Are FR4 Boards an Option for 40G?

Are FR4 boards, currently used today in the 10G platform, a viable option for the 40G platform? The short answer: No. Through extensive testing, RadiSys has found that using FR4 boards leads to a higher insertion loss, a decisive factor when measuring your 40G solution against the ICR specification (Insertion Loss-to-Crosstalk Ratio). So, true compliance to 40G cannot be achieved with FR4 boards.

In comparison, low-loss boards are designed to produce, as the name implies, lower insertion loss, and are the recommended boards for 40G. Low-loss boards do cost more—perhaps a difference of $200 to $400 per board. However, choosing an FR4 board solely based on cost may mean that you’re jeopardizing an entire platform…which may cost upward of $50,000.

Does that mean you should cross off FR4 boards entirely? Well, not necessarily. Stay tuned, as we’ll discuss some of the trade-offs of these material choices in a later blog.

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