JP3214066B2 - How to treat circuit conductors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a circuit conductor formed by electroless plating or a circuit conductor having a surface conductor formed by electroless plating.

[0002]

2. Description of the Related Art Conventionally, in a hybrid integrated circuit device, a circuit board formed by an electroless plating process on a circuit board formed of an insulating material such as an insulating synthetic resin, alumina, or ceramic, or a lower layer formed by printing. A circuit conductor having a multilayer structure in which a conductor layer is formed by subjecting a conductor to electroless plating is used. For the former circuit conductor, for example, a copper layer, for the latter circuit conductor, for example, a silver layer for the lower layer conductor to reduce conductor resistance, and for convenience of soldering, a copper layer is used for the upper layer conductor similarly to the former. Have been. Soldering is used for electrical connection between these circuit conductors and electrodes or lead frames of electronic components.

[0003]

As shown in FIG. 6, a solder layer 6 is formed by soldering on a copper layer 4 as a circuit conductor formed on a circuit board 2 by electroless plating. In this case, it is pointed out that there is a problem in mechanical strength between the solder layer 6 and the copper layer 4. That is, since the solder layer 6 formed on the surface of the copper layer 4 contains tin as a component thereof, the tin and copper forming the copper layer combine to form the tin-copper intermetallic compound 8. The tin-copper intermetallic compound 8 is formed, and the embrittlement of the tin-copper intermetallic compound 8 lowers the bonding strength between the solder layer 6 and the copper layer 4, causing a failure to maintain the required mechanical strength.

As shown in FIG. 7, a silver layer 10 as a lower conductor is formed on a circuit board 2 by printing or the like, and a copper layer 12 as an upper conductor is formed on the surface by electroless plating. Even when a circuit conductor having a layer structure is formed and a solder layer 14 is formed on the copper layer 12 by soldering, the solder layer 1
4 and the copper forming the copper layer 12 combine to form tin-
The copper intermetallic compound 8 is formed, and the embrittlement of the tin-copper intermetallic compound 8 lowers the bonding strength between the solder layer 14 and the copper layer 12, and the mechanical strength required for electrical connection of circuit conductors Cannot be maintained.

[0005] Such embrittlement of the tin-copper intermetallic compound 8 is caused by hydrogen contained in the copper layers 4 and 12, which are circuit conductors formed by electroless plating, and the crystal in the copper layers 4 and 12. It is allegedly due to a defect.

Accordingly, the present invention provides a method for treating a circuit conductor in which a reduction in soldering strength is prevented by removing hydrogen in a circuit conductor such as a copper layer formed by electroless plating in a post-treatment. The purpose is to do.

[0007]

That is, according to the method for treating a circuit conductor of the present invention, a circuit conductor (copper layer 16) is formed on the surface of a circuit board (2) by electroless plating, and this circuit conductor is rust-proofed. After the treatment, the circuit conductor is subjected to a heat treatment without hydrogen or under reduced pressure of hydrogen.

Further, the method for treating a circuit conductor according to the present invention relates to a method for treating a lower conductor (silver layer 26) formed on the surface of a circuit board (2).
Forming a conductor layer (copper layer 28) on the surface of the conductor by electroless plating, performing a rustproofing treatment on the conductor layer, and then performing a heat treatment on the conductor layer without hydrogen or under reduced pressure of hydrogen. It is characterized by.

[0009]

The circuit conductor formed by the electroless plating process is subjected to a rust-preventive process, and then the conductor layer is subjected to a heat treatment not containing hydrogen or under a reduced pressure of hydrogen. At the same time as hydrogen evolves, the heat treatment complements crystal defects in the circuit conductor by recrystallization. As a result, the circuit conductor formed by the electroless plating process is processed into a circuit conductor that is resistant to soldering.

Further, a conductor layer is formed on the surface of the circuit conductor formed on the surface of the circuit board by electroless plating, and after this conductor layer is subjected to a rust prevention treatment, the conductor layer contains no hydrogen or is subjected to reduced pressure of hydrogen. When the heat treatment is applied to the conductor layer, hydrogen in the conductor layer is diverged by the heat treatment, and at the same time, the crystal defects in the conductor layer are complemented by the recrystallization by the heat treatment. As a result, the conductor layer formed by the electroless plating process is processed into a conductor layer that is resistant to soldering.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments shown in the drawings.

FIGS. 1 and 2 show a first embodiment of the method for processing a circuit conductor according to the present invention. As shown in FIG. 1A, the circuit board 2 is formed of an insulating material such as an insulating synthetic resin, alumina, or ceramic. A copper layer 16 as a circuit conductor having a predetermined circuit pattern is formed on the surface by electroless plating.

FIG. 2 shows an example of a method of forming the copper layer 16. As shown in FIG. 2A, a plating resist layer 18 having a desired circuit pattern is formed by printing. The portion of the pattern that is not covered with the plating resist layer 18 is the portion where the circuit conductor to be obtained is formed, and this is the plating surface. Next, as shown in FIG.
The circuit board 2 is immersed in a plating solution, and a copper layer 16 which is a circuit conductor as a conductor layer is formed on the surface of the circuit board 2 exposed from the plating resist layer 18 by electroless plating. That is, the copper layer 16 forms a desired circuit pattern. Then, as shown in FIG. 2C, when the plating resist layer 18 is removed, a copper layer 16 as a circuit conductor having a desired circuit pattern is obtained on the surface of the circuit board 2.

After the circuit board 2 on which the copper layer 16 is formed is washed with pure water, a protective film 20 is formed on the surface of the copper layer 16 by a rust-proof treatment as shown in FIG. I do. This rust prevention treatment is performed by immersing the circuit board 2 in an aqueous solution containing an alcoholic organic substance at room temperature, and by this treatment, a protective film 20 made of an oxide film is formed on the surface of the copper layer 16.
Is formed. After this protective film 20 is formed, the circuit board 2 is washed with pure water,
Dry for about 15 minutes.

Next, heat treatment is performed on the copper layer 16, that is,
An annealing process is performed. As shown in FIG. 1C, for example, the circuit board 2 is housed in a chamber 22 such as a vacuum drying oven, and the inside of the chamber 22 contains no hydrogen or is supplied with oxygen under a reduced pressure of hydrogen. It is formed in an atmosphere not containing. Then, the heating source 24 is driven to 150 ° C.
Set a heating temperature of ~ 250 ° C. In this case, when the circuit board 2 is formed of a synthetic resin, the heating temperature is set to a value necessary for preventing the deterioration of the circuit board 2, for example, 150 ° C. in order to prevent deterioration and damage due to overheating. . Further, this heat treatment may be performed in an atmosphere in which the chamber 22 is filled with N ₂ gas or an inert gas.

By this heat treatment, hydrogen H contained in the copper layer 16 is vaporized, released from the copper layer 16 into the chamber 22 with a suitable suction pressure, and removed from the chamber 22 by a suitable discharging means. At this time, the recrystallization process in the copper layer 16 also proceeds by the heat treatment, and the crystal defects in the copper layer 16 are complemented by the recrystallization. Further, since the heat treatment is performed in an atmosphere containing no oxygen, unnecessary oxidation of the copper layer 16 is prevented, and the conductor resistance does not increase.

According to such a processing method, the circuit board 2
The removal of hydrogen H in the copper layer 16 as a conductor layer formed by electroless plating on the surface of the metal layer allows the crystal defects to be complemented, and even when soldered, there is no embrittlement of the compound with tin contained in the solder, It is possible to reliably prevent the mechanical bonding strength of the solder connection from lowering, and to enhance the reliability of the electrical connection by soldering.

FIG. 3 shows a second embodiment of the method for processing a circuit conductor according to the present invention. In the first embodiment, the circuit conductor is constituted only by the single copper layer 16, but in the second embodiment, the circuit layer is formed by forming the copper layer 28 as the upper conductor on the surface of the silver layer 26 constituting the lower conductor. This is a processing method when a conductor is used.

As shown in FIG. 3A, a silver layer 26 is formed on the surface of the circuit board 2 by printing or plating as a lower conductor forming a desired circuit pattern.

Next, as shown in FIG. 3B, the circuit board 2 is immersed in a plating solution, and the surface of the silver layer 26 is subjected to electroless plating to form a copper layer 28 serving as a conductor layer as an upper conductor. To form That is, in this embodiment, the silver layer 26 and the copper layer 28
Thus, the circuit conductor 30 is formed.

Next, after cleaning the circuit board 2 with pure water, as shown in FIG. 3C, a protective film 32 is formed on the surface of the copper layer 28 by rustproofing. This rust prevention treatment
Similarly to the first embodiment, the circuit board 2 is immersed in an aqueous solution containing an alcoholic organic substance at room temperature, and the protection film 3 for preventing an oxide film on the surface of the copper layer 28 by this treatment is performed.
2 are formed. The protection film 32 is formed and the circuit board 2
Is washed with pure water, and then washed in an atmosphere of about 80 ° C. for 10 minutes.
Dry for about 15 minutes.

Next, heat treatment is performed on the copper layer 28, that is,
An annealing process is performed. As shown in FIG. 3D, similarly to the first embodiment, the circuit board 2 is housed inside a chamber 22 such as a vacuum drying oven.
The inside is formed in an atmosphere containing no hydrogen or under a reduced pressure of hydrogen and containing no oxygen. Then, the heating source 24 is driven to set a heating temperature of 150 ° C. to 250 ° C. In this case, when the circuit board 2 is formed of a synthetic resin,
In order to prevent deterioration and damage due to overheating, the heating temperature is set to a value required to prevent deterioration of the circuit board 2, for example, 150 ° C. This heat treatment may be performed in the atmosphere by filling the chamber 22 with N ₂ gas or an inert gas as in the first embodiment.

By this heat treatment, the hydrogen H contained in the copper layer 28 is vaporized, released from the copper layer 28 into the chamber 22 with a suitable suction pressure, and removed from the chamber 22 by a suitable discharging means. At this time, the recrystallization process in the copper layer 28 simultaneously proceeds by the heat treatment, and the crystal defects in the copper layer 28 are complemented by the recrystallization. Further, since the heat treatment is performed in an atmosphere containing no oxygen, the oxidation of the copper layer 28 can be prevented.

According to such a processing method, as in the first embodiment, the crystal defects can be complemented while removing the hydrogen in the copper layer 28, and even if the soldering is performed, the compound with tin contained in the solder is removed. There is no embrittlement, it is possible to reliably prevent a decrease in mechanical fixing strength, and it is possible to enhance the reliability of electrical connection by soldering. In addition, the embrittled portion is a silver layer 26 serving as a lower conductor.
Because it does not lower the adhesion strength between
This contributes to improving the reliability of the circuit conductor 30.

Next, FIGS. 4 and 5 show the bonding strength of the circuit conductor processed by the processing method of the present invention. In the experiment, as shown in FIG. 3, a silver layer 26 forming a conductor layer was formed using a silver paste, and a copper layer 28 having a thickness of 10 μm was formed thereon by electroless plating to form a circuit conductor. The annealing process for the conductor is performed in the first step.
The temperature T ₁ is 80 ° C., the second temperature T ₂ is A = 250 ° C.,
B = 200 ° C, C = 150 ° C, D = 100 ° C,
The annealing time was 30 minutes, 60 minutes, 90 minutes and 1
After 20 minutes, a plurality of samples subjected to aging treatment for about 120 hours were prepared, and each sample was soldered under the same conditions, and the peel strength, that is, the adhesive strength was measured.

As shown in FIG. 4, the adhesive strength changes depending on the heating temperature, and it can be seen that the length of the heating time does not significantly affect the adhesive strength. That is, it is understood that setting the heating temperature high contributes to the enhancement of the adhesive strength, and the annealing time of about 30 minutes is sufficient. Considering the production efficiency, it can be seen that sufficient soldering strength can be obtained by annealing treatment for about 30 minutes, and a decrease in connection strength due to embrittlement of the tin-copper intermetallic compound can be prevented.

In FIG. 5, A = 250 ° C., B =
E indicates the case where the annealing process is performed at 200 ° C. and C = 150 ° C., and E indicates the case where the annealing process is not performed. As is clear from the results, the one subjected to the annealing treatment has a smaller decrease in the adhesive strength than the one subjected to the non-annealing treatment, and the higher the treatment temperature,
It can be seen that the decrease in adhesive strength is small. That is, if the processing temperature is not restricted by the material of the circuit board, etc., it is necessary to set the heating temperature to a high value and perform the annealing process, because of the diffusion of hydrogen in the copper layer and the complementation of crystal defects, the soldering strength is reduced. It turns out that a fall can be prevented.

In the embodiment, a two-layer structure of a copper layer or a silver layer and a copper layer has been described as an example of a conductor layer or a circuit conductor. However, the present invention relates to a case where a copper compound or the like is used as a conductor layer. The present invention is not limited to the copper layer because the soldering strength of various conductor layers can be improved by applying the invention to a multilayer conductor made of another metal.

[0029]

As described above, according to the present invention,
The heat treatment can remove hydrogen in the circuit conductor and the conductor layer covering the surface layer of the circuit conductor, and can complement crystal defects by recrystallization, so that soldering strength can be increased and a highly reliable circuit conductor can be provided. Can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a method for processing a circuit conductor according to the present invention.

FIG. 2 is a cross-sectional view showing a method of forming the circuit conductor shown in FIG.

FIG. 3 is a sectional view showing a second embodiment of the method for processing a circuit conductor according to the present invention.

FIG. 4 is a view showing the adhesive strength of solder to a circuit conductor processed by the circuit conductor processing method of the present invention.

FIG. 5 is a diagram showing the adhesive strength of solder to a circuit conductor processed by the circuit conductor processing method of the present invention.

FIG. 6 is a cross-sectional view showing the formation of a tin-copper intermetallic compound formed by a conventional copper layer formed as a circuit conductor and a solder layer.

FIG. 7 is a cross-sectional view showing the formation of a tin-copper intermetallic compound formed by a copper layer and a solder layer formed on the surface of a conventional circuit conductor.

[Explanation of symbols]

 2 circuit board 16 copper layer (circuit conductor) 20, 32 protective film 28 copper layer (conductor layer)

Claims (2)

(57) [Claims] 1. A circuit conductor is formed on a surface of a circuit board by electroless plating, and after a rustproofing treatment is performed on the circuit conductor, a heat treatment is performed on the circuit conductor without hydrogen or under reduced pressure of hydrogen. A method for treating a circuit conductor, the method comprising: 2. A conductor layer is formed on the surface of a lower conductor formed on the surface of a circuit board by electroless plating, and after rust prevention treatment is performed on the conductor layer, the conductor layer contains no hydrogen or is subjected to reduced pressure of hydrogen. And subjecting said conductor layer to a heat treatment.