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44 DESIGN007 MAGAZINE I JUNE 2023 of 0.5 mm and lower are becoming more pop- ular. Today, there are 0.4-mm pitch BGAs in virtually every smartphone, and 0.3-mm ultra- fine pitch BGAs are the next generation. e next step is to increase functionality within the same package. Early adopters are venturing into the 0.3-mm pitch devices. However, there are currently no formal IPC design guidelines or layout rules specifically tailored to support- ing 0.3-mm pitch devices. As a result, many PCB designers largely rely on traditional 0.5- mm pitch design guidelines and layout rules to develop new 0.3-mm pitch device-based designs. For instance, the current design guide- lines allow the use of a solder-ball-joint pad with a diameter of 20% less than the diameter of a BGA/CSP solder ball. Table 1 gives an example of the required fea- ture sizes for BGAs. is enables us to deter- mine the signal layer count required to break- out from fine-pitch BGAs. e minimum num- ber of signal routing layers required to route a particular design can be estimated once the location of the signals on the BGA is known. • e first two rows/columns will route on one signal layer • e second two rows/columns will route on a second signal layer Plus, an additional signal layer is generally required for every row of signal balls past four rows. is assumes that all balls are routed because their signals are needed for connectivity. But if some balls are no-connects, then those cor- responding ball escape lanes are free for other signals. In this regard, fewer layers may suffice if the required signals have enough viable rout- ing lanes. Blind microvias and vias-in-pad are normally required for the breakout of 0.5-mm pitch or less. Accommodating the high number of indi- vidual power supplies to the BGA is also an issue. One can generally place three to four power pours on each power layer depending on the BGA pinout. So, four power layers typi- cally are required for 10 supplies plus ground. is could be reduced if some of the power pours are combined with signals on a mixed layer. As the data rate increases, the bandwidth required for data transmission also increases, which poses challenges for PCB design such as signal integrity, crosstalk, impedance match- ing, and electromagnetic interference. e PCB designer must also balance the layer count vs. manufacturing complexity. Signal integrity requirements may also impact this decision if, for instance, parallel trace segments are over 12 mm in length with a 200 ps rise time. PCB design is a complex and challenging task that requires designers to consider vari- ous aspects that influence the performance and quality of the PCB. Among these aspects, signal integrity, power integrity, thermal man- agement, and electromagnetic compatibility are crucial for ensuring the functionality and reliability of the PCB. PCB designers need to acquire more knowledge and skills to ana- lyze and optimize these aspects of PCB design using appropriate principles, methods and tools. Table 1: Typical feature sizes for BGAs. (Source: PCBLibraries)