KR19990048003A - Metal bump manufacturing method - Google Patents

Abstract

The present invention relates to a method for manufacturing a metal bump using an electroless plating method, the metal bump manufacturing method is a protective film in all areas except the central portion of the pad on the substrate where a plurality of pads are formed in a predetermined area of the upper surface Is formed; Surface-activating the upper surface of the central portion of the pads to form an active surface layer; Forming a copper plating layer on the upper surface of the active surface layer by using an electroless plating method in which a substrate is immersed in a bath containing a copper plating solution and then taken out, and left for a predetermined time; Stacking a mask on which a plurality of openings having a size corresponding to the size of the pad are formed on the substrate and aligned and fixed to the position of the pad; The metal paste is pushed by the squeegee in the opening of the mask to be transferred; And forming the metal paste into the metal bumps by a reflow process. The present invention provides a method for forming a barrier film and forming a metal bump thereon by a simple method of immersing and removing a substrate in a bath containing a plating solution without the need for a separate expensive plating apparatus, thereby providing a simple process and a low manufacturing cost. Since the bumps can be manufactured, there is an advantage of increasing the efficiency of the process.

Description

Method for manufacturing metal bump

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor metal bump, and more particularly, to a manufacturing method of forming a metal bump on a pad of a substrate such as a printed circuit board or a semiconductor wafer by using an electroless plating method.

In accordance with the trend of lighter and shorter electronic devices, packaging technology for mounting semiconductor chips is also required to be equipped with high speed, high performance, and high density. In response to these demands, a ball grid array (BGA) package, a chip scale package (CSP), and the like, which package semiconductor chips in a minimal space, have recently emerged.

As a method of electrically connecting a semiconductor element to a circuit board, the connection system by wire bonding which connects both pads with a metal wire is common. As the number of input / output terminals of a semiconductor device increases with respect to such a connection method, a tape automated bonding (TAB) method and a flip chip method are used as methods for increasing connection density or improving characteristics of a semiconductor device. It is proposed and put to practical use. The wire bonding method connects a semiconductor chip and a substrate through a metal lead frame and a metal wire, whereas the tap method and the flip chip method implement electrical connection only through metal bumps. At this time, the metal bumps may be directly formed on the bonding pads of the semiconductor element substrate in the wafer state, or may be formed on the electrode pads of the circuit board to mediate electrical connection with the main substrate.

The metal bumps may be formed by using a wire ball, by attaching a metal ball, by evaporation, or by electroplating.

An electroplating method will be described as an example of a method of forming a conventional metal bump.

1A and 1B are cross-sectional views schematically showing a method of forming a metal bump on a substrate by a conventional electroplating method.

1A and 1B, the substrate 10 includes a top surface on which a plurality of pads 16 are installed and a circuit pattern (not shown) connecting the pads 16 to each other. A protective film 12 for protecting a circuit pattern (not shown) is formed on the entire upper surface of the substrate 10 except for the pad 16 of the substrate 10. The substrate 10 includes a printed circuit board (PCB), a ceramic substrate, a glass substrate, and a semiconductor device substrate which are commonly used. Here, in order to distinguish a printed circuit board, a ceramic board, and a glass board from a semiconductor element board | substrate, it defines as a circuit board. Next, a barrier layer 13 is formed on the passivation layer 12 including the pads 16. The blocking film 13 is formed by depositing titanium tungsten / copper (TiW / Cu) by sputtering. When the substrate 10 corresponds to a circuit board, that is, a printed circuit board, a ceramic substrate, and a glass substrate, the pad 16 formed on the substrate 10 is defined as an electrode pad to distinguish the pad formed on the semiconductor element substrate. In the case of forming the metal bumps 17 on the semiconductor device substrate, the substrate 10 of FIGS. 1A and 1B corresponds to a semiconductor device substrate, the pad 16 corresponds to a bonding pad of a semiconductor chip, and the blocking layer 13 corresponds to a passivation layer. do.

Next, a photoresist layer (not shown) is formed on the top surface of the blocking film 13, and a photoresist layer (not shown) formed on the top surface of the pad 16 is exposed and developed to remove the photoresist layer (not shown). The metal paste 15 is plated by the electroplating method on the portion of which is removed). Here, the blocking film 13 serves to conduct electricity to allow the metal to be plated on the pad 16 in the electroplating process. The electroplating method is a method of forming a plating layer on a surface of a material to be plated by connecting an electrode to a material to be plated and a plating solution to electrolyze the plating solution.

The metal paste 15 is formed of a super hemisphere metal bump 17 through a reflow process. When the photoresist layer (not shown) and the blocking layer 13 formed outside the metal bumps 17 are removed, the process of manufacturing the metal bumps 17 is completed.

By the way, the manufacturing method of the metal bump 17 enumerated above including the electroplating method has the following problems.

The electroplating method has to go through complicated processes such as photographing, plating, and etching, and the manufacturing cost of metal bumps 17 is expensive, and the method of using wire ball bonding requires a dedicated facility for cutting wires and has low productivity. There is this. In the method using the metal balls, the mounting of the metal bumps 17 is relatively simple while the process of manufacturing the metal balls is complicated and expensive. In addition, when the metal bumps 17 are formed by deposition, there is a problem in that an expensive evaporator must be used.

It is therefore an object of the present invention to provide a method for producing metal bumps with a simple process and low manufacturing cost.

1A is a cross-sectional view showing a metal bump manufacturing method by an electroplating method in a metal bump manufacturing method according to an embodiment of the prior art;

1B is a cross-sectional view showing a state in which metal bumps are formed on a substrate by an electroplating method;

2A is a cross-sectional view showing a state in which a protective film is formed on a substrate except for a central portion of a pad in the method of manufacturing a metal bump according to an embodiment of the present invention;

2B is a cross-sectional view showing a state in which an active surface layer is formed on the pad of FIG. 2A;

FIG. 2C is a cross-sectional view showing a state in which a blocking film of a copper plating layer is formed on an active surface layer by dipping a substrate into a bath containing a copper plating solution and taking it out;

FIG. 2D is a cross-sectional view showing a state in which the mask in which the opening is formed is aligned and fixed so that the blocking film is placed in the opening and the metal paste is pushed into the squeegee to transfer the metal paste to the opening;

2E is a cross-sectional view showing a state in which a metal bump is formed by removing a mask and reflowing the metal paste;

3A to 3G are cross-sectional views illustrating a metal bump manufacturing method according to still another embodiment of the present invention.

<Description of Main Parts of Drawings>

10,20,40: substrate 12,22,42: protective film

34,44 mask 14 photoresist

15,35,45: Metal paste 16,26,46: Pad

17,27,47: metal bump 28: active surface layer

48: first active surface layer 49: second active surface layer

29: squeegee 30: copper plating layer

50: first barrier 52: second barrier

13; Barrier

In order to achieve the above object, the present invention provides (a) a protective film in all regions except for the central portion of the pads on a substrate in which a plurality of pads and a circuit pattern for electrically connecting the pads to each other are formed in a predetermined region of the upper surface. Is formed; (b) surface activation on the top surface of the central portion of the pads to form an active surface layer; (c) forming a copper plating layer on the upper surface of the active surface layer by immersing the substrate in a copper plating solution and then leaving it out for a predetermined time; (d) stacking a mask on which a plurality of openings having a size corresponding to the size of the pad are formed on the substrate and aligned and fixed to the position of the pad; (e) the metal paste is transferred to the squeegee by the opening of the mask and transferred; (f) Provided is a metal bump manufacturing method, wherein the metal paste is formed into a metal bump by a reflow process.

Hereinafter, with reference to the accompanying drawings will be described in detail an embodiment of the present invention.

2A to 2E are cross-sectional views illustrating a step of forming a metal bump according to an embodiment of the present invention.

Referring to FIG. 2A, the substrate 20 includes a plurality of pads 26 and a circuit pattern (not shown) connecting the pads 26 with each other. A protective film 22 is formed on the entire surface of the substrate 20 except for the center portion of the pad 26 to protect a circuit pattern (not shown). The protective film 22 is a dielectric layer such as a silicon oxide layer. Here, the substrate 20 includes a printed circuit board, a ceramic substrate, a glass substrate, and a semiconductor element substrate as in the prior art, and when the substrate 20 corresponds to a circuit board, that is, a printed circuit board, a ceramic substrate, and a glass substrate, The pad 26 formed on the substrate 20 is defined as an electrode pad to distinguish it from the pad 26 when the substrate 20 corresponds to a semiconductor element substrate, and the pad formed on the semiconductor element substrate is defined as a bonding pad. do.

Referring to FIG. 2B, an active surface layer 28 is formed by subjecting the center portion of the pad 26 to a surface activation treatment. In order to implement the electroless plating method according to the present invention, it is necessary to first perform a surface activation treatment, for example, a zincate treatment, on the central portion of the pad 26 as a prior work. The zinc gating treatment is a treatment in which an acidic solution containing zinc ions is added to adsorb zinc ion groups on the surface of the pad 26 and make the surface of the pad 26 rough, thereby increasing the surface area to be plated.

Referring to FIG. 2C, the blocking film 30 is formed on the active surface layer 28 formed by jinating using an electroless plating method. In the embodiment of the present invention, the blocking film 30 is formed by using electroless plating, and metal bumps (not shown) are formed on the blocking film 30. The electroless plating method is a plating method that uses an oxidation / reduction reaction to remove metal ions from the metal to be plated, unlike the electroplating method using electrolysis. In an embodiment of the present invention, a copper plating layer is formed of the blocking film 30. In more detail, when the substrate 20 is immersed in a bath (not shown) containing copper plating solution and then left out for a predetermined time, the copper plating solution does not cause an oxidation / reduction reaction with the protective film 22 which is a dielectric layer. Since the zinc ion groups are adsorbed on the active surface layer 28, copper exchanges electrons and bonds on the surface, thereby exclusively forming a copper plating layer only on the active surface layer 28. In addition, a copper plating layer may be formed on a portion of the protective film 22 along the circumference of the active surface layer 28, depending on the degree of bonding of the copper plating layer and the active surface layer 28.

Referring to FIG. 2D, after the mask 34 having the opening is aligned on the substrate 20 so that the pad 26 is placed in the opening 31, the metal paste 35 is opened by the screen printing method. Is transferred). The mask 34 has an opening 31 formed at a position corresponding to the pad 26 of the substrate 20, and is typically formed of a metal or resin material. The opening 31 should have a larger area than the pad 26. The reason for this is that when the reflow of the metal paste 35 reduces its volume due to evaporation of the flux, the amount of the metal paste 35 transferred through the opening 31 is the metal bump (not shown) produced. This is because it must be larger than the volume of. The screen printing method is a method of transferring the metal paste 35 to the opening 31 of the mask 34 by pushing a solder paste 35 with the squeegee 29.

In more detail, first, the positions of the pads 26 of the substrate 20 and the openings 31 of the mask 34 are aligned, and the metal paste 35 is applied to the upper surface of the mask 34. When the metal paste 35 is pushed using the squeegee 29, the metal paste 35 is extruded through the opening 31 to be transferred onto the pad 26.

Referring to FIG. 2E, the mask (34 of FIG. 2D) is removed and then reflowed. After reflow, the mask (34 in FIG. 2D) is removed to form a metal bump 27 on the pad 26. The metal paste (35 in FIG. 2D) is typically composed of 50% each of the metal particle component forming the metal bumps 27 and the flux component combining the particle components. However, after the reflow process, the volume of the metal bumps 27 formed by evaporation of the flux component is reduced by about half compared to the amount of the initial metal paste (35 in FIG. 2D). Therefore, the opening of the mask (34 in FIG. 2D) should be wider than the pad (31 in FIG. 2D). As the metal particles of the metal paste (35 in FIG. 2D), solder having a low melting point and good wettability is mainly used. Solder is commonly used alloy of 95% lead (Pb) and 5% tin (Sn). Although the reflow process is different depending on the type of solder, it is a process of forming a metal bump 27 by melting the solder to maintain a predetermined time at about 330 ° C. to form a liquid state. The solder in the liquid state has good wettability with the metal component of the barrier film 30, and has poor wettability with the protective film 22, which is a dielectric material, and thus the metal paste (35 in FIG. 2D) formed outside the barrier film 30 has good wettability. Move up to form a super hemisphere metal bump 27.

Another embodiment of the present invention will be described with reference to the accompanying drawings.

3A to 3G, the method of manufacturing the metal bumps 47 according to another embodiment of the present invention is shown in FIGS. 2A to 2E except for forming the blocking films 50 and 52. Same as the example. As the first barrier film 50, barrier films 50 and 52 having a two-layer structure of a nickel-phosphorus (Ni-P) plating layer and a second barrier film 52 and a nickel-boron (Ni-B) plating layer formed thereon are formed. . Since the nickel-phosphorus plating layer is plated faster than the nickel-boron plating layer, the nickel-phosphorus plating layer is formed thicker than the nickel-boron plating layer, for example, about 15 µm and the nickel-boron plating layer is about 5 µm. The nickel-boron plating layer formed on the nickel-phosphorus plating layer has an advantage of maintaining excellent wettability with the metal paste 45 even after being left for a long time.

In more detail, the passivation layer 42 is formed on the surface of the substrate 40 except for the central portion of the pad 46. The upper surface of the central portion of the pads 46 is then surface activated to form the first active surface layer 48. Forming a nickel-phosphorus plating layer as the first barrier layer 50 on the first active surface layer 48 by immersing the substrate 40 in a bath (not shown) containing nickel-phosphorus plating solution and then leaving it for a predetermined time; Thereafter, the surface of the nickel-phosphorus plating layer is subjected to surface activation to form a second active surface layer 49. Subsequently, the substrate 40 is immersed in a bath (not shown) containing a nickel-boron plating solution and then left out for a predetermined time to form a nickel-boron plating layer, which is the second blocking film 52, on the second active surface layer 49. A mask 44 having a plurality of openings 51 having a size corresponding to the size of the pad 46 is laminated on the upper surface of the substrate 40 and aligned and fixed to the position of the pad 46. Next, the metal paste 45 is pushed and transferred to the squeegee 59 through the opening 51 of the mask 44, and finally, the metal paste 45 is formed of the metal bumps 47 by a reflow process to form the metal bumps. (47) The manufacturing method is completed.

As described above, according to the present invention, the metal bumps are formed by a simple process and a low manufacturing cost by forming a metal bump by a simple electroless plating method, in which a substrate is immersed in a bath containing a plating liquid and removed, without the need for a separate expensive plating apparatus. Since it can be manufactured, there is an advantage to increase the efficiency of the process.

Claims (13)

(a) forming a protective film on all regions except for the central portion of the pads on a substrate on which a plurality of pads and a circuit pattern for electrically connecting the pads are formed in a predetermined area of the upper surface; (b) surface-activating the upper surface of the central portion of the pads to form an active surface layer, (c) forming a copper plating layer on the upper surface of the active surface layer by immersing the substrate in a bath containing a copper plating solution and then leaving it out for a predetermined time; (d) A mask having a plurality of openings having a size corresponding to the size of the pad is stacked on the upper surface of the substrate, aligned and fixed to the position of the pad, and then the metal paste is pushed and transferred by the squeegee to the opening of the mask. Steps and, (e) wherein said metal paste is formed into a metal bump by a reflow process. The method of claim 1, wherein the substrate is a printed circuit board. The method of claim 2, wherein the pad is an electrode pad. The method of claim 1, wherein the substrate is a semiconductor device substrate. The method of claim 4, wherein the pad is a bonding pad. The method of claim 1, wherein the surface activation treatment adds a zinc solution to a central portion of the pad to adsorb ionic groups on the surface of the pad that can cause an oxidation or reduction reaction with the metal component of the barrier membrane. Method for producing a metal bump, characterized in that. (a) forming a protective film on all regions except the center of the pads on a substrate having a plurality of pads formed in a predetermined area of an upper surface thereof; (b) surface-activating the upper surface of the central portion of the pads to form a first active surface layer, (c) forming a nickel-phosphorus plating layer as a first barrier film on the active surface layer by immersing the substrate in a bath containing a nickel-phosphorus plating solution and then leaving it for a predetermined time; (d) surface-activating the surface of the first barrier layer to form a second active surface layer, (e) forming a nickel-boron plating layer as a second barrier layer on the second active surface layer by immersing the substrate in a bath containing a nickel-boron plating solution and then leaving it for a predetermined time; (f) A mask having a plurality of openings having a size corresponding to the size of the pad is stacked on the upper surface of the substrate, aligned and fixed to the position of the pad, and then the metal paste is pushed and transferred by the squeegee to the opening of the mask. Steps, and (g) The metal bump manufacturing method, characterized in that the metal paste is formed into a metal bump by a reflow process. 8. The method of claim 7 wherein the substrate is a printed circuit board. The method of claim 8, wherein the pad is an electrode pad. 8. The method of claim 7, wherein the substrate is a semiconductor device substrate. The method of claim 10, wherein the pad is a bonding pad. 8. The surface activation process according to claim 7 (b) or (d), wherein the surface activation treatment is an ion group capable of adding a zinc solution to cause an oxidation or reduction reaction with a metal component of the barrier membrane. The metal bump manufacturing method characterized by adsorb | sucking on the surface of a phosphorus plating layer. The method of claim 7, wherein in the steps (c) and (e), the first barrier layer is about 15 μm, and the second barrier layer is about 5 μm thick.