Jul 18, 2019
Cost-Effective Fabrication Options for PCBs with Complex Shapes
Application Manager, Nano Dimension
Many common electronic products still use square or rectangular boards to support important components and circuits. Despite the continued use of these standard boards, more products in the mobile, computer, automotive, and other industries require boards with non-standard shapes. The odd packaging and restrained space in these products limit the use of rectangular boards.
The unique board shapes required in many products have helped drive development in flex, rigid-flex, and molded interconnect device (MID) PCBs, as these boards can adapt to their mechanical enclosures. Other processes have been adapted for the fabrication of rigid PCBs on FR4 or other substrates, providing designers with more freedom to match their device’s packaging.
Manufactured PCBs with a complex shape.
If your goal is to design your next board with a complex shape while still keeping fabrication and assembly costs in check, then you will need to consider the fabrication options—and their associated compromises—for your board. There are several traditional processes available, however, you’ll need to keep design for manufacturing and design for assembly methods in mind during design to contain costs and ensure your product is manufacturable. Meanwhile, non-traditional processes, such as additive manufacturing, can provide you the low-volume production you need while also granting you greater design freedom.
Comparing Traditional Fabrication for PCBs with Complex Shapes
Once a PCB is panelized, plated, pressed, and etched, it needs to be removed from the panels prior to completing assembly. Rectangular boards can be manually removed from panels with a hand saw that resembles a pizza cutter. However, thinner boards or PCBs with complex shapes must be removed from panels with some of the following processes.
CNC Depaneling Router
This is a standard process for cut-finished PCBs from V-grooved panels; a milling bit is used to trace the outline of the board, and the PCB is easily removed with a router bit. The limitation with CNC milling is that it cannot be used to remove boards with sharp interior corners. However, it can be used to cut wide curves, making it an attractive choice for planar boards with arbitrary shape. It can be used with thinner boards, although you may need to run the router at a lower speed to reduce shear stress and prevent fracture.
Punch and Die
In this process, a hydraulic press is used to press multiple boards out of a single panel in one run. This punch process mimics that used in metal punch and die machines. While this option offers higher throughput than using a depaneling router, it also requires higher up-front costs and prolonged maintenance. Each punch must also be cast to a specific shape, so it is only cost-effective when the volume is very high. The mechanical stress applied during punching can also crack a board, thus it should not be used with thinner boards.
A high-power pulsed laser can also be used to cut boards from a panel. The laser used in this process is focused down to a very small spot and can be moved with a CNC machine. This allows the laser to scan along any curve you can imagine, and it is not limited to cutting interior corners in the same way as a routing bit. Therefore, it can be used to cut tight corners that form any angle. Because the depth of focus with these lasers is very shallow, it can only be used effectively with thinner boards. This process also carries significant upfront costs and maintenance.
These methods for working with PCBs with complex shapes illustrate the primary problem with subtractive processes: The removed rigid portions of the board are discarded and cannot be reused. This material waste motivates the use of a different type of process for fabricating PCBs with complex shapes, and even non-planar geometry without creating material waste.
Additive Manufacturing for PCBs with Complex Shapes
Compared to traditional manufacturing processes, in certain cases, additive manufacturing may offer sufficient throughput with a lower cost per board, particularly with low-volume manufacturing runs of highly complex PCBs. The layer-by-layer 3D printing process used in a digital additive manufacturing system eliminates the plating, etching, and pressing steps that drive costs in traditionally manufactured multilayer PCBs.
As additive manufacturing requires fewer fabrication steps than traditional PCB manufacturing, it offers faster prototyping throughput than traditional processes, which can reduce lead times. If you are looking to produce a prototype, an additive manufacturing system can be used to produce a single board or multiple variants of the same prototype board in parallel. Most PCB manufacturers have strict MOQs (minimum order quantities) and will not produce single boards for prototypes, and those that do simply cannot compete on cost.
This ability to produce a single board in a matter of hours allows designers and engineers to quickly test their board and devise redesigns as necessary. This decreases the overall time spent in R&D cycles and allows new products to come to market more quickly.
The PCB Fabrication Cost Structure
PCB manufacturing processes carry an interesting cost structure that depends on both volume and complexity. Note that complexity applies to complex board shapes and the architecture of the board itself. More complex boards, such as multilayer PCBs with high layer count, carry more fabrication steps and incur higher costs for a given volume. In contrast, the costs associated with fabricating PCBs with additive manufacturing are independent of complexity and volume because the fabrication process does not change with either variable. A comparison of the cost structures are shown below:
Comparing fabrication costs: additive manufacturing vs. traditional manufacturing.
As with many subtractive processes, the cost per traditionally manufactured board tends to fall with volume. For low-volume runs, some manufacturers will absorb the costs associated with producing PCBs with complex shapes, but this does little to close the cost gap between additively manufactured PCBs and traditional manufacturing processes. This is especially true for highly complex boards. At some point, when the volume gets higher, it makes more sense to switch to traditional manufacturing processes for planar boards.
Unfortunately, traditional PCB manufacturing processes are simply not useful for non-planar boards, such as MIDs. With an additive manufacturing system, you don’t have to confine your designs to a planar substrate with components on the surface layer. The layer-by-layer printing process allows components to be embedded or mounted on the side of a non-planar PCB substrate. It also allows unique interconnect architecture to be created, such as horizontal, diagonal, or curved vias. This frees designers from the constraints of traditional PCB manufacturing processes and unleashes innovation for new applications.
If you are manufacturing PCBs with complex shapes at low or medium volume, you can remain competitive on costs with an additive manufacturing system that is specialized for digital manufacturing of 3D-printed electronics. The award-winning DragonFly additive manufacturing system is built specifically for rapid manufacturing of highly complex boards with planar or non-planar geometry for a variety of applications. Read a case study or contact us today to learn more about DragonFly system.
Application Manager, Nano Dimension
Ziv Cohen has both an MBA and a bachelor’s degree in physics and engineering from Ben Gurion University, as well as more than 20 years of experience in increasingly responsible roles within R&D. In his latest position, he was part of Mantis Vision team—offering advanced 3D Content Capture and Sharing technologies for 3D platforms. The experience that he brings with him is extensive and varied in fields such as satellites, 3D, electronic engineering, and cellular communications. As our Application Manager, he’ll be ensuring the objectives of our customers and creating new technology to prototype and manufacture your PCBs.
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