impact on PCB assembly processes
The vias in a PCB provide pathways for electrical signals to travel from one side of the board to another. The holes can be filled with a conductive material, either copper or silver epoxy, to establish an electrical connection between layers of the circuit board. While conductive filled vias are essential for efficient signal transmission, they can also introduce impedance changes and reflect signals, which must be taken into account during the PCB design process.
A PCB manufacturer can either fill a via hole or leave it empty (also known as tenting the via). When a via is filled, the annual ring and the surrounding area are covered by solder mask. This makes the via a capped via and reduces the risk of moisture absorption that could cause the emergence of microscopic cracks over time. Capped vias are more durable and can withstand up to 2.8x the number of thermal cycles as compared to unfilled ones.
Via filling can be universal to the entire PCB or designers can use a special flag in the PCB design software to indicate if they would like their vias filled. This allows the manufacturer to complete the process prior to further drilling on the bare board and ensures all vias are filled. The additional processing steps for via-filling can add to the cost of the circuit board, depending on the type of fill material used, the complexity of the manufacturing process, and the testing and quality control requirements.
Do filled vias have any impact on PCB assembly processes?
The primary purpose of a copper-filled via is to enhance the conductivity of the via holes, which can improve the reliability of the circuit board. Its high thermal conductivity attracts heat and keeps it away from critical areas of the PCB, lengthening its lifespan and preventing defects.
However, there are other reasons why PCB manufacturers choose to use a copper-filled via. For example, it can save on materials costs, as a copper-filled via is cheaper than a silver epoxy-filled one. Furthermore, it is easier to inspect a copper-filled via than a silver epoxy-filled one, as the former’s color is more visible.
There are a few different ways of filling a via hole with a conductive material, including using an inline process to plate the buried vias while they are being fabricated. This is more efficient than a batch process, but it can be cost-prohibitive for large production runs. The choice of filling material is crucial, as it must be compatible with the PCB’s substrate and solder mask as well as the manufacturing process. It must also be resistant to migration and have good adhesion to the surface of the via hole.
A growing trend in PCB fabrication is to implement via-fill plug with low-temperature solder (LPI). This method allows for a more reliable and durable cap that can withstand the higher temperatures of automated assembly processes. JHYPCB’s skilled engineering teams have extensive know-how implementing durable capped vias optimized for automated processes. Contact us today for a quote on your next PCB!