ON Semi on Image Sensor Cleaning

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ON Semi application note "Image Sensor Handling and Best Practices" describes best practices of image sensor cover glass cleaning:

Do not touch the cover glass with fingers or anything other than a cleaning paper as required in this section. Finger grease can etch optical coatings and cause permanent damage. The gloves should be static and powder free. Gloves should be static dissipative Nitrile gloves.

Materials:
  • Clean compressed nitrogen
  • Ultra−clean DI water (4−6 megaohms/centimeters deionized water that has been filtered)
  • High-grade IPA (solvent grade/100% pure lab purity grade)
  • ESD protective Wipe:
    ♦ For CCD sensors: Berkshire DurX 670
    ♦ For CMOS sensors: Puritech Puritech S1091PRT or RTMKC002
  • ESD protective gloves for example: Nitrile Glove, required Ansell 93−401/402 or NiProTect CC529

Method A: Blow Off
This method is applicable for loose particle contamination. This is the only method that guarantees no residues such as drying spots.
  • Remove particles from the glass by blowing with an ionized-N2 gun.
  • Do not blow towards the other parts. If you work under a flow box, try to blow out of the box.

Method B: High-Grade IPA Clean or Ultra−Clean DI Water
  • Apply cleaning solvent using a separate lab−ware quality polypropylene squeeze bottle (Nalgene trade name), not the original bottle
  • Use a lint free wipe in one direction, with even pressure across the glass surface.
  • Never wipe the cover glass with a dry cloth. The cleaning solvent should be applied directly to the cleaning wipe and never directly on the cover glass.
  • The ESD protective wipe should not be saturated, only dampened with the cleaning agent.
  • After each wipe, either start with a fresh wipe or fold the wipe to provide a fresh surface for glass cleaning

Note: High grade IPA or ultra-clean DI water are acceptable for cleaning both plain glass and AR coated glass.

Note: Method A and B are acceptable methods to clean the CCD image sensor cover glass with the following exception. DI Water or IPA is not recommended for cleaning the CCD image sensor cover glass. Instead, 100% ethanol is required as the cleaning agent for CCD image sensor cover glass.

Caution on Cleaning Agents:
  • Use high-grade IPA only to clean the image sensor lid glass. Other solvents can contaminate the glass, attack the resin and sealant, and degrade reliability of the package.
  • Do not use acetone because it attacks the resin that glues the cover glass to the package.
  • Do not use methanol due to its toxicity and low quality cleaning properties.
  • Do not use sodium hydroxide (NaOh) because it degrades the AR coating on the glass.
  • Do not use highly alkaline (pH > 8) cleaning chemistries.
  • Do not use any solvents commonly used in paint strippers: toluene, benzene, methyl-ethyl ketones, ester solvents, acetone or methyl chloride, freons, terpens, anionic surfactants and multi−hydroxyl ethers.

If the surface is not clean, repeat these procedures. If the contaminant is not removed in two or three wipes, it is possible that the cover glass is permanently damaged. Inspect the device in optical microscope for permanent damage.

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