Plating solution, plating method and metal material

Abstract

To provide a technique regarding plating that can form a roughened surface having excellent adhesion to a mold resin with a simple process.SOLUTION: A plating treatment method plating a lead frame 10 using a plating solution that contains 200 g / L of copper sulfate pentahydrate, 25 g / L of sulfuric acid, 400 ppm of hydrochloric acid, 13.75 weight % of polyethylene glycollic as an inhibitor, 7.5 weight % of 1,2- ethane disulfonic acid dihydrate as an accelerator, the method plates the lead frame 10 by repeating by a prescribed times the following processes: the first coat destruction treatment that conducts destruction treatment for a coat at a surface of a metallic material 10 by flowing first current for a first time period using the lead frame 10 as an electrode, a first plating processing forming a plating layer by flowing second current for a second time period using the lead frame 10 as an electrode after the first coat destruction treatment, and a first coat forming processing forming a coat layer by keeping the lead frame 10 at zero voltage for a third time period.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for plating the surfaces of metal parts of lead frames or circuit boards, which method increases the adhesive strength between the plated surface and the molding resin, a plating solution used in the plating method, and metal materials plated with the plating. [Background technology]

[0002] In a conventional plating method for lead frames in which a precious metal plating layer is formed on the surface of a base metal via an undercoat plating layer, there has been a plating method in which the undercoat plating layer is formed by a smooth Ni plating layer plated on the base metal using a direct current or pulse current that does not have a polarity reversal component, and a roughened Ni plating layer plated on the smooth Ni plating layer using a current that includes a polarity reversal pulse (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-009334 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the conventional plating method described above has the problem of requiring multiple layers, such as applying a smooth Ni plating with a flat surface to the surface of the base metal, forming a roughened Ni plating layer with a roughened surface, and then forming a precious metal plating layer on that surface, resulting in a complex process. Another problem is that the roughening of the roughened Ni plating layer is insufficient, resulting in insufficient adhesion between the surface and the molding resin.

[0005] The present invention has been made in view of these problems, and aims to provide a plating solution, a plating method, and a metal material plated with the plating solution, which are capable of forming a roughened surface with excellent adhesion to the mold resin through a simple process. [Means for solving the problem]

[0006] The present invention has been made to solve at least some of the above-mentioned problems, and can be realized as the following application examples. Note that the reference symbols and supplementary explanations in this section indicate the correspondence with the embodiments described later to help understand the present invention, and do not limit the present invention in any way.

[0007] [Application example 1] The plating solution described in Application Example 1 contains 200 g / L of copper sulfate pentahydrate and 100 g / L of sulfuric acid. 23.75 The summary is that it contained 40 ppm of hydrochloric acid, 13.75 vol% of inhibitor, and 7.5 vol% of accelerator.

[0008] As will be described later, when a metal material (10) is plated using this plating solution, the surface of the metal material (10) is roughened, and when the metal material (10) is molded with a resin (30), a roughened surface with excellent adhesion to the molded resin (30) can be formed.

[0009] [Application example 2] The plating solution according to Application Example 2 is the plating solution according to Application Example 1, The inhibitor is polyethylene glycol. R It is a call, The accelerator is 1,2-ethanedisulfonic acid dihydrate.

[0010] In this way, the inhibitor is RBy using 1,2-ethanedisulfonic acid dihydrate as the accelerator, large nodular particles 20 are formed in a dense state on the surface of the metal material 10. In other words, the surface of the metal material 10 is further roughened, and when the metal material 10 is molded with a resin 30, a roughened surface with excellent adhesion to the mold resin 30 can be formed.

[0011] [Application example 3] The invention described in Application Example 3 is a plating method for plating a metal material (10), comprising: Using the plating solution described in Application Example 1 or Application Example 2, a first coating destruction treatment in which a first current is passed through the metal material (10) as an electrode for a first period of time to destroy a coating on the surface of the metal material (10); a first plating process in which, after the first coating destruction process, a second current is passed through the metal material (10) as an electrode for a second period to form a plating layer; a first coating formation process for forming a coating layer by setting the metal material (10) at zero potential for a third period; The plating method is characterized in that the metal material (10) is plated by repeating the above-mentioned steps a predetermined number of times.

[0012] In this plating method, a coating layer is formed on the surface of the metal material 10, and by repeatedly destroying the formed coating and plating the portions where the coating has been destroyed, a roughened plating can be formed on the surface of the metal material 10. Furthermore, because a roughened plating is formed on the surface of the metal material 10, when the metal material 10 is molded with a resin 30, a roughened surface with excellent adhesion to the mold resin 30 can be formed.

[0013] [Application example 4] The plating method according to Application Example 4 is the plating method according to Application Example 3, further comprising: Before the first coating destruction treatment, Pretreatment of the surface of the metal material (10); a metal deactivation treatment for forming a coating on the surface of the metal material (10) using a metal deactivator after the pretreatment; The gist of this is to:

[0014] In this plating method, the surface of the metal material 10 is pretreated or deactivated before the plating method described in Application Example 3, so that the roughened plating is formed in a more preferable form on the surface of the metal material 10. Therefore, when the metal material 10 is molded with a resin 30, better adhesion can be achieved between the metal material 10 and the molded resin 30.

[0015] [Application example 5] The metal material described in Application Example 5 is a coating (22) formed on the surface of the metal material (10); a plurality of coating-broken portions (C) formed by breaking the coating (22) at a plurality of locations to expose the metal material (10) at the broken locations; a plating particle (20) formed on the surface of the metal material (10) exposed in each of the plurality of coating destruction portions (C), the plating particle (20) having a shape in which the cross-sectional area of ​​at least a portion of the upper portion is larger than the cross-sectional area of ​​the bottom portion; The gist of the system is that it is equipped with the following:

[0016] In such a metal material 10, a plurality of nodular particles 20 are formed on its surface, roughening the surface of the metal material 10. Therefore, when the metal material 10 is molded with a resin 30, the molding resin 30 penetrates between the plurality of nodular particles 20 and is molded, thereby forming a roughened surface with excellent adhesion between the plurality of nodular particles 20 and the molding resin 30. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a diagram showing a schematic structure of a lead frame to be subjected to roughening plating treatment. [Figure 2] FIG. 2 is a diagram schematically illustrating the flow of a roughening plating treatment. [Figure 3]1 is a photograph of the surface morphology of a metal material that has been subjected to a roughening plating treatment, observed with an electron microscope. [Figure 4] FIG. 1 is a diagram showing a method for an adhesion strength test. [Figure 5] FIG. 1 is a graph comparing adhesion strength between a conventional roughening plating method and a roughening plating method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments to which the present invention is applied will be described with reference to the accompanying drawings. Note that the embodiments of the present invention are not limited to the following embodiments, and various forms may be adopted as long as they fall within the technical scope of the present invention.

[0019] (Plating Solution Composition) The composition of the plating solution used in the plating treatment (hereinafter also referred to as "roughening plating treatment") in this embodiment is as follows.

[0020] Copper sulfate pentahydrate: 200[g / L] Sulfuric acid: 23.75[g / L] Chlorine: 40 ppm (mg / L) Inhibitor (polyethylene glycol): 13.75 [vol%] Accelerator (1,2-ethanedisulfonic acid dihydrate): 7.5 [vol%]

[0021] (Lead frame structure) The structure of a lead frame 10, which is a metal material to be subjected to the roughening plating treatment, will be described with reference to Fig. 1. Fig. 1 shows a schematic structure of the lead frame 10 to be subjected to the roughening plating treatment, with Fig. 1(a) being a plan view and Fig. 1(b) being a cross-sectional view of an integrated circuit 3 in which the lead frame 10 is packaged with a molding resin 30.

[0022] The lead frame 10 is made of a copper alloy, and as shown in FIG. 1, includes a die pad 11 that supports and fixes the semiconductor element 5, inner leads 13 that are connected to the semiconductor element 5 by wiring (bonding wires 12), and outer leads 14 that bridge the wiring to the external wiring.

[0023] As shown in Fig. 1(b), this lead frame 10 is molded with a molding resin 30 to become an integrated circuit 3 such as an IC. In order to reliably remove resin burrs that occur during this resin molding, only the area of ​​the lead frame 10 that will be molded (the area indicated by "A" in Fig. 1(a)) is subjected to a roughening plating treatment, and the area that will not be molded is not subjected to the roughening plating treatment.

[0024] (Roughening plating treatment method) Next, the roughening plating method will be described with reference to Fig. 2. Fig. 2 is a diagram schematically showing the flow of the roughening plating treatment.

[0025] In the roughening plating process, roughening plating is applied to the lead frame 10 according to the following processing steps (a) to (f).

[0026] (A) Pretreatment As shown in Fig. 2(a), a pretreatment is performed on the lead frame 10. The pretreatment is a process such as degreasing and pickling, which is performed to remove oil, metal powder, and other contaminants adhering to the surface of the lead frame 10, which is made of a copper alloy, and to make the surface of the lead frame 10 clean and suitable for plating. In this embodiment, degreasing is performed.

[0027] (a) BTA coating treatment As shown in FIG. 2(b), a BTA coating 21 is formed on the lead frame 10 using benzotriazole (hereinafter also referred to as "BTA") as a metal deactivator.

[0028] (cormorant) BTA Coating destruction treatment The lead frame 10 was used as the anode and the phosphorus-containing copper plate was used as the cathode, and a current (first current) with a current density of −16 mA / d was passed through the lead frame 10 and the phosphorus-containing copper plate. This state was maintained for 50 mS (first period), and as shown in FIG. 2(c, f, i), BTA film 21 Destruction treatment will be carried out. BTA film 21 The location of the destruction is shown in Figure 2(c,f,i). B " is indicated.

[0029] (D) Plating Next, a current (second current) with a current density of +50 [mA / d] is passed and maintained for 50 [mS] (second period), and a plating process is performed to grow nodular particles 20, as shown in Figure 2 (d, g, j).

[0030] (E) Coating treatment Next, the potential difference between the anode and the cathode is kept at 0 [V] for 50 [mS] (third period), and a coating formation process is performed to form a coating 22 as shown in FIG. 2(e, h).

[0031] Steps (f), (c), and (e) are repeated until the total time reaches 26 seconds. As a result, as shown in Figures 2(c) to 2(j), the destruction of the coating 22 (indicated by "C" in each figure) and the growth of the nodular particles 20 are repeated.

[0032] Finally, a plating layer with numerous nodular particles 20 formed at high density can be obtained as shown in FIG. 2(k).

[0033] (Characteristics of roughening plating treatment) When plating is applied to a lead frame 10 using the roughening plating method described above, a plating layer of uniform thickness is not formed on the surface of the lead frame 10, but rather a plating layer (roughening plating layer) in which nodular particles 20 of different sizes grow on the surface of the lead frame 10, as shown schematically in Figure 2(k).

[0034] Photographs of the surface morphology of the metal material 10 that had undergone roughening plating, observed with an electron microscope, are shown in Figure 3. Figure 3(a) is an enlarged view, enlarged 2000 times, of the surface of the metal material 10 that had been plated using the plating solution and roughening plating method described above, and Figure 3(b) is an enlarged view, enlarged 2000 times, of the surface of the metal material 10 that had been plated using a plating method from another company.

[0035] 3(a), the surface of metal material 10 subjected to the roughening plating of the present invention is covered with nodular particles 20 of random shape, each having a size of 2 to 3 μm, which are densely and three-dimensionally connected, with even smaller nodular particles 20 formed therein. The surface roughness Sa at this time is 3.0. Here, the nodular particles 20 refer to particles with a balloon or bubble shape, in which the cross-sectional area of ​​at least a portion of the upper part is larger than the cross-sectional area of ​​the bottom part, that is, particles with a so-called undercut shape. The term also includes particles with such shapes that are continuously grown.

[0036] In contrast, the surface of the metal material 10 plated using the plating method of another company only has small particles of approximately uniform size formed on it, and the surface roughness Sa is 1.5.

[0037] That is, when the roughening plating method according to the present invention is used, large nodular particles 20 of random shapes are densely formed on the surface of the metal material 10. Therefore, when molding is performed with the molding resin 30, the molding resin 30 penetrates between the nodular particles 20, particularly into the undercut portions, and then exerts an anchoring effect.

[0038] Furthermore, since more molding resin 30 can be filled between the nodular particles 20 than with particles formed by conventional roughening plating methods, such as conventional needle-shaped, conical, or pyramidal shapes, the adhesion strength of the molding resin 30 to the plating layer is increased.

[0039] (Adhesion strength test results) The method and results of the adhesion strength test will now be described with reference to Figures 4 and 5. Figure 4 shows the method of the adhesion strength test, and Figure 5 is a graph comparing the adhesion strength between a conventional roughening plating method and the roughening plating method of the present invention.

[0040] The adhesion strength test is carried out according to the following procedures (G) to (L). (g) A test piece (metal material 10) of 1 cm square is cut from the test frame 10 to which roughening plating has been applied.

[0041] (h) The molding resin 30 is molded with the roughened plated surface facing up. (Conditions) Time: 90 seconds + α, Temperature: 180[℃] (K) Dry. (Conditions) Time: 8 hours, Temperature: 175°C

[0042] (J) Place in a constant temperature and humidity chamber and perform an environmental acceleration test. (Conditions) Time: 168 hours, Temperature: 88[℃], Humidity: 85[%] (Environmental acceleration test, JEDEC standard MSL1 compliant)

[0043] (k) Perform a reflow heating test. (Conditions) Number of times: 3, Time: 1 minute → 1 minute, Temperature: 180~190[℃]→230~240[℃] (Environmental acceleration test, JEDEC standard MSL1 compliant)

[0044] (c) Conduct a shear strength test. In the shear test, as shown in Fig. 4, metal material 10 is placed on base 40 as a test piece, and a force is applied by pressing the side of molded resin 30 molded on top of it with tool 41 (indicated by the arrow in Fig. 4). The pressure when molded resin 30 peels off from the test piece is taken as the adhesion strength.

[0045] In FIG. 5, the horizontal axis indicates the plating method and the grade of the molding resin 30, and the vertical axis indicates the pressure [Mpa]. As shown in Figure 5, when a plating layer is formed by the conventional brown oxide treatment, the adhesion strength varies depending on the grade of mold resin 30. However, when a plating layer is formed by the roughening plating treatment according to the present invention, it is clear that the adhesion strength is high even with the lowest grade of mold resin 30.

[0046] (Other embodiments) (1) In the above embodiment, benzotriazole is used as the metal deactivator, but imidazole, thiadiazole, or the like may also be used.

[0047] (2) In the above embodiment, polyethylene glycol (PEG) was used as the inhibitor, but Janus Green B (JGB) or the like may also be used. Furthermore, bis(3-sulfopropyl) disulfide (SPS) may also be used as the accelerator. [Explanation of symbols]

[0048] 3... Integrated circuit 5... Semiconductor element 10... Lead frame 11... Die pad 12... Bonding wire 13... Inner lead 14... Outer lead 20... Nodular particle 21... BTA coating 22... Coating 30... Molding resin 40... Base 41... Tool.

Claims

1. A plating solution characterized by containing 200 g / L of copper sulfate pentahydrate, 23.75 g / L of sulfuric acid, 40 ppm of hydrochloric acid, 13.75 vol % of an inhibitor, and 7.5 vol % of an accelerator.

2. The plating solution according to claim 1, the inhibitor is polyethylene glycol; The plating solution is characterized in that the accelerator is 1,2-ethanedisulfonic acid dihydrate.

3. A plating method for plating a metal material, comprising: Using the plating solution according to claim 1 or 2, a first coating destruction treatment in which a first current is passed through the metal material as an electrode for a first period of time to destroy a coating on the surface of the metal material; a first plating process in which, after the first coating destruction process, a second current is passed through the metal material as an electrode for a second period to form a plating layer; a first coating formation process in which the metal material is set at zero potential for a third period to form a coating layer; a plating method for plating the metal material by repeating the above-mentioned steps a predetermined number of times.

4. The plating method according to claim 3, Before the first coating destruction treatment, Pretreatment of the surface of the metal material; a metal deactivation treatment for forming a coating on the surface of the metal material using a metal deactivator after the pretreatment; A plating method characterized by carrying out the steps of:

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