Low temperature pre-coated flux, low temperature pre-coated solder tape and applications thereof

Abstract

The application discloses a low-temperature pre-coated flux, a low-temperature pre-coated solder strip and application thereof, and belongs to the technical field of photovoltaic solder strips. The low-temperature pre-coated flux disclosed by the application is composed of solute and water, and the mass fraction of the solute is 20-25 wt.%. The solute comprises the following components in weight fractions: 30-40 parts by weight of an activator, 30-45 parts by weight of a film forming agent, 2-4 parts by weight of a surfactant and 1-2 parts by weight of an antioxidant; the activator is composed of L-malic acid, DL-malic acid, citric acid and succinamide in a mass ratio of (1-3):(1-3):(0.5-1.5):(0.3-0.7). The low-temperature pre-coated solder strip disclosed by the application comprises a substrate, a low-temperature solder layer and a low-temperature flux layer arranged in sequence, and the low-temperature flux in the low-temperature flux layer adopts the low-temperature flux described above. The low-temperature pre-coated solder strip has high welding reliability, low virtual welding rate and low TC200 power attenuation rate when being laminated and welded with a cell sheet at a temperature of 120-140 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic welding ribbons, in particular to a low-temperature pre-coated flux, a low-temperature pre-coated welding ribbon and application thereof. BACKGROUND

[0002] With the rise of a new type of photovoltaic cell-crystalline silicon heterojunction cell (HJT), low-temperature welding technology has made great progress, among which the SMARTWIRE intelligent welding technology has attracted widespread attention from component enterprises. Currently, when foreign enterprises use the SMARTWIRE intelligent welding technology to weld HJT cells, they usually first use adhesive film to adhere the welding ribbon to the HJT cell, and then weld the welding ribbon and the HJT cell through the temperature during lamination. This method is complex in the adhesion process. In view of this, some domestic component manufacturers have made some optimizations, specifically: first, use UV glue to spot glue on the cell grid lines, then use ultraviolet light to cure the UV glue to adhere the low-temperature welding ribbon to the cell, and then laminate to weld the low-temperature welding ribbon and the cell. This method uses spot gluing instead of adhesive film, simplifying the adhesion process. However, in this welding technology, the welding temperature is usually not more than 150℃, and the low-temperature welding ribbon and the cell are usually not flux-coated, plus the poor weldability of low-temperature solder itself with electrode silver paste, the low-temperature welding ribbon and the cell are weakly welded, which is prone to empty welding and false welding, affecting the reliability of long-term use of the component.

[0003] Therefore, how to develop a flux that improves the reliability of low-temperature welding of welding ribbons and cells is a problem that needs to be solved at present. SUMMARY

[0004] To improve the welding reliability of welding ribbons and cells during low-temperature welding, the present application provides a low-temperature pre-coated flux, a low-temperature pre-coated welding ribbon and application thereof.

[0005] In the first aspect, the present application provides a low-temperature pre-coated flux, which adopts the following technical solution:

[0006] A low-temperature pre-coated flux is composed of solute and water, the mass fraction of the solute is 20-25wt.%, and the solute includes the following components by weight: 30-40 parts of activator, 30-45 parts of film-forming agent, 2-4 parts of surfactant, and 1-2 parts of antioxidant; the activator is composed of L-malic acid, DL-malic acid, citric acid and succinamide in a mass ratio of (1-3):(1-3):(0.5-1.5):(0.3-0.7).

[0007] By adopting the above scheme, the activation temperature zone of the low-temperature pre-coated flux can completely cover the lamination temperature zone of 120-140℃, the pre-coated flux can always maintain excellent activity during the lamination temperature rising process, continuously generate fluxing substances with significant fluxing effect, improve the electrical connection strength between the solder tape and the battery piece, and improve the welding reliability of the solder tape and the battery piece when welding at low temperature. In addition, succinamide in the pre-coated flux contains amino groups and has certain wetting ability, which helps the activity of the compounded acid to play, and at the same time, it can also react with organic acid to generate unstable neutralization products that decompose rapidly at welding temperature, thereby reducing the corrosion of organic acid to solder on the basis of promoting the activity of organic acid.

[0008] Preferably, the film-forming agent is composed of polyethylene glycol and aqueous rosin with a mass ratio of 4:1. Polyethylene glycol has good film-forming property but insufficient strength, and its film layer is easy to break during the drying process, thereby affecting the welding reliability. The pre-coated flux of the application selects polyethylene glycol and aqueous rosin with a mass ratio of 4:1 as the film-forming agent, the aqueous rosin with certain strength can make up for the insufficient strength of polyethylene glycol, and at the same time, the excellent film-forming property of polyethylene glycol can make up for the disadvantage of aqueous rosin that is not easy to form a film due to its large viscosity, thereby ensuring the formation of a uniform film layer on the welding point surface while making the film layer have excellent toughness, so that the film layer is not easy to break during the drying process, thereby improving the welding reliability.

[0009] Preferably, the mass ratio of L-malic acid, DL-malic acid, citric acid and succinamide is 2:2:1:0.5.

[0010] Preferably, the surfactant is at least one of Span, Tween and OP-10. The pre-coated flux of the application selects at least one of Span, Tween and OP-10 as the surfactant, which can reduce the surface tension of water and increase the wettability of the pre-coated flux.

[0011] Preferably, the antioxidant is hydroquinone or pyrocatechol. The pre-coated flux of the application selects hydroquinone or pyrocatechol as the antioxidant, which can improve the physical stability of the pre-coated flux and prolong the storage time of the solder tape.

[0012] In the second aspect, the application provides a low-temperature pre-coated solder tape, which adopts the following technical scheme:

[0013] A low-temperature pre-coated solder tape, comprising a substrate, a low-temperature solder layer and a low-temperature flux layer arranged in sequence, wherein the low-temperature flux in the low-temperature flux layer is the low-temperature flux described above.

[0014] By adopting the above scheme, the welding reliability of the low-temperature pre-coated solder tape and the battery piece when laminated and welded at a temperature of 120-140℃ is significantly improved, and the virtual welding rate and the TC200 power attenuation rate are greatly reduced.

[0015] Preferably, the substrate is a copper substrate, and the solder in the low-temperature solder layer comprises, by weight fraction, 42-44 parts by weight of tin, 52-58 parts by weight of bismuth, 0.01-3 parts by weight of silver, and 0.01-1 parts by weight of copper. The melting point of the low-temperature solder of the present application is close to that of the copper substrate, and the solder is not easy to be detached.

[0016] Preferably, the thickness of the low-temperature flux layer is 1-3 μm. The coating thickness of the low-temperature pre-coated flux of the present application only needs to be 1-3 μm to meet the welding requirements, and compared with the existing flux layer which needs to maintain a pre-coating layer of > 3 μm, the raw materials are saved.

[0017] Preferably, the welding temperature of the low-temperature pre-coated solder tape is 120-140 °C.

[0018] In a third aspect, the present application provides the use of the above-mentioned low-temperature pre-coated solder tape in the welding of photovoltaic cell pieces.

[0019] From the above description, it can be seen that the present application has the following advantages:

[0020] (1) Different complex activators have different activation ranges. By selecting specific proportions of L-malic acid, DL-malic acid, citric acid, and succinamide, a pre-coated flux can be obtained which has an activation temperature range that completely covers the lamination temperature range (120-140 °C). The pre-coated flux can maintain excellent activity during the lamination process, and has a significant fluxing effect. Compared with solder tapes without flux, the welding reliability of the low-temperature pre-coated solder tape of the present application is significantly improved when it is used for low-temperature lamination welding of cell pieces, and the rate of false welding and the power decay rate of TC200 are greatly reduced.

[0021] (2) Polyethylene glycol has good film-forming properties but insufficient strength, and its film layer is easily broken during the drying process, which affects the welding reliability. The pre-coated flux of the present application uses polyethylene glycol and water-based rosin in a mass ratio of 4:1 as a film-forming agent. The water-based rosin with certain strength can compensate for the insufficient strength of polyethylene glycol, while the excellent film-forming properties of polyethylene glycol can compensate for the difficulty of water-based rosin in film formation due to its high viscosity. Therefore, a uniform film layer is formed on the surface of the solder joint, and the film layer has excellent toughness, so that the film layer is not easily broken during the drying process, thereby improving the welding reliability.

[0022] (3) The pre-coated flux of the present application selects at least one of Span, Tween, and OP-10 as a surfactant, which can reduce the surface tension of water and increase the wettability of the pre-coated flux. The selection of hydroquinone or pyrocatechol as an oxidizing agent can improve the physical stability of the pre-coated flux and prolong the storage time of the solder tape.

[0023] (4) The melting point of the low-temperature solder selected by the present application is close to that of the copper substrate, and the solder is not easy to be detached.

[0024] (5) The coating thickness of the low-temperature pre-coated flux of the present application only needs to be 1-3 μm to meet the welding requirements, compared with the existing flux layer which needs to maintain a pre-coated layer of >3 μm, saving raw materials. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a schematic diagram of the structure of the low-temperature pre-coated solder tape in Example 1 of the present application;

[0026] Explanation of reference signs:

[0027] 1 substrate, 2 low-temperature solder layer, 3 low-temperature flux layer DETAILED DESCRIPTION

[0028] At present, when SMARTWIRE intelligent welding technology is used for welding HJT cell, the UV glue is first applied on the cell grid line, then the low-temperature solder tape is adhered to the cell by using ultraviolet light to cure the UV glue, and then laminated to weld the low-temperature solder tape and the cell. This method is simple in adhesion process, and the welding temperature does not exceed 150℃, which can prevent the cell from warping or cracking at high temperature. However, this technology still has some deficiencies, such as no fluxing treatment when low-temperature solder tape is laminated and welded with the cell, plus the poor weldability of low-temperature solder itself with the electrode silver paste, which results in weak firmness of the welding, easy to appear empty welding and false welding, affecting the reliability of long-term use of the module.

[0029] Conventional flux cannot completely release the activity of active agents at low temperature, so it cannot play its fluxing function. It is usually suitable for welding of cells at a welding temperature of 180-250℃. The present applicant has developed a low-temperature pre-coated flux through a large number of research and development. The activation temperature range of the pre-coated flux completely covers the lamination temperature range of 120-140℃, which can always maintain excellent activity during the lamination temperature rising process, continuously produce fluxing substances with obvious fluxing effect, improve the electrical connection strength between the solder tape and the cell, and improve the low-temperature welding reliability of the solder tape and the cell.

[0030] The present application will be described in detail below in conjunction with examples. The scope to be protected by the present application is not limited to the following examples.

[0031] Unless otherwise specified, the raw materials involved in the present application can be obtained through ordinary commercial channels.

[0032] Preparation Example

[0033] Preparation Example 1

[0034] The present preparation example provides a method for preparing solder, the steps are as follows:

[0035] (1) with weight parts, tin 43 parts by weight, bismuth 55 parts by weight into the heating furnace, set the heating furnace temperature to 150 ℃, stirring and keeping for 30 min, then add silver particles 1.5 parts by weight until dissolved, and set the mica sheet on the surface of the alloy liquid, continue to stir and keep for 30 min, then pour the alloy liquid into the mold, cool and shape to get solid alloy;

[0036] (2) the solid alloy prepared in step (1) is put into the tin furnace, the tin furnace temperature is set to 150 ℃, after the solid alloy is dissolved, 0.5 parts by weight of copper wire is added until completely melted, and kept for 30 min to get the target solder.

[0037] The solder prepared in this preparation example includes the following components by weight parts: tin 43 parts by weight, bismuth 55 parts by weight, silver 1.5 parts by weight, and copper 0.5 parts by weight.

[0038] Preparation Example 2

[0039] The preparation example provides a preparation method of solder, and the steps are as follows:

[0040] (1) with weight parts, tin 42 parts by weight, bismuth 52 parts by weight into the heating furnace, set the heating furnace temperature to 150 ℃, stirring and keeping for 30 min, then add silver particles 0.01 parts by weight until dissolved, and set the mica sheet on the surface of the alloy liquid, continue to stir and keep for 30 min, then pour the alloy liquid into the mold, cool and shape to get solid alloy;

[0041] (2) the solid alloy prepared in step (1) is put into the tin furnace, the tin furnace temperature is set to 150 ℃, after the solid alloy is dissolved, 0.01 parts by weight of copper wire is added until completely melted, and kept for 30 min to get the target solder.

[0042] The solder prepared in this preparation example includes the following components by weight parts: tin 42 parts by weight, bismuth 52 parts by weight, silver 0.01 parts by weight, and copper 0.01 parts by weight.

[0043] Preparation Example 3

[0044] The preparation example provides a preparation method of solder, and the steps are as follows:

[0045] (1) with weight parts, tin 44 parts by weight, bismuth 58 parts by weight into the heating furnace, set the heating furnace temperature to 150 ℃, stirring and keeping for 30 min, then add silver particles 3 parts by weight until dissolved, and set the mica sheet on the surface of the alloy liquid, continue to stir and keep for 30 min, then pour the alloy liquid into the mold, cool and shape to get solid alloy;

[0046] (2) Put the solid alloy prepared in step (1) into a tin furnace, set the temperature of the tin furnace to 150℃, after the solid alloy is dissolved, add 1 part by weight of copper wire until it is completely melted, keep warm for 30 min, and obtain the target solder.

[0047] The solder prepared in this preparation example comprises the following components by weight fraction: tin 44 parts by weight, bismuth 58 parts by weight, silver 3 parts by weight, and copper 1 part by weight.

[0048] Embodiment

[0049] Embodiment 1

[0050] The embodiment provides a low-temperature pre-coating flux, which is composed of a solvent and water, and the mass fraction of the solvent is 23wt.%. The solvent comprises the following components by weight fraction: activator A 35 parts by weight, film-forming agent A 40 parts by weight, Span 3 parts by weight, and hydroquinone 1.5 parts by weight.

[0051] The activator A is mixed by L-malic acid, DL-malic acid, citric acid and succinamide at a mass ratio of 2:2:1:0.5.

[0052] The film-forming agent A is mixed by polyethylene glycol and aqueous rosin at a mass ratio of 4:1.

[0053] The preparation steps of the low-temperature pre-coating flux in the embodiment are as follows: weigh the formula amount of each raw material component, mix the activator with water, then add the film-forming agent and stir, and then add the surfactant and antioxidant and stir uniformly, and then stand still to obtain the target low-temperature pre-coating flux.

[0054] The low-temperature pre-coating solder strip is prepared by using the low-temperature pre-coating flux in the embodiment. The low-temperature pre-coating solder strip comprises a substrate 1, a low-temperature solder layer 2 and a low-temperature flux layer 3 arranged in sequence, as shown in FIG. 1, wherein the substrate 1 is made of TU1 oxygen-free copper material with a diameter of 0.2 mm, the low-temperature solder layer 2 is an intermediate layer, and the low-temperature flux layer 3 is located at the outermost layer.

[0055] The preparation method of the low-temperature pre-coating solder strip comprises the following preparation steps:

[0056] (1) Put the substrate into a tin furnace to coat the low-temperature solder on the surface of the substrate to form a low-temperature solder layer, and control the thickness of the low-temperature solder layer to be 15 μm by using an air knife;

[0057] (2) After the substrate coated with the low-temperature solder layer prepared in step (1) passes through the container containing the low-temperature pre-coating flux at a wiring speed of 140 m / min, the excess flux is removed by using an air knife, and then dried to obtain the low-temperature pre-coating photovoltaic solder strip, and the thickness of the low-temperature flux layer in the low-temperature pre-coating photovoltaic solder strip is 2 μm.

[0058] In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0059] Example 2

[0060] This embodiment provides a low-temperature pre-coated flux, which is composed of a solvent and water, and the mass fraction of the solvent is 20wt.%. The solvent includes the following components in parts by weight: 30 parts of activator A, 30 parts of film-forming agent A, 2 parts of Span 2, and 1 part of hydroquinone.

[0061] In this embodiment, the activator A and the film-forming agent A in the low-temperature pre-coated flux are the same as those in Example 1.

[0062] The low-temperature pre-coated flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0063] Example 3:

[0064] This embodiment provides a low-temperature pre-coated flux, which is composed of a solvent and water, and the mass fraction of the solvent is 25wt.%. The solvent includes the following components in parts by weight: 40 parts of activator A, 45 parts of film-forming agent A, 4 parts of Span 4, and 2 parts of hydroquinone.

[0065] In this embodiment, the activator A and the film-forming agent A in the low-temperature pre-coated flux are the same as those in Example 1.

[0066] The low-temperature pre-coated flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0067] Example 4:

[0068] A low-temperature pre-coated flux, which is composed of a solvent and water, and the mass fraction of the solvent is 23wt.%. The solvent includes the following components in parts by weight: 35 parts of activator B, 40 parts of film-forming agent A, 3 parts of Span 3, and 1.5 parts of hydroquinone.

[0069] The activator B is a mixture of L-malic acid, DL-malic acid, citric acid, and succinamide in a mass ratio of 3:3:1.5:0.7.

[0070] The film-forming agent A in this embodiment is the same as that in Example 1.

[0071] The low-temperature pre-coated flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0072] Example 5

[0073] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23wt.%, the solvent including the following components in parts by weight: activator C 35 parts, film forming agent A 40 parts, Span 3 parts, hydroquinone 1.5 parts.

[0074] The activator C is a mixture of L-malic acid, DL-malic acid, citric acid and succinamide in a mass ratio of 1:1:0.5:0.3.

[0075] The film forming agent A in this example is the same as that in Example 1.

[0076] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this example are prepared by the same method as in Example 1, and the solder in the low-temperature solder layer in this example is the solder prepared in Preparation Example 1.

[0077] Example 6

[0078] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23wt.%, the solvent including the following components in parts by weight: activator A 35 parts, film forming agent B 40 parts, Span 3 parts, hydroquinone 1.5 parts.

[0079] The activator A is the same as that in Example 1.

[0080] The film forming agent B is polyethylene glycol.

[0081] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this example are prepared by the same method as in Example 1, and the solder in the low-temperature solder layer in this example is the solder prepared in Preparation Example 1.

[0082] Example 7

[0083] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23wt.%, the solvent including the following components in parts by weight: activator A 35 parts, film forming agent A 40 parts, Tween 3 parts, hydroquinone 1.5 parts.

[0084] In this example, the activator A and the film forming agent A in the low-temperature pre-coating flux are the same as those in Example 1.

[0085] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this example are prepared by the same method as in Example 1, and the solder in the low-temperature solder layer in this example is the solder prepared in Preparation Example 1.

[0086] Example 8

[0087] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23 wt.%, the solvent including the following components in parts by weight: 35 parts by weight of activator A, 40 parts by weight of film-forming agent A, 3 parts by weight of OP-10, and 1.5 parts by weight of hydroquinone.

[0088] In this embodiment, the activator A and the film-forming agent A in the low-temperature pre-coating flux are the same as those in Example 1.

[0089] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0090] Example 9

[0091] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23 wt.%, the solvent including the following components in parts by weight: 35 parts by weight of activator A, 40 parts by weight of film-forming agent A, 3 parts by weight of OP-10, and 1.5 parts by weight of hydroquinone.

[0092] In this embodiment, the activator A and the film-forming agent A in the low-temperature pre-coating flux are the same as those in Example 1.

[0093] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0094] Example 10

[0095] A low-temperature pre-coating flux is composed of a solvent and water, the mass fraction of the solvent being 23 wt.%, the solvent including the following components in parts by weight: 35 parts by weight of activator A, 40 parts by weight of film-forming agent A, 3 parts by weight of OP-10, and 1.5 parts by weight of hydroquinone.

[0096] In this embodiment, the activator A and the film-forming agent A in the low-temperature pre-coating flux are the same as those in Example 1.

[0097] The low-temperature pre-coating flux and the low-temperature pre-coated solder tape in this embodiment are prepared by the same method as in Example 1. In this embodiment, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0098] Comparative Example 1

[0099] This comparative example provides a solder tape, which is different from the low-temperature pre-coated solder tape in Example 1 only in that the solder tape in this comparative example has no flux layer.

[0100] The preparation method of the solder strip includes the following preparation steps: feeding the substrate (TU1 oxygen-free copper) into a tin furnace, coating a low-temperature solder on the surface of the substrate to form a low-temperature solder layer, and controlling the thickness of the low-temperature solder layer to be 15 μm by using an air knife.

[0101] In the present comparative example, the solder in the low-temperature solder layer is the solder prepared in Preparation Example 1.

[0102] Comparative Example 2

[0103] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the present comparative example uses the activator D1 to replace the activator A in Example 1 by equal mass.

[0104] The activator D1 is different from the activator A only in that the activator D1 lacks DL malic acid, i.e., the activator D1 is mixed from L malic acid, citric acid and succinamide by a mass ratio of 2:1:0.5.

[0105] The pre-coated flux and the pre-coated solder strip in the present comparative example are prepared by the same method as in Example 1, and in the present comparative example, the solder in the solder layer is the solder prepared in Preparation Example 1.

[0106] Comparative Example 3

[0107] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the present comparative example uses the activator D2 to replace the activator A in Example 1 by equal mass.

[0108] The activator D2 is different from the activator A only in that the activator D1 lacks citric acid, i.e., the activator D1 is mixed from L malic acid, DL malic acid and succinamide by a mass ratio of 2:2:0.5.

[0109] The pre-coated flux and the pre-coated solder strip in the present comparative example are prepared by the same method as in Example 1, and in the present comparative example, the solder in the solder layer is the solder prepared in Preparation Example 1.

[0110] Comparative Example 4

[0111] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the present comparative example uses the activator D3 to replace the activator A in Example 1 by equal mass.

[0112] The activator D3 is different from the activator A only in that the activator D3 uses equal mass of salicylic acid to replace citric acid, i.e., the activator D3 is mixed from L malic acid, DL malic acid, salicylic acid and succinamide by a mass ratio of 2:2:1:0.5.

[0113] The pre-coated flux and the pre-coated solder tape in the present comparative example were prepared by the same method as that in Example 1. In the present comparative example, the solder in the solder layer was the solder prepared in Preparation Example 1.

[0114] Comparative Example 5

[0115] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the activating agent A in the solute is 45 parts by weight, i.e. the pre-coated flux in the present comparative example is composed of the solute and water, the mass fraction of the solute is 23 wt.%, and the solute includes the following components in parts by weight: activating agent A 45 parts by weight, film-forming agent A 40 parts by weight, Span 3 parts by weight, and hydroquinone 1.5 parts by weight.

[0116] The pre-coated flux and the pre-coated solder tape in the present comparative example were prepared by the same method as that in Example 1. In the present comparative example, the solder in the solder layer was the solder prepared in Preparation Example 1.

[0117] Comparative Example 6

[0118] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the activating agent A in the solute is 45 parts by weight, i.e. the pre-coated flux in the present comparative example is composed of the solute and water, the mass fraction of the solute is 23 wt.%, and the solute includes the following components in parts by weight: activating agent A 45 parts by weight, film-forming agent A 40 parts by weight, Span 3 parts by weight, and hydroquinone 1.5 parts by weight.

[0119] The pre-coated flux and the pre-coated solder tape in the present comparative example were prepared by the same method as that in Example 1. In the present comparative example, the solder in the solder layer was the solder prepared in Preparation Example 1.

[0120] Comparative Example 7

[0121] The present comparative example provides a pre-coated flux, which is different from Example 1 only in that the film-forming agent A in the solute is 25 parts by weight, i.e. the pre-coated flux in the present comparative example is composed of the solute and water, the mass fraction of the solute is 23 wt.%, and the solute includes the following components in parts by weight: activating agent A 35 parts by weight, film-forming agent A 25 parts by weight, Span 3 parts by weight, and hydroquinone 1.5 parts by weight.

[0122] The pre-coated flux and the pre-coated solder tape in the present comparative example were prepared by the same method as that in Example 1. In the present comparative example, the solder in the solder layer was the solder prepared in Preparation Example 1.

[0123] Comparative Example 8

[0124] The comparative example provides a pre-coated flux which is only different from the pre-coated flux of Example 1 in that the film-forming agent A in the solute is 50 parts by weight, i.e. the pre-coated flux of the comparative example is composed of the solute and water, the mass fraction of the solute is 23 wt.%, and the solute includes the following components in parts by weight: activator A 35 parts by weight, film-forming agent A 50 parts by weight, Span 3 parts by weight, and hydroquinone 1.5 parts by weight.

[0125] The pre-coated flux and the pre-coated solder tape in the comparative example are both prepared by the same method as in Example 1. In the comparative example, the solder in the solder layer is the solder prepared in Preparation Example 1.

[0126] Test Example

[0127] The pre-coated solder tapes prepared in Examples 1 to 6 and comparative examples are welded with the battery piece at the component end by using the following steps: first, the UV glue is applied on the grid line of the battery piece, then the pre-coated solder tape is laid on the grid line of the battery piece, the UV glue is cured by using ultraviolet light to realize the adhesion of the pre-coated solder tape and the battery piece, and then the temperature is raised to 140°C for lamination to weld the pre-coated solder tape and the battery piece. The average power of the battery piece assembly after welding is tested, and the virtual welding rate of the battery piece assembly after welding is determined by using an EL detector. The results are shown in Table 1. The maximum output power decay rate of the battery piece assembly after TC200 (thermal cycle test) is shown in Table 1.

[0128] Table 1

[0129] Soldering ribbon type Average power W Percentage of false soldering Power decay rate of TC200 % Example 1 547.52 0.39 0.44 Example 2 547.51 0.45 0.50 Example 3 547.51 0.44 0.49 Example 4 547.52 0.40 0.45 Example 5 547.52 0.41 0.46 Example 6 547.50 0.55 0.57 Comparative Example 1 547.34 1.46 1.23 Comparative Example 2 547.44 0.97 0.86 Comparative Example 3 547.44 1.08 0.95 Comparative Example 4 547.45 0.91 0.82 Comparative Example 5 547.46 0.86 0.78 Comparative Example 6 547.47 0.79 0.72 Comparative Example 7 547.48 0.66 0.67 Comparative Example 8 547.51 0.42 0.47

[0130] As can be seen from Table 1, the virtual welding rate and the TC200 power decay rate of the assembly after welding of the low-temperature pre-coated solder tape provided in Example 1 and the battery piece are much lower than those of the solder tape provided in Comparative Example 1, which indicates that compared with the solder tape without a flux layer, the welding reliability of the low-temperature pre-coated solder tape of the application and the battery piece during low-temperature lamination welding is significantly improved, the stability of the solder tape and the battery piece welding point is greatly increased, and the virtual welding rate and the TC200 power decay rate of the welded assembly are greatly reduced.

[0131] As can be seen from Table 1, the false soldering rate and TC200 power decay rate of the assembly after soldering of the low-temperature pre-coated soldering tape provided by Example 1 and the battery piece are significantly lower than those of the pre-coated soldering tapes provided by Comparative Examples 2 to 4, which indicates that the soldering effect of the pre-coated flux using the activating agent A is significantly better than that of the pre-coated flux using the activating agents D1 to D3 during low-temperature pressure soldering. This can be because the activating temperature range of the activating agent A used in the application is 100 to 150°C, which can completely cover the lamination temperature range of 120 to 140°C. During the lamination temperature rising process, the activating agent A can maintain good activity from the preheating to the formal heating, so that the soldering tape can be better soldered with the solder pad to improve the soldering reliability. The activating temperature range of the activating agents D1 to D3 can only partially cover or not cover the lamination temperature range, so that the pre-coated flux using the activating agents D1 to D3 cannot maintain activity or cannot release activity during the lamination temperature rising process.

[0132] As can be seen from Table 1, the false soldering rate and TC200 power decay rate of the assembly after soldering of the low-temperature pre-coated soldering tape provided by Example 1 and the battery piece are significantly lower than those of the pre-coated soldering tapes provided by Comparative Examples 5 and 6, which indicates that the soldering effect of the pre-coated flux using the activating agent A in an amount not within the range of the application is significantly lower than that of the pre-coated flux using the activating agent A in the amount of the application. This can be because when the content of the activating agent in the pre-coated flux is too low, the activity of the pre-coated flux is insufficient, and the ability to remove the oxide film is weak, resulting in poor soldering reliability of the soldering tape and the battery piece during low-temperature lamination soldering. When the content of the activating agent in the pre-coated flux is too high, the activating agent is prone to desolubilization from the pre-coated flux and is prone to non-uniform distribution, thereby affecting the soldering reliability. In addition, a high content of the activating agent in the pre-coated flux can also cause corrosion of the soldered assembly.

[0133] As can be seen from Table 1, the false soldering rate and TC200 power decay rate of the assembly after soldering of the low-temperature pre-coated soldering tape provided by Example 1 and the battery piece are significantly lower than those of the low-temperature pre-coated soldering tape provided by Example 6, which indicates that the soldering effect of the low-temperature pre-coated flux using polyethylene glycol and water-based rosin in a mass ratio of 4:1 as the film-forming agent is significantly better than that of the low-temperature pre-coated flux using polyethylene glycol as the film-forming agent. This can be because polyethylene glycol has good film-forming property but insufficient strength, and the film layer is prone to breakage during the drying process, thereby affecting the soldering reliability. The pre-coated flux of the application uses polyethylene glycol and water-based rosin in a mass ratio of 4:1 as the film-forming agent, and the water-based rosin has a certain strength. The combination of the two can compensate for the insufficient strength of polyethylene glycol, and the excellent film-forming property of polyethylene glycol can compensate for the poor film-forming property of water-based rosin due to its high viscosity. Therefore, a uniform film layer can be formed while the film layer has excellent toughness, so that the film layer is not prone to breakage during the drying process, thereby improving the soldering reliability.

[0134] As can be seen from Table 1, the low-temperature pre-coated solder strip provided by Example 1 has a significantly lower rate of false welding and TC200 power decay rate of the assembled components after welding with the battery piece than the low-temperature pre-coated solder strip provided by Comparative Example 7, which indicates that when the content of film-forming agent A in the pre-coated flux is too low, the fluxing effect of the pre-coated flux using the amount of film-forming agent A is significantly lower than that of the pre-coated flux using the amount of film-forming agent A of the present application. This may be because the pre-coated flux with too low content of film-forming agent A cannot form a complete film layer on the surface of the solder joint during low-temperature laminated welding, thereby causing false welding and affecting the reliability of welding.

[0135] Although the low-temperature pre-coated solder strip provided by Example 1 in Table 1 has no significant change in the rate of false welding and TC200 power decay rate of the assembled components after welding with the battery piece compared with Comparative Example 8, the content of film-forming agent in the pre-coated flux is too high, which can cause the content of non-volatile matter in the pre-coated flux to be too high, resulting in too much residue after welding. The presence of too much residue can corrode the solder joint and the base metal material, thereby causing short circuit, leakage and other faults. Therefore, it is recommended that the amount of film-forming agent should not exceed the range of the present application.

[0136] It can be understood that the above specific description of the present application is only used to illustrate the present application and is not limited to the technical solutions described in the embodiments of the present application. Those skilled in the art should understand that the present application can still be modified or replaced equivalently to achieve the same technical effect; as long as it meets the needs of use, it is within the protection scope of the present application.

Claims

1. A cryogenic pre-coated welding tape characterized by, The low-temperature soldering strip comprises a substrate, a low-temperature solder layer and a low-temperature flux layer arranged in sequence. The substrate is a copper substrate. The solder in the low-temperature solder layer comprises the following components in parts by weight: 42-44 parts of tin, 52-58 parts of bismuth, 0.01-3 parts of silver and 0.01-1 part of copper. The low-temperature flux in the low-temperature flux layer is composed of a solute and water, the mass fraction of the solute being 20-25 wt.%, the solute comprising the following components in parts by weight: 30-40 parts of an activator, 30-45 parts of a film-forming agent, 2-4 parts of a surfactant and 1-2 parts of an antioxidant; the activator is composed of L-malic acid, DL-malic acid, citric acid and succinamide in a mass ratio of (1-3):(1-3):(0.5-1.5):(0.3-0.7), the film-forming agent is composed of polyethylene glycol and water-based rosin in a mass ratio of 4:1, the surfactant is at least one of Span, Tween and OP-10, and the antioxidant is hydroquinone or pyrocatechol.

2. The cryogenic pre-coated welding tape of claim 1, wherein, The mass ratio of L-malic acid, DL-malic acid, citric acid and succinamide is 2:2:1:0.

5.

3. The cryogenic pre-coated welding tape of claim 1, wherein, The thickness of the low-temperature flux layer is 1-3 µm.

4. The low-temperature pre-coated solder strip according to any one of claims 1-3 is used in soldering of photovoltaic cell pieces.

5. The use according to claim 4, wherein the compound is ###0002### The soldering temperature of the low-temperature pre-coated solder strip is 120-140 ℃.

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