Issue link: https://iconnect007.uberflip.com/i/1530269
40 DESIGN007 MAGAZINE I DECEMBER 2024 Impact of Advanced Semiconductor Packaging on PCB Stackup Designers Notebook Feature Column by Vern Solberg To accommodate new generations of high I/O semiconductor packaging, printed cir- cuit board fabrication technology has had to undergo significant changes in both the pro- cess methods and the criteria for base material selection and construction sequence (stackup). Many of the new high-function multi-core semiconductor package families require more terminals than their predecessors, requiring a significantly narrower terminal pitch. Inter- connecting these very fine-pitch, high I/O semiconductors to the PCB is made possible by an intermediate element referred to as an interposer. e interposer enables the inter- connect of the semiconductor package with an ultra-high-density socket (Figure 1), for exam- ple, that is configured to interface with a con- ventional FR-4 laminate-based, multiple layer printed circuit board. When defining the complex- ity level for the circuit board, the designer will first estab- lish a criterion for fabricat- ing the circuit board. is will include the board outline and thickness limita- tion. In regard to con- trolling the specified circuit board thickness limit, a clear objective must be established to identify the number of circuit layers that are to be dedicated to signal rout- ing and the number of layers reserved for power and ground Figure 1: AMD's universal 1,718 I/O land grid array socket developed for the Ryzen 7000 series of high-function multicore CPU products. distribution. Estimating the required number of signal layers will be determined by the com- ponent density and interconnect complexity. e number of power and ground layers will be determined by the number of ground termi- nals on the components and any requirements for multiple operating voltages. Before beginning the circuit board design process, experienced professionals advise the designer to perform an interconnect capac- ity analysis. is analysis is based on the board's usable area and terminal number for all components defined in the parts list, but it excludes the circuit conductors. To deter- mine the basic component area, the designer must first gather mechanical outline specifi- cations and electrical data for all active and passive component parts.