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Design007-June2021

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58 DESIGN007 MAGAZINE I JUNE 2021 tion of PCB technology and semiconductor technology. e main board was made with PCB technology and that circuit board had 35 GHz for the highest operating frequency. at circuit board is no problem for our current PCB fabricators to meet the requirements. However, mounted on the main board was a small glass circuit made with semiconductor technology and that circuit had castellated vias at the edges, which were used to solder- connect to the main board. e 35 GHz signal on the PCB would transition through the cas- tellated vias onto the glass circuit and it would go through a 4x frequency multiplier to get the signal up to ~140 GHz. Aer that, the 140 GHz signal would be pro- cessed as necessary on the glass circuit. at is a very interesting way to deal with a 140 GHz application, but I would question the capabil- ity of high-volume manufacturing as well as cost concerns. If PCB technology can be used to generate circuit features with extreme preci- sion, the high frequency circuit materials that we currently offer can support this technology and have benefits over the glass semiconductor technology. One PCB technology that has been around for many years is laser-defined conductors. Some of the recent laser technologies can gen- erate high precision circuit geometry. ere are limits to these processes currently, but over time, and if the PCB industry develops this technology for high-volume, this could be a process used for the future millimeter-wave PCB circuitry. Another PCB fabrication process, which may be beneficial for the industry to exert some effort in advancing, is fusion bonding technol- ogy. Fusion bonding has been around for many years, but typically not done in high volume manufacturing. ere are many things to over- come to make this technology robust for high volume manufacturing while still maintaining the exceptional electrical properties it can offer. Fusion bonding uses very controlled lami- nation equipment and processes to basically melt a thermoplastic material, which acts as a bonding material for a multilayer circuit. It will not surprise those engineers who have inves- tigated different high-frequency materials that there is one type of material that stands out for the best electrical performance, especially for very high frequency: PTFE-based material. To laminate a multilayer that uses a PTFE-based bonding material, a fusion bonding process must be used. A few years ago, Rogers Corporation brought to market a set of PTFE-based materi- als specifically formulated to meet the electri- cal needs of very high-speed digital (56 Gbps, 112 Gbps, etc.) applications. e material is Rogers XtremeSpeed RO1200 family of prod- ucts, and several independent studies have shown this material set can achieve the best electrical performance for very high-speed digital applications. However, to get the optimum benefit of this material set, the lamination of the mul- tilayer circuit using this material will need to use the XtremeSpeed RO1200 bondply and a fusion bonding process. (As a quick side note, we have achieved very good high-speed digital results when using the XtremeSpeed RO1200 core with SpeedWave 300P prepreg. SpeedWave 300P prepreg does not need fusion bonding and it will have lamination process parameters more common for high- volume PCB fabrication.) A pure package PCB using XtremeSpeed RO1200 core with XtremeSpeed RO1200 Bondply has the best electrical performance for the most demand- ing high-speed digital applications today. ese materials can support the upcoming advanced high-speed digital requirements of the future. DESIGN007 John Coonrod is technical mar- keting manager at Rogers Cor- poration. To read past columns or contact Coonrod, click here.

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