The general public has embraced technological innovation over the last several decades, fueling the demand for more advanced everyday products. For example, it is an expectation that virtually all devices, appliances, vehicles and systems have some level of intelligence. Our ”smart” devices can either alter functionality or alert us of the need for intervention, mainly to avoid inconveniences.
The high-performance levels of the products we use are made possible by the improving capabilities designed and built into electronic circuit boards. Component selection significantly impacts functionality; however, a high-quality PCBA construction process is the foundation for your board’s reliable operation. The first stage in this process is fabrication, which yields the bare board structure, during which the layer stackup based upon PCB sequential lamination is performed.
Let’s take a look at this critical process, the challenges and how to best address them now and into the future.
Conventional Circuit Board Sequential Lamination
Today, most electronic circuit boards are multilayer PCBs constructed smaller—in the xy plane—with denser component concentrations where choosing the best via options are primary design considerations. Equally important is the PCB stackup design, which consists of defining signal layers and ground planes. Optimizing your board’s PCB layers requires understanding the materials they are composed of and how they impact fabrication.
A common fabrication process for creating the layer stackup is known as sequential lamination, which can be defined as follows:
|Sequential lamination is the process of sequentially building up the PCB construction by adding layers of dielectric material and copper. Layers are built upon subcomposites, which are structures composed of alternating copper and dielectric levels enclosed by a top and bottom copper layer.|
Sequential lamination is highly successful in creating multilayer boards. It is advantageous when high-density interconnect (HDI) PCB electronics technology is utilized for communications and other board types with high signal transmission path counts. However, this process is not without challenges:
PCB Sequential Lamination Challenges
- Restriction on the number of cycles
Layer materials are typically limited to four sequential lamination cycles. Beyond four, failure modes, such as delamination and resin cracks may occur.
- Aspect ratio for drill hole equipment
Depending on the type of equipment—typically a drill press or laser drill—used to bore the vias, there are limitations on the number of layers due to the aspect ratio.
- Drill hole alignment when working from Gerber files
When working with Gerber files, there is the possibility of discrepancies or errors that may translate into misalignments on fabricated boards that can increase cost and turnaround times.
The repetitive process of sequential lamination can add days or weeks to the board build process, which can significantly increase manufacturing costs.
Sequential lamination is not a new process and there are established best practices to mitigate the challenges listed above. Best practices include reducing layer count, minimizing copper weights, choosing high glass transition temperature (Tg) materials, using thin resin materials next to surface copper layers, backdrilling through-vias to reduce the need for blind and/or buried vias and avoiding ELIC stacked microvias, if possible. Besides design and manufacturing guidelines, technology trends may successfully address some of the sequential lamination challenges.
Trends to Address the Challenges of PCB Sequential Lamination
Many of the issues and potential failure modes of PCB sequential lamination are associated with many layers. Techniques that allow for a reduction in layers are attractive solutions. One such method is the use of embedded components. The idea is to have components installed within the PCB stackup; instead of residing on the top or bottom surface.
Layer reduction is achieved by placing components where they need to be connected. For example, a capacitor can be vertically aligned with electrodes on two adjacent copper layers and eliminate the need for running a via from the surface. At present, most of the work in this area has focused on passive components and flex or rigid-flex board application; however, the prospect of embedded active components and ICs would significantly mitigate the failure modes associated with sequential lamination for large layer counts.
Sequential lamination is an additive manufacturing process as the overall stackup is built-up by adding layers. Another additive manufacturing process often included when discussing the advanced manufacturing methods driving innovative production is 3D printing. This technology is currently being used to create nanoscale multilayer boards and is also being explored for PCBA manufacturing. With a 3D solution, the entire board, including components, is constructed in a single process.
|Tempo’s Software-Driven Smart Factory Delivers the Industry’s Leading Custom Turnkey PCBA Manufacturing Services
The trends above will continue to advance, as will other ideas arise to mitigate sequential lamination challenges. At Tempo Automation, we work with fabrication partners capable of meeting the most complex PCB design requirements coupled with our advanced in-house software-driven PCB assembly process. The entire turnkey process is monitored and controlled by our digital thread manufacturing that leads the industry in high-speed, high-quality board prototyping and low-volume production.
To help you get started on the best path, we furnish information for your DFM checks and enable you to view and download DRC files easily. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in different CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on PCB sequential lamination or its role in your board build, contact us.