1. A palladium-based ternary or higher alloy, comprising:
- (a) palladium at about 45-55 wt %;
(b) copper at about 32-42 wt %;
(c) silver at about 8-15 wt %;
(d) rhenium at about 1.1-5 wt %; and
wherein the alloy exhibits a second phase of rhenium,wherein the alloy has a Pd;
Cu ratio of about 1.05 to 1.6 by weight,wherein the alloy has a Pd;
Ag ratio of about 3 to 6 by weight, andwherein a heat-treated electrical conductivity of the alloy exceeds 19.5% IACS.
Palladium-based ternary or higher alloys include palladium at about 45-55 wt %, copper about 32-42 wt %, silver at about 8-15 wt %, rhenium at about 0-5 wt %, and optionally one or more modifying elements at up to 1.0 wt %. The alloys are age-hardenable, provide hardness in excess of 350 HK (Knoop, 100 g load), have electrical conductivities above 19.5% IACS (International Annealed Copper Standard), have an elevated temperature strength above 100 ksi at temperatures up to 480° F. (250° C.), and remain ductile (tensile elongation>2%) in their fully age-hardened condition. The alloys may be used in static and moveable electrical contact and probe applications.
- 1. A palladium-based ternary or higher alloy, comprising:
(a) palladium at about 45-55 wt %; (b) copper at about 32-42 wt %; (c) silver at about 8-15 wt %; (d) rhenium at about 1.1-5 wt %; and wherein the alloy exhibits a second phase of rhenium, wherein the alloy has a Pd;
Cu ratio of about 1.05 to 1.6 by weight,
wherein the alloy has a Pd;
Ag ratio of about 3 to 6 by weight, and
wherein a heat-treated electrical conductivity of the alloy exceeds 19.5% IACS.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
- 11. A semiconductor probe comprising a palladium-based ternary or higher alloy, the alloy comprising:
(a) palladium at about 45-55 wt %; (b) copper at about 32-42 wt %; (c) silver at about 8-15 wt %; and (d) rhenium at about 1.1-5 wt %; wherein the alloy exhibits a second phase of rhenium, wherein the alloy has a Pd;
Cu ratio of about 1.05 to 1.6 by weight,
wherein the alloy has a Pd;
Ag ratio of about 3 to 6 by weight, and
wherein a heat-treated electrical conductivity of the alloy exceeds 19.5% IACS.
- View Dependent Claims (12, 13, 14)
- 15. A palladium-based ternary or higher alloy, consisting of:
(e) palladium at about 45-55 wt %; (f) copper at about 32-42 wt %; (g) silver at about 8-15 wt %; (h) rhenium at about 1.1-5 wt %; (i) up to 1.0 wt % modifying elements selected from the group consisting of;
ruthenium, zirconium, gallium, and zinc; and
(e) optionally, one or more impurities.
- View Dependent Claims (16, 17, 18, 19, 20)
This application is a continuation of pending U.S. patent application Ser. No. 15/010,690, filed Jan. 29, 2016, the disclosure of which is incorporated by reference in its entirety.
The present disclosure relates to noble metal alloys composition, probes comprising the noble metal alloy compositions and methods of producing such probes.
In the field of semiconductor manufacturing there is a continuing demand for smaller device sizes (i.e., higher transistor counts per unit area) and increased processing power (i.e., faster processing speeds).
Because of their desirable resistance to oxidation, the use of precious metal alloys for stationary and moveable or sliding electrical contacts as well as test probes enjoys widespread use for applications such as slip ring brushes, semiconductor probes, potentiometric sensors, etc. For the past 60 years, Paliney™ 7 has been recognized as the benchmark alloy for applications requiring excellent oxidation resistance and formability in its fully age hardened condition. However its electrical conductivity is very low, being only about 5.5% IACS.
U.S. Pat. No. 5,833,774 to Klein et al. discloses compositions of silver/palladium/copper alloys which are used in such applications and describes a range of noble metal alloys, which when heat treated, can offer a range of hardness levels with electrical conductivity in a range of 12-16% IACS. Even though commercial alloys consistent with this teaching (Paliney™ H3C and Paliney™ C) have conductivity values are nearly three times that of Paliney 7 (see Table 2), they still fall short of the desired current-carrying capacity of many new applications. For example, for integrated circuit (IC) test probes with diameters below 100 microns, current levels that can be successfully used remain below 2 Amps because of excessive electrical heating (“New Generation of Probe Alloys”, Smith, et. al., IEEE SW Test Workshop, June, 2013). Another shortcoming of alloys within this family is their difficulty in being formed into complex, highly toleranced shapes when in the fully age-hardened condition.
U.S. Pat. No. 6,210,636 to Klein discloses a low cost silver/palladium/copper/nickel/zinc high strength alloy suitable for sliding electrical contact applications. However, because this alloy was developed to reduce its noble metal content and resultant cost by increasing its nickel and zinc content, its oxidation resistance is poor in comparison to alloys having higher noble metal contents. Additionally, for these alloys, the overall conductivity is generally below 10% IACS (Paliney™ 5, DNI website)
Although alloys in the Pd—Cu—Ag family have been studied since the 1950'"'"'s (Raub and Worwag, Z. Metallkd., 1955, 46, 52-57), most of the published work has focused on documenting the possible phase relationships and establishing the effect of ordering on the electrical properties of the alloys. As shown in
Palladium/copper alloy systems have also been subjects of technical papers and articles. A. Yu. Volkov, in “Improvements to the Microstructure and Physical Properties of Pd—Cu—Ag Alloys,” examined and reported on a range of compositions for the ternary alloy system. Volkov examined the effect of adding silver to a palladium-copper alloy with the primary focus on improving tensile strength. Although this work shows a positive impact on strength, as illustrated in Volkov, all the Ag additions also act to increase the resistivity, e.g., going to a resistivity of roughly 8.5 micro-ohm cm (20.3% IACS) for the Pd—Cu binary alloy going from a resistivity of roughly 11 micro-ohm cm (15.6% IACS) for an alloy with 12 at % Ag. This work does not present any significant understanding regarding how to simultaneously optimize both the mechanical and electrical properties.
Additionally, U.S. Pat. No. 7,354,488 introduces the use of Re in conjunction with other elements such as B, Ni and Ru to increase the strength of high Pd content wrought alloys. In the absence of the synergistic influence of these complementary elements, the data suggests it takes Re levels of at least 10% to reach hardness levels over 300 HK. These alloys typically have very low electrical conductivity values in the 5-8% IACS level. In these systems where the Pd levels are usually above 75 wt %, the Re is thought to be a solid solution strengthening agent and not participate on a second phase or ordering reaction. Re is also occasionally used as a grain refining additive in dental casting alloys, but at very low concentrations, typically below 0.5%.
According to certain implementations, ternary or higher noble metal alloy comprise palladium, copper, silver and optionally rhenium.
According to certain implementations, a palladium-based ternary or higher alloy includes (a) palladium at about 45-55 wt %; (b) copper at about 32-42 wt %; (c) silver at about 8-15 wt %; (d) rhenium at about 0-5 wt %; and (e) up to 1.0 wt % modifying elements selected from the group consisting of: ruthenium, zirconium, gallium, and zinc. The alloy may have a Pd:Cu ratio of about 1.05 to 1.6 by weight, and a Pd:Ag ratio of about 3 to 6 by weight.
According to certain implementations, the alloy may be provided as or in a probe. According to such implementations, the probe may be configured as a Cobra probe, a cantilever probe, a vertical probe, or a pogo pin probe.
In some implementations and alternatives, the palladium in the alloy is present at about 51-55 wt %, the copper is present at about 32-40 wt %, the silver is present at about 8.5-14 wt %, and the rhenium is present at about 1.1-3 wt %. In some implementations and alternatives, rhenium may be replaced with zinc and may be present at about 0.2-0.7 wt %.
The alloy may have a heat-treated electrical conductivity that exceeds 19.5% IACS; may have a heat-treated hardness of the alloy is at least 350 Knoop; may exhibit a second phase of rhenium; may be free of one or more of: nickel, chromium, gold, platinum and boron, or iron; when age-hardened, may maintain a yield strength above 100 ksi at about 60° F. to about 450° F.; and/or when age-hardened, may have a tensile elongation of greater than 2%.
In the field of test probes, as device sizes decrease, the discrete space on each device available for being contacted by electrical test probes also decreases. At the same time, the increased processing power requires that the test probes carry higher test currents and thereby accommodate higher test temperatures. The result of these requirements is that: 1) test probe diameters must become smaller to ensure they can accurately be placed on the test pads, 2) the increase in test current coupled with the reduced probe diameter creates the requirement for improved electrical conductivity of the test probe material to avoid the danger of probe overheating and failure, 3) as the test temperatures rise, the alloys must exhibit good strength retention throughout the current rise sequence to avoid premature softening and failure during touch down and wipe, and 4) enhanced ductility is needed to allow extensive forming in the aged condition to ensure the tight dimensional tolerances needed in these miniature components.
Since power dissipation, or heating of the probe, is directly related to its electrical resistance, where:
power dissipated,in Watts=(probe current,in amperes)2×(probe resistance,in Ohms)
it is readily apparent that probe heating is directly proportional to its resistance, and that reducing the test probe'"'"'s resistance or increasing its electrical conductivity is a critical means to allow the operation of smaller diameter test probes at reasonable temperatures with increased current demands.
Moreover, in addition to lowering the bulk resistance of the probe wire, it is also imperative to maintain a low contact resistance during repeated touchdown of the probe on to the IC surface. This interfacial resistance is controlled by the normal force exerted on the probe at touchdown and the degree of wipe imposed after initial contact. In order to ensure consistent performance, the probe design must ensure that the overall loads remain in the elastic region through the test cycle. Therefore, under increased current density associated with using smaller diameter probes, it is important that the probe wire not exceed its yield strength at elevated temperatures to prevent softening, gram force reduction and eventually premature failure.
Additionally, the alloys must resist any oxidation that could increase probe-device contact resistance. The oxidation resistance of noble metal alloys is well known, while the particular advantages of palladium based noble metal alloys are universally recognized.
In view of these objectives, provided herein are palladium-based alloys which provide electrical conductivity in excess of 19.5% IACS, maintain hardness above 350 HK0.1 in order to provide wear resistance, and provide oxidation resistance. The alloys include a yield strength in excess of 100 ksi at temperatures up to 480° F. Sufficient ductility in the fully age-hardened condition enables the palladium-based alloy to be formed into finished test probes or electrical contacts, while eliminating the need for post-forming age hardening, thus avoiding attendant risks of thermal distortion of precision formed shapes during said aging treatment.
Further, and in contrast to prior approaches which do not recognize a correlation between an alloy system'"'"'s palladium to copper and palladium to silver ratios as they relate to alloy hardenability and electrical conductivity, it has been discovered that a range of an alloy'"'"'s Pd:Cu ratio achieves both aged hardness and electrical conductivity of a Pd/Cu ternary or higher alloy. In addition, it has been discovered that a range of Pd:Ag ratios in such alloys may further facilitate achieving suitable hardness and conductivity levels.
Accordingly, implementations provide Pd-based alloys having alloying additions of copper and silver with Pd:Cu and Pd:Ag ratios which provide increased electrical conductivity and sufficient hardness to meet the demands required of current test probes. Particularly, we have found that by properly controlling both the Pd:Cu and Pd:Ag ratios, it is possible to create age hardenable Pd alloys that combine high electrical conductivity, high hardness and excellent elevated temperature properties. Although the phase diagram of
The palladium-based alloys of the present disclosure are ternary or higher alloys. Alloying additions may include copper (Cu), silver (Ag) and/or rhenium (Re). Tables 1 and 2 provide alloy compositions, Pd:Cu and Pd:Ag ratios, and alloy properties of exemplary alloys of the present disclosure. These include any, any combination of, or all of Alloys 1907, 1941, 1910, 1900, 1904, 1859, 1948, 1929, 1933, 1937, 1943, 1930, 1934, 1938, 1935, 1912, 1936, 1931 and 1928.
The alloys may include palladium at about 45-55 wt %, about 45-50 wt %, about 47-55 wt %, about 50-55 wt %, about 50-54 wt % or about 51-55 wt %.
Copper may be present in the alloys at about 30-45 wt %, about 30-40 wt %, about 32-40 wt %, about 32-42 wt %, about 35-45 wt %, or about 36-43 wt %.
Silver may be present in the alloys at about 8-25 wt %, about 8-20 wt %, about 8-16 wt %, about 8-15 wt %, about 8-14 wt %, about 8.5-14 wt %, about 8-13 wt %, about 8-12 wt %, about 8-11 wt %, about 9-15 wt %, about 9-14 wt %, about 9-13 wt %, about 9-12 wt %, about 9-11 wt %, or about 8-10 wt %.
Rhenium may be present in the alloys at about 0-5 wt %, about 0.5-5 wt %, about 0.5-4.5 wt %, about 0.5-4 wt %, about 0.5-3.5 wt %, about 0.5-3.0 wt %, about 1.1-3.0 wt %, about 0.5-2.5 wt %, about 0.5-2.0 wt %, or about 0.5-1.5 wt %.
Zinc may be present in the alloys at about 0-3 wt %, about 0.1-1.0 wt %, about 0.2-0.7 wt %, about 0.5-3 wt %, about 1.0-3.0 wt %, or about 0.5-1.5 wt %.
The palladium-based alloys may additionally include up to about 1 percent of modifying elements including ruthenium, zirconium, gallium, and zinc.
The alloys of the present disclosure may consist exclusively of the specifically recited elements, such that the alloys are in a substantially pure form. For instance, where palladium is present in at least 50 wt % of the alloy, palladium makes up the remainder of the recited alloys, to the exclusion of all other (non-recited) substituents. Alternatively, it is to be understood that the presently recited palladium-based alloys may also comprise other substituents as well as those specifically recited, as may advantageously be desired. The recited alloys may also contain various impurities and other small amounts of matter, but in such amounts so as not to effect the advantageous properties of the inventive alloys. Preferably, such trace amounts of material will be present in less than 1000 ppm.
The alloys of the present disclosure may be free of nickel, chromium, gold, platinum, boron, iron, zinc, gallium and bismuth, as well as any other elemental addition. With respect to at least nickel, chromium, gold, platinum, boron, iron, these may be excluded from the disclosed alloys as being harmful to either or both electrical conductivity or aged hardness. For instance, Alloy 1856 is a Pd—Cu—Ag alloy with an alloying addition of Nickel, which results in a significant drop in conductivity (11.3 IACS) and has reduced properties compared to the Pd—Cu—Ag ternary Alloy 1943 (51.5 Pd-37.5 Cu-10.9 Ag). Alloy 1879 is another Pd—Cu—Ag alloy with an alloying addition of Chromium, which also results in a significant drop in conductivity (7.3 IACS) compared to Alloy 1943. Various trace elements may be present due to their unintentional introduction during casting and processing of the alloy as is well known by those skilled in metal casting and processing.
Alloy Ratios and Properties:
A weight ratio of palladium to copper may be at, or about, 1.05 and up to, or up to about, 1.6 by weight. A weight ratio of palladium to silver may be at, or about, 3 and up to, or up to about, 6 by weight.
The alloy in its fully age-hardened condition may have a hardness of at least 350 HK0.1, electrical conductivity of at least 19.5% IACS, tensile elongation greater than 2% in 2 inches, elevated temperature yield strength at 480° F. of at least 100 ksi.
Turning to the figures,
The discovery that, after age hardening, only one section within the ordered region shown on the palladium copper phase diagram with a specific range of Pd:Cu ratios of about 1.05 and 1.6, yielded a combination of both high hardness and exceptionally high conductivity, was unexpected. Generally, it is assumed that for all compositions within the ordered phase field would yield roughly similar hardness.
Particularly, turning to
In terms of the elevated temperature properties of these alloys, the effect of Re is very strong. As a shown in
An exemplary palladium-based alloy of the present disclosure (Alloy 1938) includes the following nominal composition:
palladium 51.5 wt %,
copper 36.5 wt %,
silver 10.5 wt %,
and rhenium 1.5 wt %.
Based on the composition of the alloy, the palladium to copper and palladium to silver ratios are: Pd:Cu ratio 1.41 by weight, and Pd:Ag ratio 4.9 by weight.
Alloy 1938 has a ductility that enables it to be fabricated into fine wire, with diameters below 0.004 in., using normal in-process anneals and drawn on conventional wire processing equipment. Final annealing of this wire by strand annealing at 900° C. (followed by an immediate water quench) softened the alloy and put it into a disordered condition, which is requisite for subsequent artificial age hardening. It was age hardened by heating it to 710° F. and holding it at that temperature for 90 min. Cooling to room temperature is not rate sensitive and took 1-2 hours. A protective atmosphere was maintained during all thermal treatments. After such annealing and aging heat treatments, the tensile and electrical properties of the 0.004 in. diameter wire fabricated from the alloy were:
The addition of rhenium with heat treatment further enhances ductility and can provide a microstructure suitable for probe tips used in electrical testing. For example, the table below illustrates the effects of initial cold work and heat treat temperature on the mechanical properties and conductivity for Alloy 1938.
Table 1 lists the nominal alloy compositions, Pd:Cu and Pd:Ag ratios of exemplary palladium-based alloys of the present disclosure, while other alloy compositions and ratios are provided for purposes of distinction from the palladium-based alloys of Applicant'"'"'s invention. Table 2 lists the conductivity, hardness, yield strength, and tensile elongation values of these various alloys.
Exemplary uses for the alloys of the present disclosure are in the fields of electrical testing and medical devices. With respect to electrical testing, the alloys may be used in static and moveable electrical contact and probe applications. For instance, the alloys may be included as a component of a probe, a slip ring assembly (either as the ring or brush), or sliding contacts in applications such as a potentiometric sensor. Probes may include electrical probes used in connection with semiconductor testing. Semiconductor test probes may be formed as the alloys of the present disclosure, or the alloys may form a portion of the probe and a probe tip may be coupled thereto. The test probes may be configured as Cobra probes, cantilever probes, pogo pin probes and vertical probes.
From the above description and drawings, it will be understood by those of ordinary skill in the art that the particular embodiments shown and described are for purposes of illustration only and are not intended to limit the scope of the present invention. Those of ordinary skill in the art will recognize that the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. References to details of particular embodiments are not intended to limit the scope of the invention.