Backlight Design Guide for Silicone Switches

Silicone Switches is also called led lights rubber switches, there is light transmission once the switches are powered on, so that it also named as backlight silicone switches. The light transmission effect needs are different for different devices. How to design a correct led lights switches for your device?

What Makes Silicone Switches Be Backlight?

Led makes rubber switches be lighting. Laser etching the icons/symbols/graphics or adding light pipe in silicone rubber switches or make the whole switches button be transparent or semi-transparent.

What’s differences between laser etching, adding light pipe and semi-transparent switches button?

For semi-transparent silicone button, there is light loss or optical dispersion, because of light transmittable transparent silicone make led light transmit from all directions. But on the other hand, the light in all directions can make the atmosphere.

For laser etching icons, first should make the switches base be silicone natural color or semi-transparent, then paint surface color to cover the base (generally be black/gray), finally laser out the icons, so that the icons color is same as the switches base. So that the icons can be lighted after power on. In a word, the first layer is the color for icons after being laser out.

For the silicone rubber switches that require high light transmission and pure light transmission, adding light pipe design is the better alternative.

What is light pipe for rubber switches buttons?

Light pipe is a clear/transparent rod made of clear plastic, also can be made from glass or high transparent silicone rubber material.

The optical components transmit light from bottom of light pipe to top of light pipe, freeing up some design constraints by eliminating the need for an LEDs to be mounted directly on the panel.

The light pipes can also help diffuse the light where hot spots would otherwise be noticeable and could even impact the safe operation of a device.

When choosing a correct material for the light pipe, application is the first to be considered.

Why choose light pipe for numeric switches?

For silicone rubber switches with requirement for light indicator function, and laser etching is not satisfying or too complicated symbols design to do laser etching.

How to design and manufacture a correct light pipe for your keyboard?

There are two types of light pipes for silicone rubber keyboard: light pipes on switches, and separately light pipes need second manually assemble on switches.

When light pipes molded together with silicone keyboard or separately molding is depend on the entire keyboard design.

1.    Generally speaking, if the light pipe shape is like a silicone button or key and designed on the keyboard, but not inside the keyboard or bottom of the keyboard, molding the light pipe and keyboard together is available.

2.    Under this case, there are two situations for the silicone rubber keyboard with light pipe on color progress: on the one hand, if the keyboard has multicolor buttons/keys, which is made by switches key-setting process, silkscreen printing process and others.

For this type switches, if mixing colors in pad base (not in keys) is acceptable, the transparent light pipe can be compression molded together with the entire switches, like this:

Transparent Silicone Light Pipe Molded Together with the Entire switches

For painted keyboard, for protecting the clear light pipe from being painted with other colors of keyboard, designing a protective cap/cover is necessary. When keyboard is being painted, cover the cap/mask on each light pipe to make sure it is still clean and clear. So that the protective cover/cap should be good fitting the light pipe, like this:

How to make the clear light pipe if the silicone switches design is not OK to cover the keycap?

Laser etching is the solution to make the transparent light pipe on switches. For example, if the light pipe is beside the switches button tightly, which is impossible to cover a keycap on the light pipe. So that can paint the light pipe together with the entire switches and then laser out the color layer to keep the light pipe top surface be clean and clear. But the necessary condition is that the bottom surface of the light pipe should be high transparent or clear as well, which means the base pad for the silicone switches should be transparent first. The final effect of this method is like this:

But the outside wall of the light pipe is not available for laser etching, so that the outside wall of light pipe by this way is with color layer same as the silicone rubber switches although it doesn’t decrease the light transmittance.

Light pipes above are on keyboard, how to design and make light pipe if it is inside of keyboard?

No matter inside or bottom of keyboard, the process for making the light pipe is separately compressing molding, then manually assemble or insert the light pipe to the keyboard. The extra processes increase development cost for the entire keyboard, like this:

How to make the separate light pipe?

The most important is determining requirement for light transmittance.

. If light transmittance requirement is high, both good mold steel and mold finish processing are important. Good mold steel with harder steel hardness and fine polish to mirror finish can satisfy the needs, but also will increase mold cost. Another problem is that if the light pipe dimensions are too small, which is difficult to do mold finish process and mold cost is expensive.

Besides mold steel and mold finish, using high transparent silicone material to make the light pipe can also optimize transmittance.

. If saving development cost is the final needs, common mold steel and common mold finish without polish is cheaper, although this affects transmittance. Meanwhile, using high transparent silicone material to make the light pipe as well, which can improve light transmittance.

The purpose of adding light pipe in/on keyboard is to decrease light loss, to improve the uniformity of daylight distribution and luminance gradient across the room under variable. Different requirements cause different processing method for light pipe and different development cost.