JP5400543B2 - Method for forming through electrode of circuit board - Google Patents

Description

  The present invention relates to a method of manufacturing a through electrode by filling a fine through hole of a wiring board used in various electric / electronic devices with a conductive metal.

  Conventionally, a plating method has been frequently used as a conductive metal filling process for the through holes of a multilayered circuit board used in various electric and electronic devices. However, filling metal by an electrochemical method such as plating requires a relatively long time, and it cannot be said that the production efficiency is good. Further, the plating method cannot cope with a through-hole having a high aspect ratio (hole depth / opening diameter) because the plating solution hardly penetrates into the hole. In recent years, circuit boards have been required to be improved because the density has been accelerated and the through-holes have become finer.

  Therefore, as a method for solving the problems caused by the plating method as described above, a technique of filling a fine hole in a molten state with a metal to be filled is disclosed (Patent Document 1). In this method, after a substrate is inserted into a molten metal tank in a vacuum chamber that has been depressurized, the inside of the vacuum chamber is pressurized to fill the molten metal into the fine holes due to an atmospheric pressure difference and solidify the molten metal.

JP 2005-109515 A

  The manufacturing method of the through electrode by filling the molten metal is to fill the hole with the metal as it is, it is excellent in work efficiency, and it is possible to fill the fine hole by appropriately setting the atmospheric pressure difference. I can say that. However, in this method, it is necessary to immerse the substrate in a molten metal, and the substrate is excessively heated. The influence of heat on the substrate includes deformation and breakage of the substrate itself, but there is a problem that the conductive film previously disposed on the substrate reacts with the molten metal and disappears. In addition, when a resist film is formed on the substrate in advance, the resist may be altered by heat. Therefore, in the above prior art, the problem due to the heat of the molten metal is large.

  In view of the above, the present invention can reduce the thermal influence on the substrate and efficiently manufacture the metal filling method for the fine through holes on the substrate in the background as described above. It is an object to provide a method.

  The present inventors have intensively studied to solve the above problems, and decided to use a predetermined metal paste for filling the through holes. That is, according to the present invention, in a method of forming a through electrode by filling a conductive metal into the through hole of the substrate having the through hole, the purity is 99.9% by weight or more, and the average particle size is 0.005 μm to Using a metal paste composed of one or more metal powders selected from gold powder, silver powder, or palladium powder that is 1.0 μm and an organic solvent, while applying mechanical vibration of a frequency of 60 Hz to 100 kHz to the metal paste Applying to the substrate and simultaneously with the application of the metal paste, or after applying the metal paste, the through hole is decompressed from the other end side to suck the metal paste into the through hole, and then sinter the metal paste This is a method of forming an electrode.

  Here, the application of the metal paste in the field of manufacturing an electronic circuit board is widely used for forming a wiring pattern on the surface of the board. The metal paste in this case is obtained by dispersing conductive metal powder and glass frit in an organic solvent. On the other hand, the metal paste used in the present invention is composed of a metal powder not mixed with glass frit and an organic solvent, unlike a general metal paste. The use of such a metal paste that does not use glass frit is that the component is substantially only metal powder (the organic solvent disappears in the drying and sintering process after application), and this is sintered. This is because the fine metal powder is firmly bonded while being plastically deformed to form a dense through electrode.

  Here, the metal powder constituting the metal paste has a purity of 99.9% by weight or more and an average particle diameter of 0.005 μm to 1.0 μm in gold (Au) powder, silver (Ag) powder or palladium ( Pd) One or more metal powders selected from powders. The reason why the purity of the metal powder is 99.9% or more is that if the purity is less than 99.9% by weight, the necessary electrical conductivity may not be ensured. In addition, the average particle size of the metal powder is 0.005 μm to 1.0 μm. In the metal powder having a particle size of more than 1.0 μm, a large gap is generated when the minute through hole is filled, and finally This is because the required electrical conductivity cannot be ensured, and when the particle size is less than 0.005 μm, it tends to agglomerate in the metal paste, and it is difficult to apply the entire surface to apply mechanical vibration to the substrate. It is.

  The organic solvent used in the metal paste is preferably ester alcohol, terpineol, pine oil, butyl carbitol acetate, butyl carbitol, carbitol, or parkrol. These solvents are less aggressive to the resist and can be volatilized even at a relatively low temperature (less than 50 ° C.), and can be easily dried after the metal paste is applied. In particular, park rolls are particularly preferred because they can be dried at room temperature.

  About the mixture ratio of the metal powder of the metal paste to apply | coat, and an organic solvent, it mix | blends metal powder as 80 to 99 weight% and an organic solvent as 1 to 20 weight%. The reason for this ratio is to prevent the metal powder from agglomerating and to supply sufficient metal powder to fill.

  Moreover, the metal paste used in the present invention may contain an additive. The additive includes one or more selected from acrylic resins, cellulose resins, and alkyd resins. For example, methyl methacrylate polymer can be cited as the acrylic resin, ethyl cellulose can be cited as the cellulose resin, and phthalic anhydride resin can be cited as the alkyd resin. These additives have an action of suppressing aggregation of the metal powder in the metal paste, and make the metal paste homogeneous. The amount of the additive added is preferably 2% by weight or less with respect to the metal paste. The metal powder content can be within a range sufficient for filling the through holes while maintaining a stable aggregation suppressing effect.

  When the metal paste described above is applied to a substrate for filling a through hole, it is necessary to give a mechanical vibration of a predetermined frequency to the metal paste. The application of paste while applying mechanical vibration is a characteristic operation that is not performed by the application of a general metal paste (including glass frit). The metal paste in the present invention is obtained by dispersing only a metal powder in an organic solvent and has poor fluidity, so that it is difficult to spread uniformly when applied to a substrate. The present invention can spread a metal paste on a substrate by applying mechanical vibration of a predetermined frequency to the metal paste.

  The frequency of mechanical vibration applied to this metal paste is 60 Hz to 100 kHz. By the vibration in this range, the poor fluidity of the metal paste can be eliminated. More preferably, the frequency is 100 Hz to 30 kHz. This is for spreading the entire surface of the substrate.

  As a method of applying the metal paste to the substrate, it is preferable to spread the entire surface of the substrate while bringing the blade (scalar) vibrated at the above frequency into contact with the metal paste after or while discharging the metal paste onto the substrate. . By applying mechanical vibration directly to the metal paste, vibration is applied to the metal powder in the metal paste, and fluidity is improved. For this purpose, the mechanical vibration is preferably applied only to the metal paste, and it is preferable to keep the blade from contacting the substrate in order to maintain the frequency within the above range. The distance (gap) between the blade tip and the base is preferably 50 to 200 μm. In addition, the board | substrate here includes the thing in the state in which the resist layer, the electrically conductive film, etc. were formed in the surface. Therefore, the gap between the blade tip and the substrate means the distance from the outermost surface of the substrate.

  The metal paste spread on the entire surface of the substrate by applying the metal paste is difficult to completely penetrate the through hole as it is. Therefore, in order to completely fill the through hole with the metal paste, it is preferable to suck the metal paste by reducing the pressure of the through hole. As a method for depressurizing the through hole, it is preferable to depressurize the back surface of the substrate (opposite to the surface to which the metal paste is applied), and it is preferable to set to −10 to −90 kPa.

  It is preferable to dry the metal paste after filling the through holes with the metal paste. This is because if the sintering is carried out immediately after filling, gas generation due to volatilization of the organic solvent is abrupt and the shape of the sintered body is affected. Moreover, it is because the metal powder in a through-hole can be temporarily fixed by once drying, and the handleability at the time of the resist removal etc. which are mentioned later can be ensured. In this drying step, the drying temperature is preferably 100 ° C. or lower, and can be about room temperature.

  The heating temperature when sintering the metal paste is preferably 150 to 300 ° C. If the temperature is lower than 150 ° C., the metal powder in the through-hole cannot be sufficiently sintered. If the temperature exceeds 300 ° C., the sintering proceeds excessively and becomes too hard due to the progress of necking between the metal powders, or the volume decreases. This is because. Further, if the sintering temperature is too high, there is a concern about the influence on the substrate and the conductive film thereon.

  By applying and sintering the above metal paste, the metal powder in the through hole is sintered and solidified to form a through electrode. The through electrode formed under the above conditions does not cause a gap with the wall surface of the through hole, and is appropriately densified to form a good conductor.

  The substrate applied in the present invention is not particularly limited. About a through-hole, the hole diameter can respond to a fine thing, and the filling to a fine hole of about 5-50 micrometers is also possible. Further, it is possible to cope with a substrate in which a resist film is formed in advance. In this case, it is preferable to remove the resist after applying (filling) the metal paste and drying the metal paste. As described above, the drying temperature can be relatively low, and the resist is not damaged at this temperature. The dried metal paste is temporarily fixed. At this time, even if the resist is removed, the metal powder in the through hole does not fall off. Therefore, an efficient through electrode can be formed by operations in the order of drying, resist removal, and sintering.

  As described above, according to the present invention, the conductive metal can be efficiently filled into the minute through hole having a high aspect ratio at a relatively low temperature. In the present invention, an efficient circuit board can be manufactured without damaging the resist and the conductive film on the board.

The conceptual diagram of the process of spreading a metal paste on a board | substrate. The figure explaining the evaluation criteria after a sintering process.

  Hereinafter, preferred embodiments of the present invention will be described. In this embodiment, first, a metal paste was manufactured, applied to a substrate while applying mechanical vibrations of various frequencies, and the spread state was evaluated to examine a suitable frequency range. The metal paste used was prepared by mixing metal powder (purity 99.99% by weight) made of gold having a particle diameter of 0.3 μm manufactured by a wet reduction method with park roll as an organic solvent (gold). Powder mixing amount 99%). Then, this metal paste was applied to a substrate (material: silicon, size: 30 mm × 20 mm, thickness 250 μm). The average particle size of the metal powder was calculated from the particle size distribution detected from the transmitted light intensity of laser light having a wavelength of 780 nm by a light transmission centrifugal sedimentation method.

  At this time, as shown in FIG. 1, the metal paste was dropped on the substrate, and the coverage was obtained from the state of the metal paste after spreading the entire surface of the substrate with a silicon blade (blade width 30 mm) vibrating at a predetermined frequency. . At this time, examination was performed while changing the gap between the blade and the substrate and the frequency of the blade. The evaluation results are shown in Table 1.

  As shown in Table 1, it can be seen that application of mechanical vibration to the metal paste has an effect of improving the application state of the metal paste. Depending on the distribution state of the through-holes filled with the metal paste, it can be said that at least “B” or more coating is required according to the above evaluation criteria, and for that purpose, the vibration frequency needs to be 60 Hz to 100 kHz. Yes, and most preferably 100 Hz to 30 kHz. It can also be confirmed that the gap between the blade and the substrate is preferably 50 to 200 μm.

  Through the above preliminary test, a through electrode was actually formed on a substrate having a through hole. About 90 through-holes (hole diameter: 10 μm) having the same dimensions as the substrate, paste application (filling), drying, and sintering were performed. The metal paste application conditions at this time were 119 Hz, 30 kHz, and 100 kHz, and a silicon blade similar to the above was used.

  Then, a porous ceramic plate was placed on a sealed container having the same dimensions as the substrate having an opening only in the upper portion, and the substrate after applying the metal paste was placed on the ceramic plate to form a sealed space. . Thereafter, the above-mentioned sealed container was decompressed at −10 kPa to −90 kPa, and the paste on the substrate coating surface was sucked through the ceramic plate. Thereafter, the entire substrate was dried at 90 ° C. for 1 hour, and then heated at 230 ° C. for 2 hours to sinter the metal powder.

  The cross section of the substrate of the through electrode formed as described above is observed by X-ray. As shown in FIG. 2, “good” means that the sintered body is formed in the entire through hole, and “bad” means that there is a void in the through hole. The number of “good” in the 90 through-holes of the substrate was counted and used as the hole embedding rate.

  In this example (frequency at the time of metal paste application: 119 Hz), the hole filling rate of the through electrode was 96%. In addition, although the penetration electrode was formed by frequency 30kHz and 100kHz in the same process, the hole embedding rate was in the range of 95-100%, and was favorable. In the above examples, the sintering temperature of the metal powder was set to 230 ° C., but the same results were obtained when sintering at 180 ° C. and 280 ° C. in addition to the above.

  The present invention is useful for forming a through electrode installed on a circuit board of various electronic / electrical devices. The present invention meets the demand for circuit board manufacturing, which will be further miniaturized and highly integrated.

Claims (7)

In the method of forming a through electrode by filling the through hole with a conductive metal of a substrate having a through hole,
Purity is 99.9% by weight or more, gold powder having an average particle diameter of 0.005Myuemu～1.0Myuemu, and one or more metal powder selected from silver or palladium powder, Ri Do and an organic solvent, a glass frit Use a metal paste that does not contain
While applying mechanical vibration with a frequency of 60 Hz to 100 kHz to the metal paste, it is applied to the substrate,
Simultaneously with the application of the metal paste, or after applying the metal paste, the through hole is decompressed from the other end side to suck the metal paste into the through hole,
Thereafter, a method of forming a through electrode in which the metal paste is sintered at a heating temperature of 150 to 300 ° C.   2. The penetration according to claim 1, wherein the metal paste is applied by spreading the metal paste discharged onto the substrate with a blade to which mechanical vibration is applied, and moving the blade in a non-contact state with the substrate. Electrode formation method.   The method for forming a through electrode according to claim 2, wherein the blade is moved while maintaining a distance between the blade tip portion and the substrate at 50 to 200 μm. The through electrode formation method according to any one of claims 1 to 3, wherein a frequency of mechanical vibration applied to the metal paste is 100 Hz to 30 kHz. The method for forming a through electrode according to claim 1 , further comprising a drying step before sintering the metal paste, wherein a drying temperature in the drying step is 100 ° C. or less. The organic solvent constituting the metal paste is ester alcohol, terpineol, pine oil, butyl carbitol acetate, butyl carbitol, carbitol, or parkrol. 6. Formation of the through electrode according to any one of claims 1 to 5. Method. The method for forming a through electrode according to any one of claims 1 to 6 , wherein the metal paste further contains one or more selected from an acrylic resin, a cellulose resin, and an alkyd resin as an additive.

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