The Superconductive Circuit Board

    Natalia Piedras

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    Can FR-4 PCBs be used at low cryogenic temperatures?

    What is FR-4?

    The short answer is "Yes," but there is a bit more to it.

    What exactly is FR-4? FR-4 is a NEMA grade designation for flame-resistant glass-reinforced epoxy laminate. "FR" stands for Flame Retardant. The materials used are not defined by it, so different formulations can be rated FR-4. Unfortunately, it has become the norm in the industry to refer to the most commonly used PCB material by its FR-4 designation. As different formulations can share this rating, the properties of FR-4, particularly at cryogenic temperatures, can vary significantly.