Gold bonding wire and preparation method and application thereof

Abstract

The invention discloses a gold bonding wire and a preparation method and application thereof. The gold bonding wire comprises, by mass, 75%-85% of gold, 8.5%-10.2% of palladium, 0.08%-0.15% of yttrium, 0.02%-0.02% of erbium, 0.003%-0.01% of cerium and the balance silver and inevitable impurities. According to the invention, through component synergy and combination of a graded heat treatment-multi-section pulse ultrasonic wire drawing-precise annealing process, the problem of synchronous improvement of strength and toughness under gold content reduction is effectively solved. Palladium provides solution strengthening, rare earth elements synergistically refine grains, purify grain boundaries and perform precipitation strengthening, and the performance loss caused by gold reduction is made up. Precipitation and structure uniformity are regulated and controlled through graded heat treatment, work hardening is remarkably reduced through multi-section gradient power ultrasonic wiredrawing, high-toughness deformation is guaranteed, and the structure is accurately annealed and stabilized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bonding wire, in particular to a bonding wire and a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of microelectronic technology, integrated circuit (IC) packaging is evolving towards high density, miniaturization and multifunctionalization, which puts forward higher requirements on the performance of bonding wire materials for packaging. Bonding wire has long been the preferred interconnection material in high-end packaging field due to its excellent electrical conductivity, thermal conductivity, corrosion resistance and reliable bonding performance. However, gold as a precious metal has high price and volatile, which leads to high packaging cost. Therefore, under the premise of ensuring or even improving the comprehensive performance of bonding wire, effectively reducing the gold content has become a key technical bottleneck to be broken through in the field of semiconductor packaging materials.

[0003] At present, base metals are often used to replace gold to reduce cost (the mass percentage of gold is less than 90%), however, this method has significant defects: when the content of base metal is too high, the plasticity and toughness of the material deteriorate sharply, leading to serious work hardening, significantly increased wire breakage rate and difficult to guarantee the yield; while the content of base metal is too low, the strengthening effect cannot be effectively played, and the strength is limitedly improved.

[0004] Therefore, it is necessary to develop a high-performance bonding wire with high strength, high toughness and low wire breakage rate under the premise of significantly reducing the gold content. SUMMARY

[0005] Therefore, the present application provides a bonding wire and a preparation method and application thereof, which are used to solve how to balance the strength and ductility of ultra-fine gold wire under high temperature and high humidity environment while significantly reducing the gold content in the bonding wire.

[0006] To achieve the above technical purposes, the present application adopts the following technical solutions: In a first aspect, the present application provides a bonding wire, which comprises the following components by mass percentage: 75-85% gold, 8.5-10.2% palladium, 0.08-0.15% yttrium, 0.02-0.02% erbium, 0.003-0.01% cerium, and the balance being silver and unavoidable impurities.

[0007] Preferably, the content of yttrium is 0.1-0.12wt%, and the content of erbium is 0.02-0.02wt%.

[0008] In a second aspect, the present application provides a preparation method of a bonding wire, comprising the following steps: S1. vacuum smelting gold, palladium, yttrium, erbium, cerium and silver under inert atmosphere to obtain an alloy melt; S2. The alloy melt is subjected to a staged heat treatment, and then the material after the staged heat treatment is subjected to multi-stage pulsed ultrasonic wire drawing until the diameter is ≤20 μm; S3. The material after the wire drawing is annealed in an inert atmosphere, and a bonding alloy wire is obtained; Preferably, the procedure of the staged heat treatment is as follows: the first stage, 510-530℃ for 10-15 min; the second stage, 550-580℃ for 5-10 min; and the third stage, 450-480℃ cooling to room temperature.

[0009] Preferably, in step S1, the temperature of the vacuum melting is 1250-1300℃.

[0010] Preferably, the heating rate of the first stage is ≤5℃ / min.

[0011] Preferably, the temperature difference between the second stage and the first stage is ≥30℃.

[0012] Preferably, the steps of the multi-stage pulsed ultrasonic wire drawing are as follows: The coarse drawing stage, under the condition of 4-4.5 W ultrasonic, the material is drawn from 8 mm to 1 mm; The medium drawing stage, under the condition of 2.5-3 W ultrasonic, the material is drawn from 1 mm to 50 μm; The fine drawing stage, under the condition of 1-1.5 W ultrasonic, the material is drawn from 50 μm to 20 μm; The final drawing stage, under the condition of 0.5-0.8 W ultrasonic, the material is drawn from 20 μm to the target value.

[0013] Preferably, in step S3, the annealing rate is 25-30 m / min; and the magnetic field annealing temperature is 520-550℃.

[0014] In a third aspect, the application provides a bonding alloy wire in an electronic material.

[0015] The application has the following beneficial effects: through the component synergy, combined with the staged heat treatment-multi-stage pulsed ultrasonic wire drawing-precise annealing process, the application effectively solves the problem of synchronous improvement of strength and toughness under the condition of reducing gold content. Palladium provides solid solution strengthening, rare earth elements cooperate to refine grains, purify grain boundaries and precipitate strengthening, which makes up for the performance loss caused by reducing gold; the staged heat treatment regulates the precipitation and uniformity of the structure, the multi-stage gradient power ultrasonic wire drawing significantly reduces the work hardening and guarantees high toughness deformation, and the precise annealing stabilizes the structure. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the application clearer, the application will be further described in detail below with examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0017] The application provides a bonding gold wire, which comprises the following components in percentage by mass: 75-85% gold, 8.5-10.2% palladium, 0.08-0.15% yttrium, 0.02-0.02% erbium, 0.003-0.01% cerium, and the balance being silver and inevitable impurities.

[0018] The application partially replaces gold with palladium (Pd), directly reduces the amount of noble metal, the atomic radius of Pd is different from that of Au, can be effectively solid-solved in the Au matrix, causes lattice distortion, hinders dislocation movement, and thus significantly improves the strength. Meanwhile, trace rare earth elements yttrium (Y), erbium (Er) and cerium (Ce) are introduced, on the one hand, these elements can effectively inhibit grain growth during solidification and subsequent heat treatment, forming fine and uniform grain structure, according to the Hall-Petch relationship, the finer the grain, the more the grain boundaries, the greater the hindrance to dislocation movement, thus improving the strength and toughness at the same time; on the other hand, the rare earth elements (Y, Er, Ce) have strong chemical activity, can combine with impurities (such as O, S) in the melt to form high-melting-point and fine compounds (such as oxides and sulfides), play a role in purifying grain boundaries, reduce brittle phases, improve material purity and interface bonding force, and thus improve toughness. At the same time, these fine and dispersed compound particles can also pin dislocations and grain boundaries, providing additional strengthening.

[0019] The application provides main solid-solution strengthening through Pd, and the rare earth elements refine grains and purify grain boundaries, which not only contributes to fine-grain strengthening, but also guarantees toughness, and at the same time, assists the strengthening effect of Pd, through mechanism synergy, makes up for the decrease in strength and toughness caused by the reduction of gold content.

[0020] It is worth noting that the components of the application are not isolated, but are related and synergistic, specifically, Au and Pd are used in combination, Au is the matrix, Pd is the main strengthening element, and the two form an Au-Pd solid solution, the amount of Pd added is optimized, which can effectively strengthen, and too much Pd will not cause the material to be too brittle or difficult to process; the three rare earth elements have synergistic effect, Y (yttrium) has the highest content (0.08-0.15%), is the main grain refiner and deoxidizing / desulfurizing agent, plays a leading role in purifying the melt and inhibiting grain growth, while Er (erbium) has very low content (0.02-0.02%), plays a micro-alloying role, further refines the grains or affects the precipitation behavior in cooperation with Y, and Ce (cerium) as a strong deoxidizing agent, can further purify the melt, and together with Y and Er, ensures clean grain boundaries, and the three together form fine rare earth oxide / sulfide composite inclusions, effectively pin the grain boundaries, inhibit recrystallization and grain growth.

[0021] In some embodiments, the content of yttrium is 0.1-0.12wt%, and the content of erbium is 0.02-0.02wt%.

[0022] In this embodiment, the strength decreases when the yttrium content is too low, and the ductility deteriorates when the yttrium content is too high.

[0023] The application provides a preparation method of a bonding gold wire, comprising the following steps: S1. vacuum smelting gold, palladium, yttrium, erbium, cerium and silver under an inert atmosphere to obtain an alloy melt; S2. performing fractional heat treatment on the alloy melt, and then performing multi-section pulsed ultrasonic wire drawing on the material after the fractional heat treatment until the diameter is ≤20 µm; S3. annealing the material after the wire drawing under an inert atmosphere to obtain the bonding gold wire; In some embodiments, the procedure of the fractional heat treatment is as follows: the first stage is 510-530 ℃ for 10-15 min; the second stage is 550-580 ℃ for 5-10 min; and the third stage is 450-480 ℃ for cooling to room temperature.

[0024] In the application, step S1 is a vacuum smelting process, high temperature ensures that high-melting-point metals such as Au and Pd are completely melted to form a uniform melt, and the inert atmosphere prevents Au, Pd and active rare earth elements from being oxidized at high temperature, so as to ensure accurate composition and pure melt, and vacuum helps to remove gas and reduce pores; step S2 is a fractional heat treatment and multi-section pulsed ultrasonic wire drawing process, wherein the first stage of the fractional heat treatment promotes the uniform precipitation or stabilization of small rare earth compounds, and prepares for subsequent processing, the second stage aims to homogenize the alloy composition and eliminate casting stress, the temperature is controlled at the palladium precipitation peak to induce 5-10 nm palladium particles to uniformly precipitate in the crystal, and the strength and ductility of the bonding gold wire are further improved, and the third stage rapidly cools to lock the nano structure to avoid the coarse precipitation of precipitated phases caused by slow cooling, thereby reducing the strength or ductility.

[0025] In some embodiments, in step S1, the temperature of the vacuum smelting is 1250-1300 ℃.

[0026] In some embodiments, the temperature rising rate of the first stage is ≤5 ℃ / min.

[0027] In some embodiments, the temperature difference between the second stage and the first stage is ≥30 ℃.

[0028] In some embodiments, the step of the multi-section pulsed ultrasonic wire drawing is as follows: The coarse drawing section is to draw the material from 8 mm to 1 mm under the condition of 4-4.5 W of ultrasonic; The medium drawing section is to draw the material from 1 mm to 50 µm under the condition of 2.5-3 W of ultrasonic; The fine drawing section is to draw the material from 50 µm to 20 µm under the condition of 1-1.5 W of ultrasonic; The final drawing stage is to draw the material from 20 µm to the target value under the condition of ultrasonic vibration of 0.5-0.8 W.

[0029] In this embodiment, after the graded heat treatment, the material has a relatively uniform structure and certain strengthening phase. The multi-stage drawing is matched with the gradient reduction of ultrasonic power to adapt to the deformation requirements at different stages; the ultrasonic vibration of the application introduces acoustic energy, which can effectively reduce the deformation resistance, refine the deformed structure, promote dynamic recrystallization, and reduce work hardening, thereby avoiding cracking under high deformation (from 800 µm to ≤20 µm), ensuring high toughness, and overcoming the brittleness problem caused by Pd and rare earth elements; a larger power is required in the rough drawing stage to overcome the initial deformation resistance; as the wire diameter decreases, the deformation resistance and thermal effect change, and the reduced power can accurately control the deformation and avoid local overheating or damage.

[0030] In some embodiments, the annealing rate in step S3 is 25-30 m / min; and the magnetic field annealing temperature is 520-550℃.

[0031] In this embodiment, this temperature is lower than the recrystallization temperature, and mainly serves for stress relief annealing to eliminate the residual stress accumulated during the drawing process and stabilize the size, while possibly promoting the precipitation strengthening, such as the further precipitation of fine Pd-rich regions or rare earth compounds, to improve the strength; and the faster annealing rate aims to control the recrystallized grain size to prevent the grains from growing too much, so as to maintain the fine-grained structure and maintain high strength and high toughness.

[0032] The application provides an application of a bonding gold wire in electronic materials.

[0033] The application is further described below through specific embodiments. Embodiment 1

[0034] A bonding gold wire includes the following components in percentage by mass: 80% gold, 9.5% palladium, 0.12% yttrium, 0.02% erbium, 0.008% cerium, and the balance being silver and unavoidable impurities.

[0035] A preparation method of a bonding gold wire includes the following steps: S1. Put the gold, palladium, yttrium, erbium, cerium, and silver raw materials with calculated mass into the crucible of a vacuum induction melting furnace, and vacuumize to 10 -2 Pa or below, fill in argon as a protective atmosphere, heat to 1280℃, and keep for 15 minutes to completely melt the raw materials and fully stir to form a uniform alloy melt, pour the melt into a preheated metal mold, and obtain an alloy ingot after cooling.

[0036] S2. The alloy ingot is heated under argon protection, and subjected to a staged heat treatment: first stage: heating to 520°C at a rate of 3°C / min, holding for 12 min; second stage: heating to 565°C, holding for 8 min; third stage: cooling to 465°C at a rate of 10°C / min, holding for 5 min, and then cooling to room temperature with the furnace; after the staged heat treatment, the alloy ingot is subjected to surface treatment (such as pickling, polishing), and then subjected to multi-stage pulsed ultrasonic wire drawing: in the rough drawing stage, the ingot is drawn to a diameter of 200 µm under the condition of an ultrasonic power of 4.3 W; in the intermediate drawing stage, the wire is drawn from 200 µm to 50 µm under the condition of an ultrasonic power of 2.8 W; in the fine drawing stage, the wire is drawn from 50 µm to 20 µm under the condition of an ultrasonic power of 1.3 W; and in the final drawing stage, the wire is drawn from 20 µm to the target diameter of 18 µm under the condition of an ultrasonic power of 0.6 W.

[0037] S3. The wire drawn to a diameter of 18 µm is subjected to continuous annealing under high-purity argon protection, with the annealing temperature set to 335°C and the annealing rate set to 28 m / min; after annealing, the wire is naturally cooled to room temperature, to obtain the final bonding alloy wire product.

[0038] Example 2-3 A bonding alloy wire, with the other contents being the same as in Example 1, except that it contains 8.5% palladium and 10.2% palladium, respectively.

[0039] Example 4-5 A bonding alloy wire, with the other contents being the same as in Example 1, except that it contains 0.08% yttrium and 0.15% yttrium, respectively.

[0040] Example 6-7 A bonding alloy wire, with the other contents being the same as in Example 1, except that it contains 75% gold and 85% gold, respectively. Example 8

[0041] A bonding alloy wire, with the other contents being the same as in Example 1, except that the multi-stage pulsed ultrasonic wire drawing is replaced by ultrasonic wire drawing at a constant power of 0.6 W.

[0042] Comparative Example 1 A bonding alloy wire, with the other contents being the same as in Example 1, except that erbium, cerium, and yttrium are replaced by palladium.

[0043] Comparative Example 2 A bonding alloy wire, with the other contents being the same as in Example 1, except that the ultrasonic step is not included in the wire drawing.

[0044] Comparative Example 3 A bonding wire, other contents are the same as example 1, the difference is that the step S2 is replaced by single-stage heat treatment at 560℃ for 25min.

[0045] Comparative example 4 A bonding wire, other contents are the same as example 1, the difference is that erbium and cerium are replaced by yttrium.

[0046] Test and evaluation The performance of the bonding wires of different examples and comparative examples is tested and evaluated, including: Tensile strength and elongation: tested according to GB / T 228.1-2021; Bending times: tested according to GB / T 41709-2022; Wire breakage rate: the number of breaks that occur during the entire multi-stage drawing process from ingot (~800µm) to final diameter (18µm) is counted per 1000 meters of wire produced; wire breakage rate (%) = (total number of breaks / total production length (km)), the data of at least 3 independent production batches are counted and averaged.

[0047] The results are shown in Table 1.

[0048] Table 1 Test results ; Compared with example 1, the tensile strength performance of example 2 decreases, the content of palladium (Pd) decreases, which leads to the weakening of solid solution strengthening effect, so the tensile strength of the material decreases; the tensile strength of example 2 is still higher than that of all comparative examples, which shows that even at a lower Pd content, through the synergistic effect of other components and processes, a higher strength level can still be maintained; the elongation and bending times of example 3 decrease compared with example 1, the content of palladium (Pd) increases, too much Pd will make the material too brittle, thereby reducing its ductility and fatigue resistance.

[0049] Compared with example 1, the tensile strength and bending times of example 4 decrease, the content of yttrium (Y) decreases, which leads to the weakening of grain refinement effect, thereby reducing the strength and toughness of the material, in addition, grain coarsening also affects the fatigue resistance of the material, leading to a decrease in bending times; the elongation of example 5 decreases slightly, the reason is that the content of yttrium (Y) increases, too high Y content may promote the formation of more rare earth compound inclusions, these inclusions can pin the grain boundary, but too much may become a crack source, thereby reducing the ductility of the material, the tensile strength of example 5 increases, which shows that the increase of Y content enhances the effects of fine-grain strengthening and precipitation strengthening to some extent.

[0050] Compared with Example 1, the tensile strength of Example 6 is slightly improved, the gold (Au) content is reduced, and the increase in the relative proportion of Pd further strengthens the solid solution effect, and the lower Au content promotes the formation of finer grain structure, thereby improving the strength of the material. The tensile strength of Example 7 decreases, the gold (Au) content increases, and the relative content of Pd decreases accordingly, resulting in a weakening of the solid solution strengthening effect, thereby reducing the tensile strength of the material, but the higher Au content helps to maintain the ductility of the material, so the elongation and bending times of Example 7 are better than those of Example 1, with excellent plasticity and fatigue resistance.

[0051] Compared with Example 1, the elongation, bending times and wire breakage rate of Example 8 all decrease, which is due to the cancellation of the power gradient of multi-stage pulse ultrasonic drawing, and the use of low power of 0.6 W throughout the process, resulting in severe early work hardening, insufficient refinement of the deformed structure, and accumulation of more residual stress, ultimately affecting the toughness and wire breakage rate of the material.

[0052] Comparative Example 1 only uses palladium to reduce gold, lacks rare earth elements, and the grain is significantly coarsened, which cannot achieve fine-grain strengthening, and impurities may be segregated at the grain boundaries, resulting in a significant decrease in strength and toughness. At the same time, the lack of pinning effect of rare earth compounds makes the material more prone to cracking during deformation, and the processing performance is extremely poor with high wire breakage rate.

[0053] Comparative Example 2 is drawn without ultrasonic assistance, with extremely high deformation resistance and severe work hardening, making it difficult to achieve high deformation processing from 800 µm to 18 µm, resulting in accumulation of a large amount of residual stress and defects in the material, with extremely poor plasticity and fatigue resistance, and almost impossible to complete the final drawing.

[0054] The single-stage heat treatment of Comparative Example 3 cannot achieve fine structure regulation, resulting in uneven alloy composition and coarsening of precipitates, with decreased tensile strength, elongation, bending times and wire breakage rate.

[0055] Although Comparative Example 4 has a higher Y content, it lacks the synergistic purification and micro-alloying effect of Er and Ce, resulting in lower melt purity and grain boundary cleanliness than Example 1, and the rare earth compound inclusions formed may not be fine and dispersed enough to weaken the pinning effect on the grain boundaries, resulting in relatively larger grain size (2.4 µm), and the comprehensive strengthening and toughening effect is not as good as Example 1.

[0056] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, which should be covered within the protection scope of the present application.

Claims

1. A bonding alloy wire, characterized in that, The composition comprises, by weight percentage, 75-85% gold, 8.5-10.2% palladium, 0.08-0.15% yttrium, 0.02-0.02% erbium, 0.003-0.01% cerium, with the balance being silver and unavoidable impurities.

2. The bonding wire according to claim 1, characterized in that, The yttrium content is 0.1-0.12 wt%, and the erbium content is 0.02-0.02 wt%.

3. A method for preparing a bonding wire as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Under an inert atmosphere, gold, palladium, yttrium, erbium, cerium, and silver are vacuum melted to obtain an alloy melt; S2. The alloy melt is subjected to graded heat treatment, and then the material after graded heat treatment is subjected to multi-segment pulsed ultrasonic drawing until the diameter is ≤20µm; S3. Anneal the drawn material in an inert atmosphere to obtain the bonding alloy wire.

4. The preparation method according to claim 3, characterized in that, The graded heat treatment procedure is as follows: first stage, holding at 510-530℃ for 10-15 minutes; second stage, holding at 550-580℃ for 5-10 minutes; third stage, cooling to room temperature at 450-480℃.

5. The preparation method according to claim 3, characterized in that, In step S1, the temperature of the vacuum melting is 1250-1300℃.

6. The preparation method according to claim 3, characterized in that, The heating rate in the first stage is ≤5℃ / min.

7. The preparation method according to claim 3, characterized in that, The temperature difference between the second stage and the first stage is ≥30℃.

8. The preparation method according to claim 3, characterized in that, The steps of the multi-segment pulsed ultrasonic fiber drawing are as follows: In the coarse drawing stage, the material is drawn from 8mm to 1mm under ultrasonic conditions of 4-4.5W. In the intermediate drawing stage, the material is drawn from 1 mm to 50 µm under ultrasonic conditions of 2.5-3 W; Fine drawing segment: Under ultrasonic conditions of 1-1.5W, the material is drawn from 50µm to 20µm; In the final drawing stage, the material is drawn from 20µm to the target value under ultrasonic conditions of 0.5-0.8W.

9. The preparation method according to claim 3, characterized in that, In step S3, the annealing rate is 25-30 m / min; the magnetic field annealing temperature is 520-550℃.

10. The application of the bonding wire as described in any one of claims 1-2 in electronic materials.