PCB Stackup Design Considerations for Intel® FPGAs

ID 683883
Date 6/28/2017
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1.4.9. Hybrid Construction

One technique to control cost in high speed designs is to use hybrid construction PCBs. In hybrid construction, only the layers where the high performance signals are required use a higher cost but lower loss copper clad laminate core. All other layers can use a lower cost FR4 derivative core material. A common requirement for hybrid construction is to maintain a homogeneous prepreg (usually FR4) throughout the PCB to bond the core layers together. Mixing prepreg in the PCB can result in lamination issues because different temperatures may be required for the different prepregs to bond properly. For example, consider a design where very high speed transceiver channels are to be routed only on the top and bottom layers using embedded microstrip topology to avoid any via stubs without backdrilling. In this case, the top and bottom layers can use a low-loss core such as Rogers 4350B while the rest of the internal layers can use typical FR4 cores.

Figure 15. Hybrid PCB Stackup