What is the Right Tolerance for a Printed Circuit Board?

Tolerance is an integral part of any PCB manufacturing process. Although the performance of a PCB depends on various factors, tolerances have an active role to play in it. Most electronics manufacturers are clueless about the right tolerances for their PCBs. This is where experts at Rigiflex recommend them to seek mid-range tolerances. The benefit of these tolerances is that they can easily source the boards from any manufacturer of their choice. Many times, they opt for strict tolerances, even if their boards don’t demand it. In such cases, the manufacturing and assembly times may exceed than normal, which will reflect in the pricing, too.

Printed ciruit board

Important PCB Design Specifications and Their Tolerances

Rigiflex provides flexible, rigid-flex, and rigid printed circuit boards in a single-, double-, and multi-layer configurations. The tolerances vary across each of these circuit boards, owing to their construction. The following are some important tolerances for printed circuit boards provided by Rigiflex.

  • Materials: Rigiflex provides PCBs in various types of materials such as DuPont: Pyralux AP, LF, FR, high-speed Pyralux TK (Teflon-Kapton); Isola: 370HR, FR406, FR408, high-speed FR408HR, polyimide; Rogers: TeflonArlon: Polyimide, metal-core, and so on.
    • Material Thickness: The choice of material will entirely depend on application requirements. The material thickness is usually kept +/- 10% depending on the manufacturer’s specifications.
    • Maximum bow and twist on boards with and without SMD’s: For boards with SMDs it is recommended to 0.75%, whereas for boards without SMDs it is recommended to 1.5%.
  • Copper Thickness: The copper thickness of a PCB will depend on its current carrying requirements. Copper weight is defined as the amount of copper pressed flat and spread over 1 sq. ft. area of the board. The weight of copper is always defined in ounces. The following are a few common copper thicknesses:
    • 0.5 Oz Copper (~17.5µm thick or 0.7 mils): This thickness is commonly preferred for non-standard construction. It is applied to the internal layer. This is a standard copper weight on external layers of the PCB that has 1 Oz finished weight.
    • 1 Oz Copper (~35µm thick or 1.4 mils): This is applied on the internal layer of PCB with 1 Oz and 2 Oz finished copper weight. This is a standard copper weight applied on the external layer of the PCB with 2 Oz finished copper weight.
    • 2 Oz Copper (70µm thick or 2.8 mils): This is the standard copper weight for the internal layers of PCBs with 3 Oz finished copper weight.

Rigiflex provides PCBs in various copper weights starting from 0.5 Oz to 6.0 Oz.

    • Finished Hole Sizes: A PCB may have three types of holes— vias, plated, and non-plated holes. The hole size tolerance depends on the size of these three holes. Rigiflex provides flexible circuits in the following hole sizes:
  • Minimum drill (mechanical) hole diameter: This is .008″ (0.2 mm) for flexible and rigid PCBs, whereas it is .006″ (0.15 mm) for rigid-flex PCBs.
  • Minimum Micro Via (Laser) Size: This may vary across flexible, rigid-flexible, and rigid printed circuit boards. The minimum micro via laser size for flexible PCB and rigid PCB is 3 mil (0.07 mm), whereas it is 1 mil (0.025 mm) for a rigid-flex PCB.
  • Minimum Via Laser Size: This is 5 mil (0.15 mm) for flexible and rigid PCBs, and 1 mil (0.025 mm) for a rigid-flex PCB.
  • PCB Board Thickness: It is important to choose the board in the right thickness to ensure their non-stop performance. The board can be thick or thin depending on the chosen thickness. A thin board will break easily when compared to a thick one. Rigiflex provides flexible and rigid-flex circuit boards in thicknesses ranging from 0.5mm to 3.0mm (0.02″–0.12″). Rigid circuit boards can be availed in thicknesses ranging from 0.2 – 5.0mm (Max).

With an industry experience of over two decades, the company has been assisting its clients to build performance-driven printed circuit boards from scratch in the right tolerances. Rigiflex Technology provides printed circuit boards for use in aerospace, military, medical, networking & communications, telecom, computing and storage, and various other industries.

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