KR102372995B1 - High density printed circuit board with plating layer and manufacturing method thereof - Google Patents

Abstract

a copper layer formed on a printed circuit board; a silver plating layer formed on the copper layer and including a silver component; a palladium plating layer formed on the silver plating layer and including a palladium component; and a high-density printed circuit board having a plating layer formed on the palladium plating layer and including a gold plating layer including a gold component.

Description

High density printed circuit board with plating layer and manufacturing method thereof

The technology disclosed in the present specification relates to a high-density printed circuit board having a plating layer formed thereon and a method for manufacturing the same, and more particularly, to a high-density printed circuit board capable of easily implementing a microcircuit and forming an excellent copper diffusion prevention layer and a plating method therefor will be.

In general, a high-density printed circuit board has a copper layer for mounting with components such as an IC chip, RAM, and the like, and a copper layer for wire bonding with semiconductors. The copper layer to be soldered and the copper layer to be wire-bonded are generally made of copper or a copper alloy. However, the copper layer exposed to the outside is oxidized and corroded over time, so there is a problem in that soldering and wire bonding are not performed smoothly. In order to solve this problem, various plating processes are performed on the copper layer.

Conventionally, technologies such as ENIG (Electroless Nickel Immersion Gold) and ENEPIG (Electroless Nickel Electroless Palladium Immersion Gold) that prevent oxidation and corrosion of copper by plating nickel, palladium, or gold on the copper layer, and facilitate soldering and wire bonding are made public But. ENIG and ENEPIG plating processes containing nickel relatively effectively prevent copper diffusion and thus have good component mounting reliability. Due to the high resistance and high transmission signal loss, there is a limit to the surface treatment of high-frequency communication components.

Republic of Korea Patent Registration No. 10-0773272 Republic of Korea Patent Registration No. 10-1883250

In order to solve the above-mentioned problems, the technology disclosed herein provides a high-density printed circuit board that does not include a nickel plating layer, has improved microcircuit responsiveness and can form an excellent copper diffusion barrier layer, and a method for manufacturing the same.

According to one aspect of the technology disclosed herein, a copper layer formed on a printed circuit board; a silver plating layer formed on the copper layer and including a silver component; a palladium plating layer formed on the silver plating layer and including a palladium component; and a high-density printed circuit board having a plating layer formed on the palladium plating layer and including a gold plating layer including a gold component.

According to another aspect of the technology disclosed herein, a copper layer formed on a printed circuit board; a silver plating layer formed on the copper layer and including a silver component; a silver-palladium composite plating layer formed on the silver plating layer and in which the silver component and the palladium component are mixed; and a high-density printed circuit board having a plating layer formed on the silver-palladium composite plating layer and including a gold plating layer including a gold component.

According to another aspect of the technology disclosed herein, the method comprising: (a) pre-processing a printed circuit board on which a predetermined circuit pattern is formed; (b) plating a silver plating layer including a silver component on the copper layer of the printed circuit board; (c) plating a palladium plating layer including a palladium component on the silver plating layer; and (d) plating a gold plating layer including a gold component on the palladium plating layer.

The plating layer of the high-density printed circuit board on which the above-described plating layer is formed has excellent resistance to microcircuits and has an excellent copper diffusion prevention layer. In addition, since the plating layer of the above-described high-density printed circuit board does not include a nickel layer, high-frequency signal transmission loss can be minimized. Meanwhile, according to the above-described method for manufacturing a high-density printed circuit board, it is possible to easily manufacture a high-density printed circuit board having a plating layer having excellent component mounting reliability and excellent copper diffusion prevention ability.

1 is a view showing a cross-sectional structure of a printed circuit board having a plating layer according to an embodiment of the technology disclosed herein.
2 is a view showing a cross-sectional structure of a printed circuit board having a plating layer according to another embodiment of the technology disclosed herein.
3 is a view showing the growth of a silver-palladium composite plating layer according to an increase in the palladium component.
4 is a view showing a cross-section of a printed circuit board to which a silver-palladium composite plating layer and a gold plating layer are introduced according to another embodiment of the technology disclosed herein.
5 shows a method of manufacturing a high-density printed circuit board having a plating layer formed thereon according to an embodiment of the technology disclosed herein.
6 is a result of analysis of the plating layer of Example 2 with a transmission electron microscope (TEM, transmission electron microscopy).
7 is a result of analyzing the components of each layer by the elemental component analysis method for the plating layer of Example 2.
8 is a result of analyzing the distribution according to the components of each layer using elemental component analysis mapping for the plating layer of Example 2;

Hereinafter, preferred embodiments of the technology disclosed herein will be described in detail. In describing the disclosed technology, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. Throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

Since the disclosed technology is capable of various transformations and may have various implementations, specific implementations are illustrated and described in detail in the detailed description. However, this is not intended to limit the presently disclosed technology to a specific implementation form, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and scope of the presently disclosed technology.

The technology disclosed herein is not limited to the implementations described herein and may be embodied in other forms. However, the embodiments introduced herein are provided so that the disclosed content may be thorough and complete, and the technical spirit of the present technology may be sufficiently conveyed to those skilled in the art. In order to clearly express the components of each device in the drawings, the sizes such as widths and thicknesses of the components are slightly enlarged. In the description of the drawings as a whole, it has been described from an observer's point of view, and when an element is referred to as being positioned above or on top of another element, this indicates that the element may be positioned directly above another element or that an additional element may be interposed between those elements. includes all meanings. In addition, those of ordinary skill in the art will be able to implement the spirit of the presently disclosed technology in various other forms without departing from the technical spirit of the presently disclosed technology. And the same reference numerals in the plurality of drawings refer to elements that are substantially the same as each other.

Hereinafter, the technology disclosed in the present specification will be described in detail with reference to the accompanying drawings.

1 is a view showing a cross-sectional structure of a printed circuit board having a plating layer according to an embodiment of the technology disclosed herein.

The high-density printed circuit board 100 on which the plating layer is formed according to an embodiment includes a copper layer 120 formed on the printed circuit board 110 ; a silver plating layer 130 formed on the copper layer 120 and including a silver component; a palladium plating layer 140 formed on the silver plating layer 130 and including a palladium component; and a gold plating layer 150 formed on the palladium plating layer and including a gold component.

The copper layer 120 is formed so that the printed circuit board 110 has a predetermined circuit pattern, and may be formed for soldering and wire bonding. In this case, the copper layer 120 may be formed without limitation as long as it is a method of forming a pattern having a predetermined shape, but preferably may be formed by a lithography method using a photoresist.

The silver plating layer 130 protects the copper layer 120 during subsequent plating of the palladium component and improves the spreadability of the solder, thereby having excellent characteristics in the soldering reaction. The silver component may be pure silver (Ag) or a silver alloy in which selenium (Se) or lead (Pb) is coexisted to further improve soldering properties. In the case of the silver plating layer 130 made of such a silver alloy, soldering properties may be improved due to capillary action, and silver particles may be refined to improve solderability and wire bonding properties. The silver alloy is preferably composed of 99 to 99.999% by weight of silver and 0.001 to 1.0% by weight of one or more metals selected from the group consisting of selenium (Se) and lead (Pb). When one or more metals selected from the group consisting of selenium (Se) and lead (Pb) are included in an amount of less than 0.001% by weight, the improvement in solderability and wire bonding properties is insignificant, and when it is included in more than 1.0% by weight, lead as a heavy metal This eluted or the amount of expensive selenium to be used increases, which may decrease economic efficiency.

The thickness of the silver plating layer 130 may be controlled within a range in which soldering properties are not impaired, and the thickness may be 0.01 to 2.0 μm, preferably 0.05 to 1.5 μm, more preferably 0.1 to 1 μm. there is. When the thickness of the silver plating layer 130 is less than the above range, it may be difficult to control the work process, so it may be difficult to implement a uniform silver plating layer 130 , and solderability and wire bonding characteristics may be deteriorated. On the other hand, when the thickness of the silver plating layer 130 exceeds the above range, the wire bondability is not significantly improved, but on the contrary, the solderability is deteriorated and the process time is long, which may be commercially inefficient.

For silver plating, a reduction plating solution or a substitution method plating solution may be used. Preferably, a substitution method plating solution has excellent plating spreading characteristics and thus easy to form a plating layer on a microcircuit pattern. In the case of silver plating using the reduction plating method, it may be difficult to respond to fine patterns due to plating spread, and in the case of the alkali type reduction method, it may damage PSR (photo imaginable solder resist) INK.

Meanwhile, since the palladium plating layer 140 is additionally formed on the silver plating layer 130 , diffusion of copper from the copper layer 120 can be prevented as much as possible. In particular, the palladium plating layer 140 stacked on top of the silver plating layer 130 not only serves as a barrier to preventing copper diffusion, but also migration that occurs during silver plating. growth) can be prevented. In addition, silver not covered by the palladium plating layer 140 has a problem in that it is deteriorated or oxidized because it is vulnerable to sulfur dioxide gas or moisture in the atmosphere when left in the air, thereby reducing solderability and wire bonding properties. The above problem can be solved by forming the palladium plating layer 140 thereon. Here, due to the presence of the silver plating layer 130 , it is possible to prevent the copper layer 110 from being attacked and damaged when the Pd component is introduced onto the copper layer 120 . If the silver plating layer 130 is not used, voids may be generated at the interface between copper and palladium, and thus solder and wire reliability may be deteriorated.

When porous silver is simply plated to improve solderability and bonding properties, copper may diffuse and flow out through the silver pores. However, in this case, it is possible to prevent copper from flowing through the silver pores by filling the silver pores with palladium. In particular, since silver and palladium are metals that do not have reactivity with copper, it is possible to minimize copper leakage when the surface is plated using them.

The thickness of the palladium plating layer 140 formed of palladium or a palladium alloy on the silver plating layer 130 may be 0.005 to 1.0 μm, preferably 0.007 to 0.5 μm, and more preferably 0.01 to 0.2 μm. When the thickness of the palladium plating layer 140 is less than the above range, it is difficult to implement a uniform palladium plating layer 140 , and Cu diffusion preventing power may be lowered, and thus wire bonding characteristics may be deteriorated. When the thickness of the palladium plating layer 140 exceeds the above range, the effect of contributing to solder and wire reliability improvement or discoloration prevention is insignificant compared to an increase in thickness, and thus it is uneconomical.

In addition, when the substitution plating method is used to form the palladium plating layer 140, pure palladium can be used, but when the electroless reduction plating method is used, palladium can be formed using a palladium alloy. The palladium plating layer 140 may be formed using a palladium alloy composed of 99.9 wt% of palladium (Pd) and 0.1-8 wt% of phosphorus (P) or boron (B). If the content of phosphorus or boron is out of the above range, desired physical properties may not be obtained, and the electroless reduction plating may not be formed to a desired thickness and shape.

Preferably, the palladium plating layer 140 is formed by a substitution plating method in order to minimize the leakage of copper through the silver pores by filling the silver pores of the silver plating layer 130 with palladium. When palladium plating is performed by the substitution plating method, it is easy to form a silver-palladium composite plating layer, and since the silver-palladium composite layer can minimize copper diffusion, excellent copper diffusion can be minimized even with a thin palladium thickness. On the other hand, during electroless plating, it is difficult to form a silver-palladium composite plating layer and its thickness can be thin. can do.

The gold plating layer 150 is formed by plating on the palladium plating layer 140 and is formed on the surface of the palladium or palladium alloy layer to prevent oxidation of the plating layer and increase bondability with the gold wire, thereby improving wire bonding reliability. If only the palladium plating layer 140 is formed without additionally forming the gold plating layer 150 to prevent copper diffusion and silver (Ag) migration, bonding properties with the gold wire may deteriorate and wire bonding properties may deteriorate. .

In forming the gold plating layer 150 , the plating layer 150 may be formed using a substitution plating method using an ionization tendency, or the plating layer 150 may be formed using a reduction plating method using a reducing agent. However, in the case of the plating layer of the above-described printed circuit board in which the silver plating layer 130 and the palladium plating layer 140 are present on the copper layer 120, it is preferable to perform plating in a reduction method. The substitution-type gold plating solution, which is plated due to a difference in ionization tendency between copper and gold, may not satisfy the gold thickness required for wire bonding reliability because the lower plating layer has a dense structure. On the other hand, in the case of a reduction plating solution, a desired thickness of gold can be sufficiently formed, so it is preferable to form the plating layer using a reduced gold plating method.

The gold plating layer 150 may be formed by plating gold (Au) alone, but gold (Au), thallium (Tl), selenium (Se), or a combination thereof is used as gold to accelerate the plating speed and improve wire bonding properties. It may be formed by alloying with Although pure gold plating alone has excellent solderability and wire bonding properties, when gold is alloyed with thallium (Tl), selenium (Se), or a combination thereof used to form a gold alloy plating layer, alloyed thallium (Tl), selenium ( Se) or a combination thereof has an advantage of accelerating the plating speed by acting as an under potential, and the precipitated tissue becomes a granular structure, so that wire bonding properties may be further increased. In this case, the gold alloy may include 99 to 99.99% by weight of gold, 0.01 to 1.0% by weight of a combination containing at least one of thallium (Tl) or selenium (Se), and thallium (Tl) or selenium (Se) When a combination containing at least one of can

The gold plating layer 150 plated as described above has low reactivity with external materials and high conductivity, so that it can serve as a protective material for palladium and silver. In the case of palladium used as an existing outer layer, although it is not a highly reactive metal, it transmits hydrogen (H) and has reactivity with oxygen (O), fluorine (F) and chlorine (Cl). In addition, in the case of palladium, when hydrogen is adsorbed, electrical conductivity may be lowered. Therefore, when exposed to such an environment, the high-density printed circuit board 100 may be damaged and deteriorated in physical properties due to the elements. However, in the case of gold, since it has little reactivity with other elements, the high-density printed circuit board 100 can be protected from these foreign substances. Conversely, since reactivity with copper used as a wire is low, the gold plating layer 150 may be used as a diffusion barrier layer that blocks the diffusion of copper flowing out from the inside.

The gold plating layer 150 formed on the palladium plating layer 140 can serve as a protective material for palladium and silver, and also serves as a barrier layer to block the diffusion of copper and improve bondability with the gold wire. The thickness of the gold plating layer 150 may be 0.005 to 1.0 μm, preferably 0.01 to 0.5 μm, and more preferably 0.02 to 0.3 μm. If the thickness of the gold plating layer 150 is less than the above range, it is difficult to expect the role of the silver plating layer 130 and the palladium layer 140 as a protective material and a copper diffusion prevention layer, and it is difficult to expect improvement in wire reliability. In addition, when the thickness of the gold plating layer 150 exceeds the above range, it is difficult to expect improvement in protection performance and physical properties, but as the amount of gold used increases, the production cost increases, and thus economic feasibility may decrease. In particular, due to the presence of the silver plating layer 130 and the palladium plating layer 140 , the ability to prevent copper diffusion is superior to the DIG method of plating the gold plating layer 150 directly on the copper layer 110 , so multi-reflow is required. In the case of the product, copper does not diffuse into the gold plating surface, so solder and wire reliability are excellent. Therefore, according to the present plating layer structure, the thickness of the gold plating layer can be much lower than that of the plating layer structure formed by the direct immersion gold (DIG) manufacturing process, for example, 1/10 to 1/5 level.

In particular, it is possible to form a plating layer with excellent storage stability and high wire bonding strength by forming a gold plating layer with excellent anti-oxidation ability as well as an excellent copper diffusion prevention layer of the Pd layer or Ag-Pd layer. In addition, since copper diffusion can be minimized, it is possible to prevent rapid deterioration of wire bonding bonding strength due to multi-reflow and thermal history.

In a preferred embodiment, a silver-palladium composite plating layer in which the silver component and the palladium component are mixed may be interposed between the silver plating layer 130 and the palladium plating layer 140 .

2 is a view showing a cross-sectional structure of a printed circuit board having a plating layer according to another embodiment of the technology disclosed herein. Referring to FIG. 2 , as described above in the previous example, a plating layer in which a silver plating layer 230 , a palladium plating layer 240 , and a gold plating layer 250 are stacked on top of the copper layer 220 of the printed circuit board 210 . In the formed high-density printed circuit board 200 , a silver-palladium composite plating layer 260 may be interposed between the silver plating layer 230 and the palladium plating layer 240 .

The silver-palladium composite plating layer 260 may be formed while plating a palladium component on the surface of the silver plating layer 230 . To form the silver-palladium composite plating layer 260 , a porous silver plating layer may be first formed using pure silver (Ag), but the silver plating layer may be formed using a silver alloy to improve soldering characteristics. If the proper thickness is maintained with pure silver plating alone, solderability and wire bonding properties are improved, but if the silver plating layer is formed using a silver alloy containing selenium (Se) or lead (Pb), the soldering properties are further improved due to capillary action. It is possible to improve solderability and wire bonding properties by refining the silver particles to be improved and formed.

The silver-palladium composite plating layer 260 may be formed by miscibility between the silver component and the palladium component. That is, in the process of plating the palladium component, the silver (Ag) component and the palladium (Pd) component are evenly mixed, and at this time, a plating layer in which the concentration of the palladium component of the silver-palladium composite plating layer 260 increases toward the top may be formed. That is, when the palladium component is plated on the silver plating layer 230 , it penetrates in the depth direction of the silver plating layer 230 . A silver-palladium composite plating layer 260 having a concentration gradient in which the components are present may be formed. As it has the concentration gradient, it may have an excellent property of adhesion between the plating layer interfaces.

The silver-palladium composite plating layer 260 is formed on the silver plating layer 230 , and may be formed to fill the pores of the silver plating layer 230 having porosity with palladium. Accordingly, the porous silver component and the palladium component may be mixed to form a layer in which silver and palladium are alloyed, and in the process of mixing the two metal components, the silver-palladium composite plating layer 260 may have a very dense structure. there is. As a result, copper diffusion can be minimized.

3 is a view showing the growth of a silver-palladium composite plating layer according to an increase in the palladium component. Referring to FIG. 3 , as the plating amount of palladium increases and the amount of the palladium component diffused downward over time increases, the silver-palladium composite plating layer 260, that is, the region where the silver component and the palladium component coexist is more You can see the increase.

The barrier property may be increased by the presence of the silver-palladium composite plating layer 260 having such a dense structure, and the silver plating layer 230 and the palladium plating layer 240 are disposed between the copper layer 220 and the gold plating layer 250 . The plating layer with silver components is denser due to palladium penetration in the depth direction than in the case of palladium penetration, so copper diffusion can be minimized even with a thin palladium thickness, and excellent wire bonding bonding reliability can be secured after multi-reflow. .

According to another aspect of the technology disclosed herein, a copper layer formed on a printed circuit board; a silver plating layer formed on the copper layer and including a silver component; a silver-palladium composite plating layer formed on the silver plating layer and in which the silver component and the palladium component are mixed; and a high-density printed circuit board having a plating layer formed on the silver-palladium composite plating layer and including a gold plating layer including a gold component.

4 is a view showing a cross-section of a printed circuit board to which a silver-palladium composite plating layer and a gold plating layer are introduced according to another embodiment disclosed in the present specification. Referring to FIG. 4 , the high-density printed circuit board 300 on which the plating layer is formed includes a copper layer 320 , a silver plating layer 330 , a silver-palladium composite plating layer 360 , and a gold plating layer 350 on the printed circuit board 310 . ) is provided. The silver plating layer 330 protects the copper layer and helps to improve spreadability during the soldering reaction, and the silver-palladium composite plating layer 360 may serve as a barrier to prevent the diffusion of copper from the copper layer 320 . and the form and function of each layer are the same as previously described in the above embodiments.

In each of the layers constituting the plating layer described in FIGS. 1 to 4 , in the case of the silver plating layers 130 , 230 , and 330 , the content of silver or a silver alloy component based on the cross section of the plating layer is defined as a region exceeding 99.99 wt %. and the palladium plating layers 140 and 240 may be defined as regions in which the content of palladium or a palladium alloy component exceeds 99.99 wt% based on the cross-section of the plating layer. Based on the cross-section of the plating layer, in the case of a region where silver or silver alloy component or palladium or palladium alloy component is 0.01 to 99.99% by weight and the remaining component is palladium or palladium alloy component or silver or silver alloy component, the silver-palladium composite plating layer ( 260, 360).

Meanwhile, in the case of the silver-palladium composite plating layers 260 and 360, the silver component and the palladium component may be present in a weight ratio of 1:0.2 to 2 over the entire range of the silver-palladium composite plating layers 260 and 360. . In the above range, excellent barrier properties may be exhibited.

In the high-density printed circuit board on which the plating layer is formed according to an embodiment of the present specification, when the thickness of the palladium (Pd) plating layer is defined in the present specification, not only the thickness of pure palladium (Pd) or palladium alloy layer but also silver in the thickness - It means the value obtained by adding the converted thickness to the amount of palladium present in the palladium composite plating layer considering the alloy ratio. Similarly, in the case of the silver (Ag) plating layer, the thickness is defined in consideration of the silver-palladium composite plating layer in which the silver component is distributed.

Meanwhile, the total thickness of the plating layer of the above-described printed circuit board including the silver, palladium, and gold plating layers plated on the copper layer may be controlled to be 0.5 μm or less. It can be seen that this has a small thickness considering that only the nickel plating layer is plated by 0.5 μm or more in order to obtain the required performance in the normal ENEPIG plating layer.

The printed circuit board having the above-described plating layer may have superior performance than the conventional plating layer based on the same thickness of the entire plating layer. In addition, in the case of the printed circuit board having the above-described plating layer based on the same performance, it is possible to have a plating layer having a thickness lower than that of the prior art, so that the cost can be reduced. That is, the printed circuit board disclosed herein performs better than when the plating layer is formed only with the silver plating layer and the palladium plating layer without using the gold plating layer, or when the plating layer is formed except for a part of the silver plating layer or the palladium plating layer while using the gold plating layer. can have

The plating layers of various structures shown in FIGS. 1 to 4 may be manufactured in the following manner. For example, when palladium plating is performed after silver plating in the plating layer manufacturing process, if the palladium plating layer is formed in a reducing method, a plating layer having the structure as shown in FIG. 1 may be formed, and if the palladium plating layer is formed in a substitution method, FIGS. A plating layer having the same structure may be formed. By adjusting the acidity of the palladium plating solution for substitution method plating, the thickness of the silver-palladium composite plating layer can be adjusted as shown in FIGS. The thickness may be greater. On the other hand, for example, when the palladium plating time is adjusted within 1 to 2 minutes, the palladium in the initial reaction first penetrates into the silver pores and grows, and then a palladium plating layer is formed. A plating layer having a structure as shown in FIG. 4 composed of a plating layer may be formed.

The uppermost gold plating layers 150 , 250 , and 350 are formed on the palladium plating layer 140 , 240 or the silver-palladium plating layer 360 , thereby preventing oxidation of the plating layer and increasing bondability with the gold wire to improve wire bonding reliability. It can protect the lower plating layer and can serve as a barrier layer to block the diffusion of copper.

As a result, in the case of a high-density printed circuit board to which the above-described plating layer is applied, there is no plating smear problem, so the microcircuit response is excellent, and since nickel is not used, it can be applied to parts for high-frequency communication and has excellent component mounting reliability.

According to another aspect of the technology disclosed herein, the method comprising: (a) pre-processing a printed circuit board on which a predetermined circuit pattern is formed; (b) plating a silver plating layer including a silver component on the copper layer of the printed circuit board; (c) plating a palladium plating layer including a palladium component on the silver plating layer; and (d) plating a gold plating layer including a gold component on the palladium plating layer.

5 shows a method of manufacturing a high-density printed circuit board having a plating layer formed thereon according to an embodiment of the technology disclosed herein. Referring to FIG. 5 , the printed circuit board on which a predetermined circuit pattern is formed in step S1 is pretreated by performing a degreasing process to an etching process in order to remove an oxide film from the copper surface and to form a roughness of the copper surface. In the case of the degreasing process, a solution containing sulfuric acid, which is an inorganic acid, may be used, and a nonionic surfactant may be used to impart wettability to the surface. The degreasing process may be performed by, for example, degreasing at 45° C. for 5 minutes. Next, an etching process is performed. For example, using PS (potassium peroxymonosulfate) and sulfuric acid, etching is performed at 45° C. for 1 minute to etch the copper surface by 0.5 to 1 μm.

In step S2, a silver plating layer including a silver component is formed on the copper layer of the printed circuit board. Preferably, the silver plating layer may be formed by a substitution plating method. For example, a silver plating layer may be formed on the copper layer by immersing the pretreated printed circuit board in a substitution-type silver plating solution at a temperature of 50° C. for 30 seconds to 30 minutes.

As an example of the substituted silver plating, silver nitrate (AgNO3), silver cyanide (AgCN), potassium silver cyanide (KAg(CN) ₂ ), silver sulfate (Ag ₂ SO ₄ ) is used as a silver source, and ethylenediaminetetraacetic acid (EDTA) is used as a complexing agent. A substituted palladium plating solution using citric acid, succinic acid as a buffer, sulfuric acid, nitric acid, and sodium hydroxide (NaOH) as a buffer, but not limited thereto, may be used.

When silver is plated by the substitution plating method as described above, a silver plating layer is formed on the copper layer as shown in the following reaction formula, and the silver plating layer may be porous.

[Scheme 1]

Cu (solid) + Ag ²⁺ (liquid) → Cu ²⁺ (liquid) + Ag (solid)

In step S3, a palladium plating layer including a palladium component is formed on the silver plating layer. In this case, a process of forming a silver-palladium composite plating layer by mixing the silver component and the palladium component by plating the palladium plating layer may be further added.

The porous silver plating layer made of the silver or silver alloy is washed with water and immersed in a substitution-type palladium plating solution at a temperature of about 40 to 70° C. for 30 seconds to 30 minutes. The palladium is filled to form a silver-palladium composite layer, and after the pores of the silver plating layer are filled, a palladium plating layer is formed on the silver-palladium composite plating layer. In this case, the palladium may be formed as shown in the following reaction formula.

[Scheme 2]

Cu (solid) + Pd ²⁺ (liquid) → Cu ²⁺ (liquid) + Pd (solid)

As a plating method for forming the palladium plating layer, a substitution plating method for forming a palladium plating layer of pure palladium by a substitution reaction, and palladium-phosphorus (Pd-P) or palladium by reduction using sodium hypophosphite or borate as a reducing agent - An electroless reduction plating method of forming a palladium alloy plating layer of boron (Pd-B) may be used.

As an example of the substitution plating, palladium sulfate (PdSO ₄ ), palladium nitrate (Pd(NO ₃ ) ₂ ) or palladium chloride (PdCl ₂ ) is used as a palladium source, citric acid is used as a buffer, and a polyethylene glycol-based nonionic surfactant ( 5 mol to 10 mol) and a substituted palladium plating solution using sulfuric acid, nitric acid or hydrochloric acid as a pH adjuster may be used, but the present invention is not limited thereto.

Preferably, it is preferable to form the palladium plating layer by a plating method of a substitution method. In the substitutional palladium plating method, it is easy to form a silver-palladium composite plating layer, and since the silver-palladium composite plating layer can minimize copper diffusion, excellent copper diffusion can be minimized even when the palladium thickness is thin.

In some embodiments, when silver plating, a silver plating layer having a dense structure with relatively few voids is formed by using a reducing method plating solution or adjusting the acidity and temperature in a substitution method to gradually increase the rate of forming the silver plating layer, An electroless palladium plating layer may be directly formed thereon. Alternatively, the silver-palladium composite plating layer can be appropriately formed as shown in FIGS. 2, 3, and 4 by adjusting the acidity and the immersion time of the substitution method palladium plating solution on the silver plating layer in which the pores are formed as described above, and the silver-palladium composite plating layer The thickness of the palladium plating layer can be adjusted.

In step S4, a gold plating layer including a gold component is formed on the palladium plating layer. The gold plating layer including gold or gold alloy may be immersed in a reduced gold plating solution at a temperature of about 70 to 90° C. for 30 seconds to 30 minutes to form a gold plating layer having a thickness of 0.02 to 0.3 μm.

The gold plating layer may be formed according to the following reaction formula.

[Scheme 3]

nAu(CN) ^2- (liquid) + ne ^- → nAu (solid) + 2nCN ^-

In this case, in the gold plating step, a commercially available plating solution may be used as a plating solution, or a substitution type gold plating solution may be used. However, the substitution method plating solution plated with copper and ionization tendency difference may not satisfy the gold thickness required for wire bonding reliability due to the dense structure of the silver-palladium composite layer, so it is preferable to perform the reduction plating method.

As an example of the gold plating, the gold compound uses potassium gold cyanide, gold chloride, and sodium gold sulfite as a gold source and as a complexing agent ethylenediamine tetraacetate acid (EDTA), diethylene triamine pentaacetate (DTPA), glycine (Glycine), and a buffer. As a phosphoric acid reducing agent, ascorbic acid, hydrazine, dimethylamine borane, hydroquinone, and formaldehyde may be used, but the present invention is not limited thereto.

According to the above-described manufacturing method, it is possible to easily manufacture a high-density printed circuit board having a plating layer having excellent resistance to microcircuits and excellent copper diffusion prevention ability.

Hereinafter, the technology disclosed in the present specification will be described in more detail through examples.

* Pretreatment process: For the evaluation substrate, a 10×10 cm BGA substrate manufactured by YMT was used, and to remove oil and oxide film on copper, SAC302 manufactured by YMT was used and degreasing was performed at 45° C. for 5 minutes. Thereafter, copper was etched by 0.5 to 1 μm using caroat to form a copper surface roughness for securing adhesion between the copper and the plating layer.

* Coating layer thickness measurement: For each plating thickness measurement, 10 random points were measured using a Hitachi (Model: FT150) XRF thickness meter to obtain an average value.

* Solder joint evaluation: SAC305, 0.3 mm was used for the solder ball, and the solder joint strength was measured using DAGE 4000. The pull speed was set to 500/sec to measure the strength, and the experiment was performed a total of 20 times to obtain an average value.

In addition, after gold plating, reflow (HELLER, 1809EXL) was performed 5 times, and the average solder pool strength was obtained in the same manner as above.

* Wire bonding evaluation: K&S Connx of CONNX was used for wire bonding device, capillary (N0814-52-22-08, PECO), wire (Heraeus Oriental Hitec, Au 1.0 mil), stage temperature 150℃, bonding power 130 mA (1st), 145 mA (2nd), tensile force was evaluated as 50 gf (1st), 70 gf (2nd) to obtain an average value.

In addition, after gold plating, reflow (HELLER, 1809EXL) was performed 5 times and heat treatment (175° C., 16 hours) was performed to evaluate more severe conditions, and then the average wire pull strength was obtained in the same manner as above.

[Example]

Example 1

After the pretreatment process, a silver plating layer of 0.30 μm was formed by plating at a temperature of 45° C. for 3 minutes using YMT’s substitutional silver plating solution (Galaxy series) on copper, and YMT’s substitutional palladium plating solution (PM) on the silver plating layer. series) to form a silver-palladium composite plating layer and a palladium layer of 0.1 μm by plating at a temperature of 62°C for 10 minutes, and then using a reduced gold plating solution (IRGOLD series) from YMT for 10 minutes at a temperature of 80°C. A gold plating layer of 0.1 µm was formed by inter-plating.

After forming the plating layer in this way, the solder joint evaluation was performed by the above-mentioned method. As a result, the strength after plating was 411 g and 393 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.8 g after plating, 9.3 g after 5 reflows, and 8.4 g after heat treatment (175° C., 16 hours).

Example 2

After the pretreatment process, the silver plating layer 0.1 µm, the silver-palladium composite plating layer and A palladium plating layer of 0.1 µm and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 409 g and 394 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.6 g after plating, 9.5 g after 5 reflows, and 8.4 g after heat treatment (175° C., 16 hours).

Example 3

After the pretreatment process, the silver plating layer 0.5 µm, the silver-palladium composite plating layer and A palladium plating layer of 0.1 µm and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 414 g and 392 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 12.1 g after plating, 9.4 g after 5 reflows, and 8.2 g after heat treatment (175° C., 16 hours).

Example 4

After the pretreatment process, a silver plating layer of 0.5 μm, a silver-palladium composite plating layer and A palladium plating layer of 0.1 µm and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 403 g and 393 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.9 g after plating, 9.6 g after 5 reflows, and 8.4 g after heat treatment (175° C., 16 hours).

Example 5

After the pretreatment process, a silver plating layer 0.3 µm in the same manner as in Example 1, except that a silver-palladium composite plating layer and a palladium plating layer were formed by plating at a temperature of 62 ° C. for 1 minute on copper using a palladium plating solution, and 0.01 µm; A silver-palladium composite plating layer, a palladium plating layer of 0.01 µm, and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 406 g and 391 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 12.0 g after plating, 9.3 g after 5 reflows, and 8.2 g after heat treatment (175° C., 16 hours).

Example 6

After the pretreatment process, the silver plating layer 0.3 µm in the same manner as in Example 1, except that the silver-palladium composite plating layer and the palladium plating layer were formed by plating at a temperature of 62° C. for 5 minutes on copper using a palladium plating solution to form 0.05 µm, A silver-palladium composite plating layer, a palladium plating layer of 0.05 µm, and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 403 g and 394 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.6 g after plating, 9.2 g after 5 reflows, and 8.3 g after heat treatment (175° C., 16 hours).

Example 7

After the pretreatment process, a silver plating layer 0.3 µm in the same manner as in Example 1, except that a silver-palladium composite plating layer and a palladium plating layer were formed by plating at a temperature of 62° C. for 25 minutes using a palladium plating solution on copper, and 0.20 µm, A silver-palladium composite plating layer, a palladium plating layer of 0.20 µm, and a gold plating layer of 0.1 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 405 g and 396 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.8 g after plating, 9.8 g after 5 reflows, and 8.3 g after heat treatment (175° C., 16 hours).

Example 8

After the pretreatment process, a silver plating layer of 0.3 µm, a silver-palladium composite plating layer, and A palladium plating layer of 0.10 µm and a gold plating layer of 0.03 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 406 g and 390 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.3 g after plating, 9.1 g after 5 reflows, and 8.2 g after heat treatment (175° C., 16 hours).

Example 9

After the pretreatment process, a silver plating layer of 0.3 µm, a silver-palladium composite plating layer, and A palladium plating layer of 0.10 µm and a gold plating layer of 0.20 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 405 g and 392 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 12.0 g after plating, 9.8 g after 5 reflows, and 8.2 g after heat treatment (175° C., 16 hours).

Example 10

After the pretreatment process, a silver plating layer of 0.3 µm, a silver-palladium composite plating layer, and A palladium plating layer of 0.10 µm and a gold plating layer of 0.30 µm were formed. After plating, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 412 g and 398 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 12.2 g after plating, 9.9 g after 5 reflows, and 8.5 g after heat treatment (175° C., 16 hours).

Comparative Example 1

After the pretreatment process, silver plating and palladium plating were not performed on the copper, but plating was performed at a temperature of 80° C. for 7 minutes using a reduced gold plating solution (IRGOLD series) of YMT to form a gold plating layer 0.10 μm on the copper. Other than that, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 388 g and 326 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 10.4 g after plating, 6.8 g after 5 reflows, and 3.4 g after heat treatment (175° C., 16 hours).

Comparative Example 2

After the pretreatment process, a gold plating layer of 0.50 μm was formed on copper in the same manner as in Comparative Example 1. Other than that, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of the evaluation, the solder pool strength after plating was 406 g and 376 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 11.1 g after plating, 8.8 g after 5 reflows, and 6.9 g after heat treatment (175° C., 16 hours).

Comparative Example 3

After the pretreatment process, without silver plating on copper, YMT's palladium catalyst (SCATA-10) was used for 2 minutes at 30°C, followed by a palladium catalyst process at 55°C using YMT's electroless palladium (ELP series). After plating at a temperature for 10 minutes to form a palladium layer of 0.10 μm, a gold plating layer of 0.10 μm was formed by plating at a temperature of 80° C. for 10 minutes using a reduced gold plating solution (IRGOLD series) of YMT.

Other than that, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 393 g and 362 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 10.8 g after plating, 8.1 g after 5 reflows, and 5.1 g after heat treatment (175° C., 16 hours).

Comparative Example 4

After the pretreatment process, a silver plating layer of 0.30 µm was formed on copper in the same manner as in Example 1, and then a gold plating layer of 0.10 µm was formed without palladium plating.

Other than that, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 388 g and 342 g after 5 reflows. In addition, the wire bonding evaluation results showed a value of 10.9 g after plating, 6.7 g after 5 reflows, and 4.4 g after heat treatment (175° C., 16 hours).

Comparative Example 5

After the pretreatment process, a silver plating layer of 0.30 μm was formed on copper in the same manner as in Example 1, and 0.10 μm was formed of palladium plating, but a gold plating layer was not formed.

Other than that, solder bonding evaluation and wire bonding evaluation were performed in the same manner as in Example 1. As a result of evaluation, the solder pool strength after plating was 382 g and 357 g after 5 reflows. In addition, as a result of wire bonding evaluation, wire bonding did not occur after plating, 4.6 g, after 5 reflows, 3.1 g, and heat treatment (175° C., 16 hours).

The test evaluation results of the plating layers of Examples and Comparative Examples are shown in Tables 1 and 2 below. In each of the embodiments, the silver-palladium composite plating layer was not separately indicated, but simply a silver plating layer and a palladium plating layer, and the thickness of the silver plating layer and the palladium plating layer was converted in consideration of the contents of the silver component and the palladium component of the silver-palladium composite plating layer. is one value.

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 plating layer thickness
(μm) Ag 0.30 0.10 0.50 1.00 0.30 0.30 0.30 0.30 Pd 0.10 0.10 0.10 0.10 0.01 0.05 0.2 0.10 Au 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.02 Solder Tensile Strength (g) after plating 411 409 414 403 406 403 405 406 Reflow
after 5 393 394 392 393 391 394 396 390 W/B Tensile Strength (g) after plating 11.8 11.6 12.1 11.9 12.0 11.6 11.8 11.3 Reflow
after 5 9.3 9.5 9.4 9.6 9.3 9.2 9.8 9.1 after heat treatment
(175℃, 16hr) 8.4 8.4 8.2 8.4 8.2 8.3 8.3 8.2

Example 9 Example 10 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 plating layer thickness
(μm) Ag 0.30 0.30 0.3 0.3 Pd 0.10 0.10 0.10 0.10 Au 0.2 0.3 0.10 0.50 0.10 0.10 Solder Tensile Strength (g) after plating 405 412 388 406 393 388 382 Reflow
after 5 392 398 326 376 362 342 357 W/B tensile strength (g) after plating 12.0 12.2 10.4 11.1 10.8 10.9 4.6 Reflow
after 5 9.8 9.9 6.8 8.8 8.1 6.7 3.1 after heat treatment
(175℃, 16hr) 8.2 8.5 3.4 6.9 5.1 4.4 no bond

- The goodness evaluation criteria are the applicant's own evaluation criteria, and it is not desirable for the tensile strength to rapidly decrease after reflow and heat treatment for both solder and W/B tensile strength.

1) Solder tensile strength (based on Solder 0.3 mm): 380 g or more after plating, 360 g or more after 5 reflows

2) W/B tensile strength (based on Au 0.1 mil): 10 g or more after plating, 8 g or more after 5 reflows, 6 g or more after heat treatment (175℃, 16hr)

6 is a result of analysis of the plating layer of Example 2 with a transmission electron microscope (TEM, transmission electron microscopy). Referring to FIG. 6 , an Ag/Pd composite plating layer (Ag rich layer, Pd rich layer) and an Au layer are observed separately on the Cu layer.

7 is a result of analyzing the components of each layer by the elemental component analysis method for the plating layer of Example 2. Referring to FIG. 7 , the plating layer of Example 2 by elemental component analysis (EDS) was matched with the distribution of elements (Cu, Ag, Pd, Au) and the TEM image analyzed in FIG. 6 to match the plating layer structure The distribution can be confirmed (FIG. 7 (a)). The components were displayed in the form of a line to indicate that the content was high or low (FIG. 7 (b)).

8 is a result of analyzing the distribution according to the components of each layer using elemental component analysis mapping for the plating layer of Example 2; Quantitative analysis of the elements included in each plating layer was carried out through mapping with the elemental component analysis (EDS) method analyzed in FIG. 7, and the contents of Au, Pd, and Ag were schematically indicated from the left below. As a result, it was confirmed that the Ag/Pd composite plating layer was divided into a Pd-rich region and an Ag-rich region.

Looking at the solder joint evaluation results of No. 10 in Example 1, the solder pool strength after reflow was slightly lowered to 400 g before reflow and 390 g after reflow 5 times, but showed a good level. In addition, in the case of wire bonding evaluation, it was 11 g before heat treatment, 9.5 g after 5 reflows, and 8 g after heat treatment (175 ° C., 16 hours). Although the pull strength was lower than before heat treatment, it showed a good value.

On the other hand, in the case of Comparative Example 1, in which only 0.1 μm of the gold plating layer was formed without forming the silver plating layer and the palladium plating layer, the solder bonding strength and the wire bonding value during reflow and heat treatment were abruptly decreased, probably because there is no copper diffusion barrier layer during heat treatment. In addition, in the case of Comparative Example 2, in which only the gold plating layer was formed by 0.5 μm, the solder bonding strength and wire bonding value during reflow and heat treatment after heat treatment were relatively gently decreased, but the economic feasibility was inferior because the gold plating layer had to be formed as thick as 0.5 μm. .

In Comparative Example 3, in which a palladium plating layer of 0.1 μm and a gold plating layer of 0.1 μm was formed without forming a silver plating layer, the solder bonding strength and wire bonding value after 5 reflows showed relatively good values, but the heat treatment (175° C., 16 time), it was confirmed that the wire bonding value rapidly decreased. This is thought to be because the diffusion of copper could not be completely prevented with the palladium plating layer alone without the silver plating layer.

Also, in Comparative Example 4, in which a silver plating layer of 0.3 μm and a gold plating layer of 0.1 μm was formed, the solder bonding strength and wire bonding value were sharply decreased after 5 reflows, and the wire bonding value after heat treatment (175° C., 16 hours) was also sharp. It was confirmed that there was a significant decrease. This is considered to be because the diffusion of copper could not be prevented with the silver plating layer alone without the palladium plating layer.

In addition, in Comparative Example 5, in which a silver plating layer of 0.3 μm and a palladium plating layer of 0.1 μm was formed, the wire bonding bondability was low after plating because there was no gold plating layer having good bondability with the wire, and after heat treatment (175° C., 16 hours) No wire bonding. This means that the role of the uppermost gold plating layer is essential to secure wire bonding reliability.

From the above, it can be confirmed from the results of this Example and Comparative Example that, when the silver plating layer and the palladium plating layer are present together, excellent mounting reliability can be ensured only by forming a thin gold plating layer.

Claims (14)

a copper layer formed on a printed circuit board;
a silver plating layer formed on the copper layer and including a silver component;
a palladium plating layer formed on the silver plating layer and including a palladium component;
a silver-palladium composite plating layer interposed between the silver plating layer and the palladium plating layer, in which the silver component and the palladium component are mixed; and
a gold plating layer formed on the palladium plating layer and including a gold component;
The silver plating layer and the palladium plating layer are formed by a substitution plating method, and the gold plating layer is formed by a reduction plating method, wherein the palladium component of the silver-palladium composite plating layer has a concentration gradient in which the concentration increases toward the top, and the silver The component and the palladium component are present in a weight ratio of 1:0.2 to 2, the thickness of the gold plating layer is 0.02 to 0.3 μm, and the total thickness of the plating layer plated on the copper layer is controlled to 0.5 μm or less , a high-density printed circuit board with a plating layer. delete delete According to claim 1,
A high-density printed circuit board with a plating layer having a thickness of 0.01 to 2.0 μm of the silver plating layer. According to claim 1,
The palladium plating layer has a thickness of 0.005 to 1.0 μm, a high-density printed circuit board having a plating layer formed thereon. According to claim 1,
The gold plating layer has a thickness of 0.005 to 1.0 μm, a high-density printed circuit board having a plating layer formed thereon. delete a copper layer formed on a printed circuit board;
a silver plating layer formed on the copper layer and including a silver component;
a silver-palladium composite plating layer formed on the silver plating layer and in which the silver component and the palladium component are mixed; and
a gold plating layer formed on the silver-palladium composite plating layer and including a gold component;
The silver plating layer and the silver-palladium composite plating layer are formed by a substitution plating method, and the gold plating layer is formed by a reduction plating method, and the palladium component of the silver-palladium composite plating layer has a concentration gradient that increases toward the top , the silver component and the palladium component are present in a weight ratio of 1:0.2 to 2, the thickness of the gold plating layer is 0.02 to 0.3 μm, and the total thickness of the plating layer plated on the copper layer is controlled to be 0.5 μm or less A high-density printed circuit board with a plating layer formed thereon. delete (a) pre-processing a printed circuit board on which a predetermined circuit pattern is formed;
(b) plating a silver plating layer including a silver component on the copper layer of the printed circuit board by a substitution plating method;
(c) plating a palladium plating layer including a palladium component on the silver plating layer by a substitution plating method; and
(d) plating a gold plating layer including a gold component on the palladium plating layer by a reduction plating method;
A silver-palladium composite plating layer is formed by mixing the silver component and the palladium component by plating the palladium plating layer, and the palladium component of the silver-palladium composite plating layer has a concentration gradient in which the concentration increases toward the top, The silver component and the palladium component are present in a weight ratio of 1:0.2 to 2, the thickness of the gold plating layer is 0.02 to 0.3 μm, and the total thickness of the plating layer plated on the copper layer is controlled to be 0.5 μm or less A method for manufacturing a high-density printed circuit board having a phosphorus and plating layer formed thereon. delete delete delete delete

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