We find tactile switches almost everywhere – on keyboards, on mice, beside the monitor, on TV sets, on set-top boxes, on toys and on mobile phones. These tiny switches give a distinctive feeling when pressed. We are so used to using tactile switches; we press them a dozen times a day and never think twice about them – that is, as long as they work. However, tactile switches can also stop working, and engineers must select tactile switches with great care so they last long. After all, most feel that a bad or nonfunctioning switch equals a bad device.
Therefore, to avoid the possibility of a quality black eye, you must essentially select the right switch. Deciding what it is that exactly makes a tactile switch right of the job, may depend on a host of factors, of which two are most important. One is the actuation force and deflection characteristics necessary to meet the requirements of the application. The other is the reliability with which the switch must work during the life of the host electronic gadget.
Thinking of switches as commodity items selected straight off a datasheet, is an expensive mistake that many engineers do make. In reality, picking a durable switch with the right feel does require somewhat more than a mere glance at its specifications. Here is what you should be looking for.
The click ratio of a switch expresses the relationship of its actuation and contact forces. A higher click ratio is indicative of a snappier or crisper switch feel. The deflection or travel distance of a pressed switch also contributes to its overall feel.
A typical datasheet holds the force and travel specifications and these can be a starting point for selecting a switch that feels just right in its intended application. However, the ideal switch depends on the application – an important thing to remember.
For example, users of portable consumer electronic devices prefer crisp tactile switches that have a relatively high click ratio and shorter travel distances. On the other hand, tactile switches for the automotive industry need lower click ratios and longer travel distances. This prevents accidental actuation while driving. Therefore, each electronic application needs to reach a unique balance between the travel distance and the actuation forces.
Consumer electronics and medical applications need tactile switches that are protected against ingress of liquids and other contaminants – IP 67. Usually, these sealed tactile switches reach their maximum lifecycle, because of the sealing.
Manufacturers have traditionally used a bonded silicone membrane to seal the innards of a tactile switch. Now, technologically improved IP67 rated tactile switches use a patented laser welding process that seals the switch with a thin nylon film. This goes over the actuator rather than under it, giving a better seal. The seal not only preserves the crisp feel, but also protects the switch against side loads.
Protecting the switch with the nylon film improves its inherent reliability by not allowing ingress of contaminants. The best switches will typically offer a life expectancy of above one million press-and-release cycles.