JP5554155B2 - Lead frame for optical semiconductor device and optical semiconductor device - Google Patents

Description

  The present invention relates to an optical semiconductor device lead frame, a method for manufacturing the same, and an optical semiconductor device.

  2. Description of the Related Art Lead frames for optical semiconductor devices are widely used as constituent members of various display / illumination light sources that use optical semiconductor elements (light-emitting elements) such as LED (Light Emitting Diode) elements as light sources. In the optical semiconductor device, for example, a lead frame is arranged on a substrate, and after the light emitting element is mounted on the lead frame, the deterioration of the light emitting element and its peripheral parts due to external factors such as heat, moisture, and oxidation are prevented. The light emitting element and its periphery are sealed with resin.

  By the way, when the LED element is used as an illumination light source, the reflective material of the lead frame has a high reflectance in the entire visible light wavelength range (400 to 700 nm) (for example, the reflectance with respect to a reference material such as barium sulfate or aluminum oxide). Is 80% or more). In recent years, LED elements have also been used as light sources for measuring / analyzing instruments using ultraviolet rays, and the reflective material is required to have a high reflectance even in the near ultraviolet region (wavelength of 340 to 400 nm). It is coming.

  In addition, as a method of realizing an LED that emits white light, a method of arranging three chips that emit all three primary colors of red (R), green (G), and blue (B), and a yellow LED on a blue LED chip. 3 using a sealing resin in which phosphors are dispersed, and further using a sealing resin in which red, green, and blue phosphors are dispersed in LED chips that emit wavelengths in the ultraviolet to near-ultraviolet region. It is roughly divided into two. Conventionally, a method using a sealing resin in which a yellow phosphor is dispersed in a blue chip has been the mainstream. However, this method has recently been changed to a light emission wavelength band from the viewpoint that the color rendering property of the red system is particularly insufficient. A technique using an LED chip including an ultraviolet region has attracted attention.

  In response to such a demand, a layer (film) made of silver or a silver alloy is formed on the lead frame on which the LED element is mounted, particularly for the purpose of improving the light reflectance in the visible light region (hereinafter referred to as reflectance). ) Is often formed. A silver film is known to have a high reflectance in the visible light region. For example, as disclosed in Patent Document 1, it is known to form a silver plating layer on a reflective surface.

  It is also known to use a metal other than silver as the reflective layer. For example, a lead frame whose outermost surface is coated with palladium (Pd) as shown in Patent Document 2 has been studied, and solderability is improved. Therefore, a lead frame in which a gold coating layer is provided on a palladium layer as shown in Patent Document 3 has been studied.

  In addition, a lead frame coated with rhodium (Rh) having a relatively good reflectivity from the ultraviolet region to the near infrared region has been studied. For example, a lead frame having a three-layer plating structure as shown in Patent Document 4, a lead frame in which the first layer is Ni, the second layer is palladium or a palladium alloy, and the outermost surface is coated with rhodium has been proposed.

Japanese Patent Laid-Open No. 61-148883 JP 59-168659 A Japanese Patent No. 2543619 JP 2005-129970 A

  However, the lead frames of each patent document have the following problems. For example, in the technique described in Patent Document 1, a phenomenon occurs in which the reflection layer in the optical semiconductor device turns black and the reflectance in the visible light region decreases to nearly 10%, thereby impairing the long-term reliability of the device. There is. This phenomenon occurs when there is a slight gap between the sealing resin and the lead frame, sulfur components in the atmosphere, halides in the flux residue, etc. enter the lead frame, and the silver on the lead frame surface becomes silver sulfide or It is thought to be caused by the fact that it becomes a silver halide compound and changes its color to black.

  In the technique described in Patent Document 2, long-term reliability is superior to that of Silver in Patent Document 1, while palladium on the outermost surface has a reflectivity of about 35 to 45% in the ultraviolet region to the near ultraviolet region, The reflectance in the visible light region is about 45 to 65%, and the reflectance is low, but the reflectance is low. In the technique described in Patent Document 3, for example, the reflectance when a gold plating of 0.02 μm is applied to an upper layer of 0.01 μm of palladium plating is 70% or more at a wavelength of 600 to 800 nm, but is reflected at the short wavelength side. The reflectance is low and the reflectance at a wavelength of 400 nm is about 30%, and other techniques are required to increase the reflectance of the lead frame.

  Moreover, in the technique described in Patent Document 4, when Rh is formed on the outermost layer, the reflectance at a wavelength of 300 to 340 nm in the ultraviolet region to the near ultraviolet region is improved more than Pd and Au, and about While it has been increased to 50% or more, it has been found that there is a problem of poor bonding with a gold bonding wire used to ensure electrical continuity with the LED chip. Although this detailed factor is unknown, it is considered that Au and Rh do not form a compound near room temperature (25 ° C.) when viewed from the phase diagram, which makes wire bonding difficult.

  Therefore, the present invention provides a lead frame for an optical semiconductor device used for an LED, photocoupler, photointerrupter, etc., having a good reflectivity from the ultraviolet region to the near infrared region, a good wire bonding property, a corrosion resistance and It is an object to provide a lead frame with excellent long-term reliability. Another object of the present invention is to provide a method for manufacturing a lead frame for optical semiconductor devices having such excellent characteristics.

As a result of intensive studies on the above problems, the present inventors have formed a layer made of rhodium or a rhodium alloy as a light reflecting layer on a conductive substrate, and further, gold, palladium, platinum or an alloy thereof is further formed thereon. The outermost surface layer is a lead frame for an optical semiconductor device coated at least on a portion to which wire bonding is performed, and the outermost surface layer has a thickness of 0.001 to 0.05 μm, and the outermost layer surface hardness _{H iT} by nanoindentation depth 0.005μm from point is by controlling so as to be 500~3000N / mm ^2, the near infrared region from ultraviolet region, specifically a wavelength 300~800nm light Based on this finding, we have found that a lead frame for semiconductor devices with excellent reflectivity, corrosion resistance, and particularly excellent wire bonding can be obtained. It has led to the completion of the present invention can.

That is, the said subject is solved by the following means.
(1) Light in which a reflective layer made of rhodium or a rhodium alloy is formed on a conductive substrate, and an outermost layer made of gold, palladium, platinum or an alloy thereof is formed on at least a part of the surface of the reflective layer. A lead frame for a semiconductor device, the thickness of the outermost layer being 0.001 to 0.05 μm, and the hardness H _IT by a nanoindentation method at a depth of 0.005 μm from the surface of the outermost layer , A lead frame for an optical semiconductor device, wherein an average value measured for any 10 points is 500 to 3000 N / mm ² .
(2) The lead frame for an optical semiconductor device according to (1), wherein the reflective layer has a thickness of 0.005 to 0.5 μm.
(3) Rhodium or rhodium alloy forming the reflective layer is rhodium, rhodium-tin alloy, rhodium-copper alloy, rhodium-cobalt alloy, rhodium-silver alloy, rhodium-aluminum alloy, rhodium-indium alloy, rhodium-iridium. The optical semiconductor device according to (1) or (2), comprising a material selected from the group consisting of an alloy, a rhodium-ruthenium alloy, a rhodium-palladium alloy, a rhodium-nickel alloy, and a rhodium-platinum alloy. Lead frame.
(4) One or more intermediate layers are provided between the conductive substrate and the reflective layer, and the intermediate layer is made of nickel or nickel alloy, cobalt or cobalt alloy, copper or copper alloy, palladium or palladium. The lead frame for optical semiconductor devices according to any one of (1) to (3), wherein the lead frame is made of a metal or alloy selected from a group of alloys.
(5) When the intermediate layer contains nickel or a nickel alloy, cobalt or a cobalt alloy, copper or a copper alloy, the thickness of the layer composed of these components is 0.2 to 2.0 μm in total. The lead frame for optical semiconductors according to (4).
(6) When said intermediate | middle layer contains palladium or a palladium alloy, the thickness of the layer which consists of said palladium or palladium alloy is 0.005-0.2 micrometer in total, It is characterized by the above-mentioned. Lead frame for optical semiconductors.
(7) An optical semiconductor device comprising the optical semiconductor device lead frame according to any one of (1) to (6) above and an optical semiconductor element, and a portion where wire bonding is performed and An optical semiconductor device, wherein the outermost layer is provided in the vicinity.
(8) The optical semiconductor device according to (7), wherein the reflective layer and the outermost layer are provided in the vicinity of a place where the optical semiconductor element is mounted.

According to the present invention, the reflectance is excellent over the entire wavelength range of 300 to 800 nm, at least 50% or more immediately after formation or after an environmental test, and the reflectance does not decrease over time. An optical semiconductor lead frame having excellent long-term reliability can be obtained. Furthermore, a lead frame for an optical semiconductor device can be obtained in which the wire bonding property, which has heretofore been insufficient with rhodium or rhodium alloys, is remarkably improved.
Furthermore, the present inventors have known that when rhodium is coated by electrolytic plating, the hardness reaches 6000 to 10000 N / mm ² , and a very hard film is obtained. It was thought to worsen. However, the hardness of the surface affecting wire bondability, the hardness of the depth 0.005μm point from the outermost layer surface, by controlling the 500~3000N / mm ² in hardness _{H IT} by nanoindentation As a result, it is possible to optimize the hardness that greatly contributes to the quality of wire bonding and to provide a lead frame with significantly improved bonding properties.
As a result, although the initial reflectivity is not as high as that of silver or silver alloy, the decrease in reflectivity during long-term use was remarkable due to sulfur discoloration in silver, whereas in the present invention, the lead having excellent corrosion resistance was used. Can provide a frame. Therefore, it can be suitably used as an optical semiconductor device lead frame having excellent long-term reliability. In addition, the conventional technology can improve the reflectance from about 30% especially in the short wavelength region to 50% or more, and it is difficult to wire bonding just by forming the conventional rhodium on the outermost layer. The lead frame having a stable bonding strength, particularly in wire bonding, can be provided.

1 is a schematic cross-sectional view of a first embodiment of a lead frame for an optical semiconductor device according to the present invention. It is a schematic sectional drawing of 2nd Embodiment of the lead frame for optical semiconductor devices which concerns on this invention. It is a schematic sectional drawing of 3rd Embodiment of the lead frame for optical semiconductor devices which concerns on this invention. It is a schematic sectional drawing of 4th Embodiment of the lead frame for optical semiconductor devices which concerns on this invention. It is a schematic sectional drawing of 5th Embodiment of the lead frame for optical semiconductor devices which concerns on this invention. It is a schematic sectional drawing of 6th Embodiment of the lead frame for optical semiconductor devices which concerns on this invention.

A preferred embodiment of the present invention will be described.
The lead frame of the present invention has an outermost layer formed of gold, palladium, platinum, or an alloy thereof on an upper surface of a reflective layer made of rhodium or a rhodium alloy on a conductive substrate at least at a place where wire bonding is performed. The outermost layer has a thickness of 0.001 to 0.05 μm, and the hardness at a depth of 0.005 μm from the surface of the outermost layer is determined by a nanoindentation method. in H _IT is 500~3000N / mm ² is intended to provide a lead frame. This is because it is important to optimize the surface hardness in the vicinity of the outermost surface in order to obtain a stable bonding strength of wire bonding, and in particular, the hardness at a point of 0.005 μm from the outermost surface greatly affects the wire bonding property. It has been found to give. Although the detailed cause is unknown, it is possible to perform wire bonding by using gold, platinum, palladium, or an alloy thereof, which forms the outermost layer, but in order to reduce the reflectance as much as possible, the outermost layer coating thickness Must be made as thin as possible. For this reason, the hardness at the point of 0.005 μm from the outermost layer is that the hardness of the reflective layer made of rhodium or rhodium alloy, which is the lower layer, plays a very important role in improving the bonding strength of wire bonding. Conceivable. The present inventors have results of extensive studies, by appropriately adjusting the hardness of the outermost layer and the reflective layer, the hardness of 0.005μm point from the surface, the hardness H _IT measured by the nanoindentation method, It has been found that particularly stable bonding characteristics can be obtained by controlling in the range of 500 to 3000 N / mm ² .
When the hardness by the nanoindentation method is less than 500 N / mm ² , the bonding strength of wire bonding is lowered. On the other hand, when it exceeds 3000 N / mm ² , not only the bonding strength is lowered, but also an error at the time of wire bonding is likely to appear, the reliability of the wire bonding is deteriorated, and a crack is easily developed at the time of bending or pressing. Therefore, it is not preferable. If it is the said range, a favorable bonding characteristic will be acquired, but since reliability becomes further more preferable, it is more preferable that it is 500-2000 N / mm < ² >.

Note that the hardness H _IT by the nanoindentation method, a hardness that is described in ISO-14577, is a technique that is suitable for the hardness measurement in small thickness. In wire bonding, the surface film thickness that contributes to bonding is at most several μm level, so it is important to define the hardness at that thickness, and it is difficult to measure with conventional Vickers hardness or Knoop hardness, and these hardnesses are several μm. It is impossible to define the outermost surface hardness of the order. Therefore, it is important measurement in hardness H _IT nanoindentation method.

  The thickness of the outermost layer made of gold, palladium, platinum, or an alloy thereof is 0.001 to 0.05 μm. If the thickness of the outermost layer is less than 0.001 μm, it is not preferable because sufficient wire bonding strength cannot be secured. On the other hand, if the thickness of the outermost layer is larger than 0.05 μm, not only the effect of improving the wire bonding property is saturated, but also the amount of noble metal used as the material of the outermost layer is increased and it takes time to cover it. Is not preferable. In addition, when the thickness of the outermost layer is thicker than 0.05 μm, the amount of light reaching the reflective layer is greatly reduced, and the reflectance at the outermost layer is inferior to the reflectance at the reflective layer. The reflectance of the rhodium or rhodium alloy to be used cannot be effectively used, causing a reduction in luminance. Therefore, even when the outermost layer is formed on the surface of the reflective layer, the thickness is 0.05 μm or less. The thickness is preferably 0.003 to 0.03 [mu] m, more preferably 0.005 to 0.02 [mu] m so as to minimize the decrease in reflectivity and improve the wire bonding property.

  Further, the purity of the metal (gold, palladium or platinum) or an alloy thereof forming the outermost layer is preferably 90% or more, more preferably 99% or more, thereby further improving the reliability of the wire bonding property. Can do. This is because when a LED chip is to be bonded to a lead frame with, for example, a gold wire, a resin having a heat resistant temperature of about 170 ° C. is often used in the LED manufacturing process. The temperature at the time of wire bonding may be about 150 ° C. However, if the purity of the metal forming the outermost layer is 90% or more, the connection reliability can be improved even if bonding is performed at this temperature. is there. On the other hand, when the purity of the metal forming the outermost layer is less than 90%, the bonding strength at the time of wire bonding is insufficient, the number of wire bonding errors increases, and the production efficiency decreases. May occur. When these metal components are alloys, the total component purity of gold, palladium, or platinum may be 90% or more, more preferably 99% or more. For example, Au (gold) -50% Pt ( Good wire bonding properties can be obtained even with platinum.

As the conductive substrate of the lead frame for optical semiconductor devices of the present invention, for example, copper or copper alloy, iron or iron alloy, aluminum or aluminum alloy, etc. are preferably used.
Among the substrates, examples of the copper alloy include C19400 (Cu-Fe based alloy material: for example, Cu-2.3Fe-0.03P-0.15Zn), C26000 as examples of CDA (Copper Development Association) standard alloys. (Brass: Cu-30Zn), C26800 (Brass: Cu-35Zn), C52100 (Phosphor Bronze: Cu-8Sn-P), C77000 (Western White: Cu-18Ni-27Zn). Also, CDA standard alloys C14410 (Cu-0.15Sn: EFTEC-3 manufactured by Furukawa Electric Co., Ltd.), C18045 (Cu-0.3Cr-0.25Sn-0.2Zn-based alloy: EFTEC-64T manufactured by the same company) C52180 (Cu-8Sn-0.1Fe-0.05Ni-0.04P: F52218 made by the company), C70250 (Cu-3.0Ni-0.65Si-0.15Mg: EFTEC-7025 made by the company), etc. are also suitable. Take as an example.
Examples of the iron alloy in the substrate include stainless steel (SUS301, SUS304, SUS401) stipulated by Japanese Industrial Standard (JIS G 4305: 2005) and 42 alloy (Fe-42% Ni) that is an Fe—Ni alloy. ) And the like.
Among the substrates, examples of the aluminum alloy include A1100, A2014, A3003, A5052 and the like defined in Japanese Industrial Standards (JIS H 4000: 2006, etc.).

It is easy to form the reflective layer and the outermost layer film on these substrates, and a lead frame with good productivity can be provided. In addition, the lead frame based on these metals has excellent heat dissipation characteristics, and heat energy generated when the light emitter emits light can be smoothly discharged to the outside through the lead frame. Long life and long-term stabilization of reflectance characteristics are expected. This depends on the conductivity of the substrate, and is preferably 10% IACS (International Annealed Copper Standard) or more, and more preferably 50% IACS or more.
Iron alloy SUS304, etc. and 42 alloy are generally less than 10% IACS, but suitable for applications that require strength as a lead frame, applications that do not require strong heat dissipation, and general-purpose LED applications. Can be used.

  The plate thickness and the plate width of the conductive substrate are not particularly limited, but the lead frame size in the LED is generally 0.05 to 1.0 mm and the plate width is about 10 to 200 mm. The optical semiconductor device lead frame should satisfy various characteristics at least in the above size.

  In the lead frame for an optical semiconductor device of the present invention, the long-term reliability of the light reflectance can be ensured by setting the thickness of the reflective layer made of rhodium or rhodium alloy to 0.005 μm or more. If the thickness of the reflective layer is too thick, the effect of long-term reliability is saturated, and cracking is likely to occur during pressing. Therefore, the thickness is preferably 0.5 μm or less. The thickness of the reflective layer is more preferably used in the range of 0.01 to 0.2 μm from the viewpoint of characteristics and production cost.

  The rhodium or rhodium alloy forming the reflective layer in the optical semiconductor device lead frame of the present invention is rhodium, rhodium-tin alloy, rhodium-copper alloy, rhodium-cobalt alloy, rhodium-silver alloy, rhodium-aluminum alloy, It is made of a material selected from the group consisting of rhodium-indium alloy, rhodium-iridium alloy, rhodium-ruthenium alloy, rhodium-palladium alloy, rhodium-nickel alloy, rhodium-platinum alloy, so that the reflectivity is good and the productivity is good. Although a lead frame can be obtained, rhodium is preferably used from the viewpoint of improving the reflectance.

Further, as a method for easily controlling the hardness by the nanoindentation method at a point of 0.005 μm from the surface of the outermost layer, it is necessary to appropriately select conditions for forming the outermost layer and / or the reflective layer. The hardness by the nanoindentation method at a point of 0.005 μm from the surface of the outermost layer is affected not only by the hardness of the outermost layer but also by the hardness of the reflective layer, and therefore it is important to control it appropriately. For example, when the method for forming the outermost layer and / or the reflective layer is a plating method, the current density during plating is adjusted to 0.05 A / dm ^{2 to} 3 A / dm ² . Inclusion of a component consisting of one or more of carbon, sulfur and nitrogen contained in the film by appropriately selecting the type (for example, thiourea, allylthiourea, saccharin, sulfamate, etc.) and adjusting the addition amount The amount can be suitably controlled, for example, by adjusting the amount by including about 0.01 to 2.0% by mass. Since the purity of the outermost layer metal is preferably 99% or more as described above, it is preferable to adjust the hardness of the reflective layer.
The content of carbon, sulfur, and nitrogen components in the film is adjusted after the film is formed, for example, energy dispersive X-ray spectrometry, fluorescent X-ray analysis, glow discharge emission spectrometry, Auger electron Measurement is performed with a qualitative quantitative analyzer such as a spectroscopic analyzer.

  The lead frame for an optical semiconductor device according to the present invention includes nickel, a nickel alloy, cobalt, a cobalt alloy, copper, a copper alloy, palladium, and a palladium alloy between the conductive substrate and the reflective layer made of rhodium or rhodium alloy. By forming at least one intermediate layer made of a metal or alloy selected from the group, the material constituting the conductive substrate diffuses into the reflective layer due to heat generated when the light emitting element emits light. Therefore, the deterioration of the reflectance characteristic due to the light is prevented, and the reflectance characteristic becomes stable over a long period of time. Since the long-term reliability is improved by forming the intermediate layer, it is possible to form the reflective layer relatively thin with the thickness within the range of the present invention. In addition, the adhesion between the substrate and the reflective layer is improved.

  Here, the thickness of the intermediate layer is determined in consideration of pressability, heat resistance, productivity, and the like. When the intermediate layer contains nickel or nickel alloy, cobalt or cobalt alloy, copper or copper alloy, the total thickness (total thickness) of the intermediate layer composed of these components is 0.2 to 2.0 μm. More preferably, 0.5 to 1.0 μm is preferable. Further, when the intermediate layer contains palladium or a palladium alloy, since the heat resistance is particularly excellent, the total thickness of the intermediate layer of these components is preferably 0.005 to 0.2 μm, more preferably 0.008 to 0.1 μm. When the intermediate layer is composed of two or more kinds of mixed layers, for example, when the intermediate layer is composed of two layers of a nickel layer and a palladium layer, the thickness of the nickel layer may be 0.2 to 2.0 μm. The thickness of 0.005 to 0.2 μm satisfies the required characteristics. Further, when palladium is formed as an intermediate layer, a further effect of corrosion resistance can be obtained by forming any layer of nickel, nickel alloy, cobalt, and cobalt alloy after forming the first layer. Although the intermediate layer can be formed of a plurality of layers, it is usually preferable to have two or less layers in consideration of productivity.

  The lead frame for an optical semiconductor device of the present invention is preferably formed by a wet or dry plating method as a method that can be formed while suitably adjusting the coating thickness. There is a cladding method as another forming method, but from the viewpoint of easy control of the thickness on the order of submicrometers and abundant methods for adjusting the film hardness, a wet or dry plating method is used. preferable.

  In addition, an optical semiconductor device formed by mounting an optical semiconductor element using the lead frame for an optical semiconductor device of the present invention seals at least the vicinity where the optical semiconductor element is mounted, that is, the light emitting element and its periphery. By using the lead frame of the present invention inside the formed resin, the reflectance characteristics can be obtained effectively at low cost. This is because the reflectance characteristic can be enhanced by forming a reflective layer made of rhodium or a rhodium alloy only in the vicinity of the portion including the mounting portion of the optical semiconductor element. In this case, the reflective layer made of rhodium or rhodium alloy may be partially formed, and may be formed by, for example, partial plating such as stripe plating or spot plating. Manufacturing a lead frame in which the reflective layer is partially formed can reduce the amount of metal used in the portion where the reflective layer is not formed, and thus can be an optical semiconductor device with less environmental load.

  In addition, the optical semiconductor device of the present invention can provide an optical semiconductor device with good wire bonding performance at low cost by using a lead frame having an outermost layer formed only at a location where wire bonding is performed. This is because the outermost layer with excellent bonding properties is formed only at the places where wire bonding is performed, and the effect of improving the wire bonding properties without greatly reducing the reflectivity of the rhodium or rhodium alloy as the reflective layer Is obtained. In this case, the outermost layer may be formed by partial plating such as stripe plating or spot plating on the entire surface of the lead frame or an upper layer of the reflection layer formed partially. Manufacturing a lead frame in which the outermost layer is partially formed can reduce the amount of metal used in a place where bonding properties are not required, so that an optical semiconductor device with less environmental load can be obtained.

  Hereinafter, preferred embodiments of a lead frame for optical semiconductor devices according to the present invention will be described with reference to the drawings as appropriate. Each figure shows a state in which an optical semiconductor element is mounted on a lead frame. In each figure, the same symbol indicates the same thing. Each embodiment is merely an example, and the scope of the present invention is not limited to each embodiment.

FIG. 1 is a schematic cross-sectional view of a first embodiment of a lead frame for an optical semiconductor device according to the present invention. In the lead frame of this embodiment, a reflective layer 2 made of rhodium or a rhodium alloy is formed on a conductive substrate 1, and an outermost layer 3 made of gold, palladium, platinum or an alloy thereof is formed on the upper layer of the reflective layer 2. The optical semiconductor element 4 is mounted on a part of the optical semiconductor element 4 and wire bonding 5 is applied between the outermost layer 3 and the optical semiconductor element 4. In the lead frame of this embodiment, the thickness of the outermost layer 3 is formed to be 0.001 to 0.05 μm, and the hardness at a point where the depth from the surface of the outermost layer 3 is 0.02 μm is determined by the nanoindentation method. in hardness _{H IT} is 500~3000N / mm ^2. As a result, the reflectivity is not substantially reduced, and the lead frame for an optical semiconductor device has excellent reflection characteristics in the ultraviolet to near infrared region of 300 to 800 nm, has a stable bonding strength, and has no bonding error. In the schematic cross-sectional view, a state in which a circuit is formed in a broken line portion via an insulator or the like, and is suitably used for an optical semiconductor application is shown.

FIG. 2 is a schematic cross-sectional view enlarging a cross-section A portion in the first embodiment of the lead frame for an optical semiconductor device according to the present invention. Gold, palladium, platinum or drawing a 0.002μm point schematically showing the surface of the outermost layer 3 composed of these alloys, the hardness _{H IT} nanoindentation method at a part indicated by a dotted line 500~3000N / Mm ² is important in the present invention. The point at the depth of 0.005 μm from the outermost surface differs depending on the thickness of the outermost layer 3, and the left side of FIG. 2 is a schematic diagram where the thickness t of the outermost layer 3 is 0.001 ≦ t <0.005 μm. Yes, the right side of FIG. 2 shows the case where the thickness t of the outermost layer 3 is 0.005 ≦ t μm. In any case, since the hardness at the point where the depth from the outermost surface is 0.005 μm is important for wire bonding, the position of the layer at the point of 0.005 μm is either in the outermost layer 3 or in the reflective layer 2. good.

  FIG. 3 is a schematic cross-sectional view of a second embodiment of the lead frame for an optical semiconductor device according to the present invention. The lead frame of the embodiment shown in FIG. 3 is different from the lead frame shown in FIG. 1 in that an intermediate layer 6 is formed between the conductive substrate 1 and the reflective layer 2. Other points are the same as those of the lead frame shown in FIG.

FIG. 4 is a schematic cross-sectional view of a third embodiment of the lead frame for an optical semiconductor device according to the present invention. FIG. 4 shows a state in which the reflective layer 2 and the outermost layer 3 are formed in the portion where the optical semiconductor element 4 is mounted and in the vicinity thereof, that is, the portion including the inside of the resin formed by sealing the light emitting element and its periphery. Is shown. In the present invention, it is also possible to form the reflective layer 2 made of rhodium or rhodium alloy at least in a portion that contributes to light reflection. In the case of this form, it is necessary that the hardness by the nanoindentation method at a depth of 0.005 μm from the outermost surface of the outermost layer 3 is in the range of 500 to 3000 N / mm ² , and the intermediate layer 6 is It does not prescribe the hardness at the location exposed on the outermost surface.
In the present embodiment, the intermediate layer 6 is formed on the entire surface of the conductive substrate 1, but may be partially formed as long as it is interposed between the conductive substrate 1 and the reflective layer 2. .

FIG. 5 is a schematic sectional view of a fourth embodiment of the lead frame for an optical semiconductor device according to the present invention. In FIG. 5, the reflective layer 2 is formed only in the portion where the optical semiconductor element 4 is mounted and in the vicinity thereof, and the outermost layer 3 as the upper layer is formed only in the vicinity of the portion necessary for wire bonding. Is shown. As in this embodiment, the outermost layer 3 can be formed only in a portion where wire bonding is necessary. In the case of this embodiment, the hardness by a nanoindentation method at a depth of 0.005 μm from the outermost surface of the outermost layer 3 is in the range of 500 to 3000 N / mm ² . It does not define the hardness at the location where the reflective layer 2 and the intermediate layer 6 are exposed on the outermost surface.

  FIG. 6 is a schematic sectional view of a fifth embodiment of the lead frame for an optical semiconductor device according to the present invention. In FIG. 6, the reflective layer 2 is formed only in the portion where the optical semiconductor element 4 is mounted and in the vicinity thereof, and the outermost layer 3 as the upper layer is formed on the entire surface including the portion necessary for wire bonding. It shows how it is. For this reason, for example, the outermost layer 3 is also formed in the region A in FIG. 6, and the outermost layer 3 is made of gold, palladium, platinum, or an alloy thereof. Therefore, when forming the optical semiconductor device, the region A Can be easily soldered. As in this embodiment, it is possible to form the outermost layer 3 entirely for the purpose of imparting solderability.

  Although any method can be used to manufacture the lead frame for a semiconductor device, the reflective layer 2, the outermost layer 3 and the intermediate layer 6 are preferably formed by a wet or dry plating method.

  Next, the present invention will be described in more detail based on examples.

Example 1
As Example 1, the conductive substrate shown in Table 1 having a thickness of 0.3 mm and a width of 50 mm is subjected to the following pretreatment, and then subjected to the following electroplating treatment, whereby it is shown in FIG. 1 or FIG. Lead frames of Invention Examples 1 to 53, Comparative Examples 1 to 4, and Conventional Examples 1 to 3 having the basic structure and the configurations shown in Table 1 were produced. Among these, the inventive examples 39 to 42 show that the intermediate layer has two layers, and is configured in the order of “left / right” elements from the side close to the conductive substrate, and the coating thickness is also Shown in the same way.
Among the materials used as the conductive substrate, “C14410”, “C18045”, “C19400”, “C26800”, “C52100”, “C52180”, “C70250”, and “C77000” are copper or copper alloy substrates The numerical value after C indicates the type according to the aforementioned CDA standard.
Further, “A1100”, “A2014”, “A3003”, and “A5052” represent aluminum or aluminum alloy bases, and their components are defined in Japanese Industrial Standards (JIS H 4000: 2006, etc.), respectively.
“SUS304” and “42 alloy” represent an iron-based substrate, and “SUS304” is a stainless steel according to Japanese Industrial Standard (JIS G 4305: 2005) (containing 18 mass% of chromium and 8 mass% of nickel). , “42 alloy” represents an alloy containing 42 mass% of nickel and the balance of iron and inevitable impurities.
When the substrate is aluminum, it undergoes electrolytic degreasing / pickling / zinc replacement process, when it is stainless steel, it undergoes electrolytic degreasing / activation process, and in the case of other substrates, electrolytic degreasing / pickling. The pre-processing which passed through the process was performed.

The treatment solution composition and treatment conditions for each pretreatment and the plating solution composition and plating conditions for each plating used in Example 1 are shown below.
(Pretreatment conditions)
[Electrolytic degreasing]
Degreasing solution: NaOH 60 g / liter Degreasing conditions: 2.5 A / dm ² , temperature 60 ° C., degreasing time 60 seconds [pickling]
Pickling solution: 10% sulfuric acid pickling condition: 30 seconds immersion, room temperature [zinc replacement] Used when the substrate is aluminum Zinc replacement solution: NaOH 500 g / liter, ZnO 100 g / liter, tartaric acid (C ₄ H ₆ O ₆ ) 10 g / Liter, FeCl _{2 2} g / liter treatment condition: 30 seconds immersion, room temperature [activation treatment] used when the substrate is stainless steel Activation treatment solution: NiCl ₂ 40 g / liter, HCl 400 g / liter treatment condition: 1.5 A / liter dm ² , temperature 40 ° C, treatment time 10 seconds

(Intermediate layer plating conditions)
[Ni plating]
Plating _{solution: Ni (SO 3 NH 2)} 2 · 4H 2 O 500g / l, NiCl ₂ 30 g / _l, H ₃ BO ₃ 30g / l Plating Conditions: current density 5A / dm ^2, temperature 50 ° C.
[Co plating]
Plating _{solution: Co (SO 3 NH 2)} 2 · 4H 2 O 500g / l, CoCl ₂ 30 g / _l, H ₃ BO ₃ 30g / l Plating Conditions: current density 5A / dm ^2, temperature 50 ° C.
[Pd plating]
Plating solution: Pd (NH ₃ ) ₂ Cl ₂ 45 g / liter, NH ₄ OH 90 ml / liter, (NH ₄ ) ₂ SO ₄ 50 g / liter Plating condition: current density 1 A / dm ² , temperature 30 ° C.
[Pd—Ni plating] Pd-20% Ni plating plating solution: Pd (NH ₃ ) ₂ Cl ₂ 40 g / liter, NiSO ₄ 45 g / liter, NH ₄ OH 90 ml / liter, (NH ₄ ) ₂ SO ₄ 50 g / liter Liter plating conditions: current density 1A / dm ² , temperature 30 ° C
[Cu plating]
Plating solution: CuSO ₄ .5H ₂ O 250 g / liter, H ₂ SO ₄ 50 g / liter, NaCl 0.1 g / liter Plating condition: current density 6 A / dm ² , temperature 40 ° C.

(Plating conditions for the reflective layer)
[Rh plating 1]
Plating solution: RHODEX (trade name, manufactured by Nippon Electroplating Engineers Co., Ltd.)
Plating conditions: 1.3 A / dm ² , temperature 50 ° C.
[Rh plating 2]
Plating solution: Precious RH02 (trade name, manufactured by Chuo Chemical Industry Co., Ltd.), sulfamate as an additive 5-10 g / liter plating condition: 0.5-2.0 A / dm ² , temperature 50 ° C.
[Ag plating] (Conventional example)
Plating solution: AgCN 50 g / liter, KCN 100 g / liter, K ₂ CO ₃ 30 g / liter Plating condition: current density 0.05 to 5 A / dm ² , temperature 30 ° C.
[Pd plating] (Conventional example)
Plating solution: Pd (NH ₃ ) ₂ Cl ₂ 45 g / liter, NH ₄ OH 90 ml / liter, (NH ₄ ) ₂ SO ₄ 50 g / liter Plating condition: current density 1 A / dm ² , temperature 30 ° C.

(Outermost layer plating conditions)
[Au plating]
Plating solution: KAu (CN) ₂ 14.6 g / liter, C ₆ H ₈ O ₇ 150 g / liter, K ₂ C ₆ H ₄ O ₇ 180 g / liter Plating condition: current density 1 A / dm ² , temperature 40 ° C.
[Au-Co plating] Au-0.3% Co plating solution: Autoronex GVC (trade name, manufactured by Nippon Electroplating Engineers Co., Ltd.)
Plating conditions: 5 A / dm ² , temperature 50 ° C.
[Pd plating]
Plating solution: Pd (NH ₃ ) ₂ Cl ₂ 45 g / liter, NH ₄ OH 90 ml / liter, (NH ₄ ) ₂ SO ₄ 50 g / liter Plating condition: current density 1 A / dm ² , temperature 30 ° C.
[Pt plating]
Plating solution: Pt (NO ₂ ) (NH ₃ ) ₂ 10 g / liter, NaNO ₂ 10 g / liter, NH ₄ NO ₃ 100 g / liter, NH ₃ 50 ml / liter Plating conditions: current density 5 A / dm ² , temperature 80 ° C.

(Plating thickness measurement)
Using a fluorescent X-ray film thickness measuring device (SFT9400: product name, manufactured by SII Nanotechnology Co., Ltd.), a calibration curve having a plating thickness configuration with a collimator diameter of 2 mm was prepared and then measured.
(Measurement of carbon, sulfur and nitrogen content)
In measuring the content of carbon, sulfur, and nitrogen components in the reflective layer coating, the depth direction analysis of the reflective layer is performed using an Auger electron spectroscopic analyzer (Model-680: product name, manufactured by ULVAC-PHI Co., Ltd.). After the implementation, the ratio of the components contained in the film was calculated by integral conversion.
(Hardness _{H IT} measured by the nanoindentation method)
On the surface of the outermost layer forming part, hardness H by the nanoindentation method with an indentation depth of 0.005 μm using an ultra-fine indentation hardness tester (ENT-2100: product name, manufactured by Elionix Co., Ltd.) _IT was measured for any 10 points, and the average value was calculated.

(Evaluation method)
The lead frames of the invention examples and comparative examples in Table 1 obtained as described above were evaluated according to the following tests and standards. The results are shown in Table 2.
(1) Reflectivity measurement: In a spectrophotometer (V660 (trade name, manufactured by JASCO Corp.)), continuous measurement was performed with a total reflectance of 300 nm to 800 nm. Among these, Table 2 shows total reflectance (%) at 300 nm, 340 nm, 400 nm, 600 nm, and 800 nm. As an evaluation standard, it means that a reflectance exceeding 50% is good in all the wavelength region of 300 to 800 nm, and it becomes a standard that is suitably used for an optical semiconductor lead frame.
(2) Wire bonding property (WB property): Under the following wire bonding conditions, a bonding strength measurement is performed after a 10-point test, and a material having a (strength-3σ) value of 49.0 mN or more is determined as “excellent”. The table is marked with “◎”, and those with 29.4 mN or more and less than 49.0 mN are judged as “good”, and the table is marked with “O” and less than 29.4 mN but can be joined. Was determined as “possible” and the table was marked with “Δ”, and those that were not joined at all were judged as “impossible” and marked with “x” in the table. Further, regarding the presence / absence of an error during bonding, “No” is indicated when there is no error, and “Yes” is indicated when an error occurs even once.
Wire bonder: SWB-FA-CUB-10, manufactured by Shinkawa Co., Ltd. Wire: 25 μm Gold wire Bonding temperature: 150 ° C.
Capillary: 1570-17-437GM
1st condition: 10 msec. , 45Bit, 45g
2nd condition: 10 msec. , 100bit, 130g
In addition, for the heat resistance evaluation, the same wire bonding property evaluation is performed even when the air heating is performed at a temperature of 150 ° C. for 3 hours. Level.
(3) Corrosion resistance: Rating number (RN) evaluation was performed about the sulfide state (described in JIS H8502), H ₂ S 3 ppm, and the corrosion state after 24 hours. The results are shown in Table 2. Here, when the rating number is 9 or more, it means that the decrease in luminance is as small as several percent even when the optical semiconductor element (LED element) is lit for 10,000 hours, indicating that long-term reliability is high. .
(4) Reflectivity measurement after the sulfurization test: In a spectrophotometer (V-660 (trade name, manufactured by JASCO Corporation)), continuous measurement was carried out over a total reflectance of 300 nm to 800 nm. Of these, at 400 nm, the value (%) comparing the reflectance before and after the sulfidation test is shown in Table 2.
(5) Bending workability: In the produced lead frame, a sample having a length of 30 mm and a width of 10 mm was cut out so that the length direction was parallel to the rolling direction, and bent by a press machine (manufactured by Nippon Automatic Machine Co., Ltd.). Bending workability was examined at a radius R = 0.5 mm. The maximum bending portion of the processed test piece was observed using a microscope (manufactured by Keyence Co., Ltd.) at a magnification of 175 to determine the bending workability. As a result of observing the maximum bending part, it is determined that the crack does not exist as “good” and the table is marked with “○”, and the one with wrinkles and minor cracks is determined as “good”. Are marked with “Δ”, those having large cracks are judged as “impossible”, and “x” is marked in the table, respectively. The bending workability was evaluated as “practical” or higher.

As is apparent from these results, Invention Example 1 in which the upper layer of rhodium is coated with gold (Au—Co alloy is Au—0.3% Co alloy), palladium, and platinum having a thickness of 0.001 to 0.05 μm. -53, the reflectance in wavelength 300nm -800nm satisfied reflectance 50% or more in all the wavelengths. In addition, all the wire bonding properties are good, but when rhodium of Conventional Example 2 is formed on the outermost layer, it is clear that wire bonding cannot be performed, and the wire bonding properties are greatly improved by the present invention. I understand that. In particular, as shown in Invention Examples 1 to 11, if the thickness of the gold is in the range of 0.001 to 0.02 μm, the reflectivity is 60% or more in the region of 300 to 800 nm, and 0.005 μm. It can be seen from the above that the wire bonding property is particularly excellent. For this reason, it is judged that the outermost layer thickness is preferably 0.003 to 0.03 μm, and more preferably 0.005 to 0.02 μm.
Further, the inventive examples 1 to 53 are greatly improved in corrosion resistance as compared with the example in which the outermost surface described in the conventional example 1 is silver, and this result is longer-term reliability than the conventional silver-plated product. It suggests that there is.
Further, when the inventive examples 1 to 53 are compared with the example in which the outermost surface described in Conventional Example 3 has an Au / Pd plating structure, the reflectance is better in the inventive example. The used optical semiconductor device (LED) is expected to have higher brightness than conventional products.
Further, as described in Invention Examples 19 to 24, when the rhodium thickness exceeds 0.005 μm, the reflectance is all 60% or more in the region of 300 to 800 nm, and a further improvement in luminance is expected. On the other hand, when the thickness exceeds 0.5 μm, the effect of improving the reflectivity is saturated, but the pressability tends to be deteriorated.
Furthermore, as described in Invention Examples 13 to 18, when the intermediate layer is Ni, if the thickness is 0.2 μm or more, the corrosion resistance is further improved, but if it exceeds 2.0 μm, the bending workability tends to deteriorate. I understand. On the other hand, as described in Invention Examples 31 to 38, when the intermediate layer is Pd, the corrosion resistance is further improved when the thickness is 0.005 μm or more, but when it exceeds 0.2 μm, the bending workability tends to deteriorate. I understand. Further, as described in Invention Examples 39 to 42 in which these intermediate layers are two layers, the corrosion resistance is remarkably improved as compared with the case of each single layer, but when the Pd thickness exceeds 0.2 μm or Ni layer When the thickness exceeds 2.0 μm, it can be seen that the bending workability tends to deteriorate.

Further, as in Comparative Example 1, when the outermost layer thickness is thinner than the range of the present invention, it can be seen that the pull strength of wire bonding is lowered and the bonding property after the heat resistance test is poor.
In Comparative Example 2, it can be seen that when the outermost layer thickness is thicker than the range of the present invention, the wire bonding is maintained, but the reflectance at a wavelength of 300 to 400 nm is less than 50%.
Also as in Comparative Example 3, if the hardness H _IT by nanoindentation depth 0.005μm point the outermost layer surface is less than 500, and an error occurs in the bonding occurs, it tends to bonding strength decreases From the above, it can be seen that it lacks stability.
Also, as Comparative Example 4, even if the H _IT is greater than 3000, it can be seen that similarly less stable bonding error occurs. From these facts, by using a lead frame manufactured in an appropriate coating thickness constitution range of the present invention for an optical semiconductor device, it has excellent reflectivity from 300 nm ultraviolet region to 800 nm near infrared region, and has long-term reliability and wire It is obvious that an optical semiconductor device excellent in bonding property can be manufactured.

(Example 2)
As Example 2, a copper alloy EFTEC-3 (Cu-0.15% Sn: equivalent to CDA standard alloy C14410) manufactured by Furukawa Electric Co., Ltd. having a plate thickness of 0.3 mm and a 30 mm square was used as the conductive substrate. After the degreasing step and the pickling step, the whole surface was formed with Ni plating as 0.5 μm as an intermediate layer, Rh plating as 0.02 μm as a reflective layer, and Au plating as 0.01 μm as the outermost layer. Invention Example 54 was produced as a full-surface plated product. On the other hand, the plating configuration was the same, and an Au plating covering portion only of the outermost layer was partially formed in a 3 mm square at the central portion of the substrate, and Invention Example 55 was manufactured as a partially plated product. The partially plated product was masked by applying an insulating masking tape (# 631S; product name, manufactured by Teraoka Seisakusho Co., Ltd.) after forming the reflective layer in the portion where plating was not performed. All pretreatment conditions and plating conditions were the same as in Example 1. As a result of measurement of a hardness _{H IT} by the nanoindentation method 0.005μm point the outermost layer of the outermost surface was both 1220N / mm ^2.
Here, the hardness by the nanoindentation method was measured using an ENT-2100 (product name, manufactured by Elionix Co., Ltd.) as an apparatus, a sample size of 2 mm square, and a temperature at room temperature.

(Evaluation method)
The following evaluation was performed about the full plating product and partial plating product which were obtained as mentioned above.
(1) Reflectivity measurement: In a spectrophotometer (V660 (trade name, manufactured by JASCO Corp.)), continuous measurement was performed with a total reflectance of 300 nm to 800 nm. The measurement area was a 20 mm square area at the center of the test piece. This is because the outermost layer of the overall plated product completely covers the reflectance measurement region, whereas the partially plated product has the outermost layer formed only in the 3 mm square portion, and the portion where the reflective layer is exposed It means that it exists.
Table 3 shows the total reflectance (%) at 300 nm, 340 nm, 400 nm, 600 nm, and 800 nm. As an evaluation standard, it means that a reflectance exceeding 50% is good in all the wavelength region of 300 to 800 nm, and it becomes a standard that is suitably used for an optical semiconductor lead frame.
(2) Wire bonding property (WB property): Under the following wire bonding conditions, a bonding strength measurement is performed after a 10-point test, and a material having a (strength-3σ) value of 49.0 mN or more is determined as “excellent”. The table is marked with “◎”, and those with 29.4 mN or more and less than 49.0 mN are judged as “good”, and the table is marked with “O” and less than 29.4 mN but can be joined. Was determined as “possible” and the table was marked with “Δ”, and those that were not joined at all were judged as “impossible” and marked with “x” in the table. In addition, the wire bonding area | region was implemented in the part in which the outermost layer was formed in 1st side and 2nd side.
Wire bonder: SWB-FA-CUB-10, manufactured by Shinkawa Co., Ltd. Wire: 25 μm Gold wire Bonding temperature: 150 ° C.
Capillary: 1570-17-437GM
1st condition: 10 msec. , 45Bit, 45g
2nd condition: 10 msec. , 100bit, 130g
In addition, for the heat resistance evaluation, the same wire bonding property evaluation was carried out even for those subjected to atmospheric heating at a temperature of 150 ° C. for 3 hours.
(3) Outermost layer coverage: From the outermost layer plating area, the outermost layer noble metal coverage during the entire plating and partial plating was calculated. The coverage was expressed as a percentage of the area of the object to be plated with respect to the covering area of the outermost layer plating.

  From these results, both of the invention examples show a reflectance of 50% or more in the entire wavelength range and excellent wire bonding properties, but the partially plated product reflects in the wavelength region of 300 to 600 nm more than the entire plated product. The rate is slightly better, close to or nearly the same as that of pure rhodium. This is the result of maximizing the reflectivity of the reflective layer by minimizing the decrease in reflectivity by forming the outermost layer only where it is necessary for wire bonding. The outermost layer is partially formed. It can be seen that this is more preferable. In addition, the precious metal coverage of the outermost layer is suppressed to 1/100 of the partially plated product, and as a result, the amount of precious metal used for the outermost layer can be reduced to 1/100, which can reduce the environmental burden. Recognize. From these facts, it can be seen that the lead frame in which only the portion requiring wire bonding is coated is more excellent in characteristics and manufacturing cost than the coating of the outermost layer on the entire surface.

DESCRIPTION OF SYMBOLS 1 Conductive base | substrate 2 Reflective layer 3 Outermost layer 4 Optical semiconductor element 5 Wire (bonding wire)
6 Middle class

Claims (8)

For an optical semiconductor device in which a reflective layer made of rhodium or a rhodium alloy is formed on a conductive substrate, and an outermost layer made of gold, palladium, platinum or an alloy thereof is formed on at least a part of the surface of the reflective layer The lead frame has a thickness of the outermost layer of 0.001 to 0.05 μm, and a hardness H _IT by a nanoindentation method at a depth of 0.005 μm from the surface of the outermost layer is an arbitrary 10 A lead frame for an optical semiconductor device, characterized in that the average value measured for the points is 500 to 3000 N / mm ² .
  The lead frame for an optical semiconductor device according to claim 1, wherein the reflective layer has a thickness of 0.005 to 0.5 μm.   The rhodium or rhodium alloy forming the reflective layer is rhodium, rhodium-tin alloy, rhodium-copper alloy, rhodium-cobalt alloy, rhodium-silver alloy, rhodium-aluminum alloy, rhodium-indium alloy, rhodium-iridium alloy, rhodium. The lead frame for an optical semiconductor device according to claim 1, wherein the lead frame is made of a material selected from the group consisting of a ruthenium alloy, a rhodium-palladium alloy, a rhodium-nickel alloy, and a rhodium-platinum alloy.   One or more intermediate layers are provided between the conductive substrate and the reflective layer, and the intermediate layer is made of nickel or nickel alloy, cobalt or cobalt alloy, copper or copper alloy, palladium or palladium alloy. The lead frame for optical semiconductor devices according to any one of claims 1 to 3, wherein the lead frame is made of a metal or an alloy selected from the group consisting of:   When the intermediate layer contains nickel or a nickel alloy, cobalt or a cobalt alloy, copper or a copper alloy, the thickness of the layer made of these components is 0.2 to 2.0 μm in total, The lead frame for optical semiconductors according to claim 4.   5. The optical semiconductor according to claim 4, wherein when the intermediate layer includes palladium or a palladium alloy, a total thickness of the palladium or the palladium alloy is 0.005 to 0.2 μm. Lead frame.   An optical semiconductor device comprising the lead frame for an optical semiconductor device according to any one of claims 1 to 6 and an optical semiconductor element, wherein the outermost layer is provided at a position where wire bonding is performed and in the vicinity thereof. An optical semiconductor device provided.   8. The optical semiconductor device according to claim 7, wherein the reflective layer and the outermost layer are provided in the vicinity of a place where the optical semiconductor element is mounted.

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