JPH0633466B2 - Surface-treated steel sheet for electronic device parts with excellent rust resistance, whisker resistance, and solderability - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is used as an electronic component for electric products, a shield material, and a frame, and has an excellent electronic performance such as corrosion resistance, whisker resistance, and solderability. The present invention relates to a surface-treated steel sheet for parts.

(Prior Art) Electroplated galvanized steel sheets are generally used for electronic parts of electric products, shield materials, frames, etc. that are not required to be soldered, and tin plates and turn sheets are used for soldering. Is used. Further, for some of the ones that are severely worked or those that are welded, a steel plate plated with lead-tin or nickel after the parts are worked is used. In this way, the surface-treated steel sheets for electronic parts are in a state where the existing plated steel sheets are used properly according to the application, and for special applications, the parts are post-plated by a method such as barrel plating after processing. There is also.

In recent years, due to the miniaturization of electric products, the distance between electronic components is narrowed, and problems such as short circuits and breakdown of insulating layers due to needle-shaped single crystals (whiskers) grown from zinc-plated layers and tin-plated layers have been invented. To prevent the occurrence of such whiskers, alloy plating (Japanese Patent Publication No. 58-2598, Japanese Patent Publication No. 55) is used.
-12192, JP-A-49-129, etc.) and post-treatment after plating (JP-B-56-47955, JP-B-56-47956, JP-A-59-143089, JP-A-59-143089) 62-77481, etc.) has been proposed. However, in reality, these methods have hardly been put into practical use because of the increase in the number of steps and cost increase due to alloy plating and post-treatment.

Further, from the viewpoint of cost reduction, it is indispensable to omit post-plating after processing the parts, and there is a strong demand for providing a pre-plated surface-treated steel sheet.

(Problems to be Solved by the Invention) As described above, surface-treated steel sheets that simultaneously satisfy whisker resistance, solderability, and corrosion resistance are required for electronic parts.

(Means and Actions for Solving the Problems) Hereinafter, the present invention will be described in detail. The present invention is a galvanized steel sheet (hereinafter referred to as E
Both G (abbreviated as G) and tin characteristics (EG: Zn corrosion resistance,
Tin plate: Corrosion resistance and solderability of Sn) are satisfied, and whisker resistance is also excellent. In order to achieve these objects, Zn plating is applied on the Sn plating layer in an appropriate amount to form Sn-Zn alloy plating that is superior in corrosion resistance and whisker resistance to normal tinplate, which has excellent corrosion resistance and solderability. After applying Ni undercoat to improve the uniformity of
Heat diffusion treatment is performed, and from the surface layer, Sn-Zn, Sn-Ni, Zn
This is made possible by forming an alloy film mainly composed of -Ni alloy and then forming a chromate film consisting only of oxide chromium on the alloy film. 3 and 4
The figure shows a conceptual diagram of the structure of the plating layer according to the present invention and an actual analysis result by GDS (Glow Discharge Optical Emission Spectroscopy).

Hereinafter, the limited range described in the claims of the present invention will be described.

First, regarding the limited range of the amount of Ni, the purpose of Ni plating is to have an effect as a base plating for improving the uniformity of the plating film as described above. Therefore, Ni
To fully exert the effect of undercoating, it is necessary to coat the surface of the steel plate evenly to a certain extent.
/ m ² is the lower limit. Regarding the upper limit, the corrosion resistance becomes better as the amount of adhesion increases, but naturally the cost increases, so the upper limit is limited to 10.0 g / m ² .

Next, the limited range of the Sn content will be described. Although Sn plating is the plating that is the basis of the present invention, as described above, the corrosion resistance changes depending on the base Ni plating amount, so when there is a large amount of Ni plating, the corrosion resistance required by a combination of a small amount of Sn plating amount and a small amount of Zn is required. Although it may be satisfied, the lower limit of Sn plating amount is 3.0 g / m ² from the viewpoint of solderability. Also, the upper limit is limited to 12.0 g / m ² in consideration of cost.

Next, the limited range of the Zn plating amount 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 described in the claims, and therefore is limited to the ratio with the amount of Sn plating.

Fig. 1 shows the amount of Ni plating on the base Ni within the limited range mentioned above.
For Sn plating amount 3.0~12g / m ² in 10 g / m ² shows an example of the relationship between the ratio and the rust occurrence rate of Zn. As shown in the figure, the generation of red rust decreased after 48 hours of SST as the proportion of Zn increased, and the generation of red rust disappeared at a Zn ratio of 5 to 25%.
On the other hand, when Zn exceeds 25%, the occurrence of white rust is observed, and when Zn = 90% or more, the occurrence of white rust considerably increases because it approaches Zn plating. FIG. 2 also shows an example of the relationship between the Sn / Zn ratio and the generation of whiskers for Sn and Ni plating in the same deposit amount range as in FIG. As shown in the figure, the generation of whiskers decreases as the proportion of zinc increases, and the generation of whiskers disappears when the Zn ratio is 10% or more. However, if the Zn ratio exceeds 80%, whiskers will be generated again because it approaches Zn plating this time.

As described above, the limited range of Zn plating is limited to 10 to 25% of the Sn plating amount from the viewpoint of rust resistance and whisker resistance.

Regarding the heat treatment conditions and method, diffusion between Sn and Zn occurs even at room temperature, but it is necessary to perform it in a short time for industrial production, in which case the general condition is heating. The temperature is 150 ℃ ~ 400 ℃, the heating rate is also in the range of several ℃ / SEC ~ several hundred ℃ / SEC.

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

Lastly, regarding the chromate coating, it is significantly different from the one disclosed in JP-A-63-266089, which is similar to the present invention, in the use thereof. Since the present invention is used for electronic parts, solderability is required, and particularly for small electronic parts, it is a short-time immersion in a molten solder bath. For example, a chromate treatment method using a bath mainly containing chromic acid is used. It is characterized in that the chromate film formed on the alloy film by the electroless method is composed of only oxide chromium up to 20 mg / m ^{2 in} terms of metal Cr, thereby ensuring solderability. If the amount of the chromate film made of only oxide chromium is 1 mg / m ² or more in terms of metal Cr, the corrosion resistance is good, and the upper and lower limits are limited to 1 mg / m ² .

(Examples) Hereinafter, the contents of the present invention will be described based on Examples.

Example 1 After degreasing and pickling the low carbon cold-rolled steel sheet cold-rolled by a normal method and annealed by a normal method, Ni plating was sequentially performed under the treatment conditions shown in (1), (2) Sn plating was performed under the treatment conditions shown in (3) and Zn plating was performed under the conditions shown in (3). The adhesion amount of each plating is shown in Table 1. Then, the steel sheet surface temperature of 250 to 350 ° C was subjected to heat treatment for 0.5 seconds or more in the atmosphere by the electric resistance heating method, and the Sn-Zn binary alloy was applied to the surface of the plating layer and Zn-Ni, Sn- was applied to the inside of the plating layer. Ni binary alloy and Fe
-Sn alloy was formed. Further, after chromate treatment under the conditions shown in (4), it was subjected to various evaluation tests.

(1) Ni plating bath conditions _{NiSO 4 · 7H 2 O: 200~} 300g / NiCl 2 · 6H 2 O: 0~ 50g / H 3 BO 3: 40g / plating conditions bath temperature: 40 to 50 ° C. Current density: 5 30A / dm ² (2) Sn plating bath conditions Tin sulphate: 20-30g / phenol-sulphonic acid: 20-30g / ethoxylated α-naphtho-sulphonic acid: 2-3g / plating conditions Bath temperature: 35-45 ° C Current ^{density: 2~30A / dm 2 (3)} Zn plating bath conditions _{ZnSO 4 · 7H 2 O: 200~} 400g / Na 2 SO 4: 50~ 150g / plating conditions bath temperature: 40 to 50 ° C. current density: 5～30A / dm ² (4) Chromate treatment Bath condition CrO ₃ : 50 to 100 g / H ₂ SO ₄ : 0 Treatment condition Bath temperature: 40 to 50 ° C Current density: 0 A / dm ² (immersion only for about 5 seconds) Example-2 In Example-1, the conditions for chromate treatment are as follows:
It is an embodiment in which (4) of 1 is replaced by (5) shown below,
Other items are the same as in Example-1.

(5) Chromate treatment Bath conditions CrO ₃ : 50 to 100 g / Na ₂ SiF ₆ : 0.1 to 10.0 g / treatment conditions Bath temperature: 40 to 50 ° C Current density: 0 A / dm ² (immersion only for about 5 seconds) Comparative example -1 Example as chromate treatment conditions in Example-1
It is an example in which (6) shown below is substituted for (4) of 1,
Other items are the same as in Example-1.

(6) Chromate treatment Bath conditions CrO ₃ : 50-100 g / H ₂ SO ₄ : 0.1-1.0 g / Na ₂ SiF ₆ : 0.1-10.0 g / Plating conditions Bath temperature: 40-50 ° C Current density: 20-100A / dm ² Cr adhesion amount: 21 to 100 mg / m ² Comparative example-2 Sn plating amount per one surface is 2.8 g / m ² , and chromate coating amount applied to the surface is 8 mg / m ² (as total Cr amount in terms of metallic Cr) Electroplated tinplate with oxide Cr amount of 8 mg / m ² (referred to as # 25 tinplate) Comparative Example-2 Sn plating amount per one side is 5.6 g / m ² , and chromate coating amount applied on the surface is metallic Cr as the total Cr amount. 8 mg / m ² (oxide Cr amount 8 mg / m ² ) of electroplated tin plate (referred to as # 50 tin plate) Comparative Example-4 11.2 g / m ² Sn plating amount per one side, amount of chromate film applied on the surface Zn but of electroplating (referred to as # 100 tinplate) tin Comparative example -5 per one side of the metal Cr converted at 8 mg / m ^{2 (oxide} Cr amount 8 mg / m ²⁾ as the total amount of Cr Tsu · The amount of 20.5 g / m ^2, the chromate film amount was applied to the surface of electro-galvanized steel sheet metal Cr converted at 70 mg / m ^{2 (oxide} Cr amount 70 mg / m ²⁾ as the total amount of Cr (EG20
Comparative Example-6 Ni plating amount per one side is 30.0 g / m ² , electric nickel plated steel plate As described above, Examples of the present invention and Comparative Examples were subjected to the evaluation tests of (a) to (e) below, The characteristics were compared.

(a) Salt spray cycle test In order to investigate rust resistance, the test material was punched and subjected to a salt spray cycle test. The salt spray cycle test was carried out by spraying 5% saline solution at 35 ° C. for 8 hours and then resting for 16 hours for 3 cycles. The evaluation is performed visually, and the evaluation criteria are: ◎ no red rust, white rust, ○ red rust, small white rust, △ small red rust or small white rust, × red rust or large white rust, × × red rust Big

(b) Humidity resistance test For the humidity resistance test, the test material was aged for 240 hours in an atmosphere of 60 ° C and 90% RH as it was. Evaluation is performed visually, and the evaluation criteria are: ○ red rust, white rust, discoloration, black rust does not occur, △ red rust, white rust, black rust does not occur, discoloration, × red rust, white rust, discoloration, black rust occurrence did.

(c) Whisker resistance test In the whisker resistance test, the test material was subjected to a cylindrical drawing of φ100 x 30 mm, and then aged for 3 to 6 months in the same atmosphere of 60 ° C and 90% RH as in the humidity resistance test. The evaluation was carried out visually and with a scanning electron microscope, and the evaluation criteria were ○ no whisker generation and x whisker generation.

(d) Solder wettability test The solder wettability test uses a device that records the time change of the solder meniscus using JIS-specified H63A solder and flux, and the test material is tested for wettability after pretreatment. did. In the evaluation, those having a wetting time of 3 seconds or less and having a wetting area of 95% or more were evaluated as ◯, and other samples were evaluated as x.

(e) Solder spread test Solder spread test is H63A containing JIS standard flux.
After using solder and pre-treatment aging of the test material,
The solder was held at a specified temperature (200 to 230 ° C.), a specified amount of solder was placed thereon, and the spread diameter of the solder was measured after a specified time (about 20 seconds). In the evaluation, those having a spread diameter greater than or equal to the regulation were rated as ◯, and those less than that were rated as x.

The test results are summarized in Table 1 above.

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

[Brief description of drawings]

FIG. 1 is a diagram showing an example of the relationship between the ratio of Zn to the Sn plating amount and the rust occurrence rate, FIG. 2 is a diagram showing an example of the relationship between the Sn / Zn ratio and the occurrence of whiskers, and FIG. 3 is the present invention. FIG. 4 is a diagram showing a conceptual diagram of a plating layer of the surface-treated steel sheet for electronic parts obtained by the above, and FIG. 4 is a diagram in which the distribution of each element in the cross-sectional direction from the surface layer of the plating layer shown in FIG. 3 is analyzed by GDS.

Claims (1)

[Claims] 1. A surface of a steel sheet, in the order of 0.1 to 10.0 from the steel sheet side.
g / m ² Ni plating, 3.0-12.0 g / m ² Sn plating,
After applying 10 to 25% of the Sn plating amount of Zn plating, the plating layer is alloyed by heat treatment to form Sn-
It has an alloy film mainly composed of Zn, Zn-Ni, Sn-Ni and Fe-Ni alloys, and 1 to 20 mg / m ^{2 in} terms of metallic Cr on this alloy film.
A surface-treated steel sheet for electronic device parts having excellent rust resistance, whisker resistance, and solderability, characterized by having a chromate film consisting only of oxide chromium.