Single welding of solar cells

Single welding of solar cells

1. Purpose

According to the requirements of the drawing, the interconnecting strips are welded straight to the main grid lines of the battery, and ensure good electrical and mechanical connections and a bright appearance.

2. Bill of Materials

(1) 72 single crystal cells.

(2) Tin-coated solder tape (specification: l. 5mm x 0. 15mm, 220mm long, 132 pieces in total; 160mm long, 12 pieces in total).

(3) Absolute ethanol (analytical grade).

(4) Flux.

(5) Clean cloth.

(6) jersey gloves.

(7) Finger sleeves.

(8) Medical absorbent cotton.

3. Equipment and tools

(1) Constant temperature welding station.

(2) Battery heating plate.

4. Proper craftsmanship

(1) Wipe the tin on the head of the electric soldering iron, measure the actual temperature of the electric soldering iron head with a thermometer, adjust the temperature adjustment switch of the electric soldering iron, and control the actual temperature between 360 and 370 °C.

(2) Take a battery sheet, check for defects such as missing edges, missing corners, and chromatic aberration, and replace if any.

(3) Put the cell face up on the welding table with the busbar facing you.

(4) Take an interconnecting strip, check whether there are defects such as blackening and copper leakage, and replace if any.

(5) Align the interconnection bar with the busbar on the front side of the cell, and align the head of the interconnection bar with the first thin gridline, as shown in Figure 1; The two thin grid lines are externally welded, as shown in Figure 1.

Single welding of solar cells
Figure 1 – Single welding process diagram of cell

(6) Start welding from the head of the interconnecting strip, the welding time of a single interconnecting strip is controlled at 23s, the speed is uniform, and the soldering iron is kept at 45% with the horizontal plane. The angle between the left and right is subject to the full contact between the tip of the soldering iron and the surface of the interconnecting strip.

(7) The temperature of the worktable is set to 45~50°C.

Note: The tip of the soldering iron must be pulled out more than 15mm from the edge of the battery, and the tin pile generated during the soldering of the interconnecting strips must be pulled out of the battery.

5. Quality requirements

The quality IPQC personnel will conduct random inspection according to the sampling level stipulated by the national standard, and determine whether the product reaches the following quality objectives:

(1) The welding surface is bright and free of tin beads and burrs.

(2) The welding starting point is 2~3mm away from the edge of the cell.

(3) The interconnection strip should be welded evenly and straightly in the busbar, and the misalignment between the welding strip and the busbar of the cell should be less than 0.2mm.

(4) No desoldering, virtual soldering and over-soldering to ensure good electrical performance.

(5) Has a certain mechanical strength, along 45. Pull the interconnect strip lightly in the direction and it will not fall off.

(6) When the interconnecting strip needs to be bent, the distance between the tip of the soldering iron and the battery is greater than 20mm.

(7) The surface of the cell should be clean after welding.

(8) Monolithic integrity without fragmentation.

(9) Interconnecting strips and cells can withstand the vertical downward 50N pulling force without falling off or deforming.

6. Precautions

(1) The interconnecting strip should be aligned with the busbar, and the exposed white on both sides of the busbar should not be greater than 0.2mm.

(2) Foreign objects such as solder, flux crystals, etc. shall not be adhered to the battery sheet.

(3) The interconnecting strips to be used are placed on the epoxy resin board or on the PTFE cloth.

(4) Wear gloves for the hand holding the soldering iron, and finger cots for those who take the battery.

(5) The temperature of the soldering iron should be calibrated before work, and the calibration frequency is 6h/time.

(6) Take out the missing edges and missing corners that exceed the specified range and hand them over to the process team leader for processing.

(7) When the surface temperature of the cell is lower than 15℃, welding is not allowed.