Electroless surface treatment plated layers of printed circuit board and method for preparing the same

Abstract

An electroless surface treatment plated layer of a printed circuit board, a method for preparing the same, and printed circuit board including the same. The electroless surface treatment plated layer includes: electroless nickel (Ni) plated coating/palladium (Pd) plated coating/gold (Au) plated coating, wherein the electroless nickel, palladium, and gold plated coatings have thicknesses of 0.02 to 1 μm, 0.01 to 0.3 μm, and 0.01 to 0.5 μm, respectively. In the electroless surface treatment plated layer of the printed circuit board, a thickness of the nickel plated coating is specially minimized to 0.02 to 1 μm, thereby making it possible to form an optimized electroless Ni/Pd/Au surface treatment plated layer.

Claims

1. A printed circuit board, comprising: an electroless surface treatment plated layer, wherein the electroless surface treatment plated layer comprises nickel (Ni) plated coating, palladium (Pd) plated coating, and gold (Au) plated coating, and wherein the nickel plated coating, the palladium plated coating, and the gold plated coating each have a thickness of 0.02 to 1 μm, 0.01 to 0.3 μm, and 0.01 to 0.5 μm, respectively.

2. The printed circuit board according to claim 1, wherein it is connected to external devices in a wire bonding scheme.

3. The printed circuit board according to claim 1, wherein 8 wt % or more of phosphorus (P) is contained in the electroless nickel plated coating.

4. The printed circuit board according to claim 3, wherein the phosphorus (P) is to prevent oxidation of the electroless nickel plated coating.

5. The printed circuit board according to claim 1, wherein even though a frequency band increases, an electrical resistance value of the electroless surface treatment plated layer does not increase.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B are, respectively, a cross-sectional view and a top view when a plated layer and a device are connected to each other using the wire-bonding scheme according to the related art;

(2) FIG. 2 is a scanning electron microscope (SEM) photograph of electroless Ni/Pd/Au surface treatment metal layer formed on a Cu layer according to the related art;

(3) FIG. 3 is a view showing a structure of electroless Ni/Pd/Au surface treatment metal layer according to an exemplary embodiment of the present invention; and

(4) FIG. 4 is a SEM photograph of electroless Ni/Pd/Au surface treatment metal layer formed on a Cu layer according to an exemplary embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) Hereinafter, the present invention will be described in more detail.

(6) Terms used in the present specification are for explaining the embodiments rather than limiting the present invention. Unless explicitly described to the contrary, a singular form includes a plural form in the present specification. The word “comprise” and variations such as “comprises” or “comprising,” will be understood to imply the inclusion of stated constituents, steps, operations and/or elements but not the exclusion of any other constituents, steps, operations and/or elements.

(7) The present invention relates to an electroless surface treatment plated layer of a printed circuit board including nickel (Ni) plated coating/palladium (Pd) plated coating/gold (Au) plated coating formed on a connection terminal in an electroless plating scheme, wherein the electroless nickel, palladium, and gold plated coatings have thicknesses of 0.02 to 1 μm, 0.01 to 0.3 μm, and 0.01 to 0.5 μm, respectively.

(8) FIG. 3 shows a structure of electroless Ni/Pd/Au surface treatment plated layer of a printed circuit board according to an exemplary embodiment of the present invention. Referring to FIG. 3, a polymer resin layer 120 is formed at a portion except for a copper layer 110 in a printed circuit board to thereby subsequently serve as a resist to plating, and electroless Ni plated coating 131/Pd plated coating 132/Au plated coating 133 are formed as a plated layer 130 using an electroless plating method in order to protect the copper layer 110.

(9) According to the exemplary embodiment of the present invention, in order to overcome a disadvantage of the scheme according to the related art, a thickness of the nickel plated coating 131 is reduced, thereby making it possible to maximally suppress an increase in resistance generated at the time of an increase in frequency, which is a problem according to the related art.

(10) The nickel plated coating 131 of the electroless surface treatment plated layer according to the exemplary embodiment of the present invention may have a thickness of 0.02 to 1 μm. When the nickel plated coating has a thickness exceeding 1 μm, a Ni layer having high electrical resistance has a relatively thick thickness, such that an improvement effect of electrical characteristics is low in a high frequency band. In addition, when the nickel plated coating has a thickness less than 0.02 μm, a problem such as deterioration of corrosion resistance, or the like, is generated.

(11) After the electroless nickel plated coating 131 is formed, the electroless palladium (Pd) plated coating 132 is plated on the nickel plated coating. The electroless Pd plated coating 132 serves to suppress a phenomenon in which an electrochemically active Ni layer is reacted and corroded with Au at the time of immersion Au or electroless Au plating. The electrode palladium plated coating according to the exemplary embodiment of the present invention may have a thickness of 0.01 to 0.3 μm. When the electroless palladium (Pd) plated coating has a thickness exceeding 0.3 μm, the cost increases.

(12) Finally, in the electroless surface treatment plated layer, after the electroless palladium plated coating 132 is formed, the electroless gold (Au) plated coating 133 is plated on the electroless palladium plated coating. The electroless Au plated coating 133 serves to prevent oxidation to thereby maintain wire bonding characteristics. The electroless gold plated coating according to the exemplary embodiment of the present invention may have a thickness of 0.01 to 0.5 μm. When the electroless Au plated coating has a thickness exceeding 0.5 μm, the cost increases.

(13) The electroless Ni/Pd/Au surface treatment plated layer 130 formed as described above may be connected to external devices in a wire bonding scheme using a gold (Au) wire.

(14) In addition, 8 wt % or more of phosphorus, and preferably, 9 to 11 wt % of phosphorus is contained in the electroless nickel plated coating 131. The phosphorus is to prevent oxidation of the electroless nickel plated coating. When relatively high wt % of phosphorus is contained in the electroless nickel plated coating, the oxidation of the electroless nickel plated coating may be effectively prevented.

(15) According to an exemplary embodiment of the present invention, a printed circuit board including the electroless surface treatment plated layer may be provided.

(16) In the case of the printed circuit board including the electroless surface treatment plated layer according to the exemplary embodiment of the present invention, even though a frequency band increases, an electrical resistance value of the electroless surface treatment plated layer does not increase. The thickness of the nickel layer forming the electroless surface treatment plated layer is minimized, thereby making it possible to basically solve a problem in which even through the frequency band increases, a current flows in the surface treatment plated layer. Therefore, a problem in which the flow of the current is concentrated only on the surface layer caused by the skin effect in the related art is solved, thereby making it possible to allow the current to uniformly flow.

(17) Further, embodiment of in the printed circuit board according to the exemplary the present invention, plated layers formed as the electroless surface treatment plated layer may have a space of 25 μm or less therebetween.

(18) A method for forming an electroless surface treatment plated layer of a printed circuit board according to an exemplary embodiment of the present invention will be described. The method for forming an electroless surface treatment plated layer of a printed circuit board includes forming an electroless surface treatment plated layer by sequentially forming nickel (Ni) plated coating/palladium (Pd) plated coating/gold (Au) plated coating, wherein the electroless nickel, palladium, and gold plated coatings have thicknesses of 0.02 to 1 μm, 0.01 to 0.3 μm, and 0.01 to 0.5 μm, respectively.

(19) Nickel, palladium, and gold plating solutions configuring the electroless surface treatment plated layer according to the exemplary embodiment of the present invention is not specifically limited but may be any solution generally used in the art. In addition, a specific plating method is also not specifically limited but conforms to a general level.

(20) However, the electroless surface treatment plated layer according to the exemplary embodiment of the present invention needs to be plated so that the electroless nickel, palladium, and gold plated coatings have thicknesses of 0.02 to 1 μm, 0.01 to 0.3 μm, and 0.01 to 0.5 μm, respectively.

(21) Particularly, as the nickel plating solution, hypophosphite is generally used, and phosphorus is contained in a precipitated coating. The phosphorus (P) may effectively serve to prevent the oxidation of the Ni plated coating. Therefore, 8 wt % or more of phosphorus (P), and preferably, 9 to 11 wt % of phosphorus (P) is contained in the electroless nickel plated coating 131 according to the exemplary embodiment of the present invention.

(22) Two methods may be used in order to allow the electroless nickel plated coating according to the exemplary embodiment of the present invention to contain the above-mentioned phosphorus content. One method is a method of lowering a pH of the electroless nickel plating solution. In the case of the widely used NPR-4 agent available from Uyemora & Co., Ltd, a nickel plating solution has a pH of 4.5 to 4.7. However, in the case of the present invention, the pH of the nickel plated coated is reduced to 4.2 to 4.4 to thereby maintain a phosphorus content at a relatively high level.

(23) The other method is a method of reducing a content of a sulfur compound additive added to the electroless nickel plating solution to thereby control a phosphorus content in the electroless nickel plated coating to be in the above-mentioned range. That is, the content, or the like, of the sulfur compound such as Thio Urea is lowered, thereby making it possible to allow the electroless nickel plated coating to have a desired level of phosphorus content.

(24) According to the exemplary embodiment of the present invention, the electroless gold plated coating may be formed in a substitution/reduction type. In addition, a substitution type of immersion gold plated coating layer may be formed. When the electroless gold plated coating is formed in a general substitution type, a corrosion hole is formed in densely formed electroless Ni and Pd plated coatings to thereby deteriorate the ability to prevent the diffusion of the copper. However, when the electroless gold plated coating is formed in the substitution/reduction type, a substitution reaction is directly performed in an early stage of a reaction. Therefore, the Ni and Pd plated coatings are not attacked, thereby making it possible to obtain a plated layer having a dense structure. However, a substitution type of Au, which may be easily managed and is inexpensive, may also be used.

(25) Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings. However, this example is only to illustrate the present invention and is not to be construed as limiting a scope of the present invention.

Example 1

(26) 1) Electroless Ni Plating

(27) A substrate subjected to pretreatment was immersed in an electroless Ni plating solution (pH: 4.2 to 4.4, NPR-4: a product available from Uyemora & Co., Ltd) allowing 10 wt % of phosphorus to be contained in a plated coating at a temperature of 65 t for 1 minute and then cleaned for 2 minutes to thereby obtain an electroless nickel plated coating having a thickness of 0.1 μm.

(28) 2) Electroless Pd Plating

(29) The substrate subjected to the electroless Ni plating was immersed in XTP (pH: 7.2, a product available from Uyemora & Co., Ltd), which is an electroless Pd plating solution, at a temperature of 50° C. for 10 minutes and then cleaned for 2 minutes to thereby obtain an electroless palladium plated coating having a thickness of 0.1 μm.

(30) 3) Electroless Au Plating

(31) The substrate subjected to the electroless Ni plating and the electroless Pd plating was immersed in an electroless gold plating solution (GoBright TSB-72, a product available from Uyemora & Co., Ltd) at a temperature of sot for 5 minutes, cleaned for 2 minutes, and then dried at a temperature of 150 t for 5 minutes by a ventilation drier to thereby obtain electroless nickel/palladium/gold plated layer in which an electroless gold plated coating having a thickness of 0.1 μm is formed.

(32) 4) Wire Bonding

(33) The electroless nickel/palladium/gold surface treatment plated layer and external devices were connected to each other by a gold wire.

Comparative Example 1

(34) Electroless nickel/palladium/gold plated layer was obtained through the same process as that of Example 1 except that an electroless nickel plated coating having a thickness of 5 μm is formed.

Experimental Example

(35) Cross-sectional photographs of the electroless nickel/palladium/gold plated layers obtained according to Example and Comparative Example were observed by a scanning electron microscope (SEM). Results of the observation were shown in FIGS. 2 and 4.

(36) Referring to FIG. 2, in the case of the nickel/palladium/gold plated layer according to the related art, it may be appreciated that the nickel plated coating has a significant thick thickness. In this case, a current flows in the nickel layer of the plated layer while mainly flowing along a surface in a high frequency band, thereby causing a problem that electrical resistance increases due to a skin effect in which the current mainly flows in the nickel layer rather than an inner layer of copper wiring.

(37) However, referring to FIG. 4 showing a cross-sectional photograph of the electroless nickel/palladium/gold surface treatment plated layer prepared according to the exemplary embodiment of the present invention, it may be appreciated that the nickel plated coating has a thickness almost similar to those of the palladium and gold plated coatings. Therefore, it is possible to solve the problem that the electrical resistance increases in the high frequency band due to a thick thickness of the nickel plated coating according to the related art. Therefore, it is possible to improve electrical characteristics of the printed circuit board including the electroless nickel/palladium/gold surface treatment plated layer.

(38) With the electroless surface treatment plated layer of the printed circuit board according to the exemplary embodiment of the present invention, the thickness of the nickel plated coating is specially minimized to 0.02 to 1 μm, thereby making it possible to form an optimized electroless Ni/Pd/Au surface treatment plated layer.

(39) In addition, with the electroless surface treatment plated layer of the printed circuit board according to the exemplary embodiment of the present invention, the thickness of the nickel coating is significantly reduced, thereby making it possible to reduce a phenomenon in which a current flows in the nickel layer having high electrical resistance caused by the skin effect phenomenon in which the current flows along a surface in a high frequency band when the electroless surface treatment plated layer is connected to the external devices in the wire bonding scheme, such that the electrical resistance increases and the electrical signal characteristics are deteriorated. That is, the thickness of the nickel coating is significantly reduced to allow a more current to flow in the cu layer having low electrical specific resistance in the high frequency band, thereby making it possible to improve the electrical characteristics.

(40) In addition, with the electroless surface treatment plated layer of the printed circuit board according to the exemplary embodiment of the present invention, the nickel coating has a thin thickness, thereby making it possible to suppress generation of an electrical bridge due to undesired abnormal Ni plating generation between pattern spaces at the time of the electroless nickel plating on the copper plated layer having a pattern space of 25 μm or less.

(41) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Accordingly, such modifications, additions and substitutions should also be understood to fall within the scope of the present invention.