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MARCH 2024 I PCB007 MAGAZINE 101 Electrical Performance Power distribution impedance was measured with both an HP 8510 network analyzer and an HP 4291A impedance analyzer over a range of 45 MHz to 1 GHz 2 . Figure 2 shows the mea- sured impedance for several substrates with combinations of decoupling capacitance. e results indicated there were minor differences between the IMPS power distribution struc- ture and one using solid planes. Any planar effects were reported to be masked by attach- ment or wirebonding impedances and by the number and type of capacitors used. e trans- mission lines are planar waveguides. 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 ultra HDI technologies can now achieve these thin-film geometries. e var- ious SAP metallizations on polyimide film or ABF organic films can be employed, including the use of metal-backed thermal laminate. e design process is shown in Figure 3. e architecture is based on the current use of a power mesh in integrated circuit design (Figure 3a). But instead of the single metal use, IMPS employs two metals and adjacent lay- ers, connected by vias to form the mesh (Fig- ure 3b). Figure 3b is the ground mesh, while Figure 3c shows the power mesh. e two are merged with the open area used of X-Y rout- ings (Figure 3d). Figure 4 illustrates a BGA example of IMPS for a BGA requiring two different voltage rails of VCC and VDD all on two-metal layers. High-Density MCM-BGA Application In 1996, HiDEC, using flexible film and Tape BGA (TBGA) technology along with microvias and the IMPS topology, was able to create an MCM-L with only two metal layers instead of the conventional four metal layers of an MCM- D 3,4 . is test vehicle puts two IMPS metal lay- ers, which provide signal wiring and power dis- tribution, on the two sides of a Kapton® film. One side contains mounting pads to which Figure 3: The IMPS design steps use only two metal layers: a) IC power mesh on one-metal layer as reference; b) The IMPS two-metal layer mesh of ground; c) The two-metal layers mesh for power distribution; d) Two-metal layer-pair conductors on the organic substrates, all integrated. Figure 4: An IMPS BGA design can be executed with two-metal layer-pair on an organic substrates.