JP2002299381A - Solder plating ball and method for manufacturing semiconductor connecting structure using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solder plating ball, which can be manufactured without limit of a size of a difference of a standard single electrode potential, and to provide a method for manufacturing a semiconductor connecting structure, using such a solder ball. SOLUTION: The solder plating ball comprises a ball-like core 10 made of a first metal material, at least one first plating layer 12 which is provided so as to surround the core and made of a second metal material, and at least one second plating layer 14 provided to surround the core and made of a third metal material. The first, second and third metal materials are each of material for constituting the solder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solder plated ball used as an input / output terminal of a semiconductor device such as a BGA and a method of manufacturing a semiconductor connection structure using the same.

[0002]

2. Description of the Related Art In BGAs, CSPs, flip chips, etc., solder balls are used to connect a substrate to a semiconductor device (package of a semiconductor chip) or to connect a semiconductor chip to a substrate. Here, a connection structure in which a solder ball can be used in an element or a device including at least a semiconductor chip is collectively referred to as a “semiconductor connection structure”.

[0003] The applicant of the present application has disclosed in Japanese Patent Application Laid-Open No. 10-163404.
Discloses that by forming an input / output terminal for a BGA using a solder-plated copper ball, the bonding strength with a Ni / Au-plated pad can be improved as compared with the case where a conventional solder ball is used. are doing. As solder for covering the surface of the copper ball, Sn-Pb, Sn-P
A b-Ag based solder is disclosed.

On the other hand, conventional solder containing lead is being replaced by lead-free solder (Pb-free solder). Sn-Ag-Cu-based solder is generally used as the lead-free solder.

[0005]

The inventors of the present invention have studied to provide a copper ball plated with Sn-Ag-Cu based solder, and have found the following problem.

[0006] It is difficult to form a Sn-Ag-Cu solder layer by electrolytic plating. This is because the standard monopolar potential of Pb is −0.1263 V and the standard monopolar potential of Sn is −0.141.
In contrast to V, Cu is +0.337 V and Ag is +0.7991 V, which is because the standard monopolar potentials of these metals are greatly different. Further, it is difficult to control the plating solution and to control the composition of the solder layer formed by plating, and it is very difficult to put it into practice industrially. This problem is not limited to the above-mentioned Sn-Ag-Cu-based solder, and is a common problem in the production of balls plated with solder containing a metal having a large difference in standard single-pole potential.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and has been made in consideration of the above points, and has a solder plated ball which can be manufactured without being limited by the magnitude of a standard unipolar potential difference, and a semiconductor connection using such a solder ball. It is a main object to provide a method of manufacturing a structure.

[0008]

According to the present invention, there is provided a solder plated ball comprising: a ball-shaped core made of a first metal material;
At least one first plating layer provided to surround the core and made of a second metal material, and at least one second plating layer made to surround the core and made of a third metal material And the first metal material, the second metal material, and the third metal material are materials constituting a solder, whereby the object is achieved.

Preferably, the melting point of the solder is 250 ° C. or less.

[0010] The second metal material and the third metal material may be configured not to contain lead.

[0011] The first metal material may be copper, one of the second metal material and the third metal material may include tin, and the other may include silver or zinc. The other preferably contains silver. Further, the first metal material, the second metal material, and the third metal material may not include lead.

[0012] At least one of the second metal material and the third metal material may further include bismuth.

The at least one first plating layer is a plurality of first plating layers, the at least one second plating layer is a plurality of second plating layers, and the plurality of first plating layers and the plurality of first plating layers are a plurality of second plating layers. The second plating layers may be provided alternately.

It is preferable that the thickness of the at least one first plating layer and the thickness of the at least one second plating layer are determined based on a composition ratio of the solder.

It is preferable that each of the at least one first plating layer and the at least one second plating layer has a thickness of 50 μm or less.

It is preferable that, of the at least one first plating layer and the at least one second plating layer, the one having excellent oxidation resistance is formed on the outermost side.

According to the method of manufacturing a semiconductor connection structure of the present invention, there are provided a step of preparing any one of the above-mentioned solder plated balls and a step of preparing a substrate on which a pad having a gold layer formed on a nickel layer is formed. Forming the molten solder containing the first metal material and the second metal material by heating the solder plating ball in a state where the solder plating ball is arranged on the gold layer; Solidifying by cooling the solder, thereby achieving the above object.

Preferably, the step of forming the molten solder includes a step of initiating the melting at a temperature lower than both the melting point of the second metal material and the melting point of the third metal material.

Preferably, the step of solidifying the molten solder includes a step of forming a eutectic containing the first metal material, the second metal material, and the third metal material.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

FIGS. 1A and 1B schematically show the cross-sectional structures of solder plated balls 100 and 110 according to an embodiment of the present invention.

The solder plated ball 1 shown in FIG.
No. 00 has a core 10, a first plating layer 12 provided so as to surround the core 10, and a second plating layer 14 further provided outside thereof. The core 10, the first plating layer 12, and the second plating layer 14 are formed of different metal materials. These metal materials are materials constituting the solder, and function as a solder when heated and melted.

Of course, it is preferable to select each metal material so that the melting point of the solder is 250 ° C. or less. For example, the core 10 is formed of copper, and the two plating layers 1
2 or 14 is formed of a metal material containing tin;
The other is formed of a metal material containing silver or zinc. Sn-
Ag-Cu-based solder and Sn-Zn-Cu-based solder (the standard monopolar potential of Zn is -0.7527 V) have a large difference in the standard monopolar potential of the metal constituted as described above, so that they are industrially electrolyzed. Although it is difficult to plate the solder, it is possible to realize a solder (at least in a bonded state) having a composition substantially equivalent to that of plating with these solders by forming a multilayer structure.

Accordingly, there is provided a solder ball which can be used in the same application as a solder ball plated with a Sn-Ag-Cu-based solder generally used as a lead-free solder. This is because the solder plating ball 1
Based on the knowledge obtained by the inventor of the present invention, the respective metal materials of the core 10, the plating layers 12 and 14 can sufficiently diffuse with each other in the process of heating 00, and can form a eutectic of these metal materials. ing.

As will be described later, Sn-Ag-Cu
By dividing into a plurality of plating layers containing a metal material constituting the system solder and forming a multilayer, there is an advantage that the bonding strength is improved as compared with the use of a Sn-Ag-Cu solder (pre-alloyed). It turned out that it could be obtained.

The metal material constituting each of the core 10, the first plating layer 12, and the second plating layer 14 does not need to be a single metal material, and may be any material that can be industrially formed by electrolytic plating. I just need. For example, the plating layer 12
And 14 may comprise bismuth.

Also, as shown in FIG. 1B, a solder plating ball 110 corresponding to the plating layer 12 of the solder plating ball 100 is referred to as two plating layers 12a and 12b, and a solder layer corresponding to the plating layer 14. May be two plating layers 14a and 14b. Of course, each plating layer may be divided into three or more layers. However, since the metal materials constituting these plating layers need to be diffused by heating, they are preferably formed alternately.

The thickness of each of the plating layer 12 and the plating layer 14 in the solder plating ball 100 is determined based on a desired solder composition ratio. Core 1
Since a metal material forming 0 has the longest diffusion distance, a material contained in a small amount in solder is selected. In the case of the solder plating ball 110, the total thickness of the plating layers 12a and 12b and the total thickness of the plating layers 14a and 14b are determined based on the target solder composition ratio.

Each of the plating layers 12 (or the plating layers 12a and 12b) and the plating layer 14 (or the plating layers 14a and 14b) has a thickness of 50
It is preferably not more than μm. When the thickness is more than 50 μm, the diffusion of the metal material becomes insufficient, or
Because it takes time to cause sufficient diffusion,
Not preferred.

Either the plating layer 12 or the plating layer 14 may be formed on the outside, but it is preferable that the one having excellent oxidation resistance is formed on the outermost side. When forming a semiconductor connection structure using solder plated balls, if an oxide layer is present,
The joining strength may decrease.

An embodiment of a solder plating ball which can be used in place of the Sn-Ag-Cu solder ball will be described below.

In the solder plating ball 100 having the structure shown in FIG. 1A, a copper core is used as the core 10, a tin plating layer is formed as the plating layer 12, and a silver plating layer is formed as the plating layer 14 (Example 1). ) Was prepared. Also,
In the solder plating ball 110 having the configuration shown in FIG. 1B, a copper core having a diameter of 670 μm was used as the core 10, a tin plating layer was formed as the plating layers 12a and 12b, and a silver plating layer was formed as the plating layers 14a and 14b. (Example 2) was produced. Furthermore, as a reference example,
A solder-plated ball was prepared by plating a copper core with a single layer of tin.

For example, the solder plated ball of Example 1 was manufactured by the following steps. Other solder-plated balls were produced by substantially the same process.

First, (a) a ball-shaped copper core is placed at 17.5.
Pre-treatment with 1% aqueous HCl at room temperature for 1 minute.
(B) This is washed with pure water at room temperature (immersion 1 minute, running water 1
Minutes). (C) Immerse in an organic acid at room temperature for 30 seconds. (D) Using a plating solution containing organic sulfonic acid stannic acid (25 ° C.), a current density of 0.05 A / dm ² and about 28 hours (for example, a thickness of 3
4 μm) Tin plating. (E) This is washed with pure water at room temperature (immersion for 1 minute, running water for 1 minute). (F) Using a plating solution (40 ° C.) containing a silver salt of an organic sulfonic acid, a current density of 0.06 A
/ Dm ² , silver plating for about 90 minutes (for example, 0.8 μm in thickness). (G) This is washed with pure water at room temperature. (A) ~
The steps up to (g) are processed in a barrel container. After this, remove the solder plating ball from the barrel container,
(H) washing with pure water at room temperature (immersion 2 minutes, running water 2 minutes),
(I) Potassium iodide (room temperature, 1
Minutes). (J) This is washed with pure water (immersion 1
Minutes, running water 1 minute). (K) Alcohol substitution (room temperature, 1 minute)
After that, (l) drying is performed at 60 ° C. for 10 minutes.

Further, as comparative examples, solder balls having different compositions (prepared by processing an alloyed solder into a ball shape) were prepared.

Examples 1 and 2, Reference Example, Comparative Example 1,
The melting points of the solders 2, 3, and 4 were evaluated using DSC (heating rate 2 ° C./sec). In each case, the DSC measurement was performed by inserting the solder plating ball or the solder ball itself into the sample pan.

The solder plating ball of Example 1 was joined to a nickel / gold plated copper pad, and the high-temperature reliability (preserved at 150 ° C.) of the joining strength was evaluated. In addition, the high-temperature reliability of the bonding strength when Comparative Example 2 (Sn-3.5Ag) was used was evaluated. Further, the thickness of the interface reaction layer formed at each joint after storage at a high temperature was determined from SEM observation. In addition, the composition of the interface reaction layer was examined using EDX (energy dispersive X-ray analyzer).

FIG. 2 shows the structure of the pad used in the bonding test. The pad 30 has a 7-μm-thick nickel plating layer 34 on a 30-μm-thick copper layer 32 and a 0.7-μm-thick gold plating layer 36 thereon. This pad structure is currently widely used in BGA and the like. The reflow condition reached the maximum temperature of 245 ° C. in 180 seconds,
The temperature was raised so as to be exposed to a temperature of 21 ° C. or more for 90 seconds or more.

The above-mentioned solder plating balls (Example 1,
Table 1 shows the structure of (2, Reference Example) and the composition of the solder balls (Comparative Examples 1 to 4). Also, the melting point of each sample,
Table 2 shows the thickness of the interface reaction layer and the bonding strength observed in the high-temperature reliability test.

[0040]

[Table 1]

[0041]

[Table 2]

As shown in Table 1, the solder plating ball of Example 1 has a tin plating layer 12 having a thickness of 34.2 μm and a silver plating layer having a thickness of 0.8 μm on a copper core 10 having a diameter of 670 μm. 14 (see FIG. 1A). Similarly, the solder plated ball of Example 2 has a diameter of 670 μm.
m on a copper core 10 having a thickness of 17.1 μm.
2a, 0.4 μm thick silver plating layer 14a, thickness 17.
It has a tin plating layer 12b of 1 μm and a silver plating layer 14b of 0.4 μm thickness (see FIG. 1B). The solder plating ball of the reference example has a tin plating layer having a thickness of 35 μm on the same copper core. Each solder plated ball had an outer diameter of about 740 μm. The outer diameters of the solder balls of Comparative Examples 1 to 4 were all about 740 μm.

Next, the melting point of each solder plated ball (multilayer structure) and the melting point of the solder ball (alloy) will be compared with reference to Table 2.

The melting points of the solder plated balls of Examples 1 and 2 were 215 ° C. and 216 ° C., respectively.
Melting point 220 of Sn-3.5Ag solder ball of Comparative Example 2
Lower than ° C. Further, the melting point of the solder plating ball (tin single layer) of the reference example is 225 ° C., which is lower than the melting point 232 of the solder ball containing only tin of the comparative example 1. Comparing each melting point with the melting point of the solder ball further mixed with copper (Comparative Examples 3 and 4), the melting point of the solder plated ball of Examples 1 and 2 was found to be the solder ball of Comparative Example 3 (Sn−
3.5Ag-0.76Cu), which almost coincides with the melting point of 216 ° C. Further, it can be seen that the melting point of the solder plated ball of Reference Example 1 is close to the melting point of 227 ° C. of the solder ball (Sn-0.7Cu) of Comparative Example 4.

That is, in the solder plated ball of the first embodiment, as schematically shown in FIG. 3A, not only silver diffuses from the silver plated layer 14 into the tin plated layer 12 but also
It can be seen that copper is diffused from the copper core 10 into the tin plating layer 12. Similarly, in the solder plating ball of Example 2, as schematically shown in FIG. 3B, the copper core 10, the tin plating layer 12a, the silver plating layer 14a, the tin plating layer 12b, and the silver plating layer 14b It can be seen that diffusion occurs in each layer.

As described above, since the melting point of the solder plating ball is close to the melting point of the ternary eutectic (alloy), the diffusion of the constituent atoms of the core and each plating layer is sufficient before reaching the melting point of the eutectic. It can be seen that the composition has already come close to the eutectic when the melting point of the eutectic is reached. Then, it is considered that the diffusion of copper and silver is further accelerated with the melting, and the whole is melted.

Further, the melting behavior of the solder-plated balls of Examples 1 and 2 was examined in various ways. As a result, it was found that the solder ball of Example 2 having a four-layer structure melted more smoothly. From these facts, in order to diffuse the constituent atoms of the core and each plating layer sufficiently quickly,
Thickness control appears to be important. It is preferable that the rate of temperature rise in an industrial reflow process is faster, and the thickness of each plating layer is preferably 50 μm or less.
It is considered that it is more preferable that it is not more than μm.

Next, the results of the high-temperature reliability test of the bonding strength will be described with reference to Table 2. Comparing the case of using the solder ball of Example 1 with the case of using the solder ball of Comparative Example 2, the case of using the solder ball of Example 1 has higher initial bonding strength and 150 ° C. The bonding strength after storage for 500 hours is also high. This is because, as shown in Table 2, the thickness of the interface reaction layer formed by high-temperature storage was higher in Example 1 (1.9 μm, 500 hours).
This is probably due to the fact that it is significantly thinner than Comparative Example 2 (9.4 μm, 500 hours).

The reason why the decrease in the bonding strength (breaking load) due to high-temperature storage in Example 1 is suppressed as compared with Comparative Example 2 is that, as a result of composition analysis of the interface reaction layer, the reaction layer It was found that this was due to the difference in the composition (compound). That is, in the solder plating ball of Example 1, a compound phase of Cu ₆ Sn ₅ is formed at the joint interface, and this compound layer is formed of Ni _i formed by the solder ball of Comparative Example 2.
Compared with the Sn ₃ phase, the growth rate during high temperature storage is slow,
As a result, a decrease in bonding strength was suppressed.

From this, it can be seen that the use of the solder-plated ball of the present embodiment can provide a semiconductor connection structure excellent in high-temperature reliability of bonding strength.

[0051]

As described above, according to the present invention, there is provided a solder plated ball which can be manufactured without being restricted by the magnitude of the difference between the standard unipolar potentials. Therefore, it is possible to form a solder having substantially the same composition as a solder ball plated with a solder having a composition that cannot be formed by an electrolytic plating method such as a Sn-Ag-Cu solder widely used as a lead-free solder at the time of melting. A possible solder plated ball is provided.

Since it is possible to provide a metal core solder plated ball having solder characteristics of various compositions such as lead-free solder, not only the process of manufacturing a semiconductor connection structure such as BGA can be simplified, but also the reliability can be improved. It is also possible to improve the performance.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic sectional views of a solder plated ball according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a pad structure used in a solder plating ball bonding test according to an embodiment of the present invention.

FIGS. 3A and 3B are schematic diagrams for explaining the melting behavior of the solder plating ball according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10 core 12, 12a, 12b plating layer (first plating layer) 14, 14a, 14b plating layer (second plating layer) 30 pad 32 copper layer 34 nickel layer 36 gold layer

Continued on the front page F term (reference) 5F044 KK01 LL04 5F067 AA13 AB04 BC01 BC12 DC12 DC16

Claims (13)

[Claims] 1. A ball-shaped core made of a first metal material, provided so as to surround the core, at least one first plating layer made of a second metal material, and provided so as to surround the core. And at least one second plating layer made of a third metal material, wherein the first metal material, the second metal material, and the third metal material are materials constituting a solder. ball. 2. The solder plated ball according to claim 1, wherein the melting point of the solder is 250 ° C. or less. 3. The solder plated ball according to claim 1, wherein the second metal material and the third metal material do not contain lead. 4. The method according to claim 1, wherein the first metal material is copper, and the second metal material is copper.
The solder plated ball according to any one of claims 1 to 3, wherein one of the metal material and the third metal material includes tin, and the other includes silver or zinc. 5. The solder plated ball according to claim 4, wherein the other includes silver. 6. The method according to claim 4, wherein at least one of the second metal material and the third metal material further includes bismuth.
Or the solder-plated ball according to 5. 7. The at least one first plating layer is a plurality of first plating layers, the at least one second plating layer is a plurality of second plating layers, and the at least one first plating layer is a plurality of first plating layers.
The solder plating ball according to claim 1, wherein the plating layers and the plurality of second plating layers are provided alternately. 8. The thickness of the at least one first plating layer and the thickness of the at least one second plating layer,
The solder plating ball according to claim 1, wherein the solder plating ball is determined based on a composition ratio of the solder. 9. The solder plating ball according to claim 1, wherein each of the at least one first plating layer and the at least one second plating layer has a thickness of 50 μm or less. 10. The one of the at least one first plating layer and the at least one second plating layer, the one having excellent oxidation resistance is formed on the outermost side.
A solder plated ball according to any one of the above. 11. A step of preparing the solder plating ball according to claim 1, a step of preparing a substrate on which a pad having a gold layer formed on a nickel layer is formed, By heating the solder plating ball in a state where the solder plating ball is arranged on the gold layer,
A method of manufacturing a semiconductor connection structure, comprising: forming a molten solder containing the first metal material and the second metal material; and cooling and solidifying the molten solder. 12. The method according to claim 11, wherein forming the molten solder includes starting melting at a temperature lower than any of the melting points of the second metal material and the third metal material. Of manufacturing a semiconductor connection structure. 13. The method of claim 11, wherein the step of solidifying the molten solder includes a step of forming a eutectic including the first metal material, the second metal material, and the third metal material. 3. The method for manufacturing a semiconductor connection structure according to 1.