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EP1971699A2 - Brasure sans plomb avec une faible dissolution du cuivre - Google Patents

Brasure sans plomb avec une faible dissolution du cuivre

Info

Publication number
EP1971699A2
EP1971699A2 EP07716333A EP07716333A EP1971699A2 EP 1971699 A2 EP1971699 A2 EP 1971699A2 EP 07716333 A EP07716333 A EP 07716333A EP 07716333 A EP07716333 A EP 07716333A EP 1971699 A2 EP1971699 A2 EP 1971699A2
Authority
EP
European Patent Office
Prior art keywords
solder
copper
weight
tin
lead
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07716333A
Other languages
German (de)
English (en)
Inventor
Brian T. Deram
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Illinois Tool Works Inc
Original Assignee
Illinois Tool Works Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US11/366,523 external-priority patent/US20070172381A1/en
Application filed by Illinois Tool Works Inc filed Critical Illinois Tool Works Inc
Publication of EP1971699A2 publication Critical patent/EP1971699A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C13/00—Alloys based on tin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/24—Selection of soldering or welding materials proper
    • B23K35/26—Selection of soldering or welding materials proper with the principal constituent melting at less than 400 degrees C
    • B23K35/262—Sn as the principal constituent

Definitions

  • the present invention relates to low-cost solder compositions for bonding electronic devices or parts to printed wiring boards (PWBs).
  • PWBs printed wiring boards
  • the present invention relates to solder compositions that prevent or minimize the dissolution of copper into the solder during the soldering process.
  • PWB printed wiring board
  • PCB printed circuit board
  • Automated soldering machines employ a conveyor to transport a printed circuit board assembly first across a fluxing unit that applies soldering flux to the bottom side of the printed circuit board and component terminations, then across a preheating unit, and then across the solder station.
  • the solder station consists of an iron or steel heated pot that maintains the solder in a melted condition, usually 50-100°C above the liquidus melting point of the solder composition.
  • the printed circuit assembly may be transported across the surface of the melted solder, known as drag soldering, or, more commonly, across a standing wave of molten solder, the wave being generated by a pumping system contained in the melted solder.
  • Solders for joining electronic parts to copper terminations of a printed wiring board traditionally have been composed of tin and lead of about 60% to 63% tin (Sn) and the balance lead (Pb). More recently, international environmental regulations are restricting the use of lead (Pb) in solders for electronic products; so, solder technologists and manufacturing personnel have been evaluating and using alternative solders for soldering electronic assemblies. The process of automated soldering results in dissolution of copper from the printed circuit board and component terminations into the melted solder. Copper is very soluble in melted tin, a primary component in solders used for electronic assembly.
  • Copper is particularly susceptible to dissolving in lead-free solders because the lead-free solders melt at higher temperatures than tin-lead solder and consist of more than 95% tin. As copper dissolves into the lead-free solder, the liquidus melting point of the solder alloy increases dramatically. For example, the eutectic melting temperature (solidus and liquidus points are the same) for tin containing 0.7% copper is 227°C. Because of the superheating required for automated wave soldering, the solder may be heated to above 300°C for reliable soldering. During the soldering process, the melted tin- copper solder can dissolve additional copper from the assembly being soldered.
  • a very small increase in copper from 0.7% to 1.0% will raise the liquidus melting point of the tin-copper solder alloy to 239°C, while an increase in copper to only 1.5% results in a liquidus melting point of 260 0 C.
  • One solution would be to increase the solder temperature to accommodate the increased amount of copper, but this would not be acceptable because of the damage caused by excessive heating of the electronic devices being soldered.
  • a solder composition of 0.7% copper in tin is the most economical lead-free solder of choice in the automated soldering machine
  • additions of solder to replace expended solder and dilute dissolved copper may contain only from 0% to 0.5% copper. This adjustment is not precise and can affect the quality of the soldering process and the reliability of the soldered electronic assembly.
  • a significant advantage of the present invention is that the dissolution rate of copper into the melted solder is sufficiently low that the use of another solder alloy is not necessary.
  • a solder wave is formed by pumping molten solder, contained within a solder pot, up through a nozzle to provide a standing wave.
  • molten solder contained within a solder pot, up through a nozzle to provide a standing wave.
  • dual waves are also employed, particularly when surface mounted devices are being soldered to the bottom side of printed circuit boards.
  • Solder cascades and solder jets also find application as wave soldering.
  • the solder may be maintained in an open solder pot where an electronic assembly may be dragged across the melted solder surface to accomplish the soldering.
  • One of the problems encountered with automated soldering processes is that the molten solder oxidizes when exposed to the oxygen in the air.
  • the oxidized solder forms a surface oxide layer, which must be removed by a flux before the components being soldered will wet with solder. Particularly with wave soldering, the surface oxide layer is continually broken by the flow of solder in the wave. This exposes fresh solder which, in turn, is also oxidized. A mixture of oxide and solder, thus, collects within the solder pot. This mixture is known as dross, which must be removed and disposed. Dross generation adds to the cost of the process due to the lost value of the solder and the maintenance time required to remove it and repair mechanical parts of the wave soldering apparatus damaged by the abrasive action of the dross.
  • Tin without the addition of other metals is unacceptable for soldering electronic assemblies for several reasons.
  • soldering temperatures required for using tin (Sn) with its high melting point (232°C) may damage electronic components.
  • the wetting ability is poor because of the high surface tension of the melted, tin.
  • the tensile strength and ductility are unacceptably low because of the course grain structure of the solidified metal. Adding other metals, such as lead, silver, copper, and/or zinc will decrease the surface tension and the melting points of the solder alloys, while increasing the tensile strengths and ductility.
  • U.S. Patent 1,239,195 describes the addition of copper and/or silver to tin to harden the composition.
  • U.S. Patent 1,437,641 describes the improvement of mechanical properties of tin-silver by adding copper to tin-silver solder compositions.
  • U.S. Patent 5,863,493 describes the addition of small amounts of copper (0-2.9%) and nickel (0.1-3%) to SnAg3.5 solder compositions to provide resistance to grain growth of tin-silver intermetallic compound in the tin matrix, especially during thermal cycling of the solder joints.
  • Tin-copper solders such as the SnCuO.7 eutectic composition, melt at an acceptable temperature (227°C) for hand or automated soldering, but the surface tension of the solder alloy is still high compared to the conventional tin-lead solder, resulting in inferior wetting ability compared to that of the tin-lead solder.
  • Tin-antimony solder such as the well-known composition SnSbO5
  • SnSbO5 the melting temperature
  • antimony seriously reduces the ability of the solder to spread on a copper surface because of the formation of a copper-antimony intermediate phase between the copper and the solder alloy.
  • Antimony is considered the most toxic metal in this grouping of solder compositions. As antimony has been added to tin-lead solder to improve strength, so to is antimony added to other tin compositions incorporating silver, copper, bismuth, and zinc, as shown in Table 1.
  • U.S. Patent 1,437,641 describes a well-known tin-zinc solder alloy with acceptable melting temperature, but unacceptably rapid oxidation and corrosion problems.
  • U.S. Patent 4,670,217 describes solder compositions for joining copper that contain up to 4% zinc added to solder compositions containing tin, silver, and antimony.
  • tin alloys containing zinc (Zn) are subject to very rapid oxidation while being pumped to generate a standing wave of solder, resulting in a large production of dross, i.e., a mixture of metal oxides and metal particles that float on the surface of the melted solder.
  • dross i.e., a mixture of metal oxides and metal particles that float on the surface of the melted solder.
  • U.S. Patent 4,193,530 describes the addition of small amounts (0.1% to 0.5%) of bismuth and indium to tin metal to improve the corrosion resistance of the tin.
  • U.S. Patent 4,879,096 describes adding 0.1% to 3% bismuth to solder compositions containing tin, silver, and copper, to increase the strength of the solder joints.
  • U.S. Patent 5,980,822 describes adding 0.1% to 5.0% bismuth to reduce the solidus melting temperature of the solder alloy that contains tin, silver, copper, and antimony.
  • U.S. Patent 4,929,423 describes adding up to 20% bismuth, preferably 3% to 6%, to solders containing tin, silver, and copper.
  • U.S. Patent 6,649,127 describes the r addition of bismuth up to 8% to tin-copper solder composition containing up to 10% zinc, for the purpose of reducing the melting temperature and improving the wetting speed when soldering to copper surfaces.
  • solders are designed for copper pipe plumbing applications.
  • solder alloys that contain more than about 2% to 5% bismuth (Bi) are incompatible with lead (Pb) that may be contained on the electronic component terminations, resulting in potential cracked solder joints.
  • Pb lead
  • bismuth can be added in small amounts to certain lead-free solder alloy compositions to improve the wetting ability and slightly reduce the melting temperature of the solder. As much as 1% bismuth is soluble in solid tin. " The much lower surface tension of bismuth compared to tin would help wetting.
  • Tin alloys containing indium (In) have the same high cost problem as those with silver, even though indium additions are able to improve the wetting ability of the solder.
  • U.S. Patent 6,843,862 describes lead-free solders containing 4% indium as dissolving the copper substrate metal at a reduced rate compared to lead- free solders that do not contain indium, there is no significant difference when bismuth is added to these alloys.
  • U.S. Patent 5,985,212 also describes the addition of gallium (Ga) to lead-free solders containing tin, copper, and indium with the purpose of increasing strength and reducing the melting point of the resulting solder composition.
  • Ni nickel
  • U.S. Patent 4,758,407 the addition of nickel in smaller amounts (0.1% to 2.0%) to tin alloys containing 3% to 5% copper is described in U.S. Patent 4,758,407 as improving wettability and increasing strength of the solder composition.
  • the specified solder compositions have high liquidus temperatures exceeding 600 0 F (315°C), which is exceedingly high for soldering of electronic assemblies.
  • Subsequent patents, as shown in Table 1 have incorporated nickel as an additive to lead-free solders also to improve the solderability and reduce the melting point of the specified solder compositions.
  • Patent 5,863,493 teaches that tin-silver solder alloys experience grain growth coarsening during thermal cycling, resulting in decreased creep and fatigue resistance, and the additions of nickel and copper to the tin-silver solder composition improves both properties.
  • U.S. Patent Nos. 6,660,226 and 6,702,176 describe the addition of cobalt (Co) to lead-free solders to prevent leaching by the lead-free solder of certain transition metals, such as copper, silver, gold, palladium, platinum, nickel, and zinc.
  • U.S. Patent 6,702,176 describes the addition of cobalt to a tin- based, lead-free solder to prevent leaching of copper metal being soldered.
  • U.S. Patent 5,980,822 describes the addition of germanium (Ge) in combination with phosphorus (P) to prevent the formation of metal oxide and improve the thermal fatigue of the solder.
  • Germanium (Ge) in combination with phosphorus (P) to prevent the formation of metal oxide and improve the thermal fatigue of the solder.
  • Table 1 has incorporated germanium (Ge) with nickel (Ni) to enhance the wettability and tensile strength of a variety of lead-free solders containing tin, silver, copper, and/or zinc.
  • the use of germanium in price competitive solder compositions is precluded because of the very high cost of germanium.
  • Phosphorus is commonly added to bulk molten metal, such as copper and solder, to remove oxides.
  • the addition of phosphorus to tin solder alloys is recognized by those skilled in the art as a standard method for deoxidizing metals during the manufacture of solder or while using the solder for joining electronic assemblies. Because the Gibb's Free Energy of Formation of phosphorus oxide (P 2 Os) is much lower than that of tin, copper, bismuth, nickel, silver, or lead oxides, the oxygen affinity of phosphorus is higher. So, phosphorus oxide preferentially forms on the melted solder surface during the solder processing. The resulting phosphorus oxide (specific gravity 2.4) floats on the surface of the solder (specific gravity 7.3).
  • Patent 6,488,888 describes adding phosphorus to reduce dressing or oxide formation resulting from using tin-zinc solders.
  • U.S. Patent 5,817,194 describes the addition of phosphorus to soldering/brazing material in the range of 0.05% to 1.5% to act as a fluxing agent to improve the wettability of the solder/brazing material to stainless steel. Also stated is that phosphorus addition must exceed 0.05% to exhibit fluxing properties, and that the nickel addition must be greater than 0.05% to be effective.
  • solder compositions that will result in smooth, shiny solder connections equivalent to those obtained when using tin-lead solder.
  • Another object of the present invention is to provide lead-free solder compositions for use in joining electronic components and other parts to printed wiring boards. Yet another object of the present invention is to provide a lead-free solder composition containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin.
  • Still yet another object of the present invention is to provide a solder paste composition
  • a solder paste composition comprising a powder containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin; a rosin-based resin; an activating agent, and a solvent.
  • Another object of the present invention is to provide a soldered article comprising a workpiece containing a transition metal conductor capable of readily diffusing into melted tin; and a lead-free solder composition containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin, the lead-free solder composition bonded to the workpiece so as to be electrically and mechanically bonded to the transition metal conductor.
  • Yet another object of the present invention is to provide a lead-free solder composition containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, and the balance of tin.
  • the melted solder compositions dissolve copper from electronic components, printed wiring boards and wires at a rate slower than that experienced in the same applications with 63% tin, 37% lead solder alloy. Additionally, the need to attempt to balance the solder composition in a solder pot by adding another solder composition with reduced copper content is eliminated. Still further, the solder compositions of the present invention are low cost, exhibit good wetting properties, have acceptably low melting temperatures, and result in the formation of reflective solder joints with a shiny appearance similar to that experienced in the same applications with 63% tin, 37% lead solder alloy.
  • a feature of the present invention is to provide a lead-free solder composition containing copper, nickel, bismuth, silver, phosphorus, tin and inevitable impurities.
  • the range of copper in the lead-free solder composition can be between 0.2 to 0.9% by weight or, in a preferred embodiment, between 0.5% and 0.7% by weight.
  • the range of nickel in the lead-free solder composition can be between 0.006 to 0.07% by weight or, in a preferred embodiment, between 0.04% by weight and 0.06% by weight.
  • the range of bismuth in the lead-free solder composition can be between 0.03 to 0.08%! by weight or, in a preferred embodiment, between 0.05% by weight and 0.07% by weight.
  • the range of silver in the lead-free solder composition is less than 0.5% by weight.
  • the range of phosphorus in the lead-free solder composition is less than 0.010% by weight.
  • the balance of the lead-free solder composition is of tin.
  • the lead-free solder composition of the present invention containing 0.2 to
  • solder bar 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder bar where the solder bar can be used in electronic assembly solder machines.
  • the lead-free solder composition of the present invention containing 0.2 to
  • solder ingot 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder ingot where the solder ingot can be used in electronic assembly.
  • the lead-free solder composition of the present invention containing 0.2 to
  • solder wire 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder wire where the solder wire can be used in electronic assembly.
  • the lead-free solder composition of the present invention containing 0.2 to
  • solder chip 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder chip where the solder chip can be used in electronic assembly.
  • the lead-free solder composition of the present invention containing 0.2 to
  • solder ribbon 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder ribbon where the solder ribbon can be used in electronic assembly.
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder powder where the solder powder can be used in electronic assembly.
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be employed in hot air leveling of printed circuit boards.
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be employed in assembling surface mounted printed circuit boards.
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be employed in the solder coating of printed circuit boards. .
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be employed in roll tinning of circuit boards.
  • the lead-free solder composition of the present invention containing 0.2 to
  • 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be employed in surface mount assembly of electronic components onto a printed circuit board.
  • the lead-free solder composition of the present invention containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin can be formed into a solder preform where the solder preform can be used in electronic assembly.
  • the solder preform can be fluxed or unfluxed.
  • Another feature of the present invention is to provide a solder paste composition
  • a solder paste composition comprising a powder containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin; a rosin-based resin; an activating agent, and a solvent.
  • Yet another feature of the present invention is to provide a soldered article comprising a workpiece containing a transition metal conductor capable of readily diffusing into melted tin; and a lead-free solder composition containing 0.2 to 0.9% by weight of copper, 0.006 to 0.07% by weight of nickel, 0.03 to 0.08% by weight of bismuth, less than 0.5% by weight of silver, less than 0.010% by weight of phosphorus, and the balance of tin.
  • the lead-free solder composition is bonded to the workpiece so as to be electrically and mechanically bonded to the transition metal conductor.
  • the transition metal conductor is selected from the group consisting of copper, silver, nickel, gold, palladium, platinum, zinc and an alloy thereof.
  • Still yet another feature of the present invention is to provide a lead-free solder composition containing copper, nickel, bismuth, tin and inevitable impurities.
  • the range of copper in the lead-free solder composition can be between 0.2 to 0.9% by weight or, in a preferred embodiment, between 0.5% and 0.7% by weight.
  • the range of nickel in the lead-free solder composition can be between 0.006 to 0.07% by weight or, in a preferred embodiment, between 0.04% by weight and 0.06% by weight.
  • the range of bismuth in the lead-free solder composition can be between 0.03 to 0.08% by weight or, in a preferred embodiment, between 0.05% by weight and 0.07% by weight.
  • the balance of the lead-free solder composition of the present invention is of tin.
  • silver can be added to the lead-free solder composition in an amount no greater than 0.5% by weight.
  • phosphorus can be added to the lead-free solder composition in an amount no greater than 0.010% by weight.
  • solder alloy compositions of the present invention are essentially free of potentially toxic metals including antimony, arsenic, cadmium, cobalt, gallium, mercury, and thallium.
  • the term "essentially free” is used in the context to mean that if any of these metals are present in the composition, the included concentration is so low that the expected health or environmental effects are insignificant.
  • the solder compositions comprise, as essential ingredients, from about 0.2% to about 0.9% by weight copper (Cu), from about 0.006% to about 0.07% by weight nickel (Ni), from about 0.03% to about 0.08% by weight bismuth (Bi), less than about 0.5% by weight silver (Ag) and the balance tin (Sn), together with incidental impurities.
  • copper copper
  • Ni nickel
  • Bi bismuth
  • Ag silver
  • Sn silver
  • phosphorus (P) may be added from about 0.001% to about 0.010%.
  • the alloy compositions of the present invention may be prepared by techniques known in the art by melting the tin metal and then adding the remaining elements while mixing until all added elements are dissolved into the tin.
  • the alloy compositions can then be cast into billets or continuous wire, and subsequently manufactured into ingots, bars, wire, or other predetermined shapes. Though primarily intended for use as bar or solid wire form in automatic wave or dip soldering machines, the alloy compositions can also be manufactured as solid or flux cored wire solder for hand soldering.
  • the eutectic composition for tin-lead solder is Sn61.9Pb38.1 weight % (Sn70.9Pb29.1 atomic %), melting at 183°C, but the convention in the solder industry is to refer to the eutectic composition as either 63/37 or Sn63Pb37 (weight %).
  • the eutectic composition for tin-silver is Sn96.5Ag3.5 weight % (Sn96.2Ag3.8 atomic %), melting at 221°C.
  • the eutectic composition for tin-copper is Sn99.3Cu0.7 weight % (Sn98.7Cul.3 atomic %) melting at 227°C.
  • solder compositions are very limited for use as alternative alloys to the tin-lead solders that are no longer acceptable for assembly of electronic products. More recently, lead-free solders have been used for automated soldering, including dip, wave, and reflow soldering techniques, as well as for hand soldering applications. The commonly acceptable lead-free solders contain more than 95% tin in combination primarily with silver and/or copper. The higher tin percentage and higher melting temperature of the lead-free solder alloys result in an increase in the rate of copper dissolution during soldering.
  • each solder alloy composition was heated in a temperature controlled solder pot that maintained the temperature of the solder at 300 0 C + 5°C.
  • One end of a copper wire measuring 0.6 mm diameter and 25 mm long was suspended vertically from a holder over the solder pot.
  • the suspended lower end of the copper wire was dipped into a mildly activated rosin soldering flux, Kester #186, to a depth of 10 mm.
  • the solder pot was raised mechanically at a speed of 2 mm/second by means of an electric elevator until 5 mm of the wire was immersed into the solder, immediately followed by starting the timer. The end of the test was determined by observing the number of seconds required for the immersed 5 mm of the copper wire to dissolve into the melted solder. The test results are shown in Table 2 for each solder alloy composition.
  • the tin in the solder composition will dissolve some copper at the surface of the copper substrate, and, because the nickel-copper solid solution melts above 1000 0 C, a nickel-copper compound is formed as a barrier on the copper to prevent additional dissolution of the copper.
  • solder sample 16 and especially samples 17 to 21 the combination of bismuth and nickel acts synergistically to greatly reduce the copper dissolution rate.
  • the solubility of bismuth in tin at 25°C is about 1.2 weight %, so the bismuth addition less than 1 weight % to the tin-copper composition is not expected to result in any crystallization problem as might be experienced with higher amounts of bismuth.
  • the solubility of copper in bismuth is only about 0.15 weight % at 270 0 C, the normal wave solder temperature for soldering electronic assemblies, which allows the nickel to form the nickel-copper compound on the copper substrate surface.
  • Bismuth additions also have the effect of reducing the surface tension of the solder alloy composition.
  • the electronics industry bases its inspection quality standards on the appearance of solder joints. Compared to the normally bright, smooth, and shiny appearance of tin-lead solder joints, the known lead-free solders by their crystalline nature solidify with a frosty or dull surface caused by precipitation of tin-silver or tin- copper intermetallics during solidification of the tin alloys. The specific gravities of these intermetallic crystals results in their rising to the surface of the solder to make the surface frosty or grainy. This visible grainy surface is also a sign that the grainy structure also may exist in the solder composition matrix, a potential mechanism for cracking of the solder joints over time with thermal cycling of the electronic assembly.
  • a deoxidized copper coupon of dimensions 50 mm x 50 mm x 0.3 mm was prepared by polishing the copper with #1500 abrasive paper, washing the copper coupon with alcohol, and then heating the copper coupon in a furnace at 150 0 C for one hour. Precisely 1.0 gram of the solder sample was placed on the copper coupon, and then 100 micro liters of mildly activated rosin soldering flux (Kester #186) was placed with a micropipette onto the solder sample. The copper coupon was then placed onto a hotplate with temperature controlled at 270 0 C + 5°C. When the solder melted and spread out onto the copper coupon, the coupon was removed, allowed to cool to room temperature (25°C), and the rosin flux residue removed with alcohol. The cosmetic appearance of the solidified solder is recorded in Table 3.
  • the quality ratings in Table 3 are based on the overall shine and texture of the solder surface.
  • the shine varies from completely reflective which is a rating of 1, down to completely dull or frosty which is a rating of 4.
  • the amount of frosty or dull appearance of the solder surface becomes a spot or spots of increasing size as the rating goes from 1 to 4.
  • the solder with the best rating of 1 is equivalent in shininess and smoothness to that experienced with the standard tin-lead solder Sn63Pb37.
  • a rating of 4 is completely frosty or grainy looking and not acceptable for quality inspection and reliability.
  • the texture column rating is the observed appearance of the frosty area.
  • the tin in the solder composition will dissolve some copper from the surface.
  • the tin in the solder can readily dissolve copper with the formation of a low-melting temperature (221°C) tin-copper eutectic composition.
  • the microstructure consists of the copper- tin intermetallic compound Cu 6 Sn S needles contained along the grain boundaries of the solidified tin.
  • the solid solubility of copper in tin at the solidification point 227°C is very low (about 0.006 weight %).
  • soldering with tin-lead solder (samples 1, 2), as the copper tin intermetallic CugSns forms between the solder and the copper surface, the residual lead (Pb) in the solder composition forms a barrier to prevent further copper dissolution by the tin.
  • Most electronic circuitry and component termination metallization is designed with copper dissolution considerations. However, as printed wiring circuitry becomes more fine-lined or when very small copper wires are being soldered, the dissolution of the copper becomes more problematic.
  • soldering with lead-free solders such as tin-silver solder compositions (samples 3, 4)
  • lead-free solders such as tin-silver solder compositions (samples 3, 4)
  • the combination of the higher melting point of the solder alloy and much higher tin content compared to that of the tin-lead compositions results in much more rapid dissolution of the copper surface.
  • the silver Upon solidification of the tin- silver solder, the silver is present as tin-silver intermetallic platelets Ag 3 Sn contained in the tin matrix. Reducing the amount of silver improves the appearance of the solidified solder.
  • the remaining nickel contained in the solder composition will solidify in the tin matrix with intermetallic compound Ni 3 Sn containing some copper in a solid solution.
  • the tin-nickel-copper compound precipitates along the grain boundaries in the tin crystals, thereby reducing the size and subsequent growth of the tin-copper crystals.
  • Sample 16 exhibits the effect of adding a small amount of bismuth to the sample 14 with the result being a significant reduction in the rate of copper dissolution, but not as good as sample 15 with the larger amount of nickel content.
  • Phosphorus content in solder compositions up to 0.010 weight % (100 parts per million) is known to reduce drossing (oxide formation) on the surface of the solder in automated wave or dip soldering machines, but over 0.010 weight % is known to cause dewetting (pulling back of the solder) on the copper surface, as experienced with sample 11.
  • Phosphorus content in tin-lead or tin-copper solder compositions only slightly increases the rate of dissolution of the copper substrate without affecting the wetting properties of the solder or the appearance of the solder joint.
  • Phosphorus content in alloys containing more than about 0.3 weight % silver causes a slight increase in the rate of dissolution of the copper substrate.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electric Connection Of Electric Components To Printed Circuits (AREA)

Abstract

La présente invention concerne des compositions de brasure sans plomb convenant pour joindre des dispositifs électroniques à des cartes de circuit imprimé, qui comprennent en poids 0,2 à 0,9 % de cuivre, 0,006 à 0,07 % de nickel, 0,03 à 0,08 % de bismuth, moins de 0,5 % d’argent, moins de 0,010 % de phosphore, le complément étant constitué d’étain et d’impuretés inévitables. La composition de brasure selon la présente invention trouve une application particulière dans les machines automatiques de brasure à la vague dans lesquelles la brasure sans plomb conventionnelle dissout le cuivre excédentaire des circuits imprimés et des bornes des composants.
EP07716333A 2006-01-10 2007-01-05 Brasure sans plomb avec une faible dissolution du cuivre Withdrawn EP1971699A2 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US75772106P 2006-01-10 2006-01-10
US76140006P 2006-01-23 2006-01-23
US11/366,523 US20070172381A1 (en) 2006-01-23 2006-03-02 Lead-free solder with low copper dissolution
PCT/US2007/000226 WO2007081775A2 (fr) 2006-01-10 2007-01-05 Brasure sans plomb avec une faible dissolution du cuivre

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EP1971699A2 true EP1971699A2 (fr) 2008-09-24

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EP2277657B1 (fr) * 2008-04-23 2012-07-11 Senju Metal Industry Co., Ltd Brasure sans plomb
WO2014002304A1 (fr) * 2012-06-29 2014-01-03 ハリマ化成株式会社 Alliage de soudure, pâte de soudure, et carte de circuits électroniques
US9320152B2 (en) * 2013-05-29 2016-04-19 Nippon Steel & Sumikin Materials Co., Ltd. Solder ball and electronic member
US10434608B2 (en) * 2013-09-11 2019-10-08 Senju Metal Indsutry Co., Ltd. Lead-free solder, lead-free solder ball, solder joint using the lead-free solder and semiconductor circuit having the solder joint
MX387156B (es) 2013-10-31 2025-03-18 Alpha Metals Aleaciones de soldadura libres de plata, libres de plomo.
HUE045443T2 (hu) * 2014-08-27 2019-12-30 Heraeus Deutschland Gmbh & Co Kg Forrasztópaszta és eljárás kohéziós kapcsolat kialakítására
JP6011709B1 (ja) * 2015-11-30 2016-10-19 千住金属工業株式会社 はんだ合金
US20180102464A1 (en) * 2016-10-06 2018-04-12 Alpha Assembly Solutions Inc. Advanced Solder Alloys For Electronic Interconnects
CN107245602B (zh) * 2017-06-09 2019-03-22 升贸科技股份有限公司 无铅锡合金及使用其的镀锡铜线
CN108941969A (zh) * 2018-07-20 2018-12-07 广东中实金属有限公司 一种适用于压敏电阻的无铅焊料及其制备方法
US11377715B2 (en) * 2019-05-27 2022-07-05 Senju Metal Industry Co., Ltd. Solder alloy, solder paste, solder ball, solder preform, solder joint, and circuit
CN112756729B (zh) * 2021-01-14 2022-02-18 深圳市兴鸿泰锡业有限公司 一种使用焊锡丝的电子元器件自动焊接方法
CN114464971A (zh) * 2022-02-28 2022-05-10 华为技术有限公司 介质滤波器和电子设备

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Also Published As

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CN101356293B (zh) 2010-12-29
WO2007081775A3 (fr) 2008-04-10
CN101356293A (zh) 2009-01-28
WO2007081775A2 (fr) 2007-07-19

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