High-reliability medium-temperature composite solder and preparation method thereof

Abstract

The invention discloses a high-reliability medium-temperature composite solder and a preparation method thereof.The high-reliability medium-temperature composite solder comprises an alloy base material and a composite material, and the alloy base material comprises, by mass, 65-85 parts of Sn, 10-30 parts of In, 0.5-3 parts of Ag, 0.5-3 parts of Bi, 0.5-1.2 parts of Cu and 0.1-0.2 part of other metal elements; wherein the other metal elements comprise one of Sb, Ge, Co and Ni; the composite material comprises the following components in parts by mass: 0.1-1.0 part of nano copper powder used for inhibiting migration and remelting of an In-rich phase and forming a solid solution strengthening phase; and nano graphene powder. By means of the mode, according to the high-reliability medium-temperature composite solder and the preparation method thereof, the melting point of the whole composite solder is stabilized to be 175-200 DEG C by adjusting the In content, so that the high-reliability medium-temperature composite solder is accurately matched with a backflow technology at the temperature of 180-210 DEG C, and the thermal requirements of different electronic devices are met; and after the nano metal powder and the nano graphene powder are added, the In-rich phase remelting rate during secondary backflow is effectively reduced, the interface bonding strength is improved, and the reliability is remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic packaging materials, in particular to a high-reliability medium-temperature composite solder and a preparation method thereof. BACKGROUND

[0002] In the field of electronic manufacturing, the melting point of solder is strictly required in the reflow soldering process: high soldering temperature of high-temperature solder (such as Sn-Pb alloy) is easy to cause thermal damage to components, and low-temperature solder (such as Sn-Bi alloy) has the problem of insufficient high-temperature reliability. Medium-temperature solder (175-210℃) needs to consider process compatibility and use stability, and becomes a key material in the scenes of multi-layer packaging, flexible electronics, etc.

[0003] However, the existing medium-temperature alloy solder has the following defects: (1) The melting point adjustment range is narrow, and it is difficult to adapt to different reflow temperature requirements; (2) In the In-containing alloy, the In-rich phase is easy to segregate and remelt in the secondary reflow or TC cycle, stress concentration is generated, and the solder joint interface or internal cracking, pits and conductivity decline are caused; (3) When trace elements are added, uneven distribution is easy to occur, which affects the comprehensive performance of the alloy.

[0004] Therefore, it has important practical value to develop a medium-temperature composite solder which can adjust the melting point by composition and improve the reliability of the solder joint. SUMMARY

[0005] To solve the above technical problems, one technical scheme adopted by the present application is: Provided is a high-reliability medium-temperature composite solder, which comprises an alloy base material and a composite material, The components and mass fractions of the alloy base material include: Sn 65-85 parts, In 10-30 parts, Ag 0.5-3 parts, Bi 0.5-3 parts, Cu: 0.5-1.2 parts, and the rest of the metal elements: 0.1-0.2 parts; wherein the rest of the metal elements include one of Sb, Ge, Co and Ni; The components and mass fractions of the composite material include: Nano-copper powder: 0.1-1.0 parts, for inhibiting the migration and remelting of In-rich phase and forming a solid solution strengthening phase, and improving the reliability of the composite solder; Nano-graphene powder: 0.5-1.0 parts, for inhibiting the diffusion of internal cracks of the solder joint and improving the strength-toughness balance of the composite solder.

[0006] In a preferred embodiment of the present application, the particle size of the nano-copper powder is 50-200 nm, and the purity is ≥99.5%.

[0007] In a preferred embodiment of the present application, the nano-graphene powder is a multi-layer sheet structure with a layer thickness of 1-2 nm and a sheet diameter of about 200-500 nm.

[0008] In a preferred embodiment of the present application, the preparation method of the composite solder comprises: (1) drying treatment: the nano-graphene powder, nano-copper powder and alloy base material are respectively placed in a vacuum drying box and dried at 60-80℃ for 2-4 hours to remove water and adsorbed organic matter, so as to obtain the composite solder; (2) material dispersion: the dried nano-copper powder and nano-graphene are poured into a high-speed mixer, and a flux is added, the stirring speed is 30-50 rpm, and the stirring time is 20-30 min, so that the nano-graphene and nano-copper powder are uniformly distributed in the flux; wherein the flux is part of the tin paste, which is mainly composed of solvent, active agent, thickening agent and other chemical raw materials. Only a specified model, no specific name, generally referred to as flux or flux.

[0009] (3) vacuum stirring: after mixing, the alloy base material is poured into the high-speed mixer for continuous mixing, the stirring speed is 50 rpm, the stirring time is 30-40 min, and the vacuum degree is-0.08 MPa, so that the flux and all the composite solder are fully combined to form a uniform solder paste. The alloy melting point of the prepared solder paste is 175-200℃, which is suitable for 180-210℃ reflow soldering.

[0010] In a preferred embodiment of the present application, the composite solder and the flux are mixed in a volume ratio of 1:1.

[0011] The present application has the following advantages: by adjusting the In content, the melting point of the overall composite solder is stabilized at 175-200℃, which accurately matches the 180-210℃ reflow process and meets the thermal needs of different electronic devices; and after adding nano-metal powder and nano-graphene powder, the In-rich phase remelting rate during secondary reflow is effectively reduced, the interface bonding strength is improved, and the reliability is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Fig. 1 is a micro-morphology diagram of the solder joint interface in the prior art without adding nano-composite material; Fig. 2 is a micro-morphology diagram of the solder joint interface in embodiment 2 of the present application. DETAILED DESCRIPTION

[0013] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0014] Please refer to Figs. 1-2 The embodiments of the present application include: The present application relates to a high-reliability medium-temperature composite solder, which is suitable for a medium-temperature composite solder for a 175-210 DEG C reflow soldering process, and in particular relates to a composite solder for realizing melting point regulation by adjusting the content of In element and for improving the reliability of a solder joint by adding nano copper powder and nano graphene.

[0015] The components and mass (or weight) parts of the alloy base material include: Sn: 65-85 parts, Sn as a matrix, for ensuring the basic mechanical properties of the solder; In: 10-30 parts, In as a core melting point adjusting element, and the content of In is increased to reduce the melting point; Ag: 0.5-3 parts, Ag for improving the strength and wettability of the solder joint; Bi: 0.5-3 parts, Bi for assisting in reducing the melting point and improving the flowability of the solder; Cu: 0.5-1.2 parts, Cu for inhibiting the excessive growth of interfacial intermetallic compounds; The remaining metal elements: 0.1-0.2 parts, wherein one of Sb, Ge, Co, Ni and the like.

[0016] The components and mass (or weight) parts of the composite material include: Nano copper powder: 0.1-1.0 parts, as a metal substance for internal strengthening of the alloy: the nano copper powder is uniformly dispersed in the alloy powder, and after reflow, the nano copper powder inhibits the migration and remelting of In-rich phases through pinning effect, and forms a solid solution strengthening phase to improve the reliability of the composite solder; Nano graphene powder: 0.5-1.0 parts, as a non-metallic substance for internal strengthening of the alloy: graphene has super-high strength and modulus, and after being uniformly dispersed in the alloy matrix, the graphene becomes a "rigid barrier", when a crack appears in the solder joint, the graphene can inhibit the crack propagation, because the two-dimensional sheet structure of the graphene has good toughness and fracture toughness, when a micro-crack is generated in the alloy, the graphene can bridge the two ends of the crack to prevent the crack from opening, or the graphene is pulled out by the crack to consume energy and delay the crack propagation, and meanwhile, the strength and toughness balance of the alloy is improved.

[0017] Furthermore, the nano-copper powder has a particle size of 50-200 nm and a purity of ≥99.5%.

[0018] Furthermore, the nano-graphene powder has a sheet-like multilayer structure with a layer thickness of 1-2 nm and a sheet diameter of approximately 200-500 nm.

[0019] Preparation method of high reliability improved composite solder (1) Drying treatment: Place the nano-graphene powder, nano-copper powder and alloy base material into a vacuum drying oven and dry at 60-80℃ for 2-4 hours to remove moisture and adsorbed organic matter; (2) Material dispersion: Pour the dried copper powder and nano-graphene into a high-speed mixer, add flux, stir at 30-50 rpm for 20-30 min, so that the nano-graphene and nano-copper powder are evenly distributed in the flux; (3) Vacuum stirring: After mixing, pour the medium-temperature alloy base material into the mixed flux, stir at 50 rpm for 30-40 min, and vacuum at -0.08 MPa to allow the flux to fully blend with all the powders and form a uniform paste. The alloy melting point of the prepared composite solder is 175-200℃, which is suitable for reflow soldering at 180-210℃.

[0020] The composite solders of Examples 1 to 6 were prepared according to the components and their mass fractions in Table 1.

[0021] The composite solders obtained in Examples 1 to 6 were subjected to performance tests, and the test results are shown in Table 2.

[0022] The test results above show that, compared with the sample without Cu powder and graphene powder, the addition of a certain amount of Cu powder and graphene powder has a certain inhibitory effect on the propagation of pits and cracks in the solder joints after secondary reflow or TC.

[0023] The beneficial effects of the high-reliability medium-temperature composite solder and its preparation method of the present invention are: (1) Melting point is adjustable: By adjusting the In content (18%-40%), the melting point of the overall composite solder can be stabilized at 175-200℃, so as to accurately adapt to the reflow process of 180-210℃ and meet the thermal requirements of different electronic devices. (2) Improved reliability: After adding nano metal powder and nano graphene powder, the solder composition was optimized, which can optimize the internal structure of the solder. The remelting rate of In-rich phase during secondary reflow was reduced by 8%-30%, the interfacial bonding strength was increased by 10%-15%, and the reliability of the solder joint was significantly improved after thermal cycling. (3) Good process compatibility: can be directly used in existing electronic packaging production line, without adjusting equipment parameters.

[0024] The above only describes the embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent process transformation, or direct or indirect application in other related technical fields, is also included in the patent protection scope of the present application.

Claims

1. A high reliability medium temperature composite solder, characterized by, The application relates to a composite solder and a preparation method thereof. The alloy base and the composite material, the components and mass fractions of the alloy base are as follows: Sn 65-85 parts, In 10-30 parts, Ag 0.5-3 parts, Bi 0.5-3 parts, Cu 0.5-1.2 parts, and the rest of the metal elements 0.1-0.2 parts; wherein the rest of the metal elements include one of Sb, Ge, Co and Ni. The components and mass fractions of the composite material are as follows: Nano-copper powder: 0.1-1.0 parts, which is used for inhibiting the migration and remelting of In-rich phases and forming a solid solution strengthening phase, and improving the reliability of the composite solder; Nano-graphene powder: 0.5-1.0 parts, which is used for inhibiting the diffusion of internal cracks of the solder joint and improving the strength-toughness balance of the composite solder. The nano-copper powder has a particle size of 50-200 nm and a purity of greater than or equal to 99.5%.

2. A high reliability medium temperature composite solder according to claim 1, wherein, The nano-graphene powder has a sheet-shaped multilayer structure, a layer thickness of 1-2 nm and a sheet-shaped diameter of about 200-500 nm.

3. The high reliability medium temperature composite solder of claim 1, wherein, The preparation method of the composite solder comprises the following steps:

4. The high reliability medium temperature composite solder of claim 1, wherein, (1) drying treatment: the nano-graphene powder, the nano-copper powder and the alloy base are respectively placed into a vacuum drying box and dried at 60-80 DEG C for 2-4 hours to remove water and adsorbed organic matters, so as to obtain the composite solder; (2) material dispersion: the dried nano-copper powder and the nano-graphene are poured into a high-speed mixer, and a flux is added, the stirring speed is 30-50 rpm, the stirring time is 20-30 min, and the nano-graphene and the nano-copper powder are uniformly distributed in the flux; (3) vacuum stirring: after mixing, the alloy base is poured into the high-speed mixer for continuous mixing, the stirring speed is 50 rpm, the stirring time is 30-40 min, the vacuum degree is-0.08 MPa, the flux is fully combined with all the composite solder, a uniform solder paste is formed, and the alloy melting point of the prepared solder paste is 175-200 DEG C, which is suitable for reflow soldering at 180-210 DEG C. The composite solder and the flux are mixed according to a volume ratio of 1:

1.

5. A high reliability medium temperature composite solder according to claim 4, wherein, ​

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