Material Matters

Bill HarginDetermining tradeoffs among various laminates.

Read more: Dk and Df Characterization Methods for PCB Laminates – Part I

Bill HarginShould you use wider trace widths? And how will you know?

An engineer recently asked me about the relationship between trace width and insertion loss, while adjusting dielectric height to maintain a 50Ω single-ended impedance.

At a high level, five variables are at work here, including trace width, copper weight, dielectric height, Dk and Df. Include frequency and resin content, and we’re really talking about seven variables. (Then there are stripline vs. microstrip configurations, which change things a bit, as well as percent-copper, which impacts prepreg thickness, and copper roughness.) We’ll keep things simple, for discussion’s sake, and address some of these factors in future columns.

Lossy transmission-line effects become significant signal integrity concerns at clock frequencies above roughly 1GHz and for interconnect lengths that exceed 12 inches. Assuming we’re talking striplines and grabbing data from a stackup I was looking at [Megtron 6 (G)], we’ll use an insertion-loss comparison between two different trace width/dielectric height combinations. (Dks are similar, but a little bit different, depending on resin content.)

Read more: Trace Width’s Effect on High-Frequency Insertion Loss

Bill HarginThe genesis of a new column, and how the author came to write it.

As I type this, I’m still considering about five column names. I have a lot to say about printed circuit materials, which I find super interesting, and all the candidates have the word “material” in them. Whatever appears at the top is what I ultimately chose. I will actually describe the decision process, because I think it’s interesting, but will first highlight the career journey that led me here.

Some 23 years ago, on Oct. 1, 1995, I joined the two HyperLynx founders as director of sales and marketing. I am a mechanical engineer by education. They explained digital signal integrity to me as analogous to the water-hammer effect – most easily described as the pipe-thumping (due to a pressure wave) heard in an old house when the water is turned on or off quickly. (“Ringing.”) I was relatively new to PCBs, but had a good background in fluids, having worked a good bit in “active” fluid-based electronic cooling up to that point.

Read more: Laminate Choice, Signal Integrity, and Other Tradeoffs

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