Describe the transmitted image explicitly
A black-and-white drawing can mean either retained opaque film or clear windows, depending on the drawing convention. Describe the physical result: for example, clear lines in an opaque field or opaque lines on clear glass. Avoid relying on the words positive and negative without that definition.
| Choice | Meaning | Common confusion |
|---|---|---|
| Polarity | Which regions retain opaque film | Dark drawing background interpreted as film |
| Film side | Physical surface carrying the pattern | Reading side assumed to be film side |
| Viewing direction | Side from which the pattern must read correctly | Mirrored labels accepted because the grid looks symmetrical |
| Illumination mode | Transmission through or reflection from the component | Visible transmission contrast assumed to equal reflection contrast |
An opening in the film leaves the substrate intact
A chrome-on-glass slit or pinhole transmits through an uncoated region and the supporting glass. Its optical behaviour includes substrate transmission, refractive effects and surface reflections. A metal aperture or drilled glass hole provides a physically open path and requires a different component definition.
Clear opening in a film
Light crosses a clear region and then the continuous glass. The film opening is not a through-hole.
Opposite viewing sides
An asymmetric mark reverses when viewed through the substrate from the opposite side.
Define the side from which the drawing is read
Specify whether the drawing is viewed from the film side or through the glass. Include a readable asymmetric mark and the intended installation direction. Viewing the same part from its opposite side reverses the apparent pattern; rotating a symmetrical grid cannot prove that mirroring is correct.
Transmission and reflection need different contrast checks
In transmission, film leakage and clear-region transmission govern contrast. In reflection, coating reflectance, substrate reflections, illumination angle and camera position matter. A chromium area that looks dark in transmission may appear bright in reflection. Specify the wavelength and observation geometry together.
Keep mask polarity separate from resist behaviour
A clear mask region admits exposure light. Whether that region later becomes an opening in the resist depends on the resist tone and process. In contact or proximity lithography, film-side orientation also changes the separation between the mask pattern and the resist. Confirm mask geometry, exposure orientation and resist response as separate steps.
Record the optical interface in the drawing
Use separate DWG layers for physical outline, retained film, clear windows and orientation marks. Define their meaning in the drawing legend. Keep the approved view and revision associated with the manufactured pattern, especially for multi-layer sets and asymmetric coordinate labels.