Signal integrity is something of a journey, and as you travel on the road to ever higher speeds, some characteristics of the PCB itself become more influential, and others less so. I am daily reminded of these changing circumstances, as Polar is based on a small island with a very large tidal range, about 33 feet (10 meters) from low to high tide. Seafaring types need to be aware that at high tide, there is a comfortable 25 feet or so beneath the keel, but at low tide, your hull may be damaged, if you’re not aground on dry land. Some less experienced yachtsmen may even be concerned with delamination, but not in a PCB way.
Several years ago, an unsuspecting French yachtsman moored his yacht to the railings of the local harbour. For a very nervous full tide cycle, he awaited to see if the cleats would pull out of the glass fiber hull—a different type of delam, certainly. Fortunately, the glass held and the yacht sailed out on the next high tide.
As circumstances change, interesting solutions to problems are often revealed with the changing situation. A yachtsman at high tide isn’t too worried about whether the seabed is rough or smooth, but at low tide, the concern about a sandy or rocky seabed is altogether different. With PCBs, the move to low-loss laminates exposes a similar situation.
In higher-loss laminate base materials in most popular applications, the bulk of the loss occurs in the laminate itself, and this is especially the case if the track geometries are on the generous side. So, you can choose to brush concerns about surface roughness to one side.
To read this entire column, which appeared in the February 2018 issue of Design007 Magazine, click here.