Patent Application
20050202598
The present invention relates to a process for producing an optical semiconductor device.
An optical semiconductor device is known which includes an optical semiconductor element encapsulated with two or more resin layers disposed in order of their decreasing refractive index from the optical-semiconductor element side toward the outermost layer so as to have an improved efficiency of light takeout (see patent document 1).
Patent Document 1: JP 10-65220 A (claim 1)
The first encapsulating resin to be in direct contact with optical semiconductor elements has hitherto been formed by dipping or potting. However, resin encapsulation by dipping or potting has drawbacks that the operation of dropping a liquid resin onto each of optical semiconductor elements in a predetermined amount is troublesome and that unevenness of the encapsulated elements in encapsulant shape is apt to result in uneven light emission.
In order to mitigate those drawbacks, the present inventors found out a process for producing an optical semiconductor device which comprises forming a resin layer on optical semiconductor elements mounted on a conductor and press-molding the resin layer. This process, however, has had the following drawback although effective in diminishing uneven light emission. When the sidewall of each optical semiconductor element make an angle of 90° with the conductor, voids are apt to be formed between the sidewall and the resin layer and this can be a cause of a deteriorated function and reliability of the optical semiconductor device.
Accordingly, an object of the invention is to provide a process for producing an optical semiconductor device in which the resin encapsulation of one or more optical semiconductor elements can be easily and evenly conducted to produce an optical semiconductor device which is highly functional and reliable.
Other objects and effects of the invention will become apparent from the following description.
The invention relates to a process for producing an optical semiconductor device, which comprises:
According to the invention, the resin encapsulation of optical semiconductor elements can be easily and evenly conducted and a high-quality optical semiconductor device can be obtained which has evenness in the efficiency of light takeout and is highly functional and reliable.
FIGS. 5(A) to (C) are plan views and sectional views of examples of optical semiconductor elements usable in the invention.
The reference numerals and used in the drawings denote the followings, respectively.
The process of the invention for producing an optical semiconductor device comprises:
In step (1), the optical semiconductor elements are not particularly limited as long as they are ones for ordinary use in optical semiconductor devices. Examples thereof include gallium nitride (GaN; refractive index, 2.5), gallium-phosphorus (GaP; refractive index, 2.9), and gallium-arsenic (GaAs; refractive index, 3.5). GaN is preferred of these because it emits a blue light and a white LED can be produced therefrom using a phosphor therewith.
The planar shape (i.e., horizontal section) of the optical semiconductor elements preferably is a regular polygon because it facilitates even light diffusion. The planar shape thereof is more preferably a square or regular hexagon because the optical semiconductor elements having such planar shape can be efficiently cut, in a closest packing state, out of an optical-semiconductor wafer.
The optical semiconductor elements each have a vertical section which is tapered from the face 14, through which the element is mounted on a conductor of a wiring circuit board (this face may be hereinafter referred to as “mounting-side face”), toward the face 13, through which light emission is observed (this face may be hereinafter referred to as “light emission-side face”), as shown in
The term “tapered” as used in this specification means that in a vertical section of an optical semiconductor element as shown in
Examples of processing methods for forming the above-explained shape include: a method in which an abrasive diamond material having a particle diameter of 1.0 to 0.05 μm or the like is used to grind the sidewall of an optical semiconductor element to attain the desired shape; and a method in which an optical semiconductor wafer is cut into elements by causing a laser light to be incident obliquely so that the desired shape is obtained. Examples of the laser for use in the cutting include YAG lasers, CO2 lasers, and excimer lasers. The irradiation energy of the laser is determined from the rate of chip cutting, etc.
The length of each side, on the mounting-side face, of each optical semiconductor element to be used in the invention is generally 0.2 to 0.4 mm in the case of a square and is generally 0.1 to 0.2 mm in the case of a regular hexagon. The thickness of the element is generally 0.06 to 0.2 mm.
The conductor on which each optical semiconductor element is to be mounted is not particularly limited as long as it is one for ordinary use in optical semiconductor devices. The conductor to be used may be a lead frame having a predetermined shape, a terminal formed on a wiring circuit board, or the like, or may be a conductor which has been made to have a predetermined shape by etching.
The wiring circuit board on which one or more optical semiconductor elements and conductors are to be mounted also is not particularly limited. Examples thereof include rigid wiring boards produced by superposing a copper wiring on a glass-epoxy substrate, and flexible wiring boards produced by superposing a copper wiring on a polyimide film. It is preferred in the invention that the device comprises two or more conductors and two or more optical semiconductor elements, mounted on one wiring board, from the standpoint of exerting the effects of the invention remarkably.
Examples of methods for mounting optical semiconductor elements on the wiring circuit board include: the face-up bonding method, which is suitable for mounting optical semiconductor elements each having an electrode disposed on the light emission-side face thereof; and the flip chip bonding method, which is suitable for mounting optical semiconductor elements each having an electrode disposed on the face thereof opposite to the light emission-side face.
The refractive index of the resin for constituting the resin layer in step (1) (This resin may hereinafter referred to as “first resin”) is preferably 1.6 or higher, more preferably 1.7 to 2.1, from the standpoint of heightening the efficiency of light takeout from the optical semiconductor elements.
Examples of the resin for encapsulating the optical semiconductor elements include polyethersulfones, polyimides, aromatic polyamides, polycarbodiimides, and epoxy resins.
Preferred of these for use as the resin constituting the resin layer in step (1) are polycarbodiimides from the standpoint of ease of processing at low temperatures and low pressures. More preferred is a polycarbodiimide represented by formula (1):
wherein R represents a diisocyanate residue, R1 represents a monoisocyanate residue, and n is an integer of 1 to 100.
In the invention, the polycarbodiimide represented by formula (1) is obtained by subjecting one or more diisocyanates to a condensation reaction and blocking the terminals of the resulting polymer with a monoisocyanate.
In formula (1), R represents a residue of the diisocyanate used as a starting material and R1 represents a residue of the monoisocyanate used as another starting material. Symbol n is an integer of 1 to 100.
The diisocyanate and monoisocyanate to be used as starting materials may be either aromatic or aliphatic. The diisocyanate and the monoisocyanate each may consist of one or more aromatic isocyanates singly or one or more aliphatic isocyanates singly, or may comprise a combination of an aromatic isocyanate and an aliphatic isocyanate. From the standpoint of obtaining a polycarbodiimide having a higher refractive index, it is preferred to use aromatic isocyanates in the invention. Namely, it is preferred that at least either of the diisocyanate and the monoisocyanate comprises an aromatic isocyanate or consist of one or more aromatic isocyanates, or that each of the diisocyanate and the monoisocyanate consists of one or more aromatic isocyanates. More preferred is the case in which the diisocyanate comprises a combination of an aliphatic isocyanate and an aromatic isocyanate and the monoisocyanate consists of one or more aromatic isocyanates. Especially preferred is the case in which the diisocyanate and the monoisocyanate each consist of one or more aromatic isocyanates.
Examples of diisocyanates usable in the invention include hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 4,4′-dichlorohexylmethane diisocyanate, xylylene diisocyanate, tetramethylxylylene diisocyanate, isophorone diisocyanate, cyclohexyl diisocyanate, lysine diisocyanate, methylcyclohexane 2,4′-diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, 2,6-tolylene diisocyanate, 2,4-tolylene diisocyanate, naphthalene diisocyanate, 1-methoxyphenyl 2,4-diisocyanate, 3,3′-dimethoxy-4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, 3,3′-dimethyl-4,4′-diphenyl ether diisocyanate, 2,2-bis[4-(4-isocyanatophenoxy)phenyl]-hexafluoropropane, and 2,2-bis[4-(4-isocyanatophenoxy)phenyl]propane.
From the standpoints of enabling the polycarbodiimide to have a high refractive index and of ease of the control thereof, it is preferred to use, among those diisocyanates, at least one member selected from the group consisting of tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, and dodecamethylene diisocyanate. More preferred is naphthalene diisocyanate.
Those diisocyanates can be used singly or as a mixture of two or more thereof. From the standpoint of heat resistance, however, it is preferred to use a mixture of two or three diisocyanates.
The one or more diisocyanates to be used as a starting material preferably comprise one or more aromatic diisocyanates in an amount of preferably 10% by mole or larger (upper limit, 100% by mole) based on all diisocyanates. These diisocyanates desirably are ones enumerated above as preferred examples.
Examples of monoisocyanates usable in the invention include cyclohexyl isocyanate, phenyl isocyanate, p-nitrophenyl isocyanate, p- and m-tolyl isocyanates, p-formylphenyl isocyanate, p-isopropylphenyl isocyanate, and 1-naphthyl isocyanate.
Preferred monoisocyanates are aromatic monoisocyanates because aromatic monoisocyanates do not react with each other and the terminal blocking of a polycarbodiimide with such monoisocyanates proceeds efficiently. It is more preferred to use 1-naphthyl isocyanate.
Those monoisocyanates can be used singly or as a mixture of two or more thereof.
The amount of the monoisocyanate to be used for terminal blocking is preferably in the range of 1 to 10 mol per 100 mol of the diisocyanate ingredient to be used, from the standpoint of storage stability.
The polycarbodiimide production according to the invention can be conducted by converting one or more diisocyanates as a starting material to a carbodiimide through condensation reaction in a predetermined solvent in the presence of a catalyst for carbodiimide formation and blocking the terminals of the resultant carbodiimide polymer with a monoisocyanate.
The diisocyanate condensation reaction is conducted at a temperature of generally 0 to 150° C., preferably 10 to 120° C.
In the case where an aliphatic diisocyanate and an aromatic diisocyanate are used in combination as starting-material diisocyanates, it is preferred to react the diisocyanates at a low temperature. The reaction temperature is preferably 0 to 50° C., more preferably 10 to 40° C. Use of a reaction temperature in this range is preferred because the condensation of the aliphatic diisocyanate with the aromatic diisocyanate proceeds sufficiently.
In the case where an excess aromatic diisocyanate present in the reaction mixture is desired to be further reacted with the polycarbodiimide formed from an aliphatic diisocyanate and an aromatic diisocyanate, the reaction temperature is preferably 40 to 150° C., more preferably 50 to 120° C. As long as the reaction temperature is within this range, any desired solvent can be used to smoothly conduct the reaction. The reaction temperature range is therefore preferred.
The diisocyanate concentration in the reaction mixture is preferably from 5 to 80% by weight. As long as the diisocyanate concentration is within this range, carbodiimide formation proceeds sufficiently and reaction control is easy. The diisocyanate concentration range is therefore preferred.
Terminal blocking with a monoisocyanate can be accomplished by adding the monoisocyanate to the reaction mixture in an initial, middle, or final stage of carbodiimide formation from the diisocyanate(s) or throughout the carbodiimide formation. The monoisocyanate is preferably an aromatic monoisocyanate.
As the catalyst for carbodiimide formation, any of known phosphorus compound catalysts can be advantageously used. Examples thereof include phospholene oxides such as 1-phenyl-2-phospholene 1-oxide, 3-methyl-2-phospholene 1-oxide, 1-ethyl-2-phospholene 1-oxide, 3-methyl-1-phenyl-2-phospholene 2-oxide, and the 3-phospholene isomers of these.
The solvent (organic solvent) to be used for producing the polycarbodiimide is a known one. Examples thereof include halogenated hydrocarbons such as tetrachloroethylene, 1,2-dichloroethane, and chloroform, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, cyclic ether solvents such as tetrahydrofuran and dioxane, and aromatic hydrocarbon solvents such as toluene and xylene. These solvents can be used singly or as a mixture of two or more thereof. These solvents are used also for dissolving the obtained polycarbodiimide.
The end point of the reaction can be ascertained by infrared spectroscopy (IR analysis) from the occurrence of absorption attributable to the carbodiimide structure (N═C═N) (2,140 cm−1) and the disappearance of absorption attributable to the isocyanates (2,280 cm−1).
After completion of the carbodiimide-forming reaction, a polycarbodiimide is obtained usually in the form of a solution. However, the solution obtained may be poured into a poor solvent such as methanol, ethanol, isopropyl alcohol, or hexane to precipitate the polycarbodiimide and remove the unreacted monomers and the catalyst.
In preparing a solution of the polycarbodiimide which has been recovered as a precipitate, the precipitate is washed and dried in a predetermined manner and then dissolved again in an organic solvent. By performing this operation, the polycarbodiimide solution can have improved storage stability.
In the case where the polycarbodiimide solution contains by-products, the solution may be purified, for example, by adsorptively removing the by-products with an appropriate adsorbent. Examples of the adsorbent include alumina gel, silica gel, activated carbon, zeolites, activated magnesium oxide, activated bauxite, Fuller's earth, activated clay, and molecular sieve carbon. These adsorbents can be used singly or in combination of two or more thereof.
By the method described above, the polycarbodiimide according to the invention is obtained. From the standpoint of enabling the polycarbodiimide constituting the resin layer in step (1) to have a higher refractive index, the polycarbodiimide preferably is one in which the backbone structure is constituted of aromatic and aliphatic diisocyanates and the terminals have been blocked with an aromatic monoisocyanate. More preferred is one in which the backbone structure is constituted of one or more aromatic diisocyanates and the terminals have been blocked with an aromatic monoisocyanate.
Specifically, the polycarbodiimide preferably is one in which 10% by mole or more (upper limit, 100% by mole) of the diisocyanate residues represented by R in formula (1) are residues of one or more aromatic diisocyanates and the monoisocyanate residues represented by R1 in formula (1) are residues of one or more aromatic monoisocyanates. The diisocyanate residues preferably are residues of at least one member selected from the group consisting of tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, and dodecamethylene diisocyanate, and more preferably are naphthalene diisocyanate residues. The aromatic monoisocyanate residues preferably are 1-naphthyl isocyanate residues.
Examples of methods for carrying out the step of forming a resin layer comprising the first resin on one or more optical semiconductor elements include: a method in which a sheet-form resin 1 is laminated by means of, e.g., a laminator 4 onto a substrate 3 having optical semiconductor elements 2 mounted thereon, as shown in
In the method shown in
In the case where the sheet from resin is melted and laminated to a substrate by thermal press bonding using a laminator or the like, it is preferred that the resin be heated to preferably 70 to 250° C., more preferably 100 to 200° C., and pressed at preferably 0.1 to 10 MPa, more preferably 0.5 to 5 MPa. When a laminator is used, the revolution speed thereof is preferably 100 to 2,000 rpm, more preferably 500 to 1,000 rpm.
In the method shown in
Step (1) as illustrated above is followed by step (2). Another significant feature of the invention resides in step (2). By press-molding the resin layer formed in step (1), the optical semiconductor elements can be easily encapsulated with an even resin layer and an optical semiconductor device having evenness in the efficiency of light takeout can be obtained.
The press molding of the resin layer can be conducted with a stamper or the like. In the invention, the stamper to be used can be, for example, one obtained by forming a polyimide sheet or polycarbonate sheet into a predetermined die by laser processing or one produced by plating such a die as a master with a metal, e.g., nickel.
The press molding of the resin layer with a stamper can be conducted, for example, in the manner shown in
Examples of conditions for the heating/pressing include a temperature for the heating of preferably 70 to 250° C., more preferably 100 to 200° C., a pressure for the pressing of preferably 0.1 to 10 MPa, more preferably 0.5 to 5 MPa, and a period of this heating/pressing of preferably from 5 seconds to 3 minutes, more preferably from 10 seconds to 1 minute.
By molding the resin layer on the optical semiconductor elements into a shape having recesses or protrusions, the light regulation and efficiency of light takeout by the resultant lenses can be improved.
It is preferred in the invention that the following step (3) be further conducted after step (2):
(3) forming, on the resin layer press-molded in step (2) (hereinafter referred to as “first resin layer”), a second resin layer comprising a second resin having a lower refractive index than the first resin constituting the first resin layer.
The second resin is not particularly limited as long as it has been selected while taking account of its refractive index. Specifically, the second resin is selected so that it has a lower refractive index than that of the first resin. However, the specific refractive index difference for the first resin and second resin {[(refractive index of first resin)−(refractive index of second resin)]/(refractive index of first resin)×100} is preferably 5 to 35% from the standpoint of heightening the efficiency of light takeout at the resin layer interface.
Examples of the second resin include the same resins as those enumerated above as examples of the first resin. However, epoxy resins are preferred from the standpoints of ease of molding and low cost.
The first resin layer and second resin layer may suitably contain a light-scattering filler, e.g., silica, and additives, e.g., a fluorescent agent.
The second resin layer can be formed by a method appropriately selected from known ones such as, e.g., injection molding, casting, transfer molding, dipping, and potting with a disperser.
One or more resin layers may be further formed on the outer side of the second resin layer according to need. In this case, it is preferred that the resulting plural resin layers be disposed in the order of their decreasing refractive index of the resin toward the outermost resin layer.
By press-molding a resin layer on optical semiconductor elements with a stamper as in the invention, the optical semiconductor elements can be easily and evenly encapsulated with the resin, and a high-quality optical semiconductor device having evenness in the efficiency of light takeout can be obtained. Consequently, the optical semiconductor device to be produced by the invention preferably is an optical semiconductor device comprising a substrate and a plurality of optical semiconductor elements mounted thereon, in particular, a light-emitting diode array. An example of light-emitting diode arrays obtained by the invention is shown in
The present invention will be illustrated in greater detail with reference to the following Examples, but the invention should not be construed as being limited thereto.
In the following Example and Comparative Examples, all synthesis reactions were conducted in a nitrogen stream. IR analysis was made with FT/IR-230 (manufactured by Nippon Bunko K.K.).
Production Example of Polycarbodiimide
Into a 500-mL four-necked flask equipped with a stirrer, dropping funnel, reflux condenser, and thermometer were introduced 29.89 g (171.6 mmol) of tolylene diisocyanate (isomer mixture; T-80, manufactured by Mitsui-Takeda Chemical), 94.48 g (377.52 mmol) of 4,4′-diphenylmethane diisocyanate, 64.92 g (308.88 mmol) of naphthalene diisocyanate, and 184.59 g of toluene. These ingredients were mixed together.
Thereto were added 8.71 g (51.48 mmol) of 1-naphthyl isocyanate and 0.82 g (4.29 mmol) of 3-methyl-1-phenyl-2-phospholene 2-oxide. The resultant mixture was heated to 100° C. with stirring and held for 2 hours.
The progress of reactions was ascertained by IR analysis. Specifically, the decrease in the amount of absorption by N—C—O stretching vibration attributable to the isocyanates (2,280 cm−1) and the increase in the amount of absorption by N═C═N stretching vibration attributable to carbodiimide (2,140 cm−1) were followed. After the end point of the reactions was ascertained by IR analysis, the reaction mixture was cooled to room temperature. Thus, a polycarbodiimide solution (to be used in Comparative Example 1) was obtained. In this polycarbodiimide, 100% by mole of the diisocyanate residues were aromatic diisocyanate residues. This polycarbodiimide was represented by general formula (1) described above wherein n ranged from 15 to 77.
Subsequently, the polycarbodiimide solution was applied to a separator (thickness, 50 μm) [manufactured by Toray Industries, Inc.] consisting of a poly(ethylene terephthalate) film treated with a release agent (fluorinated silicone). This coating was heated at 130° C. for 1 minute and then at 150° C. for 1 minute. Thereafter, the separator was removed to obtain a temporarily cured sheet-form polycarbodiimide (thickness, 50 μm).
The sheet-form polycarbodiimide obtained was cured in a 150° C. curing oven. This cured resin was examined for refractive index with a multi-wavelength Abbe's refractometer (DR-M4, manufactured by ATAGO Co., Ltd.) at a wavelength of 589 nm and a temperature of 25° C. The refractive index of the cured resin was found to be 1.748.
Production Example of Optical Semiconductor Elements
An optical semiconductor wafer substrate (diameter, 100 mm; thickness, 100 μm) was produced by forming a GaN layer (p-type or n-type) as a light-emitting layer on a sapphire substrate as a transparent substrate and then forming an electrode thereon. Optical semiconductor elements were cut out of this wafer substrate using a laser processing apparatus (Model 5330, manufactured by ESI, Inc.).
In this cutting step, the third harmonic of a YAG laser having a wavelength of 355 nm, average output of 5 W, and frequency of 30 kHz was converged with an fθ lens so as to be incident as a beam with a diameter of 20 μm on the wafer substrate surface, and this laser beam was caused to travel at a rate of 10 mm/sec with a galvanoscanner. Furthermore, the stage to which the wafer substrate was fixed was inclined at an angle of 40° to conduct sidewall processing. Thus, square optical semiconductor elements were produced which had an angle α of 500, thickness of 100 μm, and length of each side, on the mounting-side face, of 350 μm.
Four sheets of the temporarily cured sheet-form polycarbodiimide obtained in the above-described “Production Example of Polycarbodiimide” were stacked up to produce a sheet having dimensions of 50 mm×30 mm and a thickness of 200 μm. This sheet was laminated to a substrate having dimensions of 50 mm×30 mm and having mounted thereon 7×18 optical semiconductor elements obtained in the above-described “Production Example of Optical Semiconductor Elements” (2.5×2.2 mm pitch). This lamination was conducted with a laminator at a revolution speed of 500 rpm, roll temperature of 100° C., and roll pressure of 0.5 MPa. Thus, a first resin layer was formed.
Subsequently, a stamper (made of polyimide) having 0.74-mm-diameter recesses with a depth of 0.17 mm disposed in 4×4 arrangement with a pitch of 2.5×2.2 mm was superposed on the first resin layer to press-mold the first resin layer at 200° C. and 1.5 MPa for 1 minute.
An epoxy resin (NT-8006, manufactured by Nitto Denko Corp.; refractive index, 1.560) was then superposed as a low-refractive-index resin layer (second resin layer) and cured at 120° C. for 5 hours. Thus, a light-emitting diode array of the surface mounting type was obtained.
The thickness of the high-refractive-index resin layer as measured in the projecting parts was 175 μm, and the total resin thickness was 300 μm. Since the refractive index of the high-refractive-index resin layer was 1.748, the difference in refractive index between this resin layer and the low-refractive-index resin layer was 0.188.
In the light-emitting diode array obtained, the quantity of the light emitted by each light-emitting diode (absolute energy) as measured from the front was 0.13 μW/cm2/nm on the average, and the standard deviation thereof was 0.025 μW/cm2/nm.
The light-emitting diode array obtained was polished with a section-polishing apparatus (manufactured by Struers Inc.) and a section of the array was examined. As a result, no void was observed at the interface between each optical semiconductor element and the resin layers.
A light-emitting diode array was produced in the same manner as in Example 1, except that the polycarbodiimide solution was dropped onto each optical semiconductor element to form a first resin layer.
In the light-emitting diode array obtained, the quantity of the light emitted by each light-emitting diode as measured from the front was 0.08 μW/cm2/nm on the average, and the standard deviation thereof was 0.019 μW/cm2/nm.
Those results show that since Example 1 does not necessitate the operation of dropping a predetermined amount of a resin onto each optical semiconductor element as conducted in Comparative Example 1, the production process of Example 1 is simple and the diode array obtained thereby has reduced unevenness in the efficiency of light takeout from each LED chip.
An optical semiconductor device was produced in the same manner as in Example 1, except that optical semiconductor elements having an angle α of 90° were used.
The light-emitting diode array obtained was equal to that of Example 1 in evenness in the efficiency of light takeout. However, as a result of the polishing of this light-emitting diode array with the section-polishing apparatus (manufactured by Struers Inc.) and examination of a section of the array, voids were observed at the interface between the optical semiconductor elements and the resin layers. It is thought from these results that the optical semiconductor device produced in Comparative Example 2 deteriorates in function and reliability with the lapse of use time.
The optical semiconductor device produced by the invention is suitable for use as, e.g., a surface light source for personal computers, cell phones, etc.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
The present application is based on Japanese Patent Application No. 2004-066850 filed Mar. 10, 2004, the contents thereof being herein incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| P.2004-066850 | Mar 2004 | JP | national |
