Membrane Switch Cutting

Written By Mark Batson Baril

It’s amazing how many things out there involve specialty cutting.

Do you own a Microwave Oven? - a Treadmill for exercising? - a flat faced calculator? - a machine with a pressure sensitive operation switch? If you do, then chances are you own and use a Flat/Tactile Membrane Switch (or several) everyday! These switches can be used for everything from the simplest of on/off switches on a blood pressure reader to a complicated multilevel/multitasking switching/control system for a printing press.

It’s hard to say when the technology came into being because some of the simpler connectors/switches have been cut with dies since the 1950’s. When was electricity invented? Membrane switches really took off in the 1980”s when consumers were demanding lower prices and manufacturers had to push for an alternative to the traditional molded/hard printed circuit boards that were so often used as the base for switches on most machines. Their main attributes are, the relatively low price, their relatively quick turn-around production time, plus they look pretty cool!

Membrane switches are typically made up of six different layers that are all die cut (with Steel Rule Cutting Dies, or laser cut, router cut, matched metal or rotary diecut, etc... depending on the situation) separately and then assembled. The concept is nearly simple in that as with any electrical switch you are trying to create a space between two wires when the circuit is inactive and you are trying to make them touch when you are connecting or making them active.

The basic layers are;

# 1 - Graphic Layer - This layer of thin plastic material is what the user sees and touches. It acts as the guide to show you where to push the switch and it sets the tone for the product and it’s operational instructions via the graphics. As with the other layers of a membrane switch, the graphic layer is silk-screen printed. Sometimes the top/graphic layer is diecut as a final pass once everything has been assembled to it, other times it is cut into it’s shape separately. # 2 - Graphic Adhesive Layer - This layer acts as a two sided glue to bond the graphic layer to the top circuit layer. It’s shape can often times be the most intricate in that there can’t be any adhesive that touches the actual switching area. Each of the areas where there is a button or switch must be cut away. # 3 - Top Circuit Layer - This layer acts as the first half of the electrical connection. Silver Ink is printed on polyester to form the electrical paths. Protection from electrical interference from outside the circuit is stopped by printing conductive ink shields, or applying aluminum foil, metallized mylar or copper foil on the top surface of this top circuit. The feeling of the switch is created in this layer as well. You know that great “Popping” feeling you sometimes get when you press one of these switches? That’s when these switch guys have found your “tactile optimum” a.k.a. “feels good point.” The plastic that this layer is made of is put through a process where a heated mold forms little domes at the areas where you will push. When you push down on this dome you get the feeling that you are actually doing something. I hate those switches when you can’t tell that you have pressed anything! # 4 - Spacer Layer - This is the really ingenious layer! Some designer probably made a fortune on this! This layer creates the space between the two circuit layers. The general shape of the outline is cut as well as holes at the points where you want the switch to activate. When you push the dome/top circuit down it pushes through this spacer layer and makes the connection to the bottom circuit, thus completing the electrical circuit. Some of the feeling of the switch is created in this layer as well. When all of these layers are assembled there is air trapped in the “spaces”. The designers will install more cut-aways, called air-tracks, between the various spacer holes. The movement and resistance of this trapped air, when the dome is pushed by the user, can make it harder or easier to push down depending on how many they plan for and how wide they make them. # 5 - Bottom Circuit Layer - This is where the final electrical connection is passed to from the top circuit. The electrical leads from both the top and the bottom circuit pass through a part of the switch called the “TAIL.” This tail is just an extension of the printed plastics that extends beyond the visible part of the graphic layer and goes to the inner workings of the machine you are controlling. # 6 - Rear Adhesive - This double sided glue layer adheres the completed switch to the surface of the machine/circuit board, or whatever is planned for the tail to go into.

And that’s it! Of course there are about a million variations of how this can go together. Different plastics, metals, rubbers, etc..., can be used to create different electrical properties, feelings for the switch, etc.... . Backlighting can be created, LED’s, resistors, capacitors, even memory chips, can all be added to a switch of this type. Every manufacturer has their own techniques for not only making the switch work but for making it feel like it should for the user, and work for just about any situation.

The concept is fairly simple yet when you see either a set of dies, prints or even cut parts laid out in front of you, it can look like a fairly complicated puzzle.

What’s the future in this type of market? Faster and Cheaper! What else! Many manufacturers are actually producing the cuts for membrane switches with lasers. They can produce one switch or short production runs this way with no die costs and no waiting time for the tools. Diemakers hate to hear that! Digital printers now produce the top/bottom circuit and graphic layers direct from the file without having to produce screens/plates/etc.. .

I’ll be using the membrane switch on my printer now and then switching my computer off to wait for that next inspiring question to hit my desk. Thanks for reading!