PV ribbon is an important component of every mainstream solar panel, used to interconnect solar cells and provide connections to junction boxes. As we know, PV ribbon is a tinned copper strip, 1-6 mm wide and 0.08-0.5 mm thick, with a 10-30 μm thick solder coating. The quality of PV ribbon and its soldering to solar cells is an important factor in ensuring the efficiency and durability of solar panels.
PV ribbon is hot dipped tinned copper conductor used in photovoltaic solar panels. There are two types of PV strips:PV ribbon and PV busbar. Both are required in a typical silicon solar cell.
Why do we need to choose high-quality PV ribbon?
PV ribbon is a key component in solar panels and is an important factor in improving the efficiency and durability of solar panels. But the high efficiency and durability of solar panels can achieve with high-quality PV ribbon that installed in the solar panels. High-quality PV ribbons also improve productivity and reduce the scrap rate of solar panels.
To ensure high productivity in the string soldering process, it is essential to use high-quality, very straight, soft and solderable solder tapes. The precise placement of PV ribbon must also be ensured in the string welding, and wiring process. And high-quality interconnection ribbon inevitably reduces the downtime of the stringer and its scrap rate. Today’s high-speed string welders require even more demanding ribbon performance.
Three major trends in PV Ribbon performance:
1. The new generation of fully automatic high-output string welders requires increasingly stringent tolerances for flux thickness and weld strip straightness.
2. Thinning solar cells require lower yield strength (Rp0.2%) of the solder strip
3. New solar panel designs are using three interconnect strips per cell instead of two, reflecting the growing demand for smaller (narrower and thinner) strips. This in turn is driving capacity expansion for precision tinning lines for smaller interconnects.
The conductor or substrate material in PV solder tape is high conductivity high purity copper (Figure 3). The copper used for PV solder tapes is generally copper in the form of ETP, DIP or oxygen-free copper (OFC: CD-110, CD-101, CD-102).
Copper wire wound in a rolling mill to produce copper strip, followed by tin/solder plating on a tinning line. Some manufacturers use an alternative process of slitting copper strips to produce copper strip, which is usually of lower quality.
Mechanical properties of PV ribbon
●Yield strength (Rp0.2%): a) Hard＞120MPa; b) Soft＜80MPa; Super soft＜65MPa
The straightness (also called curvature) of PV welded tape measure based on the number of millimetres from a straight line on a one-meter-long sample of welded tape. The maximum curvature is determined by the string welding process and generally ranges between <8mm/m and <5mm/m.
There are many different types of flux compositions use in PV solder tapes. They depend on the string welding technology developed by the solar panel manufacturer and local health and safety standards regarding solar panel manufacturing.
Lead-free solder (Sn 100)
Lead-containing solder (SnPb 60/40)
Silver-containing solder (SnAg 96.5/3.5; SnAgCu 96.5/3.0/0.5)
Lead-containing silver solder (SnPbAg 62/36/2)
Low-temperature solder (BiSn 57/43, BiSnAg 57.7/42/0.3).
The range of flux coverage thickness is 10μm-40μm with a tolerance of ±10%-±30%. The most commonly used flux coverage thickness is 20μm±4μm.
Solder coverage thickness measurement method:
a. X-ray method is an off-line measurement method for single-sided thickness measurement
b. Manual micrometres also use to measure the total thickness of the two sides of the cover layer offline
c. Laser thickness measurement equipment commonly use for in-line measurement and can employ on tinning lines to measure the total thickness of the cover two sides during the production of PV solder tape.
PV ribbon also inspect with the naked eye or microscope for the quality of the cover layer, which should be free of defects such as stains, chips, dents, discoloration, bare copper visible through the solder cover, small pinholes and other mechanical defects.
The finished PV is mounted on a spool/reel or disc. In Europe, the most common spools for PV welding tapes are DIN K125, K160, K200 and K250, and in Asia P4 and P10 also use.