A methodology for selecting the right material and the right price point.

When I started writing this column a couple years ago, I wondered how much I’d have to say. An experienced media guy told me to watch my inbox for topics and questions that may be of general interest. That turned out to be excellent advice. Here’s one such example.

“What is the best laminate for a loss budget of x dB for y inches? I was thinking in terms of Panasonic Megtron 6 or something like it.”

Megtron 6 is an excellent material, but it’s not cheap and it’s not the only horse in the race. My response was to focus on a loss and material-planning methodology rather than making a firm material recommendation.

Why we care. Everything that improves material performance – in particular, reductions in loss – comes at a price. Loss versus cost is a classic optimization problem. Designers want to pay just enough to meet loss requirements, but not more than they need to.

In the past, speeds were slow, layer counts were low, dielectric constants (aka Dk or Er) and loss tangents (aka dissipation factor, or Df) were high, design margins were wide, copper roughness didn’t matter, and glass-weave styles didn’t matter. We called dielectrics “FR-4,” and their properties didn’t matter much.

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