal reaches the sensors  9 ,  10 , and parasitic or unwanted light  18 . 2 - 18 . 5  from the emitter  11  is suppressed practically  15  entirely. 
     According to FIG. 3, a light blocking element  19  can be embodied as a micromolded part, in particular of elastic material. The element shown is embodied circular- cylindrically on its outer circumference. On the upper side, it has radially extending channels  21 , through which an underfiller  16 , even after assembly of the flip chip assembly, can be placed with the inclusion of this light blocking element  19  in the interior  22  thereof, and through which bonding wires  13  can also be passed as needed. The channels  21  can have meandering laminations—not shown in the drawing—that enable the underfiller  16  to flow through but assure maximal lightproofness. The interior  22  can have a specially designed inner surface  23  which is conically shaped in the region. It can contribute to the light yield of the emitter  11  by reflecting the otherwise ineffective edge radiation  18 . 2  or also scattered radiation  18 . 3  inside the underfiller  16  in the direction of the desired light radiation  18 . 1 . 
     In FIG. 4, a similar arrangement to FIG. 1 is shown, but its module  1  has a light blocking element  19  as in FIG. 3. A light emitting diode  11  is also sunk into the indentation  12  of the chip  6  in such a way that as a result the sensors  9 ,  10  are already shielded from its edge radiation  18 . 2 . Thus, it is above all the scattered light components  18 . 3 - 18 . 5  that are shielded off by the light guard barrier  19 . The bonding wires—not shown—needed for the electrical connection of the LED  11  can be passed between the light blocking element  19  and the substrate  2 . Because of the elasticity of the light blocking element  19 , the bonding wires are pressed in lightproof and sealing fashion against the substrate  2  or the chip  6 . 
     In FIG. 5, another embodiment of a light blocking element  19  is shown. It includes mutually offset annular ribs  19 . 1  and  19 . 2 . One of the ribs  19 . 1  is applied as an annular shutter on the chip  6 , and the other rib  19 . 2 , of somewhat lesser diameter, is applied to the transparent substrate. The height of each of the ribs  19 . 1  and  19 . 2  is somewhat less than the spacing between the chip  6  and the substrate  2 . The ribs  19 . 1 ,  19 . 2  guarantee extensive lightproofness for the radiation  18 . 2 - 18 . 5 , but allow the underfiller  16  to flow through and also as needed allow the bonding wires  13 ,  14  to be passed through the gap between the ribs  19 . 1  and  19 . 2 . This arrangement has the advantage that the light blocking element  19  can be manufactured with greater tolerance in terms of height, yet nevertheless secure light sealing and forceless bridging of the spacing are achieved. 
     To enable manufacturing the light blocking element  19  with high tolerance in terms of height, it can alternatively include a single rib  19 , which penetrates an indentation  15  in the chip  6  and/or substrate  2 , as shown in FIG.  6 . 
     The light blocking element  19  can also perform the function of stopping the flow of underfiller  16 . Then the underfiller  16  can be disposed on only one side of the light blocking element  19 . It is advantageous to keep the space  22  around the emitter  11  free of underfiller  16 . This has the advantage that no mechanical strains act on the emitter  11 , and that the interfering radiation  18 . 3  is eliminated. One example of this is shown in FIG.  7 . 
     To avoid introducing of extraneous light laterally onto the sensors  9 ,  10 , an additional light blocking element  24  or  24 . 1  can be disposed in the outer region of the chip  6  next to the gold bumps  7 ,  8 . This light blocking element also reduces the influence of extraneous light that is reflected from the scale  200 . As a consequence, these versions have a further improved ratio of useful light to parasitic or unwanted light. In FIG. 8, this additional light blocking element is an elastic seal  24  in the form of an annular shutter and in FIG. 9 it is an encompassing opaque coating  24 . 1  of the underfiller  16 . 
     FIG. 10 shows a transmitted light arrangement, in which the module  1  is purely a receiver module. Once again it has a platelike transparent substrate  2 , which is joined to a chip  6  via gold bumps  7 ,  8 . The chip  6  has a photodiode array  9 ,  9 ′,  10 , ( 9 ,  10 ′ not shown) with light-sensitive surfaces, which are surrounded by a matrixlike light blocking element  19 . For economical production, the matrixlike light blocking element  19  can be printed on using a screen printing template. 
     Between the substrate  2  and the chip  6 , an underfiller  16  is located inside the openings of the light blocking element  19 . 
     In FIG. 10, a scale in the form of a code disk  200  is associated with the module  1  on the side of the substrate  2 ; this disk is rotatable about an axis  26 . In a region through which light can be projected, the disk has a matrix structure  20  of bright and dark fields through which light can be transmitted. On the top of the substrate  2 , a corresponding matrix structure  5 —shown only schematically, with four 90° phase-shifted scanning gratings, one of which is assigned to each of the sensors  9 ,  9 ′,  10 ,  10 ′, is associated with the matrix structure  20 . 
     A light emitting diode  28  is disposed above the code disk  200 , and a condenser  29  is disposed between them. 
     The light emitting diode  28  and the condenser  29  generate a parallel beam of light  30 , which shines through the matrix structure  20  of the code disk  200 . This rotary—position-dependent pattern of light then strikes the four 90° phase-shifted scanning gratings  5  of the substrate  2 . As a consequence, four sinusoidally modulated streams of light are created, of each of which a portion again strikes a sensor  9 ,  9 ′,  10 ,  10 ′ of the four-field diode array on the chip  6 , which generates corresponding position-dependent electrical signals. Optical crosstalk between the various light signals is prevented by the matrixlike light blocking element  19 . 
     In a manner not shown, the light blocking element can also be formed by the contacting elements  7 ,  8 , by lining up individual gold bumps next to each other, or by placing a solder wire on one face of the substrate  2  and/or chip  6 . In these embodiments, the light blocking element has a dual function, namely light shielding and electrical contacting. 
     The invention may be embodied in other forms than those specifically disclosed herein without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive, and the scope of the invention is commensurate with the appended claims rather than the foregoing description.