JPH02270970A - Surface treated steel sheet for electronic equipment parts excellent in rust resistance, whisker resistance, and solderability - Google Patents

Abstract

PURPOSE:To provide simultaneously satisfactory rust resistance, whisker resis tance, and solderability by applying, in order, Ni plating, tinning, and galvaniz ing to the surface of a steel sheet, alloying respective plating layers, and then allowing a chromate film to adhere to the above by means of electroless treat ment. CONSTITUTION:Ni plating of >=0.05g/m<2>, tinning of >=0.05g/m<2>, and galvanizing of >=10% based on the coating weight of tinning are applied, in order from a steel-sheet side, onto the surface of the steel sheet. Heating treatment is carried out at about 150-400 deg.C to alloy respective plating layers, by which a film composed principally of Sn-Zn, Zn-Ni, Sn-Ni, and Fe-Ni alloys is formed. Further, a chromate film of >=1mg/m<2> total chromium content is allowed to adhere to the above on an electroless system to improve solderability, or, a chromate film of >=20mg/m<2> total chromium content is allowed to adhere by means of electrolytic chromating.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is used as electronic components, shielding materials, and frames of electrical products, and has excellent properties such as corrosion resistance, whisker resistance, and solderability. This invention relates to surface-treated steel sheets for parts.

(Prior art) Generally, electrogalvanized steel sheets are used for surface-treated steel sheets used for electronic components, shielding materials, frames, etc. of electrical products that do not require soldering, and tin plate and turntable steel sheets are used for soldering purposes. sheet is used. Also,
For parts that require severe processing or welding, steel plates that are plated with lead-tin or Nl after the parts are processed are used. In this way, surface-treated steel sheets for electronic components are used as existing plated steel sheets, depending on the application.
For special purposes, some parts are coated after processing using methods such as barrel plating.

In recent years, due to the miniaturization of electrical products, the spacing between electronic components has become narrower, resulting in problems such as short circuits and destruction of insulating layers due to needle-shaped single crystals (whiskers) grown from galvanized and tin-plated layers.

To prevent the generation of such whiskers, alloy plating (Japanese Patent Publication No. 58-2598, Japanese Patent Publication No. 55-121) has been proposed.
No. 92, JP-A-49-129, etc.) and post-treatment after plating (JP-A-56-47955, JP-A-56-47956, JP-A-59-143089)
JP-A No. 62-77481, etc.) methods have been proposed in the past. However, the reality is that these methods are hardly ever put into practical use due to the increased steps and costs associated with alloy plating and post-treatment.

Also, from the point of view of cost reduction, it is essential to omit post-plating after processing parts, and there is a strong demand for the provision of pre-plated surface-treated steel sheets.

(Problem B to be Solved by the Invention) As described above, a surface-treated steel sheet that satisfies whisker resistance, solderability, and corrosion resistance at the same time is required for use in electronic components.

(Means and effects for solving the problems) The present invention will be described in detail below. The present invention is based on the characteristics of both galvanized steel sheets (hereinafter abbreviated as EG) and tinplate (EG: corrosion resistance of Zn, tinplate: sn
It satisfies the following requirements (corrosion resistance, solderability) and also has excellent whisker resistance. To achieve these objectives,
Appropriate amount of Zn plating is applied on the Sn plating layer to improve corrosion resistance, °
The Sn-Zn alloy plating has better corrosion resistance and whisker resistance than ordinary tinplate, which has excellent solderability.After NiT base plating, which improves the uniformity of the plating film, a heat diffusion treatment is performed, and Sn is applied sequentially from the surface layer. -7,n,
Sn-Ni.

An alloy film mainly composed of Zn-Ni alloy is formed, and further,
The subsequent chromate treatment was made possible by electrolytic or electroless treatment depending on the application. Figures 3 and 4 are conceptual diagrams of the structure of the plating layer according to the present invention and the GDS (
The actual analysis results obtained using glow discharge emission spectroscopy are shown below.

Hereinafter, the limited scope stated in the claims of the present invention will be explained.

First, regarding the limited range of Ni amount, Ni
As mentioned above, the purpose of plating is to serve as a base plating to improve the uniformity of the plating film. Therefore, in order to fully exhibit the effect of Ni undercoating, it is necessary to cover the surface of the steel plate uniformly to some extent, so the lower limit is at least 0.05 g/m2. Regarding the upper limit, corrosion resistance improves as the amount of adhesion increases, but this naturally leads to increased costs, so the upper limit is generally 30
g/m', but the present invention does not particularly limit the upper limit.

Next, the limited range of Sn amount will be described. Sn plating is the basic plating of the present invention, but as mentioned above, the corrosion resistance changes depending on the amount of underlying Ni plating, so when there is a large amount of Ni plating, the amount of Sn plating is 0.05 g/m' and a trace amount of Zn. The combination may satisfy the required corrosion resistance, and the lower limit of the amount of Sn plating is 0.05 g/m2. In addition, the upper limit cannot be strictly defined because the amount of adhesion varies depending on the required corrosion resistance, but it is generally around 20 g/m2 due to cost considerations.
The present invention is not particularly limited.

Next, the limited range of the amount of Zn plating will be described.

In the case of the present invention, the amount of Zn plating is closely related to the formation of the alloy layer after thermal diffusion as shown in the claims, so it is limited in particular in terms of the ratio to the amount of Sn plating.

Figure 1 shows the base Ni plating amount within the limited range mentioned earlier.
．． Sn plating amount that can lead to 1 to 10 g/m'' 1.0 to 1
S
ST The occurrence of red rust after 48 hours decreased, and the Zn ratio was 10~
At 25%, no red rust appears. Zr+5w25
If Znx exceeds 90%, the occurrence of white rust will be observed, and if the Znx content exceeds 90%, the occurrence of white rust will increase considerably as it approaches 2N plating. Figure 2 also shows an example of the relationship between the Sn/Zn ratio and the occurrence of voice scars for ``ns Ni plating in the same coating amount range as Figure 1.
As shown in the figure, the generation of whiskers decreases as the zinc ratio increases, and no whiskers are observed when the Zn ratio is 10% or more. However, if the Zn ratio exceeds 80%, it will approach Zn plating and whiskers will again occur.

As mentioned above, the limited range of Zn plating is limited to 10% or more and 80% or less of the Sn plating amount from the viewpoint of rust resistance and whisker resistance.

Concerning the conditions and method of heat treatment, diffusion between Sn and Zn occurs even at room temperature, but for industrial production it is necessary to conduct it in a short time, and the general conditions in that case are the heating temperature 150℃~400℃, heating rate is several'e/
It ranges from SEC to several hundred'C/SEC.

Further, the heating method may be an electric or gas heating furnace, current resistance heating, high frequency induction heating, or a combination thereof, and is not particularly limited in the present invention.

Finally, the limitations regarding chromate treatment are significantly different from those of JP-A No. 63-266089, which is similar to the present invention, as well as its use. Since the present invention is used for electronic components, solderability is required, and in particular, most small electronic components are immersed in a molten solder tank for a short time. As shown, the feature is that the solderability is greatly improved by using a bath mainly composed of chromic acid and using an electroless processing method. In this case, the amount of chromate film is total C
Corrosion resistance is good if the r amount is 1 mg/m" or more, and the upper limit of the total chromium amount is generally several hundred mg/m2, but there is no particular need to limit the upper limit in the present invention. In special applications for electronic components, especially those that involve soldering using a soldering iron, higher corrosion resistance than zinc plating may be required.In such cases, electrolytic chromate treatment is applied as defined in claim 2. This is possible by applying chromate film, and the amount of chromate film is also
As stated in Publication No. 6089, 10 to 20 B/a+2
Since corrosion resistance superior to that of zinc plating cannot be obtained with a total amount of chromium of about 200 mg, the present invention limits the amount to more than 20 mg7m2. The upper limit of the total chromium amount is several hundred B/m'' for boat fishing, but the present invention is not limited to this.Also, the chromate bath may be treated with post-treatment other than chromic acid, such as phosphate treatment. It is also possible to perform bonding treatment, etc., and the present invention does not particularly limit this.

(Example) Hereinafter, the present invention will be described in detail based on Examples.

Example-1 After degreasing and pickling a low-carbon cold-rolled steel sheet that had been cold-rolled and annealed in a conventional manner, the following steps were taken: (1)
Ni plating was performed under the processing conditions shown in (2), Sn plating was performed under the processing conditions shown in (3), and Zn plating was performed under the processing conditions shown in (3). The amount of each plating applied is shown in Table 1. Then, the steel plate surface temperature was raised to 250-350℃ using the current resistance heating method.
Heat treatment was performed at 0°C for 0.5 seconds or more in the air to form a Sn-Zn binary alloy on the surface of the plating layer and a Zn inside the plating layer.
-Ni, Sn-Ni binary alloys and Fe-Sn alloys were formed. Furthermore, after performing chromate treatment under the conditions shown in (4), it was subjected to various evaluation tests.

(1) Ni plating ■Bath conditions NiSO4・7H20: 200-3
00g/JZNiCh・6) 1zO: 0-50g
/J2H3BOs 'Og/11 ■ Plating conditions Bath temperature: 40-5.0℃ Current density = 5
~308/dm (2) Sn plating ■Bath conditions Tin sulfate = 20-30g/Il phenolsulfonic acid = 20. ~30g/IL Ethoxylated α-naphtholsulfonic acid: 2~3g/l ■Plating conditions Bath temperature = 35~45℃ Current density:
2~30^/dm' (3) Zn plating ■Bath conditions ZnSO4・IN, 0: 200~
400g/JZNa2SOa: 50-150
g/j! ■Plating conditions Bath temperature = 40~50℃ Current density = 5~30^/dm" (4) Chromate treatment ■Bath conditions Crys: 50~ioog,
Ae) 12504: 0 ■Processing conditions Bath temperature = 40 to 50°C Example-2 Example-2 as the chromate treatment conditions in Example-1
This is an example in which (5) shown below was used instead of (4) in 1, and the other items are the same as Example-1.

(5) Chromate treatment ■ Bath conditions CrO3: 50-100 g/lN
a25iFa: 0.1~10.0g/J! ■
Processing conditions Bath temperature = 40~50℃ Current density:
OA/dm2 (immersion only for about 5 seconds) Example-3 Example-3 As the chromate treatment conditions in Example-1
This is an example in which (6) shown below was substituted for (4) of 1, and the other items are the same as Example-1.

(6) Chromate treatment ■ Bath conditions Crys: 50-100g/
u) 1,504: 0.1-1.0g/JZNazS
IFa: O, 1~10.0g/A ■Plating conditions Bath temperature: 40~50℃ Current density = 20~10
0A/d field 2 C "Amount of adhesion: 21 to 100 mg/m2 Comparative example-1 The amount of Sn plating per one side is 2.8 g/m', and the amount of chromate coating applied to the surface is B as the total Cr amount in terms of metal Cr.
H7m” electroplated tinplate (referred to as #25 tinplate)
.

Comparative Example-2 Electroplated tinplate with Sn plating amount per side of 5.6 g/m' and chromate coating amount applied to the surface of 8 mg/m' as total Cr amount (metal Crfi) (referred to as #50 tinplate) Comparative Example-3 Electroplated tinplate (referred to as #100 tinplate) with Sn plating weight per side of 1.2g/m2 and total Cr content of metal C (referred to as #100 tinplate). -4 Electrogalvanized steel sheet (EG20
Comparative Example-5 The amount of Ni plating per one side is 30.0 g/m', electrolytic nickel plated steel plate or more, the present invention l examples and comparative examples are shown below (a) to (e).
) and compared their characteristics.

(a) Salt spray cycle test In order to investigate rust resistance, sample materials were punched out and subjected to a salt spray cycle test. The salt spray cycle test consisted of three cycles in which 5% saline was sprayed at 35° C. for 8 hours and then paused for 16 hours. Evaluation is done visually, and the evaluation criteria are: ◎ No red rust or white rust, O Red rust, slight white rust, △ Little red rust or white rust, × Red rust or large white rust, × × Red rust It happened.

(b) Moisture Resistance Test For the humidity test, the sample material was left in an atmosphere of 60° C. and 90% R)l for 240 hours. Evaluation is performed visually, and the evaluation criteria are: ○No red rust, white rust, discoloration, or black rust, Δ
Red rust, white rust, no black rust, discoloration, x red rust, white rust,
Discoloration and black rust were observed.

(c) Whisker resistance test For whisker resistance test, the test material is φtoo x 30+n
After performing cylindrical drawing processing of m, 60
℃, 90% R) I for 3 to 6 months.

Evaluation was performed visually and using a scanning electron microscope, and the evaluation criteria were that no O whiskers were generated and that X whiskers were generated.

(d) Solder wettability test The solder wettability test uses a device that records changes in the solder meniscus over time and uses JIS-specified H63A solder and flux, and after pre-treating the sample material, the wettability is tested. did. The evaluation is that the wet area is 95% within 3 seconds.
Those that meet the above criteria are marked as ○, and those that meet the above criteria are marked as ×.

(e) Solder floor test The solder floor test is conducted using H6 with flux as specified by JIS.
Using 3A solder, the test material was pretreated and aged, then maintained at a specified temperature (200 to 230°C), a specified amount of solder was placed on it, and after a specified time (about 20 seconds) The spread diameter of the solder was measured. In the evaluation, those whose spreading diameter was above the specified value were rated O, and those whose diameter was less than the specified value were rated X.

The above test results are summarized in Table 1.

(Effects of the Invention) As described above, the present invention has well-balanced and excellent performance in corrosion resistance, whisker resistance, solderability, etc. for use in electronic components. This invention makes it possible to supply surface-treated steel sheets for electronic components at low cost.

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the relationship between the ratio of Zn to the amount of Sn plating and the rust occurrence rate, Figure 2 is a diagram showing an example of the relationship between the Sn/Zn ratio and the occurrence of whiskers, and Figure 3 is a diagram showing an example of the relationship between the Sn/Zn ratio and the occurrence of whiskers. FIG. 4 is a diagram showing a conceptual diagram of the plating layer of the surface-treated steel sheet for electronic components obtained by the method, and FIG. 4 is a diagram obtained by analyzing the distribution of each element in the cross-sectional direction from the surface layer of the plating layer shown in FIG. 3 by GDS. Other 4 names 椋false憇廿H÷translation←Y Ward 9−剋Htant Spectral intensity (arb, unit)

Claims (1)

[Claims] 1. 0.05 g/m^2 on the surface of the steel plate in order from the steel plate side.
After applying the above Ni plating, Sn plating of 0.05 g/m^2 or more, and Zn plating of 10% or more of the Sn plating amount, the plated layer is alloyed by heat treatment, and S
It is characterized by forming a film mainly composed of n-Zn, Zn-Ni, Sn-Ni, and Fe-Ni alloys, and further adhering a chromate film with a total chromium content of 1 mg/m^2 or more by electroless treatment. A surface-treated steel sheet for electronic device parts with excellent rust resistance, whisker resistance, and solderability. 2 Apply 0.05 g/m^2 onto the surface of the steel plate in order from the steel plate side.
After applying the above Ni plating, Sn plating of 0.05 g/m^2 or more, and Zn plating of 10% or more of the Sn plating amount, the plated layer is alloyed by heat treatment, and S
It is characterized by forming a film mainly composed of n-Zn, Zn-Ni, Sn-Ni, and Fe-Ni alloys, and further adhering a chromate film with a total chromium content of more than 20 mg/m^2 by electrolytic treatment. Surface-treated steel sheet for electronic device parts with excellent rust resistance, whisker resistance, and solderability.