JP2008223147A - SURFACE-TREATED Al SHEET HAVING EXCELLENT SOLDERABILITY AND METHOD FOR PRODUCING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated Al sheet excellent in adhesiveness of a plating film, solder wettability, solder strength, and heat radiating characteristics, and suitably applicable to a heat sink, and to provide a method for inexpensively producing the surface-treated Al sheet. <P>SOLUTION: A Zn layer is formed on an Al substrate surface by displacement plating, and a Ni layer and a Sn layer are formed thereon by plating in such a manner that the Zn layer has a film amount of 5 to 500 mg/m<SP>2</SP>after the Ni plating, the Ni layer has a film amount of 0.2 to 50 g/m<SP>2</SP>, and the Sn layer has a film amount of 0.2 to 20 g/m<SP>2</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface-treated Al plate and a manufacturing method thereof, and in particular, to a heat sink that has excellent solder wettability and solder strength and has high thermal conductivity and thermal emissivity, and can be soldered and has excellent heat dissipation. The present invention relates to a suitably applicable surface-treated Al plate and a method for producing the same.

  As electronic devices are miniaturized and densified, it is necessary to suppress the temperature rise of components loaded in a narrow housing or with almost no gap. 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 heating element 1 such as a printed board. The larger the close contact area, the greater the heat conduction. 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. Moreover, as shown in FIG. 1, since the heat sink 2 is provided extending to a portion away from the heating element 1 and radiates heat from the extended portion, the surface of the heat sink is preferably excellent in thermal radiation. In FIG. 1, arrow 3 indicates the direction of heat conduction, and arrow 4 indicates the direction of heat radiation.

  In the case of a heat sink made of a steel plate-based material, it can be soldered and bonded directly to the printed circuit board. If heat dissipation is further required, it is preferable to use a material based on Al that has better thermal conductivity than the steel plate as the heat sink, but it is difficult to solder and bond directly to the printed circuit board. A dedicated pin is attached to an Al-based heat sink and soldered to the printed circuit board through the pin. When joining through such pins, the pin and the heat sink cannot be firmly attached, and the area where the heat sink and the printed circuit board are in direct contact with each other decreases, resulting in a decrease in thermal conductivity and high thermal conductivity. The characteristics of Al having the above are not fully utilized. Therefore, the following attempts have been made to obtain an Al plate having good solderability.

For example, an Al-based alloy metal plate excellent in solderability and plating adhesion, in which an Sn plating layer is formed on an Al plate or an Al-based alloy metal material via a Ni-based plating layer, is disclosed (for example, Patent Document 1). reference). In this Al-based alloy metal plate, Ni plating is performed on a base material such as a hot-dip Al-plated steel plate using a vacuum deposition method, followed by Sn plating. In this method, a vacuum deposition method is used for plating Ni and Sn. However, a large-scale apparatus such as a vacuum apparatus is necessary, and the film forming speed is low and the productivity is low. Have difficulty.
Further, tin excellent in solderability, characterized in that a tin or tin alloy layer is coated on an aluminum base material by forming a tin concentration gradient layer at the interface between the aluminum base material and the tin or tin alloy layer. Or the aluminum material which coat | covered the tin alloy layer is disclosed (for example, refer patent document 2). In this aluminum material, a tin concentration gradient is formed at the interface between the aluminum base and the tin or tin alloy layer by heating after electroplating tin on the aluminum alloy plate or by passing the aluminum alloy plate through a molten tin alloy. The layer is formed and tin-plated, but the adhesion between the aluminum substrate and the tin-plated layer is insufficient, and the tin-plated film tends to peel off from the aluminum substrate, especially when bent. is doing.

JP 05-345969 A JP 09-291394 A

  The present invention is a surface treatment that can be suitably applied to a heat sink that has excellent adhesion to a plating layer, wettability of solder, solder strength, thermal conductivity and thermal emissivity, and can be soldered and has excellent heat dissipation. An object is to provide an Al plate and a method for producing the surface-treated Al plate at a low cost.

In the surface-treated Al plate of the present invention that achieves the above object, a Zn layer, a Ni layer, and a Sn layer are formed on the Al substrate surface in this order from the substrate surface side. coating amount of to 500 mg / ^{m 2,} in which Ni layer coating weight of 0.2~50g / ^{m 2,} Sn layer is characterized by being provided with a film of 0.2 to 20 g / ^{m 2} is there. The Al substrate is not limited to a pure Al plate but may be an Al alloy plate. The surface-treated Al plate preferably has a thermal emissivity of 0.05 or more.

Furthermore, the manufacturing method of the surface-treated Al plate of the present invention is manufactured by displacement plating Zn on an Al substrate, then Ni plating, and then Sn plating, and the Zn layer is 5 to 500 mg in the state after the Ni plating. coating amount of / ^{m 2,} in which Ni layer coating weight of 0.2~50g / ^{m 2,} Sn layer is characterized by being provided with a film of 0.2 to 20 g / ^{m 2.}

In the surface-treated Al plate of the present invention, a Zn layer is formed on a surface of an Al substrate by displacement plating, and a Ni layer and a Sn layer are formed thereon by plating. coating amount of 500 mg / ^{m 2,} by the Ni layer coating weight of 0.2 to 50 g / ^{m 2,} the Sn layer is provided with a film of 0.2 to 20 g / ^{m 2,} and Al substrate A surface-treated Al plate having excellent adhesion of the plating layer is obtained. In particular, since the Sn layer is provided on the outermost surface, the solder wettability is excellent and a high solder strength is obtained. Furthermore, since the substrate is an Al plate, the thermal conductivity is large and the heat dissipation is excellent. Therefore, the surface-treated Al plate of the present invention can be suitably applied as a heat sink excellent in heat dissipation that can be soldered.

Hereinafter, the present invention will be described in detail.
As the Al plate used as the substrate of the surface-treated Al plate of the present invention, a pure Al plate and any of JIS standard 1000 series, 2000 series, 3000 series, 5000 series, 6000 series, and 7000 series Al alloy sheets may be used. it can. These Al alloy plates are degreased, then acid-etched, and after removing the smut, Zn is displacement plated. The substitution plating of Zn is performed through the steps of nitric acid immersion treatment, first Zn substitution treatment, zinc nitrate stripping treatment, and second Zn substitution treatment. In this case, the water washing process is implemented after the process of each process. Since the Zn layer formed by the first Zn substitution treatment and the second Zn substitution treatment is slightly dissolved when Ni plating is performed after this substitution treatment, the coating amount of the Zn layer is 5 to 5 in the state after Ni plating. it is preferably 500 mg / ^{m 2,} and more preferably 30 to 300 mg / ^{m 2.}
The coating amount is adjusted by appropriately selecting the concentration of Zn ions in the treatment liquid and the time of immersion in the treatment liquid in the second Zn substitution treatment. When the coating amount is less than 5 mg / m ² , the adhesion with the Ni plating layer formed on the Zn layer becomes poor, and the plating layer is easily peeled off when bending is performed. On the other hand, when the coating amount exceeds 500 mg / m ² , the Ni plating becomes non-uniform and the solder strength decreases.

Next, a Ni layer is plated on the Zn layer thus formed. The Ni plating layer may be formed using any plating method of electroplating or electroless plating. When the electroless plating method is used, since the P compound or B compound is used as the reducing agent, the Ni plating film is formed as a film made of Ni—P alloy or Ni—B alloy, but is made of pure nickel by electroplating. Similar to the coating, excellent adhesion of the plating coating to the Al substrate, and excellent solder wettability and solder strength can be obtained. Thus Ni layer obtained is preferably 0.2 to 50 g / ^{m 2} as a film weight, and more preferably 1 to 10 g / ^{m 2.} If the coating amount is less than 0.2 g / m ² , the Ni layer cannot uniformly cover the entire surface of the Zn layer, and thus sufficient solder strength cannot be obtained. On the other hand, if the coating amount exceeds 50 g / m ² , the effect of improving the solder wettability and the solder strength is saturated, which is not advantageous in terms of cost.

Next, a Sn layer is plated on the Ni layer. The Sn plating layer may be formed using any plating method of electroplating or electroless plating. The Sn layer is preferably 0.2 to ²⁰ g / m ² and more preferably 1 to 10 g / m ² as a coating amount. When the coating amount is less than 0.2 g / m ² , solder becomes difficult to wet when an inactive flux is used. On the other hand, even if the coating amount exceeds 20 g / m ² , the effect of improving the solder wettability and the solder strength is saturated, which is not advantageous in terms of cost. Thus, the surface-treated Al plate of the present invention can be obtained by forming the Zn layer, Ni layer, and Sn layer on the Al plate. In addition, the outermost Sn layer of this surface-treated Al plate is heated to the extent that free Sn remains without being lost by alloying with the underlying Ni layer or Al substrate, and the Al substrate, Zn layer, Zn layer, The adhesion strength between the Al substrate, the plating layer, and each plating layer is improved by diffusing the Ni layer, the Ni layer and the Sn layer, or the Al substrate, the Zn layer, the Ni layer, and the Zn layer, the Ni layer, and the Sn layer. You can also.

  The surface-treated Al plate of the present invention has a thermal conductivity of 60 W / m · K or more, and can suitably absorb heat from a heating element as a heat sink having excellent thermal conductivity to dissipate heat. By providing a layer for improving thermal radiation on the Sn layer, it is possible to further improve heat dissipation. Although the thermal emissivity of the surface-treated Al plate of the present invention is around 0.05 to 0.1, the thermal emissivity is improved to about 0.2 to 0.9 by providing a layer that improves the thermal emissivity. be able to. The layer for improving thermal radiation is formed on the Sn layer as follows. That is, a surface-treated Al plate in which a Zn layer, a Ni layer, and a Sn layer are sequentially formed, or a water-based acrylic resin containing a black pigment and a water-soluble rosin after the above heat-treated diffusion treatment is performed on the surface-treated Al plate. Is applied and dried to obtain a treated film. This treated film has a flux effect and improves solder wettability. The concentration of these aqueous resins is preferably 100 to 900 g / L, and the black pigment is preferably contained in the resin at 50% by weight or less based on the solid content of the resin. If the content exceeds 50% by weight, solder wettability and solder strength become poor. The thickness of the treated film after drying is preferably 0.05 to 10 μm. If it is less than 0.05 μm, the effect of improving heat dissipation is poor, and if it exceeds 10 μm, the thermal conductivity is impaired, making it impossible to improve the heat dissipation. Thus, by providing the layer which improves a thermal radiation property on Sn layer, the heat dissipation of a heat sink can be improved.

(Create test plate)
An Al alloy plate (JIS 5052H19, plate thickness 0.5 mm) was used as a plating substrate, degreased with an alkaline solution, then etched in sulfuric acid, then desmutted in nitric acid, and then sodium hydroxide: 150 g / L, Rochelle salt: 50 g / L, zinc oxide: 25 g / L, immersed in a treatment solution containing 1.5 g / L of ferrous chloride to perform a first Zn substitution treatment, and then a 400 g / L aqueous nitric acid solution After removing the Zn deposited by immersion by immersion, the second Zn substitution treatment was performed by immersing in the same treatment liquid used in the first Zn substitution treatment. In the second Zn substitution treatment, the immersion time was variously changed to obtain a Zn-plated Al plate on which a Zn layer having a coating amount shown in Table 1 was formed.

  Next, a Ni-12 wt% P alloy plating film was formed on the Zn layer with an amount of film shown in Table 1 by electroless plating on a Zn-plated Al plate. Next, an Sn plating film was formed on the Ni layer by the electroplating method on the plated Al plate on which the Zn layer and the Ni layer were formed, and used as a test plate. Some test plates were heated to 280 ° C. after these platings were performed, the Sn layer was melted, and the Al substrate, the plating layer, and the plating layers were bonded to such an extent that free Sn on the outermost surface was not lost. Diffusion heat treatment for diffusion was performed. Moreover, about the other one part test plate, the layer which improves thermal radiation was formed using the process liquid of the liquid composition shown in Table 2.

  For comparison, a test plate in which a Ni plating layer and a Sn plating layer were directly provided without providing a Zn substitution plating layer on the Al alloy plate, and a Sn substitution plating layer not provided on the Al alloy plate. A test plate provided only with a plating layer and a test plate provided with only a Sn plating layer on a low carbon steel plate (plate thickness 0.5 mm) were prepared.

(Characteristic evaluation of test plate)
The test plates obtained as described above were evaluated for the following characteristics.
[Solder wettability]
Using a SOLDERCHECKER (MODEL SAT-5000, manufactured by RHESCA) by a meniscograph method (MIL-STD-883B), a specimen having a width of 7 mm cut out from each of the above test materials is a flux (NA-200, manufactured by Tamura Kaken) The sample coated with the above flux was immersed in a solder bath (JISZ 3282: H60A) held at 250 ° C. and immersed for 2 mm at a dipping rate of 2 mm / second, and the time until the solder wetted was measured. The solder wettability was evaluated according to the following criteria. The shorter the time, the better the solder wettability.
◎: Less than 5 seconds ○: Less than 5-7 seconds △: Less than 7-10 ×: More than 10 seconds

[Solder strength]
Two cut pieces obtained by bending a specimen having a width of 7 mm and a length of 50 mm cut out from each of the above-mentioned specimens into an L-shape are stacked so that the evaluation surfaces face each other in a T-shape, A steel sheet having a thickness of 0.5 mm was sandwiched between the bar portions, and a test piece was formed in which a 0.5 mm gap was formed at the bottom of 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 the specimen, a solder bath (JISZ 3282) maintained at 250 ° C. using a solder checker (SAT-5000, manufactured by Resca). : H60A), the void portion of the specimen was immersed to a depth of 10 mm, held for 5 seconds, filled with solder in the void portion, and then taken out to obtain a T peel specimen. Next, using Tensilon, the T-shaped horizontal bar part of the T-peel specimen is sandwiched and pulled, the solder filling part of the T-shaped vertical bar part is peeled off, the solder strength is measured, and the solder strength is measured according to the criteria shown below. 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

[Adhesion of plating film]
A specimen having a width of 15 mm and a length of 50 mm was cut out from each of the above-mentioned specimens, bent 90 °, affixed a scotch tape to the bent portion, and then peeled off, and then visually observed for the presence or absence of peeling of the plating film. The adhesion of the plating film was evaluated based on the above criteria.
○: No peeling is observed.
X: Peeling is recognized.

[Heat dissipation]
A specimen having a width of 5 mm and a length of 10 mm was cut out from each of the above test materials, and the thermal conductivity was measured using an optical alternating current method thermal constant measuring apparatus (PIT-R2 type, manufactured by Vacuum Riko). In addition, the thermal emissivity was measured using an emissometer (Dand S AERD emissometer, manufactured by Kyoto Electronics Industry Co., Ltd.), and the heat dissipation was evaluated according to the following criteria.
A: Thermal conductivity 60 W / m · K or more and thermal emissivity 0.20 or more ○: Thermal conductivity 60 W / m · K or more and thermal emissivity 0.05 to less than 0.20 Δ: Thermal conductivity 40 ˜less than 60 W / m · K ×: thermal conductivity less than 40 W / m · K

 As a result, as shown in Table 3, the surface-treated Al plate of the present invention in which a Zn layer, Ni layer, and Sn layer are formed on an Al plate has excellent solder wettability, high solder strength, and high thermal conductivity. Large heat dissipation. Further, it was confirmed that the heat dissipation was further improved by providing a layer for improving the thermal radiation on the Sn layer of the surface-treated Al plate. Therefore, the present invention can be suitably applied as a heat sink excellent in heat dissipation that can be soldered.

  The surface-treated Al plate of the present invention has excellent solder wettability, high solder strength, and since the substrate is an Al plate, it has high thermal conductivity and excellent heat resistance, so soldering is possible It can be applied to various uses as an Al plate excellent in heat dissipation, and can be suitably used as a heat sink excellent in heat dissipation capable of being soldered.

It is the schematic which shows the example of the joining state of a heat sink and a heat generating body.

Explanation of symbols

1 Heating element 2 Heat sink

Claims (3)

A Zn layer, a Ni layer, and a Sn layer are formed on the surface of the Al substrate in this order from the substrate surface side. The Zn layer has a coating amount of 5 to 500 mg / m ^{2 in} the state after the Ni layer is formed, and the Ni layer is 0. coating amount of 2 to 50 g / ^{m 2,} the surface treatment Al plate Sn layer, characterized in that the thus provided with a film of 0.2 to 20 g / ^{m 2.}   The surface-treated Al plate according to claim 1, wherein the thermal emissivity is 0.05 or more. It is manufactured by displacement-plating Zn on an Al substrate, then Ni plating, and then Sn plating. The Zn layer has a coating amount of 5 to 500 mg / m ^{2 in} the state after the Ni plating, and the Ni layer is 0.2 to coating amount of 50 g / ^{m 2,} a method for producing a surface-treated Al plate Sn layer, characterized in that the thus provided with a film of 0.2 to 20 g / ^{m 2.}

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