Solar / Semiconductor

Solar / Semiconductor

Slurry

silicon-wafersSlurry reprocessing, especially when it involves silicon wafer slicing, is a precise business. As one of the pioneers in the slurry reprocessing industry, CRS has had many years to refine and perfect effective slurry management. Through innovative technology and a highly experienced staff, CRS provides customized slurry reprocessing solutions to optimize our customers wafering operations. The result is an extended team of experts working on site to deliver the highest quality cutting materials for the silicon wafer industry.

If you are interested in learning more about slurry recycling services, please contact an expert.

Slurry Proven Process

The CRS process for recovering spent slurries is a proprietary method incorporating diluents and mechanical processes, devoid of chemicals, to facilitate the separation of recoverable grit and carrier. Our process, developed over years of refinements dating back to the introduction of slurry, produces higher yields and better recovery rates that directly impact a company’s bottom line.

Step 1: During the first step, a diluent compatible with the carrier and grit is mixed with the slurry. Once mixed, the slurry blend is heated to a temperature that has been carefully predetermined from laboratory pilot studies. After heating, the mixture is processed through a unique centrifuge built to CRS specifications. This step extracts the good grit particles that are large enough to still be effective in the cutting or grinding process.

Step 2: The remaining material moves to a process designed to recover the carrier. Using our proprietary centrifuge technology, the spent grit and waste kerf is first separated from the reusable carrier.

Step 3: The system then recovers the carrier. The remaining material from this process is a small amount of waste kerf. Depending on disposal method, the consistency of this waste material can be adjusted.

Step 4: The final phase recombines the recovered grit and carrier with virgin grit and carrier to make finished slurry. The virgin makeup carrier and grit is added to replenish the loss of volume that was unusable and removed in reprocessing. Blend tanks with load cells and specific gravity sensors monitor the batch weight and adjust specific gravity to achieve target values for batch size and density. In-line density instrumentation is used as the controlling feature of the blending process. The finished slurry is sent to holding tanks where it typically will be delivered directly to the saws through a slurry distribution loop designed by CRS.

The percentage of recovery varies from slurry to slurry, but typical results for every pound of slurry processed are greater than 85% for both the grit and the carrier. The actual amount of recovered grit reused is a function of the wafering requirements. For oil-based slurries, the recovery of the cleaning solvents used to rinse wafers and equipment is typically greater than 90%.

Diamond Wire

The use of diamond wire saws in the Photovoltaic market is rapidly increasing. The use of diamond wire saws should grow substantially in the next 3-5 years. Not only is it more economical in producing mono-silicon wafers, some companies are trying to use it on poly-silicon. CRS is in lock step with developments in this market and is developing technologies and processes to help make the operators of this equipment more efficient and productive.

Currently the waste coolant after slicing is thrown away, or filter presses are used to remove the silicon kerf and the filtrated coolant is thrown away. Discarding the waste coolant using either of these methods is polluting the environment and also wastes the water and coolant additive which is added to the water to help the slicing process.

CRS has developed a new process to recycle the waste coolant utilizing our proprietary Tough Ultra Filtration system – TUF. The coolant recycled by TUF could be reused on the wire saws with a 95-97% recovery rate, and more importantly the coolant additive mixed with the water is recovered. The solid waste (silicon kerf) recovered from the TUF can be recycled for industrial applications and then refined further to solar grade silicon because the TUF keeps the silicon kerf clean during recycling.

The CRS process for recovering diamond wire coolant involves several steps. The process is a proprietary method to facilitate the separation of diamond wire coolant and additives from the kerf. Our process produces high quality recovered fluid for reuse in the diamond wire saw, lowering a company’s cost of ownership for diamond wire cutting.

Step 1: Material is fed into a filtration system which extracts the coolant from the kerf.  The solid material from this process is a small amount of waste kerf. Depending on disposal method, the consistency of this material can be adjusted.

Step 2: The recovered coolant is checked for quality and additives (if needed) are refortified. The final coolant is delivered to the customer.

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