Release of a Wire-cutting Machine for Solar Cell Wafers Offering Doubled Productivity through High-speed Cutting
-Original Technology and Use of Diamond Wire Dramatically Improve Silicon Wafer Productivity-

Whereas silicon ingot cutting using circulating-abrasive cutting is similar to lapping, diamond-wire cutting is more like grinding and therefore offers improved cutting efficiency. In the development of the T-8252B, determining the basic layout was the starting point for the design of the machine. New and original technological advances were then used to maximize the benefits offered by the diamond-wire, making it possible to achieve high levels of both productivity and cutting precision, something that has proved elusive in circulating-abrasive cutting systems.

The T-8525B uses a two-level layout that handles silicon ingots on upper and lower levels, while the pitch between the left and right wire guides has also been minimized. The four-axis wire guides are each driven and synchronized by an independent high-output motor. This provides a high maximum wire speed of 1,200 m/min. as well as high acceleration/deceleration that allows rapid back-and-forth wire movement.
The machine is capable of an average wire speed of 1,000 m/min. even during back-and-forth movement, and has the capacity to cut 125 mm diameter monocrystalline silicon ingots at high speeds of 1 mm/min. or faster, achieving productivity levels at least twice those possible with circulating-abrasive cutting. It features a wafer production capability of 350,000 wafers/month or more when cutting 125 mm diameter silicon ingots.

The wire in the T-8252B runs back and forth at high speed through the new Separate Wire Web wire layout system. It employs innovations such as highly rigid 520 mm long wire guides with a diameter of 220 mm, a retensioning mechanism to control the wire tension and maintain high tension at the cutting position, and twist-free wire management that reduces abrasive particle shedding.
This not only eliminates variations in the thickness of the wire entry and exit points but also minimizes wire vibration, jumping and flexing, giving outstanding precision of 10 µm TTV or less and excellent yields of 98% or better.
Separate Wire Web System
This is an original Toyo winding system in which a single wire runs through a web configuration consisting of two independent upper and lower levels. Compared with cutting systems with two wire guides forming a single web to cut two silicon ingots side-by-side, or cutting systems with four wire guides forming a web to cut two silicon ingots top-and-bottom, the Separate Wire Web system offers the advantage of significantly suppressing wire vibration, jumping and flexing. It also means that silicon wafers with different thicknesses can be cut by the upper and lower levels.

In circulating-abrasive cutting systems, abrasive particles are drawn into the gap between the wire and the silicon ingot so that wire is also abraded by the particles and tends to break. In diamond-wire cutting systems, the diamond grains are bonded to the wire surface, so the wire only wears if the grains are dislodged from the wire. Diamond wire is more likely to break if it rub together at any point. To avoid this, the T-8252B uses a twist-free wire management system that prevents wire skewing and catching, thereby minimizing the likelihood of breakage. And because the T-8252B takes maximum benefit of the capabilities of diamond-wire cutting, it can achieve low running costs of 1.5 m or less of wire used per wafer for 125 mm diameter ingots and 3 m per wafer or less for 156 mm diameter ingots.