TWI787896B - Plated structure and lead frame containing nickel plating film - Google Patents

Abstract

The present invention relates to a nickel electroplating film, which is a nickel electroplating film containing 0.01wt% to 1.0wt% of phosphorus. 0.1 μm to 10 μm, when the phosphorus content is 0.05wt% to 0.2wt%, the film thickness of the nickel electroplating film is 0.06μm to 10μm, when the phosphorus content is 0.2wt% to 1.0wt% Below, the film thickness of the said nickel plating film is 0.01 micrometer or more and 10 micrometers or less. An object of the present invention is to provide a Ni plating film excellent in solder wettability, and a plating structure including the Ni plating film.

Description

Plated structure and lead frame containing nickel plating film

The present invention relates to a nickel electroplating film and a plated structure provided with the plating film, and particularly relates to a plating film of a junction such as a wire bond of a semiconductor package such as an IC or an LSI.

As a method of mounting a semiconductor element on a substrate in a semiconductor package such as an IC or an LSI, there are known flip-chip methods that are electrically connected by protruding terminals called bumps, and a method of bonding with a lead frame using a lead frame. The method of electrical connection (wire bonding) of external wiring. Regarding flip-chip mounting, for example, Patent Documents 1 to 4 disclose that an electroless plating film of Ni/Pd/Au is formed on a connection terminal portion of a semiconductor element, and then solder bumps are formed thereon.

On the other hand, regarding wire bonding, the present applicant has previously provided an invention concerning a three-layer plating structure of Ge—Ni/Pd/Au formed by electroplating (Patent Document 5). Furthermore, the technique of forming a Ni/Pd-P/Au film by electroplating is also known (patent document 6). The above-mentioned plating film can be formed by electroplating or electroless plating, but since electroplating and electroless plating each have advantages and disadvantages, they are usually used according to the object to be plated.

prior art literature patent documents

[Patent Document 1] Japanese Patent Application Laid-Open No. 11-345896

[Patent Document 2] Japanese Patent Laid-Open No. 2006-179797

[Patent Document 3] International Publication No. 2006/112215

[Patent Document 4] Japanese Patent Laid-Open No. 2016-162770

[Patent Document 5] Japanese Patent Laid-Open No. 2009-228021

[Patent Document 6] Japanese Patent Laid-Open No. 2012-241260

As one of the surface treatment methods of the lead frame, there is a method called Pd-PPF (Pre Plated Frame) (see Patent Document 6). This is a three-layer plating of Ni/Pd/Au applied to the entire surface of a copper-based lead frame, thereby improving solder wettability and obtaining sufficient bonding performance. As an attempt to reduce the cost of this Pd-PPF lead frame, thinning of a noble metal film such as Au or Pd has been promoted.

Thinning of the precious metal plating film must not impair solder wettability. Whether or not this effect is maintained is determined by evaluating the solder wettability of the plated film after heat treatment. For example, as described in Patent Document 5, after heat-treating a test piece on which a plated film is formed, it is immersed in a solder bath (solder bath), and the time until the wetting stress value becomes zero (zero cross time (zero cross time) is measured. ): ZTC), if this time is sufficiently short, it can be regarded as maintaining solder wettability.

In today's technology, sufficient solder wettability can be maintained even if the plating film of Au and Pd is several to tens of nm, and the cost reduction due to thinning of the precious metal plating film has reached the limit. On the other hand, regarding the Ni plating film, there is still room for improvement. By improving the characteristics (solder wettability) of the Ni plating film, it can be thinned, and it can be expected to shorten the production time (tact time). Further reduce costs. This invention was made in view of such a problem, and it aims at providing the Ni plating film excellent in solder wettability, and the plating structure provided with this Ni plating film as a subject.

In order to solve the above-mentioned problems, the inventors of the present invention conducted intensive studies, and as a result, found the following knowledge, and completed the present invention. That is, Ni plating excellent in solder wettability can be formed by adding a specific amount of P (phosphorus) to the Ni plating film. film. The above-mentioned problems are solved by the means shown below.

1) A nickel electroplating film, which is a nickel electroplating film containing more than 0.01wt% and less than 1.0wt% phosphorus, when the content of phosphorus is more than 0.01wt% and less than 0.05wt%, the film thickness of the above-mentioned nickel electroplating film is 0.1 μm to 10 μm, when the phosphorus content is 0.05wt% to 0.2wt%, the film thickness of the nickel electroplating film is 0.06μm to 10μm, when the phosphorus content is 0.2wt% to 1.0wt% In this case, the film thickness of the above-mentioned nickel plating film is not less than 0.01 μm and not more than 10 μm.

2) A plating structure comprising three layers of a nickel plating film, a palladium plating film formed on the nickel plating film, and a gold plating film formed on the palladium plating film , the nickel electroplating film is the nickel electroplating film described in the above 1).

3) A plated structure, which is a plated structure composed of two layers of a nickel electroplated film and a palladium plated film formed on the nickel electroplated film, the nickel electroplated film is the nickel electroplated film described in the above 1) film.

4) A plated structure comprising two layers of a nickel plated film and a gold plated film formed on the nickel plated film, wherein the nickel plated film is the nickel plated film described in 1) above. film.

5) A lead frame comprising the plated structure described in any one of 2) to 4) above.

According to the present invention, there is an excellent effect that a Ni plating film excellent in solder wettability can be obtained. Furthermore, it has the excellent effect of maintaining good solder wettability and achieving thinning of the Ni plating film. In the film forming step of the plating film, the film forming time of the Ni plating film is particularly time-consuming. Therefore, by making the Ni plating film thinner, it is possible to significantly shorten the lead time.

Since electroless plating does not use electricity, it will not be affected by the current and can be uniformly plated. On the other hand, due to the use of chemical reactions to form a film, the formation of the film is slow. Moreover, the plating bath must be chemically stable. Therefore, there is a problem of maintenance and management costs for chemical solutions or plating tanks. Due to the above circumstances, when the plating film is formed on the entire surface of the lead frame, the plating film is usually formed by electroplating.

The inventors of the present invention conducted intensive research on improving the solder wettability of such a plating film, and found that the solder wettability of the plating film can be improved by adding a specific amount of P (phosphorus) to the Ni plating film. In particular, it was found that sufficient solder wettability can be maintained even when the Ni plating film is thinner. Thereby, the lead time can be shortened by thinning the Ni plating film, and cost reduction can be expected.

The Ni plating film according to the embodiment of the present invention is characterized by containing P (phosphorus) in an amount of 0.01 wt % or more and 1.0 wt % or less. The solder wettability of a Ni plating film can be made favorable by making content of phosphorus in a Ni plating film into the said range. On the other hand, if the phosphorus content is less than 0.01wt%, the effect of improving the solder wettability cannot be obtained. Moreover, if the phosphorus content exceeds 1.0wt%, the solder wettability will decrease instead. Preferably, the phosphorus content is 0.08 wt % to 0.8 wt %, more preferably 0.18 wt % to 0.61 wt %.

When the Ni electroplating film containing P (phosphorus) is observed by scanning electron microscope, it can be observed that the particles of the Ni electroplating film tend to be miniaturized as the phosphorus content increases. Furthermore, compared with before heating, when this Ni plating film was heated, the crystallization expanded, but the higher phosphorus content was, the more suppressed the crystallization expansion was observed. It is believed that the reason for the finer crystallization is that phosphorus concentrates at the grain boundary, which hinders the growth of crystals. It is believed that the decrease in solder wettability is due to the diffusion of the base metal (Cu or Cu alloy, etc.) to the outermost surface of the plating film, which is exposed to the atmosphere and oxidized. However, it is believed that this phosphorus concentrated at the grain boundary will inhibit the Diffusion, thereby inhibiting the reduction of solder wettability.

The film thickness of the Ni electroplating film can be determined by the relationship with the phosphorus content. When the phosphorus content is more than 0.01wt% and less than 0.05wt%, the film thickness of the above nickel electroplating film is 0.1μm to 10μm. When the phosphorus content is more than 0.05wt% and less than 0.2wt%, the film thickness of the above-mentioned nickel plating film is 0.06μm to 10μm, and when the content of phosphorus is 0.2wt% to 1.0wt%, the film thickness of the above-mentioned nickel plating film is It shall be 0.01 micrometer or more and 10 micrometers or less.

The Ni plating film of this embodiment is particularly excellent in that good solder wettability can be secured even when the film thickness of the Ni plating film is reduced to 1 μm or less.

When the phosphorus content is more than 0.01wt% and less than 0.05wt%, if the film thickness of the Ni plating film is thinner than 0.1μm, the diffusion prevention effect of the base metal (Cu or Cu alloy) will be weakened, and Cu will form on the surface. Oxides, solder wettability decreases.

Furthermore, when the content of phosphorus is more than 0.05wt% and less than 0.2wt%, if the film thickness of the Ni plating film is thinner than 0.06μm, the diffusion preventing effect of the base metal (Cu or Cu alloy) will be weakened, and Cu oxides are formed and solder wettability decreases.

Furthermore, when the content of phosphorus is 0.2 wt% or more and 1.0 wt% or less, if the film thickness of the nickel plating film is thinner than 0.01 μm, similarly to the above, the function of preventing the diffusion of the base metal becomes weak, and the solder wettability decreases.

The preferable film thickness is 0.06 μm or more, the more preferable film thickness is 0.1 μm or more, and the more preferable film thickness is 0.2 μm or more.

In addition, the thicker the film thickness of the Ni plating film is, the higher the solder wettability becomes. However, if the film thickness is more than necessary, excess Ni will adhere to increase the cost. Therefore, the film thickness is set to be 10 μm or less, more preferably 5 μm or less, still more preferably 1 μm or less, most preferably 0.5 μm or less.

The plated structure according to the embodiment of the present invention can adopt the following structures.

3-layer structure: (substrate)/Ni plating film/Pd plating film/Au plating film (most surface)

2-layer structure: (substrate)/Ni plating film/Pd plating film (most surface)

2-layer structure: (substrate)/Ni plating film/Au plating film (most surface)

Here, the said Ni plating film is the Ni plating film containing P of this embodiment. Any of the above-mentioned plating films can also be formed by electroplating films. Furthermore, the Pd plating film may be not only pure Pd but also a Pd alloy. The above-mentioned plated structure can be selected according to the application or required characteristics. The main purpose of the Au plating film or the Pd plating film formed on the outermost surface is to prevent oxidation of the Ni plating film or prevent Ni from diffusing to the surface.

Another embodiment of the present invention is a lead frame including the above-mentioned plated structure. Lead frames are mostly made of copper or copper alloys. By forming the plated structure of this embodiment on such a lead frame, excellent bonding can be realized at the time of wire bonding or soldering. Furthermore, the plated structure of this embodiment can be formed not only on a lead frame but also on a solder pad portion used in flip-chip mounting, and it is presumed that similarly excellent bonding can be obtained.

In addition, depending on the object to be plated, a plating film of Ni/Pd/Au is also formed by electroless plating. In the case of electroless plating, a phosphorus compound is sometimes used as a reducing agent in the plating solution. In this case, the Ni film must contain P (phosphorus). A Ni film with a P content of 0wt% can also be formed by using a reducing agent other than a phosphorus compound. However, due to the source of the reducing agent, it is very difficult to control the P content in the Ni film to 2wt% or less.

The Ni plating film of the present embodiment can be formed by electroplating using a nickel plating bath containing a phosphorus compound. As the phosphorus compound, hypophosphorous acid, phosphorous acid, phosphoric acid, etc. can be used. Furthermore, other phosphorus-containing compounds may also be substituted. As the nickel plating bath, a Watts bath, a sulfamine bath, a citric acid bath, or the like can be used. Furthermore, other nickel-containing plating baths can also be used instead. The phosphorus compound or nickel plating bath shown above is an illustration and is not intended to be limiting.

The amount of nickel salt in the Ni plating bath may be 40 to 125 g/L in terms of metal. Furthermore, the amount of the phosphorus compound may be 5 to 300 mg/L in conversion of phosphorus. It should be understood that the amounts indicated above for nickel salts or phosphorus compounds The amounts are merely examples, and are not intended to limit the disclosed range.

Ni plating conditions can be set as follows. Here, the electroplating conditions are merely examples, and it is clear that there are many processing systems or processing apparatuses for performing Ni electroplating, and the electroplating conditions can be changed according to the processing systems or processing apparatuses. Therefore, it should be noted that it is not intended to be limited to the disclosed plating conditions.

Cathode current density: 1~10A/dm ²

Electrolysis time: 5~30min

pH: 3~6

Bath temperature: 30~60℃

Cathode: copper or copper alloy

Anode: Nickel

The Pd plating film and the Au plating film can be formed using a known plating bath and known plating conditions (for example, Patent Document 5).

[Example]

Next, examples and comparative examples of the present invention will be described. In addition, the following examples are merely representative examples, and the present invention is not necessarily limited by these examples, and should be interpreted within the scope of the technical ideas described in the specification.

<About the preparation of evaluation samples>

As a pretreatment, electrolytic degreasing (liquid temperature: 68°C, current density: 10A/dm ² , immersion time: 60 seconds) was performed on the lead frame made of Cu alloy, followed by acid cleaning (5vol.% sulfuric acid, 30 seconds), and then washed with pure water. Ni plating, Pd plating, and Au plating were sequentially performed on the pretreated lead frame under the following plating conditions. At this time, the P concentration in the Ni plating solution was changed to adjust the evaluation sample.

(Ni plating condition)

Plating baths: matt Watt baths containing phosphorus compounds

Ni concentration: 66g/L

P concentration: 0~200mg/L

Current density: 5A/ ^dm2

Bath temperature: 50°C

pH: 4

Target film thickness: 0.13μm

(Pd plating condition)

Plating bath: palladium plating solution (manufactured by Matsuda Sangyo Co., Ltd.: Palla Sigma UF)

Pd concentration: 3g/L

Current density: 0.5A/ ^dm2

Bath temperature: 40°C

pH: 6.5

Target film thickness: 0.025μm

Anode: iridium oxide

(Au plating condition)

Plating bath: gold plating solution (manufactured by Matsuda Sangyo Co., Ltd.: Auru Sigma F)

Au concentration: 2g/L

Current density: ^2A /dm2

Bath temperature: 45°C

pH: 4

Target film thickness: 0.005μm

Anode: iridium oxide

(Determination of phosphorus content)

The phosphorus content in the Ni plating film of each evaluation sample was measured using a high-frequency induction coupling plasma (ICP) emission spectrometer for measurement.

(Evaluation of solder wettability)

By keeping each evaluation sample at a specific temperature condition (400°C±2°C) for a period of time, after applying a high temperature heat history, immerse it in a solder bath (63%-Sn, 37%-Pb, liquid temperature: 230°C± 5°C), and then measure the time required for the force on the solder bath to become zero (zero crossing time) to evaluate solder wettability. The shorter the zero crossing time, the better the solder wettability. The conditions of immersion in the solder bath are as follows: the immersion depth is set to 1mm, the immersion speed is set to 2mm/second, and the immersion time is set to 5 seconds. As a soldering promotion method, R-type flux (inactive type) is used.

<Evaluation of P content of Ni plating film>

Table 1 shows the relationship between the P content contained in the Ni film and the zero crossing time. As shown in Table 1, it was confirmed that the solder wettability was improved by adding phosphorus. Especially when the phosphorus content is 0.1 wt % to 0.8 wt %, the solder wettability is greatly improved. Furthermore, in general, compared to Pd-Sn solder, the solder wettability of Pd-free solder is poor, but it was confirmed that even in the case of using Pd-free solder (Sn-3.0Ag-0.5Au), the solder wettability Moisture is also no problem.

<Evaluation of Thinning of Ni Plating Film>

The P concentration in the Ni plating solution is set as 5.4mg/L, 10.9mg/L, 32.7mg/L, 76.3mg/L, 119.9mg/L, and the Ni plating film thickness is changed as shown in Table 2, except In addition, evaluation samples were produced under the same plating conditions as above. Then, solder wettability was evaluated for each sample under the same conditions as above. It should be noted that the results in Table 1 are directly cited for the plating film thickness of 0.13 μm. The results are shown in Table 2. As shown in Table 2, it was confirmed that good solder wettability can be maintained even if the film thickness of the Ni plating film is 1.0 μm or less. In addition, as the film thickness of the Ni plating film becomes thicker, the solder wettability improves more. Therefore, it was confirmed that there is no problem with the solder wettability, although it is not shown in an example when the film thickness exceeds 0.3 μm.

[Industrial availability]

The present invention has the excellent effect of being able to obtain a Ni plating film with excellent solder wettability. Furthermore, it has the excellent effect of maintaining good solder wettability and achieving thinning of the Ni plating film. The plated film or plated film structure of the present invention is useful in lead frames, printed wiring boards, rigid substrates, flexible substrates, tape carriers, connectors, power devices, wires, pins, and the like.

Claims (4)

A plated structure, which is based on a substrate made of copper or copper alloy, consisting of a nickel plating film formed on the substrate, a palladium plating film formed on the nickel plating film, and a palladium plating film formed on the palladium plating film. The plating structure composed of the three layers of the gold plating film, the above nickel plating film contains 0.01wt% to 0.61wt% of phosphorus, and when the phosphorus content is 0.01wt% or more and less than 0.05wt%, the above nickel The film thickness of the electroplating film is not less than 0.1 μm and not more than 10 μm. When the phosphorus content is not less than 0.05wt% and not more than 0.2wt%, the film thickness of the above nickel electroplating film is not less than 0.06um and not more than 10um. When the phosphorus content is 0.2wt% % to 0.61 wt%, the film thickness of the above-mentioned nickel plating film is 0.01 μm to 10 μm. A plating structure, which is based on a substrate made of copper or a copper alloy, and is a plating structure composed of two layers: a nickel plating film formed on the substrate and a palladium plating film formed on the nickel plating film body, the above nickel electroplating film contains 0.01wt% to 0.61wt% of phosphorus, when the phosphorus content is more than 0.01wt% and less than 0.05wt%, the film thickness of the above nickel electroplating film is 0.1μm to 10μm, when When the content of phosphorus is more than 0.05wt% and less than 0.2wt%, the film thickness of the above-mentioned nickel electroplating film is not less than 0.06 μm and not more than 10 μm, and when the content of phosphorus is not less than 0.2wt% but not more than 0.61wt%, The film thickness is not less than 0.01 μm and not more than 10 μm. A plated structure, which is based on a substrate made of copper or copper alloy, and consists of two layers: a nickel plating film formed on the substrate and a gold plating film formed on the nickel plating film. body, the above nickel electroplating film contains 0.01wt% to 0.61wt% of phosphorus, when the phosphorus content is more than 0.01wt% and less than 0.05wt%, the film thickness of the above nickel electroplating film is 0.1μm to 10μm, when When the content of phosphorus is more than 0.05wt% and less than 0.2wt%, the film thickness of the above-mentioned nickel electroplating film is not less than 0.06 μm and not more than 10 μm, and when the content of phosphorus is not less than 0.2wt% but not more than 0.61wt%, The film thickness is not less than 0.01 μm and not more than 10 μm. A lead frame comprising the plated structure according to any one of Claims 1 to 3.