Multilayer flex printed circuit boards are manufactured by combining single and/or double sided circuits. These combined circuits are then interconnected by plated through holes. With the help of this technology, it becomes easier to achieve high density interconnections. These interconnections are important for applications, in which one or more layers of conductor are not able to achieve circuit packaging requirements or pin addresses.
When are Multilayer Flex Circuit Boards Required?
The multilayer flex circuit boards are mainly required in the following scenarios:
- Controlled impedance with shielding
- Shielding applications
- When the layout and density of a circuit is not possible to be routed on a single layer
- EMI/RFI shielding
- Ground and power plane applications
- Increases density of the circuit
Benefits of Multilayer Flex Circuit Boards
There are various benefits of using multilayer flex circuit boards, and they are preferred in most of the industries for their design requirements.
- Reduces Assembly Costs and Time: Relatively lesser manual labor is required while designing and manufacturing multilayer flex circuits. This in turn reduces the chances of production errors. Multilayer flex circuit boards eliminate the need for costly soldering wires, wrapping, and routing. Instead of changing or installing discrete hard PCBs, whole interconnection systems are replaced or installed. This helps minimize the wiring errors, thus reducing the manufacturing costs.
- Reduces Package Size and Weight: Unlike the rigid boards, the multilayer flex PCBs are lightweight and use less space. These flex boards have the thinnest dielectric substrates, which provide more streamlined design.
- Increases Heat Dissipation: Multilayer flex circuit boards have a large surface-to-volume ratio, which allows a shorter thermal path. In addition to this, flex circuits have slim design, which helps increase the heat dissipation through both the sides of the circuit.
- Increases Durability: In designs having moving parts, a flexible circuit is the right choice as it can flex up to 500 million times. Polyimide, which is the most commonly used material in flex circuit boards has an exceptional thermal stability. Thus, a flex circuit board can easily survive high temperatures. Also, due to the excellent thermal stability of polyimide, a better quality of base is provided for surface mounting, as compared to hard boards.
- Increases System Reliability: Earlier, maximum failures in a circuit took place at the interconnection point. Multilayer flex circuit boards eliminate the need for interconnections. This helps increase the circuit’s reliability.
- Can be Used for High Density Applications: Multilayer flex circuit boards possess very fine lines, which leaves enough space for other components. Hence, multilayer flex circuit boards have high board density.
Design of Multilayer Flex Circuit Boards
Multilayer circuit boards are made of four basic elements as follows:
- Conductors: Multilayer flex circuit boards are made from different conductor materials such as copper, inconel, aluminum, carbon, etc. Copper is one of the highly preferred materials in the conductors of these circuit boards.
- Insulators: In multilayer flex circuit boards, insulating layers are present between two layers of the board. These layers can be of different materials like polyimide, polyethylene terephthalate, screen printed dielectric etc. Polyimide is the most common insulator material used in these circuit boards.
- Adhesives: The adhesives used in the circuit boards can be either acrylic, epoxy, or adhesiveless base. Adhesiveless materials have superior electrical properties than non-adhesive ones
- Finishes: Once the circuit board is ready, it requires finishing. Different finishes are available from which one can select what best suits the requirements. The finishes can be of carbon, silver, tin, immersion gold, and many other materials.
Applications of Multilayer Flex Circuit Boards
The multilayer flex circuit boards are used in static as well as dynamic flexing applications. Some of the applications include:
- Hearing aids
- Air bag systems
- Heart monitors and pacemakers
- Bar code equipment
- GPS systems
- Automotive engine controls
- Cell phones
There are many such advantages of multilayer flex circuit boards, because of which they are extensively used in a number of applications.