Inspection Systems for Glass and Coating Defect Detection

In-situ inspection with no active modules within the chamber

In coating applications, Dark Field’s SSLR technology allows inspection to be performed from outside the vacuum chamber during processing.

The laser reflector is installed in the chamber to capture and return light to the scanner. No electronics are required in the deposition chamber. Dark Field has built in-situ inspection systems with coating defect detection down to 1 micron.

30% – 75% of coated glass defects are due to unclean glass

• Glass washer performance varies with time.
• Poor washing leaves residue on the glass (washer debris).
• Glass washer manufacturers do not provide a means to measure washer debris.  No way to measure cleanliness.
• Glass coating operations suffer decreased yields, higher scrap, lower throughput as a result.

Dark Field Solution

• Special scanner detects washer debris which is invisible to the eye, but which will cause coating defects.
• Custom “Clean Number” is used to set Good, Warning and Reject limits.
• Plates with unacceptable washer debris are recycled to the washer – only clean glass enters the coater.
• Washer is maintained according to its performance.
• Throughput increases, yields improve and scrap is eliminated.

High Speed, High Resolution, 100% Coating Defect Detection

• Manual inspection is slow, subjective and inefficient.
• Many rejectable defects are not detected; bad plates get packed.
• No data captured – no process feedback to correct upset.
• No quality history.

Dark Field Solution

• Solid State Laser Reflection (SSLR) scanners.
• High speed, 100% inspection.
• Even the smallest rejectable defect is detected.
• Complete history, including quality alerts.
• Sheet grading; Good, Warning, Reject.
• Defect density threshold.
• Trends and special reports – SQL database.
• Customized HMI and reports/trends.
• Interface with marking system – feedback for plugged/dead markers.

Manual inspection of Mother Glass

• Incoming Quality Control to sort good panels from NG panels is required after the washer.
• Manual inspection cannot be used.
  • Takes too long – cannot keep up with process.
  • Manual inspection is inconsistent and expensive.
  • Manual inspection adds handling defects.
  • No data is created to correlate defects to function.
  • No trend data or other data for evaluating mother glass vendor quality.

Dark Field Solution

• Special scanner Solid State Laser Reflection (SSLR) developed for this application.
• Special Scratch/Sleek scanner developed to find very narrow Scratchs and Sleeks (to 10μm).
• Self-aligning optics automatically adjust for warp, bow and changes in glass thickness – no moving parts.
• Immediate feedback on each panel.
• Measurement of mother glass length, width, squareness.
• Edge grind check and control limits.
• Chamfer defect detection.
• Glass damage detection (cracks, digs).

Aerospace Glass Defect Detection Challenges

• Extremely high value-added; many unit operations.
• Glass can be any shape.
• No objective way to manually detect killer defects on the production line – glass volumes are too great.
• Must sort glass after each operation; pass, reject or rework.
• Rework is possible – polish out scratches.
• Missed defects can result in down stream rejects after adding many $1,000s to the glass.
• Must sort incoming glass to reject open bubbles; small closed bubbles are acceptable.

The On-Line Inspection Solution

• Special optics detect and classify open and closed bubbles, scratches, digs, contaminants and internal glass defects.
• Solid State Laser Reflection (SSLR) technology modified for the application; self-aligning optics.
• Special software detects defects in any shape part without any programming or recipe input.
• Large monitor over the line allows the operator to easily pinpoint the defect location if verification is required.
• SQL database stores all defect information; custom reports/trends created for each installation.

Manual Inspection of Cover Glass

• Incoming Quality Control to sort good parts from NG panels is required after the washer.
• Manual inspection cannot find washer defects.  Washer defects can account for over 50% of ink and coating defects.
• Manual inspection is no longer practical.
  • Takes too long – cannot keep up with process.
  • Manual inspection is inconsistent and expensive.
  • Manual inspection adds handling defects.
  • No data is created to correlate defects to function.
  • No trend data or other data for evaluating cover glass vendor quality.

Dark Field Solution

• Special scanners – Solid State Laser Reflection (SSLR) and Washer Debris scanners developed for CG inspection.
• Self-aligning optics.
• Immediate feedback on each part.
• Measurement of CG length, width, squareness.
• Glass damage detection (cracks, digs).

Conventional Glass Inspection Systems

• Require constant alignment.
• Must utilize active modules under the glass conveyor, which get damaged and require constant maintenance.

Dark Field Solution

• Solid State Laser Reflection (SSLR) technology is self-aligning; no alignment required after installation.
• No active modules under the conveyor/ribbon.

First Surface Inspection – The Problem

• The first surface of the glass may be the only surface of interest in a coating operation.
• Inspection systems should not report particles, stains, top tin and other defects on the second surface.

The Dark Field Solution

• Special SSLR scanner designed to inspect ONLY the first surface.
• Second surface is optically ignored.
• Inspection results show only first surface defects.

Haze Measurement Challenges

• Conventional haze measurement is on off-line operation; small samples, statistical, long time for feedback.
• Film and glass production need 100% on-line immediate haze mapping and measurement.  Identify areas of the web or sheet which are outside control limits.

Dark Field Solution

• Special SSLR technology provides 100% on-line, real-time haze measurement.
• Haze results correlate to Gardner Haze Gard Plus instrument and ASTM Haze Measurement standard #D1003.
• Warning and reject levels.  Real time alerts, alarms, marking.
• Data saved in XML and SQL database files.
• Integrated with defect detection results; single window operation.

Measurement Challenges

• Manual measurements are inexact and time consuming; cannot accurately measure with chamfers present.
• Conventional on-line measurements are also imprecise.

Dark Field Solution

• Special SSLR optics and measurement module measures Length, Width and Squareness with best fit lines and projected corners.
• Accurate measurements in the presence of chamfers and broken corners.

On-Line Warp/Bow Measurement

• Glass plates must be measured for warp and bow on-line before adding value.  Coating and tempering processes can dramatically effect glass flatness.
• Glass needs to be rejected if its flatness is outside quality control limits and the information fed back to the process to modify process parameters.

Dark Field Solution

• Laser scanners are positioned across the conveyor.
• Each scanner generates a real-time measurement of glass profile.
• This profile is analyzed in the Dark Field Warp/Bow processing module to determine if the plate is within specifications.
• Mapping, marking, reject outputs and warning lights are included in the system output.

Conventional Glass Inspection Systems

• Require constant alignment.
• Must utilize active modules under the glass conveyor, which get damaged and require constant maintenance.

Dark Field Solution

• Solid State Laser Reflection (SSLR) technology is self-aligning; no alignment required after installation.
• No active modules under the conveyor/ribbon.

Detection Challenges

• Worn grinding wheels leave flat spots (shiners) and a poorly ground edge.
• Manual inspection is time consuming, inexact and subjective.
• Many plates are typically passed before the problem is found.  Must regrind or scrap.

Dark Field Solution

• Special SSLR optics and measurement module measures the ground area and compares it to the control limits.
• Software settable control limits are used to alert production.

Chamfer Inspection Challenges

• Impossible to measure accurately on-line, manually.
• Must reject sheets with chamfer defects to prevent adding value and scrapping later.

Dark Field Solution

• Solid State Laser Reflection (SSLR) scanner and processing detects chamfers whose dimensions are outside of the acceptable control limits, rejects the panel and shows the defective chamfers to the operators.
• Integrated with SSLR defect detection and edge grind system.
• Software settable control limits are used to alert production.

Transient Defects – Detection Challenges

• Transient defects must be detected in a vast array of high-end products: Electronic readers, Smart Phones/Pads, Smart Windows, etc.
• Transient defects are only visible during a color or state change; they can disappear quickly.
• Transient defects will cause the final assembly to be rejected; they must be captured prior to assembly.
• On-line technologies did not exist to detect transient defects on a production line.

Dark Field Solution

• Special optics and hardware processing modules make detection of transient defects simple and robust at line speeds over 30m/min.

Detection Challenges

• Conventional laser and camera systems cannot detect defects in bent glass, on-line.
• Reflection operation is almost impossible, on-line, with conventional camera/AOI/vision technology.

Dark Field Solution

• Solid State Laser Reflection (SSLR) technology automatically adjusts for glass curvature.
• Reflection and transmission options.

Scratch Detection Challenges

• On-line Scratch and Sleek detection can be extremely difficult.
• Many systems cannot detect subtle scratches and sleeks.
• Scratches/Sleeks in the machine-direction (or conveyor direction) are the most common and the most difficult to detect.

Special Scratch/Sleek Detection

• Special optics detect subtle scratches and sleeks.
• Special  processing/software module improves scratch measurement.

Turnkey Inspection Systems – Customer Needs

• Existing production line: Integration of the inspection system with the existing customer production line.
• Complete turnkey system – Stand alone: Stand-alone system – off-line and development, including roll unwind, rewind, sheet handling.

Dark Field Capabilities

• Existing production line: Dark Field provides complete interface and integration services.  This means mounting the system to the machine frame or the floor.  Customers only need to provide mounting holes or anchor bolts and power.  Dark Field does the rest, including I/O and data interfaces.
• Complete turnkey system – Stand alone: Custom solutions.  Systems are full production systems and can be easily modified/upgraded for relocation to the production line.

Defect Detection and Metrology Challenges

• Maximize efficiency and yield.
• Eliminate scrap.
• On-line, 100% coating defect detection and scribe metrology.

Dark Field Solutions

• Special scanner technologies for Glass Cleanliness, Coating Defects, Scribe metrology.
• Dozens of systems in the field; CIGS, CdTe.