JPH09189514A - Optical displacement detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical displacement detection device in which optical characteristics of the light reception surface of a light reception element cannot deteriorate, and problems such as peeling-off due to the fluctuation in external temperature does not occur. SOLUTION: A light reception element IC21' with a light reception surface where a photo sensitive zone is formed in a fine pitch on a substrate 23 is provided on a surface which is opposed to a main scale of a substrate 29 which is arranged opposite to the main scale. A light reception means is constituted by applying a cover plate 42 made of a glass with a light transmission property onto the light reception surface of the light reception element IC21' and at the same time covering a surface excluding the light reception surface of the light reception element IC21' with a heat-resistance resin 44.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical displacement detecting device. Specifically, a main scale having an optical grating in which light transmitting portions and light blocking portions are alternately arranged at a constant pitch, an illuminating unit arranged on one side of the main scale, and the illumination with the main scale interposed therebetween. The present invention relates to an optical displacement detection device including a light receiving unit arranged on the opposite side of the system and detecting the relative displacement amount between the main scale and the light receiving unit.

[0002]

BACKGROUND ART A main scale having an optical grating having a constant pitch and an index scale having an optical grating corresponding to the main grating are arranged so as to be capable of relative displacement, and one side is sandwiched between these scales. An optical displacement that arranges the light emitting device and the light receiving device on the other side, obtains a detection signal by the light receiving device when both scales are relatively displaced, and then detects the relative displacement amount of both scales based on this detection signal. Detection devices are known.

Recently, in this type of optical displacement detection device, further miniaturization and cost reduction are required, so that the photodetector itself is composed of a photodetector array of a constant pitch and also serves as an index scale. An optical displacement detection device having such a structure has been proposed. As shown in FIG. 1, this is because the light transmitting portion 12A having substantially the same width is formed on the glass substrate 11.
A main scale 13 having an optical grating 12 in which the light shields 12B and the light blocking portions 12B are alternately arranged at a constant pitch; a lighting unit 16 including a light source 14 and a collimator lens 15 arranged on one side of the main scale 13; The light-receiving element 21 is arranged opposite to the illuminating means 16 with the main scale 13 interposed therebetween.

Here, as the light receiving element 21, as shown in FIGS. 2 and 3, a P-type semiconductor layer 24A is diffused and formed at a constant pitch on an N-type semiconductor substrate 23 made of silicon to form a photosensitive band 25. Thing, that is, N-type semiconductor substrate 2
3 and the P-type semiconductor layer 24A, the light-receiving element IC 21A having a structure in which the photosensitive band 25 is formed, or as shown in FIGS. 4 and 5, a P-type semiconductor layer 24B is formed on the N-type semiconductor substrate 23. There is known a light receiving element IC21B having a structure in which a transparent insulating film 26 made of silicon oxide or the like is formed thereon, and then a grid-like light shielding film 27 is formed on the insulating film 26 by a metal (aluminum) thin film.

Since these light receiving elements IC21A and 21B (hereinafter referred to as "light receiving element IC21 '") function as a conventional index scale and a light receiver, they have the advantages of a simple structure and high reliability. Moreover, since these can be manufactured by the IC process, there is an advantage that an amplifier circuit and the like can be built in. In such an optical displacement detection device, when the interference light transmitted through the main scale 13 is used with a fine pitch in which the intervals of the photosensitive bands 25 of the light receiving element IC 21 ′ are several tens of μm or less, the influence of waveform distortion is affected In order to reduce or obtain an optimum signal amplitude, it is necessary to perform positioning on the order of several tens of μm from the main scale 13 to the light receiving element IC 21 ′.

However, as described above, in the light-receiving element IC21 'having a structure in which the light-receiving surface also serves as an index scale, the positioning with respect to the main scale 13 is a distance from the base 23, so that this is a mechanical assembly reference plane. Is extremely difficult to use as. Because the light receiving element I
This is because the chip of C21 'is very small, such as a few millimeters square, and wire bonding is performed to extract a signal from the light receiving element IC21'. By the way, in the case of the conventional structure using the index scale and the light receiver, since the glass substrate is used for the index scale, the assembly can be performed with reference to the glass surface for positioning.

Therefore, as shown in FIG. 6, the light receiving element IC
21 'is die-bonded onto a substrate (for example, a lead frame, a ceramic substrate, a glass epoxy substrate, etc.) 29, and the upper surface of the substrate 29 is used as a reference plane for positioning with the main scale 13. The distance δ ₁ to the IC 21 ′ can be positioned on the order of several tens of μm. Usually, after the light receiving element IC21 ′ has completed the process such as forming the light receiving portion, the thickness t of the light receiving element IC21 ′ is on the order of 10 μm by passing through a process called a back lap for adjusting the thickness of the wafer. Since the upper surface of the substrate 29 is used as a reference surface for positioning with the main scale 13 (positioning with a distance δ ₂ ), the light receiving element IC is moved from the main scale 13 to the light receiving element IC.
The distance δ ₁ to the light receiving surface of 21 'can be positioned on the order of several tens of μm.

By the way, the light receiving element IC 21 'needs to be packaged in order to protect the bonding wire for taking out a signal and the light receiving surface. As a packaging method, as shown in FIG. 7, the whole is molded with a transparent resin 31, or as shown in FIG. 8, the light receiving element IC 21 ′ is sealed with a frame 32 and a cover glass 33, and the inside is sealed. There is known a method of enclosing nitrogen gas or the like in. In addition, in these FIGS.
28 is a bonding wire.

[0009]

The above packaging method has the following problems. [Molding with transparent resin (FIG. 7)] When taking out a signal from the minute light receiving surface formed on the light receiving element IC 21 ', since the signal is weak, it is desirable to provide a buffer circuit in the immediate vicinity of the wiring from which the signal is taken out. In the case where it is desired to provide a capacitor in the immediate vicinity of the light receiving element IC21 'to stabilize the power supply voltage, the light receiving element IC21', an amplifier circuit, and other peripheral components such as electronic circuits are mounted as close as possible. However, there are cases where you want to reduce the size. In these cases, in order to mount the peripheral components, it is necessary to perform soldering and high heat treatment such as reflow. At this time, the light receiving element IC21 'needs to be packaged in advance in order to prevent contamination due to handling, cutting of wires, and the like. However, since the transparent resin 31 is weak against heat, it cannot withstand the high heat at the time of component mounting due to reflow and the like, and it causes thermal deformation, so that component mounting on the same substrate is difficult.

Since the transparent resin 31 has a low hardness due to its characteristics, it is easily scratched by contact with metal (tweezers, jigs, etc.) during handling, which adversely affects optical characteristics. The expansion coefficient due to thermal expansion of the resin 31 is the light receiving element IC2
Since it is larger than 1 ', the light receiving element IC due to external heat fluctuation
It may cause peeling from the light receiving surface of 21 'or cutting of the wire 28. Since the resin 31 has water absorbency, the optical distance from the main scale 13 changes due to the swelling and the change in the refractive index due to the water absorption, and the light transmittance decreases due to coloring of the resin 31 such as white turbidity or brown. , Adversely affect the optical characteristics. When the light receiving element IC21 'includes an amplifier circuit, a logic circuit, and the like in addition to the light receiving portion, the circuit is formed by the P-N channel like the light receiving surface, and therefore, when the light is irradiated onto the circuit, the electrical characteristics are changed. It causes a malfunction of the circuit or deterioration of characteristics.

[Airtight Sealing with Cover Glass (FIG. 8)] In order to keep the airtightness inside, the substrate 29 must be made of an expensive material such as ceramics. An expensive device is required to seal the inside with nitrogen. When the light receiving element IC21 'includes an amplifier circuit, a logic circuit, and the like in addition to the light receiving portion, the circuit is formed by the P-N channel like the light receiving surface, and therefore, when the light is irradiated onto the circuit, the electrical characteristics are changed. It causes a malfunction of the circuit or deterioration of characteristics.

The object of the present invention is to solve all of the above-mentioned conventional problems, the optical characteristics of the light receiving surface of the light receiving element are not deteriorated, and there is no problem such as peeling even when the external temperature fluctuates. Moreover, it is to provide an optical displacement detection device that can be manufactured at low cost. Another object of the present invention is to provide an optical displacement detection device capable of preventing malfunction and characteristic deterioration due to incidence of light on the electronic circuit even when the light receiving element has another electronic circuit built therein. It is in.

[0013]

An optical displacement detection device according to the present invention comprises a main scale having an optical grating in which light transmitting portions and light blocking portions are alternately arranged at a constant pitch, and one side of the main scale. In the optical displacement detection device including an illuminating unit disposed on the main scale and a light receiving unit disposed on the opposite side of the main scale from the illuminating unit, the light receiving unit is opposed to the main scale. A displaceable substrate, a light-receiving element fixed to the surface of the substrate facing the main scale and having a light-receiving surface on which a photosensitive band is formed at a fine pitch, and a light-receiving surface of the light-receiving element. It is characterized in that it is provided with a cover plate made of attached glass having a light transmitting property, and a heat resistant resin for covering the outer surface of the light receiving element except the light receiving surface. Here, the light receiving element has, for example, a structure including a semiconductor base and a semiconductor layer formed on the semiconductor base and having a polarity different from that of the semiconductor base.

According to this structure, the cover plate is attached to the light receiving surface of the light receiving element. Since the cover plate is made of translucent glass, it has excellent heat resistance, and optical characteristics do not deteriorate even if other peripheral parts are attached by heating such as reflow or soldering. Therefore, small size mounting is possible. Further, since the expansion coefficient of the glass is substantially the same as the material of the substrate (eg, silicon) forming the light receiving element, the glass is not peeled off due to the fluctuation of the external temperature and is excellent in stability. At this time, if the cover plate is attached to the light-receiving surface of the light-receiving element via a translucent adhesive, the cover plate can be stably fixed to the light-receiving surface of the light-receiving element. Further, since it is made of glass, it is less likely to be scratched during handling, and there is no problem even if the surface is contaminated by washing with a solvent or the like. Furthermore, since it is excellent in moisture resistance and stability of optical characteristics (refractive index, parallelism, thickness),
The optical characteristics can be maintained for a long time.

On the other hand, the portion of the light receiving element excluding the light receiving surface is covered with a resin having heat resistance, so that it is excellent in reliability. If a resin having a light-shielding property is used as the resin, not only the heat resistance but also the transmission of light through the light-receiving surface can be prevented. Therefore, the light-receiving element is made into an IC and other electronic circuits are incorporated therein. Can prevent malfunction and deterioration of characteristics due to the incidence of light on the electronic circuit.
It is also possible to prevent light from being scattered on other than the light receiving surface. Further, since the structure is not hermetically sealed as in the conventional case, the substrate does not have to be an expensive ceramic material, and a device associated with the hermetic sealing can be eliminated, so that the cost can be reduced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG.
A detailed description will be given with reference to FIG. In the following description, the same components as those in the above-mentioned drawings are designated by the same reference numerals and the description thereof will be omitted. 9 and 10, the main scale 1 of the substrate 29 is shown.
3 on the surface (upper surface in FIG. 10) facing 3
C21 'is fixed. The cover plate 4 is provided on the light receiving surface of the light receiving element IC 21 ′, that is, the surface on which the photosensitive band 25 is formed, via a transparent adhesive 41 having a light transmitting property.
2 is directly attached.

The cover plate 42 is formed in the shape of a plate that is made of glass having heat resistance, moisture resistance, and translucency, and has a constant refractive index and thickness. Here, as the glass, one having excellent hardness and a thermal expansion coefficient substantially the same as that of the material of the base body 23 (silicon in this case) is used. As the adhesive 41, a UV adhesive, an epoxy adhesive, or the like is suitable. At this time, the light receiving element IC2
If a surfactant is applied to the surface of 1 ', it will not easily peel off.

On the substrate 29, a frame body 43 is provided in a rectangular frame shape so as to surround the light receiving element IC21 '. A resin 44 having heat resistance is provided in the frame body 43 to protect the light receiving element IC 21 ′ and the wire 28.
Is filled. That is, the outer surface of the light receiving element IC 21 ′ other than the surface to which the cover plate 42 is attached is covered with the heat resistant resin 44. Here, as a material of the resin 43, for example, an epoxy resin or the like can be used, and it is more preferable that the resin 43 is colored in black having a light shielding property.

Therefore, according to the structure of this embodiment, since the cover plate 42 made of glass having heat resistance, moisture resistance, and translucency is directly adhered to the light receiving surface of the light receiving element IC21 ', the other periphery is not formed. Even if the component is mounted on the substrate 29 by heating such as reflowing or soldering, the optical characteristics of the light-receiving surface are not deteriorated, so that small-sized mounting is possible.

The coefficient of thermal expansion of the cover plate 42 (the coefficient of thermal expansion of glass) is the material of the substrate 29 (silicon).
Since the cover plate 42 does not peel off from the light-receiving surface of the light-receiving element IC21 ′ even if the external temperature changes. In addition, since the cover plate 42 is attached to the light receiving surface of the light receiving element IC21 ′ via the translucent adhesive material 41, the cover plate 42 is attached to the light receiving element IC2.
Since it can be stably fixed to the light receiving surface 1 ', stability can be secured for a long period of time.

Further, since the glass forming the cover plate 42 has excellent hardness, it is hard to be scratched during handling, and there is no problem even if it is cleaned with a solvent when the surface is soiled. Furthermore, since it is also excellent in moisture resistance and optical characteristics (refractive index, parallelism, thickness), the optical characteristics can be maintained for a long time.

On the other hand, since the portion of the light receiving element IC21 'other than the light receiving surface is covered with the resin 44 having heat resistance, the light receiving element IC21' and the wire 28 are protected and the reliability can be secured. Further, if the resin 44 is colored black with a light-shielding property, not only the heat resistance but also the transmission of the light other than the light-receiving surface can be prevented, so that another electronic circuit can be provided inside the light-receiving element IC21 '. Even if it is built in, it is possible to prevent malfunction and deterioration of characteristics due to the incidence of light on the electronic circuit, and it is also possible to prevent light from scattering on other than the light receiving surface.

Further, since the structure is not hermetically sealed as in the prior art, the substrate 29 does not need to be made of an expensive material such as ceramics, and a device associated with the hermetic sealing can be dispensed with, so that the cost can be reduced. .

In the above-described embodiment, the light receiving element 21 includes the N-type semiconductor substrate 23 and the P-type semiconductor layers 24A and 24B formed on the semiconductor substrate 23 and having polarities different from those of the semiconductor substrate 23. Light receiving element IC21 '
However, the present invention is not limited to this structure. For example, an N-type semiconductor layer may be formed on the P-type semiconductor substrate 23 at a fine pitch.

Further, the resin 44 for covering the outer surface other than the light receiving surface of the light receiving element IC21 'is not limited to the epoxy resin mentioned in the above embodiment, and other resin may be used.
It does not matter whether it has a light-shielding property or not.

[0026]

According to the optical displacement detecting device of the present invention,
Since the cover plate made of transparent glass is attached to the light-receiving surface of the light-receiving element and the outer surface of the light-receiving element except the light-receiving surface is covered with heat-resistant resin, the optical characteristics of the light-receiving surface may deteriorate. In addition, there is no problem such as peeling even when the external temperature fluctuates, and the cost can be reduced. Further, even if the light receiving element has another electronic circuit built therein, it is possible to prevent malfunction and characteristic deterioration due to incidence of light on the other electronic circuit.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic structure of a general optical displacement detection device.

FIG. 2 is a perspective view showing a light receiving element used in an optical displacement detection device.

FIG. 3 is a sectional view taken along line III-III of FIG. 2;

FIG. 4 is a perspective view showing another light receiving element used in the optical displacement detection device.

FIG. 5 is a sectional view taken along line VV of FIG. 4;

FIG. 6 is a diagram for explaining the positioning accuracy of the optical displacement detection device.

FIG. 7 is a diagram showing a state where a light receiving element is molded with a transparent resin.

FIG. 8 is a diagram showing a state in which a light receiving element is sealed with a cover glass.

FIG. 9 is a plan view showing a light receiving means used in the optical displacement detection device of the present invention.

10 is a sectional view corresponding to line XX of FIG. 9.

[Explanation of symbols]

 12 Optical Grating 12A Light Transmitting Part 12B Light Blocking Part 13 Main Scale 16 Illuminating Means 21, 21A, 21B Photosensitive Element 23 N-type Semiconductor Substrate 24 P-type Semiconductor Layer 25 Photosensitive Band 29 Substrate 41 Adhesive 42 Cover Plate 44 Heat Resistant Resin

Claims (4)

[Claims] 1. A main scale having an optical grating in which light transmitting portions and light blocking portions are alternately arranged at a constant pitch,
Illumination means arranged on one side of this main scale,
In an optical displacement detection device including a light receiving unit arranged on the opposite side of the illuminating unit with the main scale sandwiched therebetween, the light receiving unit is a substrate arranged so as to be relatively displaceable facing the main scale. A light-receiving element having a light-receiving surface fixed to the surface of the substrate facing the main scale and having a photosensitive band formed on the substrate at a fine pitch, and a light-transmitting property attached to the light-receiving surface of the light-receiving element. An optical displacement detection device comprising: a cover plate made of glass; and a heat-resistant resin that covers the outer surface of the light-receiving element except the light-receiving surface. 2. The optical displacement detection device according to claim 1, wherein the light receiving element includes a semiconductor base and a semiconductor layer formed on the semiconductor base and having a polarity different from that of the semiconductor base. An optical displacement detection device characterized in that 3. The optical displacement detection device according to claim 2, wherein the resin has a light shielding property. 4. The optical displacement detection device according to claim 1, wherein the cover plate is attached to the light receiving surface of the light receiving element via a light-transmissive adhesive. An optical displacement detection device characterized by the above.