Ideas & Solutions
Hybrid Multilayer PCBs
Base materials made from PTFE (Teflon) are being used in larger and larger volumes. The reason for it is based on the continuously increasing operating frequencies of electrical appliances. The dielectric properties of FR4 are not adequate any longer to ensure functionality: Dielectric Constant (DK) incl. tolerance, dielectric loss, etc. The correct solution lies in the use of PTFE base material, which is manufactured according to applications, even in Europe. Multilayers made of PTFE have been virtually unknown until recent time, but total system cost analyses have changed the rules: Multilayers made entirely from thermoplastic materials are being used as well as hybrid multilayers composed of PTFE and FR4. In all-RF multilayers thermoplastic bonding films made of CTFE (for instance TacBond HT1.5 bonding film from TACONIC) or FEP are used to bond the inner layers instead of prepregs. As with FR4 multilayers, increasing packaging densities of printed circuit boards are the decisive factors. It is also possible to obtain coupler structures, whereby PTFE inner layers of different thicknesses and dielectric constants can be bonded together (pls. see a picture below). A further important aspect for the use of multilayers lies in space saving, whereby one multilayer pcb is used instead of several printed circuit boards. This automatically leads to cost savings for cables, connectors, etc. Hybrid multilayer have the additional benefit of combining the RF function of a printed circuit board with the digital function in ONE printed board. Cost savings are also possible through the thickness selection of PTFE base materials: Instead of 0.76 mm or 1.52 mm base material thickness for double-sided printed circuit boards, only the required dielectric thickness of the RF part will be used; Rigidity for SMT assembly is achieved through the FR4 section. hybrid printed circuit board

by Manfred Huschka, Taconic ADD, Mullingar

Ask our engineers if you want to know the typical materials and stack-ups to design the hybrid multilayer PCB.