Issue link: https://iconnect007.uberflip.com/i/1524164
94 PCB007 MAGAZINE I JULY 2024 wire bonded and discretes are soldered. is side is encapsulated. e other side has the lands in a ball grid array pattern. A part of the IMPS artwork is shown in Figure 8. e test vehicle was built on 2-mil Shel- dahl adhesiveless polyimide film, Viain™. e basic design rules are 50 µm lines and spaces, 150 µm via target lands over 25 µm 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. Wirebond pads consisted of 200 µm x 350 µm rectangles on both metal layers, tied together with two vias. Power Mesh Architecture (PMA) e power mesh architecture was derived from the interconnected mesh power system (IMPS) developed and patented by HiDEC 5 . e IMPS topology was created to reduce the cost and metal layers on thin-film and ceramic multichip modules. e power mesh architecture (PMA) for PCBs is presented in Figure 9. My Tech Talk on IMP 5 has impedance tables as well. e initial application of PMA is shown, as well as an application that helps develop the wiring density model for PMA. In 1993, a large electronics OEM had the problem of having to redesign the control board of their largest 3.5" hard disk drive. e boards were a standard 3.87" x 5.45" but their prob- lem was that they wanted to cut a 2.8" diam- eter 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 capacity for 1993. e solution to the loss of nearly 5.8 square inches out of 17.5 square inches was to employ microvias and microvia- in-pads. e new microvia board (called Lynx) was designed with a reduced surface area and as a six-layer design (1+4+1), two fewer layers than the original. Reading about the IMPS topology from HiDEC in 1994, the Lynx board was again rede- signed to a four-layer construction. To mini- mize the microvias, the outer two layers (1 and 4) were flooded with ground and only power Figure 9: Power mesh was adapted from the IMPS architecture but does not route GND bussing. Power mesh is an offset coplanar stripline transmission model 5 .