The most expensive mistake on this product family is not electrical, it is a part number. A latching push button switch changes state on one press and holds it mechanically after the finger leaves, and many PB-series housings are offered in both latching and momentary variants whose part numbers differ by one or two characters. In the compact alternate-action PCB type covered here, the next press returns the switch to its original state. Many of these use a heart-cam and follower mechanism, which is why the format is also sold as self lock or push-lock. Swiclick builds this class as the PB series in bodies from 5.8mm square up to 8.5mm, in surface mount and through hole. Several PB-series parts use a six-terminal DPDT contact arrangement. Bodies are available with and without a moulded cap, and pin length can be trimmed on standard parts.
The Part Number Trap
This goes first because it costs more than anything else on this page.
The same physical body, footprint, cap and colour is built in two mechanical variants. One latches. One does not. The difference is a cam inside the housing and one or two characters in the part number.
They may be visually indistinguishable before operation, especially when they share the same housing and cap. Some pairs can be told apart by button rest height, travel or a housing marking, but not reliably enough to depend on during incoming inspection.
A board built with the momentary version where the design called for latching will pass electrical test, pass ICT, and pass functional test on the bench with an engineer holding the button down. It fails in the field the first time a user presses and releases.
Two habits prevent it. Write the full part number including the suffix into the BOM rather than a shortened form. And add a step to the functional test script that presses, releases, waits, then checks the state. A press-and-hold test proves nothing about a latching mechanism.
How the Mechanism Works
In a heart-cam design, a small pin rides in a heart-shaped groove cut into the slider.
Press once and the pin travels up one side of the heart and drops into the notch at the top. Spring pressure holds it there and the contacts stay transferred. Press again and the pin lifts out of the notch, runs down the other side and returns to the base.
Two consequences follow from that geometry.
The press-to-latch and press-to-release forces are not the same, and release usually needs slightly more travel. If a moulded cap sits over the button, check that the cap does not bottom out on the housing before the pin clears the notch.
The mechanism has more moving parts than a tact switch dome, so cycle life on this family is generally lower than on a momentary tactile part of the same size. Specify the cycle count you need rather than accepting the catalog default.
Not every alternate-action pushbutton uses this mechanism, and larger panel-mount latching devices may use pull-to-release, twist-to-release or a separate reset. Those are a different product class from the PCB parts described here.
Latching or Momentary
The decision is about where the state lives.
A momentary switch with firmware is usually preferable when the controller stays powered and electronic state retention is acceptable. It is smaller, cheaper, available in surface mount at higher density, and the behaviour can be changed in software later. A tact switch covers this case well.
A mechanical latching push button switch remains useful where the state must be visible, power-independent or electrically enforced. That includes a mains-side power switch, a device that must return in the same state after a battery change, a control where the user needs to see and feel the position, and any case where standby current or hardware isolation rules out holding state in firmware.
Both are legitimate engineering answers. The one that gets chosen by habit rather than by that test is the one that causes a redesign.
Body Sizes
The PB series covers a small range of square footprints.
5.8mm square. The smallest. Available as through hole with a locking action and as surface mount with a flat knob for designs under a cap. A DPDT 5.8mm locking push switch is the reference part for this size.
7x7mm. The volume size, available through hole with and without a moulded cap.
8x8mm and 8.5mm. Larger bodies for higher actuation force and taller travel, including a double rows 8x8mm latching version with terminals in two rows for higher pin count.
High actuator handle. A taller plunger variant for designs where the button projects well above the board through a thick front panel.
Surface mount options exist at 5.8mm. A latching mechanism generates more lateral force during actuation than a momentary switch, so pad geometry and mechanical support matter more if a finger presses the button directly rather than through a guided cap.
Specifying One
- Latching or momentary, stated explicitly, with the full part number suffix
- Body size and total height above board
- Contact configuration, confirmed against the datasheet rather than assumed from the series
- Through hole or surface mount
- Actuation force and travel available in your enclosure
- Cycle life required across product service life
- Annual volume
Swiclick quotes standard parts from the self lock switch range with a 500-piece minimum order quantity. Pin trimming to a custom length is available on standard bodies. Custom cap geometry is a tooling item.
FAQ
In the compact PCB switch family covered here, self lock, push lock and alternate action normally all refer to a push-on push-off latching action. Latching switch is a broader term in the wider market and can also cover pull-to-release, twist-to-release and separately reset devices.
Often you cannot, particularly before operation, because they share bodies, caps and footprints. Rely on the part number suffix and a press-and-release functional test.
Yes, in the 5.8mm size. Account for the lateral force during actuation and confirm the pad geometry supports it.
Several PB-series parts use a six-terminal DPDT arrangement, giving two independent circuits that transfer together. Confirm per part number.
Check the published rating for the specific part. This family is designed primarily for PCB-level switching. For a mains power switch, confirm both the rating and the required safety approvals for your market before specifying.
Yes, on standard bodies. Trimming pins to suit a board stack is a routine request.
