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10 DESIGN007 MAGAZINE I JANUARY 2023 Feature Article by Kris Moyer IPC INTERNATIONAL In today's ever-shrinking world of electron- ics designs, the use of BGA parts with very fine pitch features is becoming more prevalent. As these fine-pitch BGAs continue to increase in complexity and user I/O (number of balls), the difficulty of finding escape routes and fan- out patterns increases. Additionally, with the shrinking of silicon geometry leading to both smaller channel length and increased signal integrity issues, some of the traditional BGA escape routing techniques will require a revisit and/or adjustment to allow for not only suc- cessful fan-out, but also successful functioning of the circuitry of the BGA design. Historically, BGAs could be routed using tra- ditional full through-via structures, with dog- bone traces off the BGA pad. ese BGAs were typically 1.27 mm in pitch and had sufficient clearance between the pads to place a Class 3 Level A via without violating any design rules. Additionally, the feature sizes of these pack- ages were sufficient to fabricate in 1-ounce copper without any issues. With increases in chip complexity and I/O density, most BGA packages are now 1 mm or smaller pitch, with some packages as small as 0.4 mm pitch. With these finer pitch packages, it is no longer pos- sible to use traditional full-thru via structures under the BGA. is, in turn, will require the use of sequential lamination and micro- via structures in order to successfully escape route the BGA. Figure 1 shows a comparison Figure 1: Comparison between the package and feature sizes of a 484-ball 1 mm pitch BGA (U100) and a 100-ball 0.4 mm pitch BGA (U101).

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