JPH11330678A - Method of solder bonding, circuit board, and electronic device using the circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of solder bonding for preventing soft errors due to α-rays by preventing the decrease in an insulating resistance, a circuit board, and an electronic device using the board. SOLUTION: This method for solder bonding comprises a step of solder bonding a first electrode 28, having an auxiliary solder layer 30 made of an Sn containing a Bi or an Sn containing an Sb formed on an upper surface to a second electrode 16 which has a solder bump 18 made of an Sn containing an Ag on an upper surface. As a result, even in the case of conducting a solder bonding using a solder material containing the Sn as a main component, halogen ions such as a Cl ion or the like which are contained in a residue of a flux can be captured by the Bi or Sb contained in the solder layer, and hence a growth of a dendritic crystal can be prevented, and decrease in an insulation resistance can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder bonding method, and more particularly to a solder bonding method capable of preventing a decrease in dielectric strength and preventing a soft error due to α rays. The present invention also relates to a circuit board and an electronic device using the circuit board, and more particularly to a circuit board capable of preventing a decrease in insulation resistance and preventing a soft error due to α rays, and an electronic device using the same. About.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of high-speed operation of a semiconductor device, a technique for reducing a wiring length has been required. Attention has been paid to flip chip bonding.
(nding) technology, that is, a technology in which solder bumps formed on a semiconductor chip are mounted on a circuit board on which electrodes are formed, and the solder bumps are melted and connected by applying heat.

FIG. 3 shows a conventional flip chip bonding.
This will be described with reference to FIG. First, an electrode 116 composed of a Ti film 112 and a Ni film 114 is formed on a semiconductor substrate 110 on which a predetermined element is formed, and the solder bump 1 is formed on the electrode 116.
18 are formed. On the other hand, an electrode 128 composed of a Cr film 122, a Cu film 124, a Ni film 126, and an Au film 127 is formed on a glass epoxy substrate 120.

[0004] Thereafter, the solder bumps 118 on the semiconductor substrate 110 are aligned with the electrodes 128 on the glass epoxy substrate 120 and bonded by heating. In this way, if flip-chip bonding is used, there is no need to connect using lead wires, so that the wiring length can be reduced. Conventionally, Pb-Sn based solder materials have been widely used for flip chip bonding. However, Pb (lead) contained in the Pb-Sn solder material has isotopes, and these isotopes are intermediate products or final products in the decay series of U (uranium) or Th (thorium). . Since U (uranium) and Th (thorium) are accompanied by α decay that emits He atoms, α rays are generated from the solder material. And
The α-rays may affect the operation of the semiconductor device, causing a so-called soft error.

[0005] Further, when Pb flows into the soil, Pb is dissolved by acid rain, which may adversely affect the environment. From the viewpoint of environmental problems, it is required to use a solder material not containing Pb as a main component. I was Therefore, as a solder material replacing the Pb-Sn-based solder material, for example, a solder material obtained by adding Ag (silver) to Sn (tin) has begun to be used.

[0006]

However, since flip-chip bonding is bonding using solder, flux is used. The flux used in the solder bonding is removed by a subsequent cleaning process. However, when the flip-chip bonding is performed, the flux is difficult to clean due to its structure, so that the flux may not be completely removed.

Since the flux contains Cl ions and the like, Cl ions and the like move from the flux residue,
So-called ion migration occurs. When ion migration occurs, halogen ions such as Cl ions recrystallize with Sn or Ag of the solder material, thereby generating dendritic crystals, that is, dendrite crystals.

[0008] In a conventional solder material containing Pb as a main component such as Pb-5% Sn, the content of Sn is small, so that dendrite crystals are difficult to grow.
-When an Ag-based solder material is used, dendrite crystals grow large. When the dendrite crystal grows large and reaches the vicinity of the adjacent electrode, the insulation resistance is reduced. In particular, when flip-chip bonding of a miniaturized semiconductor device or the like with a narrow wiring interval,
The decrease in insulation resistance due to the growth of dendrite crystals was remarkable.

An object of the present invention is to provide a solder bonding method and a circuit board which can prevent a decrease in insulation resistance and a soft error due to α rays, and an electronic device using the circuit board. .

[0010]

The object of the present invention is to provide a first electrode in which a preliminary solder layer made of Sn containing Bi or Sn containing Sb is formed on the upper surface, and a solder bump made of Sn containing Ag containing on the upper surface. This is achieved by a soldering method characterized by soldering the formed second electrode. Thereby, even when soldering using a solder material containing Sn as a main component is performed, Cl contained in the flux residue is removed.
Bi containing halogen ions such as ions in the preliminary solder layer
Alternatively, since it can be trapped by Sb, the growth of dendrite crystals can be prevented, and the decrease in insulation resistance can be prevented. In addition, S containing Ag
Since the soldering is performed using a solder material composed of n, that is, a solder material that emits a small amount of α-ray, the amount of α-ray emitted from the solder material can be reduced, thereby reducing the soft error of the semiconductor device due to α-rays. Can be prevented.

In the above-mentioned solder bonding method, it is preferable that the Pb content of the solder bump is 1 ppm or less. Accordingly, since the soldering is performed using a solder material having a low Pb content, that is, a solder material that emits a small amount of α-ray, the amount of α-ray emitted from the solder material can be reduced. Can prevent a soft error of the semiconductor device.

In the above-mentioned solder bonding method, it is preferable that the α dose of the solder bump is not more than 0.01 cph / cm ² . Thus, since the soldering is performed using a solder material having a small α dose, the α dose emitted from the solder material can be reduced, thereby preventing a soft error of the semiconductor device due to α rays.

Further, the above object is to provide a circuit board having a first electrode and a preliminary solder layer formed on the first electrode and made of Sn containing Bi or Sn containing Sb. Is achieved by As a result, even when soldering using a solder material containing Sn as a main component is performed, halogen ions such as Cl ions contained in the residue of the flux are captured by Bi or Sb contained in the preliminary solder layer. As a result, the growth of dendrite crystals can be prevented, and the insulation resistance can be prevented from lowering.

[0014] The above object is also made of the above circuit board, a semiconductor substrate, a second electrode formed on the semiconductor substrate, and Sn containing Ag formed on the second electrode. The present invention is achieved by an electronic device having a semiconductor device having a solder bump, wherein the first electrode and the second electrode are joined by soldering. As a result, even when soldering using a solder material containing Sn as a main component, halogen ions such as Cl ions contained in the flux residue are captured by Bi or Sb contained in the preliminary solder layer. As a result, the growth of dendrite crystals can be prevented, and the insulation resistance can be prevented from lowering. In addition, Sn containing Ag
Since the solder joining is performed using a solder material composed of, that is, a solder material that emits a small amount of α, the α dose emitted from the solder material can be reduced, thereby
The soft error of the semiconductor device due to the line can be prevented.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solder joining method according to one embodiment of the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing the solder joining method according to the present embodiment. First, a semiconductor substrate 10 on which a predetermined semiconductor element is formed is prepared. Next, a film thickness of 100 is formed on the semiconductor substrate 10 by sputtering.
A Ti film 12 of nm is formed. Thereafter, the Ti film 12 is patterned into an electrode shape. The shape of the electrode is, for example, 70 to 100 μm in diameter, and the pitch between the electrode 14 and an adjacent electrode (not shown) is, for example, 150 to 210 μm.
And

Next, a 4 μm-thick Ni film 14 is formed on the Ti film 12 by an electroless plating method or an electrolytic plating method. Thus, an electrode 16 composed of the Ti film 12 and the Ni film 14 is formed. The Ni film 14 is formed by solder bumps 18 formed on the electrodes 16 in a later step.
It functions as a barrier metal for preventing diffusion into the inside.

Next, a solder bump 18 made of a Sn-Ag type solder material is formed on the electrode 16. Solder bump 1
As a forming method of 8, for example, a DP (Dimple Plate) method can be used. The Pb concentration in the Sn-Ag based solder material is desirably 1 ppm or less.
Further, it is desirable that the amount of α emitted from the Sn—Ag based solder material is 0.01 cph / cm ² or less.

Thus, a semiconductor device 19 having the solder bumps 18 formed on the electrodes 16 of the semiconductor substrate 10 is formed. On the other hand, C on the glass epoxy substrate 20
An r film 22, a Cu film 24, and a Ni film 26 are sequentially formed. Thereafter, the Cr film 22, the Cu film 24, and the Ni film 26
Is patterned to form a Cr film 22, a Cu film 2
4 and an electrode 28 made of a Ni film 26 is formed.

Next, a film having a thickness of 50 to 100
A μm preliminary solder layer 30 is formed. The preliminary solder layer 30
For example, a solder paste can be prepared by mixing a flux with a Sn-Bi-based solder material classified into powder having a particle size of 25 μm or less, and can be formed by screen printing using the solder paste. As a solder material, for example, Sn-
57% Bi can be used.

The reason why the Sn-Bi-based solder material is used for the preliminary solder layer 30 is that the following effects can be obtained by using the Sn-Bi-based solder material. That is, when the electrode 28 on the glass epoxy substrate 20 side and the solder bump 18 on the semiconductor substrate 10 side are joined, Bi in the Sn-Bi-based preliminary solder layer 30 formed on the electrode 28 on the glass epoxy substrate 20 side is removed. , Electrode 1 on semiconductor substrate 10 side
It diffuses into the Sn-Ag-based solder bumps 18 formed on 6 to generate a Sn-Ag-Bi-based solder alloy. Bi has a high ability to capture halogen ions such as Cl ions contained in the flux residue, etc.
Reaction of Cl ions or the like with n or Ag is prevented, thereby preventing generation of dendrite crystals. Even if Sn ions or Ag ions are eluted from the solder bumps 18, Bi reacts with Sn ions or Ag ions instead of Cl ions reacting with Sn ions or Ag ions. Crystals formed by the reaction of Bi with Sn ions and Ag ions are smaller than those of Sn and Ag.
Since the crystals do not grow in dendrites, a decrease in insulation resistance is prevented.

The preliminary solder layer 30 has a thickness of 50 to 1
The reason why the thickness is set to 00 μm is as follows. That is, if the film thickness of the semiconductor device 30 is about 50 to 100 μm, Bi in the preliminary solder layer 30 diffuses into the solder bump 18, and B in the vicinity of the electrode 28 on the glass epoxy substrate 20 side.
Although the concentration of i does not become extremely high, if the film thickness of the preliminary solder layer 30 is too thick, the solder material of the preliminary solder layer 30 will not completely diffuse into the solder bumps 18. The melting point of the solder bump 18 is relatively high, for example, 200 ° C., whereas Sn-57% Bi used as the preliminary solder layer 30 has a melting point of 1
Since the temperature is as low as 39 ° C., if the material of the preliminary solder layer 30 is not sufficiently diffused into the solder bumps 18, a region having a low melting point is generated in the vicinity of the electrode 28 on the glass epoxy substrate 20 side. . Further, since the solder containing a large amount of Bi has low flexibility, a region having low flexibility is generated in the solder near the electrode 28 on the glass epoxy substrate 20 side, which may cause cracks. Therefore, in this embodiment, the thickness of the preliminary solder layer 30 is set to 50 to 100 μm so that the solder material of the preliminary solder layer 30 can sufficiently diffuse into the solder bumps 18.

In this way, a circuit board 32 having the preliminary solder layer 30 formed on the electrode 28 is formed. Next, the semiconductor device 19 and the circuit board 32 are aligned, and flip-chip bonding is performed in a reflow furnace in a nitrogen atmosphere having an oxygen concentration of 10 ppm or less. Thus, the semiconductor device 19 is mounted on the circuit board 32, and the electronic device is manufactured.

(Results of THB Test) With respect to an electronic device manufactured by using the above-described solder bonding method, THB (Ther
mal Humidity Bias) test was performed for 1000 hours, and the insulation resistance was measured. The conditions of the THB test were a temperature of 121 ° C., a humidity of 85% RH, a pressure of 1.7 atm, and an applied voltage of 5 V. The material of the solder bump 18 is Sn-10% Ag,
Sn-5% Ag, Sn-3.5% Ag, or Sn-3%
Ag is used as the preliminary solder layer 30 and has a thickness of 50 μm.
-57% Bi or 100-μm thick Sn-57% Bi
, And a THB test was performed for each combination. Table 1 shows the results.

[0024]

[Table 1]

As shown in Examples 1 to 8 in Table 1, TH
Insulation resistance before B test was 10 ^TenΩ or more, THB test
The insulation resistance after the test was 10^TenΩ or higher and good
Insulation resistance was obtained. On the other hand, as shown in FIG.
For electronic devices manufactured using the solder bonding method,
Two comparative examples, Comparative Example 1 and Comparative Example 2,
Test was carried out. The conditions of the THB test were the same as above,
As the material of the bump 118, Sn-3.5% Ag was used.
Was.

As a result, as shown in Table 1, in Comparative Example 1, the insulation resistance before the THB test was 10 ⁹ to 10 ¹⁰ Ω.
And the insulation resistance after the THB test was 10 ⁸ to 10 ⁹ Ω. In Comparative Example 2, the insulation resistance before the THB test was 10 ⁷ to 10 ⁸ Ω, and the insulation resistance after the THB test was 10 ^7.
Was ~10 ⁸ Ω. That is, when the conventional solder bonding method was used, both of Comparative Example 1 and Comparative Example 2
After the test, a good insulation resistance of 10 ¹⁰ Ω or more could not be obtained.

As described above, according to the present embodiment, even when flip-chip bonding using a solder material containing Sn as a main component is performed, halogen ions such as Cl ions contained in the residue of the flux are reserved. Since it can be trapped by Bi contained in the solder layer, it is possible to prevent the growth of dendrite crystals, thereby preventing the insulation resistance from lowering.

Also, since bonding is performed using a solder material having a low content of Pb, that is, a solder material that emits a small amount of α-ray, the amount of α-ray emitted from the solder material can be reduced. Can prevent a soft error of the semiconductor device. [Other Embodiment] A solder bonding method according to another embodiment of the present invention will be described with reference to FIG. FIG. 2 is a sectional view showing the solder joining method according to the present embodiment. The same components as those of the solder joining method according to the embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted or simplified.

The solder joining method according to the present embodiment is the same as the solder joining method according to the first embodiment except that an Sn—Sb-based solder material is used as the preliminary solder layer 30a. As a material of the preliminary solder layer 30a, for example, Sn-5
% Sb can be used. In the solder bonding method according to the present embodiment, the Sn—Sb-based solder material is used as the preliminary solder layer 30 a because the Sb included in the preliminary solder layer 30 a is used.
This is because the same effect as Bi included in the preliminary solder layer according to the first embodiment can be obtained.

(Results of THB Test) Further, a THB test was performed on the electronic devices thus joined in the same manner as in the first embodiment. In addition, as a material of the preliminary solder layer 30a, Sn-5% having a thickness of 50 μm or 100 μm is used.
Sb was used. Table 2 shows the results.

[0031]

[Table 2]

As shown in Examples 9 to 16 in Table 2, the insulation resistance before and after the THB test was 10 ¹⁰ Ω or more, and good insulation resistance was obtained. As described above, according to the present embodiment, even when performing flip-chip bonding using a solder material containing Sn as a main component, halogen ions such as Cl ions contained in the flux residue are added to the preliminary solder layer. Since it can be trapped by the contained Pb, the growth of the dendrite crystal can be prevented, and the decrease of the insulation resistance can be prevented.

Further, since bonding is performed using a solder material having a low Pb content, that is, a solder material that emits a small amount of α-ray, the amount of α-ray emitted from the solder material can be reduced. Can prevent a soft error of the semiconductor device. [Modified Embodiments] The present invention is not limited to the above embodiment, and various modifications are possible.

For example, in one embodiment, Sn-57% Bi is used as the solder material, but the Bi content is not limited to 57%. For example, as a solder material, B
An Sn-Bi-based solder material having an i content of 40 to 60 wt% may be appropriately used. In another embodiment, Sn-5% Sb is used as a solder material, but the Sb content is not limited to 5%. For example, a Sn—Sb-based solder material having an Sb content of 0.1 to 10 wt% may be appropriately used as the solder material.

In the above embodiment, an example has been described in which an electronic device is manufactured by mounting a semiconductor device on a circuit board. However, the embodiment is configured by mounting a plurality of semiconductor devices on one circuit board. Multi-chip module (MC
M, Multi Chip Module). Further, in the above embodiment, the case where the electronic device is manufactured by mounting the semiconductor device on the circuit board has been described as an example, but the case where the semiconductor package is manufactured by mounting the semiconductor chip on the circuit board is also described. Can be applied.

[0036]

As described above, according to the present invention, even when soldering is performed using a solder material containing Sn as a main component, halogen ions such as Cl ions contained in the residue of the flux are reserved. Since it can be trapped by Bi or Sb contained in the solder layer, it is possible to prevent the growth of dendrite crystals, thereby preventing the insulation resistance from lowering.

Further, according to the present invention, since the soldering is performed using a solder material made of Sn containing Ag, that is, a solder material that emits a small amount of α, the α dose emitted from the solder material is reduced. Accordingly, a soft error of the semiconductor device due to α rays can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a solder bonding method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a solder bonding method according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a conventional solder bonding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate 12 ... Ti film 14 ... Ni film 16 ... Electrode 18 ... Solder bump 19 ... Semiconductor device 20 ... Glass epoxy substrate 22 ... Cr film 24 ... Cu film 26 ... Ni film 28 ... Electrode 30 ... Spare solder layer 30a ... Preliminary solder layer 32 Circuit board 110 Semiconductor substrate 112 Ti film 114 Ni film 116 Electrode 118 Solder bump 119 Semiconductor device 120 Glass epoxy substrate 122 Cr film 124 Cu film 126 Ni film 127 Au Membrane 128 ... Electrode 132 ... Circuit board

Continued on the front page (51) Int.Cl. ⁶ identification code FI H05K 3/36 H01L 21/92 603A

Claims (5)

[Claims] A first electrode having a preliminary solder layer made of Sn containing Bi or Sn containing Sb formed on an upper surface thereof;
A solder bump made of Sn containing
Soldering method, wherein the electrodes are soldered. 2. The solder bonding method according to claim 1, wherein the Pb content of the solder bump is 1 ppm or less. 3. The solder joining method according to claim 1, wherein the α dose of the solder bump is 0.01 cph / cm ² or less. 4. A first electrode, and Sn or S containing Bi formed on the first electrode.
a preliminary solder layer made of Sn containing b. 5. The circuit board according to claim 4, a semiconductor substrate, a second electrode formed on the semiconductor substrate, and a Sn containing Ag formed on the second electrode.
An electronic device, comprising: a semiconductor device having a solder bump made of the first electrode and the second electrode.