WO2005089999A1

WO2005089999A1 - Lead-free solder ball

Info

Publication number: WO2005089999A1
Application number: PCT/JP2005/004427
Authority: WO
Inventors: Daisuke Souma; Takahiro Roppongi; Hiromi Kawamata; Hiroshi Okada
Original assignee: Senju Metal Industry Co., Ltd
Priority date: 2004-03-19
Filing date: 2005-03-14
Publication date: 2005-09-29
Also published as: JP4392020B2; JPWO2005089999A1; TW200603932A; TWI334366B

Abstract

[PROBLEMS] When Sn-Ag type, Sn-Cu type, Sn-Ag-Cu type and Sn-Sb type lead-free solder balls having a Sn content of 80 mass % or more were used for forming bumps on electrodes of BGA, the yellowing of the surface and/or the corrosion of the soldered portion in the case of exposure to a corrosive atmosphere were observed in some cases. The yellowing of the surface of a bump may cause an error in the inspection of the presence or absence of a bump by the use of an image recognition device, and thus interferes with the proper inspection, and the corrosion of a soldered portion weakens the bonding strength of a bump. [MEANS FOR SOLVING PROBLEMS] A lead-free solder ball containing Sn in a content of 80 mass % or more, which further comprises 0.0001 to 0.003 mass % of Cr.

Description

Specification

Lead-free solder balls

Technical field

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.

Background art

[0002] 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. When mounting these surface-mounted components on a printed circuit board, 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.

[0003] The above-mentioned surface-mounted components have been multifunctional to a certain degree. In recent years, electronic devices have become smaller and more multifunctional. Surface-mounted components also need to be smaller and have higher functions. (Ball urid Arrey), C¾P (Hip Size Package) ^ TAB (Tape Automated Bonding) ^ Multifunctionalized surface mount components such as MCM (Multi Chip Module) (hereinafter BGA and V) It has been increasingly used.

When mounting a BGA on a 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. Here, a method of forming a solder bump on a BGA electrode will be briefly described. First, 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. After that, 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.

[0005] When mounting the BGA on which the solder bumps are formed in this way on a printed circuit board, apply a solder paste to the land of the printed circuit board, and attach the solder bumps of the BGA to the applied portions. And mount it. Then, the BGA is heated again in a reflow furnace to melt the solder paste and the solder bumps and solder the BGA to the printed circuit board.

[0006] In a conventional BGA, 150 to 250 electrodes are formed on a 30 x 30 mm BGA substrate, and the pitch between adjacent electrodes is 1.0 to 1.2 mm. The ball could have a relatively large diameter of 0.76mm. However, in recent years, the size of BGA has been further reduced with the further miniaturization of electronic devices, and the solder balls used for the reduced BGA have also become smaller. For example, 400 electrodes are formed on a 10 × 10 (mm) BGA, and the pitch between adjacent electrodes is as narrow as 0.5 mm or less. The solder ball used for such a narrow pitch BGA has a very small size of less than 0.3mm in diameter! /

[0007] By the way, conventionally, 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. When 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. At the time of disposal of electronic equipment, 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. When acid rain comes in contact with the Pb-containing printed circuit board disposed in this way, the Pb component in the solder elutes and enters the groundwater together with the acid rain. If humans and livestock drink the groundwater containing this Pb component for many months, the Pb component will accumulate in the body and lead to lead poisoning. As a result, the use of Pb has become regulated on a global scale, and lead-free solders that do not contain Pb have been used.

[0008] 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.

[0009] 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.

[0010] As an additive element of the lead-free solder, In or Bi is added to lower the melting point, P, Ge, or Ga is added to prevent oxidation, or to improve mechanical strength. And Ni, Cr, Mo, and Fe. Among them, 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

Disclosure of the invention

Problems to be solved by the invention

[0011] By the way, when a solder bump is formed on a BGA electrode using the lead-free solder ball containing Sn as a main component, the bump surface sometimes changes color to yellow (yellowing). In other words, the formation of 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. With BGA, the ability to confirm the presence or absence of solder bumps with an image recognition device after the formation of solder bumps. If the solder bumps turn yellow, an error may occur in the image recognition device.

[0012] In addition, when electronic devices made using Sn-based lead-free solder balls are subjected to severe conditions, for example, in an automobile running around a town with a large amount of exhaust gas, the exhaust gas enters the electric control device. In the case of electronic equipment and appliances used in houses near the sea, air containing salt from seawater may enter the inside. If the parts soldered with lead-free solder balls are exposed to corrosive atmospheres such as exhaust gas and salt, the solder will corrode, cracking and peeling will occur over many years, and the bonding strength will decrease. There is.

[0013] Addition of Cr to lead-free solder containing Sn as a main component to improve bonding strength has been performed as described above. Conventional Cr-containing lead-free solder has poor solderability due to poor wettability. Was to cause. The present invention provides a lead-free solder ball that does not cause yellowing of the bump surface when a solder bump is formed, and does not cause soldering failure with force if it is hard to corrode even when exposed to a corrosive atmosphere. It is in.

Means for solving the problem

[0014] 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. As a result, the solder bumps turn yellow because the surface is oxidized when the solder balls are melted. In other words, the solder is always melted at the time of soldering. At this time, 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. However, in the case of 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.

[0015] In addition, 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.

Therefore, 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. According to the findings of the present inventors, when Cr is present in a solder alloy, when the solder is melted, an oxide film of Cr covers the surface of the molten solder and prevents contact with air or a corrosive atmosphere. On the other hand, the surface of the molten solder is not oxidized and no corrosion occurs. In addition, even after solidification, the trace amount of Cr present on the solder surface is preferentially oxidized, thereby serving to prevent oxidization of Sn, which is the main base material. The yellowing of the solder is mainly the tinting of Sn, and is caused by the growth of the Sn oxide film. The effect of Cr is to reduce the growth of the Sn oxide film. The addition of Cr is as small as 0.0001-0.003% by mass and has a yellowing resistance effect. More preferably, 0.0005-0.001% by mass of soybean curd is effective.

[0018] 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 invention's effect

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. In addition, since 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.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] The lead-free solder ball according to the present invention includes Sn-Ag, Sn-Cu, Sn-Ag-Cu,

Force that exerts an excellent effect in any of the Sn-Sb system The "system" here is the alloy itself or the alloy obtained by adding a small amount of another element to the alloy. For example, 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.

[0021] 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. [0022] In the present invention, 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. In the present invention, 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.

Hereinafter, examples and comparative examples are shown in Table 1.

[Table 1]

[0026] Description of Table 1

Yellowing: Pour l.Og (approximately 10,000 pieces) into a high-temperature bath at 150 ° C with solder balls having a diameter of 0.3 mm. After standing for 48 hours, observe the surface color visually. Table 1 shows the results obtained by counting the number of yellowing of the solder ball surface and expressing the ratio as a percentage.

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.

Claims

The scope of the claims

[1] A lead-free solder ball containing 80% by mass or more of Sn, wherein 0.0001-0.003% by mass of Cr is added to the solder ball. .

[2] The lead-free solder according to claim 1, wherein Cr is preferably in the range of 0.0005 to 0.001% by mass.

[3] The lead-free solder ball according to any one of claims 1 and 2, wherein the lead-free solder ball is any of Sn-Ag, Sn-Cu, Sn-Ag-Cu, and Sn-Sb. Lead-free solder balls.

[4] A lead-free solder paste comprising 3-4 mass% Ag, 0.0001-0.003 mass% Cr and the balance Sn.

[5] 0.5% to 1.0% by mass of Cu, 0.0001% to 0.003% by mass of Cr, with the balance being Sn force.

[6] A lead-free solder paste comprising 3-5 mass% Sb, 0.0001-0.003 mass% Cr and the balance Sn.

[7] A lead-free solder ball consisting of 1-4 mass% Ag, 0.5-1.0 mass% Cu, 0.0001-0.003 mass% Cr, and the balance Sn.

[8] A lead-free solder ball comprising 3-4 mass% Ag, 0.5-1.0 mass% Cu, 0.0001-0.003 mass% Cr, and the balance Sn.

[9] The lead-free solder ball according to claim 18, wherein the lead-free solder ball has a diameter of 0.05 to 0.6mm.

[10] per cent lead-free solder of the solder balls containing more than 80 wt% of Sn Te, 0.0001 to 0.003 mass Cr in said solder ball Lumpur ^_0/0添Ka卩yellowing of the solder ball surface by How to prevent.