Traditional printed circuit boards (PCBs) consist of non-conductive substrate materials – frequently glass fiber epoxy construction – paired with a layer of conductive elements such as copper on one or two sides (single or double-sided boards). Electronic components are placed on the boards and soldered in place, making connection through means of drilled thru holes or STM assembly. Either one or two sides of the board may be utilized for the mounting of components.
Due to the physical attributes of these PCBs, size for a particular circuit or application may result in the need for large boards, or even the use of multiple boards. This is where the advent of technology and manufacturing techniques that permits fabrication of multilayer boards has been a major leap forward for application in electronic products.
Multilayer PCB Advantages
Utilization of multilayer printed circuit boards presents board design engineers and product developers with many strategic advantages:
Space requirements – creating printed circuit board designs with multiple layers means a considerable savings of real estate within the products that take advantage of the technology. Considering that adding layers generates only a slight increase in thickness of the resulting board (depending on the number of layers), the benefits over larger single or double-sided boards can be considerable. This is critical for modern electronic devices.
Weight – just as with space benefits, combining layers of components into a single multi-layer card can provide circuit functionality with a fraction of the weight over prior technologies. Think of the advantages when introduced for use in personal electronics, laptop computers, and flat-screen televisions.
Reliability – construction of multilayer board contributes to a high level of reliability and consistent performance.
There are Downsides to Multilayer PCBs
As critical as multilayer boards are in enabling the development of high-performance, compact electronic devices such as smartphones, military equipment, aerospace instrumentation, etc., there are trade-offs to be considered in their development and use:
- Cost – this is the primary consideration. With the specialized equipment required to manufacture multilayer PCBs, manufacturers must pass that cost to the customers, making the PCBs more expensive than traditional boards. Fortunately, as demand has increased and technology has evolved, this gap has narrowed considerably.
- Design tools – creating detailed technical designs for fabricators means that design engineers and layout technicians must transition to sophisticated software to aid in the design and manufacturing processes. This requires training and a learning curve for designers.
- Replacements – due to the structure and complexity of multilayer PCBs, repair of a failed board can be extremely cumbersome, if even possible. In most cases, a failed board results in the need to replace it, rather than attempt repair.
Fabrication Considerations for Multilayer PCBs
Fabrication of multilayer boards is not available from all PCB manufacturers. With the increasing percentage of boards designed with multilayer requirements, the number of producers is expanding. Although the process is relatively straightforward, specialized equipment and attention to detail is required. Training in the techniques is also required for efficient production as quality improves with experience.
Manufacturing processes include construction of layers of conductive material such as copper foil, core material, and prepreg layers, sandwiched together with heat and high pressure applied to laminate the layers together. Heat serves to melt and cure the prepreg materials, and the pressure removes air pockets that could impact board integrity.
These processes require specialized equipment and a significant commitment to operator training, not to mention the financial consideration. This explains why some fabricators have been slower to enter the multilayer manufacturing market than others.
Technology that Supports Design of Multilayer PCBs
A significant development that enables the creation and integration of multilayer boards into so many industries and products is the creation of extremely sophisticated software tools that are available to design engineers, layout specialists, and fabricators.
PCB design software facilitates computer aided design (CAD) that empowers circuit designers to increase efficiency, spot errors or problem areas quickly, and generate files for fabricators that are less likely to be problematic for the manufacturer. Even the design files can be analyzed for missing or incorrect content, avoiding traditional back-and-forth communications when manufacturing questions or issues arise.
Design for Manufacturing (DFM) applications aid both designers and fabricators through analysis functions that validate manufacturability of the resulting design. Without a DFM tool, PCB designs can made it to a fabricator to find the PCB will be either impractical, costly, or even impossible to build as designed.
Computer Aided Manufacturing (CAM) software is used by the manufacturer to validate and automate the actual fabrication processes.
Combined, these sophisticated tools make multilayer PCB design and manufacturing more efficient, streamlining the process from end-to-end. The result is more reliable, less costly multilayer boards, with improved project timelines.