JP2005060809A - SURFACE-TREATED Al SHEET EXCELLENT IN SOLDERABILITY, ITS PRODUCTION METHOD AND HEAT SINK USING THE SAME - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated Al sheet which is solderable, is excellent in adhesivity to a plated layer, solder wettability, soldering strength and heat-radiation property and can be suitably applied to a heat sink, the heat sink using the same, and a method for inexpensively producing the surface-treated Al sheet. <P>SOLUTION: On the surface of an Al substrate, an Zn layer is formed through displacement plating, and an Ni layer is subsequently formed through plating. A layer which has a flux sticking property and improves heat-radiation property may be further formed on the heat-treated Al sheet. The layer which improves the heat-radiation property is formed by applying and drying an aqueous resin containing a black pigment and a water-soluble rosin on the surface-treated Al sheet. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  As electronic devices become smaller and higher in density, 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. Further, as shown in FIG. 1, when the heat sink 2 is provided so as to extend away from the heating element 1, heat is radiated from the extended portion, and therefore the surface of the heat sink is excellent in heat 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 joined by soldering 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 bonding via such pins, the pin and the heat sink cannot be firmly adhered, and the area where the heat sink and the printed circuit board are directly adhered 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 molten Al-plated steel plate using a vacuum deposition method, and then Sn plating is performed. 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 since the film forming speed is small and the productivity is poor, it can be manufactured at low cost. 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. Although the layer is formed and tin-plated, 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 subjected to bending. 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, and high thermal conductivity and thermal emissivity, and can be soldered and has excellent heat dissipation. An object is to provide an Al plate, a heat sink using the same, and a method for producing the surface-treated Al plate at a low cost.

The surface-treated Al plate of the present invention that achieves the above object is a surface-treated Al plate characterized in that a Zn layer and a Ni layer are formed on an Al substrate surface in this order from the substrate surface side. The Al substrate is not limited to a pure Al plate but may be an Al alloy plate. In the surface-treated Al plate, it is preferable that the Zn layer is provided with a coating amount of 5 to 500 mg / m ² , and that a layer for further improving thermal radiation is formed on the Ni layer.

In addition, the heat sink of the present invention that achieves the above object is the above-described surface-treated Al plate in which a Zn layer and an Ni layer are formed in this order on the surface of the Al substrate, or a Zn layer in the surface-treated Al plate Is a heat sink characterized by using a surface-treated Al plate provided with a coating amount of 5 to 500 mg / m ² , and preferably has a thermal conductivity of 60 W / m · K or more.
Alternatively, another heat sink of the present invention has a surface on which a layer for improving thermal radiation is further formed on a Ni layer of a surface-treated Al plate in which a Zn layer and a Ni layer are formed in this order from the substrate surface side. A heat sink characterized by using a treated Al plate, and preferably has a thermal emissivity of 0.2 to 0.9.

The method for producing a surface-treated Al plate of the present invention is a method for producing a surface-treated Al plate, characterized in that Zn plating is performed on an Al substrate, and then Ni plating is performed.
After Ni plating, it is desirable to form a layer that further improves thermal radiation. The layer for improving thermal radiation can be formed, for example, by applying a water-based resin containing a black pigment and a water-soluble rosin to the surface-treated Al plate and drying it.

  The surface-treated Al plate of the present invention is excellent in the adhesion between the Al substrate and the plating layer because the Zn layer is formed on the Al substrate surface by displacement plating and the Ni layer is formed thereon by plating. In addition, since the Ni layer is provided on the outermost surface, the solder wettability is excellent and high solder strength is obtained. Furthermore, since the substrate is an Al plate, the thermal conductivity is large and the heat dissipation is excellent. Furthermore, by providing the surface-treated Al plate of the present invention with a layer having solder flux properties and improving heat radiation properties, it is possible to further improve solderability and heat dissipation. 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.

  This surface-treated Al plate of the present invention has a thermal conductivity of 60 W / m · K or more, and as a heat sink excellent in thermal conductivity, it can absorb heat from a heating element and dissipate heat. By providing a layer that improves thermal radiation on the Ni 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 Ni layer as follows. That is, a surface-treated Al plate in which a Zn layer and a Ni layer are sequentially formed, or the surface-treated Al plate is subjected to the above heat diffusion treatment, and then an aqueous acrylic resin containing a black pigment and a water-soluble rosin is applied. , Dried to form 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 it exceeds 50% by weight, solder wettability and solder strength will be 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 the 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 thermal radiation on Ni 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. 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 (Sample No. 1) in which a Ni plating layer was directly provided without providing a Zn substitution plating layer on the Al alloy plate, and a Zn substitution plating layer was provided on the Al alloy plate. A test plate (sample number 13) in which only 5 g / m ² of an Sn plating layer was provided on a test plate (sample number 3) without a Ni plating layer and a low carbon steel plate (plate thickness 0.5 mm) was 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 immersed in a flux (CF110VH2A, manufactured by Tamura Kaken). After that, a specimen coated with the above-mentioned flux was immersed in a solder bath (JISZ 3282: H60A) maintained at 250 ° C. at a dipping rate of 2 mm / second for 2 mm, and the time until the solder gets wet was measured. The solder wettability was evaluated according to the criteria shown in FIG. 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 of the specimen, a solder bath (JISZ 3282) maintained at 250 ° C. using a solder checker (SAT-5000, manufactured by Resuka). : 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 test piece is sandwiched and pulled to peel off the solder filling part of the T-shaped vertical bar part, and the solder strength is measured. 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 test materials, bent at 90 °, a scotch tape was attached to the bent portion, and then peeled off. 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 and a Ni layer are formed on an Al plate has excellent solder wettability, high solder strength, high thermal conductivity, and high heat dissipation. Is excellent. Moreover, it was confirmed that the heat dissipation was further improved by providing a layer for improving thermal radiation on the Ni 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.

    Since the surface-treated Al plate of the present invention is excellent in solder characteristics and heat dissipation, it can be used not only as a heat sink for heat dissipation of high-density printed circuit boards, but also in various solderability and heat dissipation requirements. It can be used for a substrate.

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 (10)

  A surface-treated Al plate, wherein a Zn layer and a Ni layer are formed on an Al substrate surface in this order from the substrate surface side. The surface-treated Al plate according to claim 1, wherein the Zn layer is provided with a coating amount of 5 to 500 mg / m ² .   The surface-treated Al plate according to claim 1, wherein a layer that further improves thermal radiation is formed on the Ni layer.   A heat sink using the surface-treated Al plate according to claim 1.   The heat sink of Claim 4 whose heat conductivity is 60 W / m * K or more.   A heat sink using the surface-treated Al plate according to claim 3.   The heat sink of Claim 6 whose thermal emissivity is 0.2-0.9.   A method for producing a surface-treated Al plate, comprising subjecting an Al substrate to substitution plating with Zn and then plating with Ni.   The method for producing a surface-treated Al plate according to claim 8, wherein a layer for further improving thermal radiation is formed after the Ni plating.   The layer for improving the thermal radiation is formed by applying an aqueous resin containing a black pigment and a water-soluble rosin to a surface-treated Al plate plated with Zn on an Al substrate and then plated with Ni, followed by drying. The manufacturing method of the surface treatment Al plate of Claim 9.

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