JP2006110769A - Surface-treated al plate excellent in solderability, heat sink using it and manufacturing method of surface-treated al plate excellent in solderability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated Al plate excellent in the adhesion with a plating layer, the wettability with solder and solder strength, large in heat emissivity or heat conductivity and efficiently adaptable to a heat sink required in solderability and heat emissivity, the heat sink using it, and a manufacturing method of the surface-treated Al plate. <P>SOLUTION: The surface-treated Al plate is constituted by forming a Zn layer on the surface of an Al substrate by substitution plating, forming an Ni layer and a Cu layer on the Zn layer by plating and further providing a layer for enhancing heat conductivity on the Cu layer. This surface-treated Al plate is adapted to the heat sink 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a surface-treated Al plate, and particularly suitable for a heat sink that is excellent in solder wettability and solder strength, has high thermal emissivity and thermal conductivity, can be soldered, and requires excellent heat dissipation. The present invention relates to a surface-treated Al plate that can be used, 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 the printed circuit board, a heat sink 2 for heat dissipation is in close contact with at least one surface of the heating element 1 as shown in FIG. 1 and solder 5 is used on the metal surface 10a of the printed circuit board 10 in order to suppress the temperature rise of the components. Are joined by soldering. The larger the close contact surface, the greater the heat conduction and the higher the heat dissipation effect. 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. In addition, 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 base material, it can be soldered and bonded directly to the printed circuit board as shown in FIG. 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. Conventionally, a special solderable pin is attached by caulking to an Al-based heat sink, and soldered to the printed circuit board via the pin. However, when the pins are joined through the pins as described above, a strong coupling state between the pins and the heat sink cannot be obtained, and the heat sink may come off the pins when an impact such as dropping is applied. Therefore, in order to obtain an Al plate that can be soldered so that a strong bonding state between the printed circuit board and the heat sink can be obtained, the following attempts have been made.

  For example, Patent Document 1 discloses 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. . In this Al-based alloy metal plate, a Ni-based 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, Patent Document 2 discloses that a tin or tin alloy layer is coated on an aluminum base material by forming a tin concentration gradient at the interface between the aluminum base material and the tin or tin alloy layer. An aluminum material coated with a tin or tin alloy layer having excellent properties is disclosed. In this aluminum material, tin is electroplated on the aluminum alloy plate and then heated, or the aluminum alloy plate is passed through a molten tin alloy, whereby the concentration of tin at the interface between the aluminum base and the tin or tin alloy layer is increased. Tin plating with a gradient, but the adhesion between the aluminum substrate and the tin or tin alloy layer is insufficient, especially when bending is applied, the tin plating film tends to peel off from the aluminum substrate have.
JP 05-345969 A JP 09-291394 A

  INDUSTRIAL APPLICATION While this invention is excellent in the adhesiveness of a plating layer, the wettability of solder | pewter, and solder | pewter intensity | strength, thermal emissivity and thermal conductivity are large, it can apply suitably for the heat sink in which soldering is possible and heat dissipation is calculated | required. An object of the present invention is to provide a surface-treated Al plate, a heat sink using the same, and a method for producing the surface-treated Al plate.

In order to solve the above problems, the present inventor conceived of providing a Cu layer having excellent solder wettability on the Ni layer as a means for obtaining excellent solder wettability and high solder strength, As a result of various researches on forming an aluminum plate with excellent heat dissipation with high adhesion by non-vacuum deposition, good adhesion is achieved by forming a Zn plating layer after applying Zn plating. As a result, the inventors have found that the properties can be obtained, and have reached the present invention.
That is, the surface-treated Al plate of the present invention that achieves the above object is characterized in that a Zn layer, a Ni layer, and a Cu layer are formed in this order from the substrate side on the surface of the Al substrate (Claim 1). is there.
Although Al plate is difficult to plate, Zn can be plated with high adhesion to Al plate, and Ni plating on Zn plating is also possible to plate with high adhesion, so Al plate By forming a Zn layer, Ni layer, and Cu layer in order on the surface, it is possible to obtain a surface-treated Al plate that is excellent in plating adhesion, can be soldered, and has excellent heat dissipation.

  In the surface-treated Al plate, in order to further improve heat dissipation, it is desirable that a layer for improving thermal radiation is further formed on the Cu layer (Claim 2). Further, in the surface-treated Al plate, the thermal emissivity is 0.2 to 0.9 (Claim 3), the solder wettability by the meniscograph method is 10 seconds or less (Claim 4), and the thermal conductivity. Is preferably 60 W / m · K or more (Claim 5).

  Moreover, the heat sink of this invention is a heat sink (Claim 6) using the surface treatment Al plate in any one of the said Claims 1-5.

Furthermore, the method for producing a surface-treated Al plate of the present invention is characterized in that Zn is displacement-plated on an Al substrate, then Ni is plated, and then Cu is plated (Claim 7).
Since the Al plate cannot be soldered, in order to make it possible, it is necessary to form a metal layer with good solder wettability on the surface, but in the present invention, the metal layer can be plated with a simpler apparatus. To form. However, although the Al plate is difficult to plate, it can be easily plated by substitution plating of Zn. However, since Zn cannot be soldered over time, by applying Ni plating on the Zn plating and applying Cu plating with excellent solder wettability thereon, it is possible to have excellent plating adhesion and soldering, A surface-treated Al plate having excellent heat dissipation can be obtained.

  In the method for manufacturing a surface-treated Al plate according to the above (Claim 7), Zn substitution plating is performed in two steps of first substitution plating and second substitution plating (Claim 8), so that the Zn layer becomes uniform. , Ni plating applied thereon does not cause poor plating. Further, in the method for producing a surface-treated Al plate according to claim 7 or 8, a surface-treated Al plate having a higher heat dissipation property is formed by further forming a layer for improving thermal radiation after Cu plating (claim 9). Can be obtained. The layer for improving thermal radiation can be provided by applying a water-based resin containing a black pigment on Cu plating and drying it (Claim 10).

  The surface-treated Al plate of the present invention has a Zn layer formed on the surface of the Al substrate by displacement plating, and a Ni layer and a Cu layer are formed thereon by plating, so that the adhesion between the Al plate and the plated layer is excellent. Yes. In addition, since the Cu 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 Al used as the substrate of the surface-treated Al plate of the present invention, a pure Al plate and any JIS standard 1000 series, 2000 series, 3000 series, 5000 series, 6000 series, or 7000 series Al alloy sheet can be used. . These Al alloy plates are degreased and then acid-etched. Subsequently, the smut is removed, and then Zn is replaced by plating. The substitution plating of Zn is carried out after the nitric acid immersion treatment, but it is preferably carried out in two steps of the first Zn substitution plating treatment and the second Zn substitution plating treatment. Good. By performing the Zn displacement plating process twice, the Z layer can be more uniformly formed on the Al plate, and the Ni plating plated on it in the subsequent process does not cause poor plating (adhesion failure). There is an advantage that can be formed. In this case, the water washing process is implemented after the process of each process. The Zn plating layer formed by the first Zn substitution plating treatment and the second Zn substitution plating treatment is slightly dissolved when Ni plating is performed after the substitution plating treatment. It is preferable that it is 5-500 mg / m < ² > in a state, and it is more preferable that it is 30-300 mg / m < ² >. The coating amount is adjusted by appropriately selecting the Zn ion concentration in the treatment liquid and the time of immersion in the treatment liquid in the second Zn displacement plating 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 formed on the Zn layer thus formed by plating. Ni plating may be formed using either electroplating or electroless plating. When the electroless plating method is used, since a P compound or a B compound is used as a reducing agent, the Ni plating film is formed as a film made of a Ni-P alloy or a Ni-B alloy, but is made of pure Ni by electroplating. Similar to the coating, 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 Cu layer is formed on the Ni layer by plating. Cu plating may be formed using either electroplating or electroless plating. The coating amount of Cu plating is preferably 0.2 to ²⁰ g / m ² , and more preferably 1 to 10 g / m ² . 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, when 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.

  By forming the Zn layer, Ni layer, and Cu layer on the Al substrate as described above, the surface-treated Al plate of the present invention can be obtained. Further, this surface-treated Al plate is heated to a temperature not higher than the melting point of Al, and the Al substrate and Zn layer, Zn layer and Ni layer, Ni layer and Cu layer, or Al substrate and Zn layer, Ni layer, Zn layer, By mutually diffusing the Ni layer and the Cu layer, the adhesion strength between the Al substrate, the plating layer, and each plating layer can also be improved.

  The surface-treated Al plate of the present invention thus obtained has a thermal conductivity of 60 W / m · K or more, and efficiently absorbs heat from the heating element as a heat sink with excellent thermal conductivity. Although heat can be dissipated, the heat dissipating property can be further improved by providing a layer for improving heat radiation on the Cu layer. The thermal emissivity of the surface-treated Al plate of the present invention in which a Zn layer, Ni layer, and Cu layer are formed on an Al substrate is around 0.05 to 0.1, but by providing a layer that improves thermal radiation, The thermal emissivity can be improved to about 0.2 to 0.9.

  The layer for improving thermal radiation is formed on the Cu layer as follows. That is, a surface-treated Al plate in which a Zn layer, a Ni layer, or a Cu layer are formed on an Al substrate, or a water-based resin containing a black pigment after the surface-treated Al plate is subjected to the above heat diffusion treatment, preferably A water-based acrylic resin containing water-based urethane resin or water-soluble rosin is applied and dried to form a treatment film. These treatment films have a flux effect and improve 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 are 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, and the heat dissipation cannot be improved. Thus, by providing a layer that improves thermal radiation on the Cu layer, the heat dissipation when used as a heat sink can be improved.

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

  Next, an Ni-12 wt% P alloy plating film was formed on the Zn layer with the coating amount shown in Table 1 by using an electroless plating method on the Zn plating Al plate. Subsequently, a pure Cu plating film was formed on the Ni layer using an electroplating method on an Al plate on which a Zn layer and a Ni layer were formed, and used as a test plate. About some test plates, after performing these plating, it heated at 350 degreeC, and performed the diffusion heat processing which mutually diffuses an Al plate, a plating layer, and each plating layer. Moreover, about the other one part test plate, the layer which improves heat radiation was formed on Cu plating film | membrane using the processing liquid of the liquid composition shown in Table 2.

  For comparison, a test plate in which a Ni plating layer and a Cu plating layer were directly provided without providing a Zn substitution plating layer on the Al alloy plate, and a Cu plate without a Zn substitution plating layer provided on the Al alloy plate. A test plate provided only with a plating layer, and a test plate provided only with a Cu 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 7 mm wide test piece cut out from each of the above test plates was fluxed (NA-200, manufactured by Tamura Kaken) The test piece coated with the above-mentioned flux in a solder bath (JISZ 3282: H60A) maintained at 250 ° C. is immersed for 2 mm at an immersion speed of 2 mm / second, and the time until the solder gets wet (zero cross time) is set. The solder wettability was evaluated based on 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 seconds ×: More than 10 seconds

[Solder strength]
Two cut pieces obtained by bending a test piece having a width of 7 mm and a length of 50 mm cut out from each of the test plates into an L-shape are stacked so that the evaluation surfaces face each other in a T-shape, and the vertical direction of the T-shape. A test piece was prepared in which a 0.5 mm thick steel plate was sandwiched between the bars 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 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 taken out to obtain a T peel specimen. Next, using Tensilon, the portion of the T-shaped horizontal bar of the T-peel test piece is pulled with a chuck, and the solder filling portion of the T-shaped vertical bar is peeled off. The tensile strength at this time is measured as the solder strength. The superiority or inferiority of the solder strength was evaluated according to the following criteria.
◎: 4 fgf / 7 mm or more ○: 3 to less than 4 fgf / 7 mm Δ: less than 1 to 3 fgf / 7 mm ×: less than 1 fgf / 7 mm

[Adhesion of plating film]
A test piece having a width of 15 mm and a length of 50 mm was cut out from each of the above test plates, 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 test piece having a width of 5 mm and a length of 10 mm was cut out from each of the test plates, and the thermal conductivity was measured using an optical alternating current method thermal constant measurement device (PIT-R2 type, manufactured by Vacuum Riko). Moreover, the thermal emissivity was measured using the emissometer (D and SAERD emissometer, Kyoto Electronics Industry make), and the heat dissipation was evaluated on the basis of the following criteria.
A: Thermal conductivity of 60 W / m / K or more and thermal emissivity of 0.20 or more O: Thermal conductivity of 60 W / m / K or more and thermal emissivity of 0.05 to less than 0.20 Δ: Thermal conductivity of 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, a Ni layer, and a Cu layer are formed on an Al plate has excellent solder wettability, high solder strength, and high thermal conductivity. Excellent heat dissipation. It was also confirmed that the heat dissipation was further improved by providing a layer for improving the thermal conductivity on the Cu 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.

  A surface-treated Al plate in which a Zn layer is formed by displacement plating on the Al substrate surface of the present invention, and a Ni layer and a Cu layer are formed thereon by plating, is excellent in adhesion between the Al plate and the plating layer, Since the Cu layer is provided on the outermost surface, the solder wettability is excellent and a high solder strength is obtained. Moreover, since the substrate is an Al plate, the thermal conductivity is large and the heat dissipation is excellent. Furthermore, by providing a layer having solder flux properties and improving heat radiation on the Cu layer, 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 capable of soldering, which can be suitably applied to a heat sink that can be soldered and requires heat dissipation.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Heat generating body 2 Heat sink 3 Direction of heat conduction 4 Direction of heat dissipation 5 Solder 10 Printed circuit board 10a Metal surface

Claims (10)

  A surface-treated Al plate in which a Zn layer, a Ni layer, and a Cu layer are formed in this order from the substrate side on the surface of the Al substrate.   The surface-treated Al plate according to claim 1, wherein a layer for improving thermal radiation is further formed on the Cu layer.   The surface-treated Al plate according to claim 1 or 2, wherein the thermal emissivity is 0.2 to 0.9.   The surface-treated Al plate according to any one of claims 1 to 3, wherein a solder wettability by a meniscograph method is 10 seconds or less.   The surface-treated Al plate according to any one of claims 1 to 4, wherein the thermal conductivity is 60 W / m · K or more.   A heat sink using the surface-treated Al plate according to claim 1.   A method for producing a surface-treated Al plate, comprising subjecting an Al substrate to substitution plating with Zn, then Ni plating, and then Cu plating.   The method for producing a surface-treated Al plate according to claim 7, wherein the Zn substitution plating is performed in two steps of first substitution plating and second substitution plating.   The method for producing a surface-treated Al plate according to claim 7 or 8, further comprising forming a layer for improving thermal radiation after Cu plating.   The method for producing a surface-treated Al plate according to claim 9, wherein the layer for improving thermal radiation is provided by applying a water-based resin containing a black pigment on the Cu plating and drying the layer.

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