Solar Cell Crack Detection

Production Challenges

Wafer breakage during processing is a very 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

Goals

Solar cells manufacturers have a need for:
  • 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 limited capture rate due to closed cracks and non-crack related artifacts such as surface scratches.

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 which 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 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 specification 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 which 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.
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. A sub-millimeter length crack represents a seed point defect which dramatically reduces the cell strength. Illustrative example of sub-millimeter crack in production grade silicon cell is visualized using 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: prior to 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 show that the cells with sub-mm cracks are captured with 100% accuracy. Details of the Activation Station are reported here.