CN106607644B

CN106607644B - Ultrasonic welding method and ultrasonic welding device

Info

Publication number: CN106607644B
Application number: CN201610537479.1A
Authority: CN
Inventors: 上迫浩一; 新井杰也; 菅原美爱子; 小林贤一; 小宫秀利; 松井正五; 横山周平
Original assignee: Atlantis Corp; Tokyo University of Agriculture and Technology NUC
Current assignee: Atlantis Corp; Tokyo University of Agriculture and Technology NUC
Priority date: 2015-10-25
Filing date: 2016-07-08
Publication date: 2020-02-14
Anticipated expiration: 2036-07-08
Also published as: KR20190000346A; KR102002796B1; CN106607644A; KR20170048135A; WO2017073299A1; TWI630049B; JP6696665B2; JP2017080753A; TW201714691A

Abstract

The present invention relates to an ultrasonic welding method and an ultrasonic welding apparatus, and aims to weld an electrode or the like which does not contain Ag or lead in a welded part or has a reduced mixing amount. The invention has the following steps: a preliminary heating step of preliminarily heating a substrate or a paste portion on the substrate, on which a paste containing no Ag, Cu, Pb is applied at an arbitrary portion and which is sintered, to a first prescribed temperature lower than a melting temperature of the solder; and an ultrasonic bonding step of bonding a paste portion of the substrate preliminarily heated to a first predetermined temperature in the preliminary heating step by bringing the tip portion of the soldering iron into contact with the paste portion or moving the tip portion of the soldering iron while the tip portion of the soldering iron is in contact with the paste portion by adjusting the temperature of the tip portion of the soldering iron to a second predetermined temperature; the second predetermined temperature is a temperature at which the supplied solder melts when the ultrasonic wave is applied, and is lower than a temperature at which the solder melts when the ultrasonic wave is not applied.

Description

Ultrasonic welding method and ultrasonic welding device

Technical Field

The present invention relates to an ultrasonic welding method and an ultrasonic welding apparatus for welding a portion of a substrate to which a paste is applied and which is sintered.

Background

Conventionally, a solar cell utilizing one of renewable energy sources has been developed based on semiconductor technology which is the leading factor of the 20 th century. It is an important development of the global level that affects human survival. The development problem is not only the efficiency of converting sunlight into electric energy, but also the reduction of manufacturing cost and the problem of no pollution. To achieve these, it is particularly important to reduce or eliminate the amount of silver (Ag) and lead (pb) used for the electrodes.

In general, a solar cell is constructed from the following elements as shown in a plan view in fig. 16(a) and a cross-sectional view in fig. 16 (b): an N-type/P-type silicon substrate 43 for converting solar energy into electric energy; a silicon nitride film 45 which has a function of preventing reflection on the surface of the silicon substrate 43 and is an insulator thin film; a finger electrode (finger electrode)42 that takes out electrons generated in the silicon substrate 43; a bus bar electrode (41) for collecting the extracted electrons with the finger electrode (42); and a lead wire 47 for taking out the electrons collected in the bus electrode 41 to the outside.

Among them, silver (silver paste) and lead (lead glass) are used for the bus electrode 41 and the finger electrode 42, and it is preferable that silver is not used or the amount of silver used is reduced, and further, the amount of lead (lead glass) used is reduced or not used, so that the bus electrode and the finger electrode are formed at low cost and are pollution-free.

In particular, in order to form the electrodes (the bus bar electrodes 41 and the finger electrodes 42) by firing, conventionally, a silver paste (or a part of a copper paste) containing a silver component (powder), a glass component (lead glass), an organic material component, an organic solvent component, and a resin component is used, and therefore, it is desired to replace the silver component (powder) and the glass component (lead glass) of the former two components by a substitute (for example, NTA glass (described later)) instead of the silver component (powder) and the glass component (lead glass), and then solder a lead wire or the like to the electrode formed by screen printing and firing (without Ag, Cu, and Pb).

Disclosure of Invention

[ problems to be solved by the invention ]

In order to form the electrodes (the bus bar electrode 41, the finger electrodes 42, and the like) constituting the solar cell by firing, for example, the electrodes are replaced with an alternative (for example, NTA glass) instead of using the silver component (powder) and the glass component (lead glass) in the conventional silver paste, and in the electrode portion formed by firing the NTA paste (japanese patent application No. 2015-191857) in which silver and lead are not used or reduced, the conventional soldering method cannot be performed because Ag or the like is not present (or only a slight amount of Ag is present).

It is desirable to solve this situation while performing soldering at a portion (electrode or the like) where there is no or only a little Ag or the like.

[ means for solving problems ]

The present inventors have found that a method of soldering a bus electrode or the like made of a paste (hereinafter referred to as a paste) containing no or only a slight amount of Ag and glass (lead glass) by firing can be performed by using 100% NTA glass (vanadate glass) to be described later in the paste. It has also been found that a solar cell soldered by this method can be produced as a solar cell having more excellent characteristics than those obtained by using a conventional silver paste (as described later). The method of soldering the sintered portion (electrode or the like) of the NTA paste is not limited to the above-described bus electrode of the solar cell, and may be a soldering method that is used when forming an electrode or the like in screen printing or the like.

The present invention has been made in view of these findings, and it is possible to perform ultrasonic bonding as described below on, for example, a bus electrode (bus bar electrode) of a solar cell, which is made by firing a paste (for example, NTA paste) that is not used or mixed with only a little silver and is reduced or not used in the amount of lead (lead glass), and to solder (that is, plating solder), lead wires, and the like on the surface, so that it is possible to perform mounting as in the related art, and as a result, it is possible to perform bonding on an electrode that does not contain Ag and lead in the portion to be soldered or is reduced in the amount of mixing.

Accordingly, the present invention is a soldering method for applying a paste to an arbitrary portion on a substrate and soldering the portion after firing, and includes the steps of: a preliminary heating step of preliminarily heating a substrate coated with a paste containing no Ag, Cu, or Pb at an arbitrary portion and sintered or a paste portion on the substrate to a first predetermined temperature lower than a melting temperature of the solder; and an ultrasonic bonding step of bonding the paste portion of the substrate preliminarily heated to a first predetermined temperature in the preliminary heating step by bringing the tip portion of the soldering iron into contact with the paste portion or moving the tip portion of the soldering iron while the tip portion of the soldering iron is in contact with the paste portion in a state where the tip portion of the soldering iron is brought into contact with the paste portion; the second specified temperature is a temperature at which the supplied solder melts in a state where the ultrasonic wave is applied, and is lower than a temperature at which the solder melts when the ultrasonic wave is not applied.

At this time, the first predetermined temperature is set to a temperature in a range from room temperature or higher to the second predetermined temperature.

The second predetermined temperature is set to a temperature within a range of 10 to 40 ℃ lower than a temperature at which the solder melts when the ultrasonic wave is not applied.

The paste containing no Ag, Cu, and Pb is an NTA paste containing no Ag, Cu, and Pb and having a vanadate glass of 100 wt%, or containing no Cu and Pb and having an Ag content of 0 to 50 wt%, with the remainder being a vanadate glass.

The solder contains at least Sn, Zn, and Cl.

When the soldering is performed in the ultrasonic soldering step, the paste portion is dried or heat-dried in advance so that the organic solvent in the paste does not remain.

The paste applied to the substrate is sintered so that the paste portion becomes as smooth as possible.

The ultrasonic wave has a frequency of 20KHz to 150 KHz.

[ Effect of the invention ]

As described above, the present invention has found that, by firing an electrode using an NTA paste containing 100% of conductive NTA glass containing no Ag, Cu, or Pb, for example, or an NTA paste containing 50% or so of NTA glass (the content can be reduced more), instead of a conventional silver (or Cu) paste, and performing ultrasonic welding on the electrode, it is possible to mount a lead wire or the like by welding a paste-sintered portion without using silver or reducing the amount of silver used in the conventional silver paste, and reducing the amount of lead (lead glass) used or not used. Thereby, the following features are provided.

In order to form a bus electrode (bus electrode) of a solar cell, for example, 100% and more preferably about 50% of NTA glass (see japanese registered trademark 5009023, japanese patent No. 5333976) which is conductive vanadate glass is used instead of silver paste, and a sintered portion of the paste can be bonded by ultrasonic bonding according to the present invention even if Ag is not used or the amount of Ag used is reduced, or even if lead (lead glass) is reduced or not used.

The second 2 is to use NTA glass for the bus electrodes (bus electrodes) in an amount of about 100% to 50% (the content may be reduced), whereby an electrode formation exhibiting an effect as a bus electrode almost equal to or slightly higher than the efficiency of conversion of solar energy into electron energy can be obtained from the experimental results in the initial stage (see fig. 16). This was considered to be due to the formation of NTA glass as follows: (1) has conductivity; (2) by forming the finger electrodes into portions having the same height as the upper surface of the bus bar electrode (bus electrode) or portions protruding therefrom by using NTA glass, and joining these portions by ultrasonic bonding according to the present invention of a wire, as a result, a high electron concentration region is directly connected to the wire by the finger electrodes; and, other factors (see, for example, "3 rd" below).

The difference between the paste used in the step 3 and the conventional paste is that the paste contains a frit different from the formation of the finger electrodes and the formation of the bus electrodes. Conventionally, in the formation of finger electrodes, a phenomenon called fire through (fire through) has to be generated. This is to efficiently collect electrons generated in the silicon substrate by using the action of component molecules in the glass frit as a sintering aid for silver, for example, lead molecules in lead glass, so as to break through a silicon nitride film formed on the surface layer of the silicon substrate to form finger electrodes. However, the burn-through phenomenon is not required in the formation of the bus electrode. Conventionally, since the bus bar electrodes are also sintered using lead glass containing a lead component as a sintering aid, the bus bar electrodes and the silicon substrate having different structures form an electrical conduction path, and the conversion efficiency is reduced. By using NTA glass which does not cause a burn-through phenomenon as a sintering aid used for forming the bus electrode, reduction in conversion efficiency can be eliminated. Further, the lead wire may be welded to the bus bar electrode portion sintered with the NTA paste by ultrasonic welding according to the present invention to extract electric charges.

Drawings

FIG. 1 is a block diagram of an embodiment of the present invention.

Fig. 2 is a constitutional view of an embodiment of the present invention (2 thereof).

Fig. 3 is a flowchart illustrating an operation of the present invention (soldering of an electrode portion of a solar cell).

Fig. 4 is a flowchart (connection) for explaining the operation of the present invention (soldering of an electrode portion of a solar cell).

Fig. 5 shows an ultrasonic welding example (NTA 100%) of the present invention, (a) before ultrasonic welding (NTA 100%), and (b) after ultrasonic welding (NTA 100%).

Fig. 6 shows an ultrasonic welding example (NTA 50%), (a) before ultrasonic welding (NTA 50%) and (b) after ultrasonic welding (NTA 50%).

FIG. 7 is a configuration diagram (step completion: cross-sectional view) of an embodiment of the present invention.

FIG. 8 is a flow chart illustrating the operation of the present invention.

FIG. 9 is a detailed step explanatory diagram of the present invention (1 thereof).

FIG. 10 is a detailed step explanatory diagram of the present invention (2 thereof).

Fig. 11 is a detailed explanatory view of the present invention (firing of bus electrodes), (a) is a bus electrode (silver 100%), (b) is a bus electrode (silver 50%/NTA 50%), (c) is a bus electrode (NTA 100%), (d) is a portion also joined by ultrasonic solder formation, and the degree of mechanical joining is large; in fig. 11, the lead wire 17 is formed by solder, and the lead wire 171 is formed by ultrasonic welding.

Fig. 12 is an explanatory view of the present invention (bus electrode containing 50% silver and 50% NTA) (1), (a) is an overall view, and (b) is an enlarged view.

Fig. 13 is an explanatory view of the present invention (bus bar electrode containing NTA 100%, finger electrode fired simultaneously with bus bar electrode) (2), (c) is TKS 100% cell, and in this production example, it is clearly understood that finger electrode comes out of bus bar electrode.

FIG. 14 is an explanatory view of the present invention (ultrasonic welding), (a), (b) and (c) refer to page 13, line 22 to line 33 of the present specification, and (d) is NTA glass (100%).

FIG. 15 shows an example of measurement (efficiency) of the present invention.

Fig. 16 is an explanatory view of the prior art, wherein (a) is a plan view and (b) is a sectional view.

Description of the main Components

1. 11, 43 silicon substrate

2. 16, 46 back electrode

3 nitride film

4. 42 finger electrode

5 bus bar electrode

6 solder

7 strips

12 high electron concentration region (diffusion doping)

13 insulating film (silicon nitride film)

14 electronic outlet (finger electrode)

15. 41 bus bar electrode

17 conducting wire

21 preliminary heating stage

22 ultrasonic iron

23 ultrasonic transmitter and heater

24 tip portion of soldering iron

44N/P diffusion layer

45 silicon nitride film

47 lead-out wire electrode

71 copper

72 pre-solder.

Detailed Description

[ example 1]

Fig. 1 shows a configuration diagram of an embodiment of the present invention. Fig. 1 shows an example of ultrasonic bonding of electrodes of a solar cell, and the following description will explain in detail an example of ultrasonic bonding of a strip 7 as a lead wire to a bus electrode 5. Here, the ultrasonic welding includes plating solder (lead wire, etc.) to the counter electrode, welding a lead wire to the counter electrode, and the like, and the same is also applied to the following.

Fig. 1(a) is a schematic front view of a main part after ultrasonic welding, and fig. 1(b) is a schematic enlarged side view of a dotted circle.

In fig. 1(a) and (b), the solar cell includes: a back electrode 2 provided on the back surface of the silicon substrate 1, a nitride film 3 provided on the front surface of the silicon substrate 1, a bus bar electrode 5, a finger electrode 4 for extracting electrons generated in a PN layer of the silicon substrate 1 so as to penetrate the nitride film 3, and a ribbon 7 (lead wire) bonded with solder 6 by ultrasonic welding of the present invention on the finger electrode 4. Here, the ultrasonic welding of the bar-like shape 7 with the solder 6 is schematically shown on the upper surface of the bus bar electrode 5 as an electrode.

The bus bar electrode 5 is an electrode which cannot be soldered or is extremely difficult to be soldered by a conventional soldering method because Ag is 50% or less in the bus bar electrode 5 formed by sintering NTA paste (Japanese patent application No. 2015-202461) containing 100 wt% vanadate glass and containing no Ag, Cu and Pb, which is found by the present inventors, or the bus bar electrode formed by sintering NTA paste containing 0 to 50 wt% Ag and containing no Cu and Pb and the balance vanadate glass. Particularly, in the case of the bus bar electrode 5 which does not contain Ag, Cu, and Pb at all, conventional soldering is not possible at all, and in the case where Ag is contained at 50% or less, only the portion containing Ag may be soldered, and the other portion may not be soldered, and the mechanical strength is extremely weak, and peeling may occur. In the ultrasonic welding of the present invention, it was found that ultrasonic welding (ultrasonic plating solder) can be performed on the sintered portion of the NTA paste, that is, on the portion not containing Ag, Cu, Pb, or the like, or on all of the portions containing and not containing Ag, Cu, Pb, or the like, as in the experimental results (see the photographs of fig. 5 and 6).

In fig. 2, the solder 6 is a solder that is ultrasonically welded on the bus bar electrode 5 and contains at least Sn, Zn, and Cl, and is welded by melting the ultrasonic iron tip portion 24 of the present invention.

The strip 7 is a lead-out wire for taking out electric charges from the bus bar electrode 5 to the outside, and here, a pre-solder 72 is added to the upper and lower surfaces of the copper strip in advance, and the strip 7 of copper 71 is easily ultrasonically welded to the bus bar electrode 5 by the solder 6.

The preheating stage 21 is used to place the entire solar cell thereon and preheat the solar cell to a first predetermined temperature (a temperature within a range of room temperature or higher and a temperature or lower at which solder melts during ultrasonic welding). By performing the preliminary heating with the preliminary heating stage 21, the amount of heat supplied from the ultrasonic iron tip portion 24 of the ultrasonic welding apparatus not shown in the drawings is small in the welding portion of the bus bar electrode 5, the ultrasonic welding can be performed with a small-capacity ultrasonic welding apparatus, and the temperature control of the ultrasonic iron tip portion 24 is easy and the ultrasonic welding can be performed smoothly.

Next, the structure of fig. 1 will be described in detail with reference to fig. 2.

Fig. 2 shows a configuration diagram of an embodiment of the present invention (2 thereof).

Fig. 2(a) schematically shows a side view of a main part of the solar cell corresponding to fig. 1(b), and fig. 2(b) and (c) schematically show front views when the bus bar electrode 5 is ultrasonically welded by the ultrasonic iron 22. Fig. 2(b) shows a configuration in a case where the solder 6 is soldered to the bus bar electrode 5, that is, in a case where the solder is plated on the bus bar electrode 5, and fig. 2(c) shows a configuration in a case where the solder 6 and the pre-soldered strip 7 are soldered to the bus bar electrode 5, that is, in a case where the strip 7 is soldered on the bus bar electrode 5.

Since fig. 2(a) is the same as fig. 1(b), description thereof is omitted.

In fig. 2(b) and (c), an ultrasonic soldering iron 22 is an example 1 of the ultrasonic bonding apparatus of the present invention, and as shown in the drawing, the ultrasonic bonding apparatus is composed of an iron tip portion 24, an ultrasonic transmitter for heating the iron tip portion 24 and supplying ultrasonic waves, and a heater 23 (see table 2). Frequencies in the range of 20KHz to 150KHz are typically used, while 60KHz is used in the experiments. The heating capacity depends on the temperature of the preliminary heating stage 21, but about 10W (with automatic temperature adjustment) was used in the experiment (a capacity corresponding to the heat capacity obtained by the size of the ultrasonic welding portion (the bus bar electrode 5 portion) was used).

The solder tip portion 24 is used to melt the solder 6 and heat the temperature of the ultrasonic welding portion of the bus bar electrode 5 to perform ultrasonic welding. As shown in the experiment, the tip portion 24 of the soldering iron was cut into a 45-degree slant using a cylindrical tip head, but the shape is not limited to this, and for the purpose of mass production or the like, an elliptical shape, an arbitrary shape, a rotating rotary body, a sliding table, or the like may be used, and any shape may be used as long as the ultrasonic wave and heat can be conducted to the portion to be ultrasonically welded.

As shown in fig. 2(b), solder plating can be performed on the bus bar electrode 5 by ultrasonically soldering the solder 6 supplied to the solder tip portion 24 of the ultrasonic solder 22 onto the bus bar electrode 5.

As in the configuration of fig. 2(c), the solder 6 supplied to the soldering tip portion 24 of the ultrasonic soldering iron 22 and the pre-soldered ribbon 7 are ultrasonically soldered to the bus bar electrode 5, whereby the ribbon 7 (lead wire) is soldered to the bus bar electrode 5. Alternatively, as shown in fig. 2(b), the tape 7 may be ultrasonically welded to the pre-solder.

Table 1 shows an explanatory view of the present invention. Table 1 shows solder materials and the like. Table 1 shows 1 example of the material of the bus bar electrode 5 itself of the solar cell described in fig. 1 and 2, the material of the solder 6 to which the ribbon 7 and the like are soldered, and the like.

[ Table 1]

As described above, in the present invention, since the bus bar electrodes 5 are formed by firing the paste of NTA glass (NTA paste), it is impossible or extremely difficult to perform soldering in the case of the conventional solder, however, it has been confirmed through experiments that soldering of the plated solder and the ribbon 7 (lead wire) on the bus bar electrodes 5 is extremely good by performing soldering using the solder 6 in a preheated state by the ultrasonic soldering of the present invention.

Next, the procedure of ultrasonic bonding of the electrode portion (for example, the bus bar electrode 5) of the solar cell will be described in detail based on the configurations of fig. 1, 2 and table 1 in the order of the flowcharts of fig. 3 and 4.

Fig. 3 shows an operation explanation flowchart of the present invention.

In fig. 3, S11 is the formation of NTA bus electrodes. This is the bus electrode 5 of fig. 1, fig. 2 and table 1, and the bus electrode 5 made of NTA is formed by screen-printing NTA paste of 100 wt% (to 50 wt%) of NTA glass and sintering. The bus bar electrode 5 is described on the right side.

1. The paste is treated so that no organic solvent remains (solvent evaporation).

2. The firing is performed so that the surface of the NTA glass electrode becomes smooth.

The treatment (solvent evaporation) of 1. to prevent the organic solvent from remaining in the paste means that the solvent in the paste is sufficiently evaporated (evaporated) by drying or heat drying to prevent the organic solvent from remaining in the NTA paste. When the solvent remains, ultrasonic welding cannot be smoothly performed.

The term "sintering so that the NTA glass electrode becomes smooth" as used herein means that when the NTA paste is screen-printed and sintered on the portion to become the bus bar electrode 5 in fig. 1 and 2, screen printing is performed so as to become as smooth as possible, and sintering is performed so as to become as smooth as possible during and after firing. Conversely, care should be taken to avoid the formation of fine irregularities and to sinter the particles in a manner that is as smooth as possible. If the surface is not smooth, the ultrasonic welding cannot be smoothly performed.

S12 is a step of placing the substrate on a heating stage and heating the substrate to a temperature equal to or lower than the temperature at which the solder melts when the ultrasonic wave is supplied. This preliminary heating temperature is set (adjusted) so that the temperature of the soldering iron tip portion 24 is lower than the temperature at which the solder 6 melts when the ultrasonic wave is supplied (referred to as a second predetermined temperature) (the first predetermined temperature being equal to or higher than the room temperature and equal to or lower than the melting temperature of the solder when the ultrasonic wave is supplied)) when the ultrasonic soldering iron tip portion 24 is brought into contact with the solder 6 and heated while the ultrasonic wave is supplied, because the solder 6 melts at a temperature slightly lower than the temperature when the ultrasonic wave is not supplied. The second specified temperature is within a temperature range in which the solder 6 melts when the solder 6 is heated while the ultrasonic wave is supplied, and is lower than the melting temperature of the solder 6 in the case where the ultrasonic wave is not supplied, typically by a temperature within a range of 10 to 40 ℃.

S13 is a step of raising the temperature of the solder tip portion 24 to a temperature range at which the solder melts when the ultrasonic wave is supplied thereto.

S14 is to supply ultrasonic waves 20 to 150KHz to the soldering iron tip portion 24. These S13 and S14 are set (adjusted) to a temperature at which the solder 6 melts (second predetermined temperature) by raising the temperature of the solder tip portion 24 while supplying ultrasonic waves of 20 to 150KHz thereto.

Through the above-described S11 to S14, the preparation for ultrasonic bonding to the bus bar electrode 5 formed by sintering the NTA paste, that is, the preparation for ultrasonic bonding to the bus bar 5 by bringing the solder tip portion 24 into contact with the solder 6 and melting the solder 6 is completed.

In fig. 4, S15 of fig. 4 is followed by S14, and solder (plating solder) is soldered to the upper surface of the bus bar electrode. In order to perform ultrasonic soldering on the bus bar electrode 5, as shown in fig. 2(b), the solder 6 is supplied to the upper surface of the bus bar electrode 5 and the solder tip portion 24 is brought into contact with the solder tip portion 24 to melt the solder 6, thereby completing the preparation of ultrasonic soldering at S11 to S14. By this ultrasonic welding, as shown in fig. 5(b) and 6(b), the solder 6 is welded to the bus bar electrode 5.

With this, the solder 6 can be ultrasonically welded (solder plating) on the bus bar electrode 5.

S16 is performed in the same manner as S13 and S14 with the addition of lane 1. This is performed in the same manner as S13 and S14 of fig. 3, and in order to ultrasonically weld the pre-soldered 72 to the bus bar electrode 5, the solder tip portion 24 is set (adjusted) to the second predetermined temperature and ultrasonic waves are supplied, so that the ultrasonic welding of the strip 7 is possible. If the molten solder is the same solder as in the case of plating the solder bus electrode 5, the second specified temperature and the ultrasonic wave are the same as in S13 and S14, and if they are different, the second specified temperature and the ultrasonic wave suitable for them (experimentally determined depending on the type of the solder 6, the pre-solder 72, and the like) are supplied (applied).

S17 is to attach the tape 2 by bringing the tip portion of the ultrasonic iron into contact with the tape and soldering the tape. The ultrasonic iron tip portion 24 is brought into contact with the ribbon 7, and the solder pre-soldered 72 to the ribbon 7, the solder plated with the solder to the bus bar electrode 5, or the solder supplied from the outside is melted to ultrasonically weld the bus bar electrode 5.

S18 is complete. Meaning that ultrasonic welding of the strip 7 of copper above the bus bar electrodes 5 is completed.

As described above, the bus bar electrode 5 obtained by screen-printing and firing the NTA paste constituting the solar cell is plated with solder by ultrasonic welding, and the ribbon 7 is further welded.

Table 2 shows characteristic examples of the ultrasonic welding apparatus of the present invention. This shows 1 example of the characteristics of the ultrasonic welding apparatus used in the trial experiment described with reference to fig. 1 to 4.

In table 2, the following figures were used in trial experiments as the characteristics of the ultrasonic welding apparatus. In mass production, in view of mass productivity, any characteristics may be adopted as long as ultrasonic welding can be performed satisfactorily on the upper surface of the bus electrode 5 and the like formed by firing the NTA paste described above with reference to fig. 1 to 4.

[ Table 2]

The temperature of the solder tip portion 24 is measured by a thermometer (not shown) (for example, a thermocouple is embedded in the solder tip portion 24 and is actually measured, and then, the temperature is automatically adjusted to a second specified temperature based on the actually measured value).

Fig. 5 shows an ultrasonic welding example (NTA 100%) of the present invention. The photographs of the drawings show the photographs of the bus electrode 5(NTA 100%) formed by screen printing and firing the NTA paste (NTA 100%) described in fig. 3 and 4 before and after ultrasonic welding.

Fig. 5(a) shows an example of a photograph before ultrasonic welding (NTA 100%). In the photograph of fig. 5 a, the finger electrodes 4(Ag 100%, see fig. 1 and 2) are horizontal rods, and the bus electrodes (NTA 100%) 5 formed by firing NTA paste (100%) in the present trial experiment are vertical strips coated on the finger electrodes 4. The portion of the bus bar electrode (NTA 100%) 5 was soldered by abutting against the soldering iron tip portion 24 in the present invention, or a tape was attached to the soldering iron tip portion, and a test was conducted.

Fig. 5(b) is a photograph example of ultrasonic welding of only the solder 6 on the bus bar electrode (NTA 100%) 5 of fig. 5(a) according to the above-described steps of fig. 3 and 4. Actually, the tape 7 used as a lead-out wire for taking out electric charges to the outside is ultrasonically welded, but since the following state cannot be seen when the tape 7 is welded, it is shown here that only the solder 6 is ultrasonically welded experimentally. As shown in the figure, the solder of pale white color was clearly seen in the bus bar electrode (NTA 100%) 5 portion.

As described above, by performing ultrasonic welding on the bus bar electrodes (NTA 100%) according to the steps of fig. 3 and 4 of the present invention, it was confirmed that the solder 6 could be welded to the bus bar electrodes 5 of NTA 100% which could not be welded conventionally (the present inventors found this fact).

Next, fig. 6 shows an example of a photograph of the bus electrode 5 with NTA 50%, similar to NTA 100% in fig. 5.

Fig. 6 shows an ultrasonic welding example (NTA 50%) of the present invention. The photographs of the drawings show the bus electrode (NTA 50%) 5 formed by screen printing and firing the NTA paste (NTA 50%) described in fig. 3 and 4 before and after ultrasonic welding.

Fig. 6(a) shows an example of a photograph before ultrasonic welding (NTA 50%). The horizontal bar-shaped one at the upper end of the photograph in fig. 6 a is the finger electrode 4(Ag 100%, see fig. 1 and 2), and the vertical strip-shaped one coated on the finger electrode 4 is the bus electrode (NTA 50%) 5 formed by firing the NTA paste (50%) in the trial experiment of this time. The portion of the bus bar electrode (NTA 50%) 5 was soldered by abutting against the soldering iron tip portion 24 in the present invention, or a tape was attached thereto, and a test was conducted.

Fig. 6(b) is a photograph example of ultrasonic welding of only the solder 6 to the bus bar electrode (NTA 50%) 5 of fig. 6(a) according to the steps of fig. 3 and 4 described above. Actually, the ultrasonic welding of the tape 7 used as a lead wire for taking out electric charges to the outside is performed, and since the following state cannot be seen when the tape 7 is welded, it is shown here that only the solder 6 is experimentally ultrasonic welded. As shown in the figure, the solder of pale white color was clearly seen in the bus bar electrode (NTA 50%) 5 portion, and the solder was soldered to the bus bar electrode (NTA 50%) 5.

As described above, by performing ultrasonic welding on the bus bar electrode (NTA 50%) according to the steps of fig. 3 and 4 of the present invention, it was confirmed that the solder 6 could be welded to the bus bar electrode 5 of NTA 50% which had been impossible or extremely difficult to weld or easily peeled (the present inventors found).

Hereinafter, examples (experimental examples) of the case where the bus bar electrode 5 of the solar cell and the like subjected to the ultrasonic welding of the present invention are described in detail (examples of the following applications are the same as those of the inventor and applicant of Japanese patent application No. 2015-180720 (application date: 27, 9, 14).

FIG. 7 is a configuration diagram (step completion diagram: sectional view) of an embodiment of the present invention.

In fig. 7, the silicon substrate 11 is a conventional semiconductor silicon substrate.

The high electron concentration region (diffusion-doped layer) 12 is a region in which electrons are generated (generated) in the silicon substrate 11 and accumulated when sunlight is incident from above in the drawing, by diffusion-doping a known region (layer) equal to a desired p-type/n-type layer formed on the silicon substrate 11. Here, the accumulated electrons are extracted upward through the electron extraction port (finger electrode (silver)) 14 (see the effect of the present invention).

The insulating film (silicon nitride film) 13 is a known film that allows sunlight to pass through (penetrate) and electrically insulates the bus electrode 15 and the high electron concentration region 14 from each other.

The electron extraction port (finger electrode (silver)) 14 is a port (finger electrode) for extracting electrons accumulated in the high electron concentration region 12 through a hole formed in the insulating film 13. As shown in the present invention, when the bus bar electrode 15 is fired with 100% (to about 71%) NTA glass, the finger electrode 14 is formed (fired) in a portion having the same height as the upper surface of the bus bar electrode 15 or in a portion protruding from the upper surface, and electrons in the high electron concentration region 12 can be directly flowed into the lead 17 via the finger electrode 14 (electrons are directly extracted). That is, electrons (current) in the high electron concentration region 12 can be taken out to the outside through the lead 17 by using 2 paths, i.e., the path 1 (conventional path 1) of the high electron concentration region 12, the finger electrode 14, the bus bar electrode 15, and the lead 17, and the path 2 (path 2 added to the present invention) of the high electron concentration region 12, the finger electrode 14, and the lead 17, and as a result, the resistance value between the high electron concentration region 12 and the lead 17 can be made very small, the loss can be reduced, and as a result, the efficiency of the solar cell can be improved.

The bus electrode (electrode 1(NTA glass 100%)) 15 is an electrode electrically connecting the plurality of electron extraction ports (finger electrodes) 14, and is an electrode for which Ag is not used or the amount of Ag used is reduced (see the effect of the present invention).

The back surface electrode (electrode 2 (aluminum)) 16 is a known electrode formed below the silicon substrate 11.

A lead (formed by welding) 17 for taking out electrons (current I) to the outside, which is electrically connected to the plurality of bus electrodes 15; or further, the lead is bonded by ultrasonic welding to a portion of the same height as the upper surface of the finger electrode 14 and the bus bar electrode 15 in the present invention or a portion of the same height as the upper surface of the bus bar electrode 15, and electrons (current) are taken out to the outside.

In the structure shown in fig. 1, when sunlight is irradiated from the top to the bottom, the sunlight passes through the portion without the lead 17 and the electron extraction port 14 and the insulating film 13, and enters the silicon substrate 11, thereby generating electrons. Then, the electrons accumulated in the high electron concentration region 12 are extracted to the outside through two paths, i.e., a path 1 of the electron extraction port (finger electrode) 14, the bus bar electrode 15, and the lead 17, and a path 2 of the electron extraction port (finger electrode) 14 and the lead 17. In this case, as shown in fig. 11 to 15 described later, 100% to 71% (or less, see fig. 15) of NTA glass (conductive glass) is mixed into the paste as a frit (frit) and fired to form the bus electrode 15, so that the amount of Ag used can be reduced or eliminated. The details will be described in order below.

Fig. 8 shows an operation explanation flowchart of the present invention, and fig. 9 and 10 show detailed structures of the respective steps.

In fig. 8, S1 is a silicon substrate.

And S2, cleaning. As shown in fig. 9 a, these S1 and S2 clean the surface of the silicon substrate 11 prepared in S1 (the surface on which the high electron concentration region 12 is formed) satisfactorily.

S3 is diffusion doping. As shown in fig. 9(b), a known diffusion doping is performed on the silicon substrate 11 cleaned in fig. 9(a), thereby forming a high electron concentration region 12.

S4 is the formation of an antireflection film (silicon nitride film). As shown in fig. 9 c, after the high electron concentration region 12 of fig. 9 b is formed, a silicon nitride film, for example, is formed as an antireflection film (a film which passes sunlight and reduces surface reflection as much as possible) by a known method.

S5 is a screen printed finger electrode. As shown in fig. 9(d), after the silicon nitride film 13 of fig. 9(c) is formed, the pattern of the formed finger electrodes 14 is screen-printed. The printing material is, for example, one obtained by mixing silver into lead glass as a glass frit.

S6 is firing the finger electrodes and burning them through. The pattern of finger electrodes 14 after screen printing in fig. 9(d) (formed by mixing glass frit of silver and lead glass) is fired, and as shown in fig. 9(e), silicon nitride film 13 is fired through to form finger electrodes 14 having silver (conductive) formed therein.

S7 denotes a screen-printed bus electrode (electrode 1). As shown in fig. 10(f), after the finger electrodes 14 of fig. 9(e) are formed, a pattern of the bus bar electrodes 15 is formed by screen printing. The printing material is, for example, a glass frit using NTA gas (100%).

S8 is firing the bus bar electrode (electrode 1) to make the finger electrode penetrate out of NTA glass (bus bar electrode) or form the same height. The pattern of the bus electrode 15 after screen printing in fig. 10(f) (frit of NTA glass (100%)) is fired (firing time is within 1 minute even longer, firing time is 1 to 3 seconds or more), and as shown in fig. 10(g), the bus electrode 15 is formed on the uppermost layer, and the finger electrode 14 is formed at the same height as the upper surface of the bus electrode 15 formed on the uppermost layer or penetrates the upper surface of the bus electrode 15.

In addition, the printing of S5 and S7 may be performed by firing both at the same time.

In S9, a back electrode (electrode 2) is formed. As shown in fig. 10(h), for example, an aluminum electrode is formed on the lower side (back surface) of the silicon substrate 11.

S10 is ultrasonic bonding of lead wires, wherein the finger electrodes and NTA glass (bus bar electrodes) are formed by ultrasonic bonding together. As shown in fig. 10(i), the lead electrically connected to the bus bar electrode of fig. 10(g) is formed by soldering, for example, by ultrasonic welding, and is electrically connected, so that electrons (current) in the high electron concentration region 12 can be taken out to the outside through the lead 17 by using two paths, i.e., the path 1 of the high electron concentration region 12, the finger electrode 14, the bus bar electrode 16, and the lead 17 (the path 2 added in the present invention), and the path 2 of the high electron concentration region 12, the finger electrode 14, and the lead 17, and the resistance value between the high electron concentration region 12 and the lead 17 can be very small, thereby reducing loss, and further improving the efficiency of the solar cell. That is, the path 2 added in the present invention is a portion where one end of the finger electrode 14 is located in the high electron concentration region 12 and the other end is at the same height as the upper surface of the 100% NTA glass bus electrode 15 or a portion that penetrates the upper surface of the bus electrode 15, and a wire is directly bonded (directly bonded by ultrasonic bonding) to this portion, thereby forming the path 2 of the high electron concentration region 12, the finger electrode 14, and the wire 17. Also, path 1 is a conventional path.

Through the above steps, a solar cell can be fabricated on a silicon substrate.

FIG. 11 shows a detailed explanatory view of the present invention (firing of bus bar electrodes).

FIG. 11(a) schematically shows an example of firing a bus electrode with 100% silver and NTA 0% (by weight), FIG. 11(b) schematically shows an example of firing a bus electrode with 50% silver and NTA 50% (by weight), and FIG. 11(c) schematically shows an example of firing a bus electrode with NTA 100% (by weight). The firing time is within 1 minute even if it is long, and is set to 1 to 3 seconds or more.

As shown in fig. 11(a), 11(b) and 11(c), the experimental results shown in table 3 below were obtained by trial experiments of solar cells formed to have substantially the same structure.

[ Table 3]

		Conversion efficiency of solar cell
			Ag
100% of FIG. 11(a)	NTA 0％	On average about 17.0%
			Ag 50% of FIG. 11(b)	NTA 50％	On average about 17.0%
Ag
	0% in FIG. 11(c)	NTA 100％	On average about 17.2%

As a result of the trial experiment, the conversion efficiency of the material of the pattern of the printed bus bar electrode was about 17.0% on average in the case of the solar cell manufactured in fig. 11(a) and 11(b), and substantially the same result was obtained, and the conversion efficiency was about 17.2% on average in fig. 11 (c). From the initial experimental results, it was found that all of fig. 11(a) to (c) had substantially the same conversion efficiency, or that NTA 100% of fig. 11(c) had a slightly higher conversion efficiency. In addition, NTA glass is composed of vanadium, barium, and iron, and particularly iron is strongly bonded to the inside and remains in the inside, and has a property of extremely low bonding even when mixed with other materials (see japanese patent No. 5333976, etc.), and is presumed to be due to improvement in the path (parallel path 1 and path 2) between the high electron concentration region and the lead wire of the present invention.

Fig. 12 and 13 show explanatory views (bus electrodes) of the present invention.

Fig. 12(a) and 12(b) show NTA 50% and Ag 50%, in which fig. 12(a) shows an overall plan view and fig. 12(b) shows an enlarged view. FIG. 13(c) shows NTA 100% and Ag 0%, and FIG. 13(c) shows an enlarged view.

In fig. 12(a) and 12(b), the bus bar electrode 15 is a long electrode as shown in the entire plan view of fig. 12(a), and when this is enlarged with an optical microscope, the structure shown in fig. 12(b) can be observed.

In fig. 12(b), Ag is uniformly dispersed in the bus bar electrode 15 when fired using a conventional glass frit of Ag and lead glass, but when fired using a glass frit of Ag and NTA glass of the present invention (fired for 1 to 3 seconds or more within 1 minute even if it is long), it is clearly understood that Ag aggregates are formed in the central portion of the bus bar electrode 15 as shown in fig. 12 (b). Therefore, as described in the effect of the invention, when the NTA glass is mixed with Ag and fired for a short time (for 1 minute or 1 to 3 seconds or more even if it is long), the Ag is concentrated in the central portion to improve the conductivity (the conductivity is improved compared with the case where the conventional Ag is uniformly dispersed), and the NTA glass itself has the total effect of conductivity and the like, and even if the proportion of Ag is reduced and the NTA glass is increased, the conversion efficiency in the production of a solar cell is about 16.9% as described above, and substantially the same result can be obtained in the experiment.

The firing temperature is 500 to 900 ℃, but the optimum temperature for producing a solar cell is determined by experiment. The structure shown in fig. 12(b) cannot be obtained either too low or too high, and is determined experimentally.

In fig. 13(c), the bus electrode 15 is a strip-like electrode having a wide lateral width at the center of the drawing, and shows 1 example of an enlarged photograph of NTA 100% according to the present invention.

It can be clearly understood that the bus bar electrode 15 in fig. 13(c) has a portion where the finger electrode 14 with a narrower width in the longitudinal direction protrudes out of the bus bar electrode 15 and slightly protrudes from the upper side, and the periphery of the protruding portion is thicker than the width of the original finger electrode 14. Then, ultrasonic welding is performed on the illustrated bus electrode 15 with a width slightly smaller or larger than the width of the bus electrode 15 as described in detail with reference to fig. 14, whereby the high-concentration electron region and the lead wire can be conductively connected to each other through two paths of the path 1 (the photoelectron concentration region 12, the finger electrode 14, the bus electrode 15, and the path 1 of the lead wire 17) and the path 2 (the photoelectron concentration region 12, the finger electrode 14, and the path 2 of the lead wire 17), thereby reducing the loss of electrons (current) and efficiently extracting the electrons (current) to the outside, and obtaining a conversion efficiency substantially equal to or slightly higher than that of fig. 12(a) and (b) (about 17.2%).

The firing temperature is about 500 ℃ to 900 ℃ as in fig. 12(a) and (b), but the optimum temperature for producing a solar cell is determined experimentally. The structure shown in fig. 13(c) cannot be obtained either too low or too high, and is determined experimentally.

Fig. 14 shows an explanatory view of the present invention (ultrasonic welding). This is the case with NTA 100% in fig. 13(c) described above (and the same applies to fig. 12(a), (b)).

Fig. 14(a) shows a state after firing of the finger electrodes 14.

Fig. 14(b) shows a conventional example, in which a lead 17, which is shown by a dotted line and is slightly larger in the figure (may be the same or smaller), is welded to the bus electrode 15 of fig. 14 (a). In this conventional example, since general welding is performed, the portion (Ag) of finger electrode 14 protruding therefrom is welded to lead 17, but the portion (NTA 100%) of finger electrode 14 not protruding therefrom is not sufficiently welded to lead 17, and the mechanical strength is insufficient. On the other hand, in the ultrasonic welding shown in fig. 14(c) described later, the mechanical strength is significantly improved by welding.

Fig. 14(c) shows an example of the present invention, in which a slightly large lead wire 17 shown by a broken line is ultrasonically welded to the bus electrode 15 of fig. 14(a) (the bus electrode 15 of fig. 13 (c)). In this example of the present invention, since ultrasonic welding is performed, the portion (Ag) where the finger electrode 14 protrudes is welded to the lead 17, and the portion (NTA 100%) where the finger electrode 14 is absent is also welded to the lead 17, mechanical strength is greatly improved, and conductivity of the path 2 (the high electron concentration region 12, the finger electrode 14, the bus electrode 15, and the path 2 of the lead 17) is improved.

FIG. 15 shows an example of measurement (efficiency) of the present invention. In fig. 15, the horizontal axis of fig. 15 represents the number of samples and the vertical axis represents the efficiency (%), for a preferable measurement example in which NTA of the bus electrode 15 is changed from 100% to 70%. The samples were set as:

[ Table 4]

·NTA	100％	Ag	0％
				·NTA	90％	Ag	10％
·NTA	80％	Ag	20％
				·NTA	70％	Ag	30％

The results (efficiencies) of the solar cells produced from these samples are shown in the figure. In addition, as shown in the figure, the measurement results showed considerable dispersion, but all fell within the range of 16.9% to 17.5%, and even when the bus electrode 15 was made with NTA 100% (i.e., made without Ag) to manufacture a solar cell, the same or slightly higher efficiency as NTA 70% (or further 80%, 90%) was obtained, and it was clear that NTA 100% could be used (the inventors found this fact).

Claims

1. An ultrasonic welding method for welding a portion of a substrate, which is sintered after applying a paste to an arbitrary portion of the substrate, comprising the steps of:

a preliminary heating step of preliminarily heating a conductive paste containing no Ag, Cu, or Pb and containing 100 wt% of vanadate glass, or containing no Cu or Pb and containing 0 to 50 wt% of Ag, with the remainder being vanadate glass, to a first prescribed temperature lower than the melting temperature of solder; and

an ultrasonic bonding step of bonding solder to a paste portion of the substrate preliminarily heated to a first predetermined temperature in the preliminary heating step by moving the tip portion of the soldering iron while bringing the tip portion of the soldering iron into contact with the paste portion of the substrate or while bringing the tip portion of the soldering iron into contact with the paste portion of the substrate by adjusting the tip portion of the soldering iron into contact with the paste portion of the substrate to a second predetermined temperature; the second specified temperature is a temperature at which the solder supplied is melted in a state where the ultrasonic wave of about 10W is applied and is lower than a temperature at which the solder is melted when the ultrasonic wave of about 10W is not applied;

wherein the solder is melted while applying an ultrasonic wave of about 10W to the paste portion of the substrate, and the melted solder is soldered to the paste portion of the substrate.

2. The ultrasonic welding method according to claim 1, wherein the first prescribed temperature is set to a temperature in a range from room temperature or higher to the second prescribed temperature.

3. The ultrasonic welding method according to claim 1, wherein the second specified temperature is set to a temperature in a range of 10 to 40 ℃ lower than a temperature at which solder melts when ultrasonic is not applied.

4. The ultrasonic welding method according to claim 2, wherein the second specified temperature is set to a temperature in a range of 10 to 40 ℃ lower than a temperature at which solder melts when ultrasonic is not applied.

5. The ultrasonic welding method according to any one of claims 1 to 4, wherein the solder contains at least Sn and Zn.

6. The ultrasonic welding method according to any one of claims 1 to 4, wherein, when welding is performed in the ultrasonic welding step, the paste portion is dried in advance in order to prevent an organic solvent in the paste from remaining.

7. The ultrasonic welding method according to any one of claims 1 to 4, wherein the ultrasonic wave is set to a frequency of 20KHz to 150 KHz.

8. The ultrasonic bonding method according to any one of claims 1 to 4, wherein a portion of the substrate on which the paste is applied serves as an electrode portion of a solar cell.

9. An ultrasonic bonding apparatus for applying a paste to an arbitrary portion of a substrate and bonding the resultant portion, the apparatus comprising:

preheating means for preheating a conductive paste, which is coated with 100 wt% of vanadate glass containing no Ag, Cu and Pb, or containing 0 to 50 wt% of Ag and the balance of vanadate glass containing no Cu and Pb, to a first predetermined temperature lower than the melting temperature of the solder, on an arbitrary portion of the substrate; and

an ultrasonic bonding means for bonding a paste portion of the substrate preliminarily heated to a first predetermined temperature in the preliminary heating step by bringing the tip portion of the soldering iron into contact with the paste portion of the substrate or moving the tip portion of the soldering iron while the tip portion of the soldering iron is brought into contact with the paste portion of the substrate in a state where the tip portion of the soldering iron is brought into contact with the paste portion of the substrate; the second specified temperature is a temperature at which the solder supplied is melted in a state where the ultrasonic wave of about 10W is applied and is lower than a temperature at which the solder is melted when the ultrasonic wave of about 10W is not applied;

the solder is melted while applying ultrasonic waves of about 10W to the paste portion of the substrate, and the melted solder is soldered to the paste portion of the substrate.