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
  • 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
• • 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
  • H05K3/341—Surface mounted components
  • H05K3/3431—Leadless components
  • H05K3/3436—Leadless components having an array of bottom contacts, e.g. pad grid array or ball grid array components
• • 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 ball used for soldering a surface mount component, particularly to a lead-free solder ball containing no Pb.
• a surface mount component is a device in which electronic components are directly soldered and mounted on lands formed on the surface of a printed circuit board, and generally includes QFP, PLCC, SOP, SOJ, and the like.
• QFP Quality of Service
• PLCC Landing Component
• SOP Synchronization Protocol
• SOJ SOJ
• a surface mount component is a device in which electronic components are directly soldered and mounted on lands formed on the surface of a printed circuit board, and generally includes QFP, PLCC, SOP, SOJ, and the like.
• a solder paste is applied to the land of the printed circuit board, the surface-mounted components are mounted on the applied portion, and then the solder paste is melted in a reflow furnace.
• the surface mount components were soldered to the printed circuit board.
• solder bumps are formed on the electrodes of the BGA in advance, and the solder bumps are soldered to the printed circuit board.
• a method of forming a solder bump on a BGA electrode will be briefly described.
• an adhesive flux and solder paste are applied to the BGA electrodes, and solder balls are mounted on the applied portions by a mounting device.
• the BGA on which the solder balls are mounted is heated in a reflow furnace to melt the solder balls, thereby forming solder bumps on the electrodes of the BGA. Since the reflow temperature at this time is at least 30 ° C higher than the melting temperature of the solder ball, the surface of the molten solder ball becomes easily oxidized.
• the solder ball used for BGA has been Sn-Pb solder.
• the eutectic composition (63Sn-Pb) of the Sn-Pb solder has been widely used because it has excellent solderability and has few defects.
• electronic devices that used solder balls containing lead while being used became old and became inconvenient or broke down, they were discarded without purging up or repairing.
• plastics and metals that make up the electronic equipment could be reused.
• the printed circuit board could not be completely separated because the land and solder adhered metallically. Even if collected, they could not be reused, so they had to be disposed of in landfills.
• Lead-free solder includes Sn-Ag based, Sn-Cu based, Sn-Ag-Cu based, Sn-Sb based, Sn-Bi based, Sn-Zn based based on Sn and the like. It is obtained by further adding other elementary kashimi elements. As described above, various types of lead-free solder have certain strengths and weaknesses, and they are used differently depending on the application.
• Sn-Bi-based lead-free solder has a low melting point of 139 ° C for Sn-58Bi. Although it has the feature of little heat influence, its use is limited because it is very brittle. In the Sn-Zn system, Sn-9Zn has a melting point of 199 ° C and has a melting point close to that of conventional 63Sn-Pb eutectic solder. The force Zn, which has a large tendency to ionize, has a problem of insufficient corrosion resistance.
• Sn-3.0-4.0Ag Sn-0.5-1.0Cu, Sn-1.0-4.0Ag-0.5Cu, more preferably Sn-3.0-4.0Ag-0.5Cu (melting point: 221-227 ° C)
• Sn- Sn-based lead-free solders such as 3.0-5.0Sb have a slightly higher melting point than eutectic solders, but because of their high mechanical strength, they are suitable for soldering electronic devices, especially for forming BGA bumps in the form of solder balls. Many are used.
• Patent Literature 1-16 describes a lead-free solder to which Cr is added.
• Patent Document 1 JP-A-2-179386
• Patent Document 2 JP-A-2000-15476
• Patent Document 3 JP 2001-205476 A
• Patent Document 4 Japanese Patent Application Laid-Open No. 2002-18589
• Patent Document 5 JP-A-2002-248596
• Patent Document 6 JP-A-2003-94195
• solder bumps on the BGA is a force that mounts the solder balls on the electrodes of the BGA and also melts the solder balls in a reflow furnace.
• the present inventors have conducted intensive studies on the cause of the yellowing of the surface of a solder bump when a solder bump is formed on a BGA electrode and the cause of solder corrosion in a corrosive atmosphere.
• the solder bumps turn yellow because the surface is oxidized when the solder balls are melted.
• the solder is always melted at the time of soldering.
• the oxidized Sn and Pb of the Sn-Pb solder covers the surface. Since the Sn and Pb oxides contain Pb, they become almost white, and this white does not cause an error in the image recognition device.
• lead-free solder containing Sn as a main component Sn as the main component oxidizes during melting, and the oxidized tin becomes yellow, causing an error in an image recognition device.
• the portion soldered with a Sn-based lead-free solder ball corrodes in a corrosive atmosphere because a large amount of Sn is contained in the lead-free solder ball. This is because the resistance is lower than that of Pb.
• the present inventors have found that if the solder surface is in a state in which it is difficult to oxidize when the solder ball is melted, the solder surface does not turn yellow, or after soldering, an inert atmosphere is formed on the solder surface.
• the aim was to make it difficult to corrode even if a large amount of Sn was contained if there was a barrier to block.
• the present inventors have searched for an element that has the effect of preventing oxidation and have a barrier effect, and have found that adding a trace amount of Cr to a lead-free solder containing Sn as a main component has the effect of preventing oxidation and having a barrier effect.
• the present invention has been completed.
• the present invention relates to a lead-free solder ball containing 80% by mass or more of Sn, wherein 0.0001 to 0.003% by mass of Cr is added to the solder ball. is there.
• the lead-free solder ball of the present invention does not yellow when a solder bump is formed on a BGA, so that no error occurs when image processing is performed by an image recognition device.
• the lead-free solder ball of the present invention does not corrode even when exposed to a corrosive atmosphere for a long period of time, it does not crack or peel off, and can exhibit the bonding strength of the solder itself. It is excellent.
• the lead-free solder ball according to the present invention includes Sn-Ag, Sn-Cu, Sn-Ag-Cu,
• the “system” here is the alloy itself or the alloy obtained by adding a small amount of another element to the alloy.
• Sn-Ag-based is a binary alloy of Sn-Ag as it is, and a multi-element alloy in which one or more selected from In, Bi, Sb, Ni, P, Ge, and Ga are added to Sn-Ag alloy. It is.
• Sn-Cu system, Sn-Ag-Cu system, and Sn-Sb system are also powerful.
• the yellowing of lead-free solder occurs when a large amount of Sn is added. That is, if the added amount of Sn is 80% by mass or more, the oxidized color of Sn becomes yellow during melting, which causes an error in the image recognition device. Therefore, in the present invention, an object is to prevent yellowing in a lead-free solder containing 80% by mass or more of Sn.
• the amount of the Sn main component of force Cr is obtained by 0.0001 to 0.003 mass 0/0 added Caro the Cr to lead-free solder is less than 0.0001 wt%, and anti-yellowing The effect of preventing corrosion does not appear, but if added in excess of 0.003% by mass, the oxide film becomes too thick and impairs the solderability.
• JISZ 3198-3 solder spread rate is used as a guide for the wettability of lead-free solder S. If the solder spread rate is less than 75% for lead-free solder, good solderability with poor wettability cannot be performed.
• the preferred amount of Cr added is 0.0005 to 0.001% by mass, and within this range, yellowing can be prevented and solderability is good.
• the lead-free solder ball of the present invention is a ball having a diameter at which the bonding strength is extremely weakened by the effect of corrosion, that is, a lead-free solder ball having a fine diameter, approximately 0.05-0.6 mm. It has excellent effects.
• solderability Table 1 shows the results of the spread ratio on a conventional copper plate using a solder ball with a diameter of 0.5 mm. JISZ3198-3 (Lead-free solder test method) Method Part 3 Spreading test method).
• the solder ball of the example had good yellowing and good solder spreading.
• the amount of Cr added was 0.0005-0.001% by mass.
• the comparative solder ball satisfies both the yellowing and spreading properties. Things were powerful. Industrial applicability
• the lead-free solder ball of the present invention is suitable for forming bumps other than force BGA, such as forming bumps on top of head pins or forming bumps on connector electrodes, which are suitable for forming BGA bumps. It goes without saying that it can be applied to things.

Landscapes

• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)
• Analysing Materials By The Use Of Radiation (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=34993512

Family Applications (1)

Country Status (3)

Cited By (6)

Families Citing this family (1)

Citations (2)

• 2005
  • 2005-03-08 TW TW094106915A patent/TW200603932A/zh not_active IP Right Cessation
  • 2005-03-14 JP JP2006511176A patent/JP4392020B2/ja not_active Expired - Lifetime
  • 2005-03-14 WO PCT/JP2005/004427 patent/WO2005089999A1/ja active Application Filing

Patent Citations (2)

Also Published As

Similar Documents

Legal Events