TWI870039B - Tin solder including third phase material and application thereof - Google Patents

Abstract

The present invention relates to a tin solder including third phase material and an application thereof. The tin solder includes a matrix and a third phase material, and the third phase material includes hydrophobic cellulose nanofibers. The matrix is composed of alloy powders and a flux. There are amide groups with specific carbon numbers on surfaces of the hydrophobic cellulose nanofibers, a specific amount of the hydrophobic cellulose nanofibers can be used as nucleation sites for reflowing molten alloy powders. After the solder balls are produced by the tin solder, grains surround the hydrophobic cellulose nanofibers, thereby enhancing a binding strength of the solder balls.

Description

Tin solder containing third phase material and its application

The present invention relates to a solder and its application, and in particular to a solder containing a third phase material to improve the bonding strength of solder balls and its application.

Known solder includes alloy powder and flux. Flux usually uses a tantalum to reduce the particle size of the solder ball made from the solder, thereby increasing the bonding strength of the solder ball to the solder joint. However, the tantalum increases the amount of flux residue, requiring an additional cleaning process or reducing the residue by an acidic cleaner. However, during solder welding, the acidic cleaner may corrode the solder joint (such as the solder pad).

Another known solder may contain hydrophilic heat-resistant particles to reduce the droop effect of the solder when heated and reduce the amount of flux residue, but this solder must use water as a medium to evenly distribute the hydrophilic heat-resistant particles in the solder. In addition, the high temperature of soldering will vaporize water, thereby destroying the crystallinity of the molten alloy powder during reflow, thereby increasing the grain size of the solder ball produced by this solder, resulting in a decrease in the bonding strength of the solder ball to the solder joint.

In view of this, it is urgent to develop a new solder material to improve the above-mentioned shortcomings of the conventional solder material and the solder ball made therefrom.

In view of the above problems, one aspect of the present invention is to provide a solder containing a third phase material. The solder includes a matrix and a third phase material, the third phase material includes a plurality of hydrophobic cellulose nanofibers, and the matrix is composed of alloy powder and flux. By using a specific amount of hydrophobic cellulose nanofibers and amide groups with a specific number of carbon atoms on their surfaces, these hydrophobic cellulose nanofibers are used as nucleation points during the reflow of molten alloy powder, and a plurality of crystal grains are formed around these hydrophobic cellulose nanofibers, thereby improving the bonding strength of the solder ball.

Another aspect of the present invention is to provide a solder ball. The solder ball is made by heating the solder containing the third phase material, and has a plurality of grains inside, thereby improving the bonding strength of the solder ball.

According to one aspect of the present invention, a solder containing a third phase material is provided. The solder comprises a matrix and a third phase material, wherein the third phase material comprises a plurality of hydrophobic cellulose nanofibers. The matrix is composed of alloy powder and flux, and a plurality of surfaces of these hydrophobic cellulose nanofibers have amide groups with carbon numbers of 6 to 18. Based on a usage amount of 10 ⁶ ppm for the matrix, the usage amount of these hydrophobic cellulose nanofibers is 10 ppm to 600 ppm.

According to one embodiment of the present invention, the alloy powder comprises 1 weight percent to 5 weight percent of silver, 0.1 weight percent to 1.0 weight percent of copper, and the balance of tin.

According to another embodiment of the present invention, the flux is selected from a group consisting of resin, solvent, activator, activator and any combination thereof.

According to another embodiment of the present invention, the average diameter of the hydrophobic cellulose nanofibers is 3 nm to 4 nm.

According to another embodiment of the present invention, the average length of the hydrophobic cellulose nanofibers is greater than 1 μm to 10 μm.

According to another embodiment of the present invention, the contact angles of the surfaces of the hydrophobic cellulose nanofibers to water are 114 to 130 degrees.

According to one embodiment of the present invention, the solder does not contain water.

Another aspect of the present invention is to provide a solder ball. The solder ball is made by heating the solder containing the third phase material. The solder ball comprises an alloy body and a third phase material distributed in the alloy body. The alloy body is formed by heating the alloy powder and the flux. The third phase material comprises a plurality of hydrophobic cellulose nanofibers, and the hydrophobic cellulose nanofibers have a plurality of crystal grains around them.

According to one embodiment of the present invention, the grains are equiaxed grains.

According to another embodiment of the present invention, the average grain size of the grains is 15 μm to 22 μm.

The solder containing the third phase material of the present invention includes a matrix and a third phase material, wherein the third phase material includes a plurality of hydrophobic cellulose nanofibers, and the matrix is composed of alloy powder and flux. The hydrophobic cellulose nanofibers with a specific amount of usage and the amide groups with a specific carbon number on their surfaces can be used as nucleation points when the molten alloy powder is reflowed. When the above solder is made into a solder ball, the periphery of these hydrophobic cellulose nanofibers has a plurality of grains, thereby improving the bonding strength of the solder ball.

The making and using of embodiments of the present invention are discussed in detail below. However, it will be appreciated that the embodiments provide many applicable inventive concepts that can be implemented in a wide variety of specific contexts. The specific embodiments discussed are for illustration only and are not intended to limit the scope of the present invention.

The present invention provides a solder containing a third phase material, which includes a matrix and hydrophobic cellulose nanofibers. The matrix is composed of alloy powder and flux. A specific example of the matrix can be a commercially available lead-free solder paste, such as a silver-copper series solder paste, or a solder paste known to those of ordinary skill in the technical field to which the present invention belongs. In some embodiments, the alloy powder contains 1 weight percent to 5 weight percent of silver, 0.1 weight percent to 1.0 weight percent of copper, and a balance of tin. Preferably, the alloy powder has 3.0 weight percent of silver, 0.5 weight percent of copper, and 96.5 weight percent of tin, so as to facilitate the formation of a crystalline structure when the molten alloy powder is reflowed.

The aforementioned flux can be selectively selected from a group consisting of resin, solvent, activator, activator and any combination thereof. The following are examples of the various components of the flux. The resin can selectively include rosin resin, terpene resin, terpene phenol resin, styrene resin, xylene resin or any combination thereof.

Secondly, the above-mentioned solvent may selectively include a low-boiling point or easily vaporized solvent, such as an alcohol-based solvent, an ether-based solvent, etc., and specifically may include alcohol and propylene glycol. Furthermore, the tactile agent may selectively include a wax-based tactile agent, an amide-based tactile agent, or any combination of the above-mentioned tactile agents. For example, the wax-based tactile agent may be sesame oil, etc., and the amide-based tactile agent may be lauric acid amide, palmitic acid amide, stearic acid amide, etc.

The activator can reduce the metal oxide at the high temperature of soldering (e.g., 300°C to 450°C) to enhance the bonding strength of the solder ball to the solder joint. For example, the activator can selectively include chlorides, bromides, carbonyl acids, and amines.

The "hydrophobic cellulose nanofiber" in this case refers to a cellulose nanofiber having an amide group with carbon numbers of 6 to 18 on its surface. If the surface of the hydrophobic cellulose nanofiber does not have an amide group with carbon numbers of 6 to 18, or the amide group is not heat-resistant, or the surface of the hydrophobic cellulose nanofiber cannot be wetted by the molten alloy powder, such hydrophobic cellulose nanofiber cannot serve as a nucleation point during reflow, which will reduce the bonding strength of the solder ball to the solder joint.

For example, the contact angle of the surface of the hydrophobic cellulose nanofiber to water can be selectively 114 degrees to 130 degrees. When this contact angle is within the aforementioned range, it is helpful to mix the hydrophobic cellulose nanofiber with the oleophilic flux to enhance the effect of the hydrophobic cellulose nanofiber as a nucleation point. In addition, the surface energy of the surface of the hydrophobic cellulose nanofiber to water can be selectively 1 mN/m to 20 mN/m. When this surface energy is within the aforementioned range, it is helpful to the wetting effect of the molten alloy powder on the surface of the hydrophobic cellulose nanofiber to enhance the effect of the hydrophobic cellulose nanofiber as a nucleation point.

In some embodiments, the hydrophobic cellulose nanofibers having amide groups with carbon numbers of 6 to 18 are prepared by reacting cellulose nanofibers having carboxyl groups on the surface with alkylamine compounds having carbon numbers of 6 to 18, wherein the cellulose nanofibers having carboxyl groups on the surface are obtained by carboxyl alkylation of glucose units in cellulose molecules. The aforementioned carboxyl alkylation can be performed using conditions known to those skilled in the art to which the present invention belongs.

For example, the alkylamine compound having 6 to 18 carbon atoms may include hexylamine, heptylamine, 2-heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine, heptadecanylamine, octadecylamine or any combination of the above alkylamine compounds.

In some embodiments, the average diameter of the hydrophobic cellulose nanofibers can be selectively 1 nm to 10 nm. When the average diameter of the hydrophobic cellulose nanofibers is within the aforementioned range, it is helpful to mix the hydrophobic cellulose nanofibers with the molten alloy powder and the oleophilic flux to enhance the effect of the hydrophobic cellulose nanofibers as nucleation points.

Furthermore, in the aforementioned embodiment, the average length of the hydrophobic cellulose nanofibers can be selectively 0.5 μm to 10 μm. When the average length of the hydrophobic cellulose nanofibers is within the aforementioned range, the crystallinity of the molten alloy powder during reflow is promoted to reduce the grain size of the solder ball, thereby improving its bonding strength to the solder joint.

Based on the usage of 10 ⁶ ppm of the matrix, the usage of the hydrophobic cellulose nanofiber is 10 ppm to 600 ppm, preferably 50 ppm to 100 ppm, and more preferably 200 ppm to 500 ppm. If the usage of the hydrophobic cellulose nanofiber is less than 10 ppm, the nucleation points of the hydrophobic cellulose nanofiber are insufficient, resulting in a decrease in the bonding strength of the solder ball to the solder joint. On the contrary, if the usage of the hydrophobic cellulose nanofiber is greater than 600 ppm, it will be unfavorable for the formation of a crystal structure during the reflow of the molten alloy powder, thereby reducing the bonding strength of the solder ball to the solder joint.

In some embodiments, the solder may be selectively free of water to avoid moisture generated by high-temperature vaporized water during soldering. The moisture may destroy the crystallinity of the molten alloy powder during reflow and reduce the bonding strength of the solder ball to the solder joint.

Another aspect of the present invention is to provide a solder ball. This solder ball is made by using the aforementioned solder containing the third phase material through a heating step. This solder ball includes an alloy body and a plurality of hydrophobic cellulose nanofibers distributed in the alloy body, wherein the hydrophobic cellulose nanofibers have a plurality of grains around them. As mentioned above, the solder includes a matrix and hydrophobic cellulose nanofibers, and the matrix is composed of alloy powder and flux. The aforementioned heating step is used to provide the high temperature required for melting the alloy powder (such as the temperature used for welding, which can be 300°C to 450°C) to melt the matrix. Then, the molten matrix is cooled to form an alloy body, that is, the alloy body is formed by the alloy powder and the flux through the aforementioned heating step. As is understood by those skilled in the art, the high temperature in the heating step melts the alloy powder contained in the matrix into a molten alloy and causes other components contained in the matrix (such as resin, solvent, mutagenic agent and activator) to undergo chemical and/or physical reactions.

In some specific examples, the grains may be selectively equiaxed crystal structures. For example, a solder ball formed by a matrix containing 10 ⁶ ppm and 500 ppm of hydrophobic cellulose nanofibers has equiaxed crystal grains. When the grains are equiaxed crystals, the bonding strength of the solder ball to the solder joint can be improved. In contrast, the grains of the solder ball formed by only the matrix are non-equiaxed crystals, and the average grain size of the grains is coarser.

In some embodiments, the average grain size of the grains may be 15 μm to 22 μm. When the average grain size of the grains is within the aforementioned range, the bonding strength of the solder ball to the solder joint may be enhanced.

The following embodiments are used to illustrate the application of the present invention, but they are not used to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention.

Manufacturing of solder containing third phase material

Embodiment 1

After the hydrophobic cellulose nanofibers (as the third phase material) and isopropyl alcohol are mixed at a weight ratio of 1:3 to 1:40, the hydrophobic cellulose nanofibers are dispersed in the isopropyl alcohol to obtain a hydrophobic cellulose nanofiber solution. Then, the hydrophobic cellulose nanofiber solution and a commercially available solder paste (manufactured by Shengmao Technology Co., Ltd., product model SAC305) are mixed at a weight ratio of 0.01:99.99 to 0.5:99.5 to prepare the solder of Example 1.

The surface of the hydrophobic cellulose nanofiber has an amide group with a carbon number of 6 to 18, and its contact angle to water is 114 to 130 degrees, and its surface energy is 10 mN/m. In addition, the commercially available solder paste (as a matrix) is composed of alloy powder and flux. The flux includes a resin, a solvent, a thixotropic agent and an activator. In the above embodiment, the alloy powder has 3.0 weight percent of silver, 0.5 weight percent of copper and 96.5 weight percent of tin.

Examples 2 to 4 and Comparative Examples 1 to 2

Examples 2 to 4 and Comparative Example 2 were performed in the same manner as Example 1. The difference is that Example 2 used different amounts of hydrophobic cellulose nanofibers, and Examples 3 to 4 used different amounts of hydrophobic cellulose nanofibers, but no isopropyl alcohol was used. The solder of Comparative Example 1 only used the aforementioned commercially available solder paste without a third phase material. Comparative Example 2 used hydrophilic cellulose nanofibers with carboxyl groups on the surface as the third phase material. The specific conditions and evaluation results of the aforementioned Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1 below.

Evaluation method

1. Average diameter and average length of cellulose nanofibers

The cellulose nanofibers were photographed using a scanning electron microscope, and their diameter and length were measured. The average diameter and average length were obtained from several data. The test conditions were the conditions commonly used by those skilled in the art to which the present invention belongs. The results are shown in FIG. 1A and FIG. 1B .

Please refer to FIG. 1A and FIG. 1B, which respectively show scanning electron microscopic images of solder balls according to Example 1 (FIG. 1A) and Comparative Example 1 (FIG. 1B) of the present invention. As shown in FIG. 1A, the grains of the solder balls of Example 1 are equiaxed crystals (average grain size is 15.18±6.98 μm), which can enhance the bonding strength of the solder balls to the solder joints. In contrast, Comparative Example 1 contains only solder balls formed by the matrix, and the grains are non-equiaxed crystals (average grain size is 28.04±13.42 μm), as shown in FIG. 1B.

2. Contact angle and surface energy of hydrophobic cellulose nanofiber surfaces

Hydrophobic cellulose nanofibers were pressed into a plate with a rectangular surface of 5 cm × 5 cm, and deionized water was dropped onto the rectangular surface. Then, the contact angle of the water drop on the sample surface was measured using a commercially available contact angle analyzer (e.g. Phoenix-MT device, SEO, Korea) and commercially available software (e.g. Surfaceware 9 software, SEO, Korea), and the surface energy of the sample was calculated using the Owens-Wendt- Rabel-Kaelble (OWRK) model.

3. Average particle size and crystal structure of the tin ball, and the distribution density of hydrophobic cellulose nanofibers in the tin ball

The average grain size and crystal structure of the solder balls obtained after reflow, as well as the distribution density of hydrophobic cellulose nanofibers in the alloy body of the solder balls were measured using a scanning electron microscope and backscattered electron diffraction (EBSD) technology. The soldering condition was heating to 230°C and holding the temperature for 10 seconds.

4. Bond strength

According to the standard of MIL-STD-883F method 2019.7, the bonding strength of the solder ball to the solder pad is measured, wherein the amount of solder used is 3 mg, and the size of the solder ball is a solder ball with an average diameter of 633μm. After soldering and reflow at 230 °C, the bonding strength of the solder ball to the solder pad is evaluated by the force applied to separate the solder ball from the solder pad, and the specific evaluation standards are as follows. ◎: The bonding strength between the solder ball and the solder pad is extremely high ○: The bonding strength between the solder ball and the solder pad is very strong △: The bonding strength between the solder ball and the solder pad is fair ×: The bonding strength between the solder ball and the solder pad is very weak

Table 1 Embodiment Comparison Example 1 2 3 4 1 2 Composition Commercial solder paste Usage (ppm) 10 ⁶ 10 ⁶ 10 ⁶ 10 ⁶ Use only commercially available solder paste 10 ⁶ Hydrophobic Cellulose Nanofiber (CNF) Carbon number of amide group 6~18 6~18 6~18 6~18 No use Usage (ppm) 50~100 200~500 50~100 200~50 Diameter(nm) 3~4 3~4 3~4 3~4 Length(μm) 1~10 1~10 1~10 1~10 Hydrophilic Cellulose Nanofiber (CNF) Usage (ppm) No use No use No use No use No use 10~15 Isopropyl alcohol (IPA) Usage (ppm) 7.5~1000 7.5~1000 No use No use No use No use water Usage (ppm) No use No use No use No use No use 7.5~1000 Test results Tin Ball Grain size (μm) 15.18±6.98 14~16 28.04 28.04 28.04±13.42 Unable to form solder balls Bond strength 8.23 MPa 10.07 Mpa 7.7 MPa 7.7 MPa 7.7 MPa (×)

Please refer to Table 1. Compared with Comparative Examples 1 to 2, Examples 1 to 4 use hydrophobic cellulose nanofibers with amide groups with a specific number of carbon atoms on the surface. The hydrophobic cellulose nanofibers can provide nucleation points when the molten alloy powder is reflowed, thereby reducing the grain size of the solder ball made from the solder, thereby improving the bonding strength of the solder ball to the solder joint.

Furthermore, compared to Examples 1 to 2, Examples 3 to 4 do not use isopropyl alcohol (IPA), and directly add hydrophobic cellulose nanofibers to the matrix, which can simplify the solder process. As the amount of hydrophobic cellulose nanofibers used increases, the grain size of the solder balls produced by Examples 1 to 2 has a decreasing trend. Example 3, Example 4 and Comparative Example 1 do not contain IPA, and there is an exclusion phenomenon after reflow, so the grain size of the solder balls produced does not change. Comparative Example 2 cannot form solder balls because hydrophilic cellulose nanofibers (CNF) are added.

In summary, the solder containing the third phase material of the present invention comprises a matrix and a third phase material, and the third phase material comprises hydrophobic cellulose nanofibers. The surface of these hydrophobic cellulose nanofibers has an amide group with a specific carbon number, and the hydrophobic cellulose nanofibers with a specific usage amount can be used as a nucleation point when the molten alloy powder is reflowed. When the solder is made into a solder ball, the periphery of these hydrophobic cellulose nanofibers has a plurality of grains, thereby improving the bonding strength of the solder ball.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field to which the present invention belongs can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined in the attached patent application.

without

In order to have a more complete understanding of the embodiments of the present invention and its advantages, please refer to the following description and the corresponding drawings. It must be emphasized that the various features are not drawn to scale and are only for illustration purposes. The contents of the relevant drawings are described as follows: [Figure 1A] and [Figure 1B] respectively show scanning electron microscopic images of solder balls according to Embodiment 1 (Figure 1A) and Comparative Example 1 (Figure 1B) of the present invention.

Claims (8)

A tin solder containing a third phase material comprises: a substrate, wherein the substrate is composed of alloy powder and flux; and a third phase material, wherein the third phase material comprises a plurality of hydrophobic cellulose nanofibers, a plurality of surfaces of the hydrophobic cellulose nanofibers having amide groups with carbon numbers of 6 to 18, and a contact angle of the surfaces of the hydrophobic cellulose nanofibers to water is 114 degrees to 130 degrees, wherein based on a usage amount of the substrate of 10 ⁶ ppm, a usage amount of the hydrophobic cellulose nanofibers is 10 ppm to 600 ppm. The tin solder containing the third phase material as described in claim 1, wherein the alloy powder contains 1 weight percent to 5 weight percent of silver, 0.1 weight percent to 10 weight percent of copper, and the balance of tin. The tin solder containing the third phase material as described in claim 1, wherein the flux is selected from a group consisting of a resin, a solvent, a throttling agent, an activator and any combination thereof. The tin solder containing the third phase material as described in claim 1, wherein the average diameter of the hydrophobic cellulose nanofibers is 1nm to 10nm. A tin solder containing a third phase material as described in claim 1, wherein the average length of the hydrophobic cellulose nanofibers is 0.5 μm to 10 μm. A solder containing a third phase material as described in claim 1, wherein the solder does not contain water. A solder ball is prepared by a heating step using a solder containing a third phase material as described in any one of claims 1 to 6, wherein the solder ball comprises: an alloy body, wherein the alloy body is formed by alloy powder and flux through the heating step; and a third phase material is distributed in the alloy body, wherein the third phase material comprises a plurality of hydrophobic cellulose nanofibers, the hydrophobic cellulose nanofibers have a plurality of grains around them, and an average grain size of the grains is 15μm to 22μm. The tin ball as described in claim 7, wherein the grains are equiaxed.