US20040112474A1 - Lead-free solder ball - Google Patents

Lead-free solder ball Download PDF

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Publication number
US20040112474A1
US20040112474A1 US10/684,589 US68458903A US2004112474A1 US 20040112474 A1 US20040112474 A1 US 20040112474A1 US 68458903 A US68458903 A US 68458903A US 2004112474 A1 US2004112474 A1 US 2004112474A1
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US
United States
Prior art keywords
solder
substrate
solder balls
lead
balls
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.)
Abandoned
Application number
US10/684,589
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English (en)
Inventor
Rikiya Kato
Shinichi Nomoto
Hiroshi Okada
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.)
Senju Metal Industry Co Ltd
Original Assignee
Senju Metal Industry Co Ltd
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
Application filed by Senju Metal Industry Co Ltd filed Critical Senju Metal Industry Co Ltd
Assigned to SENJU METAL INDUSTRY CO., LTD. reassignment SENJU METAL INDUSTRY CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KATO, RIKIYA, NOMOTO, SHINICHI, OKADA, HIROSHI
Publication of US20040112474A1 publication Critical patent/US20040112474A1/en
Priority to US11/117,719 priority Critical patent/US20050248020A1/en
Abandoned legal-status Critical Current

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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
    • B23K1/00—Soldering, e.g. brazing, or unsoldering
    • B23K1/0008—Soldering, e.g. brazing, or unsoldering specially adapted for particular articles or work
    • B23K1/0016—Brazing of electronic components
    • 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
    • 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
    • B23K2101/00—Articles made by soldering, welding or cutting
    • B23K2101/36—Electric or electronic devices
    • 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
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • 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
    • 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
    • H05K3/3478—Applying solder preforms; Transferring prefabricated solder patterns

Definitions

  • the present invention relates to a lead-free solder ball suitable for use in soldering of electronic components.
  • a semiconductor chip is mounted on a lead frame made of a metal such as copper or Alloy 42 (42 Ni—Fe alloy), and the chip is electrically connected to the lead frame by wire bonding with gold wires before being sealed with ceramic or plastic.
  • a lead frame made of a metal such as copper or Alloy 42 (42 Ni—Fe alloy)
  • the chip is electrically connected to the lead frame by wire bonding with gold wires before being sealed with ceramic or plastic.
  • BGA ball grid array
  • a BGA package employs solder bumps formed from solder balls in order to connect and secure the package to a printed circuit board. Therefore, the length of electrical connection is shorter than for electronic components using lead frames, thereby making it possible to increase the speed of operation.
  • the space occupied by a lead frame is no longer necessary, so a BGA package also makes it possible to save space.
  • FBGA fine ball grid array
  • CSP's chip size packages
  • a BGA package has a substrate on which a semiconductor chip is mounted.
  • the substrate has solder bumps on its back surface which are formed from solder balls arranged in a grid-like array.
  • solder ball feeder equipped with a suction plate is used.
  • the suction plate has holes arranged in the same grid-like array as the solder bumps to be formed. Solder balls are positioned on a substrate by pulling a solder ball into each hole of the feeder by suction applied through the holes, and after positioning the feeder above a substrate, releasing the suction to place or mount each ball onto the substrate.
  • solder balls are temporarily kept in position on the substrate by the stickiness of a soldering flux, which has previously been applied to the surface of the substrate on which solder bumps are to be formed.
  • the substrate having the solder balls mounted thereon is then heated in a reflow furnace to melt the solder balls and form them into solder bumps secured to the substrate.
  • the substrate having solder bumps thus formed is normally inspected by an optical inspection machine in order to check if all the solder bumps required to make the desired grid-like array are properly formed.
  • solder balls which are used in the production of BGA packages, including CSP's have a spherical shape with a diameter in the range of 0.05-2.0 mm. It is desired for solder balls to have good sphericity and a smooth surface. If the sphericity of a solder ball is not good or if its surface has significant surface irregularities or defects such as shrinkage cavities or wrinkles, problems may occur during placement of the solder ball on a substrate, such as caused by failure of the feeder to pick up the solder ball due to a loss of suction or a failure of the feeder to release the solder ball due to biting of the ball into one of the holes in the feeder.
  • solder balls it is also desired for solder balls to form solder bumps having a smooth surface with a uniform gloss when heated in a reflow furnace.
  • the optical inspection of solder bumps formed on a substrate is conducted by focusing normally on solder bumps having a glossy surface or in some cases on solder balls having a non-glossy surface, so the formation of solder bumps, some of which have a glossy surface and others of which have a non-glossy surface, makes it difficult to adjust the focus in the optical inspection of the solder bumps and results in a failure to identify some of the bumps.
  • solder that has been used most widely in soldering is an Sn—Pb alloy.
  • Sn—Pb solder has been used since ancient times and has the advantages of a low melting point and good solderability.
  • an Sn—Pb alloy having an Sn content of 63 wt % or 75 at % which is a representative composition for an Sn—Pb solder, has the excellent properties that it forms a soldered joint having a smooth surface with good gloss.
  • Solder balls made of an Sn—Pb alloy have a smooth surface, so they can be smoothly mounted onto a substrate by use of the above-described solder ball feeder. In addition, after heating in a reflow furnace, they form solder bumps having a smooth and glossy surface which does not interfere with optical inspection of the solder bumps.
  • Lead-free solders which are considered promising at present are Sn—Ag solders and particularly Sn—Ag—Cu solders in view of their ease of handling. However, the wettability of these lead-free solders is generally lower than that of Sn—Pb solders. For example, in a spreading test, an Sn—Ag—Cu lead-free solder shows a spreading factor of approximately 80% that of an Sn—Pb solder.
  • solder balls are made from such an Sn—Ag—Cu lead-free solder
  • the surfaces of the resulting solder balls have shrinkage cavities and wrinkles, thereby increasing the occurrence of the above-described problems during mounting of solder balls on a substrate using the above-described solder ball feeder.
  • the surfaces of the resulting solder bumps tend to be glossy for some bumps and non-glossy for other bumps.
  • the formation of glossy bumps interspersed with non-glossy bumps makes optical inspection of the solder bumps difficult and increases the rate of misidentification.
  • the present invention provides a solder ball of an Sn—Cu—Ag-based, lead-free solder which has a smooth surface having little or no shrinkage cavities or wrinkles.
  • the present invention provides a solder ball made of a lead-free solder which comprises, by atomic percent, 3%-6% of Ag, 1%-4% of Cu, 0.01%-2% of at least one element of the iron group and preferably Co, optionally 0.04%-4% of P, and a balance of Sn.
  • the present invention also provides a substrate for a BGA package (including CSP) which have solder bumps formed from the above-described solder balls.
  • the present invention also relates to a method of forming solder bumps on a substrate comprising placing the above-described solder balls on the substrate followed by heating the substrate to melt the solder balls and form them into solder bumps secured to the substrate.
  • FIG. 1 is an electron photomicrograph of solder balls of an Sn—Cu—Ag—Co lead-free solder according to the present invention.
  • FIG. 2 is an electron photomicrograph of solder balls of an Sn—Cu—Ag lead-free solder.
  • FIG. 3 is an electron photomicrograph of solder balls of a conventional Sn—Pb solder.
  • Spherical solder balls can be produced either by remelting solid masses of solder of a certain size followed by cooling, or by forming droplets of a certain size from molten solder followed by cooling. In either method, molten solder of a certain size is cooled and changed into a solid. In the course of solidification, some of the elements of the solder initially crystallize out in the liquid mass, and the resulting crystals, which serve as nuclei for crystal growth, gradually grow until the entire mass becomes solid. This crystal growth may sometimes occur unidirectionally, i.e., in a certain direction, thereby forming dendrites.
  • At least one of the iron group elements Fe, Ni, and Co
  • Co is added to an Sn—Cu—Ag solder in an amount of 0.01-2 atomic percent (at %).
  • Sn—Cu—Ag solder has a melting point which is much higher than those of Sn, Cu, and Ag. Therefore, during solidification of molten solder, these elements initially crystallize out to form a large number of nuclei for crystal growth.
  • solder balls having a smooth surface in which the formation of shrinkage cavities and wrinkles is prevented, thereby making it possible to produce solder balls which can be smoothly mounted on a substrate using a solder ball feeder of the above-described type.
  • the solder balls can form solder bumps having a uniform glossy surface, which facilitates optical inspection and minimizes the occurrence of misidentification.
  • the total content of the iron group elements is less than 0.01 at %. If this content is more than 2 at %, the iron group elements become segregating on the surface of the solder balls without dissolving into the inside thereof, thereby deteriorating the wettability of the solder balls when melted and adversely affecting the surface smoothness and gloss thereof.
  • the iron group element is cobalt (Co).
  • the total content of the iron group elements is preferably in the range of 0.02-0.5 at %.
  • the Ag and Cu contents of the alloy composition in a lead-free solder ball according to the present invention are 3-6 at % and 1-3 at %, respectively.
  • Ag When present in an amount of at least 3 at %, Ag serves to lower the melting point of the solder and improve the wettability and strength thereof. However, when the Ag content increases so as to exceed 6 at %, it adversely affects both the melting temperature and wettability of the solder.
  • the Ag content is in the range of 3-5 at %. In order to lower the melting point of the solder, it is also preferable that the Ag content be selected such that the atomic ratio of Ag to Sn is approximately 3:70.
  • Cu When present in an amount of at least 1 at %, Cu serves to improve the strength of the solder.
  • the presence of a small amount of Cu also provides the solder with improved wettability.
  • the presence of an excessive amount of Cu which is greater than 4 at % for Cu, causes a rise in the melting temperature of the solder and deteriorates its wettability.
  • the Cu content is in the range of 1-3 at %. More preferably, the Cu content is selected such that the atomic ratio of Cu to Sn is approximately 1:70.
  • the addition of at least one iron group element and preferably Co is effective for preventing the formation of dendrites during solidification and producing solder balls having a smooth surface with no shrinkage cavities or wrinkles, the addition can possibly adversely affect the wettability of the solder balls.
  • phosphorus (P) may be added in a small amount.
  • the addition of P ensures that the solder can exhibit good wettability even though it contains at least one iron group element.
  • the content of P is in the range of 0.04-4 at %.
  • Sn is the remainder of the solder composition.
  • the Sn content is in the range of 86-96 at %.
  • solder composition may contain unavoidable impurities such as Pb, Sb, and Bi in a total amount of at most 0.2 at %.
  • the diameter of a solder ball according to the present invention is not limited as long as the solder ball is suitable for use in the formation of solder bumps on a substrate for a BGA package or CSP.
  • the diameter is in the range of from 0.05 mm to 1.0 mm.
  • Solder balls according to the present invention can be produced by a method which comprises forming masses of molten solder of the above-described composition having almost equal volumes and solidifying the masses to form balls having almost equal diameters.
  • Examples of such a ball forming method include an oil bath method as disclosed in U.S. Pat. No. 5,653,783 and JP P07-300606A (1995) and a direct method as disclosed in U.S. Pat. No. 5,445,666, although other methods may be employed.
  • a wire of a solder having a predetermined composition is prepared and cut into portions having a given length.
  • the wire portions are separately dropped into an oil bath having a vertical temperature gradient in which the temperature in an upper portion of the bath is higher than in a lower portion, whereby the portions are allowed to melt in the upper portion and then solidify while falling in the oil bath.
  • a molten solder having a predetermined composition is prepared.
  • the molten solder is dripped or allowed to fall in droplets of a given size through an orifice or nozzle, and then solidified while falling in a chamber.
  • the resulting solder balls have a spherical shape due to the action of the surface tension of the molten solder.
  • Solder balls having a diameter of 0.5 mm were produced from each of various solders having the compositions shown in Table 1 by a conventional oil bath method, and they were used to form solder bumps on a substrate for a BGA package by mounting the solder balls on the substrate using a solder ball feeder having holes for grasping solder balls by suction and then heating the substrate in a reflow furnace at a temperature sufficient to form solder bumps.
  • the reliability of mounting solder balls was evaluated by the percentage of solder balls with respect to which problems occurred during mounting of solder balls, i.e., the percentage of solder balls which were not grasped by the solder ball feeder by suction or which were not released from the feeder due to biting into the holes of the feeder.
  • solder bumps formed on the substrate were checked by an optical inspection machine developed for checking solder bumps to determine the percent occurrence of misidentification of solder bumps in this inspection (the percentage of solder bumps which were not identified by the inspection machine).
  • solder balls made of a conventional Sn—Cu—Ag lead-free solder in Run No. 6 showed significant surface irregularities and had shrinkage cavities on their surface when observed under a SEM, thereby resulting in significantly increased percentages of occurrence of mounting problems for solder balls and misidentification in optical inspection of solder bumps.
  • FIG. 1 shows solder balls made of a lead-free solder of Run No. 1 in accordance with the present invention in which 0.02 at % of Co was added to the solder of Run No. 6, surface irregularities were significantly suppressed and no shrinkage cavities were found on the surfaces of the solder balls, and the surfaces of the solder balls were as smooth as those of solder balls of a conventional Sn—Pb solder (FIG. 3).
  • the percentages of occurrence of mounting problems and misidentification in all the solder balls according to the present invention (Runs Nos. 1-5) were as low as those obtained with the conventional Sn—Pb solder in Run No. 7.

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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)
US10/684,589 2002-10-17 2003-10-15 Lead-free solder ball Abandoned US20040112474A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
US11/117,719 US20050248020A1 (en) 2002-10-17 2005-04-29 Lead-free solder ball

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2002303197 2002-10-17
JP2002-303197 2002-10-17

Related Child Applications (1)

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US11/117,719 Continuation US20050248020A1 (en) 2002-10-17 2005-04-29 Lead-free solder ball

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US11/117,719 Abandoned US20050248020A1 (en) 2002-10-17 2005-04-29 Lead-free solder ball

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US11/117,719 Abandoned US20050248020A1 (en) 2002-10-17 2005-04-29 Lead-free solder ball

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US (2) US20040112474A1 (de)
EP (1) EP1410871B1 (de)
AT (1) ATE390241T1 (de)
DE (1) DE60319932T2 (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050275098A1 (en) * 2004-06-15 2005-12-15 Advance Semiconductor Engineering Inc. Lead-free conductive jointing bump
CN100443246C (zh) * 2007-01-30 2008-12-17 山东大学 堆焊用填充金属颗粒及其制备方法
CN100460136C (zh) * 2007-01-30 2009-02-11 山东大学 焊接用填充金属颗粒及其制备方法
US10888960B2 (en) 2016-07-04 2021-01-12 Koki Company Limited Solder alloy and resin flux cored solder

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1894667A4 (de) * 2005-06-10 2009-12-02 Senju Metal Industry Co Verfahren zum löten eines stromlos vernickelten teils
US8641964B2 (en) 2005-08-24 2014-02-04 Fry's Metals, Inc. Solder alloy
EP1924394A2 (de) * 2005-08-24 2008-05-28 FRY'S METALS, INC. d/b/a ALPHA METALS, INC. Lötlegierung
US8013444B2 (en) * 2008-12-24 2011-09-06 Intel Corporation Solder joints with enhanced electromigration resistance
US11847651B2 (en) 2017-05-23 2023-12-19 Kenneth A Kopf Systems and methods for facilitating biometric tokenless authentication for services

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5445666A (en) * 1992-12-17 1995-08-29 Deutsche Forschungsanstalt Fuer Luft- Und Raumfahrt E.V. Method for producing small metal balls approximately equal in diameter
US5653783A (en) * 1994-01-20 1997-08-05 Nippon Steel Corporation Method of producing fine metal balls
US5817194A (en) * 1996-11-14 1998-10-06 Fukuda Metal Foil & Powder Co., Ltd. Tin base soldering/brazing material
US6179935B1 (en) * 1997-04-16 2001-01-30 Fuji Electric Co., Ltd. Solder alloys
US6231691B1 (en) * 1997-02-10 2001-05-15 Iowa State University Research Foundation, Inc. Lead-free solder
US6517602B2 (en) * 2000-03-14 2003-02-11 Hitachi Metals, Ltd Solder ball and method for producing same

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6638847B1 (en) * 2000-04-19 2003-10-28 Advanced Interconnect Technology Ltd. Method of forming lead-free bump interconnections
JP3599101B2 (ja) * 2000-12-11 2004-12-08 株式会社トッパンＮｅｃサーキットソリューションズ はんだ、それを使用したプリント配線基板の表面処理方法及びそれを使用した電子部品の実装方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5445666A (en) * 1992-12-17 1995-08-29 Deutsche Forschungsanstalt Fuer Luft- Und Raumfahrt E.V. Method for producing small metal balls approximately equal in diameter
US5653783A (en) * 1994-01-20 1997-08-05 Nippon Steel Corporation Method of producing fine metal balls
US5817194A (en) * 1996-11-14 1998-10-06 Fukuda Metal Foil & Powder Co., Ltd. Tin base soldering/brazing material
US6231691B1 (en) * 1997-02-10 2001-05-15 Iowa State University Research Foundation, Inc. Lead-free solder
US6179935B1 (en) * 1997-04-16 2001-01-30 Fuji Electric Co., Ltd. Solder alloys
US6517602B2 (en) * 2000-03-14 2003-02-11 Hitachi Metals, Ltd Solder ball and method for producing same

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050275098A1 (en) * 2004-06-15 2005-12-15 Advance Semiconductor Engineering Inc. Lead-free conductive jointing bump
CN100443246C (zh) * 2007-01-30 2008-12-17 山东大学 堆焊用填充金属颗粒及其制备方法
CN100460136C (zh) * 2007-01-30 2009-02-11 山东大学 焊接用填充金属颗粒及其制备方法
US10888960B2 (en) 2016-07-04 2021-01-12 Koki Company Limited Solder alloy and resin flux cored solder

Also Published As

Publication number Publication date
DE60319932T2 (de) 2009-04-16
EP1410871A1 (de) 2004-04-21
EP1410871B1 (de) 2008-03-26
DE60319932D1 (de) 2008-05-08
US20050248020A1 (en) 2005-11-10
ATE390241T1 (de) 2008-04-15

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AS Assignment

Owner name: SENJU METAL INDUSTRY CO., LTD., JAPAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:KATO, RIKIYA;NOMOTO, SHINICHI;OKADA, HIROSHI;REEL/FRAME:015045/0894

Effective date: 20040209

STCB Information on status: application discontinuation

Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION