flex pcb design
Printed circuit boards (PCBs) are the heart of all electronic devices, from simple cellphones to advanced medical scanners. PCBs are assembled with a variety of components, including semiconductor chips, capacitors, resistors, and other integrated circuits to create the necessary functions of the device. Using rigid-flex technology, engineers can combine rigid and flexible sections to optimize space utilization, fit components in tight spaces, and achieve unique form factors.
Unlike rigid PCBs, which are composed of thicker substrates that can limit their flexibility, flexible PCBs use thinner materials to improve their ability to bend, while maintaining a high level of strength and durability. As a result, they offer greater design flexibility, and can be molded into complex three-dimensional shapes. They can also remove the need for traditional wiring harnesses and ribbon connectors in some applications.
The first step in flex pcb design is to lay out the layout of the board. This can be done with a PCB layout software program, and is often completed in collaboration with the mechanical or additive manufacturing engineer to ensure that the board will fit into the device. During this stage, holes can be drilled for mounting and labels or identifiers can be added.
What are flex pcb design?
When the layout is complete, the next step is to route traces between each component and to connect the components. The conductor patterns should be analyzed to determine how they will behave during bending and if they can be placed at a minimum distance from the edge of the board. Similarly, the plated through hole vias should be minimized at locations that will experience the highest levels of flexing.
A good flex circuit board will be able to operate reliably even when subjected to billions of cycles of bending and unbending. To do this, the conductors must be properly routed and positioned. In addition, the thickness of the conductors should be minimized to increase the bending life of the circuit. A minimum of 0.002 inches is recommended for the diameter of a flex PCB conductor, and the thickness should be no more than 0.059 inches.
Another important consideration is the operating environment. For example, if the flex circuit will be used in a high-temperature environment, the conductor pattern should be modified to increase conductor flexibility. Finally, the bend ratio should be calculated to determine how tightly the flex circuit can be bent before failure occurs.
Some designs may require stiffeners to be added to selected areas of the flex circuit. These are essentially bits of rigid material (usually FR4) laminated to the flex circuit for added support and protection. Stiffeners can be a great solution when it is necessary to protect certain components and connectors attached to the flex circuit, and they can help to prevent solder bridges during assembly.
Flex PCBs are typically more expensive than rigid PCBs due to the increased complexity and materials involved in their manufacture. A webinar from Epec Engineered Technologies on Youtube shows that a rigid PCB requires 8 steps to be made, while a flex circuit requires 17 steps. This also includes the additional time and labor required to handle the more delicate flex PCBs during production.
