There are two critical aspects in the production of shingle modules – the interconnection medium and lasers. Generally, lasers are used for cutting cells into several pieces during the production of shingle modules. This is mainly accomplished with laser scribing – first a groove is cut with a depth of about 1/3rd of the wafer thickness; then mechanical force is applied to break the silicon slice exactly along the scribed line. One issue with this method is creation of dust during the scribing process, which is nothing but laser ablation. Moreover, mechanical separation requires some kind of automation.
Innolas from Germany has developed a technology called Laser Direct Cleaving (LDC), which, as the name indicates, is a direct cleaving method. This process directly results in two separate work pieces. Ernst Hartmannsgruber, sales director at Innolas, says that in addition to saving on automation for mechanical separation, the process does not create any dust as no material is ablated from the surface. Cleaving separates the silicon slices through tension created by the laser. First, a well defined micro crack is created at the edge of the wafer, then the heat of the laser guides the crack to the other edge. The process does not induce any damage to the cleaved edges of silicon, says Innolas.
“The purpose itself is to keep the wafer free from damaged molten areas,” said Hartmannsgruber. Since there is no dust formation, the costs associated with filtration can be eliminated completely. Another advantage of the LCD technology is that the cell pieces produced with the ‘scribe and break’ method have lower mechanical strength compared to cleaved pieces.
Innolas has integrated the technology into its ILS-TT machine platform. The standard configuration has a throughput of 4,000 half cells per hour, the ILS-TTnx comes with an hourly throughput of 6,000 half cells per hour.
While applicable for half cut cells, Innolas is promoting the tool mainly for shingle modules. As several strips need to be cut from a cell, not only the breaking mechanism becomes difficult but dust from grooving becomes a big concern as well, said Hartmannsgruber.
During the shingling process, typically 5 strips are produced with 4 cuts. Interestingly, the throughput of ILS-TTnx does not decrease accordingly to 1,500 cells, but can still process 4,000 cells per hour. Innolas would not provide details. Hartmannsgruber only said that, “For half cell cutting we are comparable, with shingling we have a real cutting edge.” This is also reflected in projected costs of ownership values – 0.18 USc per cut for shingling and 0.5 USc per per cut for half cells.