Flexible PCB with SMDs mounted

Flexible PCB Design Best Practices For Harsh Conditions

The signs that products are getting smarter are everywhere. From talking watches that automatically measure your vitals to autonomous vehicles on earth and in space, electronic circuit boards are extending the horizon of possibility. However, some of these boards face significant installation and operational challenges.

Rigid PCBAs are restricted in range of movement. However, critical application boards must often contend with constant movements caused by shock or vibration. Flexible PCBs present a better option in many cases as their flexibility enables them to absorb these movements. And by following targeted design guidelines, you can help ensure your flexible PCB boards operate reliably in harsh environments.

Before looking at flexible PCB design guidelines, it is helpful to explore the critical applications that utilize rigid and flex boards.

Rigid Versus Flexible PCB Uses for Critical Applications

For PCBA deployment, critical applications constitute applications where an installed circuit board failure may significantly disrupt system operation or pose a safety risk. Examples could include a class 3 medical device PCBA that could harm a patient if it malfunctioned or failed.

There are distinct advantages of using flex PCBs instead of rigid boards for application in critical industries such as aerospace & defense, automotive, industrial, and medical devices.

RIGID VERSUS FLEX PCB APPLICATIONS IN CRITICAL INDUSTRIES 
PCBA Attribute Flex PCB vs. Rigid
Flexibility Bendability enables flex boards to be installed in more compact spaces.
Durability Flex boards can absorb physical stress and strain without structural degradation to a much higher degree than rigid boards.
Reliability In harsh environments where vibration and constant motion occur, flex boards are less likely to experience component disengagements like tombstoning or physical breakdowns like cracking.
Size Rigid board installation in tight areas is common. However, this requires multilayer stackups. Flex PCBs, however, can be installed in various geometrical configurations enabling single-layer usage.

As the table above shows, flex PCBs can significantly improve performance and operational life of your critical application board. However, realizing these advantages requires manufacturers to follow good design guidelines for fabrication.

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Optimizing Your Flex PCB Construction for Harsh Environments

Many critical application flex boards must satisfy the criteria specified by the highest IPC performance classifications. Additionally, you should follow the flex PCB design guidelines listed below.

Flexible PCB Design Guidelines for Fabrication

  • Determine the correct flex board classification
    Including rigid-flex boards, five classifications for flex PCBs are outlined in the IPC-6013 Qualification and Performance Specification for Flexible/Rigid-Flexible Printed Boards standard. You should ensure that your design meets board type and installation specifications.
  • Ensure your design adheres to appropriate industry standards
    The overarching standard for manufacturing processes, including rigid and flex PCBs, is the ISO 9000 family of standards. Additional targeted standards for critical industries include AS9100 for aerospace and ISO-13485 for medical devices.
  • Choose the best material based on structural requirements
    A primary consideration for flex board fabrication is PCB material selection. Structural factors—as well as how electric parameters such as dielectric strength vary with bending or deformation—are important here.
  • Employ stiffeners as needed
    It is sometimes necessary to shore up your flex board with stiffeners to support certain component types. Balance usage against application requirements as stiffeners will increase fabrication time and cost.
  • Use sufficient coverlay
    Coverlay is similar to solder mask but used for flex boards. It is made from a polyamide sheet with a flexible adhesive glued on, serving to protect the flexible PCB surface during assembly.
  • Partner with a CM with flex board manufacturing expertise
    Arguably, the most important rule to follow is to select a CM experienced in flex PCB manufacturing. Failing to do so may result in your board not meeting the durability and reliability standards required.
Tempo's Custom Avionics for PCB Manufacturing Service
  • AS9100D and IPC J-STD-001E with Space Addendum certified manufacturing processes.
  • ISO-9001, IPC-600 and IPC-610 commitment to quality certifications.
  • Execute your full development cycle from proto to validation, NPI, and low volume production.
  • Accurate quote in less than a day.
  • DFX support, including DFM, DFA, and DFT from Day 1 of design.
  • Entire turnkey PCB manufacturing in as fast as 4 days.
  • Extreme space environment targeted manufacturing.
  • Use reputable components suppliers to ensure quality, security and traceability.
  • Performs multiple automated inspections during PCB assembly to ensure quality for prototyping.

Following the above guidelines will help you produce flexible PCBs that meet performance objectives over their projected lifecycles. However, attaining optimal results will depend on the experience and quality of your CM’s flex board manufacturing process.

At Tempo Automation, we build the highest quality PCBAs for every board spin at our smart manufacturing facility, where we employ our white box digital thread manufacturing process that promotes collaboration and transparency between engineers and CMs. This allows us to quickly deliver high-quality boards for standard and non-standard designs that meet rigorous defense and aerospace industry criteria for prototyping and on-demand production. We also provide downloadable DRC files in Altium Designer, Cadence Allegro, Mentor Pads, other 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 role of electronics in aerospace systems, contact us.

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