TW201420252A - High-temperature lead-free solder ball - Google Patents

Abstract

This invention discloses a high-temperature lead-free solder ball having a diameter of 10μm-1000μm and comprising a core layer that contains zinc. Preferably, the core layer further comprises 0.01-20wt% of aluminum, 0.01-12wt% of copper, or a combination of them. More preferably, the content of aluminum is 4wt%. Further, the core layer is provided with at least one coating layer at its exterior to enhance the wettability, solderability, oxidation resistance, and mechanical properties of the of the solder ball. The improvement of the present invention is mainly made possible by using zinc as the main material of the core layer, due to the fact that the zinc is nontoxic, non-polluting, and its melting temperature is greater than 260 DEG C, meeting the high-temperature requirements. It can indeed serve as a good material for package intervals balls and can improve the solder reliability between electronic components.

Description

High temperature lead-free solder ball

The invention relates to a solder ball, in particular to a high temperature lead-free solder ball.

Tin balls are widely used in electronic package modules. The solder balls can be used to bond electronic components to a printed circuit board or substrate at a predetermined interval, which is equivalent to a bonding agent and a spacer between electronic components.

The bonding material used in the first level is directly encapsulated with the Silicon Die, belonging to the innermost layer of the product, the ambient temperature is higher than the outer layer, and in order to avoid the bonding process of the second and third layers, Reflow, Wave Soldering and other steps, once the melting point of the material is not high enough, the first level of joints will even fail during the second and third level bonding steps, so the current first level Bonding is to use a material with a higher melting point (above 260 ° C), according to different packaging techniques to select the appropriate materials, including die attach (die attach), flip chip (Flip Chip) bonding and other technologies are first-level Construction technology.

The die bond refers to the process of bonding the die to the wafer carrier of the package substrate or the lead frame, and wire bonding is completed by wire bonding. Commonly used materials include Pb-5Sn of Soft Solder, Au-20Sn and Au-Si of Hard Solder, and polymer glue.

The flip chip bonding is a bonding technology developed by IBM in the United States in the 1960s. The difference from the wire bonding is that the flip chip bonding provides a high density surface. Array (Area Array), the junction density is much larger than the Peripheral Array, the solder bump is generated on the pad of the die, and the solder bump is aligned with the package substrate. The pad is re-welded to match the surface tension effect of the solder melting, so that the solder is balled to complete the bonding of the wafer to the substrate. Common bump components are Pb-5Sn, Sn-37Pb and Pb-50In alloys.

In addition to technologies such as die bonding and flip chip bonding, there are many applications where high-temperature solder balls, such as photovoltaic components, automotive electronic components, etc., which require a melting point temperature of 260 ° C or higher, can be called. High temperature solder balls. Currently known high-temperature solder balls usually use lead as the core material and tin on the outer core. Although lead can reach high temperature requirements, lead is poisonous and has a great destructive effect on the ecological environment. Another type of lead-free material is the aforementioned gold-tin alloy, but the cost of using gold is higher. Therefore, based on factors such as environmental protection, health and cost, it is necessary to develop a solder ball that does not contain lead but can reach high melting point requirements.

Therefore, the object of the present invention is to provide a high-temperature lead-free solder ball which is environmentally friendly, non-toxic and high-temperature, and which is low in cost.

Therefore, the high-temperature lead-free solder ball of the present invention has a diameter of 10 μm to 1000 μm and contains a core layer mainly composed of zinc.

Preferably, the core layer further comprises 0.01 to 20 wt% of aluminum, 0.01 to 12 wt% of copper, or a combination thereof. More preferably, the aluminum content is 4% by weight.

Preferably, the core layer further comprises 0.01 to 5 wt% of ruthenium, 0.01 to 5 wt%. Gallium, 0.01 to 1 wt% magnesium, 0.01 to 1 wt% titanium, 0.01 to 1 wt% chromium, or a combination thereof.

Preferably, the high temperature lead-free solder ball of the present invention further comprises a first cladding layer coated on the outside of the core layer, the material of which is tin, copper or nickel.

Preferably, the high-temperature lead-free solder ball of the present invention further comprises a second cladding layer coated on the outside of the first cladding layer, the second cladding layer being tin, silver, tin alloy containing nickel, and cobalt-containing Tin alloy, iron-containing tin alloy, or a combination of these.

Preferably, the high temperature lead-free solder ball of the present invention further comprises a bonding layer between the first cladding layer and the second cladding layer, the bonding layer comprising nickel.

The effect of the invention: zinc is used as the main material of the core layer, and the cost of using gold is lower than that of the prior, and since zinc is non-toxic and non-polluting, and its melting point is higher than 260 ° C and meets the high temperature requirement, it can be regarded as good. The material of the spacer ball is packaged and the soldering reliability between the electronic components can be improved. In addition, the first cladding layer and the second cladding layer can improve the wettability, solderability, oxidation resistance and mechanical properties of the solder ball, and the bonding layer is provided to facilitate the second cladding layer. Attached.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments and the embodiments. Before the present invention is described in detail, it is noted that in the following description, similar elements are denoted by the same reference numerals.

Referring to Figure 1, a first preferred embodiment of the high temperature lead-free solder ball of the present invention is packaged. And comprising: a core layer 1 and a first cladding layer 2 coated on the outside of the core layer 1. The high-temperature lead-free solder ball of the present invention mainly refers to a solder ball having a melting point of 260 ° C or higher.

The core layer 1 of the present embodiment is substantially spherical, and its material contains zinc (Zn). In fact, zinc may be completely used, or zinc may be used as a main component and other materials may be added. The concept that zinc is the main component and is a relatively large majority means that the weight percentage (wt%) of zinc in the core layer 1 is greater than the weight percentage of any other additive materials. When the weight of the core layer 1 is 100 wt%, the core layer 1 may further contain 0.01 to 20 wt% of aluminum (Al), 0.01 to 12 wt% of copper (Cu), or a combination thereof. The core layer 1 may be additionally added with aluminum or copper, or both aluminum and copper. Further, the core layer 1 may further comprise 0.01 to 5 wt% of germanium (Ge), 0.01 to 5 wt% of gallium (Ga), 0.01 to 1 wt% of magnesium (Mg), and 0.01 to 1 wt% of titanium (Ti). Between 0.01 and 1 wt% of chromium (Cr), or a combination of the above, that is, the core layer 1 may be additionally added with any one or more of yttrium, gallium, magnesium, titanium, and chromium.

The invention uses zinc as the main component of the core layer 1 because the melting point of zinc is about 420 ° C, and has the advantages of high hardness, non-toxicity and no pollution, and meets the high temperature requirement of the solder ball, so it is suitable for the core layer 1 . material. In addition, when the core layer 1 is added with one or more materials of aluminum, copper, lanthanum, gallium, magnesium, titanium, and chromium to form a zinc alloy, it has the effect of lowering the melting point of the alloy (but still meeting the high temperature requirement). Moreover, the structural strength, hardness, alloy oxidation resistance or wettability of the zinc alloy can be improved.

Wherein, in the case of adding aluminum, the core layer 1 may comprise 0.01 wt% to 20 wt% of aluminum, preferably 4 wt% of aluminum. When the core layer 1 contains appropriate In the case of aluminum, an aluminum-zinc eutectic alloy formed of aluminum and zinc can lower the melting point of the alloy. For example, when 4 wt% of aluminum is added, the melting point of the core layer 1 can be lowered to 390 ° C, and the core layer can be raised. The alloy hardness of 1 can make the core layer 1 meet the high temperature requirement and reduce the manufacturing cost. This is because the core layer 1 must be made into a molten state at a high temperature in order to be molded into a spherical body of a desired size. If the melting point temperature of the core layer material is too high, the material is heated to a molten state and formed into a spherical shape, which requires a long heating time and consumes a large amount of process energy. Therefore, the present invention conforms the core layer 1 to welding. At the same time as the high temperature requirement of the ball, it is preferable that the melting point of the core layer 1 does not need to be too high, so that the manufacturing cost can be reduced.

In addition, the addition of copper to the core layer 1 increases the hardness and strength of the alloy, improves the wear resistance of the alloy, and reduces intergranular corrosion. The addition of magnesium and titanium reduces intergranular corrosion, refines the alloy structure, and improves the wear resistance of the alloy. The addition of bismuth and gallium enhances the oxidation and color resistance of the alloy, and the bismuth and gallium have good thermal and electrical conductivity, which can wet most of the metals and oxides, thereby improving wettability and solderability. The addition of chromium increases the oxidation resistance and hardness of the alloy.

The first cladding layer 2 can be formed by, but not limited to, barrel plating, thereby completely encapsulating the core layer 1 therein. The material of the first cladding layer 2 is tin (Sn), copper or nickel (Ni), and copper is used as a cladding material because copper has good conductivity and can be used as a good electrical connection between electronic components. Moreover, copper can form a metal intermetallic compound (IMC) with the free zinc atoms in the core layer 1 to reduce the activity of zinc, avoid surface oxidation of zinc, lower the surface tension of the molten solder, and improve the wettability and resistance of the solder. oxygen Chemical. In addition, the first cladding layer 2 uses a material such as tin, copper or nickel, and can also reduce the reflow soldering temperature, and at the same time reduce the diffusion rate of the core layer 1 and the substrate solder material, thereby improving the core layer 1 The bonding interface strength with the substrate solder material has high wettability and solderability.

The main improvement of the present invention is that zinc is used as the main material of the core layer 1, and it has the advantages of being non-toxic and non-polluting with respect to the conventional use of lead, and has an advantage of low cost compared with the conventional use of gold. Moreover, the melting point of zinc is greater than 260 ° C and meets the high temperature requirements, which can meet the packaging requirements of the first level of die bonding, flip chip bonding, etc., and can be applied not only to a general ball grid array (BGA) package but also to a ball grid array (BGA) package. For example, a higher-order three-dimensional (3D) package of a stacked package on package (PoP) package can be used as a spacer ball to maintain the height between components and improve the reliability of package components. In addition, the core layer 1 itself can be used alone as a solder ball, and the present invention is not necessary to provide the first cladding layer 2. Soldering and flux are applied around the solder balls during soldering to allow solder balls to be soldered between the electronic components and the substrate or printed circuit board.

The high-temperature lead-free solder ball of the present invention has a diameter of 10 μm to 1000 μm as a whole, and the solder ball of this size can provide an appropriate distance between the electronic component and the substrate or the circuit board, which meets the required interval requirements.

Referring to FIG. 2, the second preferred embodiment of the high-temperature lead-free solder ball of the present invention is substantially the same as the structure of the first preferred embodiment. The difference is that the embodiment further includes: a coating on the first cladding a second cladding layer 3 outside the layer 2, the second cladding layer 3 completely covering the first cladding layer 2 therein, the material of which is tin, silver (Ag), tin alloy containing nickel (Ni) , tin alloy containing cobalt (Co) A tin alloy containing iron (Fe), or a combination of these. In this embodiment, the second cladding layer 3 is additionally added, and can be used to cooperate with the first cladding layer 2 to form a double coating on the outer layer of the core layer 1 to reduce the reflow soldering temperature and reduce the core layer 1 The diffusion rate of the solder material with the substrate improves the bonding interface strength of the core layer 1 and the substrate solder material, and has high wettability and solderability.

The second cladding layer 3 can be formed by, but not limited to, barrel plating, and the second cladding layer 3 can uniformly coat the first cladding layer 2 by a barrel plating method. Another advantage of providing the second cladding layer 3 is that because the second cladding layer 3 can improve the solderability of the solder ball, the assembler performing the soldering operation does not need to additionally apply tin to the solder ball. It helps to weld, and in fact it is not easy to apply evenly to apply tin. Therefore, in this embodiment, the second cladding layer 3 is directly formed by barrel plating, which is more convenient in application and has assembly advantages.

In addition, the alloy phase of copper and tin has Cu ₃ Sn and Cu ₆ Sn ₅ , so when the second cladding layer 3 is tin, it is easy to form Cu ₃ Sn and Cu ₆ Sn ₅ with the copper of the first cladding layer 2 . a metal compound. According to research, it is confirmed that the material properties of Cu ₃ Sn are brittle. If there is excessive Cu ₃ Sn in the solder ball, the solder joints may occur when the component vibration or electronic product generated during the operation of the electronic product falls to the ground. Since it is easy to form a cross section from the Cu ₃ Sn interface and peel off, excessive Cu ₃ Sn affects the joint strength of the solder joint. However, when the material of the second cladding layer 3 is a tin alloy containing nickel (doped nickel in a material mainly composed of tin, that is, Ni-doped Sn), the addition of nickel can help Cu ₆ Sn _{5 to} form, thereby suppressing Cu. ₃ The formation of Sn makes the thickness of Cu ₃ Sn thin, which is beneficial to improve the structural strength of the solder ball and the solder joint, thereby improving the reliability and durability of the electronic product.

Referring to FIG. 3, the third preferred embodiment of the high-temperature lead-free solder ball of the present invention is substantially the same as the structure of the second preferred embodiment. The difference is that the embodiment further includes: a first cladding layer 2 a bonding layer 4 with the second cladding layer 3. The bonding layer 4 is used to lift the bonding force between the second cladding layer 3 and the first cladding layer 2 to help the second cladding layer 3 to adhere. The material of the bonding layer 4 contains nickel, which also helps to enhance the overall structural strength of the solder ball. When the material of the second cladding layer 3 is tin and the material of the first cladding layer 2 is copper, the nickel of the bonding layer 4 can be used to prevent the mutual diffusion of tin and copper to react. On the other hand, even if copper and tin still partially diffuse, as described above, nickel contributes to suppressing the formation of Cu ₃ Sn, and the structural strength of the welded ball can be improved. Of course, when the material of the second cladding layer 3 is nickel, it is naturally unnecessary to use the bonding layer 4 made of nickel.

Specifically, the core layer 1 of the present invention may have a diameter of 10 μm to 800 μm, the first cladding layer 2 may have a thickness of 1 μm to 50 μm, and the bonding layer 4 may have a thickness of 1 μm to 50 μm. The thickness of the layer 3 may be from 1 μm to 50 μm. However, the above thickness is merely an example and is not intended to be a limitation of the present invention. Moreover, regardless of the fact that the present invention comprises several layers, the high-temperature lead-free solder ball has a diameter of 10 μm to 1000 μm as a whole.

Next, the effects of the present invention were confirmed by several experimental examples and several comparative examples of the present invention.

Referring to Table 1, the "core layer hardness" test method is based on the standard Vickers hardness test method. And "integral assembly" is the assembly yield. Judging, taking 1000 welding balls as an example, observing whether there is a situation in which assembly is impossible, and the fewer the balls that cannot be assembled, the lower the defect rate, that is, the higher the yield. Among them, "good" means that the assembly yield is higher than 99.5%, and "excellent" means that the assembly yield is higher than 99.9%. The so-called assembly means that the solder ball can be soldered and fixed on an object. The object in this experiment is a copper pad.

It can be seen from Table 1 that the experimental examples 1 to 17 of the present invention have a melting point of 420 ° C using a Zn core layer, which meets the melting point requirements of the high-temperature welded ball, and at the same time, the core layer has a hardness of about 55 Hv and has sufficient hardness ( In general, the hardness is more than about 20Hv, which is sufficient, and also has a very high assembly yield. It means that the solder ball of the present invention uses Zn as the main component of the core layer, and can indeed meet various conditions of the solder ball.

Referring to Table 2, the "Zn-4Al" in the table means that the core layer contains 4 wt% of Al and the balance is Zn. Similarly, "Zn-20Al" means that the core layer contains 20 wt% of Al, and the balance is Zn. As can be seen from the respective experimental examples of Table 2, when 4% by weight of Al was added to the core layer, the melting point of the core layer was lowered to 390 ° C due to the formation of a eutectic alloy of ZnAl. Moreover, the strength of the core layer is increased to 84 Hv, and thus it can be seen that the addition of an appropriate amount of Al helps to lower the melting point of the core layer and lower the manufacturing cost, and at the same time, the structural strength can be improved.

Referring to Table 3, it can be seen from Experimental Examples 25, 37-39 that when the aluminum content in the core layer is between 0.01 wt% and 20 wt% defined by the present invention, the melting point and hardness of the core layer are in accordance with the demand, and wherein 4% by weight of aluminum in Experimental Example 25 The content can achieve the best effect of lowering the melting point and enhancing the structural strength. In contrast, the aluminum content of Comparative Example 1 was too high at 22% by weight, resulting in an excessively high melting point temperature of the alloy to produce a spherical core layer.

Referring to Table 4, it can be seen from Experimental Examples 40 to 42 that when the copper content in the core layer is between 0.01 wt% and 12 wt% defined by the present invention, the melting point and hardness of the core layer are in accordance with the demand. In contrast, the copper content of Comparative Example 2 was too high at 14% by weight, resulting in an excessively high melting point temperature of the alloy to produce a spherical core layer.

Referring to Table 5, it can be seen from Experimental Examples 43 to 51 that the aluminum and copper of the core layer fall within the numerical range defined by the present invention, that is, 0.01 to 20% by weight of aluminum and 0.01 to 12% by weight of copper. In the experimental examples 43 to 51, the requirements of the melting point, hardness, and assembly property of the solder ball were also achieved. In contrast, the copper content of Comparative Example 3 is If it is too high at 14 wt%, the melting point temperature of the alloy is too high to produce a spherical core layer.

Referring to Table 6, it can be seen from the experimental examples of Table 6, that the core layer of yttrium, gallium, magnesium, titanium or chromium falls within the numerical range defined by the present invention, and the experimental examples can also reach the melting point of the solder ball. Requirements for characteristics such as hardness and assembly. In contrast, the content of the additive element in the core layer of Comparative Examples 4 to 9 was too high to produce a spherical core layer.

Referring to Table 7, the oxidation resistance was judged by placing the solder ball alloy of each sample in an oven and taking it out at a temperature of 200 ° C for 30 minutes in an air atmosphere, and taking out and observing the change in surface brightness of the solder alloy. . Among them, the ability to resist oxidation is the ability to resist color change, and the manner of recording is as follows: ○: indicates that the surface of the solder alloy still retains the brightness of the metal, and the degree of oxidation is extremely slight or almost absent; △: It means that the surface of the solder alloy exhibits a similar color to yellow or blue or purple, and the degree of oxidation is more remarkable.

It can be seen from Table 7 that in Experimental Examples 8 and 47, when antimony and gallium were not added, the oxidation resistance was insufficient but still usable. In the experimental examples 52-57, 67-69, when an appropriate amount of bismuth and gallium were added, the oxidation resistance was indeed improved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

1‧‧‧ core layer

2‧‧‧First cladding

3‧‧‧Second coating

4‧‧‧ bonding layer

1 is a schematic cross-sectional view showing a first preferred embodiment of the high-temperature lead-free solder ball of the present invention; and FIG. 2 is a cross-sectional view showing the high-temperature lead-free solder ball of the present invention. A second preferred embodiment; and Figure 3 is a cross-sectional view showing a third preferred embodiment of the high temperature lead-free solder ball of the present invention.

1‧‧‧ core layer

2‧‧‧First cladding

Claims (11)

A high-temperature lead-free solder ball having a diameter of 10 μm to 1000 μm and comprising a core layer mainly composed of zinc. The high temperature lead-free solder ball according to claim 1, wherein the core layer further comprises 0.01 to 20 wt% of aluminum, 0.01 to 12 wt% of copper, or a combination thereof. The high-temperature lead-free solder ball according to claim 1 or 2, wherein the core layer further comprises 0.01 to 5 wt% of antimony, 0.01 to 5 wt% of gallium, 0.01 to 1 wt% of magnesium, and 0.01 to 1 wt% of Titanium, 0.01 to 1 wt% chromium, or a combination of these. The high-temperature lead-free solder ball according to claim 1 or 2, further comprising a first cladding layer coated on the outside of the core layer, the material of which is tin, copper or nickel. The high-temperature lead-free solder ball according to claim 4, further comprising a second cladding layer coated on the outside of the first cladding layer, the second cladding layer being tin, silver, tin containing tin Alloy, cobalt-containing tin alloy, iron-containing tin alloy, or a combination of these. The high-temperature lead-free solder ball according to claim 5, further comprising a bonding layer between the first cladding layer and the second cladding layer, the bonding layer comprising nickel. The high-temperature lead-free solder ball according to claim 3, further comprising a first cladding layer coated on the outside of the core layer, the material of which is tin, copper or nickel. According to the high-temperature lead-free solder ball described in item 7 of the patent application scope, a second cladding layer coated on the outside of the first cladding layer, the second cladding layer being tin, silver, a tin alloy containing nickel, a tin alloy containing cobalt, a tin alloy containing iron, or the like One of the combinations. The high-temperature lead-free solder ball according to claim 8, further comprising a bonding layer between the first cladding layer and the second cladding layer, the bonding layer comprising nickel. The high temperature lead-free solder ball according to claim 1, wherein the core layer further comprises 4 wt% of aluminum. The high-temperature lead-free solder ball according to claim 1 of the patent application scope is used for a ball grid array package or a three-dimensional package.