JP2002076606A - Electronic equipment and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a drop resistance or impact resistance of an electronic equipment and to improve reliability of a solder connection of a semiconductor device in which an Si chip or the like being weak against a thermal impact in association with a large deformation is die-bonded or a power module in which a large stress is operated. SOLUTION: An electronic equipment comprises a circuit board, an electronic component electrically connected to an electrode of the board. In this case, the electrode of the board is solder connected to the electrode of the component by using a lead-free solder containing Cu of O to 2.0 mass%;, In of 0.1 to 10 mass%; and Sn of the residue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electronic device (particularly a mobile product for which impact strength is required) on which electronic components are mounted,
The present invention relates to a technology applied to connection of a CSP package requiring thermal shock resistance, a semiconductor module MCM (multi-chip module), a semiconductor device die-bonded with a Si chip or the like, a large-area power module, and the like.

[0002]

2. Description of the Related Art Currently, Pb-free solder is being promoted due to environmental problems. Regarding the solder for connection, regardless of the electronic device,
High reliability of joints can be expected from conventional Sn-Pb eutectic S
There is a worldwide trend to move to high-temperature solders of n-Ag-Cu system, for example, Sn- (2.0-4.0) Ag- (0.5-1.5) Cu. This Sn-Ag-
Compared to conventional all-purpose Sn-Pb eutectic solder, Cu-based solder may have lower connection reliability depending on the product application or usage due to the inherent difference in metal, especially due to the difference in mechanical strength characteristics. There is a need to be careful.

[0003]

SUMMARY OF THE INVENTION Sn-Ag-Cu-based solder generally has higher strength, higher rigidity, and higher joint interface strength than the current metallization, as compared to Sn-Pb eutectic. If the substrate and the like are strong, reliability equal to or higher than that of a conventional Sn-Pb solder mounted product can be secured.

[0004] On the other hand, if the components, the substrate, and the like are weak, the solder itself will not be destroyed. The major reason is that it has a particularly strong strength as a mechanical property. For example, the reliability of the joint strength etc. is high in electronic devices mounted with electronic components (especially mobile products such as mobile phones), but when compared with the conventional Sn-Pb eutectic, It has been pointed out from the empirical facts up to that it is vulnerable to impact at the time of falling, thermal shock, and the like.

Accordingly, an object of the present invention is to improve the drop resistance or impact resistance of an electronic device.

Further, thermal shock accompanied by large deformation acts.
Semiconductor devices with die-bonded Si chips, BGA, CS
It is an object of the present invention to improve the reliability of solder connection in bump mounting of P, WPP, flip chip or the like, or in a power module on which a large stress acts.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention is constituted as described in the appended claims.

More specifically, when a strong impact is applied to the solder without impairing the reliability such as the temperature cycle of the joint, the solder is more easily deformed and stretched than the Sn-Ag-Cu solder. By using an excellent material, it is possible to eliminate the stress load at the joint interface of the parts, to improve the drop resistance and impact resistance, and to improve the thermal shock mitigation action against large deformation. In other words, as Sn-based Pb-free solder used for the connection part,
In order to make the material small in stress and easily deformable, In which is softer than Sn in the matrix of Sn or Sn-Cu is dissolved to reduce the impact applied to the joint interface when it falls, The impact resistance has been improved.

As a result, since the solder itself is plastically deformed by the impact energy at the time of dropping, the stress applied to the joint interface is reduced, so that a large impact force does not act on the joint interface and the impact resistance is improved. It becomes possible.

In addition, semiconductor devices, such as BGA, CSP and WPP (Wafer Process Pac), which are die-bonded with a Si chip or the like at the time of soldering accompanied by large deformation and in a thermal shock acceleration test, etc.
Kage), solder bump connection in flip chip mounting, and connection in large area power module where large stress acts, etc. Destruction can be prevented and connection reliability can be improved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an impact when an electronic device such as a mobile phone is dropped will be described.

In the case of an electronic device such as a mobile phone, parts, LSI (BGA, CSP, TSOP, TQ)
Package such as an FP). Although it is unlikely to be broken by a normal drop, it is expected that it will be dropped accidentally at a high place, or that it will not be able to endure if it is dropped at a bad place or a hit point, and will be broken at the joint interface of the joint. Parts, L
Since the SI itself is light in weight, it is not unbearable even if the acceleration increases. The problem is the bending force of the substrate due to the impact force transmitted through the case and the substrate and the impact. It goes without saying that damping by the case and the substrate is important to reduce the impact force. Although the case is hard to bend against an instantaneous impact, it can have a role and function of a damper. The impact force is transmitted to the board via the case, and a load is applied from the board to the solder joint. The substrate is relatively large and easy to bend in the longitudinal direction, so
An impact force due to large bending is applied to a fundamental vibration mode of two wavelengths and the like. At this time, free vibration is generated in a state where the periphery of the substrate is restrained, and the vibration is attenuated. A high-frequency longitudinal wave transmitted through the substrate and a low-frequency transverse wave due to deformation are generated. Longitudinal waves are high-frequency elastic waves, which are motions that are transmitted straight to the joint in series, but originally have a bumper-like function at the support portion of the case and the substrate, and can alleviate the impact. Still, forces that cannot be absorbed are applied to the joint. If there is no damper in the board restraint, it will be transmitted straight from there to the joint through the board. On the other hand, the lateral vibration caused by the deformation of the substrate varies depending on the restrained state of the substrate, but it is instantaneously greatly deformed, causing a large bending stress and causing the interface to be broken due to the warpage of the substrate.

FIG. 1 shows a case where the end 4 of the case hits the ground 5 when an electronic device such as a mobile phone is dropped, and the impact from the case is transmitted to the substrate 6 via the restraining portion 9 such as a connector. LSI package 7 due to natural vibration of substrate
The impact model (a) exerted on the joint 8 is shown. When represented by a vibration mode with damping in a one-degree-of-freedom system, a shock transmission model as shown in FIG. Shock transmission on the ground,
The series, longitudinal vibration and lateral vibration are transmitted to the case, restraining part, board, joint, and LSI package in series. Damping is the loss due to the collision between the ground and the case, the loss due to the material damping of the case, the loss due to the material damping of the restraint, the loss due to the friction between the restraint, the case and the board, the loss due to the material damping of the board, and the damping of the solder It can be assumed that the loss due to the deformation of the solder, the material attenuation of the LSI package, and the like are mainly attenuations connected to the series. Considering the transmission system from the ground to the LSI package, the damping system can be divided into a material damping system including solder and a structural damping system including friction. Vibration transmission system is ground, case, restraint, board, joint,
In the case where the vibration is transmitted by the lateral vibration due to the transmission from the LSI package, a natural vibration mode in which the center is an antinode at a half wavelength in the longitudinal direction of the substrate is generally considered as a mode easily deformed. At this time, a large bending stress acts instantaneously on the solder joint, and with a solder having a high rigidity, the deformation cannot be absorbed by the solder. At this time, if the solder is soft, the solder undergoes plastic deformation, thereby reducing the force applied to the joint interface. Note that components such as an LSI used for a mobile phone or the like are generally small and lightweight, and therefore it is considered that an impact force due to a weight of the component itself due to a collision is small.

[0014] In view of this, we have reduced the soldering temperature, and the solder itself is liable to be deformed. In order to ensure high reliability by temperature cycling, etc., we have to modify the Sn crystal to prevent deformation. Because of the quality, it is easy to dissolve in the matrix,
And hard to harden even in solid solution, ensuring high reliability
The addition of In was studied.

In particular, since it is important that the Sn matrix (crystal) itself is rich in deformability, it was examined to add In based on a Sn--Cu eutectic solder which is soft and excellent in elongation.

FIG. 2 shows elongation 1 and tensile strength 2 when In is added to Sn-0.7Cu. The horizontal axis uses logarithm (Log).

According to the figure, about 0.2-7.0 mass% of In
It can be understood that the elongation is improved only by adding. In particular, when adding about 0.5 to 2.0 mass% of In, Sn-0.
It can be understood that about 10% or more improvement can be realized compared to 7Cu. Generally, when a small amount of metal is added to crystal grains, the strength increases and the elongation decreases. However, here, since In is softer than Sn, it has a characteristic that strength is not improved and elongation is excellent. When the strength is reduced and the elongation is increased, the stress applied to the interface is reduced, so that the impact resistance is improved, and the impact energy can be absorbed by the deformation of the solder when subjected to a strong impact.

The tensile strength does not change much until In is added at about 2 mass%, but when about 5 mass% or more is added, the melting point is lowered, but the tensile strength is greatly increased. When the tensile strength is increased, the solder is hardly deformed when a strong impact is applied, resulting in poor impact resistance. Therefore, from the viewpoint of tensile strength, it is understood that it is preferable not to add In of about 5 mass% or more.

The Sn-Cu used as the base solder
The eutectic has a melting point about 10 ° C higher than the Sn-Ag-Cu eutectic,
Although the situation was not attracting attention as surface mounting, the melting point was lowered by adding In as described above, and Sn-Ag-Cu
There is also an advantage that connection can be performed at a soldering temperature similar to that of a eutectic system. The composition of the base Sn-Cu is S
Since In is added to the n-0.7Cu eutectic, although it depends on the amount of In, Cu is desirably 0.1 to 0.7 mass%, which is smaller than that of the eutectic. If In is large, Cu should be small. In general, when the metallization is made of Cu, etc., it may be desirable to add a large amount in consideration of the prevention of cracking, so that it is effective in the range of 0 to 2.0 mass%.

Table 1 shows the melting point (liquidus line, solidus line) and hardness of the Sn-Cu-In system. The heating rate is 2 ° C./min. The load at the time of hardness measurement is 100 g. These are added to the Sn-Cu eutectic
Is added to lower the soldering temperature, further reduce the strength, and provide a connection structure that does not lower the elongation. Even though In enters, the hardness hardly changes because soft In forms a solid solution in the Sn matrix.

[0021]

[Table 1] As described above, based on the Sn-Cu eutectic system which is soft and excellent in elongation, it does not harden in this Sn matrix and maintains elongation (deformability), and the solder itself is softer than Sn.
By adding, it is possible to avoid the stress concentration at the interface and improve the impact resistance and thermal shock resistance of the electronic component even in a Sn-based electronic component. In other words, the tensile strength does not change much and the elongation increases with the addition of In, so when an impact is applied, the impact energy is absorbed by the deformation of the solder itself, so that a large force does not act at the joint interface, BGA,
In connection with a solder bump such as a CSP, a WPP, or a flip chip, it is possible to suppress the destruction at the conventional interface. This phenomenon has a similar effect not only on the impact resistance but also on the thermal shock resistance in a temperature cycle.

By the way, although the description has been made so far based on the Sn-Cu eutectic solder, the Sn-Cu eutectic solder itself is a material excellent in elongation.

As for the solder to be used as a base, in addition to the Sn-Cu eutectic solder, Sn-Ag solder and Sn-Sb solder were also examined. However, based on the Sn-Ag system, the needle-like Ag3Sn compound is dispersed and strengthened in Sn, or since Ag3Sn is formed in a network at the Sn grain boundary, the strength becomes strong, Since the stress is transmitted straight to the bonding interface at the time of thermal shock, destruction is likely to occur at the interface of a weak component.

In the Sn-Sb system, Sb forms a solid solution in Sn, but since it is dissolved and strengthened, it becomes hard and strong similarly to the Sn-Ag system, and has poor deformability. We decided to use a base solder.

Further, Sn-Ag-Cu based solder was also studied. FIG. 3 shows the relationship between elongation 1 and tensile strength 2 when Ag is added to Sn-0.7Cu eutectic (228 ° C.).

From the figure, it can be understood that the smaller the amount of Ag, the higher the elongation and the lower the tensile strength. In other words, since the elongation of Sn-0.7Cu is the maximum and the tensile strength is the minimum, it is understood that the improvement of the deformability by the addition of Ag and the improvement of reducing the stress on the connection parts of the solder cannot be expected. it can.

From this result, it can be inferred that the smaller the dispersion of acicular Ag3Sn in the Sn matrix, the better the elongation and the lower the strength. In other words, the better the impact resistance is improved without Ag. Can be estimated. Therefore, not only Sn-Ag-Cu solder, but also Sn-Ag solder can have the same effect of Ag3Sn, so it can be presumed that sufficient impact force relaxation action cannot be obtained.

On the other hand, the Sn-0.7Cu eutectic solder has a state in which Cu6Sn5 is dispersed in the Sn matrix, but the dispersion amount is smaller than that of the Sn-3.5Ag eutectic solder, and Cu6Sn5 is Ag3Sn3.
Not as acicular. Therefore, in the Sn-0.7Cu eutectic solder, Cu6Sn5 does not adversely affect the intragranular deformation.

For example, in a temperature cycle test of two through-hole joints of Sn-3Ag-0.7Cu and Sn-0.7Cu, Sn-3Ag-0.7Cu
Dendrites (dendrites) of Cu solder show a tendency to grow linearly, and plastic deformation at the position where stress is applied after a temperature cycle test is hardly observed in appearance, and linear cracks are observed. The dendrite growth of the Sn-0.7Cu solder is not very linear, and the plastic deformation is apparently apparent at the position where the stress is applied after the temperature cycle test.

From the above, Sn-Cu based solder is Sn-Ag
It was found that the joint was better in thermal shock in the joint state than the system solder or the Sn-Ag-Cu solder, and the Sn-Cu solder was selected as the base solder.

FIG. 4 shows the change over time of the impact force transmitted from the joint by the acceleration sensor attached to the LSI package due to the drop impact. The high frequency 10 indicates a longitudinal elastic wave. FIG. 4 (a) shows a situation where the vertical axis indicates the impact force, the horizontal axis indicates the time, and the time decreases with time. At this time, it is conceivable that the lateral vibration also becomes maximum even if there is a time lag. The solder shows the decay curves of (1) conventional Sn-Pb eutectic solder, (2) conventional Sn-3.5Ag-0.7Cu solder, and (3) Sn-0.5Cu-3In solder. At this time, the shock input entering the joint was the same. At the time of a large impact force, the conventional Sn-Pb eutectic solder is easy to deform itself (Sn and Pb are fine particles, so the surface area is large and it is easy to move due to deformation due to grain boundary sliding) The shock energy is absorbed by the solder due to the deformation of the solder of the joint, so that the damping property becomes remarkable. However, although the temperature dependency and the strain rate dependency are large, it is considered that good properties are obtained by impact at room temperature. On the other hand, (2) Sn-
Sn-3.5Ag-0.7Cu solder, which is a representative of the Ag-Cu series, has high strength and is difficult to deform, so it transfers the impact force straight to the joint interface.If the joint interface is weak, it will break at the interface. Will wake up.

According to the impact Charpy test, the Sn-Ag type (Sn-4
Ag) is known to have higher absorbed energy in impact tests than Sn-Pb eutectic (Sn-40Pb) (e.g., `` Mounting technology for surface-mount LSI packages and improving their reliability '', Applied Technology Publishing Co., Ltd., p368, 1988-11-16). According to this, the impact strength at room temperature is Sn-40Pb: 24 (ft-lb), Sn-4Ag:
38 (ft-lb) and Pb-10Sn: 8 (ft-lb). Bi is added to Sn-Ag.
It is also known that the absorption energy decreases with the addition of (e.g., the 12th Environmentally Friendly Mounting Technology Forum, p4-
1, 2000-11-28). Since Bi becomes brittle, the impact value is expected to decrease as a natural result. On the other hand, soft high Pb
It can be understood that the impact value of the solder (Pb-10Sn) is even lower.

The strain rate at impact is naturally high,
The -Pb eutectic has the drawback that the strain rate dependency and the temperature dependency are remarkable. Considering the fact that there is no problem with falling of mobile phones etc. using the current Sn-Pb eutectic solder, it means that this defect does not appear for drops at room temperature conditions Think. In this respect, the high Pb-based solder is excellent because it is less dependent on temperature and strain and is stable. High Sn based solder is used at low temperature (-55 ℃)
, The impact value drops sharply, but this is due to the brittleness. However, since elongation and strength are secured, there is usually no problem. From these data, the relationship with the phenomenon will be discussed below. Until now, in the case of Sn-Ag-Cu solder, in the case of a joint structure that is severe in temperature cycling, the solder itself is unlikely to be deformed, so that the bonding interface may be more likely to be broken depending on the component. The impact at the time of the fall seems to be similar behavior. If the solder is soft (small stress and excellent elongation), the solder will be deformed,
No large stress acts on the bonding interface. Originally, the function of solder is here. Sn-Pb eutectic has such an excellent function. High Pb solder (Sn-10Pb) is similarly soft and has a similar function. The mechanism of high Pb solder is a structure in which Sn is dissolved in Pb, whose base material is soft, and Sn-Pb
Although there is a difference in metallographic structure from eutectic (a collection of fine crystals), the same effect is obtained in that no stress is applied to the joint interface.

Sn-Ag-Cu with high impact value by Charpy test
The reason why the system solder joint is not preferable against a drop impact or the like is that the strength is high. As can be imagined from FIG. 3, it is considered that this is due to the fact that the needle-like Ag3Sn is dispersed in the Sn crystal to form a reinforced composite material. This can be inferred from the fact that the lower the Ag content, the more desirable the situation is that the strength decreases and the elongation increases. In addition, Sn-0.75Cu eutectic (in a state in which Cu6Sn5 is dispersed in Sn crystal) has a small amount of Cu in Sn crystal, does not become acicular crystal like Ag3Sn, and has a melting point of 232 ° C to 227 ° C. ℃. Therefore, in order to further improve the impact relaxation performance, it is necessary to reduce the strength of the solder, increase the elongation, and easily deform. To this end, it is effective to include In, which is easily dissolved in Sn crystals and is softer than Sn. by this,
The melting point can also be lowered.

(3) Sn-0.5Cu- is an example of a typical composition of the present invention.
The 3In solder does not absorb impact energy up to the Sn-Pb eutectic, but exhibits good impact relaxation characteristics due to the deformation effect due to the addition of In in the Sn matrix. This deformation characteristic is Sn
This is due to intragranular deformation based on the softness of the substrate. As long as In is increased, the melting point decreases and the effect of reducing the impact force is provided as long as the absolute value of the strength does not increase. From these facts, it can be understood that the impact resistance and the thermal shock resistance of the component joint are improved by using the Sn-Cu-In solder.

Next, a description will be given of an example in which the present invention is applied to connection in a semiconductor device in which a Si chip or the like is die-bonded or in a large-area power module on which a large stress acts to improve the connection reliability.

FIG. 5A shows a cross-sectional model of the structure of an LSI resin package 13 in which the back surface of a Si chip 11 is metallized and Ni / Au plating is applied to a Fe-Ni alloy (base) 12 by die bonding.
Terminals on the chip are electrically connected to leads 15 via bonding wires 14. Approx. 150 for soldering 16
Using a solder foil having a thickness of μm, a fluxless process was performed in a nitrogen or hydrogen atmosphere. If cleaning can be performed in a later step, a solder paste can be used. In this case, reflow connection in the atmosphere is possible. When the difference in the coefficient of thermal expansion between the Si chip and the base is large, or when connecting a large chip, the strength of the solder and the rigidity of the conventional Sn-Ag-Cu-based solder, when soldering, temperature cycle Strict use during testing can break the Si chip. By using the above-mentioned Sn-Cu-In solder, the solder is deformed by relatively low stress, so that cracking in the Si chip can be prevented. Especially when high melting point solder is required, Sn-0.1In, Sn-2In, Sn- (0.3-0.7) Cu-1In or S
n- (0.3 to 0.7) Cu-2In or the like is preferable.

FIG. 5B shows an example in which a bare chip, CSP or BGA is connected to the substrate 17. Solder for external connection terminal is chip carrier board such as CSP, BGA
There is a method of supplying the substrate 21 with a ball or a method of supplying the electrode of the substrate with a solder paste. As the package solder 18 is reinforced with resin 19, the deformability is not so important, so if the temperature hierarchy is important, the bump connection between the chip 20 and the chip carrier substrate 21 can be made of Sn-5Sb or conductive resin. good. That is, a connection structure having a temperature higher than the melting point of the solder 22 bumps may be used. Meanwhile, the substrate
Where to connect with 17, from the need to ensure impact resistance,
Sn-0.5Cu-3In solder 22 was used. It was found that the Sn-Cu-In solder is 20% to 50% stronger than the Sn-Ag-Cu solder against the substrate warpage, the thermal shock, or the shock. In this example, the chip carrier substrate 2
A Sn-Cu-In-based solder ball is supplied on the terminal electrode of No. 1 and mounted on a printed circuit board with solder supplied in paste. Also in this case, Sn-Cu-In is applied to the electrodes on the chip carrier substrate.
By supplying the system solder, it is possible to absorb an impact at a stress concentration location. In general, a material is used in which the chip carrier side of the bump tends to have a difference in thermal expansion with solder,
Since the terminal area is often small, it is often broken by stress concentration. However, depending on the structure, material, etc., the interface on the printed circuit board side may be weak. In such a case, the surface of the printed circuit board is preliminarily treated with Sn-In or In plating so that
There is an effect by n. That is, Sn-3Ag- on the chip carrier side
In the case of reflow connection via a 0.5Cu ball or Sn-3Ag-0.5Cu paste, even if mixed uniformly, the concentration of Ag occurs and In enters, so that the whole becomes soft. Depending on the process, a Sn-Ag-Cu-based solder (Ag concentration cannot be reduced to 0, but decreases) is formed near the interface on the printed circuit board side. Excellent effect can be expected.

FIG. 6 shows an example applied to a large power module. The Si chip 23 has a diameter of 20 mm and the metallized 24 is Al
/ Ti / Ni / Au, Ni plating 26 is applied to the molybdenum plate 25 of the stress buffer material, W sintered-Ni plating 28 is applied to the Al2O3 insulating substrate 27, and Ni plating 30 is applied to the Cu plate 29. It has been subjected. These solders use a solder foil having a thickness of about 150 μm and are connected by reflowing in a nitrogen or hydrogen atmosphere, so that they can be performed without cleaning. If cleaning is possible, connection by air reflow with solder paste is also possible. Sn- as solder 31 composition
Although 0.7Cu-1In, Sn-0.5Cu-4In, and Sn-1.5Cu-5In were used, all of them can prevent the destruction of the Si chip and have a high reliability of 1000 cycles in the temperature cycle test at -55 to 125 ° C. I was able to clear the sex.

It should be noted that Sn-Cu-In solder is excellent in terms of thermal shock resistance even for lead components of severe joints, chips and those for which the metallization strength of the chips is not sufficiently ensured. In the case of lead parts, Sn- (1-10) Bi plating or Sn- (0.2-2) Cu plating is applied to Fe-Ni-based, Cu-based leads, etc., compared to conventional Sn-10Pb plating. Also,
It has excellent impact resistance and thermal shock resistance, and ensures high reliability as a joint.

As described above, when mounting a weak component by surface mounting, a large stress acts on the joint portion during soldering. However, the use of Sn-Cu-In solder reduces the breaking strength. We have made it possible to join with Pb-free solder without destroying weak components. If high melting point is required, Sn-0.7Cu or Sn-0.7Cu-0.1In, if low melting point is required, Sn-0.5Cu-5In or Sn-
By using 0.5Cu-7In or the like, it can be used in a wide range. Also, if the strength of parts is secured to some extent, Sn-0.8Ag-0.5 can secure high strength as a joint.
Use of Cu-3In or the like is also possible.

Thus, with Sn-based Pb-free solder,
In order to make the material easily deformable and excellent in elongation, by dissolving In softer than Sn in the Sn matrix,
It can be expected to have the effect of reducing the impact when dropped. That is, the solder itself plastically deforms the energy of the impact at the time of the drop, thereby absorbing the stress applied to the joint by its own deformation, and a large impact force does not act on the joint interface, resulting in excellent impact resistance. . In the case of solder that is not easily deformed at the time of collision, the kinetic energy at the time of collision directly acts on the bonding interface, and the interface is likely to be broken.

The connection reliability is also improved in die bonding of large Si chips, which are easily broken parts, solder bump connection of BGA, CSP, WPP, flip chip, etc., and large area power modules on which large stress acts. Can be improved.

Further, when Ag is not contained as a component,
Migration,
There is no need to worry about short circuits and the connection reliability is high. Therefore, if the above composition is used, the drop resistance of the mobile product,
In addition to the improvement of the impact resistance, the substrate bending resistance and the probing inspection resistance (warpage resistance) in the surface mounting of BGA, CSP, bare chip, etc. are also excellent. In addition, it can be applied to a die-bonded component such as a Si chip or the like that is susceptible to thermal shock accompanied by large deformation, and to a power module mounting of a large chip. In addition, by adding In to Sn-Cu, the soldering temperature can be set to the same level as Sn-Ag-Cu. When an absolute value of strength is required in the Sn-Cu-In system, it is possible to use Ag in an amount of 1 mass% or less to suppress a decrease in elongation to some extent.

Furthermore, by adding Bi to the Sn-Cu-In system at 1 mass% or less, the life is suppressed and the flowability of the solder is improved, thereby preventing bridges required for high-density mounting and chip standing. The effect of prevention can be expected.

FIG. 7A shows BGA and CSP of wire bond.
Thus, the lower portion of the Si chip 20 is bonded with a conductive resin 48.
In this case, the terminal section is preferably made of Au, Ni / Au, or the like that is hardly oxidized on both the chip side 49 and the substrate side 50 (there is also no metallization), and is an adhesive that can withstand reflow at 250 ° C. In addition, when using this wire bond method for power products, it is possible to use a composite solder foil mixed with Cu and Sn and connect it with a Cu-Sn intermetallic compound to make a package that has the strength to withstand reflow It is. Possible compound configurations as this combination include Ni-Sn, Au-Sn, Ag-S
n and Pt-Sn. FIG. 7 (b) shows a bump of a conductive resin 47 having a flip chip structure, and the terminal portion in this case is made of Au, Ni / Au46 or the like whose surface is hardly oxidized on both the chip side and the substrate side.
This connection can withstand reflow at ℃. Further, resin 35 having a Young's modulus of 5 to 1500 kgf / mm ² and a coefficient of thermal expansion of 10 to 60 × 10 ⁻⁶ / ° C. is filled in order to secure mechanical strength and improve life.

The chip formed by applying Sn plating or the like to the terminals on the relay substrate side, applying a resin first to the entire chip bonding portion including the terminal portions, and forming bumps of Au or the like in advance. A structure in which the Au bump is adsorbed on a capillary heated by a pulse heater, the Au bump is positioned on the terminal of the relay board, and then the Au bump is brought into contact with Sn plating and then heated and melted is also possible. In this case, the gap between the chip and the relay substrate can be 50 μm or less, and a repairable thermoplastic resin (which can be reduced in expansion by inserting a quartz filler) that operates at a relatively high temperature can also be used. Note that the terminal configurations of the chip terminals and the relay board are not limited to the above configurations.

The external connection electrode terminals of the above-mentioned various BGAs and CSPs have a solder composition of Sn-0.3 to reduce the impact resistance.
Cu-3In, Sn-0.7Cu-2In, Sn-0.7Cu-0.2In, Sn-0.7Cu-5In
And so on. When Ag enters such a Sn-Cu eutectic system, the needle-like Ag3Sn disperses and forms a solid solution in the Sn matrix, so that the strength of the solder itself becomes too strong and the solder is hardly deformed. A large stress acts on the joint interface. Sn
This is exactly where the issues of -Ag-Cu based Pb-free soldering are. Even if there is no problem with a normal joint, a weak point may appear depending on the structure due to a small design margin. The Sn-Cu-In based solder has corrected this weakness. Sn-Cu is a dispersed eutectic of Cu6Sn5, but it does not become acicular like Ag3Sn,
Therefore, it has low strength and improved elongation. That is, the composition is easily deformed and hardly causes stress concentration.
Since the melting point of Sn-0.75Cu eutectic is as high as 228 ° C, by adding In, the melting point was lowered and soft In was dissolved in the Sn matrix to make the system more deformable. The composition can be selected to some extent when importance is placed on the impact resistance for which flexibility is required, when the heat resistance of parts is considered, and when the joining strength is also considered. The solder bump may be supplied on the relay board terminal by a ball, supplied by printing, supplied by electroplating, supplied by immersion plating, or the like.

FIG. 8 shows that the above-mentioned BGA
32, CSP33, TSOP56, chip component 51, functional element
(For example, a high-frequency RF module 34 used for signal processing used in a mobile phone or the like) and the like. The maximum reflow temperature is Sn-0.7Cu-5In (melting point: 222.7-215.4)
° C), the same as Sn-3Ag-0.5Cu (melting point: 221-217 ° C)
Possible at 235 ° C. RF module is GaAs or S
i-chip and passive components are mounted on an Al2O3 substrate 27 with excellent thermal conductivity and mechanical properties.
M (multi-chip module). Several □ 2mm chips 20 and chip parts 51 are small, and the size of the module board (Al2O3 board in this case) on which they are mounted is □ 10mm
Because of this level, the reliability of connection to the printed circuit board is sufficiently ensured. In particular, for a wire-bonded chip, remelting during reflow of the printed circuit board may affect the characteristics. Therefore, the back side of the chip is an Au electrode, and the Al2O3 substrate 27 side is a Ni / Sn plated electrode, which is joined by a diode. This Au-Sn intermetallic compound is 260
Does not melt in reflow at ℃. Since the chip component is at the 1005 level, even if the Sn-3Ag-0.5Cu solder is used, even if it is re-melted at the time of reflow of the printed circuit board, it is fixed by the action of the surface tension and has no effect on the characteristics. The external connection terminals 36 of the RF module are plated with Ni / Au. TSOP
The lead of the package 56 is Sn / Bi plated (about 7 μm thick) on the 42 alloy lead 55. Reflow connection is Sn-0.7 first
The lower surface of the lightweight package is made with Cu-5In or the like, and then the upper surface is similarly reflow-connected 37 with Sn-0.7Cu-5In or the like. The already connected light parts do not fall down during reflow of the upper parts because they are light even if they are on the lower side, and there is no influence on the characteristics. As described above, it is necessary to determine the composition of the Sn-Cu-In-based composition in consideration of the heat resistance, impact resistance, and bonding strength of the component.

FIG. 9 shows a CSP package as a representative example.
The figures before (a) and after expansion (b) are shown. Package 58
The solder is supplied to the relay board terminals on the Cu pad 38 or Cu / Ni / Au plating with a ball or paste.
0.3Cu-5In solder 37 was supplied. The terminals 38 on the organic substrate 54 (printed substrate) are supplied with Sn-3Ag-0.5Cu solder 59 in advance by printing. Then, this package is transferred to another LSI
The package was mounted on a printed circuit board at the same time as components, etc., and the temperature was controlled at a maximum of 240 ° C. and a conveyor speed of 1 m / min in the air using a forced circulation air reflow furnace in which the temperature distribution in the substrate was easy to be uniform. The package side of the bonded bumps is mainly Sn-Cu-In even if mixed.

Simply Sn-3Ag-0.5Cu ball, Sn-3Ag-0.5Cu
When bonded by a paste, for example, when subjected to a temperature cycle test at −55 to 125 ° C., the solder portion (A portion) 60 where stress tends to concentrate near the bonding interface near the package side is broken. Sn
In the case of -Cu-In based solder, since the solder is soft, stretched and has low strength, the stress concentration can be mitigated by the deformation of the solder, which leads to an improvement in the service life. On the other hand, a similar effect can be expected for an impact such as a fall. In other words, the stress concentration location is the same location (part A), and the impact at the time of dropping, if Sn-3Ag-0.5Cu, acts on the bonding interface due to the stress concentration and cannot withstand, the solder near the bonding interface Part or bonding interface. Even if the bonding strength by solder is high, stress concentration concentrates at one point, and even if there is no problem, it breaks at the starting point.

Therefore, phenomenologically, it is important to provide a structure in which the solder is soft and easily deformed at the stress concentration portion.
The material properties of the solder include low tensile strength, excellent elongation, and low Young's modulus. For this purpose, on the metallographic structure, Ag3Sn is not dispersed in the Sn crystal at the stress concentration part, and the soft In is dissolved in order to soften the Sn crystal, and Cu is eutectic ( It is desirable to adopt a configuration in which the melting point is reduced by In with a smaller amount than 0.75%).

As another application example, a BGA bump is formed of Sn-C
Because of the importance of repair, the low-temperature system Sn-1Ag- (40-57Bi) (solidus temperature;
(137 ° C) It is also possible to join with paste. Even after several repairs, the shape of the high-temperature Sn-Cu-In solder does not change, and the solder on the substrate side can be leveled and supplied at around 200 ° C.

[0054]

According to the present invention, drop resistance or impact resistance of an electronic device can be improved. Also, in the connection of BGA and CSP to semiconductor devices and printed circuit boards that are die-bonded to Si chips and the like that are weak to thermal shock accompanied by large deformation, Sn-Ag-Cu Pb-free solder may cause interface breakdown, In the present invention, this can be suppressed. Further, the reliability of the solder connection in the power module to which a large stress acts can be improved.

It is known that Sn changes (pest) from β-Sn (body-centered tetragonal) to α-Sn (cubic) at low temperatures (the mounting technology of surface-mount type LSI package and its transformation). Reliability Improvement, Applied Technology Publishing Co., Ltd., p357,368). And S
It is said that n-Cu easily undergoes Sn transformation. In particular, when a rapidly solidified sample is left at a low temperature for a long time, it is expected that the probability of occurrence of pest is increased, possibly due to the influence of stress. Addition of soft In, which is easy to melt into Sn, causes a decrease in stress especially at grain boundaries and the like.
The effect of delaying the generation of st can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing an impact transmission model when a mobile phone is dropped.

Fig. 2 Addition amount of In to Sn-0.5Cu and elongation, tensile strength,
The figure which shows hardness.

FIG. 3 is a graph showing the amount of Ag added to Sn-0.7Cu, elongation, and tensile strength.

FIG. 4 is a diagram showing a temporal change of an impact force due to a drop impact.

FIG. 5 is a diagram showing a cross section of a package.

FIG. 6 is a diagram showing a cross section of a power module.

FIG. 7 is a cross-sectional model diagram of BGA and CSP.

FIG. 8 is a cross-sectional model of a printed circuit board on which BGAs, CSPs, modules, chip components, etc. are mounted.

FIG. 9 is a cross-sectional model for bonding a package to an organic substrate.

[Explanation of symbols]

1. Elongation 17. Substrate 2. Tensile strength 18. Solder 3. Cell phone 19. Resin 4. Edge 20. Chip 5. Ground 21. Chip carrier substrate 6. Substrate 22. Solder 7. LSI package 23. Si chip 8. Joint 24. Metallization 9. Restraint part 25. Molybdenum plate 10. High frequency 26. Ni plating 11. Si chip 27. Al2O3 insulating substrate 12. Base 28. W sintered-Ni plating 13. Resin package 29. Cu plate 14 Bonding wire 30. Ni plating 15. Lead 31. Solder 16. Solder 32. BGA 33. CSP 34. RF module 35. Resin 36. External connection terminal 37. Sn-Cu-In solder 38. Cu pad 46. Au, Ni / Au, etc. 47. Conductive resin bump 48. Conductive resin or composite solder 51. Chip parts 53. Al fin 54. Organic substrate 55.42 Alloy lead 56. TSOP package 58. CSP package 59. Sn-3Ag-0.5Cu paste 60. Stress concentration area

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/60 H01L 23/12 501Z 23/12 501 21/92 603B (72) Inventor Tetsuya Nakatsuka Yokohama, Kanagawa 292, Yoshida-cho, Totsuka-ku, Ichitoshi, Ltd.Production Technology Research Laboratory, Hitachi, Ltd. (72) Inventor Masato Nakamura 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture, Ltd.Production Technology Research Laboratory, Hitachi, Ltd. (72) Inventor Yuji Fujita, Kanagawa 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Japan Inside Hitachi, Ltd.Production Technology Research Laboratories (72) Inventor Toshiharu Ishida 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi, Ltd. Production Technology Research Laboratories (72) Inventor Okamoto Masahide 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd. Production Technology Laboratory (72) Person Koji Serizawa 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd.Production Technology Research Institute (72) Inventor Toshihiro Haya 1410 Inada, Hitachinaka-shi, Ibaraki Digital Media Product Division, Hitachi, Ltd. 72) Inventor Hideki Mukuno 2520 Takada, Hitachinaka-shi, Ibaraki F-term (reference) 5E319 AA03 AB01 AB05 AC02 BB04 BB05 BB10 CC33 CD27 CD28 CD29 GG20 5F044 KK02 LL01 QQ03 5F047 AA11 BA17 BA19 BB04 BB11 BB16

Claims (12)

[Claims] 1. A circuit board, comprising: an electronic component electrically connected to an electrode of the circuit board, wherein the electrode of the circuit board and the electrode of the electronic component are Cu: 0 to 2.0 mass%, I
Electronic equipment characterized by being connected by soldering using a lead-free solder consisting of n: 0.1 to 7.0 mass% and the remaining Sn. 2. The method according to claim 1, wherein the lead-free solder has a Cu content of 0.1 to 1.5 mass%.
2. The electronic device according to claim 1, wherein In: 0.5 to 2.0 mass%, and the balance is Sn. 3. The lead-free solder has a Cu content of 0.1 to 1.5 mass%,
2. The electronic device according to claim 1, wherein In: 0.5 to 7.0 mass%, Ag: 0 to 1.0 mass%, and the remaining Sn. 4. The method according to claim 1, wherein the lead-free solder comprises Cu: 0.1 to 1.5 mass%,
2. The electronic device according to claim 1, wherein In: 0.5 to 7.0 mass%, Bi: 0 to 1.0 mass%, and the remaining Sn. 5. The electronic device according to claim 1, wherein the electrode of the electronic component is a solder bump formed of the lead-free solder. 6. An electrode of said electronic component is provided with Sn- (1-10).
The electronic device according to any one of claims 1 to 4, wherein a plating layer of mass% Bi is formed and connected by soldering. 7. The electrode of the electronic component has a Sn- (0.2 to
The electronic device according to any one of claims 1 to 4, wherein a plating layer of mass% Cu is formed and connected by soldering. 8. A semiconductor device comprising: a semiconductor element; and a bump electrically connected to the semiconductor element.
A semiconductor device characterized by being a lead-free solder comprising s%, In: 0.1 to 7.0 mass%, and the remaining Sn. 9. The method according to claim 9, wherein the lead-free solder is Cu: 0.1-1.5 mass%,
9. The semiconductor device according to claim 8, wherein In: 0.5 to 2.0 mass%, and the remaining Sn. 10. The lead-free solder has a Cu content of 0.1 to 1.5 mass.
9. The semiconductor device according to claim 8, comprising: 0.5% to 7.0% by mass, In: 0% to 1.0% by mass of Ag, and the remaining Sn. 11. A semiconductor device comprising Cu: 0 to 2.0 mass%, In: 0.1 to
A semiconductor device characterized by being connected to a tab using lead-free solder consisting of 7.0 mass% and the remaining Sn. 12. A circuit board comprising: a circuit board; and an electronic component electrically connected to an electrode of the circuit board. An external connection terminal serving as a connection portion with an external part electrically connected to the circuit board is provided with C.
u: A semiconductor module comprising lead-free solder consisting of 0 to 2.0 mass%, In: 0.1 to 7.0 mass%, and the remaining Sn.