Posts Tagged ‘flex pcb’

Concept & Mechanical Designs of Flex & Rigid-Flex PCBs

Written by Admin on . Posted in PCB, PCB Design, PCB Manufacturing

Concept & Mechanical Designs _PCB

When considering flex and rigid-flex circuits, there are benefits for both the manufacturer and the OEM to both be involved in the concept development and design of PCBs. Developing an initial understanding of the project details will be crucial in delivery of an effective PCB development project. Communication between the customer’s project management and engineering team should be an early focus in delivery of an effective project.

Oddly Shaped Rigid-Flex PCB

We will seek to confirm whether a flex based solution is appropriate for your proposed application. It is possible that after a review of your requirements, we conclude that using a flexible circuit board may not be appropriate. Through our review process, we hope to be able to ensure the use of appropriate PCB technology. If this means that Rigid-Flex PCBs are not the most appropriate design for your requirements, we will let you know.

When designing Oddly Shaped Rigid-Flex PCBs, there are a number of factors that the manufacturer will need to know. These include:

  • Understanding what the designer is trying to achieve in the development of the PCB;
  • Identifying the functionality of the flexible PCB;
  • The general size and shape requirements of the board;
  • Determining whether the design is an active component or a point to point interconnect; and
  • Noting whether there are any special signal requirements (such as current carrying or impedance control).

Further detail may also assist in the design, such as knowing whether shielding is required (based on the environmental situation of the board); and whether there a radio frequency design is required. Once these questions have been addressed, we can provide you with a better understanding of how flex and rigid-flex PCBs can deliver solutions for your project.

Part of our process is identifying where additional functionality can be integrated at the design stage. We will also look for opportunities to integrate the separate parts of the design, and look for opportunities to simplify complex designs, which can reduce overall project costs.

Mechanical Design

The second stage of development of a Flex and Rigid-Flex design is ensuring that the mechanical design specifications are in place. We will need to clarify the following factors to ensure there is no risk of trace breakage once the board is inserted into the end product:

  • What the minimum bend requirements are for your PCB;
  • How the PCB is going to be bent to be positioned in your product; and
  • The flex section lengths required to meet the bend requirements.

Flexible PCB with Stiffeners

It is not possible to manufacture all shapes and configurations due to the processes involved in flex and rigid-flex manufacturing. In the same vein, it’s important to be aware that not all sizes are available, as very large parts can affect the dimensional stability and manufacturing tolerances. Therefore, we need to look at the shape and size of the flex part.

We can also add value by identifying options for mechanical design that you may not have considered. Examples include Stiffeners (required to support soldered connects and components, ensuring reliability and PSAs (double sided adhesive tape used to attach the flex). When considering PSA requirements, there are other factors to consider such as the whether the board will be used in high temperatures, whether the PSA needs to be thermally conductive, or to dissipate heat, and whether it needs to be electrically conductive to ground the part to the enclosure.

In some instances there may be requirements for shielding for RF or EMI sensitive applications. If so, consideration needs to be put around the form of shielding to be used (copper, silver ink, or special shielding films).

Finally, in some designs the flex circuit may need epoxy strain reliefs. These are required if there is a bend situated close to a stiffener or to the rigid PCB section.

Risk Factors for Flexible Printed Circuit Boards

Written by Admin on . Posted in PCB

flex pcb

When PCBs are designed, the intention is to ensure they are robust and able to function effectively over the long term. However, PCBs can be damaged, and engineers need to be aware, and set risk management plans in place to avoid the risk of damage to PCB.

There are two factors that can lead to damaged PCBs. These are environmental factors, and problems that can develop during the design and production stages of flexible PCB manufacture. There are several environmental factors that can damage PCBs.

Moisture and humidity

In either form, moisture or humidity (which may condense to form moisture) can render a PCB non-functional. While an entire final product (e.g. a cell phone or television) may be able to survive a little amount of moisture, the individual PCB within these units will short out in the presence of moisture if the water crosses two channels on the PCB. While the active presence of moisture will cause this problem, similar issues may arise if the PCB is operating in damp conditions. In such circumstances, mold may form and lead to circuit failure.

Static Electricity

Small charges from static electricity can reach the boards in a variety of situations. If a static charge affects the board while it is in use, the risk is increased. PCBs need to be positioned in a location that is free from any source of static charge such as fabric or carpet.

Fumes

Liquid chemicals such as cleaning solutions may give off fumes. If the PCB is operating in close proximity to the fumes, they can build up on the unit and slowly corrode the linkages.

Temperature Extremes

Both cold and heat can have negative effects on PCBs. As noted under ‘moisture’, dampness can lead to boards shorting. Humidity is a relative entity. At higher temperatures, the air can hold more moisture than it can at cold temperatures. If the environment where the PCB is operating cools to the point that the air can’t hold the moisture, condensation will occur and as a result, shorting may also occur.  Heat is as much of an issue as cold. Heat can lead to the board warping, which may break the linkages and cause the PCB to malfunction.

Dust

Dust is present in most environments, and can cause two issues for PCBs. The first concern is that the dust may insulate the board, reducing the ability for heat from the board to dissipate. Dust can damage devices such as computers and televisions. The second way that some dust can cause damage is that it can be a medium for static charge.

Manufacturing Errors can also damage PCBs.

Every PCB design is different. By nature, each design has to be different, as they are all designed to meet different needs. While engineers will follow regular guidelines in designing their boards, and test the boards at various stages to ensure functionality, there is a risk of human error.

In addition to the risk of human error, there are inevitable risks in manufacturing. The manufacture of boards is complex, and there are several opportunities for defects to be included in the manufacturing process.  An example could be if two metal traces aren’t appropriately insulated, a high voltage may lead to arcing which will destroy the circuit.