Classifications

• • 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
• • 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
• • 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
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K3/00—Apparatus or processes for manufacturing printed circuits
  • H05K3/30—Assembling printed circuits with electric components, e.g. with resistor
  • H05K3/32—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits
  • H05K3/34—Assembling printed circuits with electric components, e.g. with resistor electrically connecting electric components or wires to printed circuits by soldering
  • H05K3/3457—Solder materials or compositions; Methods of application thereof
  • H05K3/3463—Solder compositions in relation to features of the printed circuit board or the mounting process

Definitions

• the present invention relates to a solder alloy used for mounting or plating electronic components on a printed circuit board (PCB) and the like, and, more particularly, to a Pb-free Sn-Ag based solder alloy which comprises
• soldering is a joining technology using a solder alloy, in particular, for mounting miniaturized electronic components, such as semiconductor chips or resistor chips, on a printed circuit board (PCB).
• PCB printed circuit board
• the PCB, the electronic components mounted thereon, and the solder alloy are more affected by cyclic stress caused by variation in temperature, thermal expansion differences, vibration, and the like, so that microstructure of the solder alloy is subjected to grain coarsening at a soldered joint, resulting in generation of cracks at the soldered joint due to fatigue.
• the cracks at the soldered joint act as a source of defects, such as disconnection of the electronic components mounted on the PCB.
• a binary solder alloy comprising tin (Sn) and lead (Pb), such as a solder alloy comprising 60 %wt Sn and 40 wt% Pb and a solder alloy comprising 63 %wt Sn and 37 wt% Pb, is mainly used.
• the conventional Sn-Pb based solder alloy has a problem of environmental contamination due to leakage of lead upon disposal thereof.
• a Cu-Ni- Sn tertiary solder alloy disclosed in Japanese Unexamined Patent Publication No. 2000-225490 is well known in the art.
• the Pb-free Cu-Ni-Sn tertiary solder alloy is provided by substituting some contents of Cu of the conventional solder alloy with Ni, and comprises 0.05 ⁇ 2.0 wt% of Cu, 0.001 ⁇ 2.0 wt% of Ni, and the balance of Sn.
• the Pb-free solder alloy does not contain Pb, it can reduce environmental contamination, and has a slightly increased mechanical strength.
• the Pb-free solder alloy disclosed therein has problems in that excessive dross is generated due to oxidation upon soldering, and in that a thread-shaped bridge connection is formed around a soldered joint due to low wettability and spreadability of the solder alloy, causing defects such as short- circuits.
• plating is performed on electrodes (chip components) or leads (lead elements) of the electronic components as a final process for reinforcing soldering properties and oxidation resistance (corrosion resistance).
• oxidation resistance corrosion resistance
• whiskers which are formed like whiskers on the surface of a plated portion, and grow to relieve a compressive stress when a metallic structure is subjected to compressive stress or when the surface of the plated portion is oxidized
• a Pb-free quaternary solder alloy is disclosed in Korean Patent Registration No. 10-0453074, which comprises 0.05 ⁇ 2.0 wt% of Cu, 0.001 ⁇ 2.0 wt% of Ni, 0.001 ⁇ 1.0 wt% of P, and the balance of Sn.
• the Pb-free quaternary solder alloy restricts the reaction of an oxide by adding a minute amount of P to the conventional Pb-free Cu-Ni-Sn tertiary solder alloy, and increases the strength of the solder, the stress resistance of the soldered joint to endure the thermal stress and vibration around the soldered joint while reducing the fluidity of the solder alloy, thereby reducing soldering defects.
• the temperature is increased up to 30 ⁇ 40 ° C upon soldering with the Pb-free quaternary solder alloy, it is necessary for the electronic components to secure thermal resistance.
• the Pb- free quaternary solder alloy has lower wettability and spreadability (reduced about 15 %) than those of the conventional Sn-Pb solder, it has deteriorated soldering properties, and if Pb-free plating (mainly, Sn plating on manual components, and Sn plating or Sn-Bi plating on IC series) is performed, the soldering properties of the components are also deteriorated.
• the present invention has been made in view of the above and other problems, and an aspect of the present invention is to provide a Pb-free Sn-Ag based solder alloy, which has a lower melting point, and highly enhanced wettability and joining strength, compared with the conventional Pb-free solder alloy, while having different alloy contents according to application of the solder.
• FIG. 1 is a graph illustrating the relationship between wettability and Ni content
• FIG. 2 is a graph illustrating the relationship between amount of oxide and soldering time according to whether a solder alloy contains P or not;
• FIG. 3 is a graph illustrating the relationship between amount of oxide and P content.
• a Pb-free Sn-Ag based solder alloy according to the invention contains an optimum amount of Ag, Ni, and P in order to increase strength of solder alloy, and stress resistance to endure thermal stress and vibration in a soldered joint while enhancing fluidity of the solder alloy by suppressing reaction of oxide, which is a feature of the conventional Sn-Cu based Pb-free solder alloys.
• the present invention also contains Sn as the base metal.
• the solder alloy of the invention comprises Cu and Ag in order to increase joining strength at the soldered joint, and Ni in order to suppress formation of
• solder alloy of the invention further comprises a minute amount of P in order to reduce generation of dross caused by friction between the surface of the solder alloy and oxygen upon soldering.
• solder alloy When the solder alloy comprises about 0.7 wt% of Cu and the balance of Sn, it exhibits a melting point of about 227 ° C , which is about 5 ° C lower than the 232 ° C melting point of solder alloy comprising 100 wt% of Sn.
• the optimum amount of Cu added to the solder alloy is in the range of 0.3 ⁇ 0.8 wt%.
• the melting point of the solder alloy increases again. Increased melting point of the solder alloy causes an increase of the soldering temperature, thereby having a negative influence upon electronic components having weak thermal resistance, and resulting in surface oxidation, increased viscosity, reduced wettability, and bridge or icicle-shaped defects during flow or reflow soldering.
• solder alloy about 2.3 wt% Cu may be added to the solder alloy so long as thermal resistance of objects to be joined, such as PCBs, surface mounted components, metal, and the like, is secured as with a solder ball, thereby enhancing the wettability and joining strength even if soldering or metal plating is performed.
• the wettability and spreadability of the solder alloy are better than those of Sn- Cu-Ni-P based solder alloy, but when the amount of Ag added to the Sn-Cu based solder alloy is less than 0.01 wt%, effect of enhancing the wettability and spreadability of the solder alloy is not exhibited.
• an amount of Ag added to the Sn-Cu based solder alloy is greater than 5.0 wt%, no increase in the wettability and spreadability of the solder alloy is exhibited, and addition of large quantities of Ag is economically undesirable due to its high price.
• the amount of Ag added to the solder alloy is differently determined according to whether a phenol-based or epoxy-based PCB is used.
• An optimum amount of Ag added to the solder alloy is in the range of 0.01 ⁇ 0.5 wt% (the phenol-based PCB) or in the range of 2.0 ⁇ 4.0 wt% (the epoxy-based PCB).
• Table 1 shows a wetting time and Ag costs when 0.01 ⁇ 5 wt% Ag is added to a Pb-free Sn-0.5Cu-0.1Ni-0.01P solder alloy disclosed in Korean Patent Registration No. 10-0453074.
• Testing was performed via soldering a base metal and a solder using a flux under the following conditions while observing joining properties between the base metal and the solder.
• the solder alloy preferably comprises 0.01 ⁇ 0.5 wt% of Ag for flow soldering, and comprises 2 ⁇ 4 wt% of Ag for reflow soldering.
• Ni 0.01 - 0.1 wt% is added to the solder alloy. As shown in FIG. 1 , it can be seen that wettability varies according to Ni content. Ni serves to suppress generation of intermetallic compounds, such as
• Intermetallic compounds have a high melting point, and deteriorate the fluidity of the molten metal as well as deteriorating function of the alloy as the solder due to the presence of intermetallic compounds in the molten metal when melting the alloy. As a result, when intermetallic compounds remain between solder patterns during soldering, they form bridges, thereby causing conductors to be shorted, and when they are separated from molten solder, protrusion- shaped horns can remain.
• a minute amount of P is added to the solder alloy.
• FIGS. 2 and 3 variation in amount of oxide according to P content is shown.
• Table 2 shows a melting point of solder alloys according to compositions of Pb-free Sn-Ag based solder alloys of the invention.
• the Pb-free Sn-Ag based solder alloy may have different compositions according to whether the phenol- based or the epoxy-based PCB is used, whether thermal resistance of an object to be plated, such as lead of elements, flexible printed circuit (FPC), Wire-B (Wire-Bonding), Solder Ball (S/B) and the like, is secured or not, or whether nitrogen is used or not by the soldering apparatus upon soldering.
• FPC flexible printed circuit
• Wire-B Wire-Bonding
• S/B Solder Ball
• Table 3 shows compositions of the solder alloys according to application of the Pb-free Sn-Ag based solder alloy of the invention.
• a Pb-free Sn-Ag based solder alloy comprising: 0.1 ⁇ 3.0 wt% of Cu, 0.01 ⁇ 0.5 wt% of Ni, 0.01 ⁇ 5.0 wt% of Ag, and the balance of Sn.
• the Pb-free Sn-Ag based solder alloy may comprise 0.3 ⁇ 0.8 wt% of Cu, 0.01 ⁇ 0.1 wt% of Ni, 0.01 ⁇ 0.5 wt% of Ag, and the balance of Sn.
• the Pb-free Sn-Ag based solder alloy may comprise 0.3 ⁇ 0.8 wt% of Cu, 0.01 ⁇ 0.1 wt% of Ni, 2.0 ⁇ 4.0 wt% of Ag, and the balance of Sn.
• the Pb-free Sn-Ag based solder alloy may comprise 2.1 ⁇ 2.5 wt% of Cu, 0.01 ⁇ 0.1 wt% of Ni, 2.0 ⁇ 4.0 wt% of Ag, and the balance of Sn.
• the Pb-free Sn-Ag based solder alloy may comprise 2.1 ⁇ 2.5 wt% of Cu, 0.01 ⁇ 0.1 wt% of Ni, 0.01 ⁇ 0.5 wt% of Ag, and the balance of Sn.
• the Pb-rree Sn-Ag based solder alloy may further comprise 0.003 ⁇ 0.01 wt% ofP.
• the Pb-free Sn-Ag based solder alloy of the invention has a lower melting point, and highly enhanced wettability and joining strength, compared with the conventional Pb-free solder alloy, thereby preventing generation of the bridges.
• the Pb-free Sn-Ag based solder alloy can have the optimal composition according to whether the phenol- based or epoxy-based PCB is used, whether the thermal resistance of the object to be plated, such as leads of elements, flexible printed circuit (FPC), Wire-B (Wire-Bonding), Solder Ball (S/B) and the like, is secured or not, or whether nitrogen is used or not by the soldering apparatus upon soldering.
• the Pb-free Sn-Ag based solder alloy of the invention can be applied to the components in various manners, such as flow soldering, reflow soldering, plating after soldering, the solder ball, the wire bonding, and the like.

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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)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

Country Status (6)

Cited By (4)

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Citations (4)

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• 2004
  • 2004-11-13 KR KR1020040092857A patent/KR20050030237A/ko not_active Application Discontinuation
• 2005
  • 2005-02-02 JP JP2007540243A patent/JP2008518791A/ja active Pending
  • 2005-02-02 WO PCT/KR2005/000305 patent/WO2006052049A1/en active Application Filing
  • 2005-02-02 EP EP05726536A patent/EP1824638A4/en not_active Withdrawn
  • 2005-02-02 US US11/577,927 patent/US20090129970A1/en not_active Abandoned
  • 2005-02-02 CN CNA2005800372893A patent/CN101048258A/zh active Pending

Patent Citations (4)

Non-Patent Citations (1)

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