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Printed Circuit Board Tools

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Whether you're managing relative humidity or identifying artifacts, these tools will help you achieve the highest quality images.

Size Change Calculator

Humidity and temperature fluctuations in your cleanroom are two very influential factors affecting the dimensional stability of your film, therefore directly affecting the performance of your film.

Use this tool to determine film size change effects due to humidity and temperature changes in in order to determine the appropriate course of action:

Download the  Size Change Calculator Windows Application* (zip file)

  1. You may need to select a PCB film that has lower humidity coefficient for size change. A low humidity coefficient film will immediately deliver a reduction in size change variability without the need for investment in new AC or humidity controls.
  2. You may want to consider upgrades to the environmental controls in your cleanroom.

After launching the application, you will be asked to enter the following:

  • Critical Film Length of Interest (e.g. diagonal): A value up to 9999 millimeters
  • Change in relative humidity: range: -10 to +10%
  • Change in temperature: range -10 to +10 degrees Centigrade
  • Humidity coefficient of film being measured: range: 0.0009% - 0.0015% change per % change in RH
  • Temperature coefficient of polyester: A constant for all polyester films: 0.0018% per degree Centigrade.
  • The Calculator will show you the size change in microns

* JavaScript must be enabled to use the Size Change Calculator Application.

Affects of Relative Humidity

The polyester base itself absorbs and desorbs moisture from the ambient environment. As the plastic absorbs moisture, it expands. As the plastic releases moisture, it contracts. The process is slow. It takes one hour per 0.0254 mm (0.001 inch, or 1 mil) of thickness to reach 99% equilibrium with the ambient environment. The humidity coefficient of expansion for polyester base is 0.0008%/% RH. The humidity coefficient for the base is a constant, regardless of the thickness of the polyester base.

Gelatin in the emulsion and backing layers also absorb and desorb moisture. Both layers are tightly bonded to the plastic base. As the gelatin layers expand and contract, they exert tremendous forces on the tightly bonded plastic base, causing expansion and contraction. Films with high gelatin concentration (thick layers) will exert greater forces than films with lower gelatin concentration (thin layers). The gelatin layers coated on polyester base therefore will increase the humidity coefficient from 0.0008%/% RH to a higher value, depending on the concentration of gelatin. The process is very fast. Gelatin absorbs and desorbs moisture very quickly. It takes less than 2 or 3 minutes for gelatin layers to reach 99% equilibrium with the ambient environment.

The process of absorption and desorption by both the base and the gelatin layers is considered to be completely reversible.

Humidity Expansion Coefficient (HEC) is expressed as % Size Change per % Change in Relative Humidity (% / % RH).

HEC for Kodak films can be located in the respective Technical Information Document. Consult the manufacturer for other films.