HOW-TO GUIDE
How to Solder a Replacement Tactile Switch Onto a PCB
By the OhmSavvy Research Team ·
Before you start
- Unplug the device and remove its batteries; discharge any large capacitors on the board.
- Tact switches sit close to plastic buttons and ribbon cables. Move or tape them clear of the tip.
- Ventilate flux fumes, wear safety glasses when clipping legs, and wash your hands after leaded solder.
Through-hole or SMD tactile switch?
Look at the old switch before ordering. The classic 6×6 mm through-hole tact switch has four legs through the board, usually in a 6.5 mm by 4.5 mm pattern. Surface mount versions sit on four pads on the surface, often in smaller sizes such as 3×4 mm, 4×4 mm or 5.2×5.2 mm, and some side-actuated types press from the edge of the board. The replacement must use the same mounting style and footprint.
Match the replacement's size, height and actuator force
| Property | What to check | Typical options |
|---|---|---|
| Body size | Outline and pin pattern | 6×6 mm, 12×12 mm through-hole; 3×4 to 6×6 mm SMD |
| Height | Board to top of actuator | Often 4.3, 5, 7, 9.5 or 13 mm for 6×6 parts |
| Actuator force | Grams-force or newtons | Commonly about 100 to 320 gf |
| Stem | Round, square or for a cap | Must fit the case button or keycap |
| Rating | Signal-level switching | Often tens of mA at 12 V DC; check datasheet |
Measure height with calipers from the board to the actuator top. When in doubt, match height first: a wrong height is the most common reason a fresh switch feels dead under its case button.
1Remove the old 4-pin switch
Four short legs that you cannot heat at once make this the fiddly part. Pick one of these approaches:
- Clear each pin, then wiggle: wick or pump the solder off every pin, then flex each leg in its hole while touching it with the iron until it moves freely.
- Add solder and rock it out: flood one side's two pins with fresh solder, heat them and lever that side up slightly, then switch to the other side. Alternating a little at a time walks the switch out.
- Cut it free: the old part is scrap, so clipping its legs at the body and removing each stub on its own puts the least stress on the pads.
01
Flux pins
All four legs
02
Free side A
Heat, lever slightly
03
Free side B
Alternate, a little each
04
Lift out
No force on pads
05
Clear holes
Wick or needle
2Clean the holes
The new legs need open holes. Add fresh solder and flux to each hole, then clear it with wick, a pump from the far side, or a stainless needle pushed through while the solder is molten. The full method is in removing solder from a plated through hole. Check the pads are still attached; if one has lifted, repair it as described in repairing lifted PCB pads before going further.
3Seat the new switch flat
Line the legs up with the holes in the same orientation as the original; the 6.5 mm and 4.5 mm spacings normally allow only the correct alignment. Press until the body sits flat on the board. Many tact switches have kinked legs that snap in and hold the part; if yours do not, hold it with tape or a finger on the far side of the board.
4Solder the pins
Solder one corner pin first, then look along the board edge: if the switch is tilted, reheat that pin and press it flat. Then solder the diagonally opposite pin and the remaining two. Each joint needs only two to three seconds and enough solder for a small concave fillet. A typical setting is 320 °C to 350 °C with leaded solder; see the temperature guide. Keep the tip off the plastic body.
Fitting an SMD tact switch instead
For a surface mount tact switch, flux and lightly tin one pad, hold the switch in place with tweezers and reflow that pad, then check alignment before soldering the other three. Heat the pad and terminal rather than the body, as the plastic is small and the dome inside can distort. A fine chisel suits most SMD tact pads, and the solder bridge guide helps if terminals are close together.
Test the new switch
With the board unpowered, set the meter to continuity and probe across the two pairs, for example pins 1 and 3. It should read open when released and close to zero ohms when pressed. Then check the always-joined pins read continuous. The method for finding pairs is in how to test a push button switch with a multimeter.
Test in the case too
Irons from our soldering reviews
60W with an adjustable dial, five tips and a stand. Aimed at beginners and occasional use.
100W digital station that takes the same T18 tips as the FX-888D it replaces, with a 65W iron for small switch legs.
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Frequently asked questions
Does it matter which way round a tactile switch goes?
For a four-pin through-hole tact switch it usually only matters by 90 degrees. Pins are joined in pairs internally, so turning it 180 degrees gives the same circuit, but turning it a quarter turn can leave the button permanently connected. The leg spacing differs on the two axes, so it normally only fits the correct way.
Can I replace a tactile switch with a different height?
Only if the enclosure button still works. Too short and the button cap may not reach it, leaving a dead or spongy press. Too tall and the switch is held partly pressed, or the case will not close. Measure the old switch from the board to the top of the actuator and buy that height.
Why does my new tactile switch feel different from the old one?
Tact switches come in several actuation forces, commonly given in grams-force or newtons, and stem shapes. A replacement with a heavier force feels stiff; a lighter one feels mushy or triggers on a light touch. Check the force on the original's datasheet if you can identify it, or try a mid-range value.
How hot should the iron be for a tact switch?
A normal through-hole setting is fine, typically 320 °C to 350 °C with leaded solder and a little higher for lead-free. The pins are small and short, so each joint takes two to three seconds. Avoid leaving the tip on a pin for long, as heat travels up into the plastic body and can deform the internal dome.
My replacement tactile switch does nothing. What went wrong?
Check orientation first: a switch turned a quarter turn may read as always closed or simply not connect the right pads. Then check each joint for a cold or missing fillet, and test the switch on its own with a meter. If the switch tests fine, the fault may be a lifted pad or a broken trace near the old part.
