JP2005057245A - Bump junction and electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use a tin-zinc solder, since it is impeded to form a weak intermetallic compound consisting of tin, gold and nickel by bonding zinc concentrating on a solder ball surface with nickel plating, thereby a mechanical reliability of a solder bump joint is improved. <P>SOLUTION: In place of a tin-lead solder constituting a former solder vamp, since a solder ball configured by a solder alloy which bases on tin and includes zinc is used, zinc layers concentrating on the solder ball surface participate with all bondings, thereby a reaction of the tin forming the weak intermetallic compound is impeded. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a bump bonded body and an electronic component made of a tin-zinc solder alloy.

  In recent years, with the increase in functionality and size of electronic devices, it has been required to increase the density and weight of electronic components used. SOP and QFP, which have been the mainstream until now, had leads arranged on both sides or four sides of the package. However, the number of leads is limited by the side length, so there is a limit to increasing the number of leads. It was. In addition, when a fine pitch or a multi-pin lead is used, a solder bridge is generated between the leads, and the mounting accuracy on the substrate becomes a problem, and there is a technical limit.

  Therefore, recently, BGA, CSP, and the like, which are bonding methods that do not use leads, have been developed, and are being mass-produced and used. These are not joined by leads located on the side of the package like SOP and QFP, but the electrodes and the substrate are joined by solder balls arranged in a lattice pattern on the back of the package, so that the number of pins and the pitch are reduced. It will be advantageous. Therefore, it is possible to design a circuit that is more highly integrated than ever before, and electronic components have become smaller. At present, the demand for electronic components using the bump connection method found in BGA and CSP is very high.

  Currently, in the manufacturing process of a BGA using tin-lead solder balls, nickel plating and gold plating are applied on the copper constituting the BGA electrode portion and internal wiring. Since the internal wiring portion is bonded to the integrated circuit by a gold wire, the thickness of the gold plating on the internal wiring requires about 1 μm. Accordingly, the copper electrode on the back surface on which the solder balls are mounted is similarly plated with about 1 μm.

  The mounting of solder balls in the manufacturing process is the final process for completing the BGA package. A flux is printed on a copper electrode on which nickel plating and gold plating have been applied, a solder ball is mounted thereon, and the electrode portion and the solder ball are joined by reflow. This phenomenon is well known at the joint between the electrode and solder ball after reflow because the gold diffuses into the solder during reflow, so the tin on the solder surface and the plated nickel are actually joined. ing.

  In particular, when a package is mounted on a mother board, the electrode part on the board may be gold flash / nickel plated, but since the gold flash plating thickness is 0.1 μm or less, similarly in the solder Spreading gold is not a problem.

  However, when the BGA is subjected to a high temperature standing test after mounting the solder balls, the fracture mode appears different depending on the test time and temperature conditions. For example, a crack may occur at the interface between tin and nickel, resulting in a significant increase in tensile strength. May decrease. This is presumably because gold once diffused in the solder due to high temperature aging moved to the joint interface between tin and nickel, and was brittle in strength, and an intermetallic compound of tin, gold and nickel was formed.

  Similarly, with the miniaturization of electronic components, the internal wiring has also been densified, and gold wire bonding that connects the integrated circuit and external electrodes also uses bumps arranged on the electrodes on the back of the integrated circuit for electrical conduction. Flip chip type internal bonding forms have been used.

  There are various types of flip chip methods, but gold-gold, solder-gold, and solder-solder joints are often used. Among them, the method of joining the gold bump formed on the electrode on the back surface of the integrated circuit and the solder formed on the substrate electrode can easily form the gold bump by a wire bond type and can use an inexpensive solder. The range of use is wide.

However, because of the large amount of gold, as in the case of solder bumps, the formation of an intermetallic compound of gold and tin in the bonding interface with gold or in the gold layer makes the bonding brittle in strength. There may be problems with reliability.
Japanese Patent Laid-Open No. 11-17321

  In conventional solder balls, the gold once diffused into the solder at high temperature moves to the joint interface between tin and nickel, and a strong brittle intermetallic compound of tin, gold and nickel is formed. There was a problem causing.

  Further, in the bonding between the flip-chip gold bump and tin-lead solder, there is a problem in that the strength is similarly lowered because a brittle intermetallic compound of gold and tin is formed.

  The present invention uses a tin-zinc solder alloy for gold-solder bonding in place of the conventionally used tin-lead solder, thereby inhibiting the formation of brittle intermetallic compounds, thereby causing the bonding force caused by tin-lead solder. It is an object of the present invention to provide a bump bonded body and an electronic component that solve the problem of decrease and improve the mechanical bonding force.

  The bump bonded body of the present invention comprises a substrate having an electrode wiring formed on the surface thereof, a solder layer of 8 wt% or more and 15 wt% or less of zinc formed on the electrode wiring and a solder layer of which the balance is substantially tin, And a gold bump having a thickness of 0.5 μm or more and 250 μm or less formed on the solder layer.

  The electronic component of the present invention includes a substrate having an electrode wiring formed on the surface thereof, a solder layer of 8 wt% or more and 15 wt% or less of zinc formed on the electrode wiring and a solder layer of which the balance is substantially tin, A gold bump having a thickness of 0.5 μm or more and 250 μm or less formed on the solder layer; an integrated circuit formed on the back surface of the substrate; and a connecting means for electrically connecting the integrated circuit and the electrode wiring. It is characterized by doing.

 It is preferable that a nickel layer is interposed between the electrode wiring and the gold layer.

The present invention can prevent the formation of brittle intermetallic compounds by using tin-zinc solder alloy for gold-solder bonding instead of tin-lead solder that has been used in the past, and improve mechanical bonding strength. A bump bonded body and an electronic component using the bump bonded body can be provided.

  The present inventors use a gold-solder joint made of a solder alloy containing tin as a base and containing zinc, whereby a zinc layer concentrated on the surface of the tin-zinc solder is involved in the joint, and gold, tin, and optionally nickel. The present invention has been found by inhibiting the reactivity of tin forming the brittle intermetallic compound.

  The solder bump of this embodiment contains 3 wt% to 15 wt% of zinc, and the others are effective for a solder alloy that is substantially composed mainly of tin. Here, the main component is tin, and the ratio decreases in the order of zinc and other third components. In addition, this third component is lead, silver, bismuth, copper, indium, antimony, germanium, nickel, gold, palladium, aluminum, and other inevitable metals, and when adding a metal having a lower vapor pressure than zinc, Although zinc is desirable because it concentrates on the outermost surface of the solder, it is not limited. In addition, it is desirable that the third component is 5 wt% or less, and the total amount is 7 wt% or less for each amount. Further, the oxygen content in the tin-zinc solder is desirably 10 ppm or less, but if it is 30 ppm or less, the effect of the present embodiment can be reliably achieved.

  Usually, when making a solder alloy, a predetermined amount of various metals to be used is melted and cast in the atmosphere, in an inert atmosphere, in a reducing atmosphere, or in an atmosphere such as a vacuum. However, in the case of tin-zinc solder, zinc is easily oxidized. Casting in an inert atmosphere. Tin-zinc solder has a structure in which zinc, which has a higher vapor pressure than tin, forms a concentrated layer on the outermost surface in the process of cooling and solidifying after melting, and a structure in which the zinc phase is dispersed in the tin phase is formed at the center. Yes. Further, since zinc is easily oxidized, a zinc oxide layer is further formed on the outermost surface side of the concentrated layer on the outermost surface. Finally, the tin-zinc solder has a large three-layer structure.

  Therefore, when solder bumps made of tin-zinc solder alloy are joined onto a nickel / gold plated copper pad, the zinc layer concentrates on the surface of the solder bumps, so it exists on the outermost solder surface of conventional tin-lead solder. The reaction of tin that has been performed is suppressed, and a brittle intermetallic compound composed of tin and gold is not formed at the bonding interface. In order to suppress this reaction, it is necessary that the solder alloy contains 3 wt% to 15 wt% of zinc. In this case, the tin-zinc solder does not necessarily have a bump shape, and the same applies to a plate shape. The same effect occurs in the joint region between the tin / zinc solder layer and the gold pump.

  In addition, tin-zinc solder balls, which are examples of solder bumps used in this embodiment, are not compatible only with BGA, and are compatible with all ball-type solder joint devices such as CSP that have previously used tin-lead solder balls. It is also possible to adapt to internal wiring bonding such as flip chip bonding, and there is no limitation on the method of use or the method of forming solder bumps on the device.

  In the present embodiment, the fact that zinc in the tin-zinc solder is directly involved in the joining also has a great merit of facilitating the joining of the solder and aluminum. When using internal wiring made of aluminum in an electronic device, it is necessary to perform surface treatment such as nickel / gold plating on the aluminum wiring in order to perform bonding with tin-lead solder that is difficult to solder to aluminum. By adapting the tin-zinc solder balls, the necessary surface treatment on the aluminum becomes unnecessary. Furthermore, in the case of compound semiconductors, since wiring made of gold is made, it becomes possible to directly form tin-zinc solder bumps without performing surface treatment, not only improving bonding reliability, but also drastically reducing costs, In addition, the problem of environmental pollution caused by plating wastewater treatment can be solved.

(Reference Example 1)
FIG. 1 shows a cross-sectional view of an electronic component. 1 is a ball-shaped solder prepared as a solder bump, 2 is a solder resist, 3 is a BT substrate, 4 is an integrated circuit (IC) having a semiconductor as a base material, 5 is a gold lead wire, and 6 is a mold resin. Further, FIG. 2 is an enlarged view of the periphery of the solder ball 1, 7 is a gold plating layer, 8 is a nickel plating layer, and 9 is a copper electrode. The copper electrode also functions as a wiring and extends from the front surface to the back surface of the substrate 1 and is electrically connected to the gold lead wire 5. 1 is a ball-shaped solder having a diameter of 500 μm made of solder (Sn91.0 wt% -Zn9.0 wt%), but it is not necessary to be ball-shaped, and in some cases, pyramid-shaped, conical, cylindrical Any bump may be used as long as it has various shapes.

  The BT substrate 3 used here is a multilayer resin-based printed wiring board having a build-up structure, but in some cases it is not a multilayer structure but a single-layer structure, or a ceramic-based printed wiring board that is not made of resin. is there. The electrode member in the BT substrate 3 is made of copper, and a nickel plating layer 8 having a thickness of 5 μm is formed thereon, and a gold plating layer 7 having a thickness of 1 μm is further formed thereon. This nickel plating layer is not always necessary.

  The tin-zinc solder ball mounting BT substrate 3 was manufactured by applying a flux on the nickel / gold plated copper electrode 9, mounting the tin-zinc solder ball 1, and reflowing at 230 ° C. in the atmosphere. The gold layer here refers to a gold part including pure gold of 50 wt% or more. In this example, the gold peak value of the gold layer was 90 wt%.

  In order to evaluate the mechanical reliability of the bonding between the solder ball 1 and the copper electrode 9, a high temperature storage test was performed. The condition was that the BGA mounting substrate was left at 150 ° C. in the atmosphere, and the tensile strength was measured every 24 hours. As a result, no change was observed from the initial tensile strength after being allowed to stand for 96 hours, but it was 97% of the initial tensile strength after 120 hours and 95% after 144 hours, and good results were obtained. The results are shown in FIG. In FIG. 3, the solid line black circles indicate the shear strength of Example 1, and the solid line black triangle marks indicate the results of conventional solder (Sn63.0 wt% -Pb 37.0 wt%) as a comparison. The failure mode was also broken in the bulk, and there was no problem in the mechanical reliability of the solder ball joint.

 Further, Table 1 shows the results of the same evaluations made by changing the composition of zinc in the solder balls and changing the thickness of the gold layer. Upon measurement, the tensile strength was measured after 168 hours at 150 ° C. The initial tensile strength was the same or higher than that of tin-lead solder.

  In this table, if the double circle has an initial tensile strength of 95% or more after 144 hours, the single circle has an initial tensile strength of less than 95% and 90% or more after 144 hours, the cross mark indicates a bonding failure. Each case is shown.

  From the above results, in order to achieve an initial tensile strength of 95% or more after 144 hours, which is a sufficient practical strength, the composition of zinc in the solder bumps needs to be 3 wt% or more and 15 wt% or less. In this case, it was found that the problem of reduction in bonding strength caused by an intermetallic compound of gold and tin can be avoided. Furthermore, it is desirable that gold is 0.5 μm or more and 250 μm or less. If the gold layer is thicker than this, not only will the cost be disadvantageous, but there will be a problem that a large amount of gold will be mixed in the solder bumps and the excellent mechanical properties of the solder will be impaired. This is not desirable because there arises a problem that sufficient bonding cannot be obtained by gold bonding.

In the above reference example, gold wire bonding is used as the connection means for connecting the integrated circuit and the substrate, but the connection may be made by gold bumps. In this case, the structure shown in FIG. 2 can be further employed.
(Example 1)
This embodiment differs in that gold bumps are used instead of the gold layer of Reference Example 1, and solder layers are used instead of solder balls. Example 1 will be described with reference to FIG.

  FIG. 4 is a cross-sectional view of the inside of an electronic component having a structure of a bump bonded body bonded by a flip chip method. A semiconductor chip 10 has a structure in which 11 aluminum pad electrodes are arranged and is designed for wire bonding. Reference numeral 12 denotes a gold bump formed by a wire bond method. In some cases, the gold bump is formed by another method such as a plating method. It is also possible to use a gold-core type tin-zinc solder bump that is formed by reflowing by applying tin-zinc solder plating on the gold plating. The shape is a ball-shaped joined body, but it is not necessary to be a ball shape, and may be a bump having various shapes such as a pyramid shape, a conical shape, or a cylindrical shape. At this time, the gold bump 12 had a height of 50 μm and a width of 75 μm. Reference numeral 3 denotes a BT substrate. The 9 copper electrodes arranged on the BT substrate 3 are provided with 5 μm nickel plating 8 and 1 μm gold plating 7, and 13 solder (Sn91. 0 wt% -Zn9.0 wt%) and bonded to the gold bump 12.

  The BT substrate 3 used here is a multilayer resin-based printed wiring board having a build-up structure, but in some cases, it is not a multilayer structure but a single-layer structure, or a ceramic-based printed wiring board that is not made of resin. is there. The copper electrode 9 may be an aluminum electrode, or the electrode surface may be subjected to a surface treatment other than nickel / gold plating such as palladium plating or tin plating, or may not be subjected to any surface treatment. Absent.

Further, the solder 13 is applied to the gold bumps 12 by a reflow soldering method after applying a solder paste on the nickel / gold plating on the copper electrode 9. Is pre-coated to form a solder layer, and then bonded to the gold bump 12 by thermocompression bonding or reflow soldering.
There are various solder pre-coating methods, such as a super just method, a plating method, and mounting of solder balls, but there is no limitation as long as the required amount of solder can be supplied.

  In order to evaluate the mechanical reliability of the bonding between the gold bump 12 and the solder 13, a heat cycle test was performed to evaluate the bonding reliability. The test was performed in the air at a temperature range of -25 ° C to 100 ° C under the condition of one cycle per hour. The electrical resistance of the joint was measured for each cycle, and the rupture rate at the number of cycles was determined from the number of ruptures of the joint. As a result, no fracture occurred until 175 cycles, the fracture rate was 50% after 200 cycles, and 100% fracture after 310 cycles, and good results were obtained. The results are shown in FIG. In FIG. 5, the solid line black circles indicate the joint fracture rate of Example 2, and the solid line black triangle marks indicate the results of the conventional solder (Sn63.0 wt% -Pb 37.0 wt%) for comparison. While the conventional solder break mode may break outside the solder bulk, the break mode of the solder of Example 2 (Sn91.0 wt% -Zn 9.0 wt%) is mostly broken in the solder bulk. Therefore, there was no problem in the mechanical reliability of the solder ball joint.

  Further, Table 2 shows the results of making electronic parts with various changes in the composition of zinc in the solder layer and various heights of the gold bumps and carrying out similar evaluations. In the measurement, a heat cycle test was performed under the condition of 1 cycle per hour in a temperature range of 0 to 100 ° C., and the fracture rate at 175 cycles was determined. Note that the number of cycles at the start of breakage was the same or better than that of tin-lead solder.

In this table, the double circle indicates that the fracture rate is 0% after 175 cycles, and the single circle indicates that the fracture rate is 0% or more and less than 10% after 175 hours. Each case is shown.
From the above results, in order to achieve a fracture rate of 0% after 175 cycles, which is a sufficient practical strength, the composition of zinc in the solder bumps needs to be 8 wt% or more and 15 wt% or less. In this case, it was found that the problem of reduction in bonding strength caused by an intermetallic compound of gold and tin can be avoided. Further, the gold bump is 0.5 μm or more and 250 μm or less, preferably 0.5 μm or more and 75 μm or less, and more preferably 0.5 μm or more and 10 μm or less. If the height of the gold bump is higher than this, not only is it disadvantageous in terms of cost, but also the problem that the solder is taken into the gold bump and the excellent mechanical properties of the solder are impaired, and if it is low, In the thermocompression bonding process with the solder layer, it is not desirable because it causes difficulties.

Sectional drawing of an electronic component. FIG. 2 is an enlarged view of a peripheral portion of a solder ball of the electronic component in FIG. The figure explaining the effect of the reference example 1. FIG. Sectional drawing of Example 1 of this invention The figure explaining the effect of Example 1 of this invention

Explanation of symbols

1 Ball-shaped solder 2 Solder resist 3 BT substrate 4 Integrated circuit (IC)
5 Gold lead wire 6 Mold resin 7 Gold plating layer 8 Nickel plating layer 9 Copper electrode

Claims (3)

  A substrate having an electrode wiring formed on the surface, a solder layer of 8 wt% or more and 15 wt% or less of zinc and the balance being substantially tin solder formed on the electrode wiring, and a solder layer formed on the solder layer A bump bonded body comprising a gold bump having a thickness of 0.5 μm or more and 250 μm or less.   A substrate having an electrode wiring formed on the surface, a solder layer of 8 wt% or more and 15 wt% or less of zinc and the balance being substantially tin solder formed on the electrode wiring, and a solder layer formed on the solder layer An electronic device comprising: a gold bump having a thickness of 0.5 μm or more and 250 μm or less; an integrated circuit formed on the back surface of the substrate; and a connecting means for electrically connecting the integrated circuit and the electrode wiring. parts. The electronic component according to claim 5, wherein a nickel layer is interposed between the electrode wiring and the gold layer.

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