JP2004056020A - Electrode structure and method for forming it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode structure in which high reliability is maintained even for an element with a large number of electrodes and high electrode density, etc. <P>SOLUTION: This electrode structure has a nickel plating layer for performing joining by soldering. Solid particles insoluble in a plating liquid are dispersed in the nickel plating layer. Even when tin comes from a soldering layer, the solid particles act as a physical barrier, and diffusion into the nickel plating layer is inhibited. Thereby formation of a layer with rich tin in the nickel plating layer is also inhibited. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention generally relates to a technical field for electrically connecting a semiconductor element, a circuit board, and the like, and particularly to an electrode structure having a nickel plating layer for solder bonding.
[0002]
[Prior art]
In this type of technical field, for example, it is widely practiced to bond electrodes of a semiconductor element and electrodes on a circuit board by soldering.
[0003]
FIG. 1 shows an example of an electrode structure of a semiconductor element. An electrode base conductor 11 made of, for example, aluminum is formed on a substrate 10 made of, for example, silicon. A resin 12 such as polyimide is coated on the silicon substrate 10 at a portion other than the electrode base conductor (wiring layer) 11. I have. A seed layer 13 made of titanium or copper is formed by a sputtering method or the like at a place where the electrode base conductor 11 is to be electrically connected. Using this seed layer 13, nickel electroplating is performed, a nickel plating layer 14 is formed, and a gold plating layer 15 is formed thereon. On the gold plating layer 15, a solder ball 16 for making an electrical connection is provided. The solder is made of tin-lead solder or lead-free solder, and generally, lead-free solder has a higher melting point than tin-based solder.
[0004]
FIG. 2 shows an example of the electrode structure of the circuit board. A polyimide resin layer 21 is formed on a ceramic substrate 20 made of, for example, alumina, and an electrode base conductor 22 made of, for example, copper is formed on the resin layer 21. The resin layer 21 is also formed on the electrode base conductor 22 and patterned into a predetermined shape, and an opening is provided at a place where electrical connection is to be made. After patterning the resin layer 21, a nickel plating layer 23 is formed by electroless plating, and a gold plating film 24 is formed thereon by electroless plating. The formation of nickel or gold by electroless plating is due to the advantageous property of electroless plating that does not require an external power supply or a current-carrying film (seed layer).
[0005]
When connecting the electrode structures as shown in FIGS. 1 and 2, a flux is applied to the electrodes on the circuit board 20 side, the solder balls 16 (elements having) are fixed on the electrodes, and overheated in a reflow furnace. To join.
[0006]
By the way, with the recent miniaturization of electronic devices, it is desired that semiconductor elements such as integrated circuits (IC) and large-scale integrated circuits (LSI) have higher performance, higher speed, higher density, and the like. ing. In addition to an increase in the number of electrodes and a reduction in the pitch between electrodes, thermal stress and the like of the element also increase, and the use environment becomes severe. For this reason, there has been a concern about defective bonding between the electrode and the solder, and furthermore, destruction (cracking) of the bonded portion.
[0007]
When the electrodes are connected by solder, a material in the solder material (particularly, tin (Sn) which is active with respect to solid phase diffusion) and an electrode constituent material (gold, nickel, phosphorus, etc.) are solid-phased at the joint. Diffuses by diffusion to form metal compounds. This solid phase diffusion is caused not only by heat treatment at the time of soldering but also by temperature cycling during use. As a result, very brittle metal compound to the joint portion (for _{example, AuSn, Au 4 Sn, Ni} 3 Sn 4, Ni 3 P , etc.) is formed and leads to bonding failure or breakdown at the interface. In particular, in an electrode having an electroless nickel plating layer, phosphorus (P) is used as a catalyst for performing electroless plating. However, when tin is combined with nickel by solid phase diffusion, phosphorus is converted into phosphorus in the nickel plating layer. Since a rich layer (P-rich layer) is formed and the phosphorus-rich layer is hard and brittle, there is a concern that cracks may occur at the interface. Furthermore, since the lead-free solder used more and more in the future has a higher melting point than the tin-lead-based solder, a higher temperature heat treatment is required, and there is a concern that the solid phase diffusion of tin or the like may be promoted.
[0008]
[Problems to be solved by the invention]
A general object of the present application is to provide an electrode structure capable of maintaining high reliability even for a large element such as the number of electrodes and the electrode density, and to provide a method of forming the electrode structure. is there.
[0009]
A specific object of the present application is to provide an electrode structure capable of suppressing solid phase diffusion between a constituent material of an electrode formed by electroless plating and solder, and a method for forming the electrode structure. To provide.
[0010]
[Means for Solving the Problems]
According to the solution according to the present invention, in the electrode structure having a nickel plating layer for performing bonding by solder, solid particles insoluble in a plating solution are dispersed in the nickel plating layer. An electrode structure is provided.
[0011]
According to another solution according to the present invention, there is provided a method for forming a nickel plating layer having an electrode structure by an electroless plating method, in which solid particles insoluble in the plating solution are dispersed by stirring the plating solution. A method of forming a nickel plating layer having an electrode structure, comprising: performing plating while plating; and performing plating in a state where the solid particles settle in the plating solution.
[0012]
[Action]
In the research that forms the basis of the present invention, the present inventors disperse predetermined solid particles in a nickel plating solution and perform electroless plating using phosphorus as a catalyst. However, it has been found that this can suppress the solid phase diffusion in question.
[0013]
FIG. 3 is a conceptual diagram for explaining the principle of the present invention. The nickel plating layer 32 and the solid particles 33 dispersed in the nickel plating layer 32 are shown. A gold plating layer 34 is formed on the nickel plating layer 32, and a solder layer 35 is formed on the gold plating layer 34. Unlike the conventional case, solid particles 33 are dispersed and interposed in the nickel plating layer 32. Even if tin (Sn) (not shown) arrives from the solder layer 35 by solid-phase diffusion, the solid particles 33 are prevented from becoming a physical obstacle and proceeding into the nickel plating layer 32. . Therefore, the formation of a layer rich in phosphorus in the nickel plating layer 32 is also suppressed. Even if tin diffuses through the gaps between the solid particles 33 to form a compound with nickel in the nickel plating layer 32, a phosphorus-rich layer is not formed continuously as in the conventional case. In addition, the reliability of the joint is kept high.
[0014]
A given solid particle is selected based on several criteria:
First, it is necessary that it is difficult to diffuse into solder and electrode constituent materials. Since a substance having a high melting point is less likely to be diffused than a substance having a low melting point, a substance having a high melting point is preferable.
[0015]
Second, it must be difficult to form an alloy with tin.
[0016]
Third, it must be difficult to dissolve in the plating solution. This is because, when the nickel plating layer is formed by electroless plating, composite plating or dispersion plating (precipitation of solid particles as well as nickel) can be performed.
[0017]
Based on such a criterion, a powder made of a metal such as tungsten (W), titanium (Ti), or molybdenum (Mo) can be employed as the solid particles. Also, a metal carbide such as tungsten carbide (WC) or silicon carbide (SiC), a metal nitride such as titanium nitride (TiN), or a metal oxide such as aluminum oxide (Al ₂ O ₃ ) It is also possible to employ a ceramic powder composed of However, it should be noted that if a substance having no conductivity is introduced too much, the electrical resistance of the connection may be increased.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 4 is a schematic configuration diagram of a dispersion plating apparatus 400 for producing an electrode structure according to the present embodiment. “Dispersion plating” indicates that not only nickel but also solid particles are dispersed in the plating solution. The dispersion plating apparatus 400 has a plating tank 404 filled with a plating solution 402 and a water bath 406 for accommodating the plating tank 404 to maintain the plating tank 404 at a predetermined temperature. In the plating tank 404, a ceramic substrate 401 having an electrode structure to be plated is provided. As the plating solution 402, an electroless Ni-P plating solution (6401M, manufactured by Meltex Co., Ltd.) is used, and solid particles 408 such as tungsten carbide (WC) are dispersed in the plating solution. . By rotating the stirrer 410 in the plating solution 402, the solid particles 408 in the plating solution 402 are dispersed. The temperature of the plating solution 402 is detected by a temperature sensor 412, and the temperature information is notified to a temperature controller 414. Consequently, the plating solution 402 is maintained at a desired temperature.
[0019]
The electrode structure according to this embodiment is generally formed as follows. First, the ceramic substrate 401 is fixed in the plating solution 402 by the holder 418 (plating jig). Then, for example, plating is performed for 30 minutes while rotating the stirrer 410 to disperse the solid particles (here, WC) in the plating solution 402. Thereby, a Ni-P plating layer on which solid particles are precipitated as shown in FIG. 3 is obtained. The film thickness is, for example, 5 μm. In this way, not only nickel but also solid particles are precipitated (eutectoid), so this plating can be called “composite plating”.
[0020]
Next, the stirrer 410 is stopped. As a result, the solid particles 408 settle at the bottom of the plating solution 402. In this state, for example, plating is performed for 5 minutes. Thereby, the Ni-P plating layer on which the solid particles are deposited is covered with the Ni-P layer on which the solid particles are not deposited. The solid particles 408 have a property of hardly diffusing into solder or the like, which means that the solder wettability is poor. From the viewpoint of good soldering, it is preferable that the solid particles 408 are not exposed. Therefore, the plating is performed while stopping the stirring.
[0021]
When the nickel plating is completed, the substrate 401 is washed with water to prepare for electroless gold plating. The plating of gold is performed by immersing in a substitution reaction type electroless Au plating solution (for example, OPC Mudengold manufactured by Okuno Pharmaceutical Co., Ltd., PH 5.8, liquid temperature 90 ° C.) for, for example, 10 minutes. Thereby, a gold layer having a thickness of, for example, 0.05 μm is formed on the nickel plating layer. Gold plating is performed to maintain good solder wettability. (If an oxide film is formed on the exposed nickel, the wettability will deteriorate.) Thus, the electrode structure according to the present embodiment is formed.
[0022]
Hereinafter, examples based on experiments performed by the inventors of the present application will be described.
[0023]
(Example 1)
An electrode structure (ceramic substrate) having an electroless nickel plating layer in which WC is codeposited using a bath in which 5% by weight of tungsten carbide (WC) powder is dispersed in a Ni-P plating solution by the above method. And a semiconductor element having a tin-lead (Sn-Pb) eutectic solder ball. Flux was applied to the electrode structure of the ceramic substrate, solder balls of the semiconductor element were positioned on the electrodes, and solder reflow at a peak temperature of 230 ° C. was performed. The connection resistance of the formed connection was sufficiently small at 50 to 60 mΩ, and a good resistance value was obtained.
[0024]
Next, a reliability evaluation test was performed by repeating reflow under the same conditions as the mounting conditions five times. Specifically, the junction cross section was observed with an EPMA (Electron Probe Micro Analyzer). For comparison, a similar test was performed on an electrode having a conventional Ni-P plating layer in which tungsten carbide (WC) was not eutectoid.
[0025]
As a result, in the conventional bonding portion, a thick Sn-Ni compound layer is formed on the substrate-side electrode (electrode with an electroless nickel plating layer), and under this compound layer, a phosphorus (P) -rich Ni- A P-rich layer was formed, and it was confirmed that cracks occurred at this interface. On the other hand, in the electrode according to the embodiment of the present invention in which WC was deposited, a Sn-Ni compound layer was observed in the gap between the eutectoid WCs, but the thickness was much thinner than the conventional one. There were no cracks.
[0026]
(Example 2)
The same experiment as in Example 1 was performed except that the solid particles were changed to tungsten (W), but no crack occurred as in Example 1.
[0027]
(Example 3)
An electrode structure (ceramic substrate) having an electroless nickel plating layer in which SiC is codeposited using a bath in which 5% by weight of silicon carbide (SiC) powder is dispersed in a Ni-P plating solution; A semiconductor element having a solder ball of 0.5% Ag was bonded. A flux was applied to the electrode structure of the ceramic substrate, solder balls of the semiconductor element were positioned on the electrodes, and solder reflow at a peak temperature of 250 ° C. was performed.
[0028]
This sample was also subjected to the same reliability evaluation test as in Example 1. For comparison, a joint portion between a conventional ceramic substrate having an electroless Ni-P plating layer and a semiconductor element having Sn-3.5% Ag solder balls was also formed.
[0029]
As a result, a Sn-Ni compound layer thicker than that of the comparative sample of Example 1 was formed at the conventional joint portion, and was directly under this compound layer and was richer in phosphorus (P) than that of Example 1. A Ni-P rich layer was formed. On the other hand, in the electrode according to the embodiment of the present invention in which SiC was eutectoid, no crack occurred as in the case of the first embodiment.
[0030]
As described above, according to the embodiment of the present invention, since solid phase diffusion between the constituent material of the electrode formed by electroless plating and the solder is suppressed, high reliability can be achieved even for a device having a large number of electrodes and a high electrode density. It is possible to maintain.
[0031]
According to the embodiment of the present application, since the solid particles insoluble in the plating solution are dispersed in the nickel plating layer, the formation of a brittle alloy layer is suppressed, and a highly reliable electrode structure can be provided. become.
[0032]
According to the invention of the embodiment of the present application, since the formation of an alloy related to a catalyst (for example, phosphorus (P)) used in electroless plating is suppressed, the use of electroless plating that is simpler than electrolytic plating is promoted. Becomes possible. Although the present invention does not exclude application to a nickel plating layer of electroplating, it is better to apply the present invention to an electroless nickel plating layer than to apply it to a nickel plating layer of electroplating. Many effects can be obtained. When the present invention is applied to both electrodes joined by solder, it becomes possible to more effectively suppress the solid phase diffusion of the electrode constituent material or the solder.
[0033]
According to the embodiment of the present application, after plating while stirring the plating solution containing solid particles, plating is performed without stirring, so that an electrode structure having good wettability while suppressing solid phase diffusion of electrode constituent materials and the like. It becomes possible to obtain.
[0034]
In the embodiment of the present application, the case where the electrode of the circuit board and the electrode of the semiconductor element are soldered has been described as an example, but the present invention is not limited to this, and is widely applied to the soldering of an electrode structure having a nickel plating layer. It is possible.
[0035]
Hereinafter, means taught by the present invention will be listed.
[0036]
(Supplementary Note 1) An electrode structure having a nickel plating layer for bonding by solder, wherein solid particles insoluble in a plating solution are dispersed in the nickel plating layer.
[0037]
(Supplementary Note 2) The electrode structure according to Supplementary Note 1, wherein the nickel plating layer is formed by an electroless plating method.
[0038]
(Supplementary note 3) The electrode structure according to supplementary note 1, wherein the solid particles are made of a metal, a metal oxide, a metal carbide, or a metal nitride.
[0039]
(Supplementary Note 4) In the electrode structure according to Supplementary Note 1, the solid particles may include tungsten (W), titanium (Ti), molybdenum (Mo), tungsten carbide (WC), silicon carbide (SiC), and titanium oxide. An electrode structure made of (TiO ₂ ) or aluminum oxide (Al ₂ O ₃ ).
[0040]
(Supplementary Note 5) The electrode structure according to supplementary note 1, wherein the solid particles are made of two or more kinds of substances.
[0041]
(Supplementary Note 6) The electrode structure according to Supplementary Note 1, wherein the solid particles are also dispersed in the nickel plating layer on the electrode side bonded to the nickel plating layer by solder.
[0042]
(Supplementary Note 7) The electrode structure according to Supplementary Note 1, wherein a gold plating layer is formed on the nickel plating layer.
[0043]
(Supplementary Note 8) A method of forming a nickel plating layer having an electrode structure by an electroless plating method,
A step of performing plating while dispersing insoluble solid particles in the plating solution by stirring the plating solution,
A method for forming a nickel plating layer having an electrode structure, comprising: performing plating in a state where the solid particles settle in the plating solution.
[0044]
【The invention's effect】
As described above, according to the present invention, it is possible to maintain high reliability even for an element having a large number of electrodes and an electrode density.
[0045]
[Brief description of the drawings]
FIG. 1 is a sectional view of an electrode structure of a semiconductor device.
FIG. 2 shows a sectional view of an electrode structure of a circuit board.
FIG. 3 is a conceptual diagram for explaining the principle of the present invention.
FIG. 4 is a schematic configuration diagram of a dispersion plating apparatus for producing an electrode structure according to an embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 10 silicon substrate 11 electrode base conductor 12 resin layer 13 seed layer 14 nickel plating layer 15 gold plating layer 16 solder ball 20 ceramic substrate 21 resin layer 22 electrode base conductor 23 nickel plating layer 24 gold plating layer 32 nickel plating layer 33 solid particles 34 Gold plating layer 35 Solder layer 400 Dispersion plating apparatus 401 Ceramic substrate 402 Plating solution 404 Plating bath 406 Water bath 408 Solid particles 410 Stirrer 412 Temperature sensor 414 Temperature controller 416 Heater 418 Holder

Claims (5)

An electrode structure having a nickel plating layer for bonding by solder, wherein solid particles insoluble in a plating solution are dispersed in the nickel plating layer. The electrode structure according to claim 1, wherein the nickel plating layer is formed by an electroless plating method. The electrode structure according to claim 1, wherein the solid particles are made of a metal, a metal oxide, a metal carbide, or a metal nitride. 2. The electrode structure according to claim 1, wherein said solid particles are also dispersed in a nickel plating layer of an electrode bonded to said nickel plating layer by soldering. A method for forming a nickel plating layer having an electrode structure by an electroless plating method,
A step of performing plating while dispersing insoluble solid particles in the plating solution by stirring the plating solution,
A method for forming a nickel plating layer having an electrode structure, comprising: performing plating in a state where the solid particles settle in the plating solution.

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