JP2005139489A - Steel sheet with color-treated surface and heat sink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet with color-treated surface having superior solder wettability and superior heat radiation characteristics, and to provide a heat sink. <P>SOLUTION: The steel sheet with color-treated surface has a surface-treated color film formed by applying a liquid comprising a water-based urethane resin or a water-based acrylic resin containing water-solublized rosin, and further color pigment, silica and a rust-preventive agent on a plated steel sheet, and drying it; has a superior solder wettability of less than 10 seconds when measured with a meniscograph method; has a superior thermal emissivity of 0.1 to 0.9; has a superior thermal conductivity of 40 W/m×K or higher; and is applied to the heat sink. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a colored surface-treated steel sheet formed by forming a colored surface-treated film excellent in solderability and heat radiation on a plated steel sheet, and a heat sink using the same.

  In recent years, in surface-treated metal plates applied to applications such as metal containers, home appliance chassis, cabinets, electronic component substrates, steel plates as substrates, black, white, gray and other achromatic colors, red, blue, A colored surface-treated steel sheet in which a surface-treated film colored in a color such as yellow, green, brown, pink is formed on a steel sheet is used. The surface-treated steel sheet used for these applications may be subjected to soldering for bonding with other parts or members where it needs to be bonded after being molded into a predetermined shape. In the treated steel sheet, the soldered wettability of the colored colored surface treatment film was poor, and it could not be applied to applications requiring soldering.

  In particular, in the use of electronic component boards, it is necessary to suppress the temperature rise of components loaded in a narrow housing or with almost no gap as electronic devices are miniaturized and densified. In a printed circuit board, a board to which a heat sink for heat dissipation is attached is used in order to suppress the temperature rise of components. For example, as shown in FIG. 1, the heat sink is provided in close contact with at least one surface of a large heating element 1 such as a printed circuit board. The larger the contact area, the greater the heat conduction and the greater the amount of heat dissipation. As a material used for the heat sink, it is preferable to use a material having excellent thermal conductivity so that heat can be rapidly absorbed from the heating element. Further, as shown in FIG. 1, it is preferable that the heat sink 2 is provided so as to extend away from the heating element 1 because heat is radiated from the extended portion, so that the heat radiation of the surface of the heat sink 2 is excellent. In FIG. 1, arrow 3 indicates the direction of heat conduction, and arrow 4 indicates the direction of heat radiation.

  In addition, as a prior art of a steel sheet for improving the wettability of solder, tin plating is performed on the steel sheet, and then plating mainly containing any one or more of zinc, nickel, and cobalt on the tin plating, or zinc, Two-layer plating for solder, in which at least one of nickel, cobalt, and at least one of tin, iron, lead, and copper is plated with an alloy that exhibits a potential lower than the standard electrode potential of tin A steel plate is disclosed (see, for example, Patent Document 1). However, since this plated steel sheet does not have a protective coating layer with excellent corrosion resistance like a chromate-treated coating, the corrosion resistance is not sufficient, and the coating of corrosion products results in the deterioration of solder wettability. There is a fear.

  Further, a Sn—Zn alloy layer is formed on a surface-treated steel sheet in which a Sn—Zn alloy layer is formed on the steel plate, or a surface treatment layer made of either Ni plating or Fe—Ni diffusion layer is formed on the surface. An environmentally-friendly surface-treated steel sheet for electronic parts formed by forming an inorganic film mainly composed of magnesium phosphate on a Sn—Zn alloy layer is disclosed (for example, see Patent Document 2). However, this inorganic film mainly composed of magnesium phosphate can also give high corrosion resistance to the Sn—Zn alloy, but because of its stability, it uses a weakly active or inactive flux that does not contain chlorine. In this case, the soldering property is poor.

  Furthermore, these double-layer plated steel sheets for solder and surface-treated steel sheets for electronic parts use steel sheets as substrates for forming surface treatment films, so that the steel is exposed at the cut surface, so red rust is likely to occur. It also has.

  In the case of a heat sink using a steel plate-based material, it can be soldered and bonded directly to the printed circuit board. If heat dissipation is further required, a material based on an aluminum plate is preferable, but it is difficult to solder directly on a printed circuit board based on an aluminum plate, so a dedicated pin for soldering is attached to the heat sink. And soldered to the printed circuit board through the pins. As a method for enabling soldering on a surface-treated metal plate having an aluminum plate as a substrate, the following attempts have been made.

  For example, a surface-treated metal plate in which a tin plating layer is formed on a plate made of an aluminum plate or an aluminum-based alloy via a nickel plating layer is disclosed (for example, see Patent Document 3). In this surface-treated metal plate, a nickel plating layer is formed on a base material such as a hot-dip aluminum-plated steel plate using a vacuum deposition method, and then tin plating is performed. However, according to this method, nickel plating and tin plating require a large plating apparatus such as a vacuum apparatus, the film forming speed is low, the productivity is low, and it is difficult to manufacture at low cost.

  Also, tin or tin excellent in solderability, in which a tin layer or tin alloy layer is coated on an aluminum base material and a tin concentration gradient layer is formed at the interface between the aluminum base material and the tin layer or tin alloy layer. An alloy-coated aluminum plate is disclosed (for example, see Patent Document 4). In this tin or tin alloy-coated aluminum plate, the aluminum base plate and the tin layer or tin alloy layer are formed by electroplating tin on the aluminum plate and then heating, or by passing the aluminum plate through molten tin or tin alloy. A tin concentration gradient layer is formed at the interface of the film, and tin plating is performed. However, the adhesion between the aluminum substrate and the tin layer or tin alloy layer is poor, and the tin plating film is formed on the aluminum substrate particularly when bending is performed. Have the disadvantage of being easily peeled off.

  Prior art document information relating to the present application includes the following.

JP-A 63-277786 Japanese Patent Laid-Open No. 2002-249885 JP 05-345969 A JP 09-291394 A

  This invention is made | formed in view of such a point, and it aims at providing the colored surface treatment steel plate and heat sink which have the outstanding solder wettability and the outstanding thermal radiation property.

  In order to solve the above-mentioned object, the colored surface-treated steel sheet according to claim 1 of the present invention is formed by forming a colored surface-treated film having a solder wettability of less than 10 seconds by a meniscograph method on a plated steel sheet. The rate is 0.1 to 0.9.

  The colored surface-treated steel sheet according to claim 2 is characterized in that, in claim 1, the plated steel sheet is formed by forming a zinc layer on the steel sheet.

  The colored surface-treated steel sheet according to claim 3 is characterized in that, in claim 1, the plated steel sheet is formed by forming a tin layer on the steel sheet.

  The colored surface-treated steel sheet according to claim 4 is characterized in that, in claim 1, the plated steel sheet is formed by forming a zinc-tin alloy layer on the steel sheet.

  A colored surface-treated steel sheet according to a fifth aspect is characterized in that, in the first aspect, the plated steel sheet is formed by forming a two-layer plating layer of a tin layer and a zinc layer in order from the steel sheet side on the steel sheet.

  The colored surface-treated steel sheet according to claim 6 is characterized in that, in claim 1, the plated steel sheet is formed by forming a two-layer plating layer of a zinc layer and a tin layer on the steel sheet in order from the steel sheet side.

  The colored surface-treated steel sheet according to claim 7 is characterized in that, in claim 1, the plated steel sheet is formed by forming a copper layer on the steel sheet.

  The colored surface-treated steel sheet according to claim 8 is characterized in that, in claim 1, the plated steel sheet is formed by forming a nickel layer on the steel sheet.

  The colored surface-treated steel sheet according to claim 9 is obtained by applying a water-based urethane resin containing a colored pigment, silica, and a rust inhibitor to a colored surface-treated film according to any one of claims 1 to 8 and drying. It is characterized by being a film.

  A colored surface-treated steel sheet according to a tenth aspect of the present invention is the colored surface-treated steel sheet according to any one of the first to eighth aspects, wherein the colored surface-treated film is coated with a water-based acrylic resin containing a color pigment, silica, a rust inhibitor, and rosin. It is characterized by being a film.

  The colored surface-treated steel sheet according to claim 11 is characterized in that, in claim 9 or 10, the colored pigment is a black pigment.

  A heat sink according to a twelfth aspect is characterized by using the colored surface-treated steel sheet according to any one of the first to eleventh aspects.

  A heat sink according to a thirteenth aspect is characterized in that, in the twelfth aspect, the thermal conductivity is 40 W / m · K or more.

  The colored surface-treated steel sheet of the present invention contains a water-based urethane resin or rosin having excellent solder wettability in a plated steel sheet having a steel sheet as a substrate and having a plating layer having excellent solder wettability and solder wettability. Since a water-based acrylic resin further contains an achromatic or chromatic coloring pigment, it is applied and dried to form a colored surface-treated film, so that the solder wettability by the meniscograph method is less than 10 seconds. In addition, the thermal emissivity is 0.1 to 0.9, and the thermal conductivity is 40 W / m · K or more, and the color is clear and the decorative property is excellent.

  Therefore, it can be suitably applied as an electronic device casing, an electronic component substrate, and a heat sink of the present invention that require excellent solderability and thermal radiation.

  Hereinafter, the present invention will be described in detail. As the plating layer of the plated steel sheet for forming the colored surface treatment film, a single layer of pure metal such as zinc, tin, copper, nickel, bismuth, or multiple layers formed by stacking two or more of these pure metals Layer, zinc-tin, zinc-copper, zinc-nickel, zinc-aluminum, zinc-iron, zinc alloy such as zinc-cobalt, tin-nickel, tin-copper, tin alloy such as tin-iron, copper- An alloy plating layer made of a copper alloy such as beryllium or copper-nickel can be selected depending on the application. Formation of the plating layer on the steel sheet can be appropriately selected from hot dipping, electroless plating, electroplating, and the like. The steel sheet on which the plated layer is formed may be used as a plated steel sheet as a substrate for forming the following colored surface treatment film on the plated layer as it is, but after forming the plated layer, it is heated to melt the single-layer plated layer. To make it bright, or to melt and alloy the plating layer of the multi-layer plating into a single alloy plating layer, or to solid-phase diffuse each metal between the plating layers or between the steel plate and the plating layer, etc. In addition, a plated steel sheet as a substrate on which a colored surface treatment film is formed may be used.

  Next, a surface treatment film containing a color pigment is formed on the steel sheet on which the plating layer made of these metals is formed.

  As the resin constituting the film, it is preferable to use a water-based urethane resin or a water-based acrylic resin containing rosin. The concentration of these aqueous resins is preferably in the range of 100 to 900 g / L. The rosin contained in the water-based acrylic resin is a water-soluble one obtained by neutralizing the carboxylic acid group in the abietic acid molecule, which is the main component of the rosin, with an amine salt to obtain a rosin soap, especially after aging. To improve solder wettability. It is preferable to add in the range of 50-600 g / L in an aqueous acrylic resin liquid. If it is less than 50 g / L, solder wettability after aging is insufficient, and if it exceeds 600 g / L, the viscosity becomes high and gelation tends to be difficult.

  Both organic and inorganic pigments can be applied, and one or more pigments of achromatic colors such as black and white, red, blue and yellow can be added to develop the desired color. Let When importance is attached to thermal radiation, it is preferable to use a black pigment. The amount added to the resin is preferably 1 to 50% by weight based on the solid content of the resin. When the content is less than 1% by weight, the color tone is not clear depending on the color, and when it exceeds 50% by weight, the solderability is poor. A more preferable addition amount is 3 to 30% by weight. Further, a colored ceramic powder may be used instead of the pigment. As the colored ceramic powder, it is preferable to use titanium carbide, titanium nitride, titanium boride, tungsten carbide, molybdenum nitride, and a mixed powder obtained by mixing two or more of these ceramic powders.

The aqueous urethane resin containing the above colored pigment or the aqueous acrylic resin containing rosin further contains silica and a rust inhibitor to improve the corrosion resistance of the plated steel sheet, and further contains an antioxidant and the like. As a result, solder wettability can be improved. Silica is preferably added with 10 to 400 g / L of water-dispersible silica in the resin liquid having the above concentration. If it is less than 10 g / L, there is no effect in improving the corrosion resistance, and if it exceeds 400 g / L, solder wettability is remarkably lowered, and thermal conductivity becomes poor. When importance is attached to solder wettability, the silicon amount adhering to the plated steel sheet is preferably in the range of 10 to 400 mg / m ² . As the water-dispersible silica, a silica surface coated with aluminum has a dispersing action and is particularly preferable. The particle diameter of silica is 100 nm or less, preferably 60 nm or less from the viewpoint of dispersibility.

  As the rust preventive agent, an organic amine soap used alone or in combination is used. Organic amine soaps include dodecylamine, oleoyl imidazoline, aminopropyl tallow amine, rosin amine and the like, and the amine can be used after salt formation with carboxylic acid or the like. The styrene / maleic anhydride copolymer is preferably a maleic anhydride copolymerized alkyl ester / ammonium salt. The amount added to the resin solution having the above-mentioned concentration is preferably 10 to 100 g / L. If it is less than 10 g / L, the effect of improving the corrosion resistance is not recognized, and if it exceeds 100 g / L, the solderability is lowered and the thermal conductivity is poor.

  Solder wettability is improved by adding an antioxidant to the water-based urethane resin containing the color pigment as described above, and further containing the silica and rust preventive agent or the water-based acrylic resin further containing rosin. Can be made. Antioxidants include sulfur-based antioxidants, but phenol-based antioxidants or phosphate-based antioxidants are preferred, and both may be used in combination. The amount to be added is preferably 0.5 to 100 g / L.

  On the other hand, in applications that do not place great importance on corrosion resistance and in particular those that do not require good solder wettability, and in applications that place particular importance on thermal conductivity, silica, rust preventives, antioxidants are not included, and only pigments are included. It is preferable to use an aqueous urethane resin or an aqueous acrylic resin containing a pigment and rosin.

  One of the resin liquids obtained as described above is applied to one side or both sides of the plated steel sheet. In this case, the coating film thickness may be changed on the front and back surfaces. As a coating method, a known method such as a dipping method, a roll coating method, a curtain flow coating method, or a spray coating method can be used. However, when performing double-sided coating, taking advantage of the fact that this treatment liquid is water-based, a method of performing coating by dipping and drawing in the subsequent step of the continuous plating step is easy and economical. After applying using any one of these application methods, it is dried to form a colored surface-treated film on the plated steel sheet to obtain a colored surface-treated steel sheet. The film thickness after drying is preferably 0.05 to 10 μm. This is because if the thickness of the film is less than 0.05 μm, sufficient solder wettability cannot be obtained. In addition, fingerprints are easily attached when touched with fingers. When it exceeds 10 μm, the effect of improving these characteristics is saturated and the cost merit is lost.

  The colored surface-treated steel sheet of the present invention thus obtained preferably has a solder wettability by the meniscograph method (MIL-STD-883B) shown below of less than 10 seconds, more preferably less than 5 seconds. . This is because when the solder wettability by the meniscograph method exceeds 10 seconds, the solder melted by heating does not sufficiently spread on the surface of the colored surface-treated steel sheet, and sufficient adhesive strength with the mating material to be soldered cannot be obtained. The measurement of solder wettability by the meniscograph method is performed as follows. That is, using a SOLDERCHECKER (MODEL SAT-5000, manufactured by RHESCA), a solder bath (JIS Z 3282: H60A) in which a 7 mm wide sample cut out from the above-described colored surface-treated steel sheet was immersed in a flux and then maintained at 250 ° C. The sample coated with the above flux was dipped at a dipping rate of 2 mm / sec for 2 mm, the time until the solder gets wet was measured, and the zero cross time was measured to obtain solder wettability (seconds).

  Moreover, a thermal emissivity improves to 0.1-0.9 by forming a colored surface treatment film on a plated steel plate to make a colored surface-treated steel plate.

  Hereinafter, the present invention will be described specifically by way of examples.

  Steel plates (thickness 0.5 mm) subjected to annealing and temper rolling were subjected to electrolytic degreasing in an alkaline aqueous solution, then immersed in sulfuric acid and pickled, and then the metals or alloys shown in Table 1 were used. It plated with the plating amount shown in Table 1 using the plating method shown in Table 1, and the plated steel plate shown by plating number AI was created.

  These plated metal plates of A to I are colored with water-soluble rosin, water-dispersible silica, rust preventive, and yellow, black, or red based on the content shown in Table 2 in the water-based resin shown in Table 2. A resin liquid containing a pigment or titanium carbide was applied using a dipping / drawing method, and then dried at a temperature of 90 ° C., samples Nos. 1 to 20 were prepared, and the following characteristic evaluation was performed. Table 4 shows the evaluation results.

[Characteristic evaluation]
<Solder wettability>
Using SOLDERCHECKER (MODEL SAT-5000, manufactured by RHESCA), evaluation was carried out by the meniscograph method (MIL-STD-883B). That is, a specimen having a width of 7 mm was cut out from the samples of sample numbers 1 to 20, and immersed in a weakly active flux not containing chlorine as shown in Table 4 (Rapics RMA, manufactured by Nippon Solder Industries, Ltd.) Specimens coated with the above flux in a held solder bath (JIS Z 3282: H60A) are immersed 2 mm at an immersion speed of 2 mm / second, the time until the solder gets wet is measured, and the zero cross time is measured. Sex was evaluated. A shorter wetting time indicates better solderability. Note that the test was performed in two ways, immediately after sample preparation and at a constant temperature and humidity (60 ° C., 95% RH) for 500 hours. Moreover, it was set as the acceptable range except x.
◎: Less than 5 seconds ○: Less than 5-7 seconds △: Less than 7-10 seconds ×: More than 10 seconds

<Solder strength>
Two specimens cut out from the samples of sample numbers 1 to 20 with a width of 7 mm and a length of 50 mm and bent into an L-shape are stacked so that the evaluation surfaces face each other in a T-shape. A test piece was prepared in which a 0.5 mm thick steel plate was sandwiched between the portions, and a 0.5 mm gap was formed below the T-shaped vertical bar. After applying the same flux as that used for the evaluation of the solder wettability to the void portion of this specimen, a solder bath (JIS-RH, manufactured by RHESCA) was used and a solder bath (JIS) held at 250 ° C. In Z 3282: H60A), the void portion of the specimen was immersed to a depth of 10 mm and held for 5 seconds to fill the void portion with solder, and then taken out to obtain a T peel test piece. Next, using Tensilon, the T-shaped horizontal bar part of the T-peel test piece is sandwiched and pulled, the solder filling part of the T-shaped vertical bar part is peeled off, and the solder strength is measured. The strength was evaluated.
◎: 4 kgf / 7 mm or more ○: 3-4 kgf / 7 mm or less △: 1-3 kgf / 7 mm or less X: 1 kgf / 7 mm or less

<Thermal emissivity>
A 100 mm × 100 mm square specimen was cut out from the samples of sample numbers 1 to 20, and the thermal emissivity was measured using an emissivity meter (Dand SAERD emissivity meter, manufactured by Kyoto Electronics Industry Co., Ltd.). It was evaluated with.
A: Thermal emissivity 0.5 to 0.9
○: Thermal emissivity 0.1 to less than 0.5 Δ: Thermal emissivity 0.05 to less than 0.1 ×: Thermal emissivity less than 0.05

<Thermal conductivity>
A specimen having a width of 5 mm and a length of 10 mm was cut out from the samples of sample numbers 1 to 20, and the thermal conductivity was measured using an optical AC thermal constant measuring device (PIT-R2 type, manufactured by ULVAC-RIKO Co., Ltd.). Evaluated by criteria.
○: Thermal conductivity of 40 W / m · K or more Δ: Thermal conductivity of 30 W / m · K or more and less than 40 W / m · K ×: Thermal conductivity of less than 30 W / m · K

<Color clarity>
Using the spectrocolorimeter (MODEL: CM-3500d, manufactured by Minolta Co., Ltd.), the L value, the a value, and the b value are measured for the samples of sample numbers 1 to 20, and the measured values are shown in Table 3. Those within the range of the values are indicated by ○ as acceptance criteria. A value that deviated from the acceptance criteria was shown as x for failure.

  As shown in Table 4, the colored surface-treated steel sheet of the present invention has excellent solder wettability, high solder strength, and high heat emissivity and thermal conductivity, and excellent heat dissipation. Moreover, it is excellent also in color clarity as a colored steel plate. Therefore, the colored surface-treated steel sheet of the present invention can be suitably applied as a heat sink having excellent heat dissipation that can be soldered.

  The colored surface-treated steel sheet of the present invention has excellent solder wettability, high solder strength, and high heat emissivity and thermal conductivity and excellent heat dissipation, so it can be suitably used as a heat sink for high-density printed circuit boards and the like. Not only is it possible, but it is also excellent in color clarity, so it can be suitably applied to electronic equipment housings that require solderability and heat dissipation.

Schematic which shows the joining state of a heat sink and a heat generating body.

Explanation of symbols

1 Heating element 2 Heat sink 3 Direction of heat conduction 4 Direction of heat dissipation

Claims (13)

  A colored surface-treated steel sheet, wherein a colored surface-treated film having a solder wettability of less than 10 seconds is formed on a plated steel sheet and has a thermal emissivity of 0.1 to 0.9.   The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a zinc layer on the steel sheet.   The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a tin layer on the steel sheet.   The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a zinc-tin alloy layer on the steel sheet.   2. The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a two-layer plating layer of a tin layer and a zinc layer in order from the steel sheet side on the steel sheet.   2. The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a two-layer plating layer of a zinc layer and a tin layer in order from the steel sheet side on the steel sheet.   The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a copper layer on the steel sheet.   The colored surface-treated steel sheet according to claim 1, wherein the plated steel sheet is formed by forming a nickel layer on the steel sheet.   The colored surface-treated film is a film formed by applying and drying a water-based urethane resin containing a color pigment, silica, and a rust preventive agent, according to any one of claims 1 to 8. Colored surface-treated steel sheet.   The colored surface treatment film is a film formed by applying and drying a water-based acrylic resin containing a color pigment, silica, a rust inhibitor, and rosin, according to any one of claims 1 to 8. The colored surface-treated steel sheet as described.   The colored surface-treated steel sheet according to claim 9 or 10, wherein the colored pigment is a black pigment.   A heat sink comprising the colored surface-treated steel sheet according to any one of claims 1 to 11.   The heat sink according to claim 12, wherein the heat conductivity is 40 W / m · K or more.