PB-Free Design and Fabrication Tips - Printed Circuit Boards

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	Printed Circuit Board Design & Fabrication

Pb-free Design & Fabrication Tips The physical footprint on the PCB is the main concern when a board is being designed for Pb-free assembly. If component packaging is manufactured to withstand the higher temperature for Pb-free assembly, then there should be no change in the footprint, and no change in the layout. But there can be exceptions. Therefore, it is prudent for the OEM to consult with a knowledgeable EMS provider to minimize design and fabrication issues regarding the Pb-free impact on design. When designing for Pb-free assembly, it is important to place special attention to a PCB with SMT components populating both sides of the board. PCBs ready for Pb-free assembly may have bottom side glued and re-soldered components. These must be able to withstand solder temperature of over 250 degrees C. If not, they must be shielded using a wave soldering fixture.

At Pb-free PCB design layout, impedance control calculations must be made to assure that the differential impedance specified by the fabricator is correct. These impedances could be single-ended, dual stripline or microstrip. Purpose of these impedances is to make sure all signals coming out of these components get to their destination as clean as possible without minimal noise or crosstalk in those signal transmissions.