Filled Vias Be Used in Flexible Or Rigid-Flex PCBs
Conductive filled vias are a common design element in PCBs today. They wick heat away from chips to prevent overheating and allow for thermal management, which can help improve performance and reliability. However, the use of these vias in flex or rigid-flex PCBs poses challenges. These challenges are mainly due to the different materials and manufacturing processes that these circuit boards require.
For PCBs that require a high degree of accuracy and precision, vias are typically metalized through a series of steps including laser drilling, depositing copper seed layers, imaging, specialized electroplating, and chemical mechanical polishing. These steps can take up a significant amount of time and can cause delays in production, especially for high-end rigid-flex boards.
To reduce these delays and ensure that your rigid-flex or flex board is produced with the best possible quality, it is important to choose a PCB manufacturer who utilizes the latest technology in manufacturing. For example, many of our facilities have recently made the switch to a new copper plating process that allows for the use of via-in-pad construction on multilayer flex and rigid-flex circuits. This new process is more cost-effective and offers superior electrical performance compared to traditional methods.
The use of this new plating method eliminates the need for conductive epoxy fill and can greatly increase the available space for routing traces on your flex or rigid-flex PCB. In addition, the use of this method allows for the use of thin flex layer materials such as polyimide without the need for stiffeners which reduces your overall fabrication costs.
Can Filled Vias Be Used in Flexible Or Rigid-Flex PCBs?
A downside of this technique is that the new vias may have a small divot or a bump on top. These dents are caused by the laser-drilled hole and the copper plating that follows it. While they may not be an issue for some applications, they can be a problem for those with strict requirements for flat pad surfaces such as those found in military and aerospace applications.
Another concern is that the divots or bumps on the surface of the flex circuit are a potential point of failure if the PCB is bent. This is because flex circuits are often subjected to a lot of mechanical stress when they are bent. To minimize this stress, it is recommended that you avoid the use of conductive filled vias in flex or rigid-flex circuits unless they are designed to have a circular curved corner that is much less than 180 degrees.
This is because flex circuits that have sharp angled corners will be susceptible to tearing at the corners when they are bent. This will cause a loss of continuity in the flex circuits and can lead to a short. If you need to use conductive vias in your flex or rigid-flex circuit, it is important to follow the IPC 2223 design standards regarding proper terminations of flex sections.