METAL PARTICLE, PASTE, FORMED ARTICLE, AND LAMINATED ARTICLE

Abstract

Aiming at providing a metal particle, an electro-conductive paste, a formed article, and a laminated article that are able to form a highly reliable and high-quality electric interconnect, an electro-conductive bonding portion, or a three-dimensional structure that is less likely to produce the Kirkendall void, this invention discloses a metal particle which include an outer shell and a core part, the outer shell including an intermetallic compound and covering the core part.

Claims

1. A metal particle comprising an outer shell and a core part, the core part containing a metal or an alloy; the outer shell comprising an intermetallic compound, and covering the core part; the core part containing Sn or a Sn alloy; and the outer shell containing an intermetallic compound of Sn and Cu.

2. An electro-conductive paste comprising a metal particle and a vehicle, the metal particle containing the metal particle described in claim 1, and being dispersed in the vehicle.

3. A formed article containing a metal particle, the metal particle containing the metal particle described in claim 1.

4. A laminated article having a laminated structure of a first layer and a second layer, the first layer containing the metal particle described in claim 1; and the second layer configuring a heat conductive layer or an electro-conductive layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG. 1 is an electron micrograph showing a metal particle of this invention.

[0032] FIG. 2 is a set of electron micrographs showing cross-sections of the metal particle of this invention, taken by slicing it at regular depths from this side.

[0033] FIG. 3 is a drawing illustrating an exemplary bonding portion formed by the metal particle of this invention.

[0034] FIG. 4 is an SEM image of portion “A” in FIG. 3.

[0035] FIG. 5 is an enlarged view of the SEM image in FIG. 4.

[0036] FIG. 6 is a drawing illustrating a formed article of this invention.

[0037] FIG. 7 is a drawing illustrating inter-metal joining by cold pressure welding.

[0038] FIG. 8 is a drawing illustrating a laminated article of this invention.

[0039] FIG. 9 is a drawing illustrating another example of the laminated article.

[0040] FIG. 10 is a drawing illustrating still another example of the laminated article of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041] FIG. 1 shows an electron micrograph of a spherical metal particle 1 of this invention. The metal particle of this invention may be manufactured by a technique disclosed in JP-B2-4401281. The metal particle 1 is put into practical use in the form of powder, which is an aggregate of the particle.

[0042] The metal particle 1 is composed of an outer shell and a core part, and the core part contains a metal, an alloy, or an intermetallic compound. The outer shell includes an intermetallic compound, and covers the core part. The detail will be explained, referring to a set of electron micrographs shown in FIG. 2. FIG. 2 is a set of electron micrographs showing cross-sections (A) to (F) of the metal particle 1 having a composition of 8% by mass of Cu and 92% by mass of Sn (referred to as 8Cu.92Sn hereinafter), wherein the cross-sections are taken by slicing it at regular depths from this side. FIG. 2(F) shows a cross-section taken so as to contain the diameter.

[0043] Referring now to FIG. 2(F), the metal particle 1 includes an outer shell 101 and a core part 102. The outer shell 101 includes an intermetallic compound of Cu and Sn, represented by Cu.sub.xSn.sub.y. The outer shell 101 is nanometer-thick. The core part 102 contains Sn, Cu, Cu—Sn alloy, or intermetallic compound of Cu and Sn represented by Cu.sub.xSn.sub.y. The intermetallic compound Cu.sub.xSn.sub.y is typically Cu.sub.3Sn or Cu.sub.6Sn.sub.5.

[0044] Of course, the metal particle 1 is selected depending on what kind of product is desired to obtain. For example, for the purpose of forming electric interconnects, or bonding portions for interconnecting semiconductor chips, the metal particle may contain at least one metal element selected from the group consisting of Cu, Al, Ni, Sn, Ag, Au, Pt, Pd, Si, B, Ti, Bi, In, Sb, Ga, Zn, Cr and Co. Also for the purpose of obtaining a three-dimensional structure, the metal particle may contain at least one metal element selected from the group described above.

[0045] As described above, the metal particle 1 of this invention can contain a plurality of metal components. In this case, the plurality of metal components may be a combination of a low-melting-point component and a high-melting-point component, thereby the metal particle is allowed to melt at the melting point of the low-melting-point component in the initial stage of melting, meanwhile the re-melting temperature after solidification may be elevated up to a temperature such that governed by the melting point of the high-melting-point component. For example, the metal particle 1 when configured by 8Cu.92Sn as described above in the embodiment, the metal particle 1 may be allowed to melt principally at the melting point of Sn (231.9° C.) in the initial stage of melting, meanwhile the re-melting temperature after solidification may be elevated up to a temperature such that governed by the melting point of Cu.sub.xSn.sub.y (Cu.sub.3Sn: 676° C., Cu.sub.6Sn.sub.5: 435° C.) which is higher than that of Sn. In this way, a highly heat-resistant, highly reliable, and high-quality bonding portion and a conductor portion may be formed. The metal particle 1 characterized as such is advantageous when intended for use as an electric interconnect and an electro-conductive bonding material for configuring semiconductor devices for power control (power devices) that produce a large amount heat.

[0046] Referring now to FIG. 3, a bonding portion 300 typically joins metal/alloy bodies 201, 501 respectively formed on substrates 200, 500 opposed to each other. The substrates 200, 500 are typically substrates that configure electronic/electric devices such as power devices, on which the metal/alloy bodies 201, 501, in the forms of electrode, bump, terminal or lead conductor, are provided so as to be integrated with the substrates 200, 500. In the electronic/electric devices such as power devices, the metal/alloy bodies 201, 501 are typically composed of Cu or an alloy thereof. Of course, the invention shall not exclude the case where portions corresponded to the substrates 200, 500 are composed of the metal/alloy body.

[0047] As seen in FIG. 4 and FIG. 5, each of the metal/alloy bodies 201, 501 is a Cu layer. The bonding portion 300 may be obtained by using a bonding material that contains 8Cu.92Sn. The bonding portion 300 contains Sn, Cu, Sn—Cu alloy, or an intermetallic compound of Sn and Cu, and is bonded to the surface part of the metal/alloy bodies 201, 501 by way of diffusion.

[0048] When the bonding portion 300 is formed by using a bonding material that contains the metal particle 1, the diffusion between the metal particle 1 and the metal/alloy bodies 201, 501 proceeds through the outer shell as a matter of course. Accordingly, the rates of diffusion of the metals may be suppressed, as compared with the rates shown by the conventional bonding material where the diffusion proceeds between the diffusible metals that are brought into direct contact. As a consequence, unbalanced mutual diffusion such that Sn can diffuse only to a lesser extent than Cu can may be corrected, and thereby the Kirkendall void may be prevented from occurring. In this way, it now becomes possible to form a highly reliable and high-quality electric interconnect, an electro-conductive bonding portion, or a three-dimensional structure that is less likely to cause breakage.

[0049] As a result of such diffusion under the reduced rates of diffusion, a lamellar structure with a nanometer-scale lamellar spacing is formed at the bond interface with each of the metal/alloy bodies 201, 501. The lamellar structure will be explained referring to FIG. 4 and FIG. 5.

[0050] As seen in FIG. 4 and FIG. 5, the bonding portion 300 is configured to have a first layer 301, a second layer 302 and a third layer 303 stacked in this order on the surface of each of the metal/alloy bodies 201, 501. Each of the first layer 301 and the second layer 302 has a lamellar structure that is composed of a layer made of an intermetallic compound and a layer made of a metal matrix. Referring now to FIG. 5, mountain-like portions seen in the first layer 301 and the second layer 302 are made of an intermetallic compound, and valley-like portions are made of a metal matrix.

[0051] In this structure, the first layer 301 that adjoins the metal/alloy bodies 201, 501, namely the Cu layers, will have a lamellar structure that contains a Cu-rich intermetallic compound mainly composed of Cu.sub.3Sn, and a metal matrix. The second layer distal to the metal/alloy bodies 201, 501, namely the Cu layers, will have a lamellar structure that contains an intermetallic compound mainly composed of Cu.sub.6Sn.sub.5, and a metal matrix.

[0052] In short, the bonding portion 300 can combine heat resistance under high temperatures attributable to the intermetallic compound, and flexibility attributable to the metal matrix. The bonding portions can therefore keep high levels of heat resistance, bonding strength and mechanical strength over a long duration of time, even if the devices were kept operated at high temperatures for a long duration of time, or were used under harsh environments such as exposed to large temperature changes from operational states at high temperatures down to idle states at low temperatures.

[0053] Since the lamellar structure has a lamellar spacing of nanometer scale, so that the Kirkendall void, even if it should occur, will be restricted within a narrow range. The Kirkendall void will, therefore, not grow up into cracks or other serious defects capable of degrading the reliability and quality of the bonding portion or the three-dimensional structure, further degrading the mechanical strength, and causing separation, breakage, chipping or the like.

[0054] For reference, the present inventors have obtained test results from our high temperature storage (HTS) test at 260° C., that the shear strength of the bonding portion 300 increased from approximately 35 MPa up to approximately 40 MPa over the period from the start of test up to approximately 100 hours after, and was stabilized at around 40 MPa over the period up to 500 hours after.

[0055] The present inventor have also obtained test results from our thermal cycle test (TCT) over the range from −40 to 200° C., that the shear strength stabilized approximately at 30 MPa over the entire cycles (1000 cycles), after at around the 200th cycle and thereafter.

[0056] In order to obtain the results described above, at least 50% or more of the surface area of the core part need be covered with the outer shell, in the metal particle 1 of this invention. Good results may be obtained preferably when 70% or more, and more preferably when 80% or more of the surface area is covered with the outer shell.

[0057] The electro-conductive paste of this invention contains a plurality of metal components. The electro-conductive paste is prepared typically by dispersing a powder containing the above-described metal particle 1 of this invention into a vehicle. The vehicle is typically an organic vehicle, and is used in combination with an organic solvent. Not only typical organic vehicles, but also an aqueous vehicle or a volatile organic vehicle may occasionally be used.

[0058] The electro-conductive paste of this invention, configured to contain the metal particle 1 of this invention, inherits characteristics and advantages originated from the metal particle 1.

[0059] FIG. 6 and FIG. 7 illustrate a formed article 6 of this invention. The formed article 6 illustrated in FIG. 6 has a sheet form. The formed article 6 may alternatively have the form of chip or long part, and may still alternatively be a wire with a circular cross-section or a wire with an elliptic cross-section. In short, the formed article 6 may have an arbitrarily selectable form.

[0060] The formed article 6 of this invention may be obtained typically by cold pressure welding by which a powder containing the above described metal particle 1 of this invention is allowed to join by way of inter-metal joining. A variety of methods of the inter-metal joining per se, effected by cold pressure welding, have been known, and such known methods may be applied to this invention. FIG. 7 illustrates a typical example of application. As seen in FIG. 7, a powder 4 that contains the metal particle of this invention is fed between pressure welding rollers 31, 32 that rotate in counter directions R1, R2, and pressurized by the pressure welding rollers 31, 32, to thereby allow the metal particle composing the powder 4 to cause inter-metal joining. In the practical treatment, the powder 4 is preferably heated at around 100° C. through the pressure welding rollers 31, 32. In this way, the formed article 6 illustrated in FIG. 6 and FIG. 7 may be obtained.

[0061] Inside the formed article 6 of this invention, obtained by cold pressure welding by which the powder containing the metal particle of this invention is allowed to join by way of inter-metal joining, the metal particle of this invention and other particles keep their original internal structures almost unchanged, despite some changes found in their external forms. Accordingly, the formed article 6 of this invention inherits characteristics and advantages originated from the metal particle 1 of this invention.

[0062] FIG. 8 to FIG. 10 illustrate the laminated article of this invention. Referring now to FIG. 8, a laminated article 7 illustrated here has a laminated structure of a first layer 701 and a second layer 702. The first layer 701 is the formed article 6 of this invention, and is typically the sheet-like article illustrated in FIG. 6.

[0063] The second layer 702 configures a heat conductive layer or an electro-conductive layer. Specific examples may include a layer mainly composed of Cu, and a layer mainly composed of Cu and carbon nanotube (CNT).

[0064] The laminated article 7 of this invention may be configured as illustrated in FIG. 9, by providing the first layer 701, that is the formed article 6 of this invention, on both surfaces of the second layer 702, or, may be formed as illustrated in FIG. 10, by laminating an arbitrary number of the articles illustrated in FIG. 8 and FIG. 9.

[0065] Since the laminated article 7 of this invention has the first layer 701 and the second layer 702 laminated thereon, and since the first layer 701 contains the metal particle 1 of this invention, so that the laminated article 7 inherits characteristics and advantages originated from the metal particle 1 of this invention. As a consequence, by using the laminated article 7, it now becomes possible to form a highly reliable and high-quality electric interconnect and electro-conductive bonding portion having high mechanical strength and high heat resistance, and being less likely to produce the Kirkendall void.

[0066] The laminated article 7 of this invention, configured to have the second layer 702 that is laminated to the first layer 701 and configures a heat conductive layer or an electro-conductive layer, can efficiently transfer heat or can transmit electric signals, from the first layer 701 having the Kirkendall void suppressed therein, to the second layer 702 that serves as a heat conductive layer or an electro-conductive layer. The laminated article is advantageous when intended for use as an electro-conductive bonding material or an electric interconnect for configuring power devices that produce a large amount heat.

[0067] This invention has been detailed above referring to some preferred embodiments by which this invention by no means limited. It is apparent that those skilled in the art can contemplate a variety of modifications based on the basic technical spirit and teaching of this invention.

[0068] As has been described above, this invention can provide a metal particle, a paste, a formed article, and a laminated article that are able to form a highly reliable and high-quality electric interconnect, an electro-conductive bonding portion, or a three-dimensional structure that is less likely to produce the Kirkendall void.

[0069] This invention can also provide a metal particle, a paste, a formed article, and a laminated article that are able to form a highly heat-resistant, highly reliable and high-quality electric interconnect, an electro-conductive bonding portion, or a three-dimensional structure.