KR101181878B1 - Method of manufacturing copper-based bonding wire - Google Patents

Abstract

PURPOSE: A method for manufacturing a copper group bonding wire is provided to produce uniform palladium distribution when forming a free air ball by forming a coating member on a rough surface layer. CONSTITUTION: A core member including copper and inevitable impurities is formed. A rough surface layer is formed on the surface of the core member. A coating member including palladium is formed on the rough surface layer. A bonding wire(10) including a core in which a coating layer is coated is formed by wire-drawing the core member. The coating layer has thickness of a range of 40nm to 80nm when the bonding wire has diameter of 15-20micrometers. The coating layer has thickness of a range of 50nm to 110nm when the bonding wire has diameter of 15-20micrometers.

Description

Method of manufacturing copper-based bonding wires {Method of manufacturing copper-based bonding wire}

The technical idea of the present invention relates to a method for manufacturing a copper-based bonding wire, and more particularly, to a method for manufacturing a copper-based bonding wire coated with palladium.

The semiconductor package generally has a bonding wire for electrical connection between the semiconductor chip and the printed circuit board included therein.

Gold is generally used as a material of such a bonding wire. But. Gold is expensive and development of bonding wires made of relatively inexpensive metals is required. In order to meet these demands, bonding wires made of low cost copper have been proposed. However, since copper is susceptible to surface oxidation, long-term storage is difficult, and oxidation occurs due to the progress of heat conduction from the substrate at the time of bonding, thereby degrading the bonding properties. In order to solve this problem, a copper wire coated with a corrosion resistant metal has been proposed, but the free air ball (FAB) formed at the tip of the wire at the time of joining is not suitable or uneven for joining, the bonding strength is low, and the high humidity reliability There is a limit to this deterioration.

1. Korean Patent Publication No. 2006-0090700 (published 14/14/200) 2. Korean Patent Publication No. 2004-0058014 (published Jul. 2004)

The technical problem to be achieved by the technical idea of the present invention is to provide a method for producing a copper-based bonding wire having excellent bonding characteristics.

According to an aspect of the present invention, there is provided a method of manufacturing a copper-based bonding wire, including: preparing a core member including copper and unavoidable impurities; Forming a rough surface layer on the surface of the core member; Forming a cladding member comprising palladium on the rough surface layer; And forming a bonding wire including the core material coated with the coating layer by drawing the core member on which the covering member is formed.

In some embodiments of the invention, the rough surface layer may comprise copper, palladium, or a combination thereof.

In some embodiments of the present disclosure, the method may further include pretreating the surface of the core member between preparing the core member and forming the rough surface layer.

In some embodiments of the present invention, the preprocessing may be performed using a plasma.

In some embodiments of the present invention, the core material may have a mole fraction in the range of 98.6% to 99.3%, and the coating layer may have a mole fraction in the range of 0.7% to 1.4%.

In some embodiments of the present invention, when the bonding wire has a diameter of 15 μm or more and 20 μm or less, the coating layer may have a thickness in the range of 40 nm to 80 nm, and the bonding wire is more than 20 μm. In the case of having a diameter of 25 μm or less, the coating layer may have a thickness in the range of 50 nm to 110 nm.

In the method for manufacturing a copper-based bonding wire according to the technical idea of the present invention, forming a rough surface layer having an increased surface area on a covering member including copper and forming a covering member on the rough surface layer to form a free air ball. More uniform palladium distribution can be achieved, and a reliable and nearly spherical free air ball can be provided.

1 schematically illustrates a copper-based bonding wire according to an embodiment of the present invention.
2 schematically illustrates a semiconductor package including a copper-based bonding wire according to an embodiment of the present invention.
3 is a flowchart illustrating a method of manufacturing a copper-based bonding wire according to an embodiment of the present invention.
4 is a flowchart illustrating a method of manufacturing a copper-based bonding wire according to an embodiment of the present invention.
5A to 5D are scanning electron micrographs showing surfaces of copper-based bonding wires according to manufacturing process conditions of the copper-based bonding wires according to one embodiment of the present invention.
6 is a table showing a change in the copper-based bonding wire according to the manufacturing process conditions of the copper-based bonding wire according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Embodiments of the present invention are provided to more fully explain the technical idea of the present invention to those skilled in the art, and the following embodiments may be modified in many different forms, and The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the inventive concept to those skilled in the art. As used herein, the term "and / or" includes any and all combinations of one or more of the listed items. The same reference numerals denote the same elements at all times. Further, various elements and regions in the drawings are schematically drawn. Therefore, the technical idea of the present invention is not limited by the relative size or the distance drawn in the accompanying drawings. In embodiments of the present invention, wt% (% by weight) is the percentage of the weight of the component in the weight of the total alloy.

1 schematically illustrates a copper-based bonding wire according to an embodiment of the present invention.

Referring to FIG. 1, the copper-based bonding wire 10 may include a core 12 and a coating layer 14.

The core 12 may include copper and unavoidable impurities. For example, the core 12 may include copper (Cu) having a purity of about 99.99 wt% or more. In addition, the core material 12 may further include at least one of silver (Ag), calcium (Ca), and phosphorus (P) as an additive element. For example, the core 12 may include 0.0001 wt% to 0.01 wt% of additional elements and the remainder of copper and unavoidable impurities. When the additive element is silver (Ag), it may be in a range of 0.0001 wt% to 0.003 wt%. When the additional element is calcium (Ca), it may be in the range of 0.0001 wt% to 0.003 wt%. When the additive element is phosphorus (P), it may be in the range of 0.002 wt% to 0.01 wt%.

The coating layer 14 may be formed on the surface of the core 12. The coating layer 14 may include palladium (Pd) and unavoidable impurities. The palladium may have a purity of about 99.99 wt% or more.

In addition, the coating layer 14 may include a palladium-platinum alloy and unavoidable impurities. For example, the cladding layer 14 may include palladium in the range of about 60 wt% to about 98 wt% and about 2 wt% to about 40 wt% platinum. When the coating layer 14 contains palladium and platinum, the copper corrosion of the core material 12 can be effectively prevented, and the hardness of the free air ball can be lowered as compared with the case where the coating layer 14 is composed only of palladium. Problems caused by undesirably high levels of hardness of, for example, chip cratering or pad peeling can be reduced or avoided.

In the ratio of the core material 12 to the coating layer 14, the core material 12 may have a mole fraction in the range of about 98.6% to 99.3%, based on the copper-based bonding wire 10 as a whole. 14) may have a mole fraction in the range of about 0.7% to 1.4%. Here, the mole fraction represents the ratio of the number of moles occupied by the corresponding component to the number of moles of the total alloy, and represents the ratio of the number of atoms in the coating layer corresponding to the number of atoms of copper which is the main component of the core material. For example, if core 12 is copper and coating layer 14 is palladium, core 12 may range from about 97.6 wt% to about 98.6 wt% and coating layer 14 is 1.2 wt%. To about 2.4 wt%.

In addition, the copper-based bonding wire 10 may have a diameter of about 18 μm. Here, the diameter of the copper-based bonding wire 10 may correspond to the sum of the thicknesses of the core material 12 and the coating layer 14. However, the diameter of the copper-based bonding wire 10 is exemplary and the present invention is not limited thereto. For example, the copper-based bonding wire 10 may have a diameter in the range of about 15 μm to about 25 μm.

In addition, the coating layer 14 of the copper-based bonding wire 10 having a diameter in the range of 15 μm or more and 20 μm or less may have a thickness of about 40 nm to about 80 nm from the surface of the core 12, and more than 20 μm. The coating layer 14 of the copper-based bonding wire 10 having a diameter in the range of 25 μm may have a thickness of about 50 nm to about 110 nm from the surface of the core 12. However, the diameter of this coating layer 14 is exemplary and the present invention is not limited thereto.

2 schematically illustrates a semiconductor package 100 including a copper-based bonding wire 10 according to an embodiment of the present invention.

Referring to FIG. 2, the semiconductor package 100 includes the copper-based bonding wire 10 as described above according to the spirit of the present invention. The semiconductor package 100 may include a copper-based bonding wire electrically connecting the printed circuit board 20, the semiconductor chip 30 located on the printed circuit board 20, and the semiconductor chip 30 to the printed circuit board 20. 10) and a sealing material 50 for sealing the semiconductor chip 30 and the copper-based bonding wire 10. The solder ball 40 is attached to the lower side of the printed circuit board 20, and is electrically connected to the semiconductor chip 30 through the printed circuit board 20. Here, although the semiconductor package 100 is illustrated as including one semiconductor chip 30, the case of including a plurality of semiconductor chips is also included in the technical idea of the present invention.

The copper-based bonding wire 10 includes copper and inevitable impurities, and optionally includes a core 12 (see FIG. 1) further including at least one of silver (Ag), calcium (Ca), and phosphorus (P). And a coating layer 14 (see FIG. 1) formed on the surface of the core material 12 and containing palladium (Pd) and unavoidable impurities or a palladium-platinum alloy and unavoidable impurities. The core 12 may have a mole fraction in the range of about 98.6% to about 99.3%, and the coating layer 14 may have a mole fraction in the range of about 0.7% to about 1.4%. When the copper-based bonding wire 10 has a diameter in the range of 15 μm or more and 20 μm or less, the coating layer 14 may have a thickness of about 40 nm to about 80 nm from the surface of the core material 12, and When the bonding wire 10 has a diameter in the range of more than 20 μm and 25 μm, the coating layer 14 may have a thickness of about 50 nm to about 110 nm from the surface of the core 12.

3 is a flowchart illustrating a method of manufacturing a copper-based bonding wire according to an embodiment of the present invention.

Referring to Figure 3, the manufacturing method according to an embodiment of the present invention comprises the steps of preparing a core member (S10), pre-processing the surface of the core member (S12), the coating member on the surface of the core member And forming a bonding wire by drawing the forming step (S14) and the core member on which the covering member is formed (S16).

In the preparing of the core member (S10), the core member may include copper and impurities, and may include at least one of silver (Ag), calcium (Ca), and phosphorus (P) as additional elements. Can be. For example, the core member may comprise 0.0001 wt% to 0.01 wt% of additional elements and the balance copper and inevitable impurities. When the additive element is silver (Ag), it may be in a range of 0.0001 wt% to 0.003 wt%. When the additional element is calcium (Ca), it may be in the range of 0.0001 wt% to 0.003 wt%. When the additive element is phosphorus (P), it may be in the range of 0.002 wt% to 0.01 wt%. The core member may have a diameter of about 50 μm to about 200 μm. The core member may constitute the core 12 of FIG. 1 after a subsequent step.

In the step S12 of pretreating the surface of the core member, the surface of the core member may be cleaned using plasma. The plasma is used to clean the surface of the core member. The plasma may be formed using a vacuum plasma apparatus or may be formed using an atmospheric pressure plasma apparatus. The gas used for the plasma is a mixed gas having a constant flow rate. For example, the plasma may be formed using a reaction gas of any one of oxygen, nitrogen, argon, methane, helium, carbon dioxide, ozone, hydrogen, or a mixture thereof. The power used to generate such a plasma can range from about 5 W to about 100 W. However, these figures are exemplary and the present invention is not limited thereto.

Alternatively, in step S12 of pretreating the surface of the core member, the core member may be cleaned by a degreasing process or a pickling process.

In the forming of the coating member on the surface of the core member (S14), the coating member may be formed to surround the surface of the core member. The covering member may constitute the covering layer 14 of FIG. 1 after a subsequent step.

The coating member may be formed using a method such as electrolytic plating, electroless plating, evaporation, or deposition. The covering member may have a thickness of about 100 nm to about 900 nm. The coating member may include palladium (Pd) and unavoidable impurities. In addition, the covering member may include a palladium-platinum (Pt) alloy and unavoidable impurities. For example, the cladding member may comprise palladium in the range of about 60 wt% to about 98 wt% and about 2 wt% to about 40 wt% platinum.

In the step S16 of forming the bonding wire by drawing the core member on which the covering member is formed, the core member and the coating are drawn by drawing the core member on which the covering member is formed by using a drawing apparatus (not shown). The cross-sectional area of the member can be reduced. The bonding wire may correspond to the copper-based bonding wire 10 of FIG. 1. The finally formed bonding wire may have a diameter in the range of about 15 μm to about 25 μm, and the coating layer 14 (see FIG. 1) may have a thickness of about 40 nm to about 110 nm. For example, when the bonding wire has a diameter of 15 μm or more and 20 μm or less, the coating layer 14 (see FIG. 1) may have a thickness in the range of 40 nm to 80 nm. When the bonding wire has a diameter of more than 20 μm and 25 μm or less, the coating layer may have a thickness in the range of 50 nm to 110 nm.

Optionally, the method may further comprise annealing the fresh bonding wire. At this time, the annealing temperature may be, for example, in the range of about 400 ° C to about 700 ° C. This annealing process can alleviate the work hardening of the bonding wire drawn by the drawing process. In addition, the annealing process may further remove impurities remaining on the surface of the bonding wire as described above.

4 is a flowchart illustrating a method of manufacturing a copper-based bonding wire according to an embodiment of the present invention.

Referring to Figure 4, the manufacturing method according to an embodiment of the present invention comprises the steps of preparing a core member (S20), pretreatment on the surface of the core member (S21), the surface layer rough on the surface of the core member Forming a step (S22), forming a coating member on the rough surface layer (S24) and forming a bonding wire by drawing the core member on which the coating member is formed (S26).

In the preparing of the core member (S20), the core member may include copper and impurities, and may further include at least one of silver (Ag), calcium (Ca), and phosphorus (P) as additional elements. Can be. For example, the core member may comprise 0.0001 wt% to 0.01 wt% of additional elements and the balance copper and inevitable impurities. When the additive element is silver (Ag), it may be in a range of 0.0001 wt% to 0.003 wt%. When the additional element is calcium (Ca), it may be in the range of 0.0001 wt% to 0.003 wt%. When the additive element is phosphorus (P), it may be in the range of 0.002 wt% to 0.01 wt%. The core member may have a diameter of about 50 μm to about 200 μm. The core member may constitute the core 12 of FIG. 1 after a subsequent step.

In the step S21 of pretreating the surface of the core member, the surface of the core member may be cleaned using a plasma, a degreasing process, or a pickling process. The step S21 of pretreating the surface can be optional and omitted.

In the step S22 of forming the rough surface layer on the surface of the core member, the rough surface layer may be formed to surround the surface of the core member. The rough surface layer may be formed using a method such as electrolytic plating, electroless plating, evaporation, or deposition. The rough surface layer may have a thickness in the range of several nm to several tens of nm, and may be formed to increase the surface area by forming a rough surface. In addition, the rough surface layer may be the same material as the core member, or may be the same material as the coating member formed in a subsequent process. For example, the rough surface layer may be copper, palladium, or may comprise a combination of copper and palladium. Alternatively, the rough surface layer may comprise at least one of copper, palladium, and platinum.

In the forming of the coating member on the rough surface layer (S24), the coating member may be formed on the rough surface layer to surround the surface of the core member. The covering member may constitute the covering layer 14 of FIG. 1 after a subsequent step.

The coating member may be formed using a method such as electrolytic plating, electroless plating, evaporation, or deposition. The coating member may include palladium (Pd) and unavoidable impurities. In addition, the covering member may include a palladium-platinum (Pt) alloy and unavoidable impurities. For example, the cladding member may comprise palladium in the range of about 60 wt% to about 98 wt% and about 2 wt% to about 40 wt% platinum.

Since the rough surface layer provides a larger surface area than the smooth surface, the covering member can be bonded with the core member with a stronger adhesive force. Attaching with this stronger adhesion, more uniform palladium distribution can be achieved in the formation of free air balls (FABs) and can provide reliable and near spherical free air balls.

In the step (S26) of forming the bonding wire by drawing the core member on which the covering member is formed, the coating layer 14 is covered by drawing the core member on which the covering member is formed by using a drawing apparatus (not shown). A copper-based bonding wire including the core 12 is formed. By the drawing, the cross-sectional areas of the core member and the covering member can be reduced. The bonding wire may correspond to the copper-based bonding wire 10 of FIG. 1. The finally formed bonding wire may have a diameter in the range of about 15 μm to about 25 μm, and the coating layer 14 (see FIG. 1) may have a thickness of about 40 nm to about 110 nm. For example, when the bonding wire has a diameter of 15 μm or more and 20 μm or less, the coating layer 14 (see FIG. 1) may have a thickness in the range of 40 nm to 80 nm. When the bonding wire has a diameter of more than 20 μm and 25 μm or less, the coating layer may have a thickness in the range of 50 nm to 110 nm.

Optionally, the method may further comprise annealing the fresh bonding wire. At this time, the annealing temperature may be, for example, in the range of about 400 ° C to about 700 ° C. This annealing process can alleviate the work hardening of the bonding wire drawn by the drawing process. In addition, the annealing process may further remove impurities remaining on the surface of the bonding wire as described above.

5A to 5D are scanning electron micrographs showing surfaces of copper-based bonding wires according to manufacturing process conditions of the copper-based bonding wires according to one embodiment of the present invention.

Fig. 5A shows the surface of the core member before performing the above-described steps S12 and S21 for pretreating the core member.

5B and 5C show the surface of the core member after performing the steps S12 and S21 of pretreating the core member. FIG. 5B is a surface of the core member when pretreated using plasma, and FIG. 5C is a surface of the core member when pretreated using a degreasing step / pickling step.

5D shows the surface of the core member after performing step S24 of forming a rough surface layer on the surface of the core member. Compared with the surface of FIGS. 5A to 5C, the surface of the core member of FIG. 5D exhibits a rough surface shape. This rough surface shape provides a large surface area, as described above, so that the covering member can be bonded to the core member with a stronger adhesive force.

6 is a table showing a change in the copper-based bonding wire according to the manufacturing process conditions of the copper-based bonding wire according to an embodiment of the present invention.

The characteristic change of the copper-based bonding wire 10 according to the manufacturing process conditions of the copper-based bonding wire 10 according to the technical idea of the present invention will be examined based on the experimental data. In order to examine the change in the characteristics of the copper-based bonding wire 10, the free air ball (FAB) shape, bonding bonding force, surface palladium distribution, and high humidity reliability of the copper-based bonding wire 10 were evaluated by experiment.

The copper-based bonding wire used in the experiment changed the thickness of the core member (ie, before performing the drawing) to 25 μm, 50 μm, 200 μm, and 250 μm. The core member was coated with a coating member with a molar fraction varying from about 0.4% to about 1.8%. As described above, the core member had copper as a main component, and the coating member had palladium as a main component. Subsequently, the core member coated with the covering member was drawn to have a final bonding wire of about 18 μm. At this time, the covering member had a thickness in the range of about 20 nm to about 100 nm, and the thickness changed in relation to the mole fraction. Pretreatment of the core member was performed by selecting either plasma or degreasing / pickling. The properties of the bonding wires, such as free air ball (FAB) shape, bonding strength, surface Pd distribution, and high humidity reliability, were evaluated as good (good), good (triangle), and bad (x) as the standard bond wires require. .

The FAB shape was observed by scanning electron microscope (SEM) by making 100 FABs twice the wire diameter for each condition, and the FAB shape was distorted or not properly made, and there was an oxide on the surface. Prescribed. Where ○ (excellent) is the case where none of the FABs are out of 100 FABs, △ (normal) is the case where there are 3 or fewer bad FABs out of 100 FABs, and × (bad) is 3 bad FABs out of 100 FABs. It is shown as exceeding case. Secondary bonding (stitch bonding) bonding strength was measured 100 times each by using a bond pull tester (Dage 4000) after wire bonding for each condition, where ○ (excellent) is 2 It was a case where the primary bonding bonding force exceeds an average of 5 gr, (DELTA) is a case where a secondary bonding bonding force exceeds an average of 4 gr-5 gr or less, and x (bad) was shown as the case where a secondary bonding bonding force is 4 gr or less on average. The palladium distribution on the FAB surface was observed by using an optical microscope with 100 FABs twice the wire diameter for each condition, and the distribution ratio of gray palladium and red copper on the FAB surface was evaluated. Here, the ratio of gray-colored palladium is less than 80% is defined as a defect, ○ (excellent) is a case where none of the 100 FAB defects come out, △ (usually) is a case of 3 or less defects of 100 FAB, × (bad) was expressed as the case where more than 3 defectives out of 100 FABs. High Humidity Reliability is an open-short electrical test after 336 hours in which a wire-bonded semiconductor package is placed in an unbiased Highly Accelerated Temperature and Humidity Stress Test (130 ° C / 85% relative humidity) chamber. As a result of the test, an increase of more than 20% from the initial resistance value was defined as a failure. Herein, the package refers to a state in which the copper-based bonding wire 10 is bonded to the semiconductor chip 30 and the printed circuit board 20 to be electrically connected, and then sealed with a sealing material 50. An open shot test was conducted on the bonding wire. ○ (excellent) means no defects in the open-shot test, △ (normal) means 3 or less defects in the open-shot test, and × (bad) means that more than 3 defects in the open-shot test. Indicated by case.

Referring to FIG. 6, the diameter of the core member before the coating member is formed and the drawing process is 50 μm, and 200 μm is greater than that when the diameter of the core member is 25 μm and 250 μm. The property was found to be relatively good. Therefore, it is preferable that the diameter of the core member is in the range of 50 µm to 200 µm.

In addition, when the diameter of the core member is 50 µm and 200 µm, the type of pretreatment method is examined, and the characteristics of the bonding wire are relatively superior to the case of using the degreasing / pickling method when using the plasma pretreatment method. Found. Therefore, it is desirable to perform plasma pretreatment.

In addition, when the diameter of the core member is 50 µm and 200 µm, the molar fraction of the covering member is 0.4% and 1.8% when the molar fraction of the covering member is 0.7% and 1.4%. It was found that the properties of the bonding wire were relatively superior to the case of. This showed the same result for plasma pretreatment and degreasing / pickling pretreatment. Therefore, the mole fraction of the coating member is preferably 0.7% to 1.4%, which corresponds to 40 nm to 80 nm in thickness of the coating layer after carrying out the drawing process.

Therefore, the copper-based bonding wire according to the technical concept of the present invention preferably has a diameter of the core member in the range of 50 μm to 200 μm, performs plasma pretreatment, and furthermore, the mole fraction of the covering member is 0.7% to 1.4%. Do. In particular, it is most preferable that the diameter of the core member is 50 µm, the plasma pretreatment is performed, and the mole fraction of the covering member is 0.7%.

The technical spirit of the present invention described above is not limited to the above-described embodiment and the accompanying drawings, and various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in the art.

10: copper bonding wire, 20: printed circuit board,
30: semiconductor chip, 40: solder ball, 50: sealing material, 100: semiconductor package

Claims (6)

Preparing a core member including copper and unavoidable impurities;
Forming a rough surface layer on the surface of the core member;
Forming a cladding member comprising palladium on the rough surface layer; And
Forming a bonding wire including a core material coated with a coating layer by drawing the core member on which the covering member is formed;
Containing Method for producing a copper-based bonding wire. The method of claim 1,
And said rough surface layer comprises copper, palladium, or a combination thereof. The method of claim 1,
Between preparing the core member and forming the rough surface layer,
And pretreating the surface of the core member. The method of claim 3, wherein
The pretreatment is a method of manufacturing a copper-based bonding wire, characterized in that performed using a plasma. The method of claim 1,
The core material has a mole fraction in the range of 98.6% to 99.3%,
The coating layer is a method for producing a copper-based bonding wire, characterized in that it has a mole fraction in the range of 0.7% to 1.4%. The method of claim 1,
When the bonding wire has a diameter of 15 μm or more and 20 μm or less, the coating layer has a thickness in the range of 40 nm to 80 nm,
When the bonding wire has a diameter of more than 20 ㎛ 25 ㎛ or less, the coating layer has a thickness in the range of 50 nm to 110 nm.

Images