JP2002231747A - Solder ball - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a large quantity of solder balls in which the problem of variation in the melting temperature is solved. SOLUTION: A solder ball production system comprises a supply crucible 4 for supplying molten 3 continuously to a delivery crucible 1 through a siphon tube 2. The supply crucible 4 and the delivery crucible 1 are pressurized with N2-8%H2 mixture reducing gas atmosphere from a linked pressure unit 11 to push out a specified quantity of molten to the bottom part of the delivery crucible 1 through an orifice 5. A vibration generator 6 imparts a vibration to the molten in the vicinity of the orifice 5 through a shaking rod 7 thus dividing the specified quantity of molten into liquid drops 8 of uniform size which are then discharged into a solidification chamber 9 filled with nitrogen gas atmosphere and solidified to produce solder balls 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solder ball.

[0002]

2. Description of the Related Art A solder ball used in a semiconductor package is formed by processing a solder ingot into a wire, cutting the wire into a predetermined length, and heating the solder in a liquid to a temperature equal to or higher than the melting temperature of the solder to obtain a spherical shape. It is manufactured by Another manufacturing method is a uniform droplet spraying method.For example, as disclosed in U.S. Pat.No. 5,260,098 to Jung-Hoon Chun et al., A tapping crucible holding a molten solder and having a nozzle at the bottom, and a tapping crucible. It is also proposed to provide a cooling and solidifying unit installed under the container, apply pressure to the tapping crucible, discharge the molten solder particles from the nozzle, and solidify the molten particles in the cooling and solidifying unit. .

[0003]

However, in the method of manufacturing by cutting a wire, if the solder ingot has a component segregation, the chemical composition is not uniform even in the solder ball material as the wire. For this reason, even with solder balls manufactured by cutting a fixed amount from the same wire, the chemical composition of each ball is not uniform. Such a variation in the chemical composition appeared as a variation in the melting temperature of the solder ball. On the other hand, in the case of manufacturing by a uniform droplet spraying method, since the solder ingot is melted in a crucible and the solder ball is manufactured directly from the obtained molten metal, there is little variation in the chemical composition. However, in order to pressurize the inside of the tapping crucible as in the device disclosed in US Pat. No. 5,260,098, it is necessary to connect the tapping crucible with a pressurizing device to form a closed space. As a result, it is difficult to additionally supply the molten metal or the mother alloy with respect to the decrease in the molten solder due to the molten metal, and the production amount in one batch is limited by the amount of the molten metal that can be held in the molten metal crucible. If a large number of solder balls are to be manufactured, they must be manufactured in multiple steps.

[0004] As a method of manufacturing a semiconductor package, a wafer is formed by forming wiring on a silicon wafer to form a large number of semiconductor elements and then forming the wafer in a package without performing dicing. There is level packaging (WLP). In this method, in order to form solder bumps serving as terminals on pads, about 1 to 100,000 solder balls are mounted on a silicon wafer at a time and heated to form bumps. However, when solder balls having a variation in the melting temperature are used in this heating step, depending on the heating temperature, solder balls that progress in melting and solder balls that do not reach the melting temperature will be mixed, and as a result, there will be a gap between the solder balls and the pads. A connection failure will occur. In order to melt all the solder balls, the heating temperature must be increased more than necessary, so that the resin constituting the semiconductor package, for example, an epoxy resin or a polyimide resin, is also exposed to a high temperature, and is deteriorated or deformed by heat. Causes a failure. For this reason, in wafer level packaging, a large amount of solder balls with as little variation in melting temperature as possible is required. SUMMARY OF THE INVENTION It is an object of the present invention to provide a large number of solder balls that solve the problem of variation in melting temperature.

[0005]

The inventor of the present invention has found that the variation in the melting temperature of the solder ball is due to the variation in the chemical composition of the solder ball. The method of mass production was discussed. As a result, it has been found that by adding a continuous hot water supply device having a capacity capable of dissolving and storing 5 kg or more of solder to a crucible for discharging solder, a large number of solder balls having a small variation in composition can be continuously manufactured. . That is, the present invention is a solder ball in which the variation in the melting temperature of the solder balls per 10 million pieces is within 5 ° C.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, an important feature of the present invention is that the variation in the melting temperature of solder balls per 10 million pieces is kept within 5 ° C. Specifically, for example, a solder consisting of a eutectic composition in the vicinity of Sn and a second element is targeted, and Pb, Ag, Cu, Bi, In, Zn, Ni, S
b, a solder made of Ge, and an ingot of a solder made of a composite addition of these second elements are charged into a crucible and melted by heating to a melting temperature or higher. In addition, 5 kg or more of the solder is melted, and the solder of the same composition is melted by a continuous hot water supply device having a storage capacity, and the molten metal is supplied into a crucible to continuously manufacture solder balls having a uniform composition. .

The heat-resistant temperature of the resin constituting the semiconductor package is, for example, about 150 to 250 ° C. in the case of epoxy resin. On the other hand, the melting temperature of the solder is about 183 ° C. for the Sn—Pb eutectic solder, and about 220 ° C. for the alloy of mass%, which is a powerful composition as a lead-free solder, 3.0% Ag, 0.5Cu% Cu, and the balance Sn. is there. Since it is necessary to heat above the melting temperature for reliable soldering,
It is necessary that the variation in the melting temperature of the solder ball be within 5 ° C. Desirably, it is within 2 ° C.

In wafer level packaging, about 100,000 solder balls per silicon wafer are mounted and melted at a time. For this reason, in order to perform continuous packaging, it is necessary that solder balls having a small composition variation be supplied in units of 10 million or more. Generally, the particle size of solder balls used in wafer-level packaging is 0.05 to 1.0 mm, and the total amount of molten solder required for 10 million solder balls differs depending on the particle size. If the above continuous hot water supply device is used, 5 kg or more of solder ingot is melted at a time,
It can be stored, and it is possible to produce 10 million or more solder balls having the above-mentioned particle diameter with less variation in composition.

[0009] Incidentally, an example of a specific manufacturing apparatus is as follows.
As shown in FIG. 1, a solder ball manufacturing apparatus having a supply crucible (4) for continuously supplying a molten metal (3) to a tapping crucible (1) through a siphon tube (2) is used. It is linked with the supply crucible (4) and the tapping crucible (1) and the pressurizing device (11), and N ₂ -8%
By pressurizing in a H ₂ mixed reducing gas atmosphere, a certain amount of molten metal is pushed out through a hole called an orifice (5) at the bottom of the tapping crucible (1). Vibration generated by the vibration generator (6) is transmitted to the molten metal (3) near the orifice (5) via the vibrating rod (7).
By applying vibration to the solidified material, the fixed amount of molten metal is divided into uniform sizes, and discharged as liquid droplets (8) into a coagulation chamber (9) filled with an N ₂ inert gas atmosphere. Droplets solidified in (9) become solder balls (10),
It will be recovered later.

[0010]

EXAMPLE In order to observe the difference in the molten state due to the variation in the chemical composition of the solder balls, a batch type reflow apparatus capable of observing the molten state through a glass window was used for visual observation and monitoring with a CCD camera. ma
A solder ingot composed of 2.9% of Ag, 0.5% of Cu, 0.5% of Cu and the balance of Sn was prepared, and 50 million pieces of 300 μm-diameter solder balls were produced by two methods, and 10 million of them were evaluated. . One was prepared by drawing a solder ingot to a diameter of 100 μm, cutting it quantitatively so as to have a diameter of 300 μm when spheroidized, and then spheroidizing in oil. First, a 1 kg ingot was melted with a crucible using a uniform droplet spraying method, and 10 kg of a solder having the same composition was melted with a continuous hot water supply device, and the molten solder was supplied at a time. In addition, the solder ball manufacturing apparatus shown in FIG.

Next, a silicon wafer having 10,000 pads having Ni barrier plating and a diameter of 250 μm formed thereon was prepared, a flux was applied on the pads, and one solder ball was mounted on each pad. Thus, the silicon wafer on which the solder balls were mounted was heated by a batch type reflow device, and the melting and unmelting of the solder were confirmed visually and by a CCD camera. The heating conditions are as follows: first, the flux is reacted with the solder ball, and the oxide film on the surface is reduced to activate the solder ball surface.
C. for 3 minutes. Next, the solder balls were further heated to melt them. Here, the maximum heating temperature is 216 to 2 because the melting temperature of the solder having the composition is about 220 ° C.
The temperature was set in increments of 2 ° C between 32 ° C and held at that temperature for 1 minute. Table 1 shows the results of observing the melting state of the solder balls in this manner.

[0012]

[Table 1]

In the solder ball formed from the wire, melting was observed from the maximum heating temperature of 218 ° C., but the solder ball was not melted even when heated to 230 ° C. on the other hand,
For solder balls made by the uniform droplet spraying method, which can be mass-produced, melting starts when the maximum heating temperature exceeds 220 ° C, and when heated to 224 ° C or more, all solder balls melt and the dispersion of the melting temperature varies. It turns out that there are few.

[0014]

According to the present invention, the variation in the melting temperature of solder balls can be remarkably improved, and this is an indispensable technique for practical use of solder balls.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a solder ball manufacturing apparatus.

[Explanation of symbols]

1. 1. Dissolved crucible; 2. siphon tube; 3. molten metal; 4. supply crucible; Orifice, 6. 6. vibration generator; Shaking rod, 8. Droplets, 9. Coagulation chamber; 10. 10. solder balls, Pressurizing device

Claims (1)

[Claims] 1. A solder ball, wherein the variation of the melting temperature of the solder ball per 10 million pieces is within 5 ° C.