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JULY 2024 I PCB007 MAGAZINE 93 tive to crosstalk, so the signals still must be separated. IMPS uses that separation to route power and ground. To prevent current starva- tion at devices, an adjacent metal layer running orthogonal is connected by buried vias at each junction where the two layers cross each other. is layer-pair topology is an "interconnected mesh" that can thus provide all the power/ ground connections without voltage loss and connect the signal for these devices. IMPS Design IMPS was developed in the late 1990s for MCM-D design using thin-film metallization on liquid dielectrics. Fortunately, PCB tech- nologies have improved in the last 30 years such that UHDI technologies can now achieve these thin-film geometries. e various SAP metalli- zation on polyimide film or ABF organic films can be employed, including the use of metal- backed thermal laminate. e architecture is based on the current use of a power mesh in integrated circuit design. But instead of the single metal use, IMPS employs two metals and adjacent layers, con- nected by vias, to form the mesh (Figure 8). In Figure 8, L1 and L2 are the ground mesh, while L1: VCC–L2: VCC and L1: VDD–L2: VDD shows the power mesh. e two are merged with the open area of X-Y routings, as seen in L1: signal–L2: signal. High-density MCM-BGA Application In 1996, HiDEC used flexible film and tape BGA (TBGA) technology along with microvias and the IMPS topology, to create an MCM-L with only two metal layers instead of the con- ventional four metal layers of an MCM-D. is test vehicle puts two IMPS metal layers, which provide signal wiring and power distribution, on the two sides of a polyimide film. One side contains mounting pads to which the dies are Figure 8: The IMPS design steps using only two metal layers composed of the IMPS two-metal layer mesh of ground; the two-metal layers mesh for power distribution; and two-metal layer-pair conductors on the organic substrates all integrated.