• High reliability: 91 – 95 percent
• High throughput: Under 2 seconds
• Non destructive
• In-line & Off-line configurations

The Resonance Ultrasonic Vibrations (RUV) technique was developed for off-line and in-line non-destructive crack detection in full-size silicon wafers and solar cells. The RUV methodology relies on deviation of the resonance frequency response curve measured on a wafer with peripheral or bulk millimeter-length crack and on identical noncracked wafers.

The silicon wafer is a large contributor to the overall cost of the solar cell. In addition, the silicon raw material price has roughly doubled in the last two years due to a worldwide shortage of the polycrystalline silicon feedstock. To compensate for the feedstock shortage, solar Si wafers are sliced thinner with thicknesses down to 150-200 microns. Wafer areas have also been increased to reduce overall production costs. These technological trends make wafer handling in production more challenging and reduce the yield of solar cell lines due to increased wafer and cell breakage. In-line wafer breakage also reduces equipment throughput as a result of down time.

The RUV technology allows (1) rejection of mechanically unstable Si wafers after ingot cutting before they are introduced into further cell processing, (2) identification of wafers with mechanical defects (such as cracks) during production to avoid their in-line breakage, (3) detection of cracked cells before they will be laminated into modules to avoid panel efficiency reduction and product return from the field.

Adjustable to Customer Needs

The sensitivity of the system, which refers to the length of the cracks, is adjustable to the needs of the user. The rejecting method is based on a statistical approach. In case studies the accuracy of this method was between 91 - 95%.

That means that after RUV inspection the breakage caused by cracked wafers or cells is reduced by at least a factor of 10.

In Line & Offline Configurations

An in-line and offline Quality Control Tools are readily available. Contact Ultrasonic Technologies for more information or to discuss your particular needs.