KR20150122508A - Tin filtering methods, using this method for manufacturing alloy and solder ball - Google Patents

Abstract

The present invention relates to a solder ball for a semiconductor package and, more specifically, relates to a method to filter tin in 2-7 micrometers and 3-4 bar; a method to manufacture an alloy on a high-frequency vacuum induction furnace; and a method to manufacture a solder ball using a manufactured alloy. The present invention reduces a content of impurities in tin, and manufactures an alloy with low oxidation.

Description

TECHNICAL FIELD [0001] The present invention relates to a tin filtering method, a method of manufacturing an alloy using the tin filtering method, and a method of manufacturing a solder ball using the tin filtering method.

The present invention relates to a tin-based solder ball for a semiconductor package, and more particularly to a tin filtering method for removing impurities, an alloy manufacturing method using filtered tin, and a solder ball manufacturing method using the alloy.

In recent years, packages have become smaller as more and more devices such as mobile phones and electronic parts become more sophisticated and sophisticated. Particularly, in portable products, a fine pitch of a printed circuit board (PCB) and a miniaturization of a solder ball are prominent. Also, as the thickness of the PCB becomes thinner, warpage phenomenon occurs a lot. Therefore, during the reflow process, which is a process of attaching the solder ball on the printed circuit board, a phenomenon in which the solder ball does not stick on the PCB, a large amount of missing is generated, and workability is greatly reduced. Therefore, as the solder ball becomes smaller, it is necessary to improve the machining rate (the machining rate) and the workability deterioration, which are more and more generated at the fine pitch.

Solder balls, which transfer electrical signals by connecting a semiconductor chip and a substrate in a semiconductor packaging process, are formed of a metal alloy, which has high conductivity and is easily alloyed by a thermal process. In general, Sn-Ag-Cu alloys are used for reflow solder. Sn-Ag-Cu alloys have problems of oxidation and have problems such as wettability, heat resistance, durability strength needs to be improved.

The tin-based solder ball disclosed in the prior art (Laid-Open Publication No. 2013-0017626) is composed of Ag, Cu, Ni, Bi, Sn and unavoidable impurities. And thus the durability is reduced.

Disclosure of Invention Technical Problem [8] The present invention aims at solving the problem of the solder ball's machining rate, workability, and durability.

SUMMARY OF THE INVENTION The present invention provides a tin filtering method for reducing impurity content of tin.

Another object of the present invention is to provide a method for producing an alloy having good wettability and low oxidation degree.

Another object of the present invention is to provide a method of manufacturing a solder ball having a low machining ratio.

The tin filtering method of the present invention comprises melting a tin having a purity of 99.9% to 99.99% and then passing it through a filter having a thickness of 1 to 2 mm with a hole of 2 to 7 μm at a pressure of 3 to 4 bar to form Pb, Fe, Bi, Al, Zn And the like.

The alloy manufacturing method of the present invention uses the tin filtered according to the tin filtering method to manufacture an alloy in a high frequency vacuum electric induction furnace. A charging step of weighing the filtered tin and Ag, Cu, and Ni at a weight ratio and charging the high-frequency vacuum induction furnace with a vacuum degree of 3.0 × 10 ^-2 torr to 6.0 × 10 ^-2 torr, and then maintaining the pressure for 10 minutes; Temperature step of raising the temperature from the furnace to 700 占 폚 and holding it for 10 minutes, and raising the temperature to 1100 占 폚 for 60 minutes.

A method of manufacturing a solder ball using the alloy according to the present invention comprises melting a mixture of an alloy prepared by the alloy manufacturing method and a melted alloy at a temperature of 230 ° C to 250 ° C, A heating step of inducing heating of the alloy to which the master alloy has been charged, a step of heating the alloy to be passed through the graphite nozzle hole, Forming step.

Filtering the tin according to the present invention reduces the impurity content of the tin to reduce the Mushy region and the alloy produced using the filtered tin has better wettability than the alloy made using conventional tin, The solder ball manufactured using the alloy can reduce the machining rate and improve the workability.

1 is a view showing a structure of a filter device used for filtering annotations.
Figure 2 is a perspective view of a filter used to filter tin.
3 is a top plan view of the filter used to filter the tin.
Figure 4 is a cross-sectional view of a filter used to filter tin.
5 is an oxide film analysis graph of an alloy made using filtering tin according to an embodiment of the present invention.
FIG. 6 is a wet-ability test graph of an alloy manufactured using filtering tin according to an embodiment of the present invention. FIG.
7 is a graph of Differential Scanning Calorimetry (DSC) measurement of an alloy made using filtering tin according to an embodiment of the present invention.
FIG. 8 is an electron micrograph of the texture of an alloy manufactured using the filtering tin according to an embodiment of the present invention. FIG.
FIG. 9 is an electron microscope (SEM) image of an intermetallic compound (IMC) of an alloy produced using a filtering tin according to an embodiment of the present invention.
10 is a graph of the hardness measurement of an alloy made using filtering tin according to an embodiment of the present invention.
11 is a Weibull distribution graph showing drop impact characteristics of an alloy manufactured using the filtering tin according to an embodiment of the present invention.
12 is a graph of a Missing Bump Rate of an alloy manufactured using the filtering tin according to an embodiment of the present invention.

Before describing the present invention in detail, it is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the invention, which is defined solely by the appended claims. shall. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art unless otherwise stated.

Throughout this specification and claims, the word "comprise", "comprises", "comprising" means including a stated article, step or group of articles, and steps, , Step, or group of objects, or a group of steps.

On the contrary, the various embodiments of the present invention can be combined with any other embodiments as long as there is no clear counterpoint. Any feature that is specifically or advantageously indicated as being advantageous may be combined with any other feature or feature that is indicated as being preferred or advantageous. Hereinafter, embodiments of the present invention and effects thereof will be described with reference to the accompanying drawings.

How annotation filtering works

The tin filtering method of the present invention is characterized in that tin having a purity of 99.9% to 99.99% is melted at 250 to 350 DEG C and then passed through a filter device having a filter of 2 to 7 mu m pore under a pressure of 3 to 4 bar.

Since the melting point of tin is 232 deg. C, the melting operation is not smooth at 250 deg. C or lower, and the filtering effect is insufficient because the tin is highly oxidized due to the high temperature at 350 deg. Preferably, the tin is melted at 290 to 310 占 폚.

The filter device has a structure as shown in FIG. 1, and includes an injection part 21 into which molten tin is injected, an outflow part 22 through which the filtered tin outflows, a filter 10, a spring 30, 40). The molten tin is injected through the injection part 21 under a pressure of 3 to 4 bar, and through the cylindrical filter 10, impure molten tin is obtained through the outflow part 22.

The filter 10 has a cylindrical structure with a height of 2 cm and a thickness of 1 to 2 mm as shown in a perspective view of FIG. 2 and a plan view of FIG. 3, and a lower end closed as shown in a cross-sectional perspective view of FIG.

The material of the filter is ferritic stainless steel or austenitic stainless steel. The stainless steel may further include at least one of molybdenum, nickel, and chromium. For example, when molybdenum is contained in an amount of 6% or less, it has an effect of being able to withstand cracks and stress, and when it contains 13% or more of chromium, it has an effect of giving high oxidation resistance. When the content of nickel is less than 10%, it has an effect of maintaining the austenite structure from the melting point to the low temperature. The size of the filter hole is 2 to 7 μm, and when it is less than 2 μm, the workability is deteriorated.

Also, when the pressure is less than 3 bar and greater than 4 bar, there is no filtering effect.

After the tin filtering, impurities such as Pb, Fe, Bi, Al, Zn are removed and the concentration of each impurity becomes 10 ppm or less. As shown in FIG. 5, the filtered tin has a lower concentration of oxygen than that of unfiltered tin and has a relatively high concentration of Sn, Ag, Cu and the like, and minimizes the Mushy region. When the liquid phase changes to a solid phase, the liquid phase and the solid phase are simultaneously present. When the liquid phase changes into a solid phase, impurities such as Pb and Fe are present, and the respective elements exist as one phase. By creating sites and increasing the time to solidify, the area of the machine will increase. When the solder balls are bonded, a fast reaction must occur. In the case where the machice area is large, the reaction time is long and the bonding reaction is slowed.

Method for manufacturing alloy using filtered tin

The alloy manufacturing method of the present invention uses the tin filtered according to the tin filtering method to manufacture an alloy in a high frequency vacuum electric induction furnace.

More specifically, the filtering tin is weighed in weight ratio of Ag, Cu, and Ni to be charged into a high frequency vacuum induction furnace and maintained for 10 minutes. The high frequency vacuum induction furnace is heated for 10 minutes to 700 ° C for 10 minutes And a second heating step of raising the temperature of the high-frequency vacuum induction furnace to 1100 캜 for 10 minutes and then maintaining the high-frequency vacuum induction furnace for 60 minutes.

The weight ratio of Ag, Cu, and Ni is preferably 1.2 wt% of Ag, 0.5 wt% of Cu, and 0.05 wt% of Ni based on the tin weight, but is not limited thereto.

In the charging step, the degree of vacuum of the high-frequency vacuum induction furnace is 3.0 x 10 ^-2 torr to 6.0 x 10 ^-2 torr. When the degree of vacuum drops to 10 ^-1 torr, oxygen reacts with tin to form a large amount of tin oxide. In the case of producing an alloy in a high-frequency vacuum induction furnace, the unnecessary reaction of tin to form tin oxide (SnO ₂ ) by reaction with oxygen is suppressed, so that the content of other elements is less changed and the segregation rate is reduced. Further, the agitating force due to the electrical vortex in the high-frequency vacuum induction furnace is superior to the mechanical agitating force of the conventional method using the electric furnace, and work is performed in an inert atmosphere rather than in the atmosphere.

 And a purging step of purging the high-frequency vacuum induction furnace with an inert gas between the charging step and the first temperature raising step and then keeping the furnace for 10 minutes. The purging means that the inside of the alloy is neutralized with an inert gas which does not cause a chemical or physical reaction, and the purging pressure is preferably 750 to 760 torr.

The reason why the holding time is 60 minutes after raising the temperature to 1100 占 폚 for 10 minutes in the second heating step is to homogenize alloying elements having different specific gravity such as Ag, Cu, and Ni.

Method of manufacturing solder balls using alloy

The method of manufacturing a solder ball using the alloy according to the present invention includes a charging step of charging an alloy manufactured by the alloy manufacturing method into a molten metal and then melting the molten alloy at 230 ° C to 250 ° C, 250 ° C to 280 ° C, a heating step for induction heating the alloy into which the Sn-Ge master alloy is injected, passing the heated alloy through a graphite nozzle hole using a vibrator, And a ball forming step of forming a ball.

The adding step is a method of separately making an alloy (Sn-Ge master alloy) containing a large amount of additive element (Sn) as a melting agent and adding it to a melt of a metal (filtered tin) So as to uniformly add a certain amount of alloying elements to be added when making the alloy. In addition, since the melting point (938 ° C) of Ge alone is high, a master alloy is prepared to lower the melting point. The master alloy includes tin (Sn) and germanium (Ge), and preferably includes 0.1 to 5 parts by weight of germanium relative to 100 parts by weight of tin, but is not limited thereto.

The induction heating in the heating step is a method of converting electric energy into heat energy by electromagnetic induction, and uses Joule's heat generated when a secondary current induced by electromagnetic induction flows into the material to be heated. In this case, the material to be heated is an alloy manufactured through the above-mentioned charging step.

The size of the solder ball formed in the ball forming step can be controlled by frequency and pressure. The diameter of the graphite nozzle hole is preferably 70 to 120 mu m, the frequency is 7 to 15 KHz, and the pressure is preferably 1000 to 2000 mbar. At this time, the formed solder balls have an average diameter of 150 to 250 mu m. The graphite nozzle has a cylindrical shape, and it is possible to realize a stable size by using graphite material.

Examples and Experimental Examples

Example 1

The tin was filtered using 99.9% to 99.99% purity of tin, the size of the filter was 2 탆, the pressure was 3 bar, and the temperature was 300 캜.

Examples 2 and 3

Tin was filtered in the same manner as in Example 1, except that the filter size or pressure was changed as shown in Table 1.

Comparative Example 1

The purity 99.9% to 99.99% tin without filtration according to the present invention is referred to as Comparative Example 1.

Comparative Example 2 and Comparative Example 3

Tin was filtered in the same manner as in Example 1 except that the filter size and pressure were changed to those shown in Table 1. [

Size of filter
(m) pressure
(bar) Impurity content (ppm) Pb Bi Fe Al Zn Example 1 2 3 9.8 9.5 8.8 9.7 9.5 Example 2 7 3 9.5 9.3 8.5 9.6 8.6 Example 3 2 4 9.4 9.1 8.2 9.2 7.6 Comparative Example 1 - - 289 91 92 96 88 Comparative Example 2 15 3 282 83 88 87 82 Comparative Example 3 2 5 265 81 85 83 77

The impurity content of the filtered tin is as low as 10 ppm or less per each element as in Examples 1 and 2. On the other hand, in the case of the tin without filtration or filtering out of the scope of the present invention as in Comparative Examples 1 to 3 It can be seen that the impurity content is as high as 300 ppm or less.

Experimental Example 1

The flowability of the alloy produced using the tin filtered by the present invention was evaluated. The flow rate was evaluated as the percentage of normal products shipped even if the worker did not constantly monitor the production process. More than 95% are A, more than 90% are B, more than 80% are C, more than 70% are D, and less than 70% Because the additives are uniformly alloyed due to the electrical vortex in the induction furnace and the segregation is further suppressed, the filtered tin alloy has better flow than the conventional tin alloy as shown in Table 2, and the holding time of the alloy is 60 Min, which is very good for flow. The flow criterion is from E to A.

Annotation type Alloy retention time (hrs.) Flowability <Flow criterion>
A: 95% or more
B: 90% or more
C: 80% or more
D: 70% or more
E: 70% or less Filtering annotations 30 B 60 A 90 A General annotation 30 E 60 D 90 D

Experimental Example  2

The degree of oxidation of the alloy produced using the tin filtered by the present invention was measured. SAC1205Ni alloy (1.2% Ag, 0.5% Cu + 0.05% Ni in Sn) was prepared by using the tin using the filtering. As a comparative example, SAC1205Ni alloy was manufactured using general tin and oxygen concentration was measured. The oxidation degree measurement method is a typical Inert gas fusion method in which elements are extracted from an alloy. The oxygen contained in the alloy reacts with C present in the carbon crucible and is extracted into CO form. CO is oxidized to CO ₂ by an oxidizing agent while passing through a copper oxide tube by an inert moving gas such as helium, and oxygen content is measured by Infrared detection (IR). As shown in Table 3, the degree of oxidation was 7 ppm in the case of the filtered tin alloy, while the degree of oxidation was measured in the case of the tin alloy in the case of the general tin alloy because the impurities that increase the oxidation degree are removed by filtering the tin.

Annotation type Size of filter (μm) Pressure (bar) Temperature (C) Oxidation (ppm) Filtering annotations 2 3 300 7 General annotation - - - 30

Experimental Example 3

The wet-ability of the alloy prepared using the tin filtered by the present invention was measured. 850 g of an alloy was melted in a molten liquid at 240 ° C. and a flux was added to a Cu plate to drop it in a bath. The wettability is measured by the wetting time (T0). The shorter the wetting time, the better the wettability.

As shown in FIG. 2, the wetting time of the filtering tin alloy is faster than that of the general tin alloy having a wetting time of 0.19 sec and 0.91 sec. If wettability is high, it spreads well and increases adhesion and adsorption, so it can be deduced that the sewing rate of the alloy using the filtered tin will be low. In the method of measuring the wet strength, when the alloy is immersed in the alloy, the alloy pushes the specimen by buoyancy, so that the wet strength shows a negative value, but the wet strength changes to positive value over time. When the lunar power changes from a negative value to a positive value, that is, the point at which the wetting force becomes zero is referred to as a wetting time. The wetting time should be controlled to 1.6 seconds or less, and if it exceeds 1.6 seconds, wetting failure may occur.

Experimental Example 4

Differential Scanning Calorimetry (DSC) was performed on the alloy prepared using the tin filtered by the present invention. The filtering tin alloy and the general tin alloy were heated or cooled at the same rate under the same conditions, and the difference in the amount of heat applied electrically was recorded on the ordinate axis and the temperature on the abscissa axis so that the temperature of the two alloys became equal.

As shown in Table 4 and FIG. 3, the filtering tin alloy has a smaller heat capacity area than that of the general tin alloy. In addition, the range of the temperature region between the onset point and the end point is narrow. Using filtering, the temperature range and the heat capacity of the machining area are greatly reduced because impurities that increase the oxidation of tin have been removed and other trace impurities present in the tin have been removed and the nucleation-causing particles have been relatively removed .

Annotation type Area (J / g) Onset (℃) End (℃) Peak (° C) Filtering annotations -51.55 218.4 228.7 220.6 General annotation -59.65 218.3 229.7 220.3

Experimental Example 5

The microstructure of the alloy produced using the tin filtered by the present invention was observed through an electron microscope. As shown in FIG. 4, since the impurities are removed through filtration, the filtering tin alloy can be seen to be more compact than the alloy of general tin.

Experimental Example 6

The intermetallic compound (IMC) of the alloy prepared using the tin filtered by the present invention was observed through an electron microscope. As shown in FIG. 5, the IMC formed according to the oxygen concentration has a similar shape regardless of the type of tin.

Experimental Example 7

The hardness of the alloy produced using the tin filtered by the present invention was measured. After the specimens were mounted using epoxy resin, the specimens were polished using alumina and abrasive paper. The indentation was made on the cross section of the specimen of the specular surface by a diamond impression of a quadrangular pyramid shape. The indentation was measured on the specimen with a force of 10 gf for 30 seconds using indentation, and the correlation between the length of the diagonal line and the load Hardness value. The average value was calculated by measuring 10 times for each specimen.

As shown in FIG. 6, the alloy produced using the filtered tin exhibits a low hardness value. This is because the impurities remaining in the tin are removed through filtering to form coarse grains. In addition, it can be deduced that the filtering tin alloy has a lower hardness value than that of the ordinary tin alloy.

Experimental Example 8

The drop strength of the alloy produced using the tin filtered by the present invention was measured. The experiment was conducted according to the JEDEC regulations (JESD22-B111), the acceleration of gravity was 1500G and the duration time was 0.5msec. The Weibull distribution is a probability distribution, a probability distribution suitable for representing the strength of metals and composites, and the life span of electronic and mechanical parts.

As shown in the Weibull distribution in FIG. 7, the filtering tin alloy has better drop impact characteristics than a general tin alloy. Filtering removes impurities, and there are no particles to nucleate, so they have a coarse texture. As a result, the ductility of the tin alloy is higher than that of the conventional tin alloy, so that the alloy absorbs the impact generated during the drop impact, so that the life of the solder ball manufactured using the filtering tin alloy is increased.

Experimental Example 9

The machining rate of the solder balls manufactured by the present invention was evaluated. The sewing rate evaluation method was calculated as follows.

Overall, the rate at which a missing bump occurred was calculated by dividing the number of missing bumps by the number of bumps present per unit multiplied by the number of units. The number of bumps present per unit is 778. When using filtered tin, the sewing rate and workability improvement is applicable to all alloys as well as SAC1205Ni.

As shown in FIG. 8, in the case of the filtering tin alloy, when the oxygen concentration is 10000 ppm, the sewing rate is less than 500 ppm, and when the oxygen concentration is 6000 ppm, the sewing rate is lower than 500 ppm. , The sewing rate is below 200 ppm when the oxygen concentration is 3000 ppm, the sewing rate is less than 110 ppm when the oxygen concentration is 1000 ppm, and the sewing rate is less than 500 ppm at all the oxygen concentration (O ₂ contents) have. In general tin alloy, the machinability is less than 500ppm in the reflow zone where the oxygen concentration is controlled to 1000ppm, satisfying the workability and showing the weak characteristic in the remaining conditions. When the oxygen concentration is controlled to 3000 ppm or less when reflowing, a considerable increase in cost is caused, so that the oxygen concentration is controlled to 3000 ppm in a general manufacturing factory. In the case of the alloy produced by using the filtering, even if the oxygen concentration is controlled to 10000 ppm, the workability and the sewing rate are not affected. In addition, since the impurities that increase oxidation of tin are removed by filtering, the thickness of oxidation and oxide film is minimized, and the cost reduction effect can be expected because the machining area is relatively reduced.

The features, structures, effects, and the like illustrated in the above-described embodiments can be combined and modified in other embodiments by those skilled in the art to which the embodiments belong. Therefore, it should be understood that the present invention is not limited to these combinations and modifications.

Claims (12)

A melting step of melting tin of 99.9% to 99.99% purity; And
And passing the molten tin through a 1 to 2 mm thick filter having a hole of 2 to 7 mu m under a pressure of 3 to 4 bar. The method according to claim 1,
The material of the filter is ferritic stainless steel or austenitic stainless steel,
Wherein the stainless steel further comprises at least one of molybdenum, nickel, and chromium. A process for producing a tin filter according to claim 1 or 2,
A tin having a concentration of each impurity of 10 ppm or less. Charging at least one kind of metal and tin of claim 2 into a high-frequency vacuum induction furnace, and then maintaining the furnace for 10 minutes;
A first heating step of raising the temperature of the high-frequency vacuum induction furnace to 700 캜 for 10 minutes and then maintaining the furnace for 10 minutes; And
And a second heating step of raising the temperature of the high-frequency vacuum induction furnace to 1100 DEG C for 10 minutes and then maintaining the furnace for 60 minutes. 5. The method of claim 4,
Wherein the metal in the charging step comprises Ag, Cu, Ni,
Wherein the weight ratio of Ag, Cu, and Ni is 1.2 wt% of Ag, 0.5 wt% of Cu, and 0.05 wt% of Ni based on the weight of tin. 5. The method of claim 4,
Wherein the degree of vacuum of the high-frequency vacuum induction furnace in the charging step is 3.0 占 10 ^-2 torr to 6.0 占 10 ^-2 torr. 5. The method of claim 4,
And a purging step of purging the high-frequency vacuum induction furnace with an inert gas between the charging step and the first heating step, and then maintaining the furnace for 10 minutes. A process for producing an alloy according to any one of claims 4 to 7,
An alloy having an oxidation degree of 10 ppm or less and a wetting time of 0.2 sec or less. Using a filtered tin by passing molten tin of 99.9% to 99.99% purity through a filter of a ferritic stainless steel or austenitic stainless steel with a hole of 2-7 [mu] m under a pressure of 3-4 bar,
A charging step of charging the filtered tin and at least one kind of metal into a high frequency vacuum induction furnace having a degree of vacuum of 3.0 x 10 ^-2 torr to 6.0 x 10 ^-2 torr,
A first heating step of raising the temperature of the high-frequency vacuum induction furnace to 700 DEG C for 10 minutes and then maintaining it for 10 minutes, and
And a second heating step of raising the temperature of the high-frequency vacuum induction furnace to 1100 캜 for 10 minutes and then maintaining the furnace for 60 minutes,
A melting step of charging the alloy produced by the above method into a molten metal and then melting the molten alloy at 230 to 250 ° C;
An injection step of supplying the master alloy to the molten alloy and maintaining the temperature at 250 to 280 DEG C;
A heating step of induction heating the alloy into which the master alloy is introduced; And
And a ball forming step of passing the induction-heated alloy through a graphite nozzle hole. 10. The method of claim 9,
Wherein the master alloy in the charging step comprises tin (Sn) and germanium (Ge) and is a master alloy comprising 0.1 to 5 parts by weight of germanium relative to 100 parts by weight of tin. 10. The method of claim 9,
Wherein the orifice hole of the ball forming step has a diameter of 70 to 120 mu m, a frequency of 7 to 15 KHz, and a pressure of 1000 to 2000 mbar. A solder ball manufacturing method according to any one of claims 9 to 11,
A solder ball having a sewing rate of less than 250 ppm when the oxygen concentration is 6000 ppm, a sewing rate of 200 ppm or less when the oxygen concentration is 3000 ppm, and a sewing rate of 110 ppm or less when the oxygen concentration is 1000 ppm.

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