JP4582770B2 - Sealing resin for light emitting diode and light emitting diode using the same - Google Patents

Description

  The present invention relates to a sealing resin for a light emitting diode and a light emitting diode using the same.

  A light emitter (LED chip) of a light emitting diode (LED) is a solid element made of a semiconductor, and a junction (active layer) is formed by joining a p-type semiconductor and an n-type semiconductor and applying a bias voltage in the forward direction. Thus, the electrical energy is converted into light energy, and the converted light energy is emitted from the LED chip to the outside. Although the peak emission wavelength of the light emitted from the LED chip varies depending on the semiconductor material, it is in the ultraviolet to visible to infrared region, and the emission spectrum has a steep characteristic.

  In addition, the size and shape of the LED chip is an approximately hexahedron with a side length of about 0.5 mm. Since the light source is extremely small, the amount of emitted light is small and it has optical characteristics close to that of a point light source. ing. Therefore, in designing and manufacturing an LED using an LED chip having such characteristics as a light source, the ratio of the amount of light emitted from the LED chip to the amount of light emitted from the active layer of the LED chip (external quantum efficiency). Alternatively, a method of increasing light intensity on the optical axis of the LED by concentrating light emitted from the LED chip and emitted to the outside of the LED is performed.

Incidentally, light (incident light) from _one of the boundary planes (interface) formed by transparent bodies having different refractive indexes (transparent body having a refractive index of n1) to the interface forms an interface normal at the incident point. The angle (refractive angle) between the angle (incident angle) and the light (refracted light) that enters the other side (transparent body having a refractive index of n ₂ ) sandwiching the interface from the incident point of the interface with the normal of the interface In the case of n ₁ ≦ n ₂ , all the refracted light has a refractive index of n ₂ for the incident light from the transparent body having a refractive index of n ₁ regardless of the incident angle until the incident angle reaches 90 °. Enter the transparent body.

On the other hand, when n ₁ > n _2, the refraction angle may be 90 ° or more depending on the incident angle. At this time, there is no refracted light and the refraction angle is 90 ° (the incident angle at this time is the critical angle). The incident light travels parallel to the interface, and when the refraction angle exceeds 90 °, the incident light is reflected at the interface to be totally reflected and returns to the transparent body having a refractive index of n ₁ and transparent with a refractive index of n ₂ . It will not enter the body.

  Therefore, consider the light extraction efficiency when the light emitted from the active layer of the LED chip is emitted from the LED chip to the outside of the LED chip. For example, if an LED chip having a refractive index of 3 of the semiconductor material forming the light emitting surface is caused to emit light in the atmosphere having a refractive index of 1, the critical angle is about 19.5 °. That is, only the light that reaches the light emitting surface at an angle within about 19.5 ° with respect to the normal of the light emitting surface out of the light emitted from the active layer of the LED chip and reaching the light emitting surface is emitted. The light is emitted from the surface into the atmosphere.

  However, if a member that forms an interface with the light emission surface of the LED chip is used to emit light by using a member having a refractive index of 1 or more, the critical angle becomes about 19.5 ° or more, which is higher than that when the light is emitted in the atmosphere. It is possible to extract a large amount of light from the LED chip to the outside of the LED chip.

  Based on such a theory, the technique taken for the purpose of improving the light extraction efficiency is a transparent resin having a refractive index as close as possible to the refractive index of the semiconductor material forming the light emitting surface of the LED chip. Is to seal. Specifically, when the LED chip is sealed with a translucent resin having a refractive index of 1.5, the critical angle becomes 30 °, and the light emitted from the active layer of the LED chip and reaches the light emitting surface The light reaching the light exit surface at an angle of up to 30 ° with respect to the normal of the light exit surface is emitted from the light exit surface into the translucent resin. In other words, by sealing the LED chip with a translucent resin having a refractive index larger than that of the atmosphere, much more light can be extracted from the LED chip than when the LED chip emits light in the atmosphere. A significant improvement in light extraction efficiency will be realized.

  Further, when the LED chip is sealed with a translucent resin, another effect can be obtained. As described above, since the LED chip is extremely small as a light source, the amount of emitted light is small and it has optical characteristics close to a point light source. Therefore, by forming the lens with a light-transmitting resin sealing the LED chip, the light emitted from the LED chip into the light-transmitting resin can be collected by the lens and emitted to the outside of the LED. Therefore, it is possible to increase the luminous intensity on the optical axis.

  Furthermore, in addition to the optical effects described above, a physical effect can also be obtained by sealing the LED chip with a translucent resin. Therefore, the physical effect based on the specific mounting method of the LED chip will be described with reference to the surface-mounted LED shown in FIGS.

  The electrode structure of the LED chip is based on a semiconductor material that constitutes the LED chip, and an anode electrode and a cathode electrode are provided on each of the opposing surfaces of the LED chip, and an anode electrode and a cathode electrode are provided on the same side of the LED chip. It is roughly divided into two types. FIG. 1 shows the former LED chip as a light source, and FIG. 2 shows the latter LED chip as a light source, both of which are mounted on a package called a surface mount LED.

  First, the surface-mounted LED 10 shown in FIG. 1 is provided with a lamp house 4 having a bowl-shaped recess opened upward on the upper surface of a printed circuit board 3 on which circuit conductors 2a and 2b are formed on an insulating substrate 1. . Then, the LED chip 5 is mounted on the circuit conductors 2a and 2b exposed in the lower part of the concave portion via a conductive adhesive (not shown) to establish electrical continuity between the lower electrode of the LED chip 5 and the circuit conductor 2a. In the same manner as the upper electrode of the LED chip 5, the circuit conductor 2 b that is exposed at the lower part of the recess and is separated from the circuit conductor 2 a on which the LED chip 5 is mounted is connected via a bonding wire 6 to achieve conduction. ing. In addition, a light-transmitting resin (epoxy resin or silicone resin) 7 is filled in the recess where the LED chip 5 is mounted and the bonding wire 6 is stretched.

  The surface-mounted LED 20 shown in FIG. 2 has the same configuration of the printed circuit board 3 and the lamp house 4 as in FIG. 1, but the LED chip 5 is mounted on the lower part of the recess via an adhesive (not shown), Each of the pair of electrodes provided on the upper side of the LED chip 5 and the pair of circuit conductors 2a and 2b exposed and separated at the lower part of the recess are connected via the bonding wires 6a and 6b, respectively. I am trying. In addition, a light-transmitting resin (epoxy resin or silicone resin) 7 in which a phosphor 8 is dispersed is filled in a recess where the LED chip 5 is mounted and a bonding wire is stretched, and the emitted light is white light. .

  By sealing the LED chip mounted in this way with a translucent resin, the electrode is applied by the force applied by directly touching the bonding wire having the function as described above, and the vibration and impact applied indirectly. Can prevent electrical failure caused by peeling of the bonding wire, cutting of the bonding wire, or short-circuiting due to deformation of the bonding wire. At the same time, the LED chip can be prevented from being exposed to moisture, dust, etc. It is possible to protect from the environment and maintain reliability over a long period of time.

  Therefore, when the translucent resin for sealing the LED chip and the bonding wire is an epoxy resin, it is conventionally an acid anhydride curing system, and bisphenol A glycidyl ether (11) or alicyclic epoxy (11) represented by the following structural formula: 12) and methylhexahydrophthalic anhydride (13) as main components.

  As described above, the epoxy resin for LED is generally an acid anhydride curing system, and the LED effect is obtained by sealing the LED chips mounted on the ends of a plurality of lead frames arranged in a row with a translucent resin. Thick lens formation in a bullet-type LED having a structure that provides a lens, or transfer molding in a surface-mount type LED having a structure that provides a lens effect by sealing an LED chip mounted on a resin substrate with a translucent resin Acid anhydride curing is suitable for forming a lens on a resin substrate.

Further, when the translucent resin is a silicone resin, it is a polymer having a dimethylsiloxane skeleton, and is a transparent gel-like or rubber-like elastomer.
JP-A-8-335720

  However, in recent years, LEDs have been used more frequently as light sources for display devices installed outdoors, such as information display boards attached to the walls of buildings, information display boards for various stadiums, road information boards and traffic signal lights. Yes. In that case, since it is directly exposed to the ultraviolet rays of sunlight in the outdoors, the epoxy resin for LED mainly composed of bisphenol A glycidyl ether is highly oxidized as shown in the following reaction formula (1). A carbonyl group is formed, forming a chromophore and discoloring (yellowing).

  Also, when the LED chip is thinly sealed with a resin in which a phosphor is dispersed, such as a surface-mounted LED that emits white light, the acid anhydride evaporation of the epoxy resin is markedly evaporated and the resin is cured. The volume of the resin part is greatly reduced.

  Furthermore, since the strength and heat resistance of the resin are lower than the designed values due to the evaporation of the acid anhydride, resin cracks and discoloration occur, and the reliability as an LED is greatly reduced.

  In order to solve these problems, cation curing with an aromatic onium salt has been studied. However, since sulfur in the catalyst causes resin discoloration, the problem is that discoloration is particularly likely to occur due to heat. Further, the counter anion is hexafluoroantimony, and in this case, the safety of antimony is regarded as a problem.

  In order to solve the above problems all at once, a silicone resin may be used in place of the epoxy resin as shown in the conventional example. However, the silicone resin has a lower refractive index than the epoxy resin and weak adhesion to the LED chip. Therefore, the light extraction efficiency from the LED chip is poor, and it is difficult to obtain a bright LED. Furthermore, the silicone resin has a problem that the strength is lower than that of the epoxy resin, and dust easily adheres to the surface. Also, in the case of a surface-mounted LED in which an LED chip is resin-sealed by an automatic machine on a substrate on which the LED chip is mounted, the silicone resin before curing has a higher viscosity and the workability than the epoxy resin before curing. The production efficiency is poor because it is not good, and the cured corn cone resin has a softer surface than the epoxy resin and its strength is low, so there are also problems such as restrictions on the shape when sealing with an automatic machine .

  Therefore, the present invention was devised in view of the above problems, and the object is to have a high transmittance in a short wavelength region and less discoloration (yellowing) due to ultraviolet rays and heat than conventional epoxy resins. At the same time, the present invention provides a light-emitting diode encapsulating resin that does not cause failure factors such as resin cracks that lower the reliability of the LED, and a light-emitting diode using the same.

In order to solve the above problems, the invention described in claim 1 of the present invention is a sealing for a light emitting diode that seals a light emitting element that emits light in a wavelength range of a blue wavelength region and a shorter wavelength region. The light-emitting diode encapsulating resin is a siloxane derivative having an epoxy group and / or an oxetanyl group, and is 2,4,6,8-tetra [2- (3- {oxadicyclo [4.1.0 ] Heptyl}) ethyl] -2,4,6,8, -tetramethyl-cyclotetrasiloxane, bis [(1-ethyl-3-oxetanyl) methoxyfluoro] -tetramethyldisiloxane, having ethoxy group or oxetanyl group The main component is a siloxane derivative represented by any of silsesquioxane .

  The invention described in claim 2 of the present invention is characterized in that, in claim 1, the sealing resin for light-emitting diodes contains a platinum complex in a range of 1 to 1000 ppm as a curing catalyst. To do.

  In addition, the invention described in claim 3 of the present invention is the curing catalyst according to claim 2, wherein the curing catalyst is a compound having a Si-H bond as a co-catalyst within a range of 1 to 10 moles relative to the platinum catalyst. It is characterized by containing.

  Moreover, the invention described in claim 4 of the present invention is characterized in that the light emitting element is sealed using the sealing resin for light emitting diodes described in any one of claims 1 to 3. It is.

  Compared to conventional epoxy resins by realizing a sealing resin for light emitting diodes mainly composed of a siloxane derivative having a substituent of either one or both of an epoxy group and an oxetanyl group, and a light emitting diode using the same. A sealing resin for light-emitting diodes that has high transmittance in the short wavelength region and little discoloration (yellowing) due to ultraviolet rays and heat, and does not cause defective factors such as resin cracks that reduce reliability as an LED, and Made the light emitting diode used possible.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3 (the same parts are denoted by the same reference numerals). The embodiments described below are preferable specific examples of the present invention, and thus various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. As long as there is no description of the effect, it is not restricted to these aspects.

  First, components constituting the light emitting diode sealing resin of the present invention will be described. The main component is a siloxane derivative (21) to (25) having an epoxy group and / or an oxetanyl group represented by the following structural formula, which is characterized by being cured by cationic polymerization by heat.

  Moreover, as antioxidant, phosphorus antioxidant (26) represented by the following structural formula, phenolic antioxidant (27), etc. can be used.

As the curing catalyst, hexachloroplatinic acid (H ₂ PtCl ₆ ), Wilkinson catalyst, Karlstadt catalyst, Lamoreaux catalyst, and the like are suitable, and among them, they are used for hydrosilylation reaction. Hexachloroplatinic acid (H ₂ PtCl ₆ ), which is a platinum complex, is desirable, and it is more desirable that this be contained within the range of 1 to 1000 ppm in the sealing resin. It is most desirable that hexachloroplatinic acid (H ₂ PtCl ₆ ) is contained in the sealing resin within a range of 50 to 1000 ppm.

Furthermore, as a co-catalyst for accelerating curing, a compound (28) having a Si—H bond represented by the following structural formula is suitable, which is 1 with respect to hexachloroplatinic acid (H ₂ PtCl ₆ ). It is desirable to add in the range of 10 times mole.

  Hereinafter, “Example 1” to “Example 3” of the sealing resin for light emitting diodes of the present invention by the combination of the above components will be described.

As Example 1, a characteristic measurement sample and a surface-mounted LED were produced under the following components and conditions. Incidentally, the surface-mount type LED uses the structure shown in FIGS. 1 and 2 showing a conventional example, and adopts the resin of each of the following examples as the LED chip sealing resin.
Siloxane having an epoxy group (21) 99.89% by weight
Hexachloroplatinic acid (H ₂ PtCl ₆ ) 0.01% by weight
Cocatalyst (28) 0.10% by weight
Curing conditions 110 ° C 2 hours + 150 ° C 2 hours

As Example 2, a characteristic measurement sample and a surface-mount type light emitting diode were produced under the following components and conditions.
Siloxane having epoxy group (22) 99.89% by weight
Hexachloroplatinic acid (H ₂ PtCl ₆ ) 0.01% by weight
Cocatalyst (28) 0.10% by weight
Curing conditions 110 ° C 2 hours + 150 ° C 2 hours

As Example 3, a characteristic measurement sample and a surface-mount type light emitting diode were produced under the following components and conditions.
Siloxane having an epoxy group (23) 99.89% by weight
Hexachloroplatinic acid (H ₂ PtCl ₆ ) 0.01% by weight
Cocatalyst (28) 0.10% by weight
Curing conditions 110 ° C 2 hours + 150 ° C 2 hours

  FIG. 3 shows the transmission spectra of the characteristic measurement samples prepared in “Example 1” to “Example 3” and the characteristic measurement samples prepared with an epoxy resin for comparison. In FIG. 3, since the epoxy resin has ultraviolet absorption as described above, light absorption is recognized in a wavelength region shorter than 430 nm (visible light region). On the other hand, the samples prepared in Examples 1 to 3 have high transmittance even in the ultraviolet wavelength region of 380 nm or less because the molecular skeleton forming the resin does not absorb ultraviolet rays.

In addition, a high pressure mercury lamp (5000 mW / cm) was prepared by coating the resin prepared in the “Example 1” to “Example 3” and the epoxy resin for comparison to a thickness of 10 μm on a slide glass and heat-curing. ^The ultraviolet irradiation test by ² ) was implemented. As a result, the epoxy resin changed its color after an irradiation time of 1 hour, and the transmittance at 400 nm was almost 0%. On the other hand, in Examples 1 to 3, especially in Example 1, no decrease in transmittance was observed even at an irradiation time of 300 hours.

  Then, based on the above result, the effect of this invention is demonstrated below.

  First, general acid anhydride-cured epoxy resins tend to cause problems such as cutting of LED bonding wires because the expansion coefficient of the resin changes greatly at the glass transition point. Therefore, in order to prevent such a problem, it is necessary to make the glass transition point of the resin higher than the environment in which the LED is used. Therefore, a high glass transition point is required for the resin.

  On the other hand, in the cationic curable resin, the change in the expansion coefficient before and after the glass transition point is small, and occurrence of disconnection failure can be reduced even in an environment accompanied by a temperature change. In addition, the addition of silsesquioxane, which is a ladder-like polymer, can ensure the strength and rigidity of the resin, so that the occurrence of cracks can also be suppressed.

  Furthermore, the conventional acid anhydride-cured epoxy resin significantly reduces the resin volume due to the evaporation of the acid anhydride during heat-curing, so that it is sufficient in the lamp house of the surface mount LED as shown in FIG. 1 or FIG. Even if it is filled in, there is a problem that it is greatly pulled after curing. This is a serious problem that affects light distribution as well as appearance problems.

  In addition, since the acid anhydride is selectively evaporated at the time of heat curing, the ratio of the acid anhydride to the epoxy in the resin cured product changes. As a result, desired resin performance cannot be obtained due to a change in resin composition, a decrease in weather resistance, and the like, and reliability as expected in the LED cannot be ensured.

  On the other hand, the cationic curable resin of the above embodiment has a small volume shrinkage ratio after heat curing, and can realize light distribution and reliability satisfying design specifications.

  Further, since the catalyst does not contain sulfur, thermal discoloration is greatly reduced as compared with a cationic cured product using a conventional onium salt.

  An LED in which an LED chip is sealed with a resin having such an excellent effect does not cause a change in emission color because there is no discoloration of the resin over a long period of use. This is advantageous in that a white LED in which LED chips that emit light having a shorter wavelength than the blue wavelength region are sealed with a resin in which phosphors are dispersed can be maintained over a long period of time.

  Further, in a mixed color LED in which a plurality of LED chips are sealed with a resin, the color shade after color mixing due to the combination of the LED chips can be maintained for a long time. Therefore, in a dot matrix display in which a large number of such LEDs are arranged vertically and horizontally, it is possible to enjoy a screen whose color does not change over a long period of time.

  In addition, since there is almost no resin cracking or resin shrinkage at the time of resin curing, the LED is highly reliable, and there is almost no need for maintenance when mounted on an apparatus, so that the running cost can be reduced.

It is sectional drawing of the conventional surface mount type LED which does not contain a fluorescent substance in LED chip sealing resin. It is sectional drawing of the conventional surface mount type LED which contains a fluorescent substance in LED chip sealing resin. It is a figure showing the transmittance | permeability of Examples 1-3 of the sealing resin for light emitting diodes concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Insulation board | substrate 2a, 2b Circuit conductor 3 Printed circuit board 4 Lamp house 5 LED chip 6 Bonding wire 6a, 6b Bonding wire 7 Translucent resin 8 Phosphor 10 Surface mount type LED
20 Surface-mount LED

Claims (4)

A sealing resin for a light emitting diode that seals a light emitting element that emits light within a wavelength range of a blue wavelength region and a shorter wavelength region, wherein the sealing resin for a light emitting diode has an epoxy group and / or an oxetanyl group. A sealing resin for light-emitting diodes, comprising a siloxane derivative represented by any one of the following formulas (22) to (25) as a main component.

  2. The light-emitting diode sealing resin according to claim 1, wherein the light-emitting diode sealing resin contains a platinum complex in a range of 1 to 1000 ppm as a curing catalyst.   The said curing catalyst contains the compound which has a Si-H bond as a promoter in the range of 1-10 times mole of a platinum catalyst, The sealing resin for light emitting diodes of Claim 2 characterized by the above-mentioned.   A light emitting diode, wherein the light emitting element is sealed using the sealing resin for a light emitting diode according to any one of claims 1 to 3.

Images