lamination used in HDI printed circuit boards
High-Density Interconnects (HDI) are a fast-growing part of the PCB and electronics industry. These advanced circuit boards offer a higher routing density than traditional PCBs and are used in demanding applications like mobile devices, automotive electronics, computer motherboards and more. They can be manufactured using a variety of advanced features and technologies, including through-hole and blind/buried vias, as well as stacked microvias. However, one of the most important manufacturing techniques for HDI is sequential lamination.
During this process, multiple layers of thin laminates are bonded together to form the core of the circuit board. The laminates are typically FR-4 or polyimide, and they are pre-impregnated with a curing agent to create a strong bond. The core is then surrounded by copper foil and other dielectric layers to make a layered stackup. A prepreg sheet is then inserted between each pair of copper and dielectric layers, and the entire lay-up is then laminated with another layer of prepreg to create a multilayer hdi printed circuit board.
While the process is relatively simple, it does require state-of-the-art PCB fabrication equipment to apply high amounts of temperature and pressure to the subcomposites, adhering them permanently to each other. This is particularly true with HDI boards, which feature thinner specialty materials and require a precise imaging and lamination process. In addition, the use of a clean room is crucial to maintaining consistent and high-quality results.
How is sequential lamination used in HDI printed circuit boards?
The manufacturing process for sequentially-laminated HDI boards can be lengthy and costly because of the precision needed to ensure that each layer is aligned precisely as it should be. In addition, the drilling and plating processes required for each individual layer can add time to the overall manufacturing cycle. However, this meticulous process is a necessary step to achieve the superior performance of a HDI circuit board.
Once the core of a HDI circuit board has been fabricated, it is then subjected to a series of inspection and testing procedures. This includes a visual inspection of the bare board to check for any errors or defects, as well as an electrical test to verify that all connections are functioning properly. Finally, the board is subjected to a thermal test to ensure that it can withstand high temperatures.
The next steps in the manufacturing process for an HDI circuit board involve establishing reliable electrical connections through the blind and buried vias that are drilled into the core of the circuit board. This is achieved through a combination of plating and laser-drilling technologies. The first step is electroless copper plating, which involves immersing the blank circuit board in a bath of conductive metal to deposit a thin layer of copper onto the walls of the drilled holes. Then, the board is cured to harden the coating. Laser-drilling then takes place, where a laser is used to cut through the layers of the PCB to expose the copper, and a mechanical drill is then used to finish the remaining hole openings. Lastly, the PCB is subjected to a final quality inspection and testing before it can be shipped to a customer.
