As a manufacturer of custom products, we are regularly consulted about materials to best meet our customer’s wants and needs.  However, very often we are directed on what materials to use by the customer.

After reviewing a blueprint for a new membrane switch, we noticed that for the graphic overlay, the customer was calling out a hard-coated polycarbonate material with a specific UL Rating. Furthermore, the overlay was going to have a black background and embossed areas for the metal domed keys.

At Nelson-Miller, we have experience with this specific hard-coated polycarbonate and knew that it was an excellent material for flat overlays/keypads but it was not recommended for embossing due to possible cracking of the hard-coat. The buyer was notified about our concerns but responded that this same material had been used in similar applications on a multiple of other products with no evidence of cracks/fractures after embossing.


Having concerns about this application, we proceeded to mock up a sample keypad in order to save customer from troubles they could face in the future with their application.  We took a sheet of the same polycarbonate material, printed a black flood color on the backside, embossed some random areas for keys, and assembled a faux keypad. We placed the keypad onto our life-cycle tester and cycled the parts for 10,000 actuations.


A rounded elastomeric test probe was used to simulate a human finger and the test was performed per ASTM F-1578 standards.  After 10,000 actuations, the keys that were cycled exhibited tiny white flakes around the embossed edges. This was clearly visible to the naked eye since the black background provided the needed contrast. This entire test was performed within a single day. The mock keypad was mailed overnight to the customer for review. The feedback was quick and definitive from the customer; please recommend a change to the graphics overlay material!

The great thing about this was that it was a relatively quick and effective way to guide a customer to a successful launch of a new product while averting potential problems further down the road.

Have you had an application where you used a material that didn’t turn out as expected?  What did you do?