Thank you for your interest in our webinar on low-loss materials for RF and microwave applications. It will be presented by Amit Bahl and Alex Ippich of Isola Group.
Missed the webinar? Click the link below to watch the recording.
You can ask your questions on this thread.
| Question | Answer |
|---|---|
| How is Sierra guaranteeing the surface roughness is minimally altered during fabrication? Does Sierra provide a surface roughness delta before and after fab? | The roughness of the copper foil/dielectric interface is controlled by the type of foil/dendrite structure specified. Despite ensuring the correct material is used, Sierra doesn’t have any control over that. We use an alternative oxide treatment on the inner layers before lamination. We control roughness by running it in conveyorized equipment while keeping the chemistry within spec. Specific applications, such as via in-pad and copper-filled laser req, require planarization. Here, we use state-of-the-art planarization equipment to minimize roughness, followed by straight DC copper plating that smooths the surface. We have the equipment to measure surface roughness and can supply this data, but there is usually a nominal charge for this as it takes time and is done on a 3D scanning laser microscope, which is quite expensive. |
| Can I enter Isola Material part numbers into the Sierra Impedance Calculators to get S-parameters, etc. over my bandwidth? | You cannot enter the Isola Material part number into the tool. But you can use the PCB Dielectric Material Construction table in the tool to choose a material from the list and view their dielectric thickness and construction along with the resin content and Dk, Df values at different frequencies. You can use this information to calculate your impedances, S-parameters, and signal loss. |
| In general, can the Sierra S-parameter calculator calculate S-parameter matrices over a range of frequencies? And could those results be exported in say the form of a f x m x n matrix? | S parameters are calculated at the frequency entered by the Signal Loss Calculator. You can enter different frequencies at the Signal Loss Calculator and then calculate the S-parameters each time. The outputs will be displayed in m x n matrices along with the characteristic impedance and propagation constant. However, the output cannot be exported. |
| For stack-up designer, how can you select different (multiple) dielectric materials? Thanks, Stefan. | In the PCB Stackup Designer tool, you can choose a material using the drop-down. However, you can select only one material at a time. |
| What oxide treatment processes are recommended to reduce impact of additional roughness form the lamination process? How well developed are these new oxide processes? | We use AutoTech Bond Film Ex, a high-frequency material designed to reduce roughness. It’s self-limiting and easy to control, which helps manage roughness on inner layers. The foil is also carefully selected based on its dendrite structure. We’ve been using this material for about 3 years and have the ability to measure surface roughness with a high-end 3D laser scanning microscope, a $100,000 piece of equipment. This allows us to precisely control and monitor surface roughness, ensuring optimal performance. |
| What about EPIG or EPAG finishes? | We are doing these surface finishes now. |
| For surface finish, do you have comparison plots for lower frequencies like 1-10 GHz? Thanks, Stefan. | Unfortunately, I don’t have a similar comparison that includes multiple surface finishes. The original testing was conducted using a VNA with a frequency extender, covering only the 55 to 95 GHz range. As a result, that data is limited to this frequency range. However, at lower frequencies, the differences between surface finishes are generally less significant. Ultimately, this comes down to skin effect losses. At lower frequencies, the skin depth increases, meaning the current penetrates deeper into the conductor. This reduces the impact of the thin outer layer, making surface finish variations less critical. |
| Are there any free tools out there that can help determine max allowable stub length for backdrilling? | Sierra Circuits has a free-to-use Maximum Via Stub Length Calculator. The tool allows you to determine the maximum allowable via stub length and resonant frequency based on dielectric constant and maximum data transfer rate/fastest signal rise time/maximum frequency content/3dB bandwidth. Tool Link: Maximum Via Stub Length Calculator | Sierra Circuits |
| Instead of oxide processing (brown oxide) for HVLP2/3 and RTF2/3/4 copper profiles, does Sierra circuits use adhesive bonding techniques? If yes, which adhesives? Is there a limitation to the smooth Cu profile that Sierra can process to make multilayer PCBs? | Sierra has some patented embedded trace technology, which is fully additive and eliminates the need for oxide and dendrite structures. Surface roughness is well below that of VLP foil, and initial tests show an increase in signal speed of over 30% compared to conventional above-surface trace structures. We expect to launch a 2mil line/2mil space product by the end of May and will provide more details shortly. |
| What is your typical stub length after back-drilling? | It depends on the number of layers and board thickness. Usually, customers specify their requirements to us. We have advanced drill machines equipped with an electronic feedback system that determines when the drill tip makes contact with the panel’s surface. |
| Follow on question: Does Sierra do loss testing on high performance PCBs to ensure loss is within spec… eg. DELTA-L, SFD? | Currently, we do not have this facility. |
| What are the stub Length tolerances on the back drill as a function of PCB thickness ( aka distance of MNC from top/bottom of PCB)? | Our drill machines have an electronic feedback system to determine when the drill tip touches the panel’s surface. Combined with Z-axis linear drive motors, this enables a controlled depth drill tolerance of no more than +/-.0005”. This is regardless of depth, and each hole is measured individually. |
| Do you provide data on Dk and Df versus frequency and substrate height? Or have you a simulator to estimate the simulation parameters Dk and Df? | Yes, we do. Go to our website. Check for the particular material. There are tables with different laminates. prepreg thicknesses, Dk and Df for different thicknesses/constructions, and a couple of columns for various frequencies. Sometimes, we use extrapolation techniques to derive Dk and Df. |