Design Tips for the Different Types of PCB Fabrication

January 26, 2021 , in Blog

Inspecting a fabricated PCB

Various factors affect a device’s usage in electronics, such as performance, environment, and functionality. These same parameter types affect the PCB construction process. Based on a set of well-defined steps, fabricating boards for critical applications, such as aerospace, automotive and industrial, require considerations beyond what is typically required for commercial electronics products.

Let’s look at these application-based different PCB fabrication types and establish design tips to ensure your boards meet the requirements for their intended usage.

The IPC Classification System

The leading global association helping manufacturers build better electronics through proven certifications, education and training standards, innovative solutions, thought leadership, advocacy, and industry intelligence, is the IPC (Association Connecting Electronics Industries).

IPC standards include usage class designations for various electronic devices as listed in the IPC-6011 standard. Overall, this classification system incorporates three general categories that reflect the progressive increases in sophistication, functional performance requirements, testing, and inspection frequency.

These three categories indicate the quality level to which each type of circuit board should be built and which classification the CM must adhere to when building PCBs lies with the developer.

The Categories within the IPC Classification System

  • IPC Class 1 includes General Electronic Products such as computers (desktops and laptops), computer peripherals, and consumer products. In all cases, these devices are suitable for applications where there is an allowance for cosmetic imperfections, and the primary requirement is the function of the PCBA.
  • IPC Class 2 is for Dedicated Service Electronic Products such as sophisticated business machines, instruments, and communications equipment. These are devices in use where extended life and high performance are a requirement. Although this classification desires uninterrupted service, it is not a critical requirement, and it also allows certain cosmetic imperfections.
  • IPC Class 3 is for Harsh Operating Environment Electronic Products that require High Reliability. Furthermore, this class includes devices and equipment in which they must provide on-demand performance or continuous performance. Also, there is a zero-tolerance for downtime with these devices or equipment, and they must perform when needed. Examples of devices, equipment, or systems within this class include space applications like the NASA Oxygen Generation System, flight control systems, and life support systems. In summary, PCBAs within this class are suitable for applications where service is essential, and high assurance levels are required.

It is important to note that the final performance class for a PCBA (assembled, soldered, cleaned, and tested) cannot be any higher than the performance class stipulated for the bare board or fabricated PCB. Therefore, to obtain a Class 3 PCBA, IPC Class 3 has to be specified for fabrication.

Design Tips for the Different Types of PCB Fabrication

The classification system for the various categories of products is a critical design consideration with strict adherence. The following are three industries that fit some of the different classifications outlined by the IPC-6011 standard.

We will start with the Class 3 classification, including mission-critical devices and systems and the most stringent guidelines. Furthermore, there is no industry more dependent on its equipment and procedures than the aerospace industry, except for the medical field, of course.

Aerospace Applications

  • Reliability is the key: which means zero tolerance of failures and an extended lifecycle. Therefore, designers and fabricators need to avoid using any bleeding-edge technology and adhere to the standard, proven technologies when designing and fabricating their PCBs.
  • Use heavy copper: in space, they manage heat through dissipation. Therefore, when building for these applications, use heavier copper designs, i.e., four or 5-ounce copper, with thermal vias, and utilize the chassis for heat dissipation.
  • Material choice: use Polyimide (boards), especially for an application that requires an extended lifecycle in space, i.e., more than two or three years. The advantages of using Polyimide for your PCB includes excellent flexibility, excellent tensile strength, thermal stability, high durability, and resistance to chemicals.
  • Assembly process and surface finish: use leaded HASL (Hot Air Solder Leveling) for the assembly process, and it is okay to use ENIG, for example, for the surface finish.
  • IPC 6012DS: Always refer to this standard since it is technically an enhanced IPC Class 3. It is also the release requirements, quality requirements, minimum plating, etc., for military and space applications.

Automotive Applications

The automotive industry continues to forge its path towards electric and autonomous vehicles. Growth is only possible if this path goes through the PCB industry. Additionally, the need for thermal resistance and longevity makes the automotive PCB distinct from other sectors. Adhering to IPC-6012DA and IATF 16949 (ISO 9001 automotive standards) is a critical fabrication requirement. The following are design and fabrication tips for the automotive industry:

  • If there is no other specification, use Class 3 specifications for all board properties.
  • The spacing and land specifications fall within IPC-6012DA standards for tolerance.
  • Drill holes need to meet the size and quality requirements of IPC-6012DA and conform to the contract manufacturer’s equipment aspect ratios.
  • Solder mask specifications need to fall within IPC-6012DA standards for tolerances.
  • Ensure that your CM applies reasonable quality control that includes automated optical inspection (AOI) and visual inspections throughout the assembly and fabrication processes.
  • CM should adhere to strict cleanliness guidelines and clean boards after each procedure to avoid excess debris, including before and after solder masking.

Industrial Applications

With an industrial PCBA, we embed the board within a more extensive industrial production system. Furthermore, these boards are generally custom or have special requirements. The following are some of the fabrication tips to be aware of:

  • Use conformal coating (IPC-CC-830C standard) to protect the boards from moisture and debris.
  • Choice of materials: consider the mechanical, thermal, and electrical properties of the materials during selection. Also, make sure the PCB type can endure the structural, thermal, or possibly high-speed industrial environment challenges.
  • Use proper trace routing, thus ensuring appropriate copper weights, impedances, and lengths. Proper trace routing translates into signal integrity and the necessary current carrying capabilities.
  • Testing: these types of tests include resistivity of solvent extract test (debris), AOI (solder joints and component placements), and peel test (adhesion).
  • Utilize DFM checks and simulations to analyze your board’s Power Delivery Network (PDN) and thermal resistance.
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The intended environment for a PCBA determines the level of quality, performance, functionality, and lifecycle expectancy. For critical applications, designing for harsh environmental conditions is typically required. Tempo Automation works with fabrication partners capable of meeting these strict requirements and assembly boards to meet any classification level standards.

To help you get started on the best path, we furnish information for your DFM checks and enable you to view and download DRC files easily. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in different CAD formats and Excel.

If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on the types of PCB fabrication or how PCB classification affects fabrication, contact us.

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