JP6175822B2 - Lead frame or substrate for optical semiconductor devices - Google Patents

Description

  The present invention relates to a lead frame or a substrate for an optical semiconductor device.

  2. Description of the Related Art Optical semiconductor devices such as light emitting diodes (LEDs) are widely used as light sources for lighting, various displays, liquid crystal televisions, and mobile phone backlights. These optical semiconductor devices are configured by mounting an optical semiconductor element on various substrates such as a lead frame, a printed substrate, a ceramic substrate, or a flexible substrate by die bonding or wire bonding. And in order to improve mounting reliability, it is common to perform either gold plating or silver plating on the lead frame and various substrates. Gold plating is difficult to oxidize and has high bonding reliability. However, since it easily absorbs light in the visible region emitted from the optical semiconductor element, the optical semiconductor device uses silver plating that is highly reflective to light in the visible region. Widely used (see, for example, Patent Documents 1 and 2).

JP 2007-258514 A JP 2012-089830 A

  Silver plating of lead frames or substrates used in conventional optical semiconductor devices generally requires a thickness of 2.0 μm or more to ensure high luminous flux and reliable die bonding and wire bonding properties. was there. However, to reduce the manufacturing cost, it is required to reduce the silver plating thickness of the lead frame or the substrate for the optical semiconductor device.

  Therefore, the present invention has been made in view of such circumstances, and an optical semiconductor capable of maintaining a high initial luminous flux even when the silver plating thickness is reduced and further suppressing a decrease in the lifetime of the optical semiconductor device due to sulfidation corrosion. An object is to provide a lead frame or substrate for an apparatus.

In order to solve the above problems, a lead frame or substrate for an optical semiconductor device of the present invention is a base material selected from the group consisting of copper, copper alloy, iron, iron alloy, aluminum, aluminum alloy, ceramics, and plastics. A first layer of glossy nickel plating or glossy nickel alloy plating with a thickness of 1 μm or more and 7 μm or less on the surface of the steel , containing 30 ppm or more and 1000 ppm or less of carbon or / and 50 ppm or more and 1000 ppm or less of sulfur a first layer being a second layer less than the thickness 0.005 .mu.m 0.1 [mu] m palladium plating or palladium alloy plating, a less than a thickness of 0.05 .mu.m 2.0 .mu.m, and gloss 1. It has 3rd or more silver plating 3rd layers in this order, It is characterized by the above-mentioned.

  According to the lead frame and substrate for an optical semiconductor device of the present invention, the material cost of the optical semiconductor device can be reduced. Further, since the progress of sulfidation corrosion of silver plating can be suppressed, the life of the optical semiconductor device can be improved. Furthermore, since the luminous flux of the optical semiconductor device can be improved, the number of mounted parts in the LED bulb and the backlight for the liquid crystal television can be reduced, thereby making it possible to save energy and reduce the manufacturing cost.

<Embodiment 1>
An optical semiconductor device forms an electrical circuit and die-bonds an optical semiconductor element of a compound semiconductor such as gallium nitride that emits light when a voltage is applied to a lead frame or a substrate (printed substrate, ceramic substrate, flexible substrate, etc.) using a paste It is often manufactured by wire bonding to p-type and n-type electrodes with a gold wire or the like and sealing with resin. The optical semiconductor device is mounted by solder reflow or the like when mounted on an LED bulb or the like.

  In order to industrially perform such an assembly process and a mounting process with stable quality, it is common to perform gold plating or silver plating on a lead frame or a substrate for an optical semiconductor device. In particular, silver plating has been widely put into practical use because high reflectance can be obtained. Such a silver plating film is required to have higher luminous flux characteristics in addition to requirements such as highly reliable wire bonding, stable die bonding, stable solder wettability, and sealing resin adhesion.

  Silver-plated lead frames or substrates are widely used in optical semiconductor devices because of their high reflectivity. However, silver easily reacts in an atmosphere containing hydrogen sulfide, among sulfur-containing gases. In addition, iron or copper as a base material reacts in an atmosphere containing sulfur oxides, particularly sulfur dioxide, and is easily altered (corroded). In the present specification, the gas mainly composed of these sulfur-containing gases is referred to as “corrosive gas”, and “corrosion” including sulfidation reaction generated by this gas and a complex reaction accompanying it. ".

  In order to suppress the destruction of the joint boundary due to these corrosions, and to suppress local corrosion and alteration between the silver plating and the base metal, combinations of various metal layers were examined. Hereinafter, although a specific example is demonstrated, the composition and operation conditions of the plating solution used are one example, and are not limited thereto.

  The first layer is preferably glossy nickel plating or glossy nickel alloy plating having a thickness of 1 μm or more and 7 μm or less in order to suppress sulfide corrosion or improve luminous flux. This nickel or nickel alloy has a function of improving luminous flux because its surface is glossy. In addition, if carbon or sulfur is contained in the nickel or nickel alloy film, the corrosion potential between the base metal of the nickel or nickel alloy film or the palladium or palladium alloy metal of the upper layer is adjusted. Has a suppression function. The carbon content and sulfur content in the glossy nickel plating or glossy nickel alloy plating film can be controlled by the type and concentration of the organic brightener used and the plating conditions. The carbon content in the glossy nickel plating or glossy nickel alloy plating film is not particularly limited as long as the plating film is glossy, but is preferably 30 ppm or more and 1000 ppm or less. The sulfur content in the glossy nickel plating or glossy nickel alloy plating film is not particularly limited as long as the plating film is glossy, but is preferably 50 ppm or more and 1000 ppm or less.

  Nickel plating or nickel alloy plating can be formed from bright nickel or bright nickel alloy plating solution by adding an organic substance containing no sulfur or an organic substance containing sulfur. Specifically, the copper lead frame can be degreased with an alkaline degreasing solution, acid neutralized, and nickel plated with the following bright nickel plating solution.

The composition of the nickel plating solution is as follows: nickel sulfamate = 450 g / L, nickel chloride = 5 g / L, boric acid = 30 g / L, brightener SN-1000 (Murata Co., Ltd.) or SN-20 (Murata Co., Ltd.) = 10 ml / L, pH 4.0-4.4. The nickel plating conditions are a liquid temperature of 55 ° C., strong stirring, a cathode current density of 5 A / dm ² , and a plating time of 2 minutes.

  The thickness of the nickel plating or nickel alloy plating is preferably 1 μm or more. If the thickness of the nickel plating or nickel alloy plating is less than 1 μm, the silver plating reflectivity when silver plating is performed decreases, so when assembled as an optical semiconductor device, a high luminous flux cannot be obtained and corrosion occurs. It becomes easy. The thickness of the nickel plating or nickel alloy plating is preferably 7 μm or less. When the thickness of nickel plating or nickel alloy plating exceeds 7μm, the film stress of nickel plating or nickel alloy plating increases, cracks due to lead bending of the lead frame occur, and when the board is separated into parts In addition, cutting burrs are likely to occur.

  As the nickel alloy, any one of nickel cobalt alloy, nickel tin alloy, nickel phosphorus alloy, nickel boron alloy and nickel chromium alloy is preferable.

  Note that a copper plating layer may be provided on the surface of the base material before the first layer of nickel plating or nickel alloy plating. The thickness of the copper plating is preferably 0.1 μm or more and 10 μm or less. This is because if the thickness of the copper plating is less than 0.1 μm, scratches or hole defects in the copper material cannot be sufficiently prevented. Further, when the thickness of the copper plating exceeds 10 μm, the dimensional error of the lead frame and the substrate becomes large.

  The second layer is preferably palladium plating or palladium alloy plating with a thickness of 0.005 μm or more and 0.1 μm or less in order to suppress sulfide corrosion. Palladium plating or palladium alloy plating adjusts the corrosion potential between the underlying nickel plating layer or nickel alloy plating layer and the silver plating layer, and has a function of suppressing sulfide corrosion. After performing nickel plating or nickel alloy plating, it is preferable to wash with water and perform palladium plating or palladium alloy plating.

The composition of the palladium plating solution is Parabright SST-L (manufactured by Nippon Kojun Kagaku Co., Ltd.), a palladium concentration of 5 g / L, and a pH of 8.5. The palladium plating conditions are a liquid temperature of 55 ° C., strong stirring, a current density of 1 A / dm ² , and a plating time of 8 seconds.

  The thickness of palladium plating or palladium alloy plating is preferably 0.005 μm or more. When the thickness of the palladium plating or palladium alloy plating is less than 0.005 μm, the corrosion potential state between the underlying nickel plating layer or nickel alloy plating layer and the silver plating layer tends to show a corrosion tendency. Moreover, as thickness of palladium plating or palladium alloy plating, 0.1 micrometer or less is preferable. When the thickness of the palladium plating or palladium alloy plating exceeds 0.1 μm, the material cost increases.

  As the palladium alloy, any one of a palladium nickel alloy, a palladium copper alloy, a palladium iron alloy, a palladium tin alloy, a palladium tellurium alloy, a palladium bismuth alloy, a palladium germanium alloy, and a palladium platinum alloy is preferable.

  A gold plating layer or a gold alloy plating layer may be provided between the second layer and the silver plating layer (referred to as the third layer). The thickness of gold plating or gold alloy plating is preferably 0.002 μm or more. If the thickness of the gold plating or gold alloy plating is less than 0.002 μm, the corrosion potential state of the underlying palladium plating layer or palladium alloy plating layer and silver plating layer tends to show a corrosion tendency. Moreover, as thickness of gold plating or gold alloy plating, 0.05 micrometer or less is preferable. When the thickness of gold plating or gold alloy plating exceeds 0.05 μm, the material cost increases. After palladium plating or palladium alloy plating, washing with water and subsequent gold plating or gold alloy plating can be performed.

The composition of the gold plating solution is potassium gold cyanide = 2 g / L, potassium citrate = 150 g / L, and pH 5.5. The gold plating conditions are a liquid temperature of 50 ° C., weak stirring, a current density of 2 A / dm ² , and a plating time of 5 seconds.

  As the gold alloy, any of gold-silver alloy, gold-nickel alloy, gold-copper alloy, gold-indium alloy, gold-tin alloy, gold-zinc alloy, gold thallium alloy, and gold-cobalt alloy is preferable.

  The silver plating solution is preferably a plating solution containing a cyanide compound by adding a small amount of a selenium compound, a sulfur compound or an antimony compound. After the underlying palladium plating or palladium alloy plating is performed, or after gold plating or gold alloy plating is performed, the substrate is washed with water and subsequently subjected to silver plating. However, silver strike plating may be performed before silver plating in order to improve adhesion and maintain uniformity of plating appearance.

The composition of the silver plating solution is: potassium potassium cyanide = 80 g / L, potassium cyanide = 100 g / L, potassium carbonate = 30 g / L, silver glow 3K = 30 ml / L (Meltex Co., Ltd.). The silver plating conditions are a liquid temperature of 25 ° C., strong stirring, and a current density of 3 A / dm ² .

  The thickness of the silver plating is preferably 0.05 μm or more. When the thickness of the silver plating is less than 0.05 μm, the luminous flux of the optical semiconductor device is lowered. The thickness of the silver plating is preferably less than 2 μm. When the thickness of the silver plating exceeds 2 μm, the material cost becomes high. Furthermore, the thickness of the silver plating is more preferably 1 μm or less. The presence of the above-mentioned glossy nickel plating or glossy nickel alloy plating on the base of the silver plating reduces the thickness of the silver plating to 1 μm or less while having high initial luminous flux and corrosion resistance. be able to.

  The glossiness of silver plating is preferably 1.3 or more. The glossiness of silver plating is a numerical value of glossiness commonly used in the silver plating lead frame industry. For example, Densitmeter Model 144 manufactured by GAM or a micro surface colorimeter / reflectometer VSR400 manufactured by Nippon Denshoku Industries Co., Ltd. Or a densitometer (reflection densitometer) ND-11. The glossiness of silver used in the optical semiconductor device is preferably 1.3 or more. When the glossiness of silver plating is less than 1.3, the reflectance is lowered, and the luminous flux of the optical semiconductor device is lowered. On the other hand, the upper limit is not limited, but the detection limit of the measuring device is the upper limit. Generally, it is around 3.0.

  Of course, the silver plating film of the present invention is also excellent in highly reliable wire bonding properties, stable die bonding properties, stable solder wettability, sealing resin adhesion, and the like.

  The plating thickness of the present invention can be measured with a micro fluorescent X-ray film thickness meter widely used in the plating industry.

  The plating of the present invention is a plating method in which the lead frame or the substrate is used as an anode, metal silver, stainless steel, platinum group metal or titanium coated with a platinum group metal is used as a cathode, and immersed in the silver plating solution of the present invention for electroplating. Can be realized.

  The plating method of the present invention is a so-called rack type plating method of a manual or automatic elevator system, a reel-to-reel type electroplating tank is an overflow type plating method, or a jet type plating method in which a semiconductor lead frame is partially plated Any of these can be accommodated.

  Further, the lead frame after silver plating of the present invention can be plastically deformed by rolling or the like. In addition, the lead frame of the present invention can be formed by press punching after performing the plating treatment of the present invention. Furthermore, a protective film can be provided on the silver plating surface of the lead frame or the substrate of the present invention by a method such as sputtering or chemical vapor deposition. This protective film can be applied before or after the optical semiconductor device is assembled.

  EXAMPLES Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

<Example>
As the lead frame, a copper alloy KLF194 (CDA No. C19400, iron content rate 2.3%) flat plate made by Kobe Steel Co., Ltd. with a thickness of 0.11 mm was used, and Enomoto's LED open frame FLASH Die-cut type LED 6PIN OP1 (outer dimension 5050) is used. After degreasing with an alkaline degreasing agent, the solution is neutralized with dilute sulfuric acid, and then copper plating is applied in a thickness of 0.5 μm using a cyan bath. Then, after sequentially performing the metal plating layers of the present invention, silver plating is performed, washed with clean pure water, and then dried to produce a lead frame with silver plating. Silver plating shall be whole surface silver plating. The lead frame is placed in a mold, polyphthalamide resin is injected as a molding material, and cured to be removed from the mold. Then, an InGaN-based blue light emitting diode chip is die-bonded with a paste on the obtained lead frame after resin molding, and then heated and bonded at 150 ° C. for 1 hour. Thereafter, the electrode of the light emitting diode chip and the lead frame are wire-bonded with a gold wire having a diameter of 25 μm. Next, 20% of YAG phosphor blended with the modified silicone resin is filled into the molding opening and cured with a hot air dryer (curing conditions: 150 ° C., 4 hours) to complete sealing. To do. After that, it is separated into individual LEDs. Samples are prepared in the same manner for the substrate.

  The manufactured lead frame is assembled as an optical semiconductor device manufactured according to the above procedure, and an initial total luminous flux Φv (lm) is measured as an LED using an integrating total luminous flux measuring device.

  Further, after the LED is processed by a sulfuration test as described below, the luminous flux is measured with an integral-type total luminous flux measurement device in the same manner as the initial luminous flux. The sulfidation test is performed by placing the optical semiconductor device in a mixed gas atmosphere of hydrogen sulfide and sulfur oxide. Specifically, it is carried out by a method according to JIS C0048, and the temperature is 30 ° C. and 75 RH, hydrogen sulfide: 0.1 to 3 ppm, nitric oxide: 0.1 to 0.5 ppm, chlorine 0.01 to 0.05 ppm. To do. The luminous flux maintenance factor is a luminous flux ratio with respect to the luminous flux before the sulfidation test. The higher the luminous flux maintenance factor, the smaller the influence of the corrosive gas and the better the corrosion resistance.

  Table 1 shows comparative examples and examples. The brackets in Table 1 represent the plating thickness (μm). The plating configuration indicates the type of metal with an element symbol.

  As shown in Table 1, compared with Comparative Examples 1 to 3, the luminous flux maintenance rates after the sulfurization test treatment are improved in the luminous flux values of Examples 1 to 25.

Claims (8)

On the surface of the base material selected from the group consisting of copper, copper alloy, iron, iron alloy, aluminum, aluminum alloy, ceramics, plastics,
A first layer of glossy nickel plating or glossy nickel alloy plating having a thickness of 1 μm or more and 7 μm or less, and containing 30 ppm or more and 1000 ppm or less of carbon and / or 50 ppm or more and 1000 ppm or less of sulfur When,
A second layer of palladium plating or palladium alloy plating with a thickness of 0.005 μm to 0.1 μm;
A lead frame or substrate for an optical semiconductor device, comprising a third layer of silver plating having a thickness of 0.05 μm or more and less than 2.0 μm and a glossiness of 1.3 or more in this order.   2. The lead frame or substrate for an optical semiconductor device according to claim 1, wherein a thickness of the third layer is 0.05 μm or more and 1.0 μm or less. Wherein the surface of the base, a lead frame or a substrate for an optical semiconductor device according to claim 1 or 2 having the following copper plating layer 10μm or more thick 0.1 [mu] m. Said nickel alloy plating, nickel-cobalt alloy, nickel-tin alloy, nickel phosphorus alloy, nickel boron alloy, for an optical semiconductor device according to any one of claims 1 to 3 is any one of a nickel-chromium alloy Lead frame or substrate. The palladium alloy plating, palladium nickel alloy, palladium copper alloy, palladium-iron alloy, palladium-tin alloy, palladium tellurium alloy, palladium bismuth alloy, palladium germanium alloy of claims 1 to 4 is any one of a palladium platinum alloy The lead frame or board | substrate for optical semiconductor devices as described in any one. Between the third layer and the second layer, an optical semiconductor device according to any one of claims 1 to 5 having a thickness of 0.002μm or more 0.05μm or less of the gold plating layer or gold alloy plating layer Lead frame or substrate for use. The optical semiconductor device according to claim 6 , wherein the gold alloy is any one of a gold-silver alloy, a gold-nickel alloy, a gold-copper alloy, a gold-indium alloy, a gold-tin alloy, a gold-zinc alloy, a gold thallium alloy, and a gold-cobalt alloy. Lead frame or substrate for use. An optical semiconductor device in which an optical semiconductor element is mounted on a lead frame or a substrate for an optical semiconductor device according to any one of claims 1 to 7 .