An Improved Membrane Switch for Medical Equipment

A Solution to New FDA Standards

Today's marketplace sets high demands for fast, accurate, and reliable human-machine interface solutions. Original equipment manufacturers, in order to meet industry and government standards, must incorporate interfaces that provide ease of use, satisfactory tactile response, and rapid functionality. Membrane switches meet those criteria more reliably than any alternative methods available.

In the medical device market, a sealed tactile membrane switch provides a switch function with significant advantages. These advantages prove especially important in a clinical or research environment: clear graphics, cleanliness, gaskets, shielding, illumination, and tactile feedback. It weighs less and has a smaller footprint at a cost lower than most other switch technologies.

Few other machine manufacturers are required to meet the demanding needs of the medical sector, with the most challenging requirements coming from the federal government’s Food & Drug Administration. The FDA has set a high bar for these manufacturers, requiring their products to pass stringent compliance testing before going to market. Every component is tested—including the membrane switch.

A Case Study

Recently a medical device manufacturer approached the Cubbison Company, a leading U.S. membrane switch manufacturer, with problems that have kept their equipment from getting to market. A problem with the machine’s current membrane pads caused it to fail to meet new standards set forth by the FDA. Cubbison needed to diagnose the problem and recommend a solution.

The diagnosis

Upon reviewing the failing membrane pad, it was clear to Cubbison engineers that the problem was inadequate shielding design. The current design had an ITO film EMI shield covering the printed circuitry, with a ground trace running around the perimeter of the part. The ITO material is ideal for the display windows, but there is no ESD protection over the pushbuttons, or around the circular cutout.

The solution

Cubbison recommended a full-coverage, conductive silver printed shield be used in conjunction with the ITO film behind the display windows. This would provide the necessary level of ESD protection (15KV) needed to pass testing. Cubbison also discovered that some of the conductive traces on the sample were too close to the edge of the part, making them susceptible to ESD flash around. Those traces would need rerouted. The printed shield would be extended to the edges of the part in order to minimize and prevent ESD flash around.

The Cubbison team quickly attacked the issue by completely redesigning the shield and creating a prototype. Upon review, the customer agreed that this new design could be the solution. An initial run of the redesigned part was made and sent to the customer for testing by their engineers. The test proved successful.

Understanding the criteria

Membrane switches are designed to meet a very specific set of criteria depending on the application. Effective membrane switch design requires a good understanding of the application and the ability to communicate what is required for a successful and efficient design. It is of particular importance when developing equipment for use in the medical field.

Cubbison designers and engineers are experienced in looking beyond the interface’s basic functionality. They work very closely with equipment manufacturers in developing a membrane switch that performs flawlessly in the end-user environment.