PCB Materials for End Use Environment Fabrication

It’s not unusual to use technological leaps as markers to denote significant periods in the history of printed circuit boards. But it is becoming more difficult as the tools and methods that determine how PCBAs are built are continually evolving, including increased automation, the use of robotics, greater agility, and an emphasis on sustainability or environmental impact. In many cases, these transformations are motivated or supported by regulations and standards.

Rules and guidelines, such as the RoHS directives, ensure safe and responsible technological advancement in PCBA development. Accordingly, the environment in which your board is installed can significantly affect its operation and reliability. To mitigate any negative effects, board design and manufacturing should incorporate end use environment conditions into their processes. Doing so begins with choosing PCB materials that possess the right properties to offset any environmental hazards.

Important PCB Materials Properties to Know

Component selection is a critical aspect of board functionality and performance. Your choices are also important when it comes to minimizing or eliminating risks, such as procurement uncertainty and component failure. One of the most common causes of board failure is not accounting for the environment. Neglecting to design your PCBA to properly withstand end of use environmental conditions will often result in premature failure, early replacements, recalls, or perhaps even redesigns—all of which increase time and costs.

Board failures can include delamination, warping, breakage, surface arcing, and fires. Therefore, it is important to know which properties of PCB materials, like those listed below, determine end use environmental limits within which your board can maintain its structural integrity.

Important PCB Material Properties 

• Glass transition temperature (Tg)
• Coefficient of thermal expansion (CTE)
• Decomposition temperature (Td)
• Time to delamination
• Peel strength
• Flexural strength
• Electrical strength
• Combustibility
• Water absorption

The above parameters are typically included in specifications provided by PCB material manufacturers. However, knowing what values are acceptable for your board depends on its application and end use environment.

Important End Use Environmental Material Considerations

Commercial PCBAs are often required to meet lower IPC classification manufacturing standards, which means general purpose materials like FR-4 will likely suffice. For other environments, such as aerospace, automotive, defense and industrial, additional hazards may mandate more careful consideration of certain PCB material attributes, as shown in the table below.

End Use Environment vs PCB Material Attributes
End Use Environment	Environmental Conditions	PCB Material Attributes
Aerospace	Radiation Extreme temperatures Extreme Pressure Vibration	Tg, CTE, Td, Time to delamination, flexural strength, peel strength, combustibility
Automotive	High temperatures Low temperatures Vibration Constant motion	Tg, CTE, Td, Time to delamination, flexural strength, peel strength, combustibility
Defense	Rugged terrain Vibration Constant motion	Flexural strength, peel strength
Industrial	Vibration Constant/intermittent motion Fluid/moisture	Flexural strength, peel strength, electrical strength, water absorption

As the table illustrates, when choosing PCB materials for boards deployed in critical industry applications, the impact of temperature, pressure, motion, vibration, and moisture must be taken into account to avoid board failure.

Environment-Optimized PCBA Material Selection

Choosing PCB materials for your design is always important and should be based on where your board will be deployed. For critical system PCBA development, however, your choice is especially significant to ensure functionality and reliable operation while avoiding failure or premature breakdown. Following the guidelines below will help you meet this objective.

Guidelines for End Use Environment PCB Material Selection Know the PCB material parameters that define the range within which the board can maintain its structural and electrical integrity. Know the environmental conditions of your board’s intended operational environment. Select board materials based on environmental extremes, not nominal conditions.