Types Of HDI Material Suitable For Your Application
Signal energy loss considerations at high frequencies require PCB materials that have a low Dielectric loss tangent or dissipation factor (Df) and a flatter Df versus frequency response curve. There are four categories of HDI-suitable materials:
Medium speed and loss: Medium speed materials are the most common PCB materials—the FR-4 family. Their dielectric constant (Dk) versus frequency response is not very flat and they have higher dielectric loss. Therefore, their suitability is limited to a few GHz digital/analog applications.
High speed, low loss: High Speed materials have a flatter Dk versus frequency response curve, and have a dielectric loss about half that for medium speed materials. These are suitable for up to ~0 GHz.
High speed, low loss, high signal integrity: These materials also have flatter Dk versus frequency response curves and low dielectric loss, and they also generate less unwanted electrical noise compared to other materials.
High speed, very low loss, high signal integrity, RF and microwave:
Materials for RF/Microwave applications have the flattest Dk versus frequency response and the least dielectric loss. They are suitable for up to ~20 GHz applications.
Be aware that these stackup materials are much harder to process and are not suitable to every HDI stackup. For more information, check out our HDI materials video.
In general, to get better signal transmission performance in very high speed digital applications, use materials with lower Dk, Df, and better SI features. For RF and microwave applications, use materials with the lowest possible Df materials. use lowest Df materials, and when signal attenuation is important, use a low loss high speed material. If crosstalk is an issue, reduce it by using a material with a lower Dk. When working with microelectronic substrates where the PCB size and layout features are small, BT materials are suitable.
Keep in mind these materials are much harder to process and not suitable for every stackup. For more information on HDI stackups, check out our tech talk on HDI manufacturability and cost.