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FEBRUARY 2020 I SMT007 MAGAZINE 73 the conductor metal pattern on the substrate. Moreover, unde- ployed terminals consume real estate and become rout- ing obstacles. One result in the present paradigm is that the choice for the packaged func- tion will be made by choosing from numerous different pack- age formats, outlines, heights, lead pitches, and termination finishes. This cacophony of choice (aside from height) is often a routing nightmare as designer and design software try to find the best possible routing solution and then deal with and provide redress to the early inevitable electrical and electronic problems that can affect signal integrity. The Occam concept proposes that all devices on the assem- bly have a common base lead pitch depopulated as required to hold to the objective (Fig- ure 2). This includes every- thing from discrete devices to CPUs. This simple act can greatly relieve the routing chal- lenge and result in a significant reduction in terms of design spins, the number of routing layers, and the overall size of the assembly. Figure 3 shows a comparison of results using the same number of compo- nents but with the latter design having all components of 0.5- mm pitch. Grid-based routing was com- mon in the early days of elec- tronics manufacturing when nearly all components had leads provided on a 0.100" pitch. Unfortunately, surface- mount technology followed an "80% rule" for successive gen- erations of component termi- Figure 2: Multiple lead pitches and termination designs (L) make for less efficient designing and a greater waste of space and layer burn to accommo- date non-uniformity. In contrast, designs where all terminations are on a pre-determined (e.g., 0.5 mm) circuit routing is immensely simplified. Note: The base grid pattern is shown for illustrative purposes only. Figure 3: The Occam concept offers significant advantages in design execution and increased simplicity. The design comparison above was performed by Darren Smith of Athena Tech, who designed both assemblies. The component count and type are the same for both designs, but for this "thought experiment" demonstration, the Occam design used only fully tested components envisioned to have all their terminations located on a 0.5-mm grid pitch. The data in the table speaks for itself.