A surface imperfection not visible to the naked eye can become a glaring defect when magnified in the end product. A particle of glass, a finger print, a water spot may go unnoticed until enhanced by the application of optical films. As technologies continue to advance, as devices become smaller, more powerful, brighter and clearer, it is essential that your glass requirements are understood and met.

To help define your needs, following is an overview of general cosmetic specifications, inspection methods and Coresix capabilities. Coresix can work to known cosmetic specifications or help the customer to determine the appropriate specifications for a given application.

Defect Size

  • Scratch and Dig Defined
    Although this standard is based on comparison to a certified optical comparator, the following general guideline is commonly accepted when referencing a scratch and dig specification:The first number represents the maximum allowable scratch width in microns (20/10 = no scratches greater than 20um wide allowed). The second number represents the maximum allowable dig in 10's of microns as measured LxW/2 (20/10 = no digs greater than 100um allowed).

Typical Scratch and Dig Specifications

  • 120/80 - Defects are clearly visible in normal room lighting. This is generally a commercial specification for glass that will be exposed to further wear.

  • 80/50 - Defects are discrete but visible in normal room lighting. Typical for commercial and non critical optical applications.

  • 60/40 - Defects are visible under fluorescent lighting (1.5K Lux). Common for non-magnified optical applications.

  • 40/20 - Defects difficult to detect under fluorescent light and may require low-intensity halogen lamp (5K Lux). Typical optical applications.

  • 20/10 - Defects require hi-intensity halogen lighting to identify (10K Lux). Specified for critical optical applications.

  • 10/5 - Defects require hi-intensity halogen lighting to identify (15K Lux or greater). Specified for the most critical optical applications.

 A scratch and dig specification can be written and inspection standard developed around any known requirements. The sample specifications listed above are intended to provide a general guideline and encompass the most commonly used values.

Light Conditions
When inspecting glass components, Coresix incorporates the light condition to define the cosmetic requirements as “no defects visible" with the unaided eye under the specified light intensity, in the specified position and within the specified inspection time.

Coresix uses a standard “K Lux” to describe the required light intensity for a given inspection criterion. Any existing or known light intensity such as foot candle, wattage, etc. can generally be converted to a K Lux standard.

Typical Light Intensity Specifications:

  • 1.5K Lux - Identifies scratches beyond 60um wide and digs greater than 400um for low-end optical or high end industrial applications.

  • 5K Lux - Used to identify scratches beyond 40um wide and digs greater than 200um for common optical applications.

  • 10K Lux - Identifies scratches beyond 20um wide and digs greater than 100um for high end optical applications.

  • 15-50 K Lux - Various collimated lighting used to identify defects to 1um for critical optical applications.

Light reflection diagram Position
The angle, distance and/or orientation of the glass being inspected to the light source.

  • Angle
    The angle at which the part is held to the light source can influence the visibility of a defect. The specified angle may be driven by the final application (coatings to be applied, angle to be viewed, etc.) or to achieve maximum effectiveness.

  • Orientation
    The orientation of the part to the light source can influence the visibility of a defect. The specified orientation may be driven by the final application or to achieve maximum effectiveness.

  • Distance
    The distance of the glass from the light source is generally defined by the specified light intensity. However, under certain conditions it may be necessary to specify distance in conjunction with light intensity.

The longer an inspector looks at a glass component under any condition, the more likely he or she is to identify defects. For production efficiency, the specification is designed to identify the necessary cosmetic quality level in a minimal inspection time. Our standard inspection time averages 5-10 seconds per part.

At Coresix, we continually invest in the metrology equipment necessary to verify and advance our process results. Following is an overview of our inspection methods and capabilities:

Measurement Equipment Capabilities
Dimensional SmartScope™ Flash 500
(Non-contact Optical CMM)480mm x 430mm x 200mm measurement range

1µm resolution 

ErrorXY = 2.5 + 5L/1000 ìm where L = Length of part measured

  SmartScope™ Flash 200
(Non-contact Optical CMM)
200mm x 200mm x 150mm measurement range

ErrorXY = 2.5 + 6L/1000 ìm where L = Length of part measured

ErrorZ = 5.0 + 6L/1000 ìm where L = Length of part measured
3D Surface Map & Transmitted Wavefront Zygo PTI 250P™ Fizeau Interferometer

Phase Measuring Interferometry for ë/100 uncertainty

RMS Repeatability: ë/6000 (1ó)
Surface Roughness Zygo NewView 6300™ Non-contact, three-dimensional, closed-looped, Piezo-based scanning white light interferometry

RMS Repeatability:
Flatness Tropel FlatMaster© 200 25mm to 200mm measurement range

Repeatability: 0.5 ìm
TTV (Thickness Variance) Air Gauge Non-contact air gage system

Repeatability: 0.7 ìm