Buried discreetly inside of nearly every electronic device is a printed circuit board. Usually green in color, PCBs will have a diverse number of electronic components soldered to them depending on their function. Circuit boards like this are at the core of the electronics industry today, but there is much more to them than what can be gleaned in a casual inspection.
Printed circuit boards go through an intense process of design and manufacturing to function as required. This process involves incredible amounts of engineering expertise to produce the final result, and each step has multiple steps that must be followed meticulously for the board to operate correctly. The materials used for the manufacturing of the circuit board are a perfect example of how many details are being considered. They can vary according to the electrical performance, thermal conditions, and physical environment that the board will be operating in. Here are some particulars about PCB material properties, and how they can impact the manufacturing process of the circuit board.
Manufacturing and the Materials Used for Circuit Board Fabrication
For the majority of circuit boards that are manufactured, cost and performance are the main determiners of what raw materials to use for PCB fabrication. Circuit boards used in critical environments like space flight or military applications will typically use exotic and costly board materials for durability. Most other circuit boards are made from a glass-reinforced epoxy laminate substrate, with FR-4 being the most common grade used.
FR-4 is a category of flame retardant circuit board materials that are strong and serve as a good insulator for their cost. There are several composites of FR-4 options in the fabrication of circuit boards. Options vary according to the temperature required for the circuit board to operate. To build PCBs with these diverse materials, manufacturers alter and fine-tune their fabrication and assembly processes as necessary.
Drilling holes through the board is another area where the materials in use can affect PCB manufacturing. Depending on the fiber content used in the pre-preg and core materials of the board, there could be an impact on the minimum diameters of the holes that are drilled. As these materials use glass, kevlar, and carbon fibers in their makeup, some of these fibers can be denser than others. This can affect how long a drill can be effectively used, and how small the hole can be made. The fibers in some materials can be strong enough to push the drill tip out of alignment as it penetrates the board, which may compromise the integrity and connectivity of the hole. To compensate, manufacturers will use different tool types or sizes, or switch to a different board material altogether.
Solder and Finishing Materials on a Printed Circuit Board
In addition to the raw board materials used in its fabrication, the circuit board will also require solder, finishing, and cleaning materials to complete its assembly:
- Soldering: There are different automated soldering processes available for a circuit board depending on its design, and each process uses its own unique mixture and solder temperature. These processes are solder reflow, wave soldering, and selective soldering. Additionally, the temperature of the solder, as well as the duration of the soldering process, will be adjusted for each board according to a soldering profile set up uniquely for that board. The soldering profile is designed to accommodate how the components are connected and aligned on the board and will alter soldering temperatures and durations accordingly.
- Metal finishes: Different finishes can be applied to the circuit board depending on where and how it is to be used. Each of these requires different manufacturing processes and include:
- Hot air solder leveling (HASL) is easier than other processes to work with and maintains its consistency.
- Electroless nickel immersion gold (ENIG) is more difficult to consistently lay down uniformly.
- Immersion silver has a time limit on its application to seal before it can oxidize.
- Cleaning: The solder types and operations that are used on the board will affect which cleaning processes are required to finish the job. In some cases, there are residue problems that must be removed due to being conductive. Those are difficult to access and require more attention during cleaning.
Working Together with the Experts in PCB Material Properties
Yes, there are a lot of properties in the materials used for circuit board manufacturing that are important to know for the best results. While PCB designers may request certain materials for reasons of price and/or circuit board performance, it may not always be the best choice for that particular board. As we have seen, all of these different factors need to be considered together to make the best possible materials choices. Fortunately, there are PCB contract manufacturers who have the industry knowledge and experience to help make these choices.
At VSE we have been working with PCB designers for over 30 years, and it is our goal to make sure that each printed circuit board is built with the materials that are best suited for its unique application. We have a team of design and process engineers that will review the PCB layouts and requirements of the circuit boards we build to present the best material choices to our customers.