Solar cell welding operation method and post-welding inspection method

Oct 08, 2021 tinned solder tape and flux

Solar cell welding operation method and post-welding inspection method

The welding of the cell is to weld the bus strap to the main grid line on the front (negative) of the battery. The bus strap is a tin-plated copper strip. An incorrect welding process will cause the power of the component to decrease and the reverse current to increase.
Solar cell single welding
Single welding is also called monolithic welding, which refers to the welding of two welding ribbons on the main grid line on the front of the cell.
①Single welding operation
(1) The selection of the interconnection belt should conform to the design documents.
(2) Take out the battery slices and inspect them; take out the soaked welding tape and place it in front of the heating table. The battery slice to be welded is placed in the upper left handy position, and only one battery slice is taken at a time.
(3) Place the cell face up on the single-welding heating table.
(4) Use your left hand to hold directly or clamp the front 1/3 of the soldering ribbon with tweezers, and lay it flat on the main grid line of the battery slice. The soldering tape should be aligned with the main grid line, and the front end of the soldering tape is about 2mm away from the right edge of the battery slice. ; Hold the electric soldering iron handle in your right hand, and the electric soldering iron and the battery sheet are welded at a 45° angle.
(5) When soldering, put the soldering iron tip on the soldering tape. The soldering point should exceed the soldering tape head by about 1mm. After the solder of the soldering tape head is melted, push the soldering force uniformly from right to left at one time. The plane should always be close to the soldering tape without stopping. When soldering to the end, stop about 4-6mm away from the left end of the cell, and lift the electric soldering iron to move away from the cell quickly.
(6) Weld the busbar wire ribbon under the battery first, and then weld the busbar wire ribbon above the battery.
(7) During the welding process, if the welding is not strong enough, it is necessary to dip a cotton swab into the flux, apply it to the welding tape, dry it slightly, and repair it again.
(8) Place the soldered cell face up and place it on a light soft object.
The single-piece welding of the cell is shown in Figure 1.
②Technical regulations for single-piece welding process
(1) The temperature of the soldering iron must be calibrated before starting the operation and every 4 hours of use.
(2) Set the temperature of the heating plate at 50°C.
(3) The soldering temperature is 350°C~380°C (depending on the melting point of the solder).
(4) The welding speed is 30~40mm/s (125 single product battery is 3~4s; 156 polycrystalline battery is 4~5s).
(5) The false welding rate of each interconnection bar is not more than 30%.
(6) The soaking time of the interconnection bar is not allowed to exceed 5s (refer to the method of using solder resist).
(7) The amount of flux for soaking the interconnection strips should be moderate each time, soak the cover and cover as soon as you open it. The flux used for more than 16h shall not be reused.
(8) The soaked interconnection strips must be used after the flux has dried.

Solar cell welding operation method and post-welding inspection method
Figure 1 Check whether the welding is smooth after the single-chip welding of the cell

Solar cell series welding, which is also called series welding, refers to the welding of single-piece welded solar cells in series according to the quantity required by the process. As with the monolithic welding of solar cells, improper welding process will cause lower module power and increased reverse current.
①Tandem welding operation
(1) Apply flux evenly to the solder ribbon on the exposed part of the cell after single soldering. The flux should not touch the cell and wait for it to dry.
(2) According to the process requirements, the cells are arranged at equal intervals, and the welding ribbon falls into the back electrode of the next cell. If there is a template, the cell can be positioned according to the template.
(3) Use the fingers of your left hand to gently press the soldering ribbon and the battery slice to avoid relative position shift. Use the electric fuse iron to solder from the left edge of the battery slice with the right hand. After the solder on the soldering tape is melted, solder from left to right at one time.
(4) When soldering to the end of the ribbon, the electric soldering iron slides down and drags the solder away.
(5) When soldering, the soldering iron tip and the battery piece form an angle of 45°.
(6) When welding the next cell, make sure that the position of the previous cell is correct.
(7) Weld two ribbons on the main back electrode of the last cell of each series battery pack.
(8) During the welding process, check whether the back electrode and the front welding tape are in the same straight line at any time to prevent the welding tape from being misaligned between the sheets.
②Technical regulations of tandem welding process
The technical specifications of the tandem welding process and the monolithic welding process are basically the same, but the following points need to be paid attention to:
(1) When welding battery slices in series, the minimum distance between battery slices and battery slices is (2±0.5) mm.
(2) Weld the welding ribbon evenly in the main grid line, and the misalignment of the welding ribbon and the back electrode of the battery shall not be greater than 0.5mm.
(3) The main grid lines of each single string of cells should be in a straight line, and the misalignment should not be greater than 1mm.
(4) Keep the surface of the cell clean.
(5) The single chip is complete without damage.

Solar cell welding operation method and post-welding inspection method
Figure 2 Schematic diagram of monolithic welding of solar cells

Post-weld inspection is divided into post-weld inspection for single welding and post-welding inspection for series welding
① Post-weld inspection of single welding
(1) The first three pieces of welding shall be subjected to a tensile test, and the tensile force is not less than 3N as qualified (according to the process requirements).
(2) Visual inspection, no cracks or incompleteness; the welding surface is even and smooth, and the welding strip is not bent, as shown in Figure 2.
(3) There is no false welding or missing welding, and the welding is reliable. The welding strip will be gently lifted in the direction of 45° and will not fall off, as shown in Figure 3.
②Post-weld inspection of string welding
(1) Whether the battery string after welding is in a straight line, and whether the distance between the battery slices is accurate and consistent.
(2) Visual inspection, whether the welding surface is flat and smooth, and whether there are cracks.
(3) Check whether there are open welding, false welding, burrs and other phenomena on the front of the battery string due to welding of the back electrode.
(4) Check whether there is excess flux crystals near the front soldering ribbon, and wipe it with alcohol; when wiping, use a non-woven cloth dipped in a small amount of alcohol, and gently wipe along the small area of ​​the soldering tape.
(5) When removing the soldered interconnection strip by welding, a uniform silver-tin alloy should be left on the main grid line; the interconnection strip should be welded smoothly, without burrs, false soldering, desoldering, and no tin bead stacking tin.

Solar cell welding operation method and post-welding inspection method
Figure 3 Check whether the welding is reliable after the single-chip welding of the cell