(09/30/2011)

A new silicon ingot bonding material has been developed for the solar market by LORD Corporation.

Developed to meet the needs of ingot manufacturers requiring the use of an automatic slicing machine, LORD® 781 epoxy adhesive allows manufacturers to address the continued pressure to reduce waste, improve utilization and lower operating costs. All of these are accomplished while increasing the life of the slicing wire. LORD 781 is an ingot adhesive that can join dissimilar ingot lengths together to facilitate easy slicing and minimize waste. This epoxy adhesive is a two-component, thixotropic adhesive system designed to temporarily bond silicon ingots to a holding fixture for the purpose of wafer slicing. Providing excellent adhesion to a wide variety of surfaces, LORD 781 remains in position when applied on vertical or overhead surfaces, allowing for greater process flexibility. Further, it develops high bond strength in 12 to 16 hours at room temperature.

The process of slicing the ingot involves adhering two or more ingot blocks onto a piece of glass and then mounting the joined blocks onto the wire sawing equipment. The new combined ingot will be sawn into a slice, or wafer by a steel wire with a cutting liquid. LORD 781 is an adhesive that bonds and fills the gaps between the ingots. The adhesive alleviates the movement caused by the steel wire interacting with the ingot gap, which can lead to breaks in the wire, failure and excess waste of up to four to six silicon slices for every gap. Excess ingot waste also increases cost and repair time. For example, it can take approximately 20 minutes to reset the sawing wire, and then an additional nine hours to repeat the cutting operation.

To combat these challenges, LORD 781 acts as a plaster on the end-face of the ingot to fill the slopes, fasten ingot to ingot and increase wire saw stability at elevated temperatures. The adhesive maintains excellent hardness and adhesion at these high temperatures, and largely reduces the risk of wire jump. The reduced waste during the slicing process and cost savings are significant benefits to the solar market with the use of LORD 781. In addition, it can reduce Total Thickness Variation (TTV) and warping of silicon slices.

According to Larry Wang, Staff Scientist, LORD 781 builds on a long history of innovation and technical leadership in semiconductor and solar technology.

"We discovered the need for an advanced process for cutting ingots, based on a client's work in the semiconductor market. At the time, the ingot bonding material needed to be fully cured and had to withstand the sawing process. Through extensive research and development at LORD Corporation, we were able to create a material that solved the client's problem," said Wang.

Today, LORD Corporation's research helped develop a new method of cutting ingots with bonding strength, curing speed and temperature tolerance in mind, which can be applied to the solar market. The recommended curing speed created ensures bonding strength and reduces the stress on the ingot during the slicing process. In addition, LORD 781 is a high viscosity material that reduces adhesive flow to avoid ingot contamination and is low odor-emitting.

According to Jianping Zhao, Sales Manager, LORD China, LORD 781 has demonstrated scrap and cost saving results when compared to other materials. "When we tested competitive adhesive materials, the results showed higher occurrence of wire breakage, increased waste and costs. Without the use of an adhesive, these results were increasingly negative. With LORD 781, there was a low risk of wire breakage and no ingot scrap," said Zhao.

Harnessing the sun's energy to produce electricity is once again garnering interest from eager consumers looking for a cheaper, environmentally-friendly power source. During the last energy crisis of the 1970s, solar power gained attention as an alternative to more costly fossil fuels, but the high cost of producing solar energy at that time made it impractical for most consumers, especially for large installations. However, according to the Solar Energy Industries Association (SEIA), due to current concerns about rising costs, energy security and supplies, coupled with new state and federal incentives, the solar energy industry has seen tremendous growth since 2005. The U.S. now ranks fourth in the world for cumulative installed solar capacity, after Germany, Spain and Japan. Solar energy is the cleanest, most abundant, renewable energy source available and making solar systems more cost-effective will expand consumer availability.

More information on LORD 781 can be found at http://www.lord.com/solarenergy. Additional information can be obtained by contacting LORD Corporation by e-mail at solarenergy@lord.com or by phone at +1 877 ASK LORD (275 5673).