Flexible Printed Circuits for 3D Printing Applications
Flexible Printed Circuits
The printed circuits industry has made some impressive advances, particularly in flex circuit technology. These circuits are fabricated using screen printing conductive inks on flexible substrates, like polyester or FR-4. The flexible traces are then encapsulated with adhesive-backed polymer films. These encapsulating materials act as solder masks, preventing the copper traces from being exposed to external damage during assembly and operation.
Traditionally, these encapsulating materials have been epoxy, but they’re not as mechanically and electrically robust as solder. As a result, many flexible printed circuit utilize a second encapsulating adhesive layer that’s also a high-temperature evaporative reflow glue. This allows for higher operating temperatures while still maintaining a good electrical and physical bond between the flex circuit and the underlying laminate.
Aside from a different manufacturing process, most of the similarities between traditional rigid PCBs and flexible circuits remain the same. In general, designers must consider the maximum bending radius of a flexible section early in the design process. This is to ensure that the copper can handle the bending without damaging it.
Flexible Printed Circuits for 3D Printing Applications
Flex circuits have also become increasingly popular in electric vehicle (EV) power drive inverters and compute modules that process sensor signals from autonomous driving sensors, like LIDAR and radar. Since these circuits are lighter than wire harnesses, they help EVs achieve their range and speed targets while lowering the overall weight of the vehicle.
However, the adoption of flex technology has lagged behind traditional rigid PCBs due to fabrication limitations. In order to enable broader use, the industry needs new fabrication techniques and materials.
The earliest FPCs were made with flexible polyester film, which is only.002” to.005” thick. Today, a much wider range of flex substrates is available including polyimide and FR-4, which can be made at the same manufacturing process as rigid PCBs. These flex materials can be used with both rigid-flex and multilayer designs, enabling a greater degree of flexibility than traditional PCBs. Additionally, they can be printed with the same conductive inks used for rigid boards.
When designing a flex circuit, it’s important to choose the right substrate for your application and operating environment. For example, the operating temperature typically determines what type of heat the flex circuit can withstand. In order to increase the heat resistance of flex circuits, different inks can be used, and substrates with higher thermal capabilities have been developed.
Another factor that affects a circuit’s performance is its ability to conduct power. Inks for flex circuits have lower metal content than copper traces, so they require more current to transmit power. As a result, more power is needed to push a signal over a long distance, and more resistors are required.
In addition, the conductive adhesives used in flex circuits aren’t as strong as solder, and there are concerns about their stability with varying environmental conditions. To address these concerns, a growing number of fab houses offer a secondary soldering process that provides an electrically and mechanically robust connection between the conductive components and the underlying substrate.