Patent Application
20110058979
The present invention relates to bonding wire bonding with semiconductor devices and outer leads.
When connecting the outside wiring with an electrode of an IC chip, wire-bonding methods wired through a wire are known. Among these methods as a manner of bonding with Al electrodes of an IC chip, thermo-compression and thermo-sonic bonding are in the mainstream. In thermo-sonic bonding, ball-bonding method is conventionally used. Bonding method by ball bonding is explained using the figure illustrated in Reference Patent 1 (Japanese Patent Application No. 3657087) shown herein. As shown in
For the wire bonding unit, cylindrical capillary 1 is made of high melting point material such as alumina, zirconia, ruby and sapphire, and there is a diamond coated tip of capillary of a high melting point material for longer life, the representative material is alumina. Capillary 1 has a wire lead hole 102 of its inside in order to insert metallic wire for bonding. For example, in the case of using around 25μ meters diameter of metallic wire, the size of wire lead hole 102 is selected in the range from 33μ meters to 40μ meters. The outside of the bottleneck of capillary 1 has around 10 degrees of taper angle because of the bonding interval and shape and size of the metallic wire after bonding. In this connection, the hole diameter H is 38μ meters, the tip diameter is 152 μmeters, and the chamfer diameter CD is 64μ meters.
Many various bonding wires have been developed so far. For example, it is well known that an Au matrix alloy with partial additives of rare earth elements enhances tensile strength. And, as a bonding wire which enhances tensile strength and shear strength, Au alloy thin wire comprising 1-10 wt ppm of Sr, 1-20 wt ppm of Be, 1-50 wt ppm and the residual Au is known in Reference Patent 2 (Japanese Patent Application No. 3059314) hereinafter described. And 1 wt % Au alloy bonding wire for improving bonding stability for long period use is also known. It is considered that these materials are completely alloyed in the pure Au matrix, and the mischief on sublimation of trace additive elements has not been researched so far.
In the bonding process, the tip of the capillary 1 is heated to around 200 degrees Celsius conventionally, and at initial ball forming process by arc discharge, surface temperature of the tip of the capillary 1 rises instantly to higher than 1,000 degrees Celsius. For this reason, as repeated bondings at high speeds of ten and several times a second, hundreds of thousands of times under unmanned condition, the tip 100 of the capillary 1 is contaminated by transferred materials from the metallic wire nevertheless material of tip of capillary 1. After all, these contaminated materials are accumulated in homogeneously for a moment at tip 100 of the capillary 1. Sooner or later, the contaminated capillary 1 by these accumulated contaminations suffers such that necessary energy amount for bonding isn't impressed by disturbance of transformation of ultrasonic and force at the second bonding. In the case of the capillary using a conventional bonding wire material, by accumulated contaminations such as partial additive elements to tip 100, cutting off of the wire would not work well on the outer wiring 8 of lead frame after second bonding, or by once of percentage at hundreds of thousands of times this accumulated contamination is used to come off from tip 100 of capillary 1. A stop of bonding equipment occurs frequently by this second bonding defect, and a suspended situation of the bonding process had often formed. Moreover, though bonding equipment didn't come to a stop, considerable decrease of bonding strength at second bonding occurred.
The present invention has been done to provide bonding wire, in view of the past's above-mentioned circumstances, which is the same as the conventional bonding wire at pull strength and superior roundness, moreover when repeating bondings by high speeds of ten and several times a second, hundreds of thousands of times, accumulated contamination does not occur at the tip of the capillary and does not decrease the second bonding strength.
The inventors of the present invention had made every effort and investigated Au alloy wires superior at strength of bonding wire. Consequently the effect that contamination does not accumulate at the tip of the capillary, though tip of capillary is contaminated by partial additive elements under the appropriate range of partial additives such as Mg, In, Al, and Yb to the purity of 99.995 wt % Au or the purity of 99.995 wt % Au—Pd alloy, has been discovered and the present invention is accomplished.
Concretely, according to the present invention, an Au alloy bonding wire comprising: 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: 5-20 wt ppm Ca, and 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: at least one element among 5-20 wt ppm La, 5-20 wt ppm Lu, 5-100 wt ppm Sn, 5-100 wt ppm Sr, and others of 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: at least one element among 5-20 wt ppm La, 5-20 wt ppm Lu, 5-100 wt ppm Sn, 5-100 wt ppm Sr, and others of 5-20 wt ppm Ca, 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
On the other hand, according to the present invention, an Au alloy bonding wire comprising: 0.01-1.2 wt % Pd, 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: 0.01-1.2 wt % Pd, 5-20 wt ppm Ca, 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: at least one element among 5-20 wt ppm La, 5-20 wt ppm Lu, 5-100 wt ppm Sn, 5-100 wt ppm Sr, and others of 0.01-1.2 wt % Pd, 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
And according to the present invention, an Au alloy bonding wire comprising: at least one element among 5-20 wt ppm La, 5-20 wt ppm Lu, 5-100 wt ppm Sn, 5-100 wt ppm Sr, and others of 0.01-1.2 wt % Pd, 5-20 wt ppm Ca, 5-100 wt ppm Mg, 5-20 wt ppm In, 5-20 wt ppm Al, 5-20 wt ppm Yb, and the residual Au of 99.995 wt % purity or higher is provided.
Au alloy bonding wire of the present invention resolves obstacles of bonding defects and coming off by the contaminated substances, since at ball forming by micro discharge and at the first bonding, contaminated substances of oxide of trace additive elements are formed and sublimated, and it does not accumulate and transcript to objective bonding wire with ultrasonic and thermo-compressed operation at the second bonding.
In the present invention, there are a few kinds of trace additive elements, and the range of components is narrow and definitive. Pure Au without any impurity is most superior for the second bondability of bonding wire, but all trace additive elements of the present invention do not disturb the superior second bondability of pure Au so much. When the balance of ratio of trace additive elements of the present invention is missing, the shape of the bonding portion that is compressed bonded is affected considerably at the second bonding.
By the way, in the case of an Au alloy system, it is commercially advantageous, since it is available to display as high purity bonding wire with 99.99 wt % or more, if the total amount of trace additive elements except Au and impurity elements is less than 100 wt ppm.
In the alloy system of the present invention, Pd is an element to contribute to reliability of bonding for a long period at the first bonding section. More additive of Pd increases reliability of bonding for a long period, but it becomes difficult to bond because of generating chip cracks and hardening of the initial ball under the more than 1.2 wt % Pd condition.
In the alloy system of the present invention, Mg is a crucial element for better second bondability, and it is an effective element for roundness of compressed ball diameter after melting the ball. On the other hand, Mg has little effect of enhancing strength of bonding wire, though Ca has it. In the alloy system of the present invention, it is necessary that the amount of Mg should be 5 wt ppm or more. If Mg is less than this, there is little effect for second bondability. In the alloy system of the present invention, it is preferable that the amount of Mg is 30 wt ppm or more in order to make second bondability of the wire stable. On the other hand, in the alloy system of the present invention, in the case that the amount of Mg is more than 100 wt ppm Mg, it has the wrong effect for second bondability since oxide accumulates at the capillary when initial forming the ball. In the alloy system of the present invention, it is preferable that the amount of Mg is less than 70 wt ppm Mg in order to make second bondability stable.
In the alloy system of the present invention, In is a crucial element for better second bondability, and it is an effective element for roundness of compressed ball diameter after moltening the ball. On the other hand, In has little effect of enhancing strength of bonding wire, though Ca has it. In the alloy system of the present invention, it is preferable that the amount of In is more than 5 wt ppm In in order to make second bondability of the wire stable. Because if In is less than this, there is little effect for second bondability. On the other hand, in the alloy system of the present invention, in the case that the amount of In is more than 20 wt ppm In, it has the wrong effect for second bondability since oxide accumulates at the capillary.
In the alloy system of the present invention, Al is a crucial element for better second bondability. On the other hand, Al has little effect of enhancing strength of bonding wire, though Ca has it. In the alloy system of the present invention, it is necessary that the amount of Al should be 5 wt ppm Al or more. If Al is less than this, there is little effect for second bondability. On the other hand, in the alloy system of the present invention, in the case that the amount of Al is more than 20 wt ppm Al, it has the wrong effect for second bondability since oxide accumulates at the capillary.
In the alloy system of the present invention, Yb is a crucial element for better second bondability, and moreover, it is an effective element for roundness of compressed ball diameter after moltening the ball. On the other hand, Yb has little effect of enhancing strength of the bonding wire, though Ca has it. In the alloy system of the present invention, it is necessary that the amount of Yb should be 5 wt ppm Yb or more. If there is less than this, there is little effect for second bondability. On the other hand, in the alloy system of the present invention, in the case that the amount of Yb is more than 20 wt ppm Yb, it has the wrong effect for second bondability since oxide accumulates at the capillary.
In the alloy system of the present invention, Ca is the most effective element to improve tensile strength of the wire. However, since Ca is apt to accumulate oxide on the surface of chamfer at tip of capillary, in the alloy system of the present invention, Ca is an optional additive element, and the additive amount of Ca is definitive. In the alloy system of the present invention, in the case of less than 5 wt ppm Ca, there is little effect for tensile strength, and in the case of more than 20 wt ppm Ca, it is apt to accumulate oxide on the surface of chamfer at the tip of the capillary, and it has the wrong effect for second bondability. Therefore additive amount of Ca is within the range of 5-20 wt ppm Ca.
In the alloy system of the present invention, La is an effective element to improve tensile strength of wire. Moreover, La is an effective element for second bondability. Furthermore, it is an effective element for roundness of compressed ball diameter after melting the ball. However, since La is apt to accumulate oxide at the tip of the capillary, in the alloy system of the present invention, La is an optional additive element, and the additive amount of La is definitive. In the alloy system of the present invention, in the case of less than 5 wt ppm La, there is little effect for tensile strength, and in the case of more than 20 wt ppm La, it accumulates oxide on the surface of chamfer at the tip of the capillary and it has the wrong effect for second bondability. Therefore the additive amount of La is within the range of 5-20 wt ppm La.
In the alloy system of the present invention, Lu is an effective element to improve tensile strength of the wire. Moreover, Lu is an effective element for second bondability. However, since Lu is apt to accumulate oxide on the surface at the tip of the capillary, in the alloy system of the present invention, Lu is an optional additive element, and the additive amount of La is definitive. In the alloy system of the present invention, in the case of less than 5 wt ppm Lu, there is little effect for tensile strength, and in the case of more than 20 wt ppm Lu, it accumulates oxide on the surface of chamfer at the tip of the capillary and it has the wrong effect for second bondability. Therefore the additive amount of Lu is within the range of 5-20 wt ppm Lu.
In the alloy system of the present invention, Sn is an effective element for second bondability. However, Sn is apt to accumulate oxide on the tip surface of the capillary, in the alloy system of the present invention, Sn is an optional additive element and the additive amount of it is definitive. In the alloy system of the present invention, it is necessary that the amount of Sn is 5 wt ppm Sn or more. In the case of less than 5 wt ppm Sn, there is little effect for second bondability. In the alloy system of the present invention, it is preferable that Sn is more than 30 wt ppm Sn in order to make second bondability of the wire stable. On the other hand, in the alloy system of the present invention, in the case of more than 100 wt ppm Sn, which is too much, oxide accumulates on the surface of the tip at the capillary, and it has the wrong effect for second bondability. In the alloy system of the present invention, in order to make second bondability stable, it is preferable that the additive amount of Sn is less than 70 wt ppm Sn.
In the alloy system of the present invention, Sr is an effective element for second bondability. Moreover, it is an effective element for roundness of compressed ball diameter after melting the ball. However, Sr is apt to accumulate oxide on the tip surface of the capillary, in the alloy system of the present invention, Sr is an optional additive element and the additive amount of it is definitive. In the alloy system of the present invention, it is necessary that the amount of Sr is 5 wt ppm Sr or more. In the case of less than 5 wt ppm Sr, there is little effect for second bondability. In the alloy system of the present invention, it is preferable that Sr is more than 30 wt ppm Sr in order to make second bondability of the wire stable. On the other hand, in the alloy system of the present invention, in the case of more than 100 wt ppm Sr, which is too much, oxide accumulates on the surface of the tip at the capillary, and it has the wrong effect for second bondability. In the alloy system of the present invention, in order to make second bondability stable, it is preferable that additive amount of Sr is less than 70 wt ppm Sr.
On the bonding wire of the present invention, second bondability, tensile strength and roundness of compressed ball diameter after moltening the ball have been measured by the following manner.
Second bondability is defined as easiness to bond to lead frame and deforming the wire by applying thermo-load-ultrasonic on stitch bonding, while the bonding wire is pressed to Ag plated 42 alloy on the lead frame. On second bondability, during the 500 thousand repeated bonding test, it has been measured as the number of un-bonded.
It was measured by using conventional tensile testing machine at 4% elongation. Measurement was done at room temperature, at 100 mm gauge length, and at 10 mm/min speed, and was calculated from the acquired value of load and elongation as fracture. By the way, elongation was calculated by using next equation from elongation as fracture.
(3) Compressed Diameter after Moltening the Ball
Evaluation of compressed diameter after moltening the ball was done by the following manner. It was ball bonded to an Al electrode (thickness of Al: around 1×10−6 m) on Si chip, then it was wired to an Ag plated 42 alloy on a lead frame by stitch bonding. Then, it was evaluated under a condition of span being 3×10−3 m, to optionally select 50 bonded wires from 200 bonded wires. After measuring the compressed ball diameters of applied direction of ultrasonic wave and parallel direction and vertical direction, it was shown as “Good” for the ratio range of 0.95-1.05, as “Fair” for the ratio range of 0.90-1.00 (where except 0.95-1.05), and as “Worse” for other range.
The preferable manufacturing method of Au alloy wire of the present invention is explained. It is casted into an ingot after melting in the vacuum furnace adding the prescribed amount of elements into high purity Au. It is applied to cold metal forming using ditch roll and drawing mill to said ingot, and intermediate annealing, after getting thin wire which diameter is 25×10−6 meters by final drawing, it is conditioned at 4% elongation by final annealing.
The bonding wire of the present invention is favorable to the method which bonds the IC chip to the lead frame. Where, said ball bonding means when wiring with wire and electrode of IC chip, especially Al electrode, and outer lead, and other electrode, it is formed into a molten ball, but at second bonding, without ball forming, the side of the wire is compressed. Corresponding to needs, it is impressed with ultrasonic wave, and it is heated.
When using the Au alloy bonding wire and/or the Pd—Au alloy wire of the present invention, after several hundreds of thousands repeated bondings at such high speed the reason why second bondability is not deteriorated is not exactly known, but it is considered as the following manner Namely, an oxide of trace additive elements is formed and attached at the tip of the capillary when ball forming by arc discharge and at first bonding, it is considered that attached oxide is printed to the wire side by each second bonding. Therefore, though there is a thin layer of oxide at the tip of the capillary, it does not form a thick layer of contamination. It is considered that such attached oxide is transferred to the wire side during second bonding before making a thick layer of contamination at the tip of the capillary. Consequently, it is considered that Au alloy bonding wire and/or Pd—Au alloy wire of the present invention has superior effects for second bonding. Bonding wire of the present invention has superior effect of pull strength and roundness.
It is explained the most preferred embodiment and compared examples and are shown in Table 1-1, Table 1-2, Table 1-3 and Table 2.
After adding the prescribed amount of additive elements to high purity Au of purity of 99.999 wt % and/or high purity Au alloyed with the prescribed amount of Pd were melted in the vacuum furnace, then Au alloy ingots were formed, which components are shown in Table 1-1 and Table 1-2 and Table 1-3 after casting. These ingots were roll formed by ditch roll, and were cold worked by using a drowing mill and intermediated annealing. A finished thin wire was formed, which diameter was 25 μmeters by final drawing, and was conditioned at 4% elongation by final annealing.
These Au alloy wires were examined by the 500 thousands cycle test, in which they were continuously ball bonded with an ultrasonic wave onto Al electrodes on an IC chip and onto outer wiring, using ball bonding equipment, which brand name is Maxμm Plus from K&S Corporation. Where, it was done under the condition of ball bonding load being 0.2 N, time of ball bonding was 10 ms, ball bonding power was 0.30 w at ball bonding of the IC chip side, and at second bonding of outer wiring, it was done under condition of ball bonding load being 0.3 N, time of ball bonding being 10 ms, ball bonding power being 0.40 w. From this test, it was counted the number of stops of ball bonding equipment by failure of second bonding. The result is shown in Table 2.
(3) Roundness of Compressed Diameter after Moltening Ball
Evaluation of roundness of compressed diameter after moltening the ball was done from 700 wires by making samples mentioned in the manner above, by a way different from 500 thousand cycle test. Namely, measuring compressed diameters of parallel direction of ultrasonic applied and vertical direction of it, comparing with each data, it was shown as “⊚” for the ratio range 0.97-1.03, as “◯” for the ratio range 0.95-1.05 (where except the range of 0.97-1.03), and as “Δ” for other ranges. The result is shown in Table 2.
From the results shown herein above, in Table 1-1, Table 1-2, Table 1-3 and Table 2, Examples 1-6 have the same range of components described in claim 1, and the number of failure of second bonding are 1-3 times in 500 thousand cycles, and the roundness is “Fair”. From these results, it is known that effect of additive elements such as Mg, In, Al and Yb is great. Moreover, in the same manner, Examples 7-9 have the same range of components described in claim 2, and have a decrease in the number of failure of second bondings and improved roundness by adding Ca as the same as before. In the case of Examples 10-21, in same manner, have the same range of components as described in claim 3, and it is recognized that these examples decrease the number of failure of second bondings and also have improved roundness by the effect of adding La, Lu, Sn and Sr to the component of Examples 1-6. Examples 22-35 have the same range of components as described in claim 4, and these show the effect of adding Ca. Examples 36-41 have the same range of components as described in claim 5, Examples 42-50 have the same range of components described in claim 6, and to each example is added 0.1-1.0 wt % Pd to the component of claim 1 and/or claim 2, and they show the same effect. Examples 51-58 correspond to the same range of components described in claim 7, and Examples 59-70 correspond to the same range of components described in claim 8, and they show the effect of adding Pd to the component of claim 3 and claim 4 described above.
Contrary to these examples, conventional 1 and conventional 2 are lacking in the range of additive elements, though roundness was good, but 4 times of second bonding failures occurred for the 500 thousands bonding cycles. Comparative 1-3 show the case of out of the range from the present invention, which means less and over. In these cases, roundness is good as the same as described before, but it shows tendency of deterioration such as 4-5 times of second bonding failures, and it is shown that it is important to keep the range of components.
As described herein before, each bonding wire of the present invention considerably decreases bonding failures at 500 thousands bonding cycle test.
According to the bonding wire of the present invention, Au alloy of prescribed additive elements of Mg—In—Al—Yb and/or Au alloy with Pd, more over, with added Ca to these alloys, and with added trace additive elements of La, Lu, Sn and Sr to these alloys, are superior at second bondability, more over, have superior effect of pull strength and second bondability as same as conventional bonding wire so far. It is effective to improve reliability of semiconductor devices.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-289091 | Nov 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/066442 | 9/11/2008 | WO | 00 | 9/30/2010 |
