Membrane Switch for Industrial Gauge
A manufacturer of heavy industrial/ agricultural equipment invited GDSI to propose a design solution for a gauge display. There were a large number of field failures and end user complaints with this membrane switch. The issues with the current design included:
· Poor backlighting
· Moisture penetration causing silver migration and electronic failures
· Cracked conductor traces causing catastrophic failures
GDSI's circuit technology, Double Sided Polymer Circuitry (D/SPC®), provided a solution for all three problems. The following design changes were made::
1) Circuit trace widths were reduced to maximize light transmission from the light source, and by eliminating a structure that blocked the light in the previous design, which also eliminated an inactive area of the membrane switch keypad.
2) Circuit tail traces were moved to the inside radius, reducing the risk of opens created during assembly, and the risk of high resistance opens developing over time.
3) D/SPC® was applied to reduce the overall circuit size to allow space for a complete perimeter seal against water and chemical penetration.
4) Carbon ink overcoat on silver ink to prevent silver migration and increase resistance to water and chemical attack.
5) D/SPC® provided a common circuit pattern which allowed interchangeability with 14 different overlays.
6) The outside cut line of the circuit subassembly was reduced slightly to allow it to be recessed into the case and ‘trapped’ by the now oversized overlay; increasing the barrier to water and chemical penetration.
Not only did the new design eliminate field problems, but the overall cost of the product decreased substantially.
Since 1995, approximately 37,000 of these switches have been manufactured and shipped for assembly into the gauge display. No part has been rejected, and there is no report of field failures due to GDSI workmanship.