The “10% When 80%” Rule - Post Thumbnail

The “10% When 80%” Rule

Finally! Summer is here. Warm weather, green grass, golf and fishing, and fun in the sun... as long as you are on vacation, that is. For a screen maker summer weather usually means more stencil problems. "Why so?" you ask.

Summer weather, as nice as it is, also increases the humidity. Humidity can cause a stencil to breakdown. An easy fix is to increase the exposure time by 10% when humidity is over 80%. This will also increase the stencil durability. Give it a try.

This actually covers a couple of different scenarios, depending on whether you are dealing with high humidity while making your stencil, or afterwards.

First, if the humidity is high when a diazo-based stencil is first exposed, residual water picked up from humid air may reduce the speed of the photochemical crosslinking, leading to a somewhat underexposed stencil. The extra exposure time can make up for this.

Alternatively, if you have a stencil that was developed under lower humidity conditions, it can absorb some water from humid air and slightly soften the photoresist (since it’s based on a water-processable polymer). If you anticipate that high-humidity conditions are coming, increasing the exposure time increases the degree of crosslinking in the stencil, making it a bit more humidity resistant.