Tact (Tactile) Switches

In this section, the focus will be on tact switches. Tact switches are also referred to as "key switches" or "soft touch switches." Tact switches are push-button devices with a physical feedback to the user and an audible "click" under most normal conditions.

Tact switches are specified as "Normally Open (N.O.)" or "Normally Closed (N.C.)." This specification refers to the position of the contacts when the switch is not actuated. With a few exceptions, the N.O. tact switch is used in most circuit applications.

Tact switches are single-pole single-throw (SPST) devices. In other words, there is one moving contact (pole) and one fixed contact (throw).

Process Sealed Models 7914 and ST (H, M, J) W

The 7914 and ST(H, M, J)W switch families are miniature 4mm and 6mm square process sealed models. These models are available in J-hook, gull-wing, and through-hole terminal configurations. Also available in the model 7914 are top and side actuation configurations. These switches are compatible with most board soldering and board washing process. Designed for minimum board space, these models meet EIA/EIAJ/IPC/VRCI surface mount outline dimensions and are compatible with automatic placement systems.

Typical features include:

• 4mm and 6mm sizes
• J-hook, gull-wing, and through-hole terminal configurations
• Sealed for board process and board wash compatibility
• Tape & reel and tube packaging options available
• Miniature lightweight and suitable for high density mounting

Dust Cover Models SDT and SDTM

The dust cover tact switch families are 6mm and 12mm square sizes. Most models are available with a ground terminal option for RF isolation. Most models are also available in either vertical or horizontal actuation versions and with a variety of actuation button heights. The SDT models are compatible with wave soldering processes, the SDTM models are compatible with reflow soldering processes.

Typical features include:

• 6mm and 12mm sizes
• Compatible with wave soldering or reflow soldering processes
• Tape & reel and bulk packaging options available
• Popular actuation force options
• Popular actuation button height configurations

Super Thin Models STJN-4 and STJN-5

The super thin tact switches are available in 4.5mm and 5mm square sizes. These low profile switches are only 0.55mm and 0.8mm FMS and are compatible with automatic placement equipment.

Typical features include:

• Super thin design for high density board mounting
• Compatible with reflow soldering processes
• Tape & reel packaging
• Actuating force options

Construction of a Tact Switch

A tact switch has the following basic features:

• The terminal lead frame
• The housing which is molded on the lead frame
• The contact spring dome
• The actuator pad
• The spring clip cover

There are variations in construction depending on the model type and requirement for process seal. Figure 13.1 shows an exploded view of Bourns model 7914.

Figure 13.1

Tact Switch Applications

There are many new opportunities open to you through the switch line of products. Markets that have not been served by our trimmer products in the past can now be approached. They include the automotive and appliance markets, industrial process controls, instrumentation, electronic test equipment, consumer grade products, and telecommunications.

Some specific areas to explore are manufacturers of:

• Garage door openers
• Automotive alarm systems
• Pagers
• Remote controls
• Joy sticks
• Radar detectors
• Cellular & PCS phones
• Digital phones
• Compact disc players
• Printers
• VCRs
• DVD players

Instrumentation customers can use these products on the front panels (with key caps) for access to their on-board microcomputers for function select, moving a cursor, or any other operation that might lend itself to a keypad input without requiring a full keypad installation.

Competition

There are few competitors for sealed switches. Bourns is the only known supplier of a sealed switch in a 4mm package. On the other hand, there are many suppliers of 6mm and 12mm tact switches that compete with the dust cover models. There are a few competitors that now have the super thin tact switches. Some of the competitors are:

• Panasonic
• Augat/Alco
• C & K
• Omron
• E-Switch
• Apem
• Alps
• NTE
• Mors