A low-temperature solder

Abstract

This invention discloses a low-temperature solder, particularly a low-temperature solder with a soldering temperature of 160 to 190°C. By weight percentage, the low-temperature solder comprises 74-85% raw materials, 11-15% flux, and 2-12% porous carrier. The raw materials include tin and bismuth, and the porous carrier is mainly composed of polypropylene (PP) spherical carrier particles. When using this solder, the solder joints not only have a good surface gloss but also exhibit good acid and corrosion resistance. This solder effectively solves the technical problems of insufficient surface hardness and inadequate corrosion resistance of current lead-free solders after use.

Description

Technical Field

[0001] This invention relates to the field of electronic solder technology, specifically to a low-temperature solder. Background Technology

[0002] In the electronic packaging industry, the connection between components is mainly based on soldering materials. Traditional solder is mainly tin-lead solder. Lead itself is highly toxic and will cause long-term pollution. The harm to the environment and human body is self-evident. In order to meet environmental protection requirements, tin-lead solder will be gradually replaced by lead-free solder.

[0003] With the development of electronic information products towards ultra-large-scale integration and miniaturization, solder paste has become the most important process material in surface mount technology (SMT). Traditional solder paste generally uses SAC series alloys (tin-silver-copper series alloys) as soldering materials, and the soldering temperature usually needs to be higher than 240℃. In the soldering process of highly integrated microelectronic devices, it is easy to cause problems such as device deformation. Therefore, solder pastes with tin-bismuth series alloys as low-temperature solders are now more commonly used.

[0004] However, because this type of solder paste contains a large amount of bismuth metal, the solder joints have low toughness, causing electronic devices to fail to meet performance requirements. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature solder to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A low-temperature solder with a soldering temperature of 160 to 190°C, comprising, by weight percentage, 74 to 85% raw materials, 11 to 15% flux, and 2 to 12% porous carrier, wherein the raw materials include tin and bismuth, and the porous carrier is composed of polypropylene (PP) spherical carrier particles.

[0008] Furthermore, the diameter of the polypropylene (PP) spherical carrier particles is N, 200μm≤N≤1200μm, and the internal porosity is not less than 55%. Specifically, microporous foamed polypropylene (MPP) is used.

[0009] Furthermore, the raw materials also include silver, copper, molybdenum, indium, and antimony, wherein bismuth accounts for 14%, indium for 7%, molybdenum for 1.8%, silver for 1.5%, copper for 0.3%, antimony for 0.1%, and the remainder is tin.

[0010] Furthermore, the flux includes rosin, thickener, additives, and deionized water.

[0011] Furthermore, the rosin comprises 20%, the thickener comprises 30%, and the additive comprises 5%, wherein the rosin is one or more of acrylic rosin, disproportionated rosin, hydrogenated rosin, and polymerized rosin, the thickener comprises triethylamine and Span in a weight ratio of 30:2, and the additive comprises glutaric acid and salicylic acid in a weight ratio of 1:1.

[0012] Furthermore, the flux also includes a 3% mixture, which includes one or more of polyethylene glycol, terpene oil, alcohol ether, and alkyl alcohol.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] A method for preparing a low-temperature solder, comprising:

[0015] Step 1: Place the flux into a melting crucible, heat to melt, and stir thoroughly;

[0016] Step 2: Then place the raw material and porous carrier in the mixture, heat to 120-150℃, and maintain for 5-10 minutes;

[0017] Step 3: Remove the impurities from the surface of the molten alloy, then pour it into the mold and let it cool.

[0018] Furthermore, the temperature in step 1 is 100-120℃, and the heating rate in step 2 is 80-100℃ / min.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] In this invention, a porous carrier is employed. At temperatures of 120-150°C, the micropores of the porous carrier can be enlarged, resulting in larger diameter and denser micropores. This facilitates the rapid dispersion and filling of raw materials such as tin, bismuth, copper, and antimony, reducing preparation time. Simultaneously, it improves the metallographic structure of the reinforcing material and promotes dispersion hardening of the mixture's interior and surface, increasing the surface hardness of the prepared solder joints. Furthermore, a soldering temperature of 160-190°C allows the solder to be used for soldering. At this temperature, the porous carrier begins to melt, allowing it to be released along with the raw materials onto the circuit board (substrate) to be soldered. This results in good solder flowability, enabling rapid soldering. Simultaneously, the liquid solder has very low viscosity, allowing it to quickly wet the soldering surface upon reaching its melting temperature, improving the tight contact between the substrate and the solder, and facilitating the contact reaction and melting process. Due to the presence of a porous carrier, a dense protective film can form on the surface of the solder joint after cooling, provided the raw material contains silver. This results in solder joints with not only a good surface gloss but also excellent acid and corrosion resistance. Furthermore, the addition of copper, molybdenum, indium, and antimony further enhances the hardness and corrosion resistance of the solder joints. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) reveal that the solder joints have a smooth and relatively flat outer surface. Visually, the solder joints are exceptionally bright, full, and free of bridging. During use, they readily bond well with the substrate (solid material), resulting in smooth and aesthetically pleasing welds. Therefore, the solder of this invention effectively solves the technical problems of insufficient surface hardness and inadequate corrosion resistance of current lead-free solders. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the preparation method of the low-temperature solder of the present invention.

[0022] Figure 2 This is a schematic diagram showing the results of testing the flowability of solder A and solder B according to the present invention.

[0023] Figure 3 This is a schematic diagram showing the results of testing the flowability of solders A and C according to the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Please see Figures 1 to 3 The present invention provides a technical solution:

[0026] Example 1

[0027] A low-temperature solder, by weight percentage, comprises 76% raw material, 13% flux, and the balance being a porous carrier, wherein the raw material comprises tin and bismuth, and the porous carrier is mainly composed of polypropylene (PP) spherical carrier particles.

[0028] Specifically, the diameter of the polypropylene (PP) spherical carrier particles is N, 200μm≤N≤1200μm, and the internal porosity is not less than 55%.

[0029] Specifically, the raw materials also include silver, copper, molybdenum, indium, and antimony, of which bismuth accounts for 14%, indium for 7%, molybdenum for 1.8%, silver for 1.5%, copper for 0.3%, antimony for 0.1%, and the remainder is tin.

[0030] Specifically, the flux includes rosin, thickener, additives, and deionized water.

[0031] Specifically, the rosin is 20%, the thickener is 30%, and the additive is 5%. The rosin is one or more of acrylic rosin, disproportionated rosin, hydrogenated rosin, and polymerized rosin. The thickener includes triethylamine and Span, with a weight ratio of 30:2. The additive includes glutaric acid and salicylic acid, with a weight ratio of 1:1.

[0032] Specifically, the flux also includes a 3% mixture, which includes one or more of polyethylene glycol, terpene oil, alcohol ether, and alkyl alcohol.

[0033] A method for preparing a low-temperature solder, comprising:

[0034] Step 1: Place the flux into a melting crucible, heat to melt, and stir thoroughly;

[0035] Step 2: Then place the raw material and porous carrier in, heat to 129°C, and maintain for 7 minutes;

[0036] Step 3: Remove the impurities from the surface of the molten alloy, then pour it into the mold and let it cool.

[0037] Specifically, the temperature in step 1 is 108℃, and the heating rate in step 2 is 88℃ / min.

[0038] Example 2

[0039] A low-temperature solder, by weight percentage, comprises 81% raw materials, 14% flux, and the balance being a porous carrier, wherein the raw materials include tin and bismuth, and the porous carrier is mainly composed of polypropylene (PP) spherical carrier particles.

[0040] Specifically, the diameter of the polypropylene (PP) spherical carrier particles is N, 200μm≤N≤1200μm, and the internal porosity is not less than 55%.

[0041] Specifically, the raw materials also include silver, copper, molybdenum, indium, and antimony, of which bismuth accounts for 14%, indium for 7%, molybdenum for 1.8%, silver for 1.5%, copper for 0.3%, antimony for 0.1%, and the remainder is tin.

[0042] Specifically, the flux includes rosin, thickener, additives, and deionized water.

[0043] Specifically, the rosin is 20%, the thickener is 30%, and the additive is 5%. The rosin is one or more of acrylic rosin, disproportionated rosin, hydrogenated rosin, and polymerized rosin. The thickener includes triethylamine and Span, with a weight ratio of 30:2. The additive includes glutaric acid and salicylic acid, with a weight ratio of 1:1.

[0044] Specifically, the flux also includes a 3% mixture, which includes one or more of polyethylene glycol, terpene oil, alcohol ether, and alkyl alcohol.

[0045] A method for preparing a low-temperature solder, comprising:

[0046] Step 1: Place the flux into a melting crucible, heat to melt, and stir thoroughly;

[0047] Step 2: Then place the raw material and porous carrier in, heat to 138°C, and maintain for 6 minutes;

[0048] Step 3: Remove the impurities from the surface of the molten alloy, then pour it into the mold and let it cool.

[0049] Specifically, the temperature in step 1 is 115℃, and the heating rate in step 2 is 90℃ / min.

[0050] Example 3

[0051] A low-temperature solder, by weight percentage, comprises 84% ​​raw materials, 13.6% flux, and the balance being a porous carrier, wherein the raw materials include tin and bismuth, and the porous carrier is mainly composed of polypropylene (PP) spherical carrier particles.

[0052] Specifically, the diameter of the polypropylene (PP) spherical carrier particles is N, 200μm≤N≤1200μm, and the internal porosity is not less than 55%.

[0053] Specifically, the raw materials also include silver, copper, molybdenum, indium, and antimony, of which bismuth accounts for 14%, indium for 7%, molybdenum for 1.8%, silver for 1.5%, copper for 0.3%, antimony for 0.1%, and the remainder is tin.

[0054] Specifically, the flux includes rosin, thickener, additives, and deionized water.

[0055] Specifically, the rosin is 20%, the thickener is 30%, and the additive is 5%. The rosin is one or more of acrylic rosin, disproportionated rosin, hydrogenated rosin, and polymerized rosin. The thickener includes triethylamine and Span, with a weight ratio of 30:2. The additive includes glutaric acid and salicylic acid, with a weight ratio of 1:1.

[0056] Specifically, the flux also includes a 3% mixture, which includes one or more of polyethylene glycol, terpene oil, alcohol ether, and alkyl alcohol.

[0057] A method for preparing a low-temperature solder, comprising:

[0058] Step 1: Place the flux into a melting crucible, heat to melt, and stir thoroughly;

[0059] Step 2: Then place the raw material and porous carrier in, heat to 146°C, and maintain for 7 minutes;

[0060] Step 3: Remove the impurities from the surface of the molten alloy, then pour it into the mold and let it cool.

[0061] Specifically, the temperature in step 1 is 117℃, and the heating rate in step 2 is 92℃ / min.

[0062] Comparative Example 1

[0063] In Comparative Example 1 of this embodiment, a portion of the flux, specifically the thickener and additives, was omitted, while the remaining material composition and parameters were the same as in Example 3.

[0064] Solder A was prepared according to Example 3, and solder B was prepared according to Comparative Example 1. Twenty circuit boards were then soldered using solder A and solder B respectively, with one sample randomly taken from each board. The Brinell hardness of the solder joints was tested according to standard DL / T868-2004, and the specific results are shown in Table 1 below.

[0065]

[0066] Table 1

[0067] Solder A was prepared according to Example 3, and solder B was prepared according to Comparative Example 1. The base material was copper. Appropriate dimensions were selected, such as 0.4 mm, with a side length of 30 × 30 mm. The solders were soaked in a 15% dilute hydrochloric acid solution to remove surface oil stains, then dried and placed in a sealed container. The flowability of the solders was tested according to GB11364289 "Test Methods for Brazing Spreadability and Filling Properties". Solders A and B were tested at temperature points of 160℃, 170℃, 180℃, and 190℃. The area of ​​the solder spread on the copper sheet surface was measured using a planimeter, and the average value was taken as the test result. See details below. Figure 2 .

[0068] Comparative Example 2

[0069] In Comparative Example 2 of this embodiment, the porous carrier was omitted, and the remaining material composition and parameters were the same as in Example 3.

[0070] Comparative Example 2: Solder C was prepared, and then 20 circuit boards were soldered using solder C, with one point randomly selected from each board. The Brinell hardness of the solder joints was tested according to standard DL / T868-2004, and the specific results are shown in Table 2 below.

[0071]

[0072] Table 2 below

[0073] The same solder flowability test was conducted, maintaining consistent test parameters except for solder C. Solder A was used as a reference; see details below. Figure 3 .

[0074] A salt spray test was conducted, with the standard-specified salt water concentration being 5 mass%. One circuit board from each of solders A, B, and C was randomly selected and tested for 336 hours. After the test, the solder joints of the test pieces were observed using an electron scanning microscope (EPMA) and an energy dispersive spectroscopy (EDS) instrument. It was found that solder A had the least degree of corrosion (random dotted distribution, accounting for approximately 7% of the entire surface), followed by solder B (random area distribution, accounting for no more than 16% of the entire surface), and lastly solder B (accounting for approximately 42% of the entire surface).

[0075] Table 2 analysis shows that the Brinell hardness of the solder joint surface is generally in the range of 16.4 to 17.2, which is a relatively normal level. In contrast, the Brinell hardness of solder A in Table 1 is generally in the range of 22.1 to 23.5, showing a significant increase compared to Table 2. Although solder A and solder B have different flux compositions in Table 1, their overall performance is not significantly different. The Brinell hardness of solder B joint surface is generally in the range of 22.1 to 22.8, but it is significantly higher than the Brinell hardness of solder C joint surface surface in Table 2. This is because the porous carrier used in this invention not only allows the micropores of the carrier to expand at temperatures of 120-150°C, resulting in larger diameter and denser micropores, but also facilitates the rapid dispersion and filling of raw materials such as tin, bismuth, copper, and antimony, thus reducing preparation time. Simultaneously, it improves the metallographic structure of the reinforcing material and promotes dispersion hardening of the mixture's interior and surface, increasing the surface hardness of the prepared solder joints. Furthermore, the soldering temperature of 160-190°C allows for soldering use. At this temperature, the porous carrier begins to melt, allowing it to be released along with the raw materials onto the circuit board (substrate) to be soldered, giving the solder good fluidity and enabling rapid soldering. Simultaneously, the liquid solder has very low viscosity, and upon reaching its melting temperature, it quickly wets the soldering surface, improving the tight contact between the substrate and the solder, which is beneficial for the contact reaction and melting process. Due to the presence of a porous carrier, a dense protective film can form on the surface of the solder joint after cooling, provided the raw material contains silver. This results in solder joints with not only a good surface gloss but also excellent acid and corrosion resistance. Furthermore, the addition of copper, molybdenum, indium, and antimony further enhances the hardness and corrosion resistance of the solder joints. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) reveal that the solder joints have a smooth and relatively flat outer surface. Visually, the solder joints are exceptionally bright, full, and free of bridging. During use, they readily bond well with the substrate (solid material), resulting in smooth and aesthetically pleasing welds. Therefore, the solder of this invention effectively solves the technical problems of insufficient surface hardness and inadequate corrosion resistance of current lead-free solders.

[0076] This invention discloses a low-temperature solder that can be used in low-temperature lead-free soldering processes for high-end instruments, computers, and other electronic products. The application of this low-temperature lead-free alloy solder significantly saves energy, reduces emissions, and contributes to protecting the production environment and lowering production costs.

[0077] The remaining parts not described in this invention are prior art.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-temperature solder, characterized in that, By weight percentage, the solder comprises 74-85% raw material, 11-15% flux, and 2-12% porous carrier, wherein the raw material comprises tin and bismuth, and the porous carrier is composed of polypropylene (PP) spherical carrier particles. The raw materials also include silver, copper, molybdenum, indium, and antimony, wherein bismuth accounts for 14%, indium for 7%, molybdenum for 1.8%, silver for 1.5%, copper for 0.3%, antimony for 0.1%, and the remainder is tin; The diameter of the polypropylene (PP) spherical carrier particles is N, 200μm≤N≤1200μm, and the internal porosity is not less than 55%. Heating to 120-150℃ and maintaining it for 5-10 minutes expands the micropores of the porous carrier, giving it a larger diameter and denser micropores, which facilitates the rapid dispersion and filling of raw materials such as tin, bismuth, copper, and antimony.

2. The low-temperature solder as described in claim 1, characterized in that, The flux includes rosin, thickener, additives, and deionized water.

3. The low-temperature solder as described in claim 2, characterized in that, The rosin comprises 20%, the thickener comprises 30%, and the additive comprises 5%. The rosin is one or more of acrylic rosin, disproportionated rosin, hydrogenated rosin, and polymerized rosin. The thickener includes triethylamine and Span, with a weight ratio of 30:

2. The additive includes glutaric acid and salicylic acid, with a weight ratio of 1:

1.

4. The low-temperature solder as described in claim 3, characterized in that, The flux also includes a 3% mixture, which includes one or more of polyethylene glycol, terpene oil, alcohol ether, and alkyl alcohol.

5. A method for preparing a low-temperature solder according to any one of claims 1 to 4, characterized in that, include: Step 1: Place the flux into a melting crucible, heat to melt, and stir thoroughly; Step 2: Then place the raw material and porous carrier in the mixture, heat to 120-150℃, and maintain for 5-10 minutes; Step 3: Remove the impurities from the surface of the molten alloy, then pour it into the mold and let it cool.

6. The method for preparing a low-temperature solder as described in claim 5, characterized in that, The temperature in step 1 is 100-120℃, and the heating rate in step 2 is 80-100℃ / min.

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