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86 PCB007 MAGAZINE I APRIL 2024 tichip modules. Power distribution character- istics of IMPS are presented as measured from various test vehicles 1 . In this column, the PMA for PCBs and imped- ance tables are presented. e initial applica- tion of PMA is shown, as well as an application that helps develop the wiring density model for PMA. Finally, the eight-step design process is outlined to create a PMA board. An Introduction to the Benefits In the mid-1990s, thin film multichip mod- ules (MCM-D) were supposed to be the salva- tion of the interconnect industry. e fine-line lithography would allow miniaturization with ease. Unfortunately, the four or five metal layers to which integrated circuits were wire bonded proved to be too expensive when compared to printed circuit multilayers and the emerging silicon integration on ball grid arrays. e test vehicle was built on 2-mil Sheldahl material, an adhesiveless polyimide film called Viain. e basic design rules are 50 µm lines and spaces and 150 m via target lands over 25 m laser-drilled vias. e IMPS mesh consisted of 200 µm lines and 50 µm spaces, with the lines offset from the via row or column centers. Wire-bond pads consisted of 200 µm x 350 µm rectangles on both metal layers, tied together with two vias. e test vehicle showed conclusively that the IMPS topology could be applied to MCM-Ls and BGA substrates without the use of multi- layering. Power Mesh Architecture In 1993, a large electronics OEM had the problem of having to redesign the control board of its largest 3.5" hard disk drive. e boards were a standard 3.87" x 5.45", but the problem was that they wanted to cut a 2.8"-diameter hole in the board so that another platter could be added to the drive. is would enable the drive to have a capacity of 16 GB, quite a capac- Figure 2: The impedance and crosstalk model for power mesh is an offset coplanar stripline. The table presents single-ended and differential impedances for various traces and thicknesses.