JPH07326702A - Manufacturing method of leadframe for semiconductor device - Google Patents

Abstract

PURPOSE:To enable a palladium plated iron alloy material to sustain an excellent corrosion resistance by minimizing the pinholes made in an underneath layer of the palladium plating. CONSTITUTION:In order to manufacture the title lead frame For semiconductor device, the plating step is mandatory. Firstly, an Ni plating film is formed as an underneath plating palladium. Later, a palladium plating film or palladium alloy film is to be plated at least in an inner lead part and an outer lead part. Next, when an Ni plating film is formed, a pulse current is impressed so as to form an Ni plated film by pulse plating step. At this time, if the duty cycle 5-25% of the pulse waves is specified, the iron elusion amount is diminished below that of the specimen made by smooth DC so as to weaken the corrosion resistance i.e., the pin holes. Furthermore, if the period is specified to be 1-100ms, the iron elusion amount is relatively small down to the level posing no practical problems at all.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device lead frame, and more particularly to an improved nickel plating method.

[0002]

2. Description of the Related Art Generally, a semiconductor device is assembled using a lead frame as follows. A silver plating layer is provided in advance on the tip of the inner lead portion of the semiconductor device lead frame in order to improve the bondability with the semiconductor chip. After bonding the semiconductor chip on the semiconductor chip mounting portion, the electrodes of the semiconductor chip and the silver plating layer at the tip of the inner lead portion are bonded with an ultrafine wire such as gold. After that, molding is performed with a molding resin. further,
In order to improve the mountability when mounting the semiconductor package on the printed circuit board, after cutting the outer frame portion of the lead frame, a solder plating layer is provided on the portion including the outer lead portion to complete the product.

However, in order to provide the solder plating on the outer lead portion, the resin mold is cracked due to thermal shock due to the heating exceeding 200 ° C. during the hot dipping for dipping the outer lead portion, or during the hot dipping. The flux used contaminates the semiconductor package, the outer lead portion, and the like, and reduces the moisture resistance, which causes the reliability of the semiconductor device to be reduced. In addition to the solder plating, it is necessary to provide silver plating, resulting in poor productivity and high cost.

In order to solve such a problem, in recent years,
At the stage of manufacturing a lead frame, a technique of previously providing palladium having a good wire bonding property and solderability as a surface treatment film is being studied. A lead frame having a palladium plating layer on the outermost surface of the lead frame in advance has good wire bonding and solderability only with the palladium plating layer, and therefore the plating process can be simplified. For this reason, in recent years, a technique that has attracted attention is replacing the lead frame in which silver plating and solder plating are provided in advance.

[0005]

By the way, the metal substrate for lead frame is roughly classified into a copper alloy material and an iron alloy material.
A semiconductor component manufactured by using a lead frame obtained by plating a copper alloy material with Ni and then with a palladium plating film has good corrosion resistance, and a palladium plating copper alloy lead frame has already been put into practical use.

However, when the palladium plating film is provided on the iron alloy material, the potential difference between the palladium and the iron alloy material is large even if nickel is plated on the underlayer of the palladium. Therefore, the iron alloy is passed through the pin hole of the nickel plating film. The material corrodes violently, making it difficult to put the palladium-plated iron alloy material lead frame to practical use.

As a method for reducing pinholes in the undercoat plating film, brightening nickel plating can be considered, but it cannot be used because sulfur as a brightener component is included in the plating film and the corrosion resistance deteriorates.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to minimize the pinholes of the nickel plating film provided on the base of the palladium plating film, and to apply the palladium plating film to the iron alloy material. The purpose of the present invention is to provide a lead frame for a semiconductor device that can maintain good corrosion resistance.

[0009]

In order to achieve the above object, the present invention comprises a step of applying a Ni plating film to a lead frame for a semiconductor device and then applying a palladium plating film or a palladium alloy plating film, When the nickel plating film is applied, it is applied by pulse plating.

[0010]

[Function] In pulse plating, current application and resting appear repeatedly. Even if the metal ion concentration on the surface to be plated decreases due to a violent deposition reaction when current is applied, the metal ions are replenished by migration during resting of the current. It is a method of obtaining a dense and smooth plating film with small crystal grains by repeating the above. Since there are few pinholes in the plating film electrodeposited by pulse wave, the corrosion resistance is better than that when electrodeposited by smooth DC wave.

Therefore, if a pulse wave is used during the deposition of the nickel plating film as the base of the palladium plating film, even if the palladium plating film is provided on the iron alloy material, the number of pinholes in the nickel plating film of the base is small, so Corrosion of the iron alloy material is less likely to occur through the plated film, and good corrosion resistance can be maintained.

According to the present invention, the pulse wave at the time of depositing the nickel plating film has a pulse cycle of 1 to 100 ms and a duty cycle of 5 to 5 which is a ratio of the current application time to one cycle.
25% is good. If the period is shorter than 1 ms, the switching between the application of current and the pause is too early, and the recovery of the metal ion concentration on the plated surface cannot be expected. On the other hand, if it is longer than 100 ms, the rate of change in current is small and the effect of the pulse wave cannot be sufficiently enhanced. Further, if the duty cycle is less than 5%, the peak current becomes too high, and the deposited plating film becomes burnt plating, and is rather full of pinholes. For example, when the average current density is 4 A / dm ² , and the duty cycle is 4%, the peak current density is 100 A / dm ^2.
It can be dm ² . On the other hand, when the duty cycle is larger than 25%, the current application time becomes long, so that fine crystals are hard to deposit.

[0013]

EXAMPLES Examples of the present invention will be described below. In order to plate a substrate of a lead frame for a semiconductor device, first, a Ni plating film is plated on the entire surface as a base plating of palladium. A lead frame for a semiconductor device generally includes a semiconductor chip mounting portion, an inner lead portion, an outer lead portion, an outer frame portion, etc., but after nickel plating, at least the inner lead portion and the outer lead portion are coated with a palladium plating film or a palladium alloy film. .

Although the plating is performed twice as described above, in the present embodiment, when the first Ni plating film is applied, the place where the direct current is normally applied is pulse plating and the nickel plating film is deposited by the pulse current. I am trying.
By adopting pulse plating, the number of pinholes, which greatly contribute to corrosion resistance, will be drastically reduced.

Therefore, even if nickel plating is applied to the base of palladium, the iron alloy material is hardly corroded through the pin holes of the nickel plating film, and the palladium plated iron alloy material lead frame can be put to practical use. .

Further, since the pinholes of the nickel plating film are reduced by the pulse plating, it is not necessary to brighten the nickel plating, and sulfur as a brightener component is not contained in the plating film to deteriorate the corrosion resistance.

In this example, the following experiment was conducted for nickel plating by pulse plating. A nickel plating film of about 1 μm was formed on the entire surface of the 42 alloy plate (30 × 40 mm) using the matte nickel plating solution shown in Table 1.

[0018]

[Table 1]

At this time, a nickel plating film was deposited under the pulse current conditions shown in Table 2. Where i _av
The average current density, i _p is the peak current density, t _on the pulse length, t _off is the rest time. The upper half of the table changes the duty cycle with the cycle time fixed at 10 ms, and the lower half of the table changes the cycle time with constant duty cycle = 9%.

[0020]

[Table 2]

Further, a palladium plating film having a thickness of about 0.1 μm was formed on the nickel plating film under the conditions shown in Table 3.

For the purpose of comparison with the present embodiment using pulse current, a sample using smooth direct current was also prepared during the nickel plating film deposition.

[0023]

[Table 3]

The palladium-plated 42 alloy plate thus prepared was placed in a small pressure vessel (volume: 70 ml) filled with 0.05 mol / l of saline solution and hermetically sealed, and kept in a constant temperature bath at 121 ° C. for 24 hours. Held Next, the sample plate was taken out, and the amount of iron component from the 42 alloy plate eluted in saline was quantified by the atomic absorption method. In this case, the smaller the elution amount of iron, the better the corrosion resistance.

FIG. 1 shows the relationship between the change in duty cycle θ and the elution amount of the iron component from the 42 alloy material when a pulse current is applied during the deposition of nickel undercoat on the palladium plating film. It was found that when the duty cycle was 9%, the iron elution amount was the smallest and the corrosion resistance was good. It was also found that in the range of 5 to 25%, the corrosion resistance was improved as compared with the sample prepared with smooth DC (100%).

Next, the duty cycle is kept constant at 9%,
FIG. 2 shows the analysis results of the amount of iron component elution from the palladium-plated 42 alloy material when the period of the pulse current was changed in the range of 0.1 to 1000 ms. From this result, cycle 10
At ms, it was found that the iron elution amount was the smallest and the corrosion resistance was good. Moreover, in the range of the cycle 1-100ms,
It was confirmed that the amount of iron elution was relatively small and there was no practical problem.

As is clear from this experiment, if nickel plating is performed by pulse plating, a highly reliable palladium-plated iron alloy lead frame with few pinholes can be put to practical use.

The iron alloy material represented by the 42 alloy material has high rigidity, and thus is in great demand as a material for a multi-pin fox pitch frame. On the other hand, since the lead frame provided with the palladium plating film can omit the external solder plating in the subsequent step, the assembly time can be shortened and the semiconductor manufacturing cost can be reduced. In addition, there is no concern about solder bridges, which makes it ideal for fox pitch frames. Moreover, there is no lead pollution problem that has been pointed out recently. Furthermore, since there is no silver plating for wire bonding, there is no fear of migration phenomenon due to silver. As described above, the practical use of the palladium-plated iron alloy material lead frame has a great effect.

In the present invention, the nickel plating film provided on the base of the palladium plating film is deposited by pulse current,
This is a plating film with few pinholes.
Therefore, there is no problem even if a plating film is provided below the nickel plating film. Further, not only an iron alloy material but also a copper alloy material may be used as the material of the lead. In that case, the corrosion resistance is further improved.

[0030]

According to the present invention, since the nickel plating film provided on the base of the palladium plating film or the palladium alloy plating film is formed by pulse plating,
The pinholes of the nickel plating film are reduced as much as possible, and good corrosion resistance can be maintained even if the palladium plating film or the palladium alloy plating film is applied to the iron-based or iron alloy-based lead frame.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of manufacturing a lead frame for a semiconductor device according to an embodiment of the present invention, which shows a change in duty cycle (θ) of a pulse current during deposition of nickel-plated undercoat, and a corrosion test of a palladium-plated 42 alloy material. FIG. 6 is a characteristic diagram showing the relationship between the amount of iron eluted from the steel.

FIG. 2 is a characteristic diagram showing the relationship between changes in the cycle of the pulse current at the time of depositing nickel undercoat and the amount of iron elution after a corrosion test of a palladium plated 42 alloy material for explaining the present example.

Claims (2)

[Claims] 1. A step of applying a nickel plating film to a semiconductor device lead frame and then applying a palladium plating film or a palladium alloy plating film, wherein the nickel plating film is applied by pulse plating. A method for manufacturing a semiconductor device lead frame. 2. The pulse wave used for the pulse plating is
The method for manufacturing a lead frame for a semiconductor device according to claim 1, wherein the cycle is 1 to 100 ms and the duty cycle is 5 to 25%.