Membrane switches are a widely used interface technology, offering a cost-effective, highly reliable, and customizable solution for user input applications. These switches are found in industries ranging from medical devices to industrial controls, where durability and functionality are paramount.
One critical aspect of designing a membrane switch is determining how to connect it to the rest of the electronic system. While Zero Insertion Force (ZIF) terminations are the industry standard, there are cases where a wired lead must be attached. Selecting the best attachment method depends on the type of membrane switch circuit and the design constraints of the application.
This blog post explores the best ways to attach an electrical connection to a membrane switch, considerations for different circuit types, and best practices to ensure optimal performance.
What Makes Membrane Switches So Popular?
Membrane switches have become a staple in modern electronics and are seamlessly mounted on the products we see every day in our homes, offices, and vehicles. This includes the simplest of buttons like the defrost button on your microwave, to the most complex of button assemblies on your SUV's interior.
Unlike traditional mechanical switches, membrane switches use flexible circuits and thin layers of pressure-sensitive adhesive to laminate a switch assembly. Most have dome switches sandwiched between which creates a high fidelity and inexpensive product that is completely custom.
Membrane switch showing dome switches.
Dome switches, also called snap domes, are thin metal discs carefully placed on the circuit layer creating the mini-switch assembly. These domes are designed in an array where one dome is dedicated to each individual button. Once the design is complete, all domes should work as normally open switches that correspond to a specific pin on the connector. Press one of the buttons and a switch registration event should be detected across the corresponding pins.
Once finished, a graphical overlay is then laminated to the outermost layer and this sealed button assembly is now ready for use as a membrane switch. These finished products are usually laminated to another surface using the typical types of rear adhesive, also known as pressure-sensitive adhesive or PSA.
With domes that can be rated for millions of cycles, this design helps reduce the risk of mechanical failure and also can serve as a sealing surface to block out contaminants like dust and water. Membrane switch versatility allows engineers to design compact, durable, and lightweight keypad solutions for even the most cost-sensitive projects.
With the decision to use a membrane-style keypad comes one of the most important steps in the design process- selecting the base circuit material. This decision then drives how the circuit is electrically connected to the rest of the system via a cable or tail.
Various membrane switch assemblies.
Choosing the Right Circuit Type for a Membrane Switch
The first step in determining how to attach a wired lead is to understand the type of circuit used in the membrane switch.
The three most common types include:
- Polyester Circuit – The most cost-effective option, this ultra-low-cost circuit is screen-printed with conductive inks, making it ideal for commercial and cost-sensitive applications.
- Flexible Printed Circuit (FPC) – Made with etched copper on a flexible polyimide substrate, this circuit type offers enhanced reliability and precision. It also allows for SMT components to be adhered directly to the membrane switch circuit.
- Rigid PCB (FR4) – Manufactured using fiberglass-reinforced epoxy (FR4), rigid PCBs provide the most durable solution and allow for direct soldering of wired leads.
The choice of circuit material plays a significant role in determining the best method for attaching a wired lead, as each has different mechanical and electrical properties and characteristics.
What Is a ZIF Termination?
ZIF terminations are a widely used method for connecting flexible membrane switch circuits to other electronic components. These connectors are designed to eliminate the wear and tear associated with traditional friction-based connectors.
ZIF tails are an integral part of polyester and FPC membrane switches, allowing for quick, secure, and cost-effective connections. They are commonly used in medical devices, industrial equipment, and consumer electronics where space and reliability are critical concerns.
Membrane switch with ZIF tail.
The Most Common ZIF Pin Pitches
ZIF terminations come in various pin pitches, with the most common being:
- 0mm pitch – The industry standard for most membrane switch applications.
- 5mm pitch – Used in fine-pitch applications where space is limited.
- Smaller fine-pitch variants – Designed for specialty applications requiring compact interfaces.
While ZIF terminations are the preferred connection method for flexible membrane circuits, there are cases where a wired lead must be attached directly to the circuit.
How Should a Wired Lead Be Attached to a Membrane Switch?
Whenever possible, wired leads should be avoided in membrane switch designs. They can be bulky and it is difficult to terminate directly to the switch circuit. The best practice and frequent design suggestion is to utilize a PET or FPC membrane switch with a ZIF tail or crimped housing. These designs ensure a reliable and cost-effective connection. However, certain applications require direct wire soldering or specialty crimping, necessitating specialized attachment methods driving up costs and lead times.
How to Attach a Wired Lead to a Flexible Tail
If a wired lead must be connected directly to a flexible tail, the best approach is to use a crimp-style connector. These connectors pierce the flexible circuit and provide a secure electrical connection, allowing lead wires to be terminated efficiently.
Some of the best crimp-style connectors for membrane switches include:
- Crimpflex™ Contacts by Nicomatic – A high-reliability solution designed specifically for flexible circuits.
- Memcon Crimp Contacts – A trusted brand offering crimp solutions for membrane switches and flexible circuits.
- TE and Molex Crimp Contacts – Additional options from major connector manufacturers.
These crimp contacts ensure stable and low-resistance connection, making them an ideal solution for applications requiring wired leads on flexible circuits.
Attaching a Wired Lead Directly to a Membrane Switch
For applications where a wired lead must be permanently attached to the membrane switch, the best option is to use a rigid PCB (FR4) base circuit and do solder the wire directly to the circuit board. Rigid PCBs paired with a membrane switch allow for:
- Direct soldering of lead wires – A strong and durable connection that ensures longevity in high-use applications.
- Surface-mounted or through-hole connectors – Instead of soldering wires directly, lead wires can be terminated into a housing that mates with a surface-mounted or through-hole header.
Membrane switch with wire soldered directly to PCB.
This approach is commonly used in rugged applications where the membrane switch is subjected to mechanical stress, vibration, or frequent flexing. The rigid PCB provides structural integrity, reducing the risk of damage to the electrical connection.
Summary
Selecting the best method to attach a wired lead to a membrane switch depends on the circuit type and application requirements. ZIF terminations remain the preferred method due to their cost-effectiveness, ease of use, and reliability. However, for applications that require direct-wired connections, crimp-style connectors or rigid PCB soldered leads offer practical solutions.
By choosing the right connection method, engineers can enhance the durability and performance of membrane switches, ensuring they meet the demands of their specific use cases. Whether integrating a simple polyester circuit or a high-reliability FPC, selecting the correct attachment method is crucial to achieving a long-lasting and efficient user interface.
Key Takeaways
- ZIF terminations are the preferred method for connecting membrane switches, offering cost-effective, reliable, and space-saving solutions for most applications.
- The choice of circuit material, polyester, FPC, or rigid PCB, determines the best attachment method for wired leads, with rigid PCBs allowing for direct soldering while flexible circuits benefit from crimp-style connectors.
- Crimp-style connectors such as Crimpflex™, Memcon, TE, and Molex provide secure, low-resistance electrical connections for wired leads on flexible circuits, reducing termination complexity.
- Wired leads should be avoided whenever possible due to bulkiness and termination difficulties, but in cases where they are necessary, selecting the right crimping or soldering method ensures durability and performance.
- Rigid PCB-based membrane switches provide the most robust solution for direct wire soldering, making them ideal for high-stress environments where mechanical stability is critical.
