HMI Assembly for Portable Digital CR System


A customer requested Epec to design and manufacture a custom Human Machine Interface (HMI) for a portable digital imaging system used in industrial applications. The HMI needed to be designed so it could be mounted into a shallow pocket in their preexisting designed plastic enclosure. The maximum overall stack-up height requirement was 0.150".

A secondary challenge was that the assembly would need to withstand extreme outdoor environments. The assembly would also need to withstand chemical wash downs, hydraulic oils, and heavy cleaning solvents.

Lastly, the customer had no formal documentation for the project to include electrical or mechanical engineering drawings, schematics, or artwork files for the graphics overlay layers.


The customer provided Epec's engineering team with a hand sketch that provided the overall size and shape for the switch assembly. The customer indicated that the mounting pocket that would house the HMI assembly was not an enclosed solid pocket. With this information the engineering department determined that a rigid printed circuit board (PCB) switch assembly was required for the design.

  • Front View of HMI Assembly for Portable Digital CR System
  • Back View of HMI Assembly for Portable Digital CR System

Taking that into consideration we were able to develop the overall construction and stack-up for the complete user interface assembly. This allowed us to identify a hard coated polyester material that would withstand the harsh industrial environment.

The next step was to determine the correct PCB thickness to meet the 0.150" overall height requirement. A 0.032" thick PCB was chosen which would provide a rigid back plate for the HMI assembly and allows positive switch feedback to the user.

Finally, the graphics layer was designed and a secondary matte finish was applied to the graphic overlay. This provided reduced glare in a sunlight environment and added increased durability.


Epec's knowledge of membrane switch technology used in harsh environments and Mechanical / Electrical design engineering experience allowed Epec to assist the customer to meet several critical design requirements. Epec's engineers were able to design and develop all aspects of the customer's project allowing them to meet the development schedule and provide a high reliability switch assembly.

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