TWI467792B - Connecting method for different metals of the thin-film solar cell - Google Patents

Description

Method for dissimilar metal bonding of thin film solar cells

This invention relates to a method of dissimilar metal bonding, and more particularly to a method of dissimilar metal bonding for use in thin film solar cells.

In recent years, due to the rise of environmental awareness and the gradual depletion of petrochemical energy (such as oil and coal), countries around the world have realized the importance of new energy development. Because sunlight is an inexhaustible source of natural energy, in addition to the lack of energy exhaustion, it can also avoid the problem of monopolization of energy. Therefore, countries around the world are actively developing the application technology of solar energy sources, and expect to reduce the dependence on petrochemical energy by increasing the utilization of solar energy sources. One of them is a solar cell, which directly converts light energy into electrical energy.

It is known that the electrode of a thin film solar cell is usually a plated structure of aluminum metal, and in order to extract the electric power generated by the thin film solar cell, a copper foil is usually used to bond the thin film solar cell. However, in the field of thin film solar cells, the bonding of aluminum metal and copper metal has certain difficulty. In the prior art, the bonding of the aluminum electrode of the thin film solar cell to the copper foil is generally performed by ultrasonic bonding or silver bonding. Wait for the way.

In the joining technique using ultrasonic waves, the energy generated by the high-frequency vibration generated by the ultrasonic waves is mainly used to heat the joint surface to bond the aluminum electrode to the copper foil. In addition, in the silver bonding technology, the local dispensing is mainly performed on the aluminum electrode or the copper foil of the thin film solar cell, and then the two are joined and baked to cure and complete the bonding of the two metals. However, in the above two bonding techniques, not only expensive equipment and technology but also too much process time are required, and of course, high manufacturing costs are also incurred.

Therefore, how to provide a dissimilar metal bonding method for a thin film solar cell has not only reduced the process time but also reduces the manufacturing cost, and has become one of important topics.

In view of the above problems, it is an object of the present invention to provide a method of dissimilar metal bonding of a thin film solar cell which can reduce the manufacturing time and reduce the manufacturing cost.

In order to achieve the above object, a method of dissimilar metal bonding according to the present invention is applied to an aluminum electrode of one of a thin film solar cell and a copper foil for extracting the same. The method of dissimilar metal bonding comprises the steps of: providing a fluxing material to the aluminum. On the electrode; a solder ball is disposed on the aluminum electrode; and a copper foil is placed on the solder ball and reflowed to bond the thin film solar cell and the copper foil.

In one embodiment, the fluxing material is a no-clean flux, or a mixture of no-clean flux and flux.

In one embodiment, the no-clean flux is at least 20% by weight of the fluxing material.

In one embodiment, the solder ball material comprises lead solder or lead-free solder.

In one embodiment, the solder balls are disposed on the aluminum electrode in a high temperature inkjet manner.

As described above, the method for dissimilar metal bonding of the present invention comprises: providing a fluxing material on the aluminum electrode; providing a solder ball on the aluminum electrode; and providing a copper foil on the solder ball and reflowing to bond Thin film solar cells and copper foil. Therefore, compared with the conventional ultrasonic bonding technology or the silver bonding technology, not only the process and the device are relatively simple, but also the copper foil and the thin film solar cell can be effectively bonded together, and therefore, the invention can not only reduce the processing time, It also reduces manufacturing costs. In addition, in an embodiment of the present invention, the solder is printed on the aluminum electrode coated with the flux material by using the high temperature piezoelectric nozzle, thereby facilitating the bonding of the thin film solar cell and the copper foil to improve the processing speed, and Increase production and its application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method of dissimilar metal bonding according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings, wherein the same elements will be described with the same reference numerals.

Please refer to FIG. 1 , which is a schematic flow chart of a method for dissimilar metal bonding according to the present invention. The method of dissimilar metal bonding of the present invention is applied to bonding an aluminum electrode of a thin film solar cell and a copper foil which is derived from the power, in other words, a thin film solar cell (aluminum electrode) and a copper foil which are difficult to bond. Bonded to draw power from the thin film solar cell.

The method for dissimilar metal bonding comprises: providing a fluxing material on the aluminum electrode (P01); providing a solder ball on the aluminum electrode (P02); and providing a copper foil on the solder ball and reflowing to bond the thin film solar energy Steps such as battery and copper foil (P03).

Referring to FIG. 2A, step P01 is: providing a flux F on an aluminum electrode 11 of a thin film solar cell 1. The thin film solar cell 1 includes an aluminum electrode 11 and a battery element 12. Since the aluminum electrode 11 is not easily bonded to the solder, the present invention needs to first provide the flux F on the aluminum electrode 11. Among them, the fluxing material F is a no-clean flux, or a mixture of no-clean flux and flux. The no-clean flux is the ROHS commonly used in the industry, and the flux is 51 flux commonly used in the industry. Further, when the weight percentage of the no-clean flux can be at least 20% of the flux F, the bonding effect between the thin film solar cell 1 and the copper foil 2 is preferable.

Referring to FIG. 2B, step P02 is: setting a solder ball S on the aluminum electrode 11. Here, a plurality of solder balls S are provided on the aluminum electrode 11. Among them, the material of the solder ball S may include lead solder or lead-free solder. Further, in the present invention, the solder ball S is printed on the aluminum electrode 11 by high-temperature ink jet. Among them, in order to melt the solder having a melting point of 217 degrees Celsius, the piezoelectric ink jet device and the solder are heated to more than 217 degrees Celsius (for example, heated to 230 degrees). Further, in the present invention, the solder is printed on the aluminum electrode 11 coated with the flux F by a high temperature piezoelectric nozzle of a piezoelectric ink jet device to form a solder ball S, and the diameter of the solder ball S is about 77.0 μm. The thin film solar cell 1 also needs to be heated at the same time to prevent the high temperature solder ball S from directly contacting the low temperature aluminum electrode 11 and being unable to adhere. It is worth mentioning that since the piezoelectric inkjet device needs to be heated from normal temperature to 230 degrees Celsius, it is necessary to protect the nozzle by nitrogen gas to prevent the molten solder ball S from being unable to form droplets due to oxidation, thereby plugging the nozzle.

Referring to FIG. 2B and FIG. 2C simultaneously, in step P03, a copper foil 2 is placed on the solder ball S and reflowed to bond the thin film solar cell 1 and the copper foil 2. Here, the copper foil 2 is bonded to the thin film solar cell 1 to extract the electric power generated by the thin film solar cell 1. Among them, the reflow temperature is at least 240 degrees Celsius, and the reflow time is at least 30 seconds. After the reflow process, the solder ball S and the flux material F are melted to form a bonding layer C of FIG. 2C. In particular, the illustrations are only schematic and do not show the ratio between actual components.

Hereinafter, please refer to the photomicrographs of FIGS. 3A to 3C to illustrate the practical results of the method of dissimilar metal bonding of the present invention applied to the bonding of the thin film solar cell 1 and the copper foil 2. 3A to 3C are photomicrographs of the thin film solar cell 1 under different reflow conditions, respectively.

In the embodiment of 3A to 3C, since the thickness of the aluminum electrode 11 is very thin, after the high-temperature reflow, the aluminum electrode 11 has been melted, and the partially melted aluminum metal is driven to both sides of the bonding layer C, and partially joined. In the layer C, only the battery element 12 and the bonding layer C are shown in the drawing, and the copper foil 2 is not shown (if the thick aluminum electrode 11 is used, it can be displayed in the battery element 12 and the bonding layer C). between). In addition, in the bonding process of FIGS. 3A to 3C, the materials of the solder balls S used are respectively lead-free solders, and the compositions thereof are: Sn-3.0 wt% Ag-0.5 wt% Cu, and the sputtered solder balls S The diameter is about 300 μm. Further, in the bonding process of FIGS. 3A to 3C, in the flux F, the mixing ratio of the no-clean flux to the flux is 3:1. In other words, the weight percentage of the no-clean flux accounts for 75% of the flux F.

In the embodiment of Figure 3A, the reflow temperature is 240 degrees and the reflow time is 30 seconds. Additionally, in the embodiment of Figure 3B, the reflow temperature is 240 degrees and the reflow time is 75 seconds. Further, in the embodiment of Fig. 3C, the reflow temperature is 240 degrees and the reflow time is 120 seconds.

As can be seen from the photomicrographs of Figs. 3A to 3C, the bonding between the bonding layer C and the battery element 12 is quite good (the adhesion is quite good).

In addition, please refer to FIG. 4 , which is a graph showing the relationship between the total resistance of the thin film solar cell 1 and the measured distance in the embodiment of FIGS. 3A to 3B .

As shown in FIG. 4, in the three embodiments, the total resistance of the thin film solar cells 1 of different distances is 2.5 ohm or less, which means that the copper foil 2, the bonding layer 2 and the thin film solar cell 1 are The bonding is quite good so that the total resistance at different distances can be below 2.5 ohms.

In summary, the method for dissimilar metal bonding of the present invention comprises: providing a fluxing material on the aluminum electrode; providing a solder ball on the aluminum electrode; and providing a copper foil on the solder ball and reflowing to bond Thin film solar cells and copper foil. Therefore, compared with the conventional ultrasonic bonding technology or the silver bonding technology, not only the process and the device are relatively simple, but also the copper foil and the thin film solar cell can be effectively bonded together, and therefore, the invention can not only reduce the processing time, It also reduces manufacturing costs. In addition, in an embodiment of the present invention, the solder is printed on the aluminum electrode coated with the flux material by using the high temperature piezoelectric nozzle, thereby facilitating the bonding of the thin film solar cell and the copper foil to improve the processing speed, and Increase production and its application.

The above is intended to be illustrative only and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

1. . . Thin film solar cell

11. . . Aluminum electrode

12. . . Battery component

2. . . Copper foil

C. . . Bonding layer

F. . . Welding material

P01～P03. . . step

S. . . Solder ball

1 is a schematic flow chart of a method for dissimilar metal bonding according to the present invention;

2A to 2C are schematic views respectively showing the dissimilar metal bonding of the present invention;

3A to 3C are respectively photomicrographs of thin film solar cells under different reflow conditions;

4 is a graph showing the relationship between the total resistance of the thin film solar cell and the measured distance in FIGS. 3A to 3B.

P01～P03. . . step

Claims (4)

A method for dissimilar metal bonding is applied to bonding an aluminum electrode of a thin film solar cell and a copper foil for extracting the same. The method for bonding the dissimilar metal comprises the steps of: providing a fluxing material on the aluminum electrode; a solder ball is disposed on the aluminum electrode, wherein the solder ball is disposed on the aluminum electrode by a high temperature inkjet method; and the copper foil is disposed on the solder ball and reflowed to bond the thin film solar cell and the copper foil . A method of joining dissimilar metals as described in claim 1, wherein the fluxing material is a no-clean flux, or a mixture of no-clean flux and flux. The method of dissimilar metal joining as described in claim 2, wherein the no-clean flux comprises at least 20% by weight of the fluxing material. The method of dissimilar metal bonding according to claim 1, wherein the solder ball material comprises lead solder or lead-free solder.