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The State of High-Speed Materials

Choosing the right material for your PCB was so simple a few decades ago. All but the most high-tech PCBs were constructed with FR-4. The lowly FR-4 has been improved and re-engineered many times in the past few decades, and rumors of its demise have proven unfounded.

But at today’s high speeds, FR-4 often doesn’t measure up, and designers must select an advanced low-loss PCB material with low Df and Dk values that isn’t prohibitively expensive or terribly difficult for fabricators to register during lamination. High-speed PCB signals now exhibit characteristics previously seen only in the RF and microwave world, requiring PCB designers to consider using lok-Dk RF materials such as PTFE and Teflon, which are much “softer” than FR-4 and tougher for the fabricator to work with.   

We started out with a reader survey. We asked, “If you are a PCB fabricator or designer, what are the greatest challenges for you working with high-speed materials?” and some of the answers were quite interesting.

Answers included:

• Dielectric constant is too high
• Material movement
• Getting accurate performance data
• Customer knowledge
• Performance for signal integrity
• Getting accurate dielectric material properties from data sheets
• Availability
• Too many materials to stock
• Mechanical stability in the z-axis
• Materials adhesion
• As a PCB fabricator, understanding designers' needs
• Hole wall quality
• Educating the customers on what they actually need
• Impedance control
• Lead time
• Cost

Many of the fabricators’ biggest challenges were related to manufacturability. The more high-tech materials are softer and pose problems with adhesion and registration. But many of the problems cited by designers centered on the lack of good data for advanced materials.

To read this entire column, which appeared in the April issue of The PCB Design Magazine, click here.