Power inductor and manufacturing method thereof

Abstract

The invention discloses a power inductor and a manufacturing method thereof.The coil of the power inductor comprises at least two electrode composite layers, each electrode composite layer is provided with a double-face Cu layer, the at least two electrode composite layers are connected in a laminated mode, Ni layers are arranged on the Cu layers at the connecting positions of every two adjacent electrode composite layers respectively, and the Ni layers are arranged on the connecting positions of the two adjacent electrode composite layers respectively. The two Ni layers are connected in a laminated mode through the connecting layer. According to the method, nickel is electroplated on the Cu layer, so that the state of a bonding layer between the electrode and the tin-containing solder layer can be improved, and the morphology of the IMC layer is obviously improved; meanwhile, the mechanical strength of a welding spot joint is enhanced, and the high-temperature load reliability test performance of a product is improved; and the oxidation resistance of the nickel layer is also enhanced by tinning.

Description

Technical Field

[0001] The invention relates to a power inductor and a manufacturing method thereof. Background Art

[0002] With the continuous progress of the communications industry, the application of 5G has become popular, and the research and development of 6G is also underway. More miniaturized inductor components have become a development trend. In order to meet the higher performance requirements of inductor components, such as electrical properties and reliability, it is particularly important to carefully design the internal electrode structure and composition of the inductor components.

[0003] In the prior art, the internal coil of some power inductor structures is a single-layer electrode composite layer (flexible circuit board) prepared by a subtractive method and connected together by printing solder paste reflow soldering. The copper electrode is in direct contact with the solder paste, which will generate a very thick IMC (intermetallic compound) layer, and the IMC layer is generated at a relatively fast speed. Due to the existence of the Kirkendall effect, a certain number of holes are generated on one side of the copper electrode at the solder joint, and a crack will gradually form over time, which will affect the high-temperature load performance of the product.

[0004] On the other hand, the copper electrode surface has poor wettability to molten solder paste after oxidation, and a large number of bubbles and voids are generated at the solder joints during the reflow soldering process, causing the interlayer electrode bonding force to deteriorate, affecting the contact reliability performance of subsequent products. Summary of the invention

[0005] The embodiments of the present application provide a power inductor and a method for manufacturing the same, thereby reducing the rate and number of hole generation at the interface layer between the Cu layer and the solder layer (tin paste) in the coil, thereby reducing the current density and temperature rise under high temperature load and reducing the risk of open circuit.

[0006] To this end, an embodiment of the present application provides a power inductor, wherein the coil of the power inductor includes at least two layers of electrode composite layers, the electrode composite layer has a double-sided Cu layer, and the at least two layers of electrode composite layers are stacked and connected, wherein Ni layers are respectively arranged on the Cu layers at the connection between two adjacent electrode composite layers, and the two Ni layers are stacked and connected through a connecting layer.

[0007] In some embodiments, the invention also has the following technical features:

[0008] The thickness of the connection layer is 20 μm to 200 μm.

[0009] The Ni layer has a thickness of 0.5 μm to 3 μm.

[0010] A scallop-shaped intermetallic compound is present at the interface between the connection layer and the Ni layer.

[0011] The thickness of the scallop-shaped intermetallic compound is 1 μm to 10 μm.

[0012] The intermetallic compound is (Cu, Ni)6Sn5.

[0013] The present invention also provides a method for manufacturing a power inductor, comprising the following steps:

[0014] S1: sequentially forming a Ni layer and a Sn layer on the Cu layer of a single electrode composite layer that needs to be connected to each other;

[0015] S2: forming a tin-containing solder layer on the Sn layer to obtain a symmetrically distributed structure of Cu layer / Ni layer / Sn layer / tin-containing solder layer / Sn layer / Ni layer / Cu layer, and pressing at least two electrode composite layers together through a welding process to obtain a coil sample, wherein during the welding process, the Sn layer and the tin-containing solder layer melt into a connecting layer, and the obtained coil sample has a symmetrically distributed structure of Cu layer / Ni layer / connecting layer / Ni layer / Cu layer;

[0016] S3: Insulate and coat the coil sample in S2;

[0017] S4: hot pressing, insulating and coating, dicing and terminal electrode are performed on the coated coil sample and magnetic material to prepare the power inductor.

[0018] In some embodiments, the invention also has the following technical features:

[0019] In step S1, the electrode composite layer is obtained by a subtractive process; and the welding process in step S2 refers to reflow welding.

[0020] In step S2, the thickness of the Sn layer is 4 μm to 20 μm.

[0021] In step S2, the thickness of the tin-containing solder layer is 20 μm to 200 μm.

[0022] One or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:

[0023] Due to the use of a new electrode composite layer structure, the Cu layer is electroplated with Ni and Sn, which can not only prevent the oxidation of Ni, but also improve the state of the bonding layer between the Cu layer and the solder layer, and the morphology of the IMC layer is significantly improved; at the same time, it suppresses the occurrence of the Kirkendall phenomenon during product manufacturing and storage, enhances the mechanical strength of the solder joint connection, and improves the product's high-temperature load reliability test performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a three-dimensional schematic diagram of a power inductor according to an embodiment of the present invention;

[0025] Figure 2It is a schematic diagram of the cross-sectional structure of an electrode unit in a coil of a power inductor in the prior art;

[0026] Figure 3 It is a schematic cross-sectional structure diagram of an electrode unit in a coil of a power inductor according to an embodiment of the present application;

[0027] Figure 4 It is a schematic diagram of the cross-sectional structure of an inductor coil composed of multiple electrode units in the prior art;

[0028] Figure 5 This is a real shot of the IMC state of the bonding layer of the coil of the existing power inductor;

[0029] Figure 6 This is a real shot of the IMC state of the bonding layer of the coil of a power inductor according to an embodiment of the present invention;

[0030] Figure 7 It is a schematic diagram of an enlarged partial cross section of an inductor coil composed of a plurality of electrode units in a power inductor according to an embodiment of the present invention.

[0031] In the figure, 1 is a copper layer, 2 is an insulating film layer, 3 is a tin-containing solder layer, 4 is a connecting layer, 5 and 6 are lead-out terminal electrodes, 7 is a Ni layer, 10 is a connecting point, and 11 is an electrode unit. DETAILED DESCRIPTION

[0032] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0033] like Figure 1 As shown, it is a schematic diagram of the three-dimensional structure of the power inductor of the present invention, the power inductor includes a coil and lead-out terminal electrodes 5 and 6 connected to the coil, the coil of the power inductor includes at least two layers of electrode composite layers, the electrode composite layer is a component of the coil in the power inductor, and the electrode composite layer has a double-sided Cu layer (for example, Figure 2 As shown, the electrode composite layer includes an insulating film layer (such as a PI layer) 2, and a Cu layer 1) disposed on the upper and lower surfaces of the insulating film layer, respectively. Figure 3 As shown, a Ni layer is provided on the Cu layer 1 at the connection of two adjacent electrode composite layers, and the two Ni layers are laminated and connected by a connecting layer 4 (as shown in FIG. Figure 1 As shown, 10 is the connection point when the stack is connected).

[0034] The thickness specifications of the above-mentioned single electrode composite layer: the shape and size specifications of the Cu layer are designed according to the electrical properties of the product, the thickness of the Ni layer is 0.5 to 3.0 μm, and the thickness of the connecting layer is 20 μm to 200 μm.

[0035] In some embodiments, a scallop-shaped intermetallic compound is present at the interface between the connection layer and the Ni layer. The thickness of the scallop-shaped intermetallic compound is 1 μm to 10 μm. The intermetallic compound is (Cu, Ni)6Sn5.

[0036] like Figure 2 , 4 As shown, the internal coil of the power inductor structure in the prior art is a single electrode composite layer (flexible circuit board) prepared by a subtractive method and connected together by reflow soldering through printed solder paste (i.e., tin-containing solder layer 3), and the mass fractions of Sn, Ag, and Cu in the solder paste are respectively: Sn 96%, Ag 3.5%, and Cu 0.5%. However, the power inductor has the aforementioned disadvantages. The following embodiments of the present invention have made improvements on this.

[0037] like Figure 3 As shown, in this embodiment, after the electrode composite layer is prepared by the subtractive method, a certain thickness of Ni (nickel) and Sn (tin) (such as Figure 3 As shown, the Cu layer on one side of the top electrode composite layer and the bottom electrode composite layer that do not need to be connected to other electrode composite layers does not need to be electroplated with Ni (nickel) or Sn (tin), and then at least two electrode composite layers are stacked together using reflow soldering. Specifically, the following steps are included:

[0038] Step 1: After using the subtractive method to make the single electrode composite layer required for the power inductor sample, the Cu layer 1 of the single electrode composite layer that needs to be connected to each other is electroplated with a Ni layer (1 μm) and a Sn layer (5 μm) in sequence, wherein the thickness of Ni and Sn can be adjusted according to the situation. In this embodiment, the optimal values ​​are Ni (1 μm) and Sn (5 μm).

[0039] Step 2: forming a tin-containing solder layer on the Sn layer on the electrode composite layer in step 1 (the mass fractions of Sn, Ag and Cu in the tin-containing solder are: Sn 96%, Ag 3.5% and Cu 0.5% respectively) to obtain a symmetrically distributed structure of Cu layer / Ni layer / Sn layer / tin-containing solder layer / Sn layer / Ni layer / Cu layer, and laminating the layers together by reflow soldering to obtain a coil sample; the reflow soldering process is the same as the prior art; wherein, during the reflow soldering lamination lamination process, the Sn layer and the tin-containing solder layer are melted into one layer as a connecting layer 4, as shown in FIG. Figure 3 As shown, the obtained coil sample has a symmetrically distributed structure of Cu layer / Ni layer / connection layer / Ni layer / Cu layer. In addition, a scallop-shaped intermetallic compound (such as Figure 6 shown);

[0040] Step 3: The electrode composite layer coil sample in step 2 is insulated and coated with an insulating material; the insulating material is the same as that in the prior art;

[0041] Step 4: The coated coil sample and magnetic material are hot pressed, insulated, cut, and terminated to prepare the finished product (i.e., power inductor).

[0042] like Figure 7 As shown, the red square box represents an electrode unit 11 (that is, two adjacent electrode composite layers connected together are an electrode unit), the coil is composed of n such electrode units, and the black dotted line in each electrode unit is the axisymmetric line.

[0043] A scallop-shaped intermetallic compound (also called a cometallic compound) (Cu, Ni)6Sn5 appears at the interface between Ni and the connecting layer, and the thickness of the intermetallic compound ranges from 1 to 10 μm.

[0044] After testing, the performance parameters of the product made by the above method (hereinafter referred to as Model 2) and the prior art product (hereinafter referred to as Model 1) are compared as follows:

[0045] Table 1 Comparison of performance parameters of different models

[0046] sample L / nH DCR / mΩ Isat / A Proportion of high temperature load open circuit samples Model 1 482 18 6.5 1％ Model 2 485 18 6.4 /

[0047] As can be seen from the table above, the electrical properties of the samples in the embodiment, such as inductance L, DCR (direct current resistance), and saturation current Isat, are comparable to those of the original structure products and have not deteriorated. At the same time, the samples did not have open circuit defects when doing high temperature load experiments.

[0048] Through comparative analysis, it was found that Figure 5 The IMC layer Cu6Sn5 at the junction of the Cu layer (represented as "Cusubstrate") and the solder layer (represented as "solder") of the coil of the prior art shown in the figure presents a prism shape, and compared with the existing power inductor coil, Figure 6 In the embodiment shown, the morphology of the IMC layer (Cu, Ni) 6Sn5 changes from a prism shape to a fan-shaped structure, and the size of the IMC layer becomes smaller. According to actual measurements, this shape of the IMC state can improve the bonding strength of the product. At the same time, the specific implementation of the present invention adds an intermediate barrier layer Ni layer to the existing coil structure, which can effectively inhibit the occurrence of the Kirkendall phenomenon, thereby reducing the rate and number of hole generation at the interface layer, reducing the current density and temperature rise during high-temperature load experiments, and avoiding the risk of open circuits.

[0049] It can be seen that the technical solution in the above-mentioned embodiment of the present application adopts a new electrode composite layer coil plating structure, which can improve the state of the bonding layer between the Cu layer and the tin-containing solder layer, and the morphology of the IMC layer is significantly improved; at the same time, it suppresses the occurrence of the Kirkendall phenomenon during product manufacturing and storage, enhances the mechanical strength of the solder joint connection, and improves the product's high-temperature load reliability test performance.

[0050] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0051] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A power inductor, wherein the coil of the power inductor comprises at least two electrode composite layers, wherein the electrode composite layer has a double-sided Cu layer, and wherein the at least two electrode composite layers are laminated and connected, characterized in that: A Ni layer is respectively arranged on the Cu layer at the connection of two adjacent electrode composite layers, and the two Ni layers are laminated and connected via a connecting layer.

2. The power inductor according to claim 1, characterized in that: The thickness of the connection layer is 20 μm to 200 μm.

3. The power inductor according to claim 1, characterized in that: The Ni layer has a thickness of 0.5 μm to 3 μm.

4. The power inductor according to claim 1, characterized in that: A scallop-shaped intermetallic compound is present at the interface between the connection layer and the Ni layer.

5. The power inductor according to claim 4, characterized in that: The thickness of the scallop-shaped intermetallic compound is 1 μm to 10 μm.

6. The power inductor according to claim 4, characterized in that: The intermetallic compound is (Cu, Ni)6Sn5.

7. A method for manufacturing a power inductor, characterized in that: The steps include: S1: sequentially forming a Ni layer and a Sn layer on the Cu layer of a single electrode composite layer that needs to be connected to each other; S2: forming a tin-containing solder layer on the Sn layer to obtain a symmetrically distributed structure of Cu layer / Ni layer / Sn layer / tin-containing solder layer / Sn layer / Ni layer / Cu layer, and pressing at least two electrode composite layers together through a welding process to obtain a coil sample, wherein during the welding process, the Sn layer and the tin-containing solder layer melt into a connecting layer, and the obtained coil sample has a symmetrically distributed structure of Cu layer / Ni layer / connecting layer / Ni layer / Cu layer; S3: Insulate and coat the coil sample in S2; S4: hot pressing, insulating and coating, dicing and terminal electrode are performed on the coated coil sample and magnetic material to prepare the power inductor.

8. The manufacturing method according to claim 7, characterized in that: In step S1, the electrode composite layer is obtained by a subtractive process; and the welding process in step S2 refers to reflow welding.

9. The manufacturing method according to claim 7, characterized in that: In step S2, the thickness of the Sn layer is 4 μm to 20 μm.

10. The manufacturing method according to claim 7, characterized in that: In step S2, the thickness of the tin-containing solder layer is 20 μm to 200 μm.

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