Article: Fine lines in high yield (Part CXXXIII): safe lighting in yellow room exposure areas.(Tech Talk)

The subject of Safe Lighting has been previously covered in Tech Talk (No. 71, August, 2001). This column includes some updates, mostly concerning sourcing. The PWB industry standard photolithographic process uses negative working photoresists exposed with UV radiation in the near UV range, whereby the photoresist UV-radiation sensitivity is peaking around 365nm. More correctly, the photoresist is not only sensitive to UV radiation but also to near-UV visible light in the 410 to 430nm range which makes up the violet and blue light of the visible spectrum. This visible light is not "safe," i.e. it can lead to premature polymerization of the photoresist after the dry film ...

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