Photoresists are light-sensitive, they are affected by light exposure and high temperatures, and also age-related changes occur during storage. Resists are therefore filled in light-protected amber glass bottles, stored in a cool place, and may only be processed under yellow safe light (λ > 500 nm). Date of expiry and recommended storage temperature are indicated on the product label of each bottle. Following these recommended storage guidelines, resists are stable until expiry date, at least however for 6 month after date of sale. Short-term temperatures deviations have no influence on general product properties.
If resists are to be used later than 6 month after date of sale or are processed within a very small process window, storage at 4 – 8 °C is recommended. Exceptions are only resists with recommended storage temperatures between 18 – 25 °C. These resists should not be stored cooler. Photoresists stored for several years are outdated and may only be used with considerable restrictions (see also Question 3.).
Bottles which were kept in the refrigerator should never be opened immediately, since in this case air moisture may precipitate on the cold resist. Resists should be adapted to room temperature before opening.