HK1069482A - Ultra fine pitch capillary - Google Patents

Description

Ultra-fine pitch capillary

Technical Field

The present invention relates generally to a tool for bonding a wire to a semiconductor device, and more particularly to a bonding tool (bonding tool) for bonding a fine wire to a bonding region set at a very small pitch.

Background

Modern electronic devices rely to a large extent on printed circuit boards that require semiconductor chips or Integrated Circuits (ICs) to be mounted thereon. The mechanical and electrical connections between the chip and the substrate present challenges to the chip designer. Three known techniques for interconnecting an IC to a substrate are: wire bonding (or wire bonding), Tape Automated Bonding (TAB), and flip chip.

The most common of these methods is wire bonding. In the wire bonding method, a plurality of lands are provided in a pattern on the top surface of a substrate, and a chip is mounted in the center of the land pattern with the top surface of the chip facing away from the top surface of the substrate. A filament, which may be aluminum or gold, is connected between contacts on the top surface of the chip and contacts on the top surface of the substrate. In particular, the bonding wires are fed through a capillary (i.e., a bonding tool or bonding tool as described below) and bonded to the die and substrate.

Capillary tubes (bonding tools) are used for ball bonding wires to electronic devices, particularly to bond pads of semiconductor devices. These capillaries are typically formed of ceramic materials such as primarily alumina, tungsten carbide, ruby, Zirconia Toughened Alumina (ZTA), Alumina Toughened Zirconia (ATZ). A very thin wire, such as a gold, copper or aluminum wire, typically on the order of about 1 mil, is threaded through an axial passage in the capillary and forms a small ball at the end of the wire, which ball is located outside the capillary tip. The ball is initially bonded to a bonding pad on the semiconductor device, and then a portion thereof is further bonded along the wire to a lead frame or the like. During periodic bonding operations, these capillaries perform multiple functions.

After the ball is formed, the capillary must first partially center the ball within the capillary so that the bond pads are aligned. The ball is bonded to a bonding pad on the semiconductor device by a first bonding step. When the capillary tube brings the ball down into contact with the bonding area, the ball will be squeezed and flattened. Since the lands are typically made of aluminum, a thin layer of oxide is formed on the surface of the lands. In order to form a proper weld, it is preferable to break the oxide surface to expose the aluminum surface. One effective way to destroy the oxide is to "scratch" the oxide surface with wire balls. The wire ball is placed on the surface of alumina and the capillary rapidly moves in a linear direction according to the expansion and contraction of a piezoelectric element disposed within an ultrasonic electrode arm connected to the capillary. This rapid motion creates an effective weld by transferring molecules between the wire and the weld zone in addition to the heat applied by the weld zone.

The capillary then manipulates the wire during the circular looping motion, thereby smoothly transporting the wire out of the capillary and back into the capillary. The capillary then forms a "stitch" weld (stitch) and a "tack" or "pin tail" weld.

Currently, thermosonic wire bonding is an alternative process for interconnecting semiconductor devices to their supporting substrates. The thermosonic bonding process relies in part on the transfer of ultrasonic heat from a transducer attached to a movable bonding head to the semiconductor device or supporting substrate by a tool such as a capillary or wedge.

In conventional capillaries (bonding tools), the geometry of the bonding tool and the Free Air Ball (FAB) formed thereby is such that the bonding tool can only be used to bond wires with spacing (pitch) greater than 60 microns (0.060 mm; 15.34X 10)^-4Inches). Thus making them unsuitable for soldering wires on devices produced to meet the higher density requirements of the semiconductor industry. These prior art bonding tools are not suitable for use with down to 0.4 mil (10 microns) diameter bondsThe wire is wire bonded. The inventors of the present invention have developed a bonding tool that can meet the requirements imposed by these high density devices while maintaining the structural integrity of the bonding tool.

Fig. 1A shows a known prior art fine pitch bonding tool. Bonding tool 100 has a cylindrical portion 101 and a tapered portion 102 connected between cylindrical portion 101 and working tip 104. Working tip 104 (at one end of bonding tool 100) has a tip angle of 15 degrees relative to the longitudinal axis of bonding tool 100. In other words, working tip 104 has an overall angle 106 of 30 degrees. The working tip 104 has a reduced width relative to the cylindrical portion 101 to allow ball pressing on a weld zone having a spacing of about 0.0032 inches without the need to contact adjacent wire loops as described in US5,558,270.

Fig. 1B shows an enlarged cross-sectional view of working tip 104. As shown in FIG. 1B, the working face 111 has a face angle 108 of 4 degrees and the tapered portion 104 has an overall angle 118 of 10 degrees. Also adjacent to the working surface 111 is a first internal bevel 110, which in turn is adjacent to a second internal bevel 112. The first interior chamfer 110 has a chamfer angle 114 of 90 degrees and is connected or continuous with a second interior chamfer 112, the second interior chamfer 112 having an included angle greater than 60 degrees. These bevels are designed to guide a filament (not shown) into a filament aperture 116 having a diameter 106 to accommodate a filament having a diameter of about 1 mil.

However, these prior art techniques suffer from the drawback that their design does not meet the ultra fine pitch (30 microns or less) bond pad requirements set forth in the art by semiconductor manufacturers. In addition, these bonding tools are formed of materials that are not capable of being stressed and do not meet the spring requirements necessary to provide a bonding tool having a working tip size sufficient to meet the needs of the semiconductor industry.

Summary of The Invention

To address the above-mentioned deficiencies of conventional bonding tools, the present invention is directed to a bonding tool having a working tip with a diameter of less than 39 microns.

The bonding tool includes a working tip at one end thereof. This work top includes: i) a tapered portion having a predetermined angle relative to a longitudinal axis of the first cylindrical portion; ii) a working face having a first annular chamfer formed at an outboard portion of an end of the working tip; and iii) a second annular chamfer formed at an inner portion of the end of the working tip, the first and second annular chamfers being adjacent to one another; and a substantially cylindrical axial passage communicating with an upper portion of said second annular ramp.

According to another aspect of the invention, said second annular chamfer has an overall angle of less than 90 °.

According to another aspect of the invention, the first annular chamfer has a face angle greater than 8 °.

According to another aspect of the invention, the bonding tool is formed from a material containing at least 80% zirconium oxide (ZrO) by weight₂) Is formed of the material of (1).

According to yet another aspect of the invention, the bonding tool is formed from a material selected from the group consisting of i) zirconia + yttria (ZrO)₂+Y₂O₃) And ii) alumina + zirconia + yttria (Al)₂O₃+ZrO₂+Y₂O₃) The material of (1).

These and other aspects of the invention are presented in the following description with reference to the figures and exemplary embodiments of the invention.

Brief description of the drawings

The present invention is best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various elements are arbitrarily expanded or reduced for clarity. In these drawings:

FIGS. 1A and 1B are different side views of a conventional bonding tool;

FIGS. 2A-2E are different views of a bonding tool according to an exemplary first embodiment of the present invention; and

fig. 3 is a detailed cross-sectional view of a working tip of a bonding tool according to an exemplary second embodiment of the present invention.

Description of The Preferred Embodiment

The present invention overcomes the deficiencies in conventional capillary bonding tools by providing a bonding tool having a working tip that includes i) a tapered portion having a predetermined angle with respect to the longitudinal axis of a first cylindrical portion; ii) a working face having a first annular chamfer formed at an outboard portion of an end of the working tip; and iii) a second annular chamfer formed at an inner portion of the end of the working tip, the first and second annular chamfers being adjacent to one another; and a substantially cylindrical axial passage communicating with an upper portion of said second annular ramp. The resulting bonding tool is capable of applying as little as 10 micron wire to bond pads having a pitch of 30 microns or less.

Fig. 2A is a side view of a bonding tool 200 according to a first embodiment of the present invention. As shown in fig. 2A, the bonding tool 200 has a cylindrical body portion 201, a tapered portion 202 connected to the cylindrical body portion 201, and a working tip 204 connected to the end of the tapered portion 202. In a preferred embodiment, bonding tool 200 is formed from a single piece of material. The materials used to form the bonding tool will be described in detail below.

Fig. 2B is a side cross-sectional view of bonding tool 200. As shown in fig. 2B, the diameter 227 of bonding tool 200 is between about 1.5 and 1.6mm, and preferably 1.588 mm. Additionally, bonding tool 200 has a length between approximately 9.5 and 11.1 mm. Beginning at the intersection with the cylindrical portion 201, the tapered portion 202 has a substantially constant taper 218 of between about 18 ° and 22 °. In one exemplary embodiment, the taper is between about 19 ° and 21 °, and preferably 20 °. An axial passage 220 extends from the upper end 222 to the working tip 204 of the bonding tool 200. In an exemplary embodiment, axial passage 220 has a substantially continuous conical shape with a predetermined angle 226 of about 13 ° ± 1 ° over a portion of the length. The taper transitions to approximately 6 ° ± 1 ° as axial passage 220 approaches working tip 204. However, the present invention is not so limited and it is contemplated that axial passage 220 may have a substantially constant diameter or may be tapered for only a portion of the length of bonding tool 200. The latter is desirable to facilitate wire insertion at the upper end 222 of bonding tool 200. Examples of these alternative axial channels are shown in fig. 2D and 2E.

As shown in fig. 2D, axial passage 220 has a substantially constant diameter 230 along the length of bonding tool 200. In fig. 2E, axial passage 220 has a substantially constant diameter 240 along a portion of the length of bonding tool 200 and a taper 242 near upper end 22 of bonding tool 200.

Fig. 2C is a detailed cross-sectional view of working tip 204 of bonding tool 200. As shown in fig. 2C, the working tip 204 has an annular working surface 211 having a face angle 208 between 8-15 degrees. In one exemplary embodiment, the face angle is at least 11 degrees, and preferably between 11-12 degrees, and most preferably 11 degrees, to provide a strong second weld (wedge bond) with the welding tool. Adjacent to the working face 211 is an annular chamfer 213 having an overall angle 214 of less than 90 degrees. In a preferred embodiment, the bevel angle 214 is between 60 and 90 degrees, and most preferably about 60 degrees, to provide a first bond (ball bond) that meets shear and tensile testing requirements. In addition, the width of the annular chamfer 213 is 1-4 microns. A cylindrical passage 224 connects between the upper portion of the ramp 213 and the axial passage 220. In an exemplary embodiment, cylindrical passage 224 has a diameter 206 of about 14 microns to accommodate a bonding wire (not shown), chamfer 213 has an outer diameter 212 of about 18 microns, and working tip 204 has a diameter 216 of about 33 microns. The diameter 206 of the cylindrical passage 224 may be determined based on the diameter of the bond wire plus 4 microns. In addition, as shown in fig. 2C, working tip 204 has a substantially constant taper 219 of between about 0 and 10 degrees and preferably about 7 degrees to avoid contact of adjacent bonding wires by bonding tool 200, and has a length 210 of between about 60 and 90 microns. In a preferred embodiment, the length 210 is approximately 76.2 microns.

Since the taper angles 218 and 219 of the tapered portion 202 and working tip 204, respectively, are different, a transition region 225 may be provided between the tapered portion 202 and working tip 204. In a preferred embodiment, the transition region 225 has a radius of about 3.8 microns. Additionally, to prevent chipping or breaking of the bonding tool 200, a transition region 315 having a radius between about 4 and 6 microns may be provided between the lower portion of the working tip 204 and the working face 211.

Fig. 3 is a detailed cross-sectional view of working tip 304 according to another exemplary embodiment of the present invention. As the cylindrical body portion, since the tapered portion and the axial passage of the bonding tool in this embodiment are substantially the same as those of the first embodiment, the description thereof will not be repeated.

As shown in fig. 3, working tip 304 has a working face 311 having a face angle 308 between 8 and 15 degrees. In an exemplary embodiment, the face angle 308 is between about 10 and 12 degrees, and preferably 11 degrees. Adjacent the working surface 311 is an annular chamfer 313 having an overall angle 314 of less than 90 degrees. In a preferred embodiment, the chamfer angle 314 is between 60 and 90 degrees, and most preferably about 60 degrees. In addition, the width of the annular chamfer 313 is between 1 and 3 microns. A cylindrical passage 324 is connected between an upper portion of the ramp 313 and the axial passage 220. In an exemplary embodiment, cylindrical passage 324 has a diameter 306 of between about 14 and 16 microns and preferably 15 microns to accommodate a bonding wire (not shown), chamfer 313 has an outer diameter 312 of between about 17 and 19 microns and preferably 18 microns, and working tip 304 has an outer diameter 316 of between about 37 and 39 microns and preferably about 38 microns. The diameter 306 of the cylindrical passage 324 may be determined based on the wire diameter plus 2 microns. Additionally, as shown in fig. 3, working tip 304 has a substantially constant taper 319 of between about 0 and 10 degrees and preferably about 7 degrees to avoid contact of adjacent wires by bonding tool 200 and has a length 310 of between about 117 and 137 microns. In a preferred embodiment, length 310 is approximately 127 microns.

Providing bonding tools as described above has been only half successful in meeting the needs of the semiconductor industry. It is important to be able to form the bonding tool from a material that is sufficiently resistant to the forces exerted on the tool during bonding, but still has sufficient elasticity to bend without breaking when necessary. The inventors have determined that by using a composition containing at least 80% by weight of zirconium oxide (ZrO)₂) To form a bonding tool may meet these needs.

In one embodiment of the invention, yttria stabilized zirconia is used to form the bonding tool. In this example, about 95 t% (by weight) of zirconia and about 5% (by weight) of yttria (Y) were mixed₂O₃) And (4) combining. The present inventors have determined that pure zirconium oxide will undergo a phase transformation process during heat treatment. Pure zirconia is monoclinic at room temperature and transforms into a more compact tetragonal morphology at about 1000 ℃. This involves a large volume change and cracks will develop within its structure during sintering at temperatures between about 1350 and 1500 c.

An additional amount of Y₂O₃A mixture of cubic and monoclinic phases is produced at low temperatures (e.g. less than 900 ℃). The phase transformation process will proceed in the presence of cubic phases and involves much less volume change, which in turn will reduce thermal stress and minimize the formation of microcracks. The material has a much greater bending strength than conventional alumina-based materials and thus improves the manufacturability of the bonding tool.

In another exemplary embodiment, will be up to 20%(weight percent) of Al₂O₃Added to yttria stabilized zirconia. The material has acoustic properties similar to those of conventional alumina-based materials.

Although the present invention has been described with reference to exemplary embodiments, the present invention is not limited thereto. Rather, the appended claims should be construed to include other modifications and embodiments that may occur to one of ordinary skill in the art without departing from the true spirit and scope of the invention.

Claims (33)

1. A bonding tool for bonding a filament to a substrate, the bonding tool comprising:

a working tip at one end of the bonding tool, the working tip comprising:

i) a tapered portion having a predetermined angle relative to a longitudinal axis of the bonding tool;

ii) a working face having a first annular chamfer formed at an outboard portion of an end of the working tip; and

iii) a second annular chamfer formed at an inner portion of the end of the working tip, said first and second annular chamfers being adjacent to each other; and

a substantially cylindrical axial passage communicating with an upper portion of said second annular ramp.

2. The bonding tool according to claim 1, wherein the second annular chamfer has an overall angle of less than 90 °.

3. The bonding tool according to claim 2, wherein the first annular chamfer has a face angle greater than 8 °.

4. The bonding tool according to claim 1, wherein the second annular chamfer has an overall angle of less than 60 °.

5. The bonding tool according to claim 4, wherein the first annular chamfer has a face angle between 10 ° and 12 °.

6. The bonding tool according to claim 1, wherein the axial passage has a diameter of less than about 16 microns.

7. The bonding tool according to claim 1, wherein the tapered portion has a length of less than about 137 microns.

8. The bonding tool according to claim 7, wherein the tapered portion has an outer diameter of less than about 39 microns.

9. The bonding tool according to claim 1, wherein the bonding tool is composed of at least 80% ZrO in weight percent₂Is formed of the material of (1).

10. The method of claim 1Is characterized in that the welding tool is made of a material selected from i) ZrO₂+Y₂O₃And ii) Al₂O₃+ZrO₂+Y₂O₃The material of (1).

11. The bonding tool according to claim 1, wherein the bonding tool is composed of, in weight percent, approximately 95% ZrO₂And about 5% Y₂O₃Is formed of the material of (1).

12. The bonding tool according to claim 11, wherein the material has up to about 20% Al by weight₂O₃。

13. The bonding tool according to any of claims 9-12, wherein the material is sintered at a temperature of at least 1350 ℃.

14. The bonding tool according to claim 1, wherein the bonding tool is formed from a unitary piece of material.

15. The bonding tool according to claim 1, wherein the total angle of the tapered portions is less than 10 °.

16. The bonding tool according to claim 1, wherein the total angle of the tapered portions is about 7 °.

17. A bonding tool for bonding a filament to a substrate, the bonding tool comprising:

a cylindrical portion having a diameter;

a first tapered portion connected to one end of the cylindrical portion and having a first predetermined angle with respect to a longitudinal axis of the cylindrical portion;

a second conical portion having: i) a second predetermined angle relative to the longitudinal axis of the first cylindrical portion; ii) a first slope formed at an outer portion of one end portion thereof; and iii) a second slope formed at an inner portion of one end portion thereof, the second taper portion being connected to one end of the first taper portion; and

an axial passage extending from a first end of the cylindrical portion to the second ramp.

18. The bonding tool according to claim 17, further comprising a third tapered portion disposed between the first tapered portion and the second tapered portion.

19. The bonding tool according to claim 17, wherein the second bevel has an angle of less than 90 °.

20. The bonding tool according to claim 17, wherein the second bevel has an angle of about 60 °.

21. The bonding tool according to claim 17, wherein the first bevel has a face angle between about 10 ° and 12 °.

22. The bonding tool according to claim 17, wherein the axial passage has a first diameter at a first end of the first cylindrical portion and a second diameter at a tip of the second conical portion, the first diameter being greater than the second diameter.

23. The bonding tool according to claim 17, wherein the bonding tool is composed of, in weight percent, at least 80% ZrO₂Is formed of the material of (1).

24. As in claimThe bonding tool of claim 17, wherein the bonding tool is composed of a material selected from the group consisting of i) ZrO₂+Y₂O₃And ii) Al₂O₃+ZrO₂+Y₂O₃The material of (1).

25. The bonding tool according to claim 17, wherein the first predetermined angle of the first tapered portion is between about 19 ° and 21 °.

26. The bonding tool according to claim 17, wherein the first predetermined angle is about 20 °.

27. The bonding tool according to claim 17, wherein the second predetermined angle of the second tapered portion is about 7 °.

28. The bonding tool according to claim 17, wherein the second predetermined angle of the second tapered portion is less than 10 °.

29. A bonding tool for bonding a filament to a substrate, the bonding tool comprising:

a cylindrical portion having a diameter;

a first tapered portion connected to one end of said cylindrical portion and having a first predetermined included angle with respect to the longitudinal axis of said cylindrical portion;

a second tapered portion connected to one end of the first tapered portion, the second tapered portion having:

i) a length between about 117 microns and 137 microns;

ii) at an angle of about 7 ° relative to the longitudinal axis of the cylindrical portion; and

iii) an annular chamfer of about 60 ° formed at the inner portion of the second conical portion and near the end thereof.

30. The bonding tool according to claim 29, wherein the bonding tool is made of a material selected from the group consisting of i) ZrO₂+Y₂O₃And ii) Al₂O₃+ZrO₂+Y₂O₃The material of (1).

31. The bonding tool according to claim 29, wherein the bonding tool is composed of, in weight percent, at least 80% ZrO₂Is formed of the material of (1).

32. A bonding tool for bonding a filament to a substrate, the bonding tool being formed from a material selected from the group consisting of i) ZrO₂+Y₂O₃And ii) Al₂O₃+ZrO₂+Y₂O₃The material of (1).

33. A method of manufacturing a bonding tool for bonding a wire to a bonding area, the method comprising the steps of:

forming a working tip at an end of the bonding tool;

forming a tapered portion on the working tip at a predetermined angle relative to a longitudinal axis of the bonding tool;

forming a working surface at one end of the working tip;

forming a first annular inclined surface having a face angle of at least 8 ° at an outer side portion of one end portion of the working tip;

forming a second annular chamfer having an overall angle of less than 90 ° at an inner portion of the end of the working tip and adjacent to said first annular chamfer; and

a substantially cylindrical axial passage is formed at the upper end of the second annular chamfer.