0
\$\begingroup\$

I've been reading into how CRTs were assembled and how they work, but I can't seem to find any concise information behind how the coloured phosphors inside the inner glass tube were applied. There is a bit of a write-up here that explains some techniques but it's hard to visualise without having a background in CRT manufacturing.

Are there any resources available that show this process of the red, green and blue phosphors being applied to the inside glass?

\$\endgroup\$
8
  • \$\begingroup\$ That link says photolithography. Do you not know what that is at all? Or did you want more detail on that? It's basically the same method they use to etch silicon wafers to make integrated circuits and microprocessors, as well as how they produce the copper traces on a PCB. \$\endgroup\$
    – DKNguyen
    Jul 4, 2022 at 4:03
  • \$\begingroup\$ I have somewhat of an idea of how photolithography works. It sounds like they suggest putting the phosphor solution onto the glass and exposing the certain areas to light to remove the parts of phosphor and leaving the specific phosphor colour? I guess I'm after more of a detailed process on actually how this would work. \$\endgroup\$ Jul 4, 2022 at 4:07
  • \$\begingroup\$ On the right track but some things are reversed. They use successively apply layers and use UV exposure to cure material that needs to remain behind and chemically wash the rest away. \$\endgroup\$
    – DKNguyen
    Jul 4, 2022 at 4:12
  • \$\begingroup\$ But how would you protect the other phosphor colours from uv exposure when you're trying to apply more phosphor colours? Wouldn't they also disappear from uv light? For eg. if you apply the red phosphor using the photolithography process, then when you want to apply the green phosphor dots, wont this process destroy the red dots? (if that makes sense) \$\endgroup\$ Jul 4, 2022 at 4:18
  • \$\begingroup\$ Read what I said previously. The UV is not involved in the material that is to be removed. There is no need to protect the material you want to keep from the UV; In fact quite the opposite. The UV decides what material you want to keep. And then when you wash it, the material that was not exposed to UV is washed away. \$\endgroup\$
    – DKNguyen
    Jul 4, 2022 at 4:25

1 Answer 1

4
\$\begingroup\$

A CRT consists of three parts

  • The screen - a slightly curved piece of glass facing the viewer
  • The funnel - basically connects the screen to
  • The electron gun assembly

Phosphors are applied to the inside of the screen before the screen and funnel are joined.

The main issue with a colour CRT is getting the phosphor dots to line up with the electron beams that will be sent through the mask. This was originally a triad-type shadowmask, but was later improved to a slotmask or aperture grille. To this end they are applied photolithographically, using the mask itself to define the exposure.

Photolithography consists of applying a thin film of active ingredient, mixed with some sort of photosensitive binder, to the inside of the screen. This is then selectively cured with an appropriately patterned light source.

For each colour phosphor, first a thin film of phosphor+binder is applied to the screen, and dried. Then the mask is fitted temporarily, and the screen is exposed using a point light source in the position of the electron gun that will be illuminating that particular colour. The light hardens the binder, and then all of the non-exposed phosphor is removed, with a rinse or an etch depending on the chemistries used, leaving the hardened dots in the correct positions. This is repeated for the other two colours. A final application of a light-proof layer may be added to prevent light bleeding between the phosphor dots.

Now the mask is permanently attached to the screen. Then it is fitted to the funnel, then the electron gun assembly added. Finally the tube is purged, evacuated and sealed.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you, this is sort of what @DKNguyen helped me summarise in the comments of the post, but this was a nice summary overall. I'm assuming this process is basically the same for trinitron style monitors, using the aperture grille instead of the shadow mask? \$\endgroup\$ Jul 4, 2022 at 4:34
  • \$\begingroup\$ What is the purpose of the permanently attached shadow mask? \$\endgroup\$
    – DKNguyen
    Jul 4, 2022 at 4:35
  • \$\begingroup\$ Oh I didn't realize that was also called a shadow mask. \$\endgroup\$
    – DKNguyen
    Jul 4, 2022 at 4:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.