JP4172893B2 - Method for manufacturing metal-based circuit board - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is excellent in high heat dissipation and thermal shock resistance suitable for high heat generation electronic components or hybrid integrated circuits in which high heat generation electronic components and control circuit electronic components are mounted at high density, and therefore in reliability. The present invention relates to a metal base circuit board for a hybrid integrated circuit capable of obtaining an excellent high density hybrid integrated circuit and a method for manufacturing the same.
[0002]
[Prior art]
As a circuit board for mounting a highly exothermic electronic component, a metal plate having good thermal conductivity, for example, a metal plate such as aluminum or copper is used as a base material, and an inorganic filler having a thickness of about several tens of μm on the metal plate A metal base circuit board in which an insulating layer made of a resin containing resin is provided and a circuit made of a conductive foil is laminated on the insulating layer is used. The metal base circuit board is preferably used for applications in the high power field and the like because it has high thermal conductivity and can be mounted and used with an electronic component having a large calorific value.
[0003]
However, regarding the metal base circuit board for the application field, as the functions become more sophisticated, the number of elements and the number of inputs and outputs mounted on the board increase, and accordingly, the number of inputs and outputs and the number of wirings between elements increase. ing. For this reason, as the number of wirings in the circuit board increases, the area required for wiring increases, and the increase in the size and cost of the circuit board has become a problem to be solved in the industry.
[0004]
As a method for forming a circuit in a metal base circuit board, a method of forming a circuit by etching a conductive foil provided on an insulating layer on a metal plate is known. In this method, Etching resist ink is printed on the surface of the conductive foil to be a circuit by a screen printing method, and after the ink is cured, etching is performed by immersing the conductive foil in a soluble etching solution. It was not easy to adjust the amount, and it was not possible to easily obtain a circuit with a narrow circuit interval (see Japanese Patent Application Laid-Open No. 7-44087). That is, if the ink amount is reduced, there is a problem that disconnection or conductor loss occurs and a satisfactory product cannot be obtained. Conventionally, only a minimum circuit interval of about 250 μm has been obtained.
[0005]
In addition, there is a method of forming a wire bonding pad and a soldering pad by selective etching of aluminum and copper with respect to a circuit in which copper is disposed in an upper layer as an upper layer. In order to etch aluminum, an alkaline etching solution is used. In order to use it, it is necessary to use an organic solvent peeling type etching resist because an alkali peeling type etching resist cannot be used. Non-flammable organic solvents that can be used for resist stripping have problems such as carcinogenicity and environmental destruction such as ozone layer destruction, and flammable materials require explosion-proof production facilities and work environments. The solvent-removable photoresist has a similar problem.
[0006]
Furthermore, in a circuit board having a circuit in which copper is disposed in an upper layer and copper in a lower layer, and a resistance circuit is formed of copper foil, parts are soldered to the lower layer copper foil, but the copper foil portion is an aluminum layer Therefore, there is a problem that a soldered portion of a circuit that requires a large current has a large electric resistance and cannot have a large current capacity.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and an object thereof is to enable the use of an alkali peeling type screen printing etching resist or an alkali peeling type photoresist as a circuit forming etching resist. Another object of the present invention is to provide a metal base circuit board having an improved current capacity by reducing the electrical resistance of a soldered portion of a large current circuit.
[0008]
[Means for Solving the Problems]
That is, the present invention is a method of manufacturing a metal base circuit board in which a circuit made of a composite foil of copper / aluminum / copper is provided on a metal plate via an insulating layer, and (1) an insulating layer is provided on the metal plate. A step of forming a metal base substrate by laminating a copper / aluminum / copper composite foil, (2) a step of etching away a desired portion of the exposed copper layer of the metal base substrate, and (3) the copper Etching the exposed aluminum using the layer as an etching resist, and (4) providing an etching resist on a desired portion of the copper layer and etching the surface copper layer and the lower copper layer together. a metal base circuit board manufacturing method characterized by undergoing sequentially, the metal base circuit board etching resist is characterized by a screen printing etch resist alkali peeling type It is a manufacturing method.
[0009]
The present invention is characterized in that after the step (4), (5) a step of etching away an aluminum layer other than the aluminum layer below the surface copper layer is added, and the step (4) is further repeated. A method of manufacturing the metal base circuit board.
[0010]
The present invention is the method for manufacturing a metal base circuit board according to the step (4), wherein the etching is performed while removing the upper copper layer while leaving the lower copper layer remaining.
[0011]
The present invention is the above-described method for producing a metal base circuit board, wherein a solder resist layer is provided so that solder can be provided at a desired position of a circuit made of a copper layer as a final step.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various experimental studies in view of the circumstances of the known technology, the present inventor has used a copper / aluminum / copper composite foil as a metal foil for circuit formation, and an alkali peeling etching for the copper layer etching. By using a copper layer when etching an aluminum layer, and by combining these etching methods, an organic solvent peeling type etching resist is not used, and a minimum circuit that has not been obtained in the past. The inventors have obtained the knowledge that a metal base circuit board having a width of 150 μm or less and a small electric resistance at a soldered portion of a circuit and a large current capacity can be obtained, and the present invention has been achieved.
[0014]
The manufacturing method of the metal base circuit board of this invention is demonstrated with figures.
The first step of the present invention is a step of forming a metal base substrate 7. The metal base substrate 7 is made of copper 3 via an insulating layer 2 on a metal plate 1 as illustrated in FIG. A composite foil 6 of aluminum / aluminum 4 / copper 5 is laminated.
[0015]
As the metal plate 1, a general-purpose metal having high thermal conductivity such as aluminum, copper, iron, stainless steel, or an alloy or composite material thereof is used. Since the metal plate 1 is rich in thermal conductivity and lightweight, aluminum or The alloy is preferred. The thickness is generally 0.5 to 3 mm.
[0016]
Insulating layer 2 is generally made of an inorganic filler-containing resin in order to satisfy electrical insulation and thermal conductivity. In order to achieve the above object, ceramic powder such as aluminum oxide, silicon oxide, aluminum nitride, silicon nitride, boron nitride is often used as the inorganic filler. You may use individually or in combination. As the resin, a thermosetting resin such as an epoxy resin or a polyimide resin is often used. Of these, an epoxy resin excellent in adhesion to a metal is preferably used.
[0017]
The copper / aluminum / copper composite foil used in the present invention may be either copper plated on both sides of aluminum or a composite of aluminum foil and copper foil by a rolling method.
[0018]
The copper thickness of the composite foil may be 1 μm or more. If it is less than 1 μm, the etching resist effect of aluminum may not be sufficient. The upper limit is about 10 μm because there is no technical limitation if a foil can be formed, but if it is too thick, etching takes time, which is not preferable in terms of productivity. Also, within the above range, the upper copper layer thickness is divided into a portion where the upper copper layer is etched and completely disappeared, and a portion that remains on the circuit surface after etching and forms a soldered portion. It is necessary to take into account the two aspects of becoming, preferably 2 μm or more and 5 μm or less. On the other hand, the thickness of the lower copper layer is preferably 8 μm or more and 300 μm or less in consideration of the case where the lower copper layer remains at a desired thickness to form part of the circuit.
[0019]
The aluminum thickness of the composite foil is preferably 10 μm or more and less than 500 μm. This is because when the thickness is less than 10 μm, an aluminum wire bonding defect may occur, and when it exceeds 500 μm, a short circuit between circuits due to an etching defect may occur.
[0020]
The second step of the present invention is a step of etching away a desired portion of the exposed copper layer (upper copper layer) of the metal base substrate 7 obtained in the above step. In this case, a conventionally known etching method can be employed, but in order to achieve the object of the present invention, it is preferable to use an alkali-peeling resist as the resist. As the etching solution, conventionally known sulfuric acid-hydrogen peroxide solution, ammonium persulfate aqueous solution, sodium persulfate aqueous solution and the like can be used (see FIG. 2).
[0021]
The third step of the present invention is a step of etching the exposed aluminum using the upper copper layer to which a desired shape is added by the above operation as a resist when etching the aluminum. As an etching solution in this case, an aqueous caustic soda solution, an aqueous caustic potash solution, or the like can be used (see FIG. 3). In this process, it is conceivable to apply a cupric chloride aqueous solution or a ferric chloride aqueous solution capable of etching both copper and aluminum, but the copper and aluminum in one etching solution may be applied. Since the etching rate is different, it is difficult to form a fine pattern.
[0022]
The fourth step of the present invention is a step of providing an etching resist at a desired portion of the copper layer, and etching the surface copper layer and the lower copper layer together, which is the most characteristic feature of the present invention. It is a process. As for the etching resist provided in a desired portion of the copper layer, as described above, an alkali-peeling etching resist is used to achieve the object of the present invention. Through this step, as illustrated in FIG. 4, a circuit made of copper / aluminum / copper and / or a circuit made of aluminum / copper is formed. The former is suitable for soldering a semiconductor element, and the latter is suitable for wire bonding using an aluminum wire or a gold wire.
[0023]
In particular, in this process, while the thickness of the upper copper layer of the copper / aluminum / copper composite foil is selected in advance to be thinner than the thickness of the lower copper layer, the lower copper layer remains. By removing the upper copper layer, it is possible to form a circuit made of aluminum / copper while leaving a circuit made of lower layer copper. Conventionally, the number of times of etching required for forming the circuit is plural, It can be completed at once.
[0024]
Furthermore, in the present invention, after the fourth step, a portion other than the aluminum layer existing below the upper copper layer is removed by etching to form a copper circuit composed of the lower copper layer, By repeating the fourth step, the height of the circuit is different from that of the copper / aluminum / copper circuit, and the surface is made of copper suitable for soldering. The copper in which a part of the lower copper layer is exposed. It is also possible to form a circuit made of / aluminum / copper and a circuit made of copper / aluminum / copper in which a part of the aluminum layer is exposed, and the circuit can be freely designed (see FIG. 5). ).
[0025]
In addition, the present invention is characterized in that, as a final step, in addition to the above steps, a solder resist layer is provided so that solder can be provided at a desired position of a circuit made of a copper layer. As described above, the circuit surface is composed of a copper layer, and electronic components such as semiconductor elements or electrical components are joined and mounted via solder. In that case, the solder adheres to the unnecessary portions. It remains and is likely to cause an abnormality such as an electrical short circuit between circuits under actual use. In order to prevent this, in the present invention, a solder resist layer is provided at a desired position of a circuit made of a copper layer.
[0026]
Furthermore, the present invention is a metal base circuit board in which a circuit comprising a composite foil of copper / aluminum / copper is provided on a metal plate via an insulating layer, and the minimum circuit width is 25 μm or more and 100 μm or less. In a more specific embodiment, the metal base circuit board is characterized in that the maximum current flowing in the circuit is 1 μA or more (8 μA or less) per 1 μm of circuit width, It can be easily obtained based on the manufacturing method of the metal base circuit board.
[0027]
The minimum circuit width of the metal base circuit board of the present invention is 25 μm or more and 100 μm or less. If it is less than 25 μm, an electrical short circuit between the circuits may occur. On the other hand, the upper limit value of the minimum circuit width is not technically limited, but when it is too large, the degree of circuit integration on the circuit board does not increase, and when it exceeds 100 μm, the difference from the conventionally known one is small. It will be insufficient to achieve this goal.
[0028]
In addition, the metal base circuit board of the present invention has a copper / aluminum / copper circuit, and electronic parts and electrical parts can be soldered to this part, so that the current capacity is limited by the conventional soldering part. The problem is solved and it has a large electric capacity. Based on the experimental results of the present inventors, the minimum circuit width is 25 to 100 μm, and a current of 1 μA or more to 8 μA or less can be loaded per 1 μm of circuit width.
[0029]
【Example】
[Example 1]
Thickness of the insulating layer after hardening a bisphenol A type epoxy resin (manufactured by Yuka Shell; EP828) containing 55% by volume of aluminum oxide (manufactured by Showa Denko; SRW) on an aluminum plate having a thickness of 1.5 mm The metal foil composed of a composite layer of an aluminum layer and a copper layer is disposed so that the copper layer is in contact with the insulating layer, and the insulating layer is cured by heating under pressure. Thus, a metal base substrate was produced. At this time, the thickness of the aluminum layer was 40 μm, and the thickness of the copper layer was 10 μm.
[0030]
After a protective sheet made of polypropylene is pasted on the back surface of the aluminum plate of the metal base substrate, a zinc coating is formed on the aluminum foil of the metal foil made of a composite layer of aluminum and copper by a displacement plating method. A 3 μm thick copper layer was plated. Further, after masking the etching resist at a desired position using a screen printing method, the copper layer was etched using sulfuric acid-hydrogen peroxide solution. After the etching resist was removed with a 2% aqueous solution of caustic soda, aluminum was etched with a 15% aqueous solution of caustic soda using copper as the etching resist.
[0031]
Next, a resist is applied again to a desired portion of the copper layer, and an etching resist is formed using the aluminum, and the upper and lower copper layers are mixed with a mixed solution of sulfuric acid 120 g / l and hydrogen peroxide 45 g / l. Was etched. Thereafter, the etching resist is removed and aluminum is etched using the copper layer as an etching resist. Next, a resist is applied again to a desired portion of the copper layer, the upper and lower copper layers are etched with a mixed solution of sulfuric acid 120 g / l and hydrogen peroxide 45 g / l, and the etching resist is removed to remove the metal base circuit. A substrate was obtained.
[0032]
In the metal base circuit board, the maximum current flowing in the circuit can flow 1 μA or more per 1 μm circuit width in the signal circuit portion, and the minimum circuit width is 25 μm and the minimum conductor interval is 25 μm. As a result, the area of the signal circuit portion can be reduced to one third of the area required for the conventional metal base circuit board. As a result, the entire area of the metal base circuit board is reduced. Densification was achieved with about 40% of the product.
[0033]
【The invention's effect】
In the present invention, a copper / aluminum / copper composite foil is used as a metal foil for forming a circuit, an alkali peeling type screen printing etching resist is used for etching a copper layer, and a copper layer is used for etching an aluminum layer. By using these methods and combining these etching methods, a minimum circuit width of 150 μm or less, which has not been obtained in the past without using an organic solvent-peeling etching resist, is used. A metal base circuit board having a small electric resistance and a large current capacity can be obtained.
[0034]
In addition, according to the method of the present invention, a metal base circuit board having the above-mentioned cross-sectional shape and having a minimum circuit distance of 25 to 100 μm and a circuit having a circuit width of 25 to 100 μm is stabilized. It is very useful in industry.
[0035]
Furthermore, according to the method of the present invention, the minimum circuit width is 25 to 100 μm and the circuit integration is high without using an organic solvent peeling type etching resist having problems such as carcinogenicity, ozone layer destruction, and environmental destruction. In addition, a metal base circuit board having a large electric capacity is provided, which is very useful in industry.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a metal base substrate obtained in a first step of the present invention.
FIG. 2 is a cross-sectional view of an intermediate product after the second step of the present invention.
FIG. 3 is a cross-sectional view of an intermediate product after the third step of the present invention.
FIG. 4 is a cross-sectional view showing an example of a metal base circuit board after the fourth step of the present invention.
5 is a cross-sectional view showing an example of the metal base circuit board according to the present invention after etching the upper copper layer while etching the lower copper layer of the metal base circuit board according to FIG. 4;
6 is a cross-sectional view showing an example of a hybrid integrated circuit in which a semiconductor element or the like is mounted using the metal base circuit board according to FIG.
[Explanation of symbols]
1 Metal plate 2 Insulating layer 3 Copper layer (lower layer)
4 Aluminum layer 5 Copper layer (upper layer)
6 Composite foil 7 Metal base substrate 8 Solder resist 9 Solder 10 Semiconductor element 11 Terminal 12 Bonding wire

Claims (4)

On a metal plate via an insulating layer Ri manufacturing method der metal base circuit board having a circuit comprising a composite foil of a copper / aluminum / copper, copper via an insulation layer on the (1) metal plate / aluminum / Forming a metal base substrate by laminating a copper composite foil, (2) etching away a desired portion of the exposed copper layer of the metal base substrate, and (3) using the copper layer as an etching resist. A step of etching exposed aluminum, and (4) a step of providing an etching resist in a desired portion of the copper layer and etching the surface copper layer and the lower copper layer together. A method for manufacturing a metal base circuit board, wherein the etching resist is an alkali peeling type screen printing etching resist. 2. The step (4) is characterized in that, after the step (4), (5) a step of etching away an aluminum layer other than an aluminum layer below the surface copper layer is added, and the step (4) is further repeated. The manufacturing method of the metal base circuit board of description. 3. The method of manufacturing a metal base circuit board according to claim 1, wherein in the step (4), etching is performed so as to remove the upper copper layer while leaving the lower copper layer remaining. 4. The metal base circuit board according to claim 1, wherein a solder resist layer is provided so that solder can be provided at a desired position of a circuit made of a copper layer as a final step. Manufacturing method.

Images