JPS6339097B2 - - Google Patents

Abstract

PURPOSE:To perform the coating of solder of high mass productivity by a very simple operation by a method wherein a holding jig to make wafers float and slide on a fused solder is used by utilizing the difference of specific gravities. CONSTITUTION:The wafer 1 is held at the position in contact with the internal surface of the bottom of a vessel 2, and the holding jig is automatically carried and then dipped into the fused solder 7 in a fused solder bath 6 to the fixed depth of the lower part thereof. The fused solder 7 flows into the vessel 2 via an aperture 3. The specific gravity of the solder 7 is approx. 8.8, which turns a very large difference when compared with the specific gravity approx. 2.3 of the Si wafer 1, accordingly the wafer 1 contained in the holding jig is made to float and slide on the surface of the fused solder 7 by utilizing this difference of specific gravities and the surface tension of the fused solder 7, and then creeping to the upper surface is prevented resulting in coating formation of the uniform layer of the solder 7 only on one surface of the wafer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solder coating method in which substantially the entire surface of a semiconductor wafer used for solar cell elements or the like is coated with molten solder.

Conventionally, solder is coated on both sides of Si wafers used as solar cell elements in order to form electrodes for extracting electromotive force, but this solder coating is carried out on the wafer using a molten solder bath. This is done by bringing the molten solder into contact with the molten solder. When coating both sides of a wafer with solder, a method is generally used in which any areas where no solder is needed are masked, the wafer is immersed in molten solder, and molten solder is simultaneously applied to both sides. On the other hand, when coating solder in an automated process, it is more convenient to coat each side of the wafer with solder from the viewpoint of automatic wafer transport. A method is used in which solder is applied only to the surface. However, when one side of the wafer is coated with tape or resin, it is necessary to peel it off in a post-process, and this peeling process is very complicated and has the disadvantage that there is a risk of cracking or damaging the wafer. In addition, the yield is also poor and mass productivity is hindered.

The present invention utilizes the difference in specific gravity between the molten solder and the wafer to apply solder to only one side of the wafer, and uses a holding jig that allows the wafer to float and slide on the molten solder, making mass production possible with very simple operations. It is an object of the present invention to provide a new and useful solder coating method that can provide a solder coating with high properties.

Hereinafter, one embodiment of the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of a wafer holding jig used in the present invention.

A Si single-crystal wafer 1 serving as a solar cell element is formed into a circular thin plate shape, and a holding jig for storing this wafer 1 is composed of a cylindrical container 2 whose inner diameter is sufficiently larger than the diameter of the wafer 1. . The container 2 is made of stainless steel, aluminum, Teflon, etc., which have low affinity for solder, and the height of the cylinder is set sufficiently high relative to the thickness of the wafer 1.
An opening 3 having a diameter smaller than the diameter of the wafer 1 is formed at the bottom of the wafer 1, and this opening 3 serves as a flow path for molten solder.

FIG. 2 is a configuration diagram illustrating a solder application process using the holding jig shown in FIG. 1.

When wafer 1 is inserted into container 2, wafer 1
is held in this position by abutting against the inner surface of the bottom of the container 2. A lid 4 is attached to the top of the container 2 to prevent the wafers 1 from jumping out and falling during transportation. This lid body 4 is provided with a monitoring window 5 which also serves to discharge internal air. The holding jig holding the wafer 1 is automatically transported, and its lower part is immersed in the molten solder 7 in the molten solder tank 6 to a predetermined depth. A heater 8 is disposed in the molten solder tank 6, whereby the molten solder 7 is maintained in a high temperature molten state. When the holding jig is immersed, the molten solder 7 flows into the container 2 through the opening 3 of the container 2. Here, the specific gravity of the molten solder 7 varies slightly depending on the composition, but for example, it is about 8.8 for eutectic solder of lead and tin, and it is about 8.8 for Si
This is a very large value compared to the specific gravity of wafer 1, which is approximately 2.3. Therefore, wafer 1 has molten solder 7
, and only one side is in contact with the molten solder 7. In this state, when the holding jig is moved horizontally as shown by the arrow in the figure, the wafer 1 inside is pushed by the inner wall of the container 2, follows the holding jig, and slides on the surface of the molten solder 7. With this operation, wafer 1
The lower surface of the wafer 1 is compatible with the molten solder 7, and when the holding jig is pulled up and the wafer 1 is taken out, the lower surface of the wafer 1 is uniformly coated with the solder 7.

As described above, by utilizing the difference in specific gravity between the wafer 1 and the molten solder 7 and the surface tension of the molten solder 7, the wafer 1 housed in the holding jig is floated and slid on the surface of the molten solder 7, and the molten solder 7 A uniform layer of molten solder 7 can be formed on only one side of wafer 1 by preventing it from going around to the upper surface.

Note that the wafer to which the present invention is applied is not limited to a Si single crystal, and may be a single crystal, polycrystal, amorphous substrate, etc., as long as the specific gravity is lighter than that of molten solder. In addition to the cylindrical shape, the holding jig has the function of transporting the wafer and the function of holding the wafer with a degree of freedom in the vertical direction, as shown in Figure 3A and B. Various shapes are applicable as long as they can be brought into contact. FIG. 3A is a perspective view illustrating a holding jig having a cage-shaped structure, and FIG. 3B is a perspective view illustrating a holding jig having a four-sided claw structure using a spring material.

According to the present invention, it is not necessary to apply a mask to the wafer surface where solder is not required, and even if the thickness of each wafer is uneven, one side can be coated with molten solder very easily. It is also suitable for mass production and can be easily automated. Furthermore, since the wafer is operated in a mechanically released state without external stress generation, there is no mechanical damage such as cracking or distortion, and the production yield is dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of a holding jig used in the present invention. FIG. 2 is a configuration diagram illustrating a solder application process using the holding jig shown in FIG. 1. 3A and 3B are perspective views showing other embodiments of the holding jig. 1... Wafer, 2... Container, 3... Opening, 6
... Molten solder tank, 7... Molten solder.

Claims (1)

[Claims] 1. After storing the wafer in the holder, the lower part of the holder is immersed in molten solder, the molten solder is allowed to flow into the holder, and the wafer is floated on the molten solder liquid surface within the holder. A solder application method characterized in that the molten solder is applied to one side of the wafer by sliding on the molten solder liquid surface following the holder.