Solar Cell Crack Detection

Production Challenges

Wafer breakage during processing is a high-cost issue:
  • Propagation of cracked cells into the end modules
  • Several minutes of downtime to clean up scattered parts
  • Source of potential contamination, failure at print steps
  • Electrical failures during cell and module tests
Yearly loss of ~$252K per in single module line:
  • Production: 1 cell every 2 seconds, 80% up-time
  • Production: 12.6 million cells per year
  • 0.5% undetected defective cells end-up in modules: 63,000 defective cells per year
  • $4 per delivered cell ~ $252K in lost revenue due to undetected cracks per year per production line
  • 30% yeld loss
Solar Cell Crack Detection during processing

Goals

Solar cells manufacturers need:
  • A method to detect and reject cracked wafers before they are processed
  • Detect cracked wafers at any stage of the cell production
  • Detect and reject cracked solar cells before lamination into panels
  • Non-destructive, non-invasive
  • Perform at planned automation rates (1 cell every 2 seconds or faster)
  • CCD crack inspection (luminescence and IR transmission) are the only options with a limited capture rate due to closed cracks and non-crack related artifacts such as surface scratches and grain-boundaries.

Solutions

  • Ultrasonic Technologies offers a complete range of products and services aimed to provide accurate and fast crack detection in Si wafers and solar cells.
  • Ultrasonic Technologies provides on-site consultation services, after- sale support, and comprehensive training.
  • Patented and proven technology is built into the Resonance Ultrasonic Vibration system which accurately detects mm size cracks at every stage of cell production.
  • Our customers benefit from the flexibility of choosing R&D systems or full production systems that are fully integratable into solar cell or module lines.
  • Significant Cost Reduction of typical solar cell/module production lines is achieved.
  • ROI is estimated from 6 to 12 months.

RUV in Production: In-line Crack Detection.

Ultrasonic Technologies offers a complete range of products and services aimed to provide accurate and fast crack detection in Si wafers and solar cells.

Resonance Ultrasonic Vibration System, Model RUV-3

System Description
Ultrasonic Technologies is offering Resonance Ultrasonic Vibration model (RUV-3) for inline detection of cracked wafers and cells in standard solar cell production lines with automatic, pick-and-place robot-controlled wafers loading and unloading.
This model can be further integrated into the belt-conveyor solar cell line for real-time crack detection in bare wafers, it can be used at the front-end of the solar panel production cycle.
This tool is customizable to different solar cell production lines.
Tact time:
> 2 sec per wafer (single ultrasonic head)
< 2 sec per wafer (multi ultrasonic head)
0.40 sec for data acquisition and analysis
Wafer Dimensions:
Minimum: 100 mm. x 100 mm.
Maximum: 156 mm x 156 mm
Thickness: >80 microns
Wafer load/unload:
Robot pick-and-place
Full software control
Operational modes:
Calibration and production
Customization:
Plug and play to specific production line
System stability:
24/7, 97% up-time, 1.73 sec (peak) per cell
The system utilizes a concept of fast, non-destructive measurements on full-size Si wafers increasing the yield of the PV production lines. RUV system is a computer-controlled unit with Windows-based software providing the system operation, data acquisition, and data processing.
Contact us for additional system specifications and information about pricing and delivery terms.

Sub-Millimeter Crack Detection


‍Ultrasonic Technologies developed a new method to identify silicon wafers and solar cells with small, sub-millimeter seed cracks. Seed crack represents a small anomaly that dramatically reduces wafer and cell strength and ultimately leads to breakage and yield reduction. UST developed and designed an Activating Station add-on which once integrated with the RUV system allows successful detection of seed cracks.
Sub-Millimeter Crack Detection
Ultrasonic Technologies has a proven record of detecting small to medium size ( > 1 mm) cracks and defects in solar cells and wafers using Resonance Ultrasonic Vibration (RUV) tool. It was indicated by our customers that other mechanical problem poses a high probability of wafer/cell breakage in production. An illustrative example of a sub-millimeter crack in production-grade silicon cell is visualized using a high-resolution Scanning Acoustic Microscope (SAM) on the 3.6 x 3.6 mm map. Note, that unopened cross cracks provide directions when the cell is broken.
To address this production problem, Ultrasonic Technologies developed a proprietary protocol to identify the wafers and cells with seed cracks quoted here as an “Activation Station” (AS).
Activation Station concept: before RUV testing the cell is passing through the AS with settings defined by the operator. After activation the cell is transferred to the RUV system and analyzed using a new RUV statistical algorithm. Some heavily damaged cells are broken during the activation step and automatically removed by the hardware. Our tests in solar module production show that the cells with sub-mm cracks are captured with 100% accuracy. Details of the Activation Station are reported here.