JP2875655B2 - Manufacturing method of wiring board - 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 forming a wiring board on which various electronic components such as LSIs and diodes are mounted, and more particularly to a method for forming a good plating film having no defects such as blisters and dents on a wiring pattern. The present invention relates to a method for manufacturing a wiring board suitable for the invention.

[0002]

2. Description of the Related Art Conventionally, generally known methods for manufacturing a wiring board, for example, manufacturing a wiring board in which a plating film of nickel, gold or the like is formed on a wiring pattern of tungsten, molybdenum or the like on a substrate made of ceramics such as alumina. The method is as follows.

That is, after a wiring pattern such as tungsten is formed on a ceramic base by a method such as screen printing, the wiring pattern is sintered. Next, pretreatments such as degreasing, pickling, and activation necessary for plating are performed, and then a plating film of nickel or the like is formed to a predetermined thickness by electroless or electroplating. Thereafter, the substrate is subjected to a heat treatment to improve the adhesion between the wiring pattern such as tungsten and the plating film. Japanese Patent Publication No. 59-33665 is an example of a method for manufacturing this type of wiring board.

[0004]

However, in the above-mentioned prior art, there is a disadvantage that blisters and dents are generated in the plating film in the last heat treatment step. That is, a wiring pattern such as tungsten is generally a paste obtained by mixing a powder of a metal such as tungsten or molybdenum with a component such as an organic substance or glass, and then printing and sintering the paste. There are many voids. If a plating film is formed on a wiring pattern having such voids, the plating film is formed in a state where moisture such as a plating solution and washing water is taken in. When the next heating step is performed in this state, for example, in the case of a tungsten wiring pattern and a nickel plating film, heating at a temperature of 650 ° C. or more is necessary to obtain sufficient adhesion, and the adhesion between the two is sufficient. At a low temperature before it is obtained, the moisture taken in the voids evaporates and evaporates to push up the plating film and generate blisters. In a more severe case, the plating film is broken, and a part of the plating film is scattered, resulting in cissing.

The blisters and blemishes tend to occur as the plating film becomes thicker and as the number of voids increases. When blisters are generated on the plating film, the electronic components are connected to the plating film by soldering or the like, and when the wire bonding is performed, the blister portion between the plating film and the wiring pattern is not in close contact, so that solder connection and wire bonding are not performed. There is a problem that connection reliability is significantly reduced. Further, if the blisters exceed a certain size, solder connection and wire bonding itself cannot be performed well. Further, when nicks occur in the plating film, the solder does not wet at the nicks, so that bonding cannot be performed by wire bonding, resulting in poor connection.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and even if moisture is trapped in voids, scratches, etc. existing in the surface layer of the wiring pattern,
It is an object of the present invention to provide an improved method for manufacturing a wiring board which does not cause blistering or burrs on a plating film in a heating step.

[0007]

SUMMARY OF THE INVENTION The above objects are attained by ceramics.
Forming a wiring pattern made of a sintered body of metal to click wiring board
A step of, on the wiring pattern, to form a plated film
That a step, after forming the plated film, engineering a heat treatment
In the method for manufacturing a wiring substrate formed by organic and degree, before performing the heat treatment, by pre-heat treatment at pre said heat treatment temperature lower than the temperature, it is achieved. This reserve
Heat treatment removes voids and scratches on the substrate surface
The trapped moisture can escape to the outside.

[0008] The starting temperature of the preliminary heat treatment must be 100 ° C. or higher and lower than the heat treatment temperature, preferably 80% or less of the heat treatment temperature. At a temperature of 100 ° C. or lower, there is no effect of releasing moisture trapped in voids and scratches to the outside. Further, the temperature during the preheating treatment is not necessarily required to be constant, and the temperature gradient is 0 to 0.
It may be in the range of 10 ° C./min. This temperature gradient is 1
When the temperature is higher than 0 ° C./min, the temperature rises in a short time, so that the moisture evaporates before the water escapes to the outside and the pressure rises to a value necessary for blistering the plating film. Will be generated.

The present invention is also effective in preventing blistering of the plating film due to the difference in the coefficient of thermal expansion between the substrate and the plating film. That is, for example, when nickel plating is applied to a tungsten wiring formed on an alumina substrate, the coefficient of thermal expansion of alumina is 6 to 7 × 10 to ⁶ , and the coefficient of thermal expansion of tungsten is 4.5 × 10 to ⁶ . On the other hand, the thermal expansion coefficient of nickel is as large as 14 × 10 to ⁶ . Therefore, when the temperature is rapidly increased to about 650 ° C. where sufficient adhesion between tungsten and nickel can be obtained, the elongation of nickel increases,
Peeling occurs between nickel and tungsten, resulting in blistering of the nickel plating film. However, as in the present invention, the temperature gradient up to the preheating start temperature is 1 to 30 ° C.
/ Min does not cause blistering due to the difference in thermal expansion, and diffusion and reaction of nickel and tungsten partially start during the preheating treatment, so that the adhesion between the two is improved. Does not occur.

[0010]

The present inventors have obtained the findings shown in FIGS. 1 to 3 through experiments, and the present invention has been made based on such findings. That is, FIG. 1 shows the relationship between the heating time and the amount of released water, and is a characteristic diagram when a substrate plated with nickel to a thickness of 5 μm on a tungsten wiring pattern is heated at 350 ° C. As shown in the figure, 30 minutes after heating, 1.5 ml / 0 ° C.
atm water is released and after 1 hour 1.6 ml / 0
C., 1 atm, released, and after 30 minutes, the amount of released water hardly increased.

FIG. 2 shows the relationship between the heating temperature and the amount of released moisture, showing the amount of moisture released by heating for one hour on the same substrate as in FIG. As shown in the figure, the amount of released water in the temperature range of 100 ° C. or higher is 1.6 ml / 0 ° C., 1
Atm, but below 100 ° C., the amount of release decreases sharply. As described above, in the case of the above-mentioned substrate, it is understood that the moisture trapped between the wiring pattern and the plating film can be substantially removed by performing the preheating treatment at a temperature of 100 ° C. or more for 30 minutes or more. Further, the time required to remove almost all the trapped moisture depends on the thickness of the plating film, and is 10 minutes when the film thickness is 3 μm as shown in FIG. 3, and 60 minutes when the film thickness is 8 μm. is there.

Note that the preheating treatment and the heating treatment do not necessarily have to be performed continuously, and the heating treatment may be performed by cooling once after the preheating treatment and then heating again.

The atmosphere for performing the preheating is preferably a non-oxidizing atmosphere, that is, a vacuum or reducing atmosphere or an inert atmosphere when the plating film is made of a substance which is easily oxidized such as nickel or copper. If the vacuum is preferably ^{10 ~ 1 ~10 ~ 4 Torr,} 10 ~ no effect greater the antioxidant than ¹ Torr, antioxidant effect in the following 10 ~ ⁴ Torr is unchanged. In the case of a reducing atmosphere, hydrogen or a mixed atmosphere of hydrogen and an inert gas such as nitrogen, helium, argon or the like is preferable, and the mixing ratio of the two is not particularly limited, but practically 4: 6 to
6: 4 is preferred. As the inert atmosphere, an atmosphere containing an inert gas such as nitrogen, helium, or argon and having an oxygen content of 10 ppm or less is suitable.

The wiring pattern is preferably a sintered body of a high melting point metal such as tungsten or molybdenum, or other metal such as copper or palladium. The plating metal is preferably a simple substance or an alloy of nickel, copper, cobalt, gold or the like.

[0015]

The present invention will be described below in more detail with reference to typical examples of the present invention. <Examples 1 to 3> A wiring pattern was printed on an alumina substrate in advance using a tungsten paste by a well-known method, and this was sintered to form a tungsten wiring pattern. This wiring board is generally subjected to an alkali treatment with an aqueous sodium hydroxide solution, an acid treatment with hydrochloric acid, and then an activation with a palladium activating solution, and then an electroless nickel plating solution using dimethylamine borane as a reducing agent. Was used to form a nickel plating film having a thickness of 5 μm on the wiring pattern. Thereafter, a preheating treatment was performed under the conditions shown in Table 1, and further heating was performed at 750 ° C. for 10 minutes to cause the nickel plating film and tungsten to react with each other, thereby bringing the both into close contact with each other.

[0016]

[Table 1]

As shown, the number of blisters and burrs generated in the plated film after the heat treatment was 0 under the conditions of the present invention, and the appearance, solderability, and wire bonding properties were also good. Similar good results were obtained when the plating film was formed by electroplating instead of electroless plating.

Examples 4 to 6 A nickel plating film having a thickness of 5 μm was formed on a tungsten wiring pattern formed on an alumina substrate in the same manner as in Example 1 by an electroless plating method. Thereafter, a pre-heating treatment was performed under the conditions shown in Table 2, and the mixture was further heated at 650 ° C. for 15 minutes to cause a reaction between the nickel plating film and tungsten, thereby bringing the both into close contact with each other.

[0019]

[Table 2]

The rate of occurrence of blisters and dents in the plated film after the heat treatment was as shown, and was 0 under the conditions of the present invention, and the appearance, solderability, and wire bonding properties were also good. In Comparative Example 3, the temperature gradient during preheating was too large than 10 ° C./min of the present invention.

<Examples 7 to 9> A nickel plating film having a thickness of 8 μm was formed on a tungsten wiring pattern formed on an alumina substrate in the same manner as in Example 1 by an electroless plating method. Thereafter, a preheating treatment was performed under the conditions shown in Table 3, and the mixture was further heated at 650 ° C. for 15 minutes to cause a reaction between the nickel plating film and tungsten, thereby bringing both into close contact.

[0022]

[Table 3]

The number of blisters and burrs generated in the plated film after the heat treatment is 0 under the conditions of the present invention as shown, and
Solderability and wire bonding properties were also good.
In Comparative Example 4, the preheating time was 20 min, which was shorter than the 30 min or more of the present invention.

Examples 10 to 12 A nickel plating film having a thickness of 5 μm was formed on a tungsten wiring pattern formed on an alumina substrate in the same manner as in Example 1 by electroless plating, and gold was further formed to a thickness of 2.5 μm. A plating film was formed. Thereafter, preheating was performed under the conditions shown in Table 4, and further heating was performed at 700 ° C. for 10 minutes to cause the nickel plating film and tungsten to react with each other, so that both were brought into close contact with each other.

The number of blisters and peeling of the plated film after the heat treatment is 0 under the conditions of the present invention as shown,
Solderability and wire bonding properties were also good.
In the case of Comparative Example 5 as well, the blisters and cissing were 0, but the heating gradient was 0.5 ° C./m, which was smaller than the lower limit of 1 ° C./min of the present invention.
Since it was in, it took a lot of time to reach the preheating temperature, which was not practical. On the contrary, Comparative Example 6 is an example in which the temperature rise gradient is too large than the upper limit of 30 ° C./min. The present invention provides good results not only in the case where the plating film is a single layer, but also in the case of a multiple layer in which a gold plating film is formed on a nickel plating film, for example.

[0026]

[Table 4]

[0027]

According to the present invention, when the underlying wiring pattern has voids, flaws, etc. and moisture is trapped during plating, or when there is a difference in thermal expansion between the underlying wiring pattern material and the plating film material. Also, it was possible to prevent blistering and burrs of the plating film due to the heat treatment after plating. As a result, the reliability of connection such as soldering and wire bonding has been improved, and a wiring board can be manufactured with good yield.

[Brief description of the drawings]

FIG. 1 is a characteristic curve diagram showing a relationship between a heating time and a released moisture amount.

FIG. 2 is a characteristic curve diagram showing a relationship between a heating temperature and a released moisture amount.

FIG. 3 is a characteristic diagram showing a relationship between a plating film thickness and a time required for releasing moisture.

[Explanation of symbols]

 No sign.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-234395 (JP, A) JP-A-59-129489 (JP, A) JP-A-61-236192 (JP, A) 14719 (JP, B2) JP-B-58-38505 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) H05K 3/24

Claims (5)

(57) [Claims] 1. A ceramic wiring base made of a metal sintered body.
Forming a that wiring pattern, the wiring pattern on, forming a plating film, after it was the plating film is formed <br/>, preparation of a wiring board formed by perforated and heating treatment In the method, as a pretreatment step of performing the heat treatment ,
A method for manufacturing a wiring board, comprising a step of performing a preliminary heat treatment in a temperature range of 100 ° C. or higher and lower than the heat treatment temperature. 2. The method according to claim 2, wherein the temperature gradient during said preheating treatment is 0-10.
2. The method for manufacturing a wiring board according to claim 1, wherein the temperature is ° C / min. 3. A temperature gradient during heating up to the preheating treatment starting temperature is 1 to 30 ° C./min.
The method for manufacturing the wiring board according to the above. 4. The method for manufacturing a wiring board according to claim 1, wherein the wiring pattern formed on the wiring base is a sintered body containing a high melting point metal as a main component, and the plating film is a metal containing nickel. . 5. The method for manufacturing a wiring board according to claim 1, wherein the atmosphere in which the preheating treatment is performed is a non-oxidizing atmosphere.