COMPOSITIONS OF SUEDE OF TIN ALLOY
Cross Reference to the Related Request This application claims the priority of the US Provisional Patent Application. No. 60 / 679,869, filed May 11, 2005. Field of the Invention The invention relates to a lead-free, bismuth-free tin alloy containing antimony and nickel or cobalt. BACKGROUND OF THE INVENTION The present invention relates generally to an improved solder composition. More specifically, the present invention relates to an improved solder composition that does not contain lead or bismuth and still achieves superior solder characteristics. In the electronic manufacture of printed circuit boards and the assembly of components thereon, the solders used generally contain tin and lead to provide mechanical and electrical connections. Solders containing tin and lead typically produce highly reliable connections in both automated and manual welding and provide a surface on printed circuit boards that are extremely conductive to soldering.
Tin-lead alloys of, for example, sixty (60%) percent tin, forty (40%) percent lead; and sixty-three (63%) percent of tin, thirty-seven (37%) percent of lead has historically been used for most electronic soldering operations. These alloys have been selected and preferred because of their low melting temperatures, mechanical strength, relatively low cost as well as superior wetting and electrical conductivity characteristics. However, the use of such tin-lead solders in the manufacture of printed circuit boards and assembly of components has become more problematic due to the toxic effects of workers' exposure to lead and the inevitable generation of hazardous waste. For example, even small amounts of lead can affect the neurological development of fetuses in pregnant workers. Due to these environmental problems, action is being taken to limit the amount of lead that enters the environment. Federal government agencies and many state agencies have begun lobbying the electronics industry to find alternatives to tin-lead solder to reduce lead exposure of workers and decrease the amount of lead waste returned to the environment.
Due to the materials used, many components and printed circuit boards are easily damaged by exposure to high temperatures during manufacturing or assembly. Due to thermal transfer and limitations and distribution problems, printed circuit boards are typically exposed to temperatures higher than the liquefaction temperature of the alloy used. In response to this problem, electronics manufacturers are exploring alternative alloys to replace tin-lead alloys. The prior art has not provided a solder composition exhibiting optimum wetting and flow properties without toxicity. Currently, federal, military and commercial welding specifications lack adequate non-toxic composition. The following patents in the prior art illustrate inadequate attempts to meet these needs. The Patent of the Soviet Union No. 183,037 of A. I. Gubin et al. , describes an alloy containing antimony of 1 ± 0.3%; copper 2 ± 0.3%; silver 5 ± 0.3% and the remainder tin which has a melting point of 225 ° -250 ° C. This alloy has a liquefaction temperature that does not allow it to be used in electronic solders because the soldering temperature required for the alloy to flow would destroy the printed circuit board and many of the components. There is currently no equipment or feasible means to allow this alloy to be used for the purpose of soldering or coating electronics. Due to the high silver content, this alloy has an economic disadvantage in the market. The U.S. Patent No. 3,503,721, issued to Lupfer, describes a tin-silver alloy of 96.5% tin and 3.5 ± 0.5% silver with marginally acceptable wetting and electrical conductivity characteristics to suit the needs of the electronics industry. However, this alloy has mechanical strength weaknesses that would prohibit its use in a wide range of electronic printed circuit board assemblies. For example, the creep strength, a flow measurement under pressure and the percentage of elongation, stretching of the metal before fracture are considerably less than those of the tin-lead alloys now used. Even with common tin-lead alloys, stress fractures from solder joints are the cause of many field failures on printed circuit boards where vibration or temperature variations occur. In addition, the liquefaction temperature of 221 ° C requires that the automated solder is made at a temperature that in many situations would damage the printed circuit board and / or the components. Due to the high silver content, the cost of this alloy is considerably higher than that of tin-lead alloys. For each percentage point of silver added to the alloy, the price increases by approximately $ 0.75 / pounds (based on the silver market of $ 5.00 / troy ounce). The U.S. Patent No. 4,778,733, issued to Lubrano et al. , describes an alloy that contains, by weight, from 0.7% to 6% copper; from 0.05% to 3% silver; the remaining tin being with a temperature range of 440 ° -630 ° F. This alloy has a melting temperature that is too high to be used in a wide range of electronic soldering applications without damaging printed circuit boards or components. In addition, the alloy described by Lubrano et al. , exhibits lower weld performance, slow wet times and poor mechanical resistances for electronic assembly applications. The U.S. Patent No. 4,695,428, issued to Ballentine et al. , describes an alloy containing 0.5-4% antimony; 0.5-4% zinc; from 0.1-3% silver; 0.1-2% copper; of 88-98.8% tin. The zinc content in this alloy causes the alloy to oxidize rapidly. This inhibits wetting and flow, producing a high foam formation which results in extremely high levels of defect. The loss of productivity when using such composition for electronic mass solders, makes it an unacceptable alternative for tin-lead solders. The U.S. Patent No. 4,758,407, issued to Ballentine et al. , describes an alloy containing tin, copper, nickel, silver and antimony. All the alloy combinations described by Ballentine et al. , have liquefaction temperatures in excess of those required for electronic assembly. The lowest liquefaction temperature described is 238 ° C, which is unacceptable for use in the electronics industry. The most commonly used lead-free alloy comprises tin-silver-copper. Industry tests have proven that lead-free tin-silver-copper solder alloys do not offer sufficient shock resistance test characteristics compared to tin-lead solder alloys, especially in BGA 0.3 devices. mm. Common tin-silver-copper alloys, known as SAC alloys, contain 3-4% silver and 0.5-1% copper. The main problem with these alloys in the application of type BGA is the formation of intermetallic plate of AgSn as well as the Kirkendal emptying that occurs. To make SAC alloys more stable, several elements have been added to reduce copper erosion as well as limit the formation of large intermetallic plates. For example, P, Ge, rare earth metals, Sb, Ni, and Co. have been tested. In addition, the solder alloys composed of tin-silver-copper-antimony described in the US Patent. Nos. 5,352,407 and 5,405,577, issued to Seelig et al. , show an improvement against tin-silver-copper alloys. However, this alloy allows some improvements of the alloys of tin, silver, copper; however, there is still a need for improved performance. Since no acceptable substitutes have been found for tin-lead alloys in BGA applications, there is still a need in the electronics industry for a lead-free or bismuth alloy composition that can achieve the physical characteristics and application performance of the alloys. tin-lead solder but without the toxic elements. SUMMARY OF THE INVENTION The present invention provides alloys for soldering with new advantages not found in currently available solder compositions, and overcomes many of the disadvantages of currently available compositions. The invention is generally directed to new and unique solder compositions with particular application in the electronic manufacture of printed circuit boards and the assembly of components thereon, as well as lead-free component shock arrangements and column arrangements. The solder compositions of the present invention achieve the desired physical characteristics, such as wetting, peel strength, low melting point, physical strength, fatigue resistance, electrical conductivity, matrix stability., and uniform bond strength, but without the toxic elements found in the known tin-lead solder alloys. The alloy compositions of the present invention include a combination of tin, silver, copper, antimony and either nickel or copper, to provide a unique set of physical characteristics that allow it to be used as a viable alternative to tin-lead alloys in electronic soldering and coating of printed circuit boards, as well as in lead-free component shock arrangements and column arrangements. The alloy of the present invention possesses physical characteristics which result in stronger mechanical bonding with a fatigue strength superior to tin-lead alloys, tin-silver alloys, or alloys containing bismuth. In addition, the melting point temperature is lower than in any other lead-free bismuth or alternative bismuth alloy. The preferred embodiment of the present invention has a reduced toxicity and a melting point of about 217 ° C and consisting of, in weight percent, 85-99% tin; 0.01-4.5% silver; 0.01-3.0% copper; and 0.002-5.0% antimony and either 0.0001-1.0% nickel or 0.0001-1.0% cobalt. It is therefore an object of the present invention to provide solder compositions that are viable substitutes for tin-lead solder alloys. Another object of the present invention is to provide solder alloy compositions that are well suited for the electronic manufacture of printed circuit boards and the assembly of components thereon. It is further an object of the present invention to provide acceptable solder alloy compositions for the electronics industry that does not contain lead or bismuth. It is still a further object of the present invention to provide solder alloy compositions that are free of toxic elements and that are safe for the environment. DETAILED DESCRIPTION OF THE INVENTION Preferred embodiments of the present invention are lead and bismuth-free solder compositions containing tin, silver, copper, antimony and nickel or containing tin, silver, copper, antimony and cobalt. The solder alloy compositions of the present invention have the physical characteristics and performance of the application to economically satisfy the needs of the electronics industry and the assembly and coating of printed circuit boards. In particular, the alloy exhibits ideal physical characteristics even without containing toxic elements such as alloys found in the prior art that could be harmful to workers and the environment. The alloys of the present invention have advantages over the tin, silver, copper, antimony alloy described in the prior art. Below is an independent comparison test between tin alloys, silver, copper, antimony, as described in the U.S. Patent. No. 5,405,577 and a prior art tin-lead solder alloy containing 63% tin and 37% lead. As noted below, the mechanical strength of this alloy is superior to the known tin-lead alloys.
The alloy compositions of the present invention exhibiting the desired physical characteristics are comprised by weight as follows:
In one embodiment, the solder composition comprises from about 1.75% to about 2.0% silver; approximately 0.8% copper; approximately 0.5% antimony; approximately 0.08% nickel; and approximately 96.6% to approximately 96.9% tin. The melting point temperature of the composition is in the range of about 217 ° C. The liquefaction temperature of approximately 217 ° C coupled with superior wetting allows the alloy of the present invention to be used with existing mass and manual welding equipment without damaging most printed circuit boards or electronic components. In addition, this alloy when tested in JEDEC shock resistance tests of 1500g X 0.5 meters demonstrated twice the fatigue longevity of known SAC alloys. In comparison, an SAC alloy containing antimony but not nickel (eg, having the composition from about 1.75% to about 2.0% silver, about 0.8% copper, about 0.5% antimony, and about 96.6% to about 96.9% tin) showed only a 30% increase in fatigue longevity. In another embodiment, the solder composition comprises from about 0.5% to about 1.75% silver; about 0% to about 0.5% copper; from about 0.002% to about 0.2% antimony; from about 0.08% to about 0.04% nickel; and from about 97.5% to about 99.4% tin. In another embodiment, the solder composition comprises about 1.0% to about 1.75% silver; approximately 0.8% copper; approximately 1.0% antimony; approximately 0.008% cobalt; and from about 96.44% to about 97.2% tin. This alloy also shows improved fatigue life compared to SAC alloys in the JEDEC shock resistance tests of 1500g.X 0.5 meters. In another embodiment, the solder composition comprises from about 0.02% to about 1.0% silver; about 0.2% to about 0.8% copper; from about 0.2% to about 0.8% antimony; from about 0.008% to about 0.4% cobalt; and from about 97% to about 99.6% tin. The present solder compositions may comprise from about 85% to about 87% tin; from about 87% to about 89% tin; from about 89% to about 91% tin; from about 91% to about 93% tin; from about 93% to about 95% tin; from about 95% to about 97% tin; or from about 97% to about 99% tin; or a combination of two or more of the above ranges (e.g., from about 95% to about 99% tin). The present solder compositions may comprise from about 0.01% to about 0.05% silver; from about 0.05% to about 0.1% silver; from about 0.1% to about 0.5% silver; from about 0.5% to about 1.0% silver; from about 1.0% to about 2.0% silver; from about 2.0% to about 3.0% silver; from about 3.0% to about 4.0% silver; or from about 4.0% to about 4.5 silver or a combination of two or more of the above ranges
(e.g., from about 1.0% to about 3% silver). The present solder compositions may comprise from about 0.01% to about 0.05% copper; from about 0.05% to about 0.1% copper; from about 0.1% to about 0.5% copper; from about 0.5% to about 1.0% copper; from about 1.0% to about 2.0% copper; from about 2.0% to about 3.0% copper; or a combination of two or more of the above ranges. { e. g. , from about 0.1% to about 1% copper).
The present solder compositions may comprise from about 0.002% to about 0.005% antimony; from about 0.005% to about 0.01% antimony; from about 0.01% to about 0.05% antimony; from about 0.05% to about 0.1% antimony; from about 0.1% to about 0.5% antimony; from about 0.5% to about 1.0% antimony; from about 1.0% to about 2.0% antimony; from about 2.0% to about 5.0% antimony; a combination of two or more of the above ranges (e.g., from about 0.1% to about 1% antimony). The present solder compositions may comprise from about 0.002% to about 0.005% nickel; from about 0.005% to about 0.01% nickel; from about 0.01% to about 0.05% nickel; from about 0.05% to about 0.1% nickel; from about 0.1% to about 0.5% nickel; from about 0.5% to about 1.0% nickel; or a combination of two or more of the above ranges. { e. g. , from about 0.01% to about 0.1% nickel). The present solder compositions may comprise from about 0.002% to about 0.005% cobalt; from about 0.005% to about 0.01% cobalt; from about 0.01% to about 0.05% cobalt; from about 0.05% to about 0.1% cobalt; from about 0.1% to about 0.5% cobalt; from about 0.5% to about 1.0% cobalt; or a combination of two or more of the above ranges. { e. g. , from about 0.01% to about 0.1% cobalt). Without being bound by any particular theory, the combination of antimony with nickel or cobalt can inhibit the SAC alloy to dissolve copper and form large intermetallic lamellae, thus producing a more stable matrix over time and providing better stability and bond strength uniform. The alloys of the invention exhibit, for example, excellent wetting and melting temperatures, as well as superior physical strength, electrical conductivity and thermocyclic fatigue. As a result of these excellent physical characteristics, the solder alloy compositions of the present invention can successfully replace the currently known tin-lead alloys used for the assembly of electronics and the manufacture of printed circuit boards, as well as for the arrangements of lead-free component shock and column arrangements. Most of the capital goods used in electronic welding can employ these compositions. The low melting temperature is low enough not to cause heat damage to the board or the components in it. The alloy compositions of the present invention are very suitable for many different applications. The alloys can be used in the coating of circuit boards and the manufacture of printed circuit boards through the use of "heat-air leveling" or "tin-plating". These processes improve weldability over the circuit board. Alloys can also be used in the assembly of electronic components on printed circuit boards when a wave soldering machine is used. The alloys are also very suitable for forming in various shapes and sizes, such as bars, ingots, wire, chips, slats, powder, preform and can be used with a flux core. Therefore, the alloys of the present invention can be used for assembly of electronic components using solder wire and a heating device for manual soldering of the components to the board. In the coating application of printed circuit boards, the compositions of the present invention have superior wetting characteristics and improved productivity. The tin-lead alloys of the prior art are easily contaminated by copper from PC boards that are immersed in a bath during processing. Since the compositions of the present invention contain copper, minor increases in copper content do not easily affect the performance of the compositions. In addition, these new compositions will not absorb copper as quickly as the lead-tin solders of the prior art. As a result, these new alloys can remain functional for much longer than the tin-lead alloys of the prior art to drastically reduce the total solder consumption and reduce operating expenses by the manufacturers. In addition, the weldability of the coated board is extended because the intermetallics are distributed evenly throughout the intergranular board of the composition. The result is a higher quality printed circuit board that can not be achieved by using the prior art solder compositions. In the outdoor mounting installation or wave soldering of the components to the printed circuit boards, the compositions of the present invention can employ the same heat temperatures, pre-heat temperatures and processing parameters as in tin solders. lead of the prior art now currently in use. The nominal composition is very close to the eutectic alloy which exhibits important physical characteristics for high-speed, low-defect welding. Since the solder alloys of the invention contaminate less easily than tin-lead alloys, this results in an increased life of the solder bath. In addition, the solder joints formed by wave solder produce higher bond strengths and excellent electrical conductivity with a uniform distribution of the intermetallics throughout the solder joint. The solder alloy compositions of the present invention can also be used in the assembly of electronic components using a solder wire in a heating device for manual welding of the components to the board. Such a method requires a composition that is rapidly wetted and distributed from about 235 ° C to about 260 ° C. The composition of the present invention can easily be formed in a core wire weld and used easily and successfully in manual soldering. In summary, the alloy compositions of the present invention enjoy a combination of a sufficiently low melting temperature for electronic applications, superior wetting characteristics and superior mechanical strength to make it an excellent alternative to tin-lead alloys for needs of the electronic industry for the manufacture of printed circuit boards and the assembly of components on the boards. Superior weldability and wetting characteristics still produce damping thicknesses and low copper solubility to provide a tremendous advantage in the solder coating of printed circuit boards, such as by heat-air leveling. Incorporation through Reference The contents of all cited references (including literature references, patents, patent applications and Web sites) that may be cited by this application are expressly incorporated herein by reference. The practice of the present invention will employ, unless otherwise indicated, techniques for the production and use of alloys that are well known in the art. Equivalents Those skilled in the art will appreciate that various changes and modifications may be made to the described embodiments without departing from the spirit or essential characteristics thereof. All such modifications and changes are proposed to be covered by the appended claims. The foregoing modalities are therefore considered in all aspects, illustrative rather than limiting of the invention described herein. A) Yes, the scope of the invention is indicated by the appended claims rather than by the foregoing description and all changes that fall within the meaning and range of equivalence of the claims are therefore proposed to be encompassed therein.