Improved Membrane Switch Design for GPS Application
A manufacturer of GPS devices invited GDSI to review their current membrane switch design and make recommendations to improve field performance. There were a number of field failure issues including circuitry shorting due to failed cross over insulation, inconsistent tactile feel from the elastomeric keypad and form/fit issues due to warping of the platform.
Cross-over issues: A cross over design consists of two printed polymer thick film circuit traces, one printed over the other. There is an intermediate insulation layer that is normally printed and prevents the two circuit traces from shorting. This design has significant reliability issues as the printed dielectric layer has micro-pores that can allow the top silver trace to leach through and contact the bottom silver trace. This design often passes initial electrical testing, but can fail over time.
Working with the customer's design engineers, GDSI’s first priority was to understand the complete assembly to ensure that the proposed circuit design was optimal in relation to the design of the platform and the elastomeric keypad. This understanding led to the following product improvements:
- The cross over design was replaced by GDSI’s D/SPC® technology which completely eliminates the crossover failure point.
- D/SPC® allowed circuit tail traces to be moved to the inside radius, reducing risk of creating opens during the assembly process.
- Printed carbon over silver traces in the interconnect and keypad areas of the circuit to increase durability against abrasion and water/chemical penetration.
- The Platform was redesigned to reduce warping and stability problems.
- The molded elastomeric keypad and mounting assembly was redesigned to improve consistency of tactile feel and reduce the risk of the keypad shifting or being pulled out during use.
By combining GDSI design talent and D/SPC® with the expertise of the customer’s designers, GDSI eliminated multiple failure points with significant cost reduction. Additional savings were achieved by the reduction of field failures.