A customer called us last year, frustrated. They had designed an outdoor kiosk for a public park, with a membrane switch keypad. They specified IP65, which means "protected against water jets from any direction." They tested the keypad in their lab with a garden hose, and it worked fine. Six months later, the kiosk was in the field, and the buttons were failing. Water had gotten behind the membrane, and the contacts were corroded.
We looked at the design. The membrane switch was mounted to the enclosure with a simple adhesive. The adhesive was 3M 467MP, which is a good acrylic adhesive, but it is not designed for outdoor use. After six months of sun, rain, and temperature cycling, the adhesive had delaminated at the edges, and water was seeping in. The customer thought the membrane switch itself was the problem. It was not. The enclosure design was the problem.
Here is what we tell every customer who asks for a waterproof membrane switch.
IP rating is not just about the membrane
The IP rating of a device is the rating of the whole enclosure, not just the membrane switch. A membrane switch can be IP67 by itself, but if the enclosure around it has a gap, the whole device is only as good as the weakest point.
The most common IP ratings for membrane switch applications are:
IP54 - dust-protected, splash-water protected. Good for indoor use, like an office copier or a medical device in a dry room.
IP65 - dust-tight, water-jet protected. Good for outdoor use, like a kiosk or an industrial panel that gets hosed down.
IP67 - dust-tight, protected against temporary immersion (up to 1 meter for 30 minutes). Good for handheld devices that get dropped in water, or equipment that gets washed down with a pressure washer.
IP69K - dust-tight, protected against high-pressure, high-temperature water jets. This is the rating for food processing equipment, where the panel gets cleaned with a steam cleaner every day.
IP65-rated membrane switch installed on an outdoor industrial enclosure.
Three ways to seal a membrane switch
There are three common ways to mount a membrane switch to an enclosure, and each has a different water sealing performance.
1. PSA adhesive (pressure-sensitive adhesive). This is the simplest method. The membrane switch has a layer of acrylic adhesive on the back, and you peel off the liner and stick it to the enclosure. It works for IP54 and below, but not for outdoor use. The adhesive will delaminate over time, especially if the enclosure is made of powder-coated aluminum, which is a low-surface-energy material. We recommend using a 3M VHB tape instead of standard PSA for outdoor applications, which has better adhesion and UV resistance.
2. Gasket and screws. This is the most reliable method for IP65 and above. You cut a foam gasket (silicone or EPDM) to the outline of the membrane switch, and you clamp the membrane switch to the enclosure with screws. The gasket compresses between the membrane and the enclosure, creating a water-tight seal. This method is re-serviceable - you can remove the membrane switch, service the electronics, and reinstall it. We recommend using a silicone gasket with a Shore A hardness of 40-50, and compressing it by 20-30% of its thickness.
3. Ultrasonic welding. This is the most permanent method. The membrane switch is welded directly to a plastic enclosure, using ultrasonic energy to melt the plastic around the edge. This creates a hermetic seal that is truly IP67, and it will never delaminate. The downside is that you cannot remove the membrane switch for service. This method is used for consumer products like waterproof remote controls and wearable devices.
Four-legged stainless steel domes with gold plating used in waterproof outdoor keypads.
What about the cable exit?
The most overlooked leak point in a membrane switch enclosure is the cable exit. The membrane switch has a tail that connects to the PCB inside the enclosure. Where that tail passes through the enclosure wall, you need a seal.
The simplest way is to use a strain relief gland, which compresses around the cable tail. For IP67, we recommend using a silicone grommet, which you glue into the enclosure wall and then feed the cable through. For IP69K, you need a cable gland with an IP rating, which is a threaded fitting with a rubber seal that compresses around the cable.
We have seen customers get a perfect IP67 seal on the membrane switch itself, only to have water leak in through the cable exit. Always test the whole assembly, not just the membrane.
How we test for water resistance
When a customer orders a waterproof membrane switch from us, we do not just build it and ship it. We test it.
For IP65: we spray the assembly with water at 100 liters per minute, from a distance of 3 meters, for 15 minutes. Then we open the enclosure and check for water inside.
For IP67: we submerge the assembly in 1 meter of water for 30 minutes. Then we open it and check.
We also do a thermal cycle test, which is what most customers skip. We cycle the assembly from -20C to +60C, 10 cycles, and then re-test the water resistance. The temperature cycling expands and contracts the materials, and it can reveal seal weaknesses that a simple water test would miss. The customer's kiosk failed after six months because the temperature cycling had delaminated the adhesive. A thermal cycle test would have caught that in a week.
If you are designing a waterproof keypad or FPC button assembly, send us your enclosure drawing. We will review the seal design, recommend the right mounting method, and build a sample assembly that you can test before you commit to production.
- John Smith, Senior Application Engineer, Shanyo
