Solar Power World

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A supplier of thermal management materials, adhesives, coatings and encapsulants has developed a silicon ingot bonding material for the solar market. LORD Corporation says its 781 epoxy meets the needs of ingot manufacturers requiring the use of an automatic slicing machine.

The 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 adhesion to a wide variety of surfaces,  the manufacturer says the epoxy remains in position when applied on vertical or overhead surfaces. This allows 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 combined ingot will be sawn into a slice, or wafer by a steel wire with a cutting liquid. The adhesive bonds and fills the gaps between the ingots and 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, according to the manufacturer.

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. In addition, it can reduce Total Thickness Variation and warping of silicon slices.

According to Larry Wang, Staff Scientist at LORD Corporation, the epoxy builds on a history 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,” he says.  ”At the time, the ingot bonding material needed to be fully cured and had to withstand the sawing process. Through research and development, we were able to create a material that solved the problem.”

The 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.

 Lord Corp. www.lord.com