Microvias or High-Density Interconnect (HDI) printed circuits are now being designed in ever increasing quantities. HDI brings some interesting new solutions to age-old signal integrity (SI) and density concerns, and concerns that will grow as rise-times continue to drop.

This article focuses on four major areas of SI concerns: 1) Noise (including Noise-reflections, Noise-crosstalk, and Noise-simultaneous switching), 2) Electro-Magnetic Interference (EMI), 3) Interconnect Delays and 4) Decoupling.

In each case, HDI offers improvements and alternatives, but it is not a panacea. A couple of ‘cautions are listed that can be a major obstacle to HDI implementation; fortunately, these caveats are not SI-based. Important to SI are the materials used in HDI. Although not the focus of this article, the selected materials, the dimensional stack-up, and the PCB design rules will influence SI and electrical performance (impedance, crosstalk and signal conditioning). Miniaturization provided by HDI will be a major contributor to SI performance.

In Part 2 of this article, the HDI wiring of three fine pitch BGAs and CSP are highlighted. These are typical of the growing use of fine-pitch components. The three are: 1) 676 I/O, 1.00 mm pitch BGA, 2) 384 I/O, 0.8 mm pitch BGA and 3) 218 I/O, 0.65 mm pitch microBGA.

Finally, the SI example is also a case study in cost reduction. The ‘before’ and ‘after’ conditions are reviewed to emphasize the cost reduction and “time-to-market” advantages of HDI technology.

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