JP2012238654A - Translucent wiring board and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a translucent wiring board including a translucent alumina substrate and a wiring pattern formed on a surface of the translucent alumina substrate, in which adhesion between the wiring pattern and the translucent alumina substrate is maintained after the application of heat cycles, and translucency of the wiring board can be obtained.SOLUTION: A translucent wiring board 8 includes a translucent alumina substrate 1 and a wiring pattern 2 formed on a surface 1a of the translucent alumina substrate 1. A smooth surface 5 and a rough surface 6 are formed on the surface 1a of the translucent alumina substrate 1, and the wiring pattern 2 is formed on the rough surface 6 but not formed on the smooth surface 5.

Description

  The present invention relates to a translucent wiring board having high translucency and having high adhesion strength of a wiring pattern even after thermal cycling.

  Alumina ceramics are widely used as substrates for electronic components because of their characteristics such as electrical insulation and chemical stability. In recent years, the number of cases used as a substrate for a semiconductor light emitting device is increasing by taking advantage of the characteristics of high thermal conductivity. However, general alumina ceramics are opaque, and only one side of the light emitted from the semiconductor light emitting element can be used directly, and the light emitted to the opposite side of the substrate is used after being subjected to treatment such as reflection. (Patent Document 1). If a light-transmitting substrate is used, such a structure is not necessary. However, when glass or resin, which is a general light-transmitting material, is used as the substrate, the thermal conductivity is low, so the temperature of the semiconductor light-emitting element increases. In addition, the light emission efficiency of the light emitting element itself is lowered.

  On the other hand, particularly high-purity alumina ceramics have high translucency by firing in a reducing atmosphere such as vacuum or hydrogen. As an arc tube for high-intensity discharge lamps such as high-pressure sodium lamps and metal halide lamps. Used (Patent Document 2).

  Translucent alumina ceramics have high thermal conductivity in addition to translucency, and if this can be used as a substrate for semiconductor light-emitting devices, the light-emitting efficiency will not decrease due to temperature rise from both sides of the light-emitting device. Can be extracted (Patent Document 3).

  In addition, a metal wiring pattern is formed on the surface of an alumina substrate. Here, in order to improve the adhesion between the wiring pattern and the alumina substrate, it is known that the entire surface of the alumina substrate is etched using alkali, acid, ion beam or the like, and then the wiring pattern is formed (Patent Document). 4, 5). Moreover, a method of providing irregularities larger than alumina particles on the surface of an alumina substrate is known (Patent Document 6).

JP 2003-243717 A Japanese Patent No. 2780941 JP 2002-289925 A JP-A-61-251589 Japanese Patent Laid-Open No. 5-24959 JP 2010-30280 A

When an alumina substrate is used as a substrate for a semiconductor light emitting device, it is necessary to form a wiring pattern for supplying power to the light emitting device on the surface of the substrate. The wiring pattern is usually a silver or copper paste printed by a thick film process and then heat treated to combine the binder component contained in the paste with the components other than alumina (mainly SiO ₂ ) contained in the substrate. To make it in close contact. However, translucent alumina ceramics have a higher purity than general alumina, and the amount of impurities is extremely small, so that the adhesion is insufficient, and the wiring pattern is easily peeled off due to repeated temperature cycles due to lighting.

  Even in translucent alumina ceramics, impurities exist in a small amount in the crystal grain boundary. However, in order to improve translucency, it is necessary to enlarge the diameter of crystal grains as much as possible. This problem becomes more noticeable because the area of the crystal grain boundary appearing on the substrate surface is reduced.

  Increasing the amount of impurity components in alumina can increase the adhesion to the wiring pattern, but the translucency is lowered, making it difficult to use the light emitted from the light emitting element. Further, if the crystal particle diameter is reduced, the adhesion can be improved, but the translucency is lowered and it becomes difficult to use the light emitted from the light emitting element.

  In order to solve this problem, the present inventor also tried a method as described in Patent Documents 4, 5, and 6. In Patent Document 4, an alumina substrate that is not translucent is etched with an acid / alkali, whereby the surface of the alumina substrate is finely roughened over the entire surface. The surface roughness does not change before and after etching. Next, a wiring pattern is deposited on the alumina substrate.

  However, according to the study of the present inventor, even if the surface of the translucent alumina substrate is processed by acid / alkali etching, the translucent alumina has few impurities and has a high smoothness as described above. For this reason, fine etching that does not increase the surface roughness as described in Patent Document 4 has no effect of improving the adhesion of the wiring pattern, and the wiring pattern peels off after the thermal cycle. Further, when the surface roughness of the translucent alumina substrate is roughened by etching, the light transmittance is lowered.

  Moreover, etching of the surface of a translucent alumina substrate using an ion beam as described in Patent Document 5 was also examined. However, this method also causes the same problem as in Patent Document 4.

  As described in Patent Document 6, a method of providing irregularities larger than alumina particles was also examined. However, in the case of translucent alumina, the average particle diameter of the alumina particles is very large in order to develop translucency. For this reason, if unevenness sufficiently larger than the alumina particles is provided, a fine pattern or a complex pattern cannot be formed on the substrate surface, and the wiring cannot be made finer. For this reason, this technique cannot be used industrially in the field of translucent wiring boards. Moreover, if the substrate surface has irregularities sufficiently larger than the translucent alumina particles, the printing plate making is damaged when the wiring pattern is screen-printed on the substrate surface.

  An object of the present invention is to provide a light-transmitting wiring board having a light-transmitting alumina substrate and a wiring pattern formed on the surface of the light-transmitting alumina substrate. It is intended to maintain adhesion to the alumina substrate and to obtain the translucency of the wiring substrate.

The present invention is a translucent wiring board comprising a translucent alumina substrate and a wiring pattern formed on the surface of the translucent alumina substrate,
A smooth surface and a rough surface are formed on the surface of the translucent alumina substrate, and a wiring pattern is formed on the rough surface, and is not formed on the smooth surface.

Further, the present invention is a method for manufacturing the translucent wiring board,
A molding process in which alumina raw material powder is gel cast molded using a mold to obtain a molded body, and at this time, the mold is provided with a smooth portion corresponding to the smooth surface and a rough surface portion corresponding to the rough surface,
The method includes a sintering step of obtaining a light-transmitting alumina substrate by sintering the formed body, and a step of forming a wiring pattern on a rough surface of the light-transmitting alumina substrate.

  According to the present invention, a smooth surface and a rough surface are formed on the surface of a translucent alumina substrate, a wiring pattern is formed on the rough surface, and not formed on the smooth surface. The adhesion to the translucent alumina substrate is maintained, and the translucency of the wiring substrate can be obtained.

(A) is a top view which shows typically the wiring board 8 which concerns on one Embodiment of this invention, (b) is typical sectional drawing of the translucent alumina substrate 1, (c), It is sectional drawing of the wiring board 8 after providing a wiring pattern. It is a schematic diagram which shows the measuring method of the translucency of a wiring board.

  First, a translucent alumina substrate is produced by molding and sintering alumina raw material powder. At this time, the surface of the translucent alumina substrate is a smooth surface. This is because if the substrate surface is rough, the total transmittance of the substrate is significantly reduced.

  Next, as shown in FIG. 1B, a rough surface is formed in the wiring pattern formation region 3 in the surface 1 a of the substrate 1. In this example, the rough surface is not formed in the region 4 where the wiring pattern is not formed. Next, as shown in FIGS. 1A and 1C, the wiring pattern 2 is formed on the rough surface 6 in the wiring pattern formation region 3. The wiring pattern 2 is formed on the rough surface 6 and is not formed on the smooth surface 5.

(Translucent alumina substrate)
Translucent alumina can be used, for example, as a substrate for mounting a light-emitting diode element, which can dramatically extend the life of the light-emitting diode element.

  The thickness of the translucent alumina substrate is preferably 0.2 mm or more and 2 mm or less. If the substrate is too thin, it will be easily cracked by impact, or the ratio of linearly transmitted light will be too high, and light diffusion will be insufficient. If the substrate is too thick, the total light transmittance is lowered and the heat dissipation is also lowered.

  The linear transmittance in the visible light region of the translucent alumina substrate is preferably 40% or less, and more preferably 15% or less, for light diffusion. The total front transmittance of the translucent alumina substrate is preferably 30% or more from the viewpoint of light emission efficiency.

  The crystal grain size of the translucent alumina constituting the substrate is not particularly limited, but from the viewpoint of obtaining translucency, it is preferably 15 μm or more, and more preferably 20 μm or more. The crystal grain size of alumina is preferably 100 μm or less, and more preferably 40 μm or less.

  The relative density of the translucent alumina constituting the substrate is preferably 98% or more, and more preferably 99% or more, from the viewpoint of ensuring translucency. The pores in the alumina scatter incident light and significantly reduce the total light transmittance.

  The method for forming the translucent alumina substrate is not particularly limited, and may be any method such as a doctor blade method, an extrusion method, or a gel cast method. Particularly preferably, the substrate is manufactured using a gel cast method. In a preferred embodiment, a molded article is obtained by casting a slurry containing ceramic powder, a dispersion medium and a gelling agent and gelling the slurry, and the molded article is sintered.

Particularly preferably, a raw material in which an auxiliary of 150 to 1000 ppm is added to high-purity alumina powder having a purity of 99.9% or more (preferably 99.95% or more) is used. Examples of such high-purity alumina powder include high-purity alumina powder manufactured by Daimei Chemical Co., Ltd.
As the above-mentioned auxiliary agent, magnesium oxide is preferable, but ZrO ₂ , Y ₂ O ₃ , La ₂ O ₃ ,
Sc ₂ O ₃ can also be exemplified.

  In a preferred embodiment, the amount of impurities other than alumina in the translucent alumina substrate is 0.2% by mass or less, thereby improving the total transmittance. The present invention is particularly effective because the adhesion after the thermal cycle application with the wiring pattern is reduced due to the small amount of impurities.

The average particle diameter of the raw material powder is not particularly limited, but is preferably 0.5 μm or less, and more preferably 0.4 μm or less, from the viewpoints of densification during low-temperature sintering and improvement of translucency. More preferably, the average particle diameter of the raw material powder is 0.3 μm or less (primary particle diameter). The lower limit of the average particle size is not particularly limited. The average particle diameter of the raw material powder can be determined by direct observation of the raw material powder by SEM (scanning electron microscope).
The average particle diameter here is n = the value of (longest axis length + shortest axis length) / 2 of primary particles excluding secondary agglomerated particles on an SEM photograph (magnification: X30000, arbitrary two fields of view). It is an average value of 500.

Examples of the gel casting method include the following methods.
(1) Along with inorganic powder, a prepolymer such as polyvinyl alcohol, epoxy resin, phenol resin, or the like, which becomes a gelling agent, is dispersed in a dispersion medium together with a dispersing agent to prepare a slurry. The slurry is solidified by crosslinking and gelation.
(2) The slurry is solidified by chemically bonding an organic dispersion medium having a reactive functional group and a gelling agent.

(Rough surface and smooth surface)
In the present invention, a smooth surface and a rough surface are formed on the surface of the translucent alumina substrate. The surface roughness Ra of the smooth surface is preferably 0.3 μm or less from the viewpoint of improving the total transmittance. Further, although there is no particular lower limit of the surface roughness of the smooth surface, 0.1 μm or more is practical for processing.

  Further, the surface roughness Ra of the rough surface is preferably 0.5 μm or more, and more preferably 1.0 μm or more, from the viewpoint of adhesion to the wiring pattern after application of the heat cycle. Further, by setting the roughness roughness Ra of the rough surface to 3.0 μm or less, it is possible to prevent blurring and disconnection when printing a fine pattern, and damage to the screen mask during printing.

  The surface roughness Ra of the rough surface and the smooth surface is a centerline average surface roughness defined by JIS B 0601, and is measured by, for example, a stylus type surface roughness measuring device as defined by JIS B 0651. .

  In the present invention, the wiring pattern is formed on the rough surface and is not formed on the smooth surface. In a preferred embodiment, as shown in FIG. 1C, the wiring pattern 2 covers the entire surface of the rough surface 6, and the rough surface 6 is not exposed to the substrate surface side. However, a part of the rough surface 6 may be exposed to the substrate surface without being covered with the wiring pattern 2. In this case, the area of the exposed portion of the rough surface 6 is preferably 10% or less of the total area of the rough surface 6. The smooth surface is exposed on the substrate surface.

(Rough surface and smooth surface forming method)
In order to form a smooth surface on the translucent alumina substrate, a smoothing portion corresponding to the smooth surface can be provided in the molding die. Further, a smooth surface can be formed by polishing the surface of the translucent alumina substrate using diamond paste or the like.

  In order to form a rough surface on the translucent alumina substrate, a rough surface portion corresponding to the rough surface can be provided on the molding die. Moreover, after making the surface of a translucent alumina substrate into a smooth surface over the whole surface, a rough surface can be formed by milling the wiring pattern formation region of the smooth surface with a grindstone with a shaft or the like.

(Formation of wiring pattern)
As a method for forming a wiring pattern, there are a screen printing method, an ink jet printing method, and a pad printing method.

  The heat treatment temperature when forming the wiring pattern is preferably 500 to 1000 ° C. The wiring pattern material is preferably Au, Ag, W, Mo, Pt, or a compound containing these. Furthermore, the thickness of the wiring pattern is preferably 0.5 to 20 μm from the viewpoint of the present invention.

Example 1
The translucent alumina ceramic substrate 1 was produced as follows. That is, 100 parts by weight of alumina powder as raw material powder and 0.025 part by weight of magnesia, 30 parts by weight of polybasic acid ester as dispersion medium, 4 parts by weight of MDI resin as gelling agent, and Marialim AKM0351 (trade name, A mixture of 2 parts by weight of Nippon Oil & Fat Co., Ltd. and 0.2 parts by weight of triethylamine as a catalyst was used. The slurry was cast at room temperature in a mold made of an aluminum alloy having a rough surface on the surface corresponding to the wiring pattern, left at room temperature for 1 hour, solidified and then released. Furthermore, it was left at room temperature and then at 90 ° C. for 2 hours to obtain a substrate-like powder compact. This was calcined at 1200 ° C. in the atmosphere to obtain a calcined body.

  Next, this calcined body was fired at 1800 ° C. in an atmosphere of hydrogen: nitrogen = 3: 1 to be densified and translucent. As a result, a translucent alumina ceramic substrate having a rough surface corresponding to the wiring pattern on the surface could be obtained. When the surface roughness of the rough surface of this substrate was measured, Ra = 0.5 μm, and the surface roughness Ra of the other smooth surfaces was 0.1 μm.

  A silver paste was printed on the surface 1a of the obtained substrate 1 using a screen plate having a desired wiring pattern. Thereafter, the substrate was dried for 15 minutes with a dryer at 95 ° C. and heat-treated at a temperature of 850 ° C.

When soldering was performed on this wiring pattern and the adhesive strength was measured, it was found that the wiring pattern had a sufficient strength of 18 N / mm ² . Furthermore, when the adhesive strength was measured after 1000 times of a temperature cycle in which −40 ° C. and 200 ° C. were alternately repeated every 30 minutes, it was inferior to the initial value of 10 N / mm ² , but still sufficient I found out.

  Further, the total front transmittance of the portion other than the wiring pattern of the substrate was measured and found to be 65%. However, the total front transmittance was measured with an apparatus schematically shown in FIG. That is, monochromatic light having a wavelength of 555 nm is incident on the surface 1a of the wiring board 8 from the light source 10 as indicated by an arrow A, and radiated light emitted from the back surface 1b toward each point of the integrating sphere 12 as indicated by an arrow B. Detection is performed by the detector 11.

(Examples 2 to 4)
A wiring substrate 8 was produced in the same manner as in Example 1. However, the surface roughness Ra of the rough surface and the smooth surface was changed as shown in Table 1. The measurement results are shown in Table 1.

  As can be seen from Table 1, in the embodiment of the present invention, the bonding strength of the wiring pattern after 1000 cycles of thermal cycles is maintained, and the total transmittance of the wiring board is also high.

(Comparative Examples 1-5)
A wiring substrate 8 was produced in the same manner as in Example 1. However, the surface roughness Ra of the surface of the translucent alumina substrate was changed as shown in Table 2. The measurement results are shown in Table 2.

In Comparative Examples 1 and 2, since the surface roughness of the translucent alumina substrate is low, the total transmittance of the wiring substrate is high. However, the wiring pattern was peeled off after 1000 thermal cycles were applied. In Comparative Examples 3, 4, and 5, the bonding strength of the wiring pattern was obtained to some extent after 1000 thermal cycles were applied, but the total transmittance of the wiring board was low, making it difficult to use as a translucent wiring board. Is something.

Claims (6)

A translucent wiring board comprising a translucent alumina substrate and a wiring pattern formed on the surface of the translucent alumina substrate,
A smooth surface and a rough surface are formed on the surface of the translucent alumina substrate, the wiring pattern is formed on the rough surface, and is not formed on the smooth surface. , Translucent wiring board.   2. The light transmitting device according to claim 1, wherein a surface roughness Ra of the smooth surface is 0.1 to 0.3 μm, and a surface roughness Ra of the rough surface is 0.5 to 3.0 μm. Wiring board.   The translucent wiring board according to claim 1, wherein an amount of impurities other than alumina in the translucent alumina substrate is 0.2 mass% or less.   The translucent wiring substrate according to any one of claims 1 to 3, wherein the translucent alumina substrate has an average particle size of 15 µm or more.   The translucent wiring board according to any one of claims 1 to 4, wherein the wiring pattern is formed by screen printing. A method for producing the translucent wiring board according to any one of claims 1 to 5,
A molding process in which alumina raw material powder is gel cast molded using a mold to obtain a molded body, and at this time, the mold is provided with a smooth portion corresponding to the smooth surface and a rough surface portion corresponding to the rough surface,
A step of sintering the molded body to obtain the light-transmitting alumina substrate; and a step of forming the wiring pattern on the rough surface of the light-transmitting alumina substrate. Manufacturing method of optical wiring board.

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