JP3900595B2 - Photoelectric device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a photoelectric device having a light emitting element and a light receiving element used for a photo interrupter, an LED display, an image scanner, and the like, and more particularly to a photoelectric device having stable photoelectric characteristics regardless of manufacturing conditions and use environments. is there.
[0002]
[Prior art]
Today, with the development of silicon technology such as LSI, a large amount of information can be processed and used. Along with this, there is an increasing demand from society for photoelectric devices capable of detecting or displaying various information.
[0003]
Specifically, examples of the optical semiconductor element include a light emitting element such as an LED chip and an LD (hereinafter also referred to as a laser diode), a light receiving element such as an optical sensor, and a solar cell. The optical semiconductor element is placed on a substrate and covered with a mold resin from the viewpoint of protecting the element itself from moisture, dust, or the like or making it easy to mount. The photoelectric device having such a configuration has begun to be used in various fields such as an LED display, an optical disk, and FA (factory automation). As the field of use expands, it has begun to be used in various environments such as outdoors.
[0004]
As an optical semiconductor element used for a photoelectric device, a structure in which a pair of electrodes are provided via a semiconductor and a structure in which electrodes corresponding to a positive electrode and a negative electrode are provided on the same plane side of the optical semiconductor element (hereinafter referred to as “optical semiconductor element”) , Also called planar structure).
[0005]
As shown in FIG. 6, a photoelectric device using an optical semiconductor element provided with an electrode through a semiconductor is electrically connected to one external electrode on a substrate using an Ag pace. Further, the other electrode of the optical semiconductor element is electrically connected to the other external electrode formed in a pair by wire bonding using a gold wire or the like. The optical semiconductor element that is electrically connected to the external electrode is molded with an epoxy resin or the like to form a photoelectric device that can be used in various environments. By supplying or receiving power to the external electrode provided on the substrate, the optical semiconductor element can emit light or generate power. Such a photoelectric device can be formed relatively easily, but the wire is easily damaged by an external force and is difficult to reduce in size. Furthermore, there is a problem that the wire becomes an obstacle to light.
[0006]
On the other hand, a photoelectric device using an optical semiconductor element having a planar structure, as shown in FIG. 5, uses a pair of external electrodes provided on a substrate and an electrode of an optical semiconductor element provided on the same plane side using an Ag paste. Connecting. An optical semiconductor device is formed by molding an optical semiconductor element electrically connected to an external electrode formed on a substrate with an epoxy resin or the like. This photoelectric device has a feature that there is no inconvenience caused by wires.
[0007]
[Problems to be solved by the invention]
However, a photoelectric device using an optical semiconductor element having a planar structure has an increased contact resistance after the molding member is formed, compared to a photoelectric device using an optical semiconductor element in which an electrode is formed through a semiconductor element. There is a strong tendency to not. Further, there is a tendency that the light emission luminance or the like is lowered or the probability of non-lighting is high under an environment where the temperature and humidity cycle is intense. Similarly, as the translucent resin, which is a mold member that protects from the external environment, is made thicker, the probability that light emission luminance is reduced or non-lighting tends to increase. Nowadays, where more excellent photoelectric characteristics are required, the photoelectric device having the above configuration is not sufficient, and further improvement in characteristics is required.
[0008]
[Means for Solving the Problems]
The present invention relates to a planar structure type optical semiconductor element having a positive electrode and a negative electrode on the same plane electrically connected to each other via a conductive member on a pair of electrodes provided on a substrate, and the optical semiconductor element And a mold member to be sealed.
[0009]
In particular, according to the present invention, the width of the pair of external electrodes becomes narrower as it approaches between the electrodes facing each other, and the area of the external electrode projected on the electrode of the optical semiconductor element is the electrode of the optical semiconductor element. Each is smaller than the area.
[0010]
In the photoelectric device according to claim 2 of the present invention, the surface height of the external electrode is higher than that of the substrate surface.
[0011]
In the photoelectric device according to claim 3 of the present invention, the optical semiconductor element is a nitride compound semiconductor formed on a sapphire substrate.
[0012]
[Action]
In the present invention, when an optical semiconductor element having an electrode on the same plane side is electrically connected to an external electrode on a substrate using a conductive member, a mold member is disposed in the space between the optical semiconductor element, the substrate and the opposing external electrode. Adhesiveness can be improved by making it easy to flow. Furthermore, it is possible to further improve the adhesion while preventing a short circuit between the electrodes due to the inflow of an extra conductive member.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various experiments, the present inventor has found that the photoelectric characteristics in a photoelectric device using an optical semiconductor element having electrodes on the same plane side are greatly changed depending on the shape of a specific electrode provided on the substrate. The present invention has been achieved.
[0014]
The reason for the improvement in characteristics according to the present invention is not clear, but there is a large relationship between the mold member flowing into the space between the electrodes on the same plane provided in the optical semiconductor element and the external electrode provided on the substrate, and the adhesion. It is believed that there is.
[0015]
That is, the mold member functions to protect and fix the optical semiconductor element. However, when the mold member is cured or a temperature change occurs, the mold member is subjected to a stress that contracts in a substantially central direction of the mold member. Usually, since the mold member is formed on the optical semiconductor element, the center where the mold member contracts is on the optical semiconductor element. Therefore, when viewed from the optical semiconductor element side, a force is applied in a direction in which the optical semiconductor element is peeled off from the substrate as shown in FIG.
[0016]
The space between the external electrodes provided on the same plane side is extremely narrow, usually several hundred μm or less as the size is reduced. Further, since the mold member must be inserted from the gap between the pair of electrodes, the mold member is difficult to enter. Therefore, it is easy to create a place where there is no mold member or between the electrodes of the optical semiconductor element. The place where the mold member does not enter becomes a hole, and the force for bonding the optical semiconductor element and the external electrode is weakened. Therefore, if the optical semiconductor element and the substrate are not firmly bonded, the conductive member may be peeled off, cracked, or the optical semiconductor element itself may be damaged during thermal curing or in an environment where the temperature changes rapidly. It seems that it tends to be easy. FIG. 2 shows a specific configuration example of the present invention.
[0017]
A nitride semiconductor formed on a sapphire substrate was used as an optical semiconductor element. The nitride semiconductor is formed by sequentially forming an N-type semiconductor and a P-type semiconductor and etching a part of the P-type semiconductor to expose the surface of each PN semiconductor of the gallium nitride-based compound semiconductor. Each electrode is formed on the exposed surface of the semiconductor by sputtering. In this way, an LED chip which is an optical semiconductor element having electrodes on the same plane side is formed.
[0018]
On the other hand, a copper plate is bent as an external electrode. A package having a copper plate as an external electrode was formed by insert molding. Here, the copper plate is adapted to the distance between the electrodes of the LED chip to be mounted. Further, the electrodes of the opposing substrates are formed in a convex shape (triangular shape) so that the area becomes smaller as they approach. After applying the Ag paste to the external electrodes of the substrate, the electrodes of the LED chip were aligned and die-bonded. The photoelectric device of the present invention was constituted by injecting a mold member around the LED chip after curing the Ag paste. The LED chip can be made to emit light by supplying power to an external electrode provided outside the substrate. In addition, a light-emitting device having excellent photoelectric characteristics can be obtained even in an environment where the temperature and humidity cycle is relatively severe. Hereafter, each structure of this invention is explained in full detail.
[0019]
(External electrodes 101, 111, 121)
The external electrode 101 can be connected to each electrode 113 provided on at least the substrate and formed in the planar structure type optical semiconductor element by the conductive member 201. The external electrode 101 may be formed by a conductive pattern provided on the substrate, or may be formed by processing a lead frame. Since the external electrode 101 is connected to the electrode of the optical semiconductor element, it is desired that the external electrode 101 has excellent electrical conductivity and adhesion. In addition, the external electrode 101 used in the present invention has a structure in which a mold member can easily enter the space between the substrate and the optical semiconductor element to improve adhesion. As a specific structure, as shown in FIG. 1, the tip is a pair of electrode shapes convex to each other, and a triangular shape can be mentioned. In addition, various structures such as a circular shape, an elliptical shape, a polygonal shape, and a three-dimensionally polygonal shape can be cited as the structure in which the mold member can easily enter.
[0020]
In particular, the electrode 113 of the optical semiconductor element itself is extremely small, and it is necessary to consider photoelectric characteristics, electrical conductivity, and adhesion, and the degree of freedom in design is small. On the other hand, the external electrode 101 is formed by etching a conductive pattern such as a copper foil provided on a substrate, or by forming a lead frame previously formed in a desired shape by insert molding or the like. Therefore, the degree of freedom in design can be widened regardless of the optical characteristics of the optical semiconductor element 103. Further, it can be easily formed in a relatively large area.
[0021]
Further, the external electrode 101 can be formed on the same plane as the integrated substrate plane 102 or can be made higher than the substrate plane 102. If the external electrode 101 is made higher than the substrate plane 102, the thickness of the flexible conductive resin member 201 other than the external electrode is increased. Therefore, even if distortion occurs due to heat or the like during self-heating of the optical semiconductor element 103 or heating from the surroundings, the amount of strain that can be absorbed is large and the conductive contact can be stabilized. Further, since the tip is convex, the mold member 202 can easily flow.
[0022]
Specific examples of such a material for the external electrode 101 include copper, aluminum, and those obtained by plating them with gold, silver, platinum, or the like.
[0023]
(Substrate 102)
The substrate 102 has external electrodes 101, 111, and 121 that support the optical semiconductor element 103 and can be electrically connected to the electrodes of the optical semiconductor element 103. Further, at least a part of the optical semiconductor element 103 fixed on the substrate 102 is covered with a translucent mold member 202 and bonded thereto. The substrate 102 may have a structure only on a plane, or may have a side wall 112 or the like integrated with a package that can store an optical semiconductor element.
[0024]
Specifically, it is possible to adopt a form in which an opening is provided inside the package and the optical semiconductor element 103 is mounted on the bottom surface of the opening. Utilizing such a side wall 112 can also improve the light utilization efficiency. In any case, the optical semiconductor element 103 has a plane that can be supported. Therefore, it is desirable that these and the substrate 102 have good adhesion. Furthermore, in order to accommodate and use the optical semiconductor element 103 having spectral characteristics in the visible light region, it is preferable that the optical semiconductor element 103 is colored so as to function as a light-shielding reflecting member. In addition, it is desirable to have an insulating property in order to electrically isolate the optical semiconductor element 103 from the outside.
[0025]
When the substrate 102 is affected by heat from the optical semiconductor element 103 or the like, it is preferable that the substrate 102 has a low coefficient of thermal expansion in consideration of adhesion to the mold member 202. The surface of the substrate 102 can be embossed to increase the adhesion area, or can be plasma-treated to improve adhesion with the mold member 202 or the conductive member 201.
[0026]
Specific examples of materials used for the substrate 102 include polycarbonate resin, polyphenylene sulfide (PPS), liquid crystal polymer (LCP), ABS resin, epoxy resin, phenol resin, acrylic resin, PBT resin, and the like, AlN, BN A ceramic made of Al ₂ O ₃ or the like can be preferably used.
[0027]
(Optical semiconductor element 103)
As the optical semiconductor element 103, a light receiving element that changes light into electricity or a light emitting element that changes electricity into light is used. The light receiving element is formed using a single crystal semiconductor such as Ge, Si, InAs, and CdS formed by using a liquid phase growth method, or by using various CVD methods using energy such as plasma, heat, and light. Suitable examples include photosensors using microcrystals such as Si, SiC, and SiGe, non-single-crystal semiconductors of amorphous semiconductors, and solar cells. Semiconductor structures include those having a Schottky junction, a MIS junction, a homostructure having a PN junction or a PIN junction, and a heterostructure. The light receiving wavelength of the light receiving element can be variously selected depending on the semiconductor material and the mixed crystal degree. A light-receiving element can be formed by forming a semiconductor having the above-described structure in a desired size on a glass, a heat-resistant resin, or a metal substrate and establishing electrical connection. As the electrode of the light receiving element, various metals such as Al, Ag and Au formed by sputtering and vacuum deposition, metal oxides such as SnO ₂ and ZnO, and n ⁺ semiconductors can be used.
[0028]
On the other hand, as a light emitting element, a semiconductor such as ZnS, ZnSe, SiC, GaP, GaAs, GaAlAs, GaAlP, AlInGaP, GaN, InN, AlN, InGaN, GaAlN, and AlInGaN is emitted on a substrate by a liquid phase growth method, MOCVD method, or the like. An LED, LD, or the like formed as a layer is used. Examples of the semiconductor structure include a homo structure having a MIS junction and a PN junction, a hetero structure, and a double hetero structure. Various emission wavelengths can be selected from ultraviolet light to infrared light depending on the material of the semiconductor layer and the degree of mixed crystal. Furthermore, the light emitting layer may have a single well structure or a multiple well structure in order to give a quantum effect.
[0029]
The formed semiconductor can be selectively formed, or etched after being formed, thereby forming an optical semiconductor element having a planar structure in which electrodes corresponding to a positive electrode and a negative electrode are formed on the same plane side.
[0030]
(Conductive members 201, 301, 302)
As the conductive member 201, each electrode 113 of the optical semiconductor element 103 and the external electrode 101 can be electrically connected and fixed. The conductive member 201 can be variously selected depending on the material of the external electrode 101 and the electrode 113 of the optical semiconductor element. Various conductive materials such as solder, gold, silver, platinum, copper, and carbon can be selected from epoxy resin and acrylic resin. An electrically conductive paste contained in a resin such as an imide resin can be suitably used.
[0031]
(Mold member 202)
The mold member 202 is provided in order to protect each optical semiconductor element 103 and the conductive member 201 for electrical connection thereof from external force or moisture. Specifically, a resin excellent in weather resistance such as an epoxy resin, a urea resin, a silicon resin, a fluororesin, and a polycarbonate resin is preferably used as the material of the mold member 202. The mold member 202 can cover the entire optical semiconductor element 103 in order to cover the substrate 102, the conductive member 201, and the electrode 113 of the optical semiconductor element, or at least a part thereof.
[0032]
A colorant that works as a filter effect according to the wavelength of light emitted from the optical semiconductor element 103 or the wavelength of light received, or at least a part of the light emitted from the optical semiconductor element 103 or a fluorescent substance that converts the wavelength from the outside may be included. it can. Furthermore, a diffusing agent may be mixed as desired. Specific embodiments of the present invention will be described in detail below, but the present invention is not limited thereto.
[0033]
【Example】
Example 1
As an optical semiconductor element having a planar structure, an LED chip using a gallium nitride based semiconductor as a light emitting layer on a sapphire substrate was used. The LED chip is formed by stacking N-type GaN, non-doped InGaN, and P-type GaAlN on a sapphire substrate using MOCVD. Note that GaN is formed as a buffer layer on the sapphire substrate, and InGaN serving as a non-doped light-emitting layer is a thin film having a quantum effect. A part of the formed P-type semiconductor is partially etched to expose the N-type semiconductor surface. A mask is formed in order to form an insulating layer except for the surfaces in contact with the positive and negative electrodes. Using a photomask, SiO ₂ that is an insulating layer is formed by sputtering so that both the positive and negative electrodes can be formed larger. A rectangular electrode is formed on each semiconductor exposed surface of PN and the insulating layer by sputtering.
[0034]
On the other hand, as an external electrode formed on the substrate, a lead frame obtained by punching a copper foil is used as the external electrode. The tip of the lead frame connected to the electrode of the optical semiconductor element has a semicircular shape that is thinned according to the electrode width of the optical semiconductor element. For this reason, the area of the external electrode projected on the electrode of the optical semiconductor element is smaller than the electrode area of the optical semiconductor element. The tips of the lead frames are arranged close to each other to about 100 μm, and insert molding is performed by an LCD containing a white pigment. The substrate thus formed has a pair of lead frames exposed at the bottom of the surface side. Between the lead frames, the tips facing each other have a semicircular shape with a convex shape. In addition, side walls for reflecting light from the optical semiconductor element and condensing light to the optical semiconductor element are integrally formed around the bottom surface. The lead frame on the bottom surface of the package, which is the substrate surface, is formed to be approximately 10 μm higher than the polycarbonate resin surface.
[0035]
A silver paste containing Ag in an epoxy resin was applied to the tip of the pair of lead frames on the lead frame on the bottom of the package. Thereafter, the lead frame coated with the Ag paste and the electrode of the LED chip were combined and die-bonded. After die bonding, the Ag paste was cured at 120 ° C. for 20 minutes to perform electrical connection and temporary fixing. In this state, power was supplied to the external electrode to form 300 LED chips capable of emitting light.
[0036]
Next, an epoxy resin serving as a translucent mold member was injected into the opening of the package. A surface mount LED was constructed by curing an epoxy resin as a mold member at 150 ° C. for 2 hours. Electric power was supplied to the formed photoelectric device, and each photoelectric device was examined with a photometer. All the photoelectric devices were able to emit light before and after forming the mold member. The luminous intensity increased by 50%, which is considered that the refractive index difference from the LED chip was relaxed by the mold member. Furthermore, after repeating 100 cycles of −5 ° 5 minutes 80 ° 10 minutes as a temperature and humidity cycle test, the light emitting characteristics of the photoelectric device formed in the same manner were examined, but there was no change.
[0037]
(Comparative Example 1)
It was formed in the same manner as in Example 1 except that the opposing external electrode tips were flat with each other, and the external electrode surface and the substrate surface were substantially flat. The light-emitting diode, which was a surface-mounted LED that could emit light before forming the mold member, exhibited the same light-emitting characteristics as in Example 1. When the same light-emitting diode after forming the mold member was examined, the light emission luminance was lower than that of Example 1, or 21% of the light-emitting diodes did not emit light.
[0038]
(Example 2)
A light receiving element was used in place of the LED chip which is a light emitting element. The lead frame was formed in the same manner as in Example 1 except that the tip of the lead frame was changed from a semicircular shape to a triangular shape. The light receiving element used was an N-type gallium nitride semiconductor formed on a sapphire substrate using MOCVD. On the N-type gallium nitride semiconductor, a pair of Au electrodes is formed by vacuum deposition so as to be an optical sensor having a planar structure. There was almost no difference in flowing current before and after the temperature and humidity cycle test.
[0039]
(Comparative Example 1)
As the optical semiconductor element, the same light receiving element as in Example 2 was used. Further, a photoelectric device was formed in the same manner as in Example 2, except that the opposing external electrode tips were flat with each other, and the external electrode surface and the substrate surface were substantially flat. A temperature and humidity cycle test was conducted in the same manner as in Example 1. After the temperature / humidity cycle test, about 15% of the internal resistance increased as compared with Example 2.
[0040]
【effect】
With the structure of the present invention, a photoelectric device with stable photoelectric characteristics can be obtained. In particular, stable photoelectric characteristics can be exhibited regardless of the formation and use environment of a photoelectric device in which an optical semiconductor element having a planar structure electrically connected to a substrate is covered with a mold member. It is to be noted that the optical semiconductor element is extremely small, and the degree of freedom in design is reduced when the electrodes are formed in various shapes. On the other hand, the degree of freedom in design can be improved by making the external electrodes provided on the substrate in a desired shape as in the present invention.
[0041]
By adopting the configuration described in claim 2 of the present invention, even if there is an extra conductive member, it can be formed without a short circuit between the pair of external electrodes. That is, the adhesion can be improved by increasing the number of conductive members. However, in a planar structure type photoelectric device, if the number of conductive members is increased, there is a risk that a short circuit will occur. The present invention can improve the adhesion without short-circuiting by utilizing the fact that the amount of the conductive member applied on the substrate depends to some extent on the size on the substrate.
[0042]
By adopting the configuration described in claim 3 of the present invention, it is possible to further improve the adhesion by using an extra conductive member protruding from the external electrode. In addition, since the thickness of the conductive member formed between the substrate surface and the electrode can be partially increased, electrical conduction and adhesion can be functionally separated. Therefore, between the electrode of the optical semiconductor element and the external electrode, the amount of strain that can be absorbed by thermal contraction can be increased without reducing the electrical conductivity by reducing the thickness of the conductive member.
[0043]
According to the configuration of the fourth aspect of the present invention, the force applied to the semiconductor element itself can be suppressed, so that the effect of the present invention can be made remarkable.
[Brief description of the drawings]
FIG. 1 is a schematic plan view showing a photoelectric device of the present invention.
2 is a cross-sectional view taken along the line AA in FIG. 1 showing the photoelectric device of the present invention.
3 is a cross-sectional view taken along the line BB in FIG. 1 for explaining the operation of the photoelectric device of the present invention.
FIG. 4 is a plan view of a photoelectric device using an optical semiconductor element having a planar structure shown for comparison with the present invention.
5 is a cross-sectional view taken along line AA in FIG. 4, which is a photoelectric device shown for comparison with the present invention.
FIG. 6 is a cross-sectional view of a photoelectric device using an optical semiconductor element having a pair of electrodes through a semiconductor shown for comparison with the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... External electrode 111 projected on the electrode of an optical semiconductor element ... The external electrode 121 continuous with the front-end | tip part ... The external electrode 102 electrically connectable with the exterior ... The board | substrate 112 used as a package bottom face ... Side wall 103 constituting package ... Optical semiconductor element 113 having planar structure ... A pair of electrodes 201 formed on the optical semiconductor element ... Conductive member 202 ... Mold member 203 ... Space 301 between electrodes of optical semiconductor element and external electrode provided on substrate ... conductive member 302 on external electrode ... conductive member 401 protruding from external electrode ... external electrode 421 ... External electrode 402 that can be electrically connected to the outside, substrate 412 serving as the bottom of the package, side wall 403 constituting the package, and optical semiconductor element having a planar structure 413: A pair of electrodes 501 formed on the optical semiconductor element ... Conductive member 502 ... Mold member 503 ... A space 601 between the electrodes of the optical semiconductor element and an external electrode provided on the substrate. ... Conductive wire 603 ... Optical semiconductor element 613 having electrodes provided through a semiconductor ... Electrodes formed on the optical semiconductor element

Claims (3)

An optical semiconductor element having a positive electrode and a negative electrode on the same plane electrically connected to each other via a conductive member on a pair of external electrodes provided on the substrate; a mold member for sealing the optical semiconductor element; A photoelectric device comprising:
The width of the pair of external electrodes becomes narrower as it approaches between the electrodes facing each other, and the area of the external electrode projected onto the electrode of the optical semiconductor element is smaller than the electrode area of the optical semiconductor element, respectively. A photoelectric device. The photoelectric device according to claim 1, wherein a surface height of the external electrode is higher than a surface of the substrate. The photoelectric device according to claim 1, wherein the optical semiconductor element is a nitride-based compound semiconductor formed on a sapphire substrate.

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