High-Reliability Copper Alloy Bonding Wire for Electronic Packaging and Preparation Method Therefor

Abstract

The present invention discloses a high-reliability copper alloy bonding wire for electronic packaging and a preparation method therefor; the bonding wire comprises the following raw material components in percentage by weight: a copper content being 99.75%-99.96%, a tungsten content being 0.01-0.1%, a silver content being 0.01%-0.03%, a scandium content being 0.01%-0.02%, a titanium content being 0.001%-0.03%, a chromium content being 0.001%-0.03%, and an iron content being 0.001%-0.02%. The preparation method therefor comprises: extracting high-purity copper with a purity greater than 99.99%, preparing same as copper alloy ingots, and further preparing same as as-cast copper alloy crude bars, drawing the crude bars to form copper alloy wires, subjecting same to a heat treatment, and then precise drawing, a heat treatment, and cleaning to obtain copper alloy bonding wires of different specifications.

Claims

1. A high-reliability copper alloy bonding wire for electronic packaging, wherein it comprises the following raw material components in percentage by weight: a copper content being 99.75%-99.96%, a tungsten content being 0.01-0.1%, a silver content being 0.01%-0.03%, a scandium content being 0.01%-0.02%, a titanium content being 0.001%-0.03%, a chromium content being 0.001%-0.03%, an iron content being 0.001%-0.02%, and inevitable impurities; the content of S and O in the impurities being 10 wt. ppm in the entire copper alloy bonding wire, and the sum of the content of all elements being equal to 100%.

2. The high-reliability copper alloy bonding wire for electronic packaging according to claim 1, wherein the purity of copper in the raw materials is greater than 99.99%.

3. The high-reliability copper alloy bonding wire for electronic packaging according to claim 1, wherein the purity of any one of tungsten, silver, scandium, iron, titanium, and chromium in the raw materials is required to be greater than 99.999%.

4. A method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 1, wherein it comprises the following steps: 1) extracting high-purity copper: after electroplating a copper material, extracting the high-purity copper with a purity greater than 99.9999%, then cleaning and drying same for later use; 2) preparing copper alloy ingots: adding tungsten, silver, scandium, iron, titanium, and chromium into the high-purity copper obtained in step 1), mixing same and then heating same under the protection of argon to prepare the copper alloy ingots; 3) continuous casting into as-cast copper alloy bars: adding the prepared copper alloy ingots into a metal horizontal continuous casting chamber protected by nitrogen, heating, melting, refining and degassing same, injecting a molten solution into a liquid storage tank for heat preservation, and completing the horizontal continuous casting of the copper alloy molten solution to obtain as-cast copper alloy bars of 4-6 mm; 4) homogeneous annealing: subjecting the as-cast copper alloy bars of 4-6 mm to homogeneous annealing, wherein the annealing temperature is controlled to be 600-900 C., the annealing time is 6-10 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2, and the protective gas is continuously introduced during the process of cooling to room temperature; 5) coarse drawing: drawing the as-cast copper alloy bars of 4-6 mm after homogeneous annealing into copper alloy bars of 2-3 mm, and then drawing same into copper alloy wires with a diameter of 0.5-1 mm; 6) heat treatment: subjecting the copper alloy wires with a diameter of 0.5-1 mm to intermediate annealing, wherein the annealing temperature is 400-600 C., the annealing time is 2-6 hours, and the protective atmosphere is 95% N.sub.2+5% H.sub.2; 7) precise drawing: subjecting the copper alloy wires after the heat treatment to precise drawing to from finished copper alloy bonding wires with a diameter of 15 m-50 m respectively; 8) heat treatment: subjecting the copper alloy single crystal bonding wires after the precise drawing to annealing, wherein the annealing temperature is 400-600 C., the annealing time is 0.2-0.6 seconds, and the protective atmosphere is 95% N.sub.2+5% H.sub.2; and 9) cleaning the surface and drying same to obtain finished copper alloy bonding wires.

5. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the content of impurities S and O in the high-purity copper in step 1) is less than 5 wt. ppm.

6. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the mixing in step 2) is mechanical mixing.

7. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the heating and melting in step 2) are performed in a high-purity graphite crucible, and the heating and melting are performed by electric arc furnace heating.

8. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the heating and melting in step 3) is performed by using intermediate frequency induction heating.

9. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the surface cleaning in step 9) includes washing the bonding wires with a diluted acid solution, then ultrasonically washing same, and further washing same with high-purity water.

10. The method for preparing the high-reliability copper alloy bonding wire for electronic packaging according to claim 4, wherein the surface cleaning and drying in step 9) also includes rewinding, winding and packaging the finished copper alloy bonding wire.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a morphology diagram of a bonding joint when the copper alloy bonding wire of Example 1 is used for ball bonding.

DETAILED DESCRIPTION OF EMBODIMENTS

[0035] In order to better support the present invention, the present invention will be further described with reference to the drawings in combination with the examples, but the examples of the present invention are not limited thereto.

[0036] The examples relate to the test of performance parameters. The reference standards are YS/T 678-2008 (Copper wire for bonding lead device) and GB/T 8750 (Gold bonding wire for semiconductor package). The test method for breaking force and elongation is GB/T 10573 (Tensile testing method for fine wire of non-ferrous metals). With regard to the method for testing the bonding strength, reference is made to US MIL-STD 883G test standard (Test method standard microcircuits, 2006). With regard to the reliability test, reference is made to Wire bonding quality assurance and testing methods, D. T. Ramelow and the conventional reliability test methods of the electronic packaging industry. The specific test items include flitch reflow bonding (1705 C.-2605 C., 7 minutes, 100 cycles), storage test (40 C.-100 C., 1000 hours), high temperature and humidity (85 C.5 C., 85% RH, 1000 hours), high temperature cooking (50 minutes in a pressure cooker, and then cooling for 5 minutes, refrigerate at 40 C. for 50 minutes for 1 cycle, 1000 cycles), and air tightness (red ink mixed with water=1:1, hot plate 50 C.).

Example 1

[0037] A copper alloy bonding wire with high-purity copper as a main material. The material constituting the bonding wire is composed of the following raw materials by weight percentage: a tungsten (W) content being 0.1%, a silver (Ag) content being 0.020%, a scandium (Sc) content being 0.013%, a titanium (Ti) content being 0.03%, a chromium (Cr) content being 0.03%, an iron (Fe) content being 0.01%, and the content of S and O in the entire copper alloy bonding wire being 10 wt. ppm, the balance being copper and inevitable impurities, and the sum of which being equal to 100%; the purity of copper is required to be greater than 99.99%, and the purities of tungsten, silver, scandium, iron, titanium, and chromium are all required to be greater than 99.999%.

[0038] The preparation process steps and method of the copper alloy single crystal bonding wire for microelectronic packaging are as follows:

[0039] (1) extracting high-purity copper: immersing TU00 copper (99.99% copper) in an electrolyte as an anode, and immersing a high-purity copper foil in the electrolyte as a cathode; inputting a 9 V (2.5 A) direct current between the anode and the cathode, and maintain the temperature of the electrolyte not exceeding 60 C. by supplementing a fresh electrolyte; when the cathode accumulates a certain weight of high-purity copper with a purity greater than 99.9999%, replacing the high-purity copper foil in time, and then washing and drying same for later use.

[0040] (2) preparing copper alloy ingots: extracting high-purity copper with a purity of greater than 99.9999%, and the content of impurities S and O in the high-purity copper is less than 5 wt. ppm, and then adding tungsten, silver, scandium, iron, titanium and chromium; the contents of the components thereof are as follows in percentage by weight respectively: tungsten accounts for 0.1%, silver accounts for 0.02%, scandium accounts for 0.013%, titanium accounts for 0.03%, chromium accounts for 0.03%, iron accounts for 0.01%, the balance being copper and inevitable impurities, and the sum of which is equal to 100%. After mechanically mixing these metals, placing these metals in a high-purity graphite crucible, and melting same by using electric arc furnace heating under the protection of an argon gas to prepare the copper alloy ingots.

[0041] (3) continuous casting into as-cast copper alloy bars: adding the prepared copper alloy ingots into a metal horizontal continuous casting chamber protected by nitrogen and heating same to 1300 C. by using intermediate frequency induction heating, after completely melting, refining and degassing same, injecting a molten solution into a liquid storage tank in the middle of the continuous casting chamber for heat preservation, and completing the horizontal continuous casting of the copper alloy molten solution in a continuous casting chamber maintaining the flow rate of purified nitrogen at 5 L/min to obtain as-cast copper alloy bars of 6 mm.

[0042] (4) homogeneous annealing: subjecting the 6 mm as-cast copper alloy bar to homogeneous annealing; the annealing temperature is 900 C., the annealing time is 6 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2, and the protective gas is continuously introduced during the process of cooling to room temperature;

[0043] (5) coarse drawing: drawing the as-cast copper alloy bars of 6 mm after homogeneous annealing into copper alloy bars of 3 mm, and then drawing same into copper alloy wires with a diameter of 1 mm.

[0044] (6) heat treatment: subjecting the copper alloy wires with a diameter of 1 mm to annealing treatment; the annealing temperature is 600 C., the annealing time is 2 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2.

[0045] (7) precise drawing: precisely drawing the copper alloy wires after annealing treatment into copper alloy single crystal bonding wires with a diameter of 18 m.

[0046] (8) heat treatment: subjecting the copper alloy bonding wires after the precise drawing to annealing treatment; the annealing temperature is 450 C., the annealing time is 0.3 seconds, and the protective atmosphere is 95% N.sub.2+5% H.sub.2. After the annealing is completed, copper alloy bonding wires for electronic packaging are obtained.

[0047] (9) surface cleaning: washing the copper alloy single crystal bonding wire for electronic packaging after annealing treatment with a diluted acid solution, then ultrasonically washing same, further washing same with high-purity water and drying same, and

[0048] (10) winding: rewinding, winding and packaging the copper alloy single crystal bonding wires for finished microelectronic packaging.

[0049] The copper alloy single crystal bonding wire has a breaking force of 5.960.16 cN (the standard requirement is >5 cN, which is 20% or more higher than the standard), and an elongation rate of 14.620.82% (the standard requirement is 4-10%, and the elongation rate is 45% or more higher than the material of the prior art), a minimum fusing current of 0.28 A (the standard requirement indicates being accepted when it is 0.23 A or more, which is increased by 20% or more), which indicates that it has a good conductivity, a high strength and a good ductility, and can be continuously drawn to 10,000 meters without breakage (the standard requirement is 5000 ms without breakage, which is 100% higher than the standard). This is mainly due to the addition of the W and Sc elements improves the strength of the bonding wire, the addition of Ag and Fe ensures the conductivity of the bonding wire, and meanwhile the addition of Sc and formation of a single crystal structure ensure its excellent ductility. After 23,000 bondings, the wire is broken only once, indicating that it has good a ductility. The copper alloy bonding wire has a moderate hardness and a good ballability by bonding; as shown in FIG. 1, it is a morphology of a bonding joint when using the copper alloy bonding wire of this Example to perform ball bonding (parameters of ball bonding: the ball forming current is 50 mA, ball forming time is 0.24 s, bonding time is 6 s, bonding power is 60-80 W, bonding pressure is 20 cN, and the protective gas is 95% N.sub.2+5% H.sub.2) the roundness of the bonding joint is very good without eccentricity, indicating that the oxidation resistance and ballability of the copper alloy bonding wire are good. This is mainly because the addition of the W and Cr elements improves the oxidation resistance of copper alloy bonding wires, and the addition of Ti and Cr at the same time ensures that W solid-dissolves into the copper alloy to form a single crystal solid solution structure without grain boundaries, and the hardness thereof is reduced. The test results of bonding strength are the thrust of the ball bonding joint is 18-26 g (it is required to be no less than 14 g, which is increased by more than 14%), and the tensile force is 5-10 g (it is required to be no less than 4.5 g, which is increased by more than 11%), which all meet the requirements. The reliability test items include: flitch reflow bonding test (1870 samples, test passed), storage test (1600 samples, test passed), high temperature and high humidity test (1600 samples, test passed), high temperature digestion test (100 samples, test passed), gas tightness test (100 samples, 5 permeations, defective rate 5%. A defective rate no more than 10% means that the test is passed, which is increased by 100% or more). The good bonding strength and bonding reliability are due to the addition of the W, Sc and Ti elements, which can suppress the recrystallization temperature of the ball bonding joints during ball bonding, refine the grains, greatly improve the bonding strength, and the addition of the W and Cr elements can greatly improve its corrosion resistance.

[0050] It can be seen from above that the copper alloy bonding wire of this embodiment has good oxidation resistance and ballability, a high strength, a good plasticity, an excellent corrosion resistance, a high bonding strength and a bonding reliability, and is very suitable for high-density, multi-pin and low-cost integrated circuits and LED packaging.

Example 2

[0051] A copper alloy bonding wire with high-purity copper as a main material. The material constituting the bonding wire is composed of the following raw materials by weight percentage: tungsten (W) content being 0.05%, the silver (Ag) content being 0.025%, the scandium (Sc) content being 0.015%, the titanium (Ti) content being 0.02%, the chromium (Cr) content being 0.01%, and the iron (Fe) content being 0.015%, and the content of S and O in the entire copper alloy bonding wire being 10 wt. ppm, the balance being copper and inevitable impurities, and the sum of which being equal to 100%; The purity of copper is required to be greater than 99.99%, and the purities of tungsten, silver, scandium, iron, titanium, and chromium are all required to be greater than 99.999%.

[0052] The preparation process steps and method of the copper alloy single crystal bonding wire for microelectronic packaging are as follows:

[0053] (1) extracting high-purity copper: immersing TU00 copper (99.99% copper) in an electrolyte as an anode, and immersing a high-purity copper foil in the electrolyte as a cathode; inputting 8 V (3 A) direct current between the anode and the cathode, and maintain the temperature of the electrolyte not exceeding 60 C. by supplementing a fresh electrolyte. When the cathode accumulates a certain weight of high-purity copper with a purity greater than 99.9999%, replacing the high-purity copper foil in time, and then washing and drying same for later use.

[0054] (2) preparing copper alloy ingots: extracting high-purity copper with a purity of greater than 99.9999%, and the content of impurities S and O in the high-purity copper is less than 5 wt. ppm, and then adding tungsten, silver, scandium, iron, titanium and chromium; the contents of the components thereof are as follows in percentage by weight respectively: tungsten accounts for 0.05%, silver accounts for 0.025%, scandium accounts for 0.015%, titanium accounts for 0.02%, chromium accounts for 0.01%, iron accounts for 0.015%, the balance being copper and inevitable impurities, and the sum of which is equal to 100%. After mechanically mixing these metals, placing same in a high-purity graphite crucible, and melting same by using electric arc furnace heating under the protection of argon gas to prepare copper alloy ingots.

[0055] (3) continuous casting into as-cast copper alloy bars: adding the prepared copper alloy ingots into a metal horizontal continuous casting chamber protected by nitrogen and heating same to 1200 C. by using intermediate frequency induction heating, after completely melting, refining and degassing same, injecting a molten solution into a liquid storage tank in the middle of the continuous casting chamber for heat preservation, and completing the horizontal continuous casting of the copper alloy molten solution in a continuous casting chamber maintaining the flow rate of purified nitrogen at 4 L/min to obtain as-cast copper alloy bars of 4 mm.

[0056] (4) homogeneous annealing: subjecting the 4 mm as-cast copper alloy bar to homogeneous annealing; the annealing temperature is 800 C., the annealing time is 8 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2, and continuously introducing the protective gas during the process of cooling to room temperature;

[0057] (5) coarse drawing: drawing the as-cast copper alloy bars of 4 mm after homogeneous annealing into copper alloy bars of 2 mm, and then drawing same into copper alloy wires with a diameter of 0.5 mm.

[0058] (6) heat treatment: subjecting the copper alloy wires with a diameter of 0.5 mm to annealing treatment; the annealing temperature is 550 C., the annealing time is 4 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2.

[0059] (7) precise drawing: precisely drawing the copper alloy wires after annealing treatment into copper alloy single crystal bonding wires with a diameter of 20 m.

[0060] (8) heat treatment: subjecting the copper alloy bonding wires after the precise drawing to annealing treatment; the annealing temperature is 500 C., the annealing time is 0.3 seconds, and the protective atmosphere is 95% N.sub.2+5% H.sub.2. After the annealing is completed, copper alloy bonding wires for electronic packaging are obtained.

[0061] (9) surface cleaning: washing the copper alloy single crystal bonding wire for electronic packaging after annealing treatment with a diluted acid solution, then ultrasonically washing same, further washing same with high-purity water and drying same, and

[0062] (10) winding: rewinding, winding and packaging the copper alloy single crystal bonding wires for finished microelectronic packaging.

[0063] The copper alloy single crystal bonding wire has a breaking force greater than 8 cN (the standard is >6 cN, which is 30% higher than the standard or more), an elongation rate greater than 15% (the standard is 6-12%, which is 25% higher than the standard or more), a minimum fusing current of 0.29 A (the standard is 0.24 A, which is 20% higher than the standard or more), has a moderate hardness and a good ballability of bonding, and is very suitable for high density and multi-pin integrated circuit packaging.

Example 3

[0064] A copper alloy bonding wire with high-purity copper as a main material. The material constituting the bonding wire is composed of the following raw materials by weight percentage: tungsten (W) content being 0.01%, the silver (Ag) content being 0.03%, the scandium (Sc) content being 0.02%, the titanium (Ti) content being 0.001%, the chromium (Cr) content being 0.01%, and the iron (Fe) content being 0.02%, and the content of S and O in the entire copper alloy bonding wire being 10 wt. ppm, the balance being copper and inevitable impurities, and the sum of which being equal to 100%; The purity of copper is required to be greater than 99.99%, and the purities of tungsten, silver, scandium, iron, titanium, and chromium are all required to be greater than 99.999%.

[0065] The process steps and method for preparing the copper alloy single crystal bonding wire for microelectronic packaging are as follows:

[0066] (1) extracting high-purity copper: immersing TU00 copper (99.99% copper) in an electrolyte as an anode, and immersing a high-purity copper foil in the electrolyte as a cathode; inputting 7 V (3.5 A) direct current between the anode and the cathode, and maintain the temperature of the electrolyte not exceeding 60 C. by supplementing a fresh electrolyte. When the cathode accumulates a certain weight of high-purity copper with a purity greater than 99.9999%, replacing the high-purity copper foil in time, and then washing and drying same for later use.

[0067] (2) preparing copper alloy ingots: extracting high-purity copper with a purity of greater than 99.9999%, and the content of impurities S and O in the high-purity copper is less than 5 wt. ppm, and then adding tungsten, silver, scandium, iron, titanium and chromium; The contents of the components thereof are as follows in percentage by weight respectively: tungsten accounts for 0.01%, silver accounts for 0.03%, scandium accounts for 0.02%, titanium accounts for 0.001%, chromium accounts for 0.01%, iron accounts for 0.02%, the balance being copper and inevitable impurities, and the sum of which is equal to 100%. After mechanically mixing these metals, placing same in a high-purity graphite crucible, and melting same by using electric arc furnace heating under the protection of argon gas to prepare copper alloy ingots.

[0068] (3) continuous casting into as-cast copper alloy bars: adding the prepared copper alloy ingots into a metal horizontal continuous casting chamber protected by nitrogen and heating same to 1130 C. by using intermediate frequency induction heating, after completely melting, refining and degassing same, injecting a molten solution into a liquid storage tank in the middle of the continuous casting chamber for heat preservation, and completing the horizontal continuous casting of the copper alloy molten solution in a continuous casting chamber maintaining the flow rate of purified nitrogen at 3 L/min to obtain as-cast copper alloy bars of 5 mm.

[0069] (4) homogeneous annealing: subjecting the 5 mm as-cast copper alloy bar to homogeneous annealing; the annealing temperature is 750 C., the annealing time is 10 hours, the protective atmosphere is 95% N.sub.2+5% H.sub.2, and continuously introducing the protective gas during the process of cooling to room temperature.

[0070] (5) coarse drawing: drawing the as-cast copper alloy bars of 15 mm after homogeneous annealing into copper alloy bars of 3 mm, and then drawing same into copper alloy wires with a diameter of 1 mm.

[0071] (6) heat treatment: subjecting the copper alloy wires with a diameter of 1 mm to annealing treatment; the annealing temperature is 500 C., the annealing time is 6 hours, and the protective atmosphere is 95% N.sub.2+5% H.sub.2.

[0072] (7) precise drawing: precisely drawing the copper alloy wires after annealing treatment into copper alloy single crystal bonding wires with a diameter of 25 m.

[0073] (8) heat treatment: subjecting the copper alloy bonding wires after the precise drawing to annealing treatment; the annealing temperature is 450 C., the annealing time is 0.6 seconds, and the protective atmosphere is 95% N.sub.2+5% H.sub.2. After the annealing is completed, copper alloy bonding wires for electronic packaging are obtained.

[0074] (9) surface cleaning: washing the copper alloy single crystal bonding wire for electronic packaging after annealing treatment with a diluted acid solution, then ultrasonically washing same, further washing same with high-purity water and drying same, and

[0075] (10) winding: rewinding, winding and packaging the copper alloy single crystal bonding wires for finished microelectronic packaging.

[0076] The copper alloy single crystal bonding wire has a breaking force greater than 11.5 cN (the standard is >8 cN, which is 30% higher than the standard or more), an elongation rate greater than 18% (the standard is 8-16%, which is 12% higher than the standard or more), a minimum fusing current of 0.3 A (the standard is 0.26 A, which is 7% higher than the standard or more), has a moderate hardness and a good ballability of bonding, and is very suitable for high density and multi-pin integrated circuit packaging.