KR100400263B1 - Sintered material for capillary of alumina-zirconia composite used in wire bonding and method for manufacturing the same - Google Patents

Abstract

In order to improve the impact resistance and abrasion resistance of the capillary, the capillary sintered body was made from 70 to 95 wt% of α-alumina (Al ₂ O ₃ ) powder and 5 to 30 wt of zirconia-yttria (ZrO ₂ -Y ₂ O ₃ ) powder. %, 5-20 wt% of liquid polyethylene glycol is mixed with the mixed powder of alumina and zirconia-yttria to make an alumina-zirconia composite, and the composite is dried, pulverized, two stages of compression / molding and three stages. The sintering process including the heat treatment of the. Two-stage compression / molding allows the upper core mold with the conical tip to flow into the composite inserted into the cylindrical mold, and then moves the lower core mold upwards by a predetermined distance, for example, about 5 mm, to compress the spheroidized composite first. And returning the lower core mold to a position prior to primary compression and then moving the upper core mold downward to secondary compress the primary compressed composite. The three-stage heat treatment means a preliminary heat treatment step for stabilizing grain growth between the heat treatment step for degreasing the binder and the heat treatment step for growing the shaped particles.

Description

Sintered material for capillary of alumina-zirconia composite used in wire bonding and method for manufacturing the same

The present invention relates to a capillary sintered body of a wire bonding system, and more particularly, to a capillary sintered body for improving the impact resistance and abrasion resistance of the capillary tip and a manufacturing method thereof.

In the semiconductor package manufacturing process, the wire bonding apparatus is used to connect external connection passages of packages such as lead frames, ceramic circuit boards, and printed circuit boards, and input / output pads or dies of semiconductor chips using aluminum, gold, or copper. Used.

An essential capillary for the wire bonding process using the wire bonding apparatus is shown in FIG. 1. The capillary 10 is composed of a cylindrical body 12 and a fine hole 14 provided therein. In the microhole 14, a ball bonding wire (not shown) having a diameter of 1.0 to 1.3 mils (one mil is 1/1000 inch) is accommodated. The microholes 14 have a conical shape whose diameter decreases toward the tip 20, and the lower end of the microholes 14 is referred to as a chamber 16. To perform the bonding process, the capillary 10 forms balls at the ends of the wires through high voltage discharge. This ball is contacted / pressurized to the pad of the chip under the control of the wire bonding device, ultrasonic energy is transferred to the bottom of the capillary and when the pad is heated, the ball is pressed and bonded first to the pad. The capillary is pulled out of the primary bond to form a wire loop of constant trajectory, which is connected to the lead of the lead frame with a secondary stitch bond. This operation is repeated several times to connect the pad of the semiconductor chip and the external connection passage of the package.

However, the capillary capillary portion of the tip 20 forming the ball is brought into contact with the semiconductor input / output pad and the lead of the lead frame at the time of the first bond and the second bond, and is placed in a high voltage discharge state. Lee's tips are indispensable for impact resistance (must have high fracture toughness) and wear resistance (must have high Vickers hardness).

In particular, in terms of cost reduction, the pre-plated lead frame (Pre-Plated Frame) is preferred because the tin process is not performed because it can reduce the manufacturing cost than the general lead frame. By the way, the Vickers hardness of the pre-plated lead frame is considerably larger than the Vickers hardness of the capillary, resulting in severe wear of the capillary tip.

As a capillary sintered body, pure alumina having a purity of 99.99% or more is generally used, and its fracture toughness is still low. In addition, alumina grains are enlarged during the sintering process of alumina, so that the density of the particles is lowered and the surface flatness and the Vickers hardness are lowered. Therefore, the tip of the capillary composed of a pure alumina sintered body lacks abrasion resistance and impact resistance and it is difficult to perform the wire bonding operation because the tip is broken or worn. In addition, when performing wire bonding using ultrasonic waves, it is difficult to accurately form a ball at an end portion of the wire inserted in the capillary by blocking the ultrasonic waves by the internal pores at the tip portion. As one technique for solving this problem, a technique of coating Zr and Ti on the tip portion of the capillary is disclosed in Korean Patent No. 1997-32653.

On the other hand, impact resistance and abrasion resistance are related to the pore content of the structure of the structure corresponding to the capillary sintered body, especially the tip of the capillary. If the pore content is large and the structure of the capillary sintered body (specifically, the portion corresponding to the tip of the capillary) is not dense, not only the impact resistance and the abrasion resistance of the sintered body and the capillary will be insufficient, There is a problem that a second bonding defect occurs.

However, when a binder is added to uniformly bond the powder particles during compression / molding, pores after sintering increase. Therefore, if the compression molding rate is increased by increasing the molding pressure of the sintered compact as a means for reducing the pore content without increasing the amount of the binder, it is difficult to remove the capillary molded body from the molding die of the capillary.

Accordingly, the technical problem to be achieved by the present invention is to provide a capillary sintered body and a method for producing the same, which have reduced pore content and improved wear resistance and impact resistance.

Another technical problem to be achieved by the present invention is to provide a capillary sintered body and a method for producing the same, which can be easily removed from the capillary forming apparatus while reducing the pore content.

1 shows a cross-sectional view of a capillary for wire bonding.

Figure 2 is a flow chart showing the manufacturing process of the alumina-zirconia composite capillary sintered body according to the present invention.

3A to 3G are views illustrating the compression / molding process of FIG. 2.

4 is a graph illustrating a first sintering process of FIG. 2.

5 is a view showing the fracture toughness and Vickers hardness of the pure alumina sintered body and the sintered alumina-zirconia composite according to the present invention.

6 is a diagram showing the number of wire bonding times using a capillary manufactured using a pure alumina sintered body and an alumina-zirconia composite sintered body according to the present invention.

7 shows a state of the surface of the alumina-zirconia composite sintered body according to the present invention taken with a scanning electron microscope.

In order to achieve the technical problem to be achieved by the present invention, 70-95wt% of α-alumina (Al ₂ O ₃ ) powder and 5-30wt% of zirconia-yttria (ZrO ₂ -Y ₂ O ₃ ) powder, the mixture thereof Alumina-zirconia composites are made comprising 5-20 Wt% of liquid polyethylene glycol relative to the powder. The composite is then converted into a sintered body for capillary with fracture toughness of 5.2 to 5.4 MPam ^0.5 and Vickers hardness of 1970 to 2010 Mpa through drying, pulverization, sintering process including two stages of compression / molding and three stages of heat treatment. Let's do it. Here, the alumina powder has a particle size of 0.2 to 0.8 μm, and the zirconia-yttria powder has a particle size of 0.2 to 0.8 μm.

And it is preferable that the molecular weight of liquid polyethylene glycol is 400-600.

On the other hand, in order to manufacture the alumina-zirconia sintered body with reduced pore content, first, 70 to 95 wt% of α-alumina powder and 5 to 30 wt% of zirconia-ytria powder, and 5 to 30 wt% of liquid polyethylene glycol with respect to the mixed powder thereof. 20 Wt%, alumina balls and dispersant are mixed and ground to form an alumina-zirconia complex. Then, the alumina ball is removed from the composite, the composite is dried, and the dried composite is pulverized and spheroidized. For compression / molding, a cylindrical capillary forming mold having a through hole, a cylindrical lower core mold having a diameter equal to the diameter of the through hole, and an upper core having the same size and shape as the lower core mold and having a conical tip. Prepare the mold. This tip forms a fine hole in the capillary. And using these, the spherical composite is inserted into a through hole and compressed in two steps to form a capillary molded body. Next, the capillary molded body is put into a sintering furnace and heated to form a sintered body. It is preferable to use the thing of 400-600 molecular weight of liquid polyethylene glycol here.

In particular, when the molded body is heat-treated in three stages in consideration of the grain growth of the capillary sintered body in the sintering step, the grain growth of the molded body becomes uniform, thereby reducing the pore content of the sintered body. Specifically, the three-stage heat treatment is the first step of raising the temperature of the sintering furnace including the capillary molded body to 300-500 degrees at 1 ° C / minute and maintaining the temperature of 500 ° C for about 30-50 hours, and the sintering furnace at 5 ° C / minute. The step of raising the temperature to 1000-1200 degrees and maintaining about 1 hour and the step of raising the sintering furnace to about 1550-1650 degrees at 10 ℃ / min and maintaining for about 10 minutes. On the other hand, after the sintering step to the sintered body in a high-temperature compression furnace further comprises a secondary sintering step of maintaining a predetermined time at 1000-1500 ℃, 500-1500 bar (bar) can further lower the pore content.

Meanwhile, the capillary molded body is formed by compression / molding in two steps. First, a cylindrical mold, a lower core mold, and the upper core mold are prepared. The lower core mold closes the bottom of the through hole of the cylindrical mold. The spherical composite is inserted into the through-hole closed at one end. After the tip of the upper core mold is introduced into the inserted composite, the spheroidized composite is first compressed by moving the lower core mold upward a predetermined distance, for example about 5 mm. Then, the lower core mold is returned to the position before the primary compression, and then the upper core mold is moved downward to compress the primary compressed composite to form a molded body. Then, the upper core mold is fixed while the upper core mold is continuously moved downward and the molded body is discharged out of the cylindrical mold, so that the tip of the upper core mold is separated from the molded body.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

As a method of minimizing the pore content, there are methods for reducing pores between particles, a method for controlling the molding method of the alumina-zirconia composite, and a method for controlling the sintering temperature of the molded body. It was.

2 is a flowchart showing a step of producing a capillary sintered body according to the present invention. In a container, zirconia-ytria (ZrO ₂ -Y ₂ ) having a purity of 99.99% or more and an α-alumina (Al ₂ O ₃ ) powder having a particle size of 0.2 to 0.8 μm at 70 to 95 wt% and a particle size of 0.2 to 0.8 μm. O ₃ ) The powder is mixed at 5 to 30 wt% to form an alumina-zirconia mixture (S1). Since zirconia powder is unstable during sintering, it is stabilized by adding yttria to zirconia.

5-20 wt% of liquid polyethylene glycol as a binder is added to the mixture, and alumina balls (Φ 5 mm) are added to 1/3 of the mixing vessel, and 100 wt% of a dispersed organic solvent such as ethanol or methanol is added to the mixed powder as a binder. To form an alumina-zirconia composite in the slurry state. The reason for the use of liquid polyethylene glycol is that the pores are reduced only when the particles are completely broken between the particles during compression / molding, and if the materials are severely hard during compression molding as binders, the above functions cannot be performed. Because. Preferably, the liquid polyethylene glycol uses a molecular weight of 400 to 600. As the alumina balls rotate in the mixing vessel, they serve to mix them evenly while grinding each powder smaller. The organic solvent acts as a solvent, inhibits agglomeration of the same kind of particles in each powder during grinding and drops the agglomerated particles so that they can be combined with other particles by the binder. Here, the addition amount of the binder is not limited to the above-mentioned numerical value, and the binder is enough to be pushed out of the structure of the molded body at the time of compression / molding and can also play a role as a lubricant at the time of removing the molded body.

Looking at the role of the binder in detail, the liquid polyethylene glycol as a binder is filled in the space between the alumina particles and zirconia (or zirconia-yttria) particles before the compression / molding step (S4 in Figure 2) to uniformly bind them However, in the compression molding step (S4) it is pushed between these particles and buried in the inner wall of the capillary molding mold (30 in Figure 3a) also serves as a lubricant when removing the molded body (44 in Figure 3e) from the molding mold. . That is, the capillary molded body can be easily removed from the molding die even when the compression molding rate is further increased by lowering the internal stress of the capillary molded body when the powder is compressed. Therefore, the compression ratio of the molded body is generally recognized in the industry dealing with ceramic materials is about 40%, the realization of the above is not achieved due to the difficulty of molding, the compression rate of the molded body in the case of using the present invention, in particular about 15w% binder This becomes 65% or more, and together with the ease of removing the molded body, the pores of the molded body or the sintered body can be reduced to obtain the effect of compacting the structure.

Next, the alumina-zirconia composite is placed in a rotary mill and rotated for about 24 hours at a speed of 80 rpm to mix and grind. Subsequently, the composite is poured into a predetermined sieve to filter the alumina balls from the composite, and the remaining slurry is dried at 50 to 70 ° C. on a hot plate to evaporate the organic solvent (S2).

The dried alumina-zirconia composite mass is put into alumina-induced powder and pulverized, and then finely spheroidized the alumina-zirconia composite mass using a sieve having a mesh size of 200 μm (S3).

Next, the pulverized and spheroidized alumina-zirconia composite is put into a capillary forming mold (30 in FIG. 3A) and compressed / molded to produce a capillary molded body (44 in FIG. 3E) (S4). The process of making the capillary molded body is shown in detail in FIGS. 3A-3G.

As shown in FIG. 3A. The compression mold 30 is cylindrical having a through hole 32 therein. And in order to form a molded object, the upper core mold 34 and the lower core mold 36 are prepared. The upper core mold 34 and the lower core mold 36 have the same size and are aligned with the through hole 32 of the cylindrical mold 30. The upper core mold 34 has a conical tip 38. The cylindrical mold 30, the upper core mold 34, and the lower core mold 36 consist of cemented carbide.

In FIG. 3B, the lower core mold 36 is inserted into the hole 32 to block the lower portion of the through hole 32 of the cylindrical mold. Then, the pulverized / spheroidized powder 40 is inserted into the hole 32 in which the lower portion is blocked. The upper core mold 34 is inserted into the hole 32 by about 1 mm.

And as shown in Figure 3c, the lower core mold 36 is moved slightly upward. For example, by moving upward 5mm, the crushed / spheroidized powder is slightly compressed. Reference numeral 42 denotes a powder in a compressed state compared to the powder indicated by 40. By this preliminary compression process, the forming density of the tip 38 portion of the upper core mold 34 is increased, so that the internal pores in this portion can be reduced. That is, the shaping density of the tip portion of the capillary becomes high. In addition, about 5 mm, which is the moving distance or the compression depth of the lower core mold 36, the molding density of the portion compressed by the lower core mold 36 becomes high, and in the subsequent final compression process, the tip 38 of the upper core mold 34 ) Can be varied depending on the amount of the binder added and the mixing ratio of the mixed powder.

As shown in FIG. 3D, the lower core mold 36 compressed by about 5 mm is returned to the pre-compression position. In FIG. 3E, the upper core mold 34 finally compresses the pre-compressed crushed / sphered powder to the point controlled by the compression stop device to form the molded body 44. Then, as shown in FIG. 3F, when the final compression is completed, the lower core mold 36 moves to the standby position of FIG. 3A while the upper core mold 34 pushes the compression / molding body 44 into the cylindrical mold 30. ), The molded body 44 expands outside the cylindrical mold 30. At this time, the jig 46 catches the upper core mold 34 to suppress expansion of the upper core mold. Accordingly, the tip 38 and the molded body 44 of the upper core mold 34 are separated to smooth the inner surface of the conical hole of the molded body 44. Next, as shown in FIG. 3G, when the upper core mold 34 is returned to the position in the atmosphere of FIG. 3A, the molded body falls down.

Returning to FIG. 2 again, after the forming step, the capillary molded body (44 in FIG. 3G) is placed in a high temperature sintering furnace and subjected to primary sintering. By primary sintering, the temperature of the capillary molded body 44 rises to about 1600 degreeC. By the way, in reality, since the capillary molded body 44 is laminated | stacked in the sintering furnace, the temperature which the capillary molded body 44 shows is lower than the moment when the temperature of a sintering furnace reaches 1600 degreeC, and the capillary The temperature of the capillary molded body 44 disposed at the lower, upper and middle portions of the laminated structure is different. Therefore, a long time is required for the temperature of the capillary molded laminate to reach the same level as that indicated by the sintering furnace. And even if the temperature of the capillary laminate reaches the temperature level of the sintering furnace, a difference occurs in the particle growth rate of the capillary molded bodies located at the top, the bottom and the middle of the laminate, so that the size of the particles in each part is uniform. There is a problem that the structure of the capillary sintered compact is not dense. If the structure of the capillary sintered body is not dense and the surface of the capillary sintered body is not smooth, foreign substances are easily adhered to the capillary tip during wire bonding, and the probability of defects during stitching bonding increases, ultimately using capillary. The life will be shortened.

Therefore, in the present invention, the process of raising the temperature of the capillary molded body 44 to 1600 ° C. is carried out in three stages, and the temperature of the capillary molded body 44 is maintained by maintaining a predetermined temperature for each period. The time taken to rise to the temperature level of the sintering furnace was shortened and the temperature difference between the moldings located at the top, bottom and middle of the capillary molded body laminate at the same sintering furnace temperature was reduced. As a result, the molded articles in the upper, lower and intermediate positions of the capillary molded laminate were all grown into uniform structures.

More details will be described with reference to the graph of FIG. 4. In a first step, the temperature of the sintering furnace in which the capillary molded body is provided therein is raised to 1 ° C per minute in a normal temperature state, and then raised to 300 to 500 ° C. By maintaining the temperature of the sintering furnace at about 300 to 500 ° C. for about 30 to 50 hours, the binder contained in the molded body is degreased, and the temperature difference between the sintering furnace and the molded body and the temperature of the upper, lower and middle parts of the molded body are reduced. Make it uniform. The temperature of the first stage is sufficient if it is above the degreasing temperature of the binder.

In two steps, the temperature of the sintering furnace is raised from 300 to 500 ° C., from 1000 to 1200 ° C., at 5 ° C. per minute, and maintained at about 1 hour at 1000 to 1200 ° C., thereby preliminary operation of the molded particles. Stabilize growth energy. The two stages bring the temperature of the capillary molded body closer to the temperature level of the sintering furnace, and the capillary molded body stack remains at a uniform temperature level as a whole.

The third step is a full-scale sintering step, which controls the growth of the particles of the molded body but grows in a large scale, thereby densifying the structure of the sintered body, and rapidly raises the sintering furnace to about 1550-1650 ° C. at 10 ° C. per minute. Since the particle growth energy of the capillary molded body is stabilized in step 2, even if the temperature is rapidly increased in this step, the uneven growth of the particle of the molded body can be suppressed. However, when the molded particles become huge, the density of the particles may be lowered and the tissue may not be dense, so that the retention time of the three steps may be adjusted in consideration of this. Next, the sintered compact is gradually cooled.

The temperature and holding time at each step can vary depending on the content of alumina, zirconia-yttria or binder.

The characteristics of the capillary sintered body completed until the first sintering step can be seen from FIG. 5. The toughness and Vickers hardness of the pure alumina sintered body after the sintering process in which the second stage of the three-stage first sintering process is omitted is about 4.3 (MPam ^0.5 ) and about 1850 (MPa), respectively, while the alumina-zirconia composite according to the present invention is The toughness and Vickers hardness of the sintered body subjected to the three stages of heat treatment were increased to about 5.4 (MPam ^0.5 ) and about 1970 (MPa), respectively. That is, it can be seen that the impact resistance and wear resistance of the alumina-zirconia composite sintered body according to the present invention are improved.

The above-described pure alumina sintered body and alumina-zirconia composite sintered body were manufactured to prepare a capillary as shown in FIG. 1, and then the wire bonding operation was performed to measure the life of the capillary. Is shown.

While the capillary using pure alumina sintered body is 400K (1K means 1000 times), it can be seen that the capillary using alumina-zirconia sintered body according to the present invention increased to 600K.

Next, returning to FIG. 2 again, after the first sintering over the three steps is completed, the second sintering may be selectively performed (S6).

The first sintered sintered body is placed in a ceramic container and placed in a hot isostatic press at 1000-1500 ° C. and 500-1500 bar for a predetermined time (for example, about 1500 ° C. for 60 minutes in an atmosphere of 1000 bar). It is maintained to remove residual fine pores inside the sintered body to further densify the tissue. Therefore, the wear resistance and impact resistance of the sintered compact are further improved.

Thereafter, the capillary sintered body is processed to produce an alumina zirconia composite capillary for wire bonding as shown in FIG. 1.

In summary, in the present invention, the amount of the binder is increased to enable the role of the lubricant when removing the molded body in addition to the binder, so that the upper core mold (34 in FIG. 3F) is formed into the molded body (44 in FIG. 3F). ) To prevent getting stuck or broken.

By the way, since the binder burns away in the sintering step to form pores, the amount of the binder increases, the pores also increase, which causes the structure of the sintered compact not to be dense. However, in the present invention, when the molded body 44 is formed, the powder is inserted into the cylindrical mold 32, and then the powder is compressed / molded in two steps. That is, the upper core mold 34 and the lower core mold 36 are moved downward and upward to preliminarily compress and then the lower core mold 36 is returned to the position before the preliminary compression. Then, the powder is compressed using only the upper core mold 34. Therefore, by increasing the molding density of the tip 38 of the upper core mold to reduce the internal pores, the fracture resistance and the wear resistance of the tip portion of the capillary using such a sintered body can be increased.

In addition, during the sintering, a three-step heat treatment was performed in which the particles were degreased, followed by preliminary growth of the particles, and finally grown. As a result, the grain growth of the molded body is uniform, resulting in a denser structure of the sintered body and a reduction of pores. The figure which shows the photograph which image | photographed the surface of the alumina zirconia sintered compact after sintering with the scanning electron microscope is shown in FIG. Looking at Figure 7, it can be seen that all the particles have a dense structure and grown uniformly in size.

If the secondary sintering is further performed in the high-temperature compression furnace after the primary sintering, the porosity of the sintered body can be further reduced.

Claims (12)

70 to 95 wt% of α-alumina powder and 5 to 30 wt% of zirconia-yttria powder, including 5 to 20 Wt% of liquid polyethylene glycol with respect to the mixed powder of α-alumina powder and zirconia-yttria powder A capillary sintered body, which is formed through a sintering process including two stages of compression / molding and three stages of heat treatment, has a fracture toughness of 5.2 to 5.4 MPam ^0.5 and a Vickers hardness of 1970 to 2010 Mpa. The capillary sintered body according to claim 1, wherein the alumina powder has a particle size of 0.2 to 0.8 μm. 2. The capillary sintered body according to claim 1, wherein the zirconia-yttria powder has a particle size of 0.2 to 0.8 mu m. The capillary sintered compact according to claim 1, wherein the liquid polyethylene glycol has a molecular weight of 400 to 600. To 70 to 95 wt% of α-alumina powder and 5 to 30 wt% of zirconia-yttria powder, 5 to 20 wt% of liquid polyethylene glycol, alumina ball and dispersant were added to the mixed powder of α-alumina powder and zirconia-yttria powder. Mixing and grinding them to form an alumina-zirconia complex, Removing the alumina balls from the composite and drying the composite, Pulverizing the dried composite to spheroid, Cylindrical capillary forming mold having a through hole of a predetermined diameter therein, a cylindrical lower core mold having a diameter equal to the diameter of the through hole, and an upper core mold having the same size and shape as the lower core mold and having a conical tip. Using to form the capillary molded body by inserting the spherical composite into the through hole and compressing in two steps; And inserting the capillary molded body into a sintering furnace and heating to sinter the capillary molded body. The method for producing a capillary sintered body according to claim 5, wherein the liquid polyethylene glycol has a molecular weight of 400 to 600. The method of manufacturing a capillary sintered body according to claim 5, wherein in the sintering step, the molded body is heat-treated in three steps in consideration of grain growth of the capillary sintered body. The method of claim 7, wherein the three-step heat treatment is a first step of raising the temperature of the sintering furnace including the capillary molded body to 300-500 degrees at 1 ° C / min and maintaining 500 ° C for about 30-50 hours. Heating the sintering furnace to 1000-1200 degrees at 5 ° C./minute and maintaining the temperature for about 1 hour; and heating the sintering furnace to about 1550-1650 degrees at 10 ° C./minute and maintaining the temperature for about 10 minutes. The manufacturing method of a capillary sintered compact. [6] The capillary sintered body according to claim 5, further comprising a second sintering step in which the sintered body is placed in a high-temperature compression furnace after the sintering step and maintained at 1000-1500 ° C. and 500-1500 bar for a predetermined time. Manufacturing method. The method of claim 5, wherein the forming of the capillary molded body, Preparing the cylindrical mold, the lower core mold and the upper core mold, Blocking the lower end of the through hole of the cylindrical mold with the lower core mold; Inserting the spherical composite into the through hole closed at one end; Allowing the tip of the upper core mold to flow into the inserted composite, and then moving the lower core mold upward to first compress the spheroidized composite, Returning the lower core mold to a position prior to first compression and Moving the upper core mold downward to compress the first compressed composite to form a molded body, wherein the capillary sintered body is manufactured. The tip of the upper core mold of claim 10, wherein after the forming of the molded body, the upper core mold is fixed while continuously moving the upper core mold downward and discharging the molded body out of the cylindrical mold. Method for producing a capillary sintered body further comprising the step of separating. The method of claim 10, wherein in the first compression step, the lower core mold moves about 5 mm.