PH12015000222A1

PH12015000222A1 - Bonding capillary

Info

Publication number: PH12015000222A1
Application number: PH12015000222A
Authority: PH
Inventors: Jumpei Onishi; Soichiro Oka
Original assignee: Toto Ltd
Priority date: 2014-06-30
Filing date: 2015-06-29
Publication date: 2017-01-09
Also published as: TWI609437B; JP2016029745A; KR101941486B1; JP2016027602A; TW201601229A; JP6126144B2; KR20160002343A

Abstract

[OBJECT] It is an object to increase bond strength while suppressing occurrence of cracking in a bonding wire. [SOLUTION] A bonding capillary according to an embodiment includes a pressing surface that presses a bonding wire, an insertion hole into which the bonding wire is inserted, a tapered hole that connects the insertion hole to the pressing surface and that expands toward the pressing surface, and a chamfer that is disposed between the tapered hole and the pressing surface. The chamfer has asperities on a surface thereof, and a sharpness of peaks of the asperities is smaller than a sharpness of valleys of the asperities.

Description

DESCRIPTION | = © BONDING CAPILLARY on [Technical Field] ~

The disclosed embodiment relates to a bonding = capillary. Lr [Background Art]

Wire bonding is one of presently known methods for i electrically connecting a semiconductor chip to a lead = frame.Wire bonding is a method of electrically connecting a In semiconductor chip to a lead frame by bonding a metal wire, - ~ which is called a bonding wire, to an electrode of the : semiconductor chip and to the lead frame. ;

In wire bonding, a tubular tool, which is called a bonding capillary, is used.To be specific, a bonding wire is inserted into thebonding capillary so as to protrude from a tip of the bonding capillary, and the protrudingbonding wire is pressed against an electrode by using a tip surface of the bonding capillary.Moreover, thebonding wire is rubbed against the electrode by vibrating the tip surfaceby applying an ultrasonic wave to the bonding capillary. Thus, the bonding : wire is bonded to the electrode.

To prevent adhesion of a bonding wire to a tip surface, there are some known bonding capillaries in which a rounded portion having a predetermined curvature is formed at the i Sq :

periphery of an insertion hole into which the bonding wire o is inserted (see, for example, PTL 1). w " [Citation List] = [Patent Literature] HH [PTL 1] Japanese Unexamined Patent Application -

Publication No. 9-326411 | . [Summary of Invention] - [Technical Problem] o

However, there is a problem in that, when wire bonding oo is performed by using the bonding capillaryincluding the rounded portion, it is difficult to obtain sufficient bond strength.This is because, by forming the rounded portion, a grip force for gripping the bonding wire is reduced, and : therefore it becomes difficult to rub the bonding wire against the electrode. ‘ :

The problem of bond strength becomes significant in a case where wire bonding is performed by using an aluminum : (Al) bonding wire.This is because aluminum is oxidized more easily than gold (Au), which is generally used as the : material of a bonding wire, and an oxidized film formed on a surface of the bonding wire is likely to hinder bonding of the bonding wire to theelectrode.

Aluminum bonding wires also have a problem in that cracking is more likely to occur in aluminum bonding wires : - 2 - E than in gold bonding wires.Accordingly, it is desirable to o increase bond strength and to suppress occurrence of o crackingin the case of performing wire bonding by using an Cl aluminum bonding wire. =

Co

An object of an aspect of an embodiment is to provide © a bonding capillary that can increase bond strength while osuppressing occurrence of cracking. - [Solution to Problem] © °

According to an aspect of an embodiment, a bondingcapillary includesa pressing surface that presses a bonding wire,an insertion hole into which the bonding wire is inserted, a tapered hole that connects the insertion hole to the pressing surface and that expands toward the pressing surface, anda chamfer that is disposed between the tapered hole and the pressing surface.The chamfer has asperities ona surface thereof, and a sharpness of peaks of the asperities is smaller than a sharpness of valleys of the asperities.

By providing the chamfer between the tapered hole and the pressing surface, a stress applied to thebonding wire can be reduced, and therefore occurrence of crackingin the bonding wire can be suppressed.Moreover, by providingthe asperities on thesurface of the chamfer, a grip force with which the bonding capillary grips the bonding wire when rubbing the bonding wire against an electrode can be i

Cs increased, and therefore bond strength can be increased.On > the other hand, by simply providing the asperities, edges o of theasperities might damage thewire, and the damage might i, cause cracking of the wire more likely to occur.To prevent = :

LA i this, the sharpness of the peaks of the asperities is made ~ + smaller than the sharpness of the valleys of the © asperities.Thus, occurrence of crackingdue to the ol asperities can be suppressed. =

The asperities of the chamfer may have a skewness of - = 0.164or smaller and an average height of 0.035um or larger and 0.092um or smaller. :

Thus, when performing wire bonding by using an aluminum bonding wire, occurrence of cracking in the bonding wire after the first bonding step can be appropriately suppressed.Moreover, sufficient bond strength can be obtained at a tail after the second bonding step.

The pressing surface may have asperities, and a ; sharpness ofpeaks of the asperities of the pressing surface may be larger than the sharpness of the peaks of the asperities of the chamfer.

As compared with the chamfer, the pressing surface is : less likely to cause cracking in the bonding wire. Therefore, thepressing surface may have the above structure in prioritizing an increase of a grip ‘force over preve cracking.With the above structure, a grip force for - gripping the bonding wire can be further increased. =o

The asperities of the pressing surface may have an - average height of 0.113um or larger. ~

Thus, when performing wire bonding by using an on aluminum bonding wire, sufficient bond strength can be ~ obtained at a stitch after the second bonding step. = | =

The chamfer may have a curved surface that is smoothly continuous with the tapered hole and the pressing surface, and a radius of curvature of the curved surface may be 4.55um or larger and 20.30um or smaller.

Thus, when performing wire bonding by using an aluminum bonding wire, occurrence of cracking in thebonding wire can be appropriately suppressed.Moreover, occurrence of inappropriate cutting of the bonding wire after the second bonding step can be appropriately suppressed.

The chamfer may have a curved surface that is smoothlycontinuous with the tapered hole and the pressing surface, and a radius of curvature of the curved surface may be 12.8um or larger and 20.30um or smaller.

Thus, when performing wire bonding by using an aluminum bonding wire, even if the loop length of the - 5 - L bonding wire is 3mm or larger, occurrence of cracking in = the bonding wire can be appropriately suppressed.Moreover, x occurrence of inappropriatecutting of the bonding wire - after the second bonding step can be appropriately = suppressed. - oo

A taper angle ofthe tapered hole may be 100° r smaller. o

Thus, occurrence of cracking in the bonding wire at a o boundary edge between the insertion hole and the tapered i hole can be appropriately suppressed. :

An outside diameter of the pressing surface may be 4.0 times a wire diameter of the bonding wireor larger and 5.7 times the wire diameteror smaller.

Thus, desired bond strength can be obtained. [Advantageous Effects of Invention]

According to an aspect of an embodiment, bond strength can be increased while suppressing occurrence of cracking in a bonding wire. [Brief Description of Drawings]

Fig. 1 is a schematic side view of a bonding capillary according to an embodiment.

Fig. 2 is a schematic enlarged view of a region H1 shown in Fig. 1.

C6

Fig. 3 is a schematic side sectional view of - an end portion of a bottleneck. ;

Fig. 4 is a schematic enlarged view of a O © region H2shown in Fig. 3. =

Fig. 5 is a schematic side sectional view - illustrating the surface profile of a pressing surface. -

Fig. 6 is a schematic side sectional view illustrating the surface profile of a chamfer. i}

Fig. 7 is a schematic side sectional view @ illustrating a first bonding step. =

Fig. 8 is a schematic side sectional view illustrating a second bonding step.

Fig. 9 is a graph representing an example of the roughness curve of the surface of the chamfer. | Fig. 10 is a table showing evaluation results of a case where the skewness and the average height of asperities of the chamfer and the average height of asperities of the pressing surface were respectively changed.

Fig. 11 is table showing theevaluation results of a case where the radius of curvature of the chamfer was changed.

Fig. 12 is a table showing the evaluation resultsof a case wherethe radius of curvature of the chamfer was changed.

Fig. 13 is a table showing the evaluation resultsof a case wherethe angle of the tapered hole was changed.

Fig. 14 is a schematic perspective view - : : illustrating an example ofthe result of a simulation of . bonding. .Fig. 15 shows schematic plan views of ~ examples ofthe result of a simulation of bonding."

Fig. 16 is a table showing the evaluation = resultsof a case wherethe ratio of the outside diameter of the pressing surface to the wire diameter was changed. ~

Fig: 17 is a flowchart representing an © example of a part ofa method of making a bonding capillary. o [Description of Embodiments]

Hereinafter, referring to the attached drawings, a bonding capillary according to an embodiment of the present disclosure will be described in detail. The present invention is not limited by theembodiment described below. (Embodiment)

First, referring to Figs. 1 and 2, -theoverall : structure of thebonding capillary according to the present embodiment will be described.Fig. 1 is a schematic side view of the bonding capillary according to the present : embodiment. .Fig. 2 is a schematic enlarged view of a region

Hl shown in Fig. 1.

As illustrated in Fig. 1, a bonding capillary 1 according to the present embodiment (hereinafter, referred . to as "capillary 1") has an insertion hole 11, into which a - 8 - 4

~ bonding wire (hereinafter, referred to as "wire") is > inserted.The capillary 1 is made of, for example, a o ceramicmaterial.The material of the capillary 1 is, for sO example, alumina.Alternatively, the material of the = capillary 1 may be a compositematerial including alumina - and at least one of zirconia and chromia or the like. =o a

The capillary 1 includes a shank 12, a cone 13, and a - bottleneck 14.The cone 13 is disposed at an end of theshank o 12 and has a diameter that decreases toward an end thereof .The bottleneck 14 is disposed at the end of thecone 13 and has a smaller diameter than the cone 13.The : insertion hole 11 extends through the shank 12, thecone 13, and the bottleneck 14.

As illustrated in Fig. 2, a tapered hole 20 is formed between a pressing surface 30, which is an end surface of the bottleneck 14, and the insertion hole 11.The tapered : hole 20 is formed so that thediameter thereof increases from the insertion hole 11 toward the pressing surface 30.

The capillary lstructured as described above bonds a wire, which protrudes from thetapered hole 20 to the outside, to an electrode by pressing the wire against the ; electrode using the pressing surface 30 and by rubbingthe wire againstthe electrode whilevibrating the pressing surface 30 using an ultrasonic wave. :

Gold (Au) is generally used as the material of the = wire. In contrast, aluminum (Al) is generally used as the material of a pad electrode, which is an electrode of a ~ : semiconductor chip.When gold and aluminum, which are metals - of different types, are bonded to each other, the bond - strength may be reduced due to generation of a void at a - bonded interface.Moreover, there is a problem in thatthe » cost of making semiconductor devices is increased due to - use of gold, which is a precious metal. o

Therefore, in recent years, it has been proposed to : use aluminum, which is the material of pad electrodes of semiconductor chipsand less precious than gold, as the material of thewire.

However, the strength of aluminumis lower than that of gold.Therefore, there is a problem in thatcracking is likely to occur at a bent portion of a. wire after a first bonding step (described below) . Moreover, aluminum is oxidized more easily than gold, and an oxidized film formed on thesurface of the wire tends to hinder bonding between : the wire and theelectrode.Therefore, there is a problem in that it is not easy to obtain sufficient bond strength.

For this reason, in the capillary 1 according to the : present embodiment, occurrence of cracking in a bent : portion of the wire is suppressed by forming a chamfer at theboundary between the pressing surface 30 and the tapered hole 20.Moreover, in the capillary 1 according to the 0 present embodiment,a grip force with which the capillary 1 » grips a wire when rubbing the wire against the electrode by ~ vibrating the pressing surface 30 is increased by forming - fine asperities on the chamfer, and thereby the bond . strength is increased. =

On the other hand, by simplyformingtheasperities, the ” wire may become damaged due to edges of peaks of the o asperities, and cracking of the wire may become more likely = to occur due to the damage to the wire.Therefore, in the © capillary 1 according to the present embodiment, the sharpness of the peaks of the asperities is made smaller than the sharpness of the valleys of the asperities. Thus, occurrence of crackingdue to theasperities can be suppressed.The term "sharpness" refers to thedegree of sharpness of peaks and valleys.Accordingly, the phrase "the : sharpness of the peaks is made smaller than the sharpness of the valleys" means that the peaks are made less sharp than the valleys.

Hereinafter, referring to Figs. 3 and 4, the structure of the chamfer, which is formed at the boundary between the pressing surface 30 and the tapered hole 20, and the structure of the asperities formed on the chamfer will be described in detail.Fig. 3 is a schematic side sectional view of an end portion of the bottleneck 14. Fig. 4 is a : schematic enlarged view of a region H2shown in Fig. 3. - 11 - 5

As illustrated in Fig. 3, thepressing surface 30 has a 0 convexly curved surfacethat slightly bulges from a - peripheral portion toward a central portion.The tapered = hole 20 is formed in the central portion of the pressing - surface 30.Accordingly, in the capillary 1, the boundary “ between thetapered hole 20 and thepressing surface 30 is a 7 part that protrudes furthest in the distal direction, and ~ cracking of the wire is ‘likely to occur at this part. © oo

A chamfer 40 is formed at the boundary between the tapered hole 20 and the pressing surface 30.As illustrated in Fig. a, the chamfer 40 has a curved surface that is smoothly continuous with the tapered hole 20 and the pressing surface 30.

Fig. 5 is a schematic side sectional view illustrating the surface profile of the pressing surface 30.Fig. 6 is a schematic side sectional view illustrating the surface profile of the chamfer 40.As illustrated in Figs. 5 and 6, fine asperities are formed on the surfaces of thepressing surface 30 and the chamfer 40.The asperities are formed so that thesharpness of peaks 31 and the sharpness of peaks 41 ; are respectively smaller than the sharpness of valleys 32 and the sharpness of valleys 42.

The asperities of thepressing surface 30illustrated in :

Fig. 5 are formed so that the sharpness of the peaks 31 is

+ larger than the sharpness of the peaks 41 of theasperities > of the chamfer 40illustrated in Fig. 6.Thus, in the = capillary 1 according to the present embodiment, a gripping Cl force with which the pressing surface 30 grips a wire is = made larger than a grip force with which the chamfer - 40grips the wire. oo] a]

Next, referring to Figs. 7 and 8, the function of the - structure described above and a wire bonding operation will = be described.Fig. 7 is a schematic side sectional view = illustrating a first bonding step.Fig. 8 is a schematic side sectional view illustrating a second bonding step. : - Wire bonding includes a first bonding step, a loop forming step, and a second bonding step.The first bonding step is a step of bonding a wire to one of electrodes.The loop forming step is a step of forming a loop of the wirebetween theelectrodes by moving the capillary 1 along a : predetermined path after the first bonding step.The second bonding step is a step of bonding the wire to the other electrode after the loop forming step. Through these steps, the electrodes are connected to each other through the wire, - and semiconductor chip and thelead frame are electrically connected to each other.

Fig. 7illustrates a first bonding stepthat is performed in a case where wire bonding is performed by using a wire made of aluminum (hereinafter, referred to as

"aluminum wire") instead of an existing wiremade of gold - (hereinafter, referred to as "gold wire") . ws

In wire bondingusing an existing gold wire, ball - bonding is performed as the first bonding step.Ball bonding - is a method of bonding a wire to an electrode by forming a 0 gold ball by melting an end of the wire by - causingelectrical discharge and by thermally press-bonding ~ the ball to thewire.A bonding capillary is used in ball bonding. -

On the other hand, when performing wire bonding by using an aluminum wire, it is difficult to perform ball bonding as described above.This is because it is difficult to form a ball as in the case of using gold, because aluminum is oxidized more easily than gold. Therefore, when performing wire bonding by using an aluminum wire, a wedge bonding tool, which bonds a wire to an electrode without forming a ball, is generally used (see, for example,

Japanese Unexamined Patent Application Publication No. 2001-156100) . :

However, wedge bonding tools, which have a structure that is more complex than that of ponding capillaries, are more expensive and less durable than bonding : capillaries.Therefore, in the present embodiment, wire : bonding using an aluminum wire is performed by using the capillary 1, which is a bonding capillary that is less 14 - J expensive and more durable thanwedge bonding tools.Thus, > : the productivity of semiconductor devices can be increased. oo | | .

As illustrated in Fig. 7, first, the capillary 1 = presses an aluminum wire W against one of electrodes, such : as a lead electrode 100 of a lead frame, by using the = pressing surface 30.At this time, a predetermined gap is .

Cn formed between the chamfer 40 and the lead electrode 100 so 3 thataluminum wire W may not be cut between the chamfer 40 @ and the lead electrode 100. -

Next, an ultrasonic wave is applied to the shank 12 of the capillary 1 (see Fig. 1).Thus, the pressing surface 30 is vibrated, and the aluminum wire W is rubbed against the lead electrode 100.Thus, thealuminum wire W is bonded to the lead electrode 100.

Next, a loop of the wire is formed by moving ; thecapillary 1 along a predetermined path.At this time, a bent portion is formed at the boundary, such as a region B shown in Fig. 7, between a part of thealuminum wire W that is bonded to the lead electrode 100 and a part of the aluminum wire W that is not bonded to the lead electrode 100.Cracking is likely to occur in thebent portion. ]

As a measure against this, the capillary 1 according to the present embodiment has the chamfer 40 at the boundary between the tapered hole 20 and thepressing - 15 - i surface 30.Thus, as compared with a case where the chamfer . 40 is not provided, stress concentration on the region B is reduced, and therefore occurrence of cracking in the bent - portion of the aluminum wire W can be suppressed. -

As described above, there is also a problem in that it - is more difficult to obtain sufficient bond strength by o using an aluminum wire W than by using a gold wire, because ~ an oxidized film formed on thesurface of the bonding wire © tends to hinder connection between the bonding wire and 0 theelectrode.

As a measure against this, in the capillary 1 according to the present embodiment, fine asperities are formed on the surface of the chamfer 40.Thus, a grip force with which the chamfer 40 grips the aluminum wire W is increased. Therefore, sufficient bond strength can be obtained even when using the aluminum wire W, with which it is difficult to obtain high bond strength as compared with a gold wire.

Moreover, the asperities of the chamfer 40 are formed so that the sharpness of the peaks 41 is smaller than the sharpness of the valleys 42.Therefore, withthe capillary 1 according to the present embodiment, high bond strength can be obtained while suppressingoccurrence of cracking due to the asperities.

In the capillary 1 according to the present embodiment, = fine asperities are formed also on the. pressing surface - 30.As compared with the chamfer 40, the pressing surface 30 is less likely to cause cracking in thealuminum wire -

W.Therefore, in view of prioritizing increase of grip force - over prevention of cracking, the asperities of the pressing © surface 30 are formed so that the sharpness of the peaks 31 o is larger than the sharpness of the peaks 41 of the _ asperities of the chamfer 40 (see Figs. 5 and 6).Thus, a = grip force for gripping thealuminum wire W can be further oO increased.

Next, the capillary 1 performs thesecond bonding step.First, as illustrated in Fig. 8, the capillary 1 presses the aluminum wire W against the other electrode, such as a pad electrode 200 of the semiconductor chip, by using the pressing surface 30.In the second bonding step, it is necessary to cut the aluminum wire W after the aluminum wire W has been bonded to the pad electrode 200.Therefore, the gap between the chamfer 40andthepad electrode 200 are set to be smaller than that of the first bonding step. :

Next, thecapillary 1 rubs thealuminum wire Ww against the pad electrode 200 by vibrating the pressing surface 30 using an ultrasonic wave.Thus, thealuminum wire W is bonded to the pad electrode 200. a

Next, the capillary 1 moves upward over a - predetermined distance.At this time, ‘as illustrated in Fig. ow 8, the aluminum wire W has been bonded to the pad electrode =o 200 not only in a stitch S, which is located outside of = thechamfer 40, but also in a tail T, which is located : inside of the chamfer 40.Therefore, when the capillary 1 o moves upward, the aluminum wire W is pulled out from o thecapillary 1 in accordance with the upward movement. A ~ part of the aluminum wire W that is pulled out is to be © bonded to the lead electrode 100 in the next first bonding o step. : Subsequently, for example, as the capillary lmoves leftward and rightward, the aluminum wire W is cut between the stitch S and thetail T.

As described above, in thesecond bonding step, it is ~ necessary that the aluminum wire W be temporarily bonded to the pad electrode 200 in the tail T so that the aluminum wire W can be pulled out from thecapillary 1.However, as described above, it is difficult to obtain sufficient bond strength in the tail T, because an oxide film can be easily formed on the aluminum wire W.

However, with the capillary 1 according to the present embodiment, sufficient bond strength can be obtained also in the tail T, because a grip force with which the chamfer 40 grips the aluminum wire W is increased by forming fine asperities on the chamfer 40. : - :

As heretofore described, the capillary 1 according to C the present embodiment includes the pressing surface 30, = the insertion hole 11, the tapered hole 20, and thechamfer o 40.The pressing surface 30 is a surface that presses 5 thebonding wire. The insertion hole 11 is a hole into which I the bonding wire is inserted.The tapered hole 20 is a hole ~ that connects the insertion hole 11 to the pressing surface @ 30and thathas a shape thet expends toward the pressing oO surface 30.The chamfer 40 is disposed between thetapered hole 20 and thepressing surface 30.The chamfer 40 has asperities on the surface thereof, and. the sharpness of the peaks 41 of the asperities is smaller than the sharpness ofthevalleys 42 of theasperities.

Accordingly, the capillary 1 according to the present embodiment can increase bond strength while suppressing occurrence of cracking of a bonding wire. (Examples)

Next, referencing to Figs. 9 to 11, examples of the capillary 1 according to the present embodiment will be described.Fig. 9 is a graph representing an example of the roughness curve of the surface of the chamfer.Fig. 10 is a table showing the evaluation results of a case where the : skewness of theasperities of the chamfer 40 and the average height of theasperities of the pressing surface 30 were respectively changed.Fig. 11 is table showing theevaluation > results of a case where the radius of curvature of the o chamfer 40 was changed. »

The asperities on the pressing surface 30 and the B chamfer 40can be represented by, for example, the mean © " height Rc and the skewness Rsk.The mean height Rc and the o skewness Rsk are calculated on the basis of JIS B 0601-2001. = 5

The skewness Rsk is a measure of symmetry betweenpeaks 7 and valleys of asperities.If theasperities are symmetrical, the skewness Rsk is 0.If the skewness Rsk is negative, the : sharpness of the peaks of the asperities is smaller than the sharpness of the valleys, that is, the area of tip portions of the peaks is larger than the area of bottom portions of the valleys when theasperities are viewed in plan.

In the present embodiment, theroughness curves of the pressing surface 30 and thechamfer 40 were measured by using a laser microscope (OLS4000 made by Olympus :

Corporation) .The measurement conditions were as follows.

Measurement Magnification:50 times : Evaluation Length (roughness measurement) :500um to 800um

Cutoff (phase-compensation high-pass filter) Ac:25um

The mean height Rc of the roughness curve measured under the above conditions was calculated by using equation > (1) below, and the skewness Rsk of the roughness curve was - calculated by using equation (2) below. O : po [Equation 1] ~ om :

Re=—>7ti 7

Mi=1 =]

[0072] | iy [Equation 2] 1 18,

Rsk = — —Y Zn “+e (2) 73 | N = n=1

In equation (1), m is the number of the profile elements, and Z2ti is the average height of the profile elements.In equation (2), Zg is the root-mean-square height, and Zn is the value of the height in the roughness curve.

Fig. 9 illustrates an example of a roughness curve that was obtained by measuring the surface of the chamfer 40 by using a laser microscope.In Fig. 9, the vertical axis represents a height (micrometer:um), and the horizontal axis represents a measurement position (Um) . In theroughness curve shown in Fig. 9, theskewness Rsk of the asperities of :

the chamfer 40 is -0.164, and the average height Rc of the > asperities of the. chamfer 40 is 0.073. 2 »

Fig. 10 shows the evaluation results of items "crack", =

Cr "tail bond", and "stitch bond" in a case where the skewness ~

Rsk of thechamfer 40, the average height Rc of thechamfer © 40, and the average height Rc of the pressing surface 30 - were respectively changed. | be

The item "crack" represents whether or not cracking occurred in the aluminum wire W after the first bonding step.Regarding the item "crack", a case where cracking did not occur is denoted by "O".The item "tail bond" and the item "stitch bond"respectively represent whether or not sufficient bond strength was obtained after the second bonding step in thetail T and the stitch Sillustrated in

Fig. 8.Regarding the item "tail bond" and the item "stitch ~ bond", a case where sufficient bond strength was obtained is denoted by "0". :

As shown in Fig. 10, in comparative examples 1 and 2, sufficient bond strength was not obtained in the tail T and the stitch S after the second bonding step.In comparative examples. 3 to 6, cracking occurred in the aluminum wire W after the first bonding step.

In contrast, in examples 1 to 5, cracking did not occur in the aluminum wire W after the first bonding step, - 22 - 4 and sufficient bond strength was obtained in the tail T and - : the stitch S after the second bonding step. o

From these results, preferably, the skewness Rsk of - the asperities of the chamfer 40 is -0.1l64or smaller, and - the average height Rc of the asperities is 0.035um or o larger and 0.092um or smaller.Preferably, the average o height Reof the asperities of the pressing surface 30 is ~ 0.113um or larger. = 5

If the skewness Rsk of the asperities of the chamfer 40 is made smaller than -1.4, it is difficult to make the average height Rc of the asperities of thechamfer 40, for example, 0.035um or larger due to limitations on the processing principle.Therefore, preferably, the skewness

Rsk of the asperities of the chamfer 40 is -1.4 or larger.

The average height Rc of the asperities of the pressing surface 30 can be made 4.642um or smaller.If the average height Rc of the asperities of the pressing surface 30 becomes larger than 4.642um, after forming the chamfer 40, asperities having an average height Rc of 0.092um or larger may remain on thechamfer 40.Therefore, preferably, ; the average height Rc of the asperities of the pressing surface 30 is 4.642um or smaller.The average height

Rcd. 6420mof the asperities of the pressing surface 30 is calculated by adding the lower limit value 4.55um of the radius of curvature of the chamfer 40 (see Fig. 11) to theupper limit value of 0.092um of the average height Rc of ol : theasperities of the chamfer 40 (see Fig. 10). - .

The asperities of the pressing surface 30 are formed - by, for example, sandblasting.In the case where the - asperities of the pressing surface 30 are formed by © . sandblasting, the average height Rc of the asperities of ou the pressing surface 30 can be made 0.45um.Ifthe average ~ height Rc of the asperities of the pressing surface 30 is - larger than 0.45um, for example, ceramic particles may z become removed from (may come off) the pressing surface 30. Therefore, preferably, the average height Rc of the asperities of the pressing surface 30 is 0.45um or smaller.

Fig. 11 shows theevaluation results of the items "crack" and "inappropriate wire cut" in a case where the radius of curvature of the chamfer 40 was changed.

The item "crack" is the same as that shown in Fig. 10.The item "inappropriate wire cut" represents whether or not the aluminum wire W was appropriately cut after the second bonding step.Regardingthe item "inappropriate wire cut", a case where inappropriate cutting of the aluminum wire W did not occur is denoted by "O".

As shown in Fig. 11, in comparative examples 7 and 8, cracking occurred in the aluminum wire W after the first bonding step.In comparative example 9, inappropriate - 24 - 1 cutting of the aluminum wire W occurred after the second - bonding step. | -

In contrast, in examples 6 to 10, cracking did not - occur in the aluminum wire W after the first bonding step, . and inappropriate cutting of the aluminum wire W did not = occur after the second bonding step. on

From these result, preferably, the radius of curvature = of the chamfer 40 is 4.55um or larger and 20.3um or smaller. -

Fig. 12 is a table showing the evaluation resultsofthe item "crack!" in a case wherethe radius of curvature of the chamfer 40 was changed.

The evaluation was performed for a case where the loop length between a bonding point of first bonding (such as a point on the lead electrode 100) and a bonding point of second bonding (such as a point on the pad electrode 200) was3mm or larger.The term "loop length" refers to the length of an imaginary line connecting the central lines of both bonding portions.In a package or the like having such a comparatively large loop length, a tension applied to the aluminum wire W in theloop forming step becomes large and cracking becomes more likely to occur.

In Fig. 12, the item "crack"is the same as that shown in each of Figs. 10 and 11.

As shown in Fig. 12, in comparative example 10, ° cracking occurred in the aluminum wire W after the first w bonding step. -

In contrast, in examples 11 to 13, cracking did not ~ occur in the aluminum wire W after the first bonding step. -

From these results, preferably, the radius of = curvature of the chamfer 40 is 12.8um or larger and 20.3um J or smaller. ~ . Thus, even if the loop length between a bonding point @ of first bonding and a bonding point of second bonding ” is3mm or larger, occurrence of cracking in thealuminum wire

W can be appropriately suppressed.Moreover, occurrence of inappropriate cutting of thebonding wire after the second bonding step can be appropriately suppressed.

Fig. 13 is a table showing the evaluation resultsof the item "crack" in a case wherethe taper angle 61 (see Fig. . 3) of the tapered hole 20 was changed.

The taper angle 01 determines theangle 02 of a boundary edge 50 between theinsertion hole 11 and the tapered hole 20.If thetaper angle 01 is relatively large, the angle 62 of the boundary edge 50 is relatively small. Therefore, if the taper angle 01 is excessively large, cracking occurs, for example, in a part of the aluminum wire W that has been in contact with the boundary edge 50.

In Fig. 13, the item "crack" represents whether or not cracking occurred in a part of the aluminum wire W that had been in contact with theboundary edge 50after the first - bonding step.Regarding the item "crack", a case where = cracking did not occur is denoted by "0". =oa

As shown in Fig. 13, in comparative examples 11 and 12, Bn because the taper angle of 01 of the tapered hole 20 was w excessively large, cracking occurred in the aluminum wire W on after the first bonding step. -

In contrast, in examples 14 and 15, cracking did not = occur in the aluminum wire W after the first bonding step. 0

From these results, preferably, the taper angle of 01 of the tapered hole 20 is 100° sr smaller.

Thus, occurrence of cracking in thealuminum wire W can be appropriately suppressed.

Preferably, the taper angle of 01 of thetapered hole 20 is 0° or larger.By setting the radius of curvature of the chamfer 40 at a predetermined value (for example, 4.55um or larger and 20.3um or smaller, or, 12.8um or larger and 20.3um or smaller), even if the taper angle 01 of thetapered hole 20 is 0° or close to 0°, occurrence of cracking in a part of the aluminum wire W that has been in contact with the chamfer 40 can be suppressed.

During wire bonding, an energy for bonding the aluminum wire Ww to the lead electrode 100 is generated at an interface between thealuminum wire W and thelead electrode 100 (hereinafter, simply referred to as - 27 - 1

"interface") .The distribution of the energy affects the > bond strength. =

Fig. 14 is a schematic perspective view illustrating = an example oftheresult of a simulation of bonding. ~

Fig. 15 is a schematic plan view illustrating an 0 ~ example ofthe result of a simulation of energy distribution ol during bonding. . er

Fig. 16 is a table showing the evaluation resultsof Z the item "bond strength" in a case wherethe wire diameter oO

Dwand the outside diameter Dp of thepressing surface were changed.

Fig. 14 illustrates a bond as viewed from obliquely below.In the example shown in Fig. 14, the interface has a substantially elliptical shape.Fig. 14 shows the contour diagram along the interface, representing an energy distribution obtained through a simulation.

For example, theenergy distribution is changed by : changing the ratio Rd (= Dp/Dw) of the outside diameter :

Dpof the pressing surface (see Fig. 3) to the wire diameter

Dw (see Figs. 7 and 8).As illustrated in Fig. 3, the outside diameter Dp of the pressing surface isthe diameter of an imaginary circle Cr, which is the intersection of an extension of the outer peripheralsurface of the bottleneck 14 and a plane including an end of the tapered hole 20.

Fig. 15(a) illustrates the result of a simulation in a case where the ratio Rd of the diameter Dw to the outside 5 diameter Dp of the pressing surface was smaller than 6.Fig. . 15(b) illustrates theresult of a simulation in a case where - ratio Rd of the diameter Dw to the outside diameter Dp of the pressing surface was 6 or larger. -

Figs. 15(a) and 15(b) each illustrate a half of the o energy distribution. .

Sillustrated in Fig. 8 after the second bonding step.Regarding the item "stitch bond", a case wheresufficient bond strength was obtained is denoted by "O".The average height Rc of the asperities of the pressing surface 30 of each sample used in the present evaluation was 0.20um or larger and 0.23um or smaller.

As shown in Fig. 16, in comparative examples 13 and 15, in which the ratio Rd was comparatively large, predetermined bond strength was not obtained.This is because the area of the pressing surface 30 was excessively large relative to the wire diameter Dw, and the amount of energy generated at the interface per unit area was small.In such a case, predetermined bond strength is not : obtained, and thealuminum wire W may become separated from : the lead electrode 100 at the interface.

Also in comparative example 14, in which the ratio Rd - 29 - E was comparatively small, predetermined bond strength was = not obtained.This is because the area of the pressing > surface 30 relative to the wire diameter Dw was so small - that an efficiently large bonding area was not obtained. -

In contrast, in examples 16 to 19, the ratio Rd was - 4.0 or larger and 5.7 or smaller.In examples 16 to 19, o> desired bond strength was obtained. o

From these results, preferably, the ratio Rd is 4.0 or ~ : larger and 5.7 or smaller. =

Thus, desired bond strength can be obtained. 0 (Method of Making Capillary)

Next, referring to Fig. 17, an example of a method ofmaking the capillary 1 according to the present embodimentwill be described.Fig. 17 is a flowchart representing a part of the example of the method of making the capillary 1.Fig. 17 illustrates a step of forming the chamfer 40 and steps of forming asperities on the pressing surface 30 and the chamfer 40, which are included in the method of making thecapillary 1.

As shown in Fig. 17, first,thechamfer 40 is formed at the boundary between the pressing surface 30 and the tapered hole 20 by roundly chamfering the boundary (step $5101) .Chamfering is performed by, for example, brush polishing.By optimizing the conditions of brush polishing, such as the polishing pressure and the polishing time, the chamfer 40 having a desired radius of curvature can be ]

formed. -

Next, by sandblasting the pressing surface 30 and the ~ : chamfer 40, theasperities are formed on the pressing surface © 30 and on the surface of the chamfer 40(step S102). -

Next, by brush polishing only the chamfer 40, the : sharpness of the peaks 41 of the asperities of the chamfer - 40 is made smaller than the sharpness of the peaks 31 of o the asperities of the pressing surface 30 (step S103) . Thus, > the capillary 1, which has the chamfer 40 between the ; pressing surface 30 and thetapered hole 20 and has fine ~ asperities on each of the pressing ‘surface 30 and the surface of the chamfer 40, is made.

The steps of the method described above are examples, and the chamfer 40 and the asperities may be formed by using other processes.For example, after performing : sandblasting in step S102 andbefore brush polishing only the chamfer 40 in step S103, both of the pressing surface 30 and the chamfer 40 may be brush polished.Thus, on both of the pressing surface 30 and the surface of the chamfer 40, asperities in which the area of the tip portions of the ~ peaks 31 and 41 is larger than the area of the bottom ; portions of the valleys 32 and 42, that is, the sharpness of thepeaks 31 and 41 is smaller than the sharpness of thevalleys 32 and 42, can be formed without fail.Blush polishing of the pressing surface 30 and the chamfer 40 may — 31 — bE be performed after step S103. ; (Modifications) x

In the embodiment described above, a bonding capillary = of a so-called bottle neck type is described.However, it is LE not necessary that thebonding capillary disclosed in the - present application be a bonding capillary of a bottle neck type.For example, the bonding capillary disclosed in the - present application may bea bonding capillary that does not = have a bottleneck, that is, a bonding capillary of a normal type that does not have a sharpened tip. h

In the embodiment described above, asperities are formed on the pressing surface and the chamfer.However, it is not necessary that the asperities be formed on the pressing surface.Asperities may be formed on the chamfer and thetapered hole. :

In the embodiment described above, a case of electrically connecting a pad electrode of a semiconductor chip to a lead electrode of a lead frame is described as an example.However, thebonding capillary disclosed in the present application can be used to bond a bonding wire to an object that is different from these electrodes.

Ce

Additional advantages and modifications can be easily : conceived by a person having ordinary skill in the art.Therefore, broader aspects of the present invention are ;

not limited to the specific, detailed, and = . representativeembodiment described .above.Accordingly, w : various modifications can be made within the spirit and ~ scope of the general conGepts of theinvention that are - : defined by the claims and the equivalents thereof. Lr oo [Reference Signs List] ; :

W: aluminum wire 2

Ti tail | <

S: stitch ;

Cr: imaginary circle

Dp: outside diameter of the pressing surface

Dw: - wire diameter 1: bonding capillary 11: insertion hole 12: shank : 13: cone : 14: bottleneck 20: tapered hole 30: pressing surface : 40: chamfer 50: boundary edge 100: lead electrode . 200: pad electrode ’ — 3 3 —

Claims

[Claim 1] =A bonding capillary comprising: iy a pressing surface that presses a bonding wire; = ! an insertion hole into which the bonding wire is - inserted; 0 atapered holethat connects the insertion hole to the 0 pressing surface and that expands toward the pressing = surface; and = | achamferthat is disposed betweenthe tapered hole and 5 the pressing surface, whereinthe chamfer has asperities on a surface thereof, and a sharpness of peaks of the asperities is smaller than a sharpness of valleys of the asperities.
[Claim 2] The bonding capillary according to Claim 1, whereinthe asperities of the chamfer have a skewness of -0.164or smaller and an average height of 0.035um orlarger and 0.092pm or smaller.
[Claim 3] The bonding capillary according to Claim 1 or 2, whereinthe pressing surface has asperities, and a sharpness of peaks of the asperities of the pressing surface is larger than the sharpness of the peaks of the asperities of the chamfer.
[Claim 4] oo The bonding capillary according to Claim 3, ) - oo ] wherein the asperities of the pressing surface have an average height of 0.113um or larger. > (Claim 5] = The bonding capillary according to any one of Claims 1 ol to 4, - whereinthe chamfer has a curved surface that is ~ smoothly continuous with the tapered hole and the pressing be surface, and a radius of curvature of the curved surface is 0

4.55um or larger and 20.30um or smaller. Bn

[Claim 6] © The bonding capillary according to any one of Claims 1 to 4, whereinthe chamfer has a curved surface that is . smoothly continuous with the tapered hole and the pressing surface, and a radius of curvature of the curved surface is

12.8um or larger and 20.30um or smaller.

[Claim 7] The bonding capillary according to any one of Claims 1 to 6, wherein a taper angle ofthe tapered hole is 100°or smaller.

[Claim 8] The bonding capillary according to any one of Claims 1 to 7, wherein an outside diameter of the pressing surface is :

4.0 times a wire diameter of the bonding wire or larger and :
5.7 times the wire diameteror smaller.