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98 PCB007 MAGAZINE I MARCH 2024 A significant decrease in HDI substrate pro- duction cost can be achieved by reducing the number of substrate layers from conventional through-hole multilayers and microvia multi- layers of eight, 10, 12, and more to only two layers. Besides reducing direct processing steps, the yield will increase as defect-produc- ing operations are eliminated. e integrated mesh power system (IMPS) was invented in the latter years of MCM-D use for thin-film fabrication. ose geometries fit today into our use of ultra HDI. A Look at the Benefits In the late 1990s, thin film multichip modules (MCM-D) were supposed to save the inter- connect industry. e fine-line lithography would allow miniaturization with ease. Unfor- tunately, the four or five metal layers to which Integrated Mesh Power System (IMPS) for PCBs integrated circuits were wire bonded proved to be too expensive when compared to printed circuit multilayers (Figure 1a) and the emerg- ing silicon integration on ball grid arrays. IMPS topology was created to reduce the cost of metal layers on thin-film and ceramic multichip modules. e IMPS topology can reduce the metal layers to only two or three. is results in substantial cost reduction and simplification while not affecting electrical performance. IMPS Background e scientists at the High Density Electron- ics Center (HiDEC) at the University of Arkan- sas invented IMPS in the mid-1990s 1 . IMPS allows for low inductance co-planar power and ground distribution, as well as dense, con- trolled-impedance, low crosstalk signal trans- Happy's Tech Talk #27 by Happy Holden, I-CONNECT007 Figure 1: Interconnected mesh power system (IMPS) is a very cost-effective structure. a) Conventional multilayers of power-ground-signal X and signal Y on separate metal layers; b) The IMPS utilizes a "mesh" structure on just two-metal layers; c) IMPS course grid; d) A fine grid for the structure.

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