Controlled Impedance

Figure 13. (a) Experimental approach for simultaneous collection of potential and current noise, (b) Schematic for remotely controlled impedance and noise multichannel data collection system. (Reprinted from F. Mansfield, C. Chen, C. C. Lee, and H. Xiao, The Effect of Asymmetric Electrodes on the Analysis of Electrochemical Impedance and Noise Data, Corros. Sci. 38 (3) 497, Fig. 1. Copyright 1996 with permission of Elsevier Science.)...

Much of the newer technology is driven by the needs for low dielectric constant and controlled impedance, a low dielectric constant being an advantage of foamed materials. Clearly, dimensional stability is becoming increasingly important for printed wiring boards. 

Figure 2). Orientation of the films is used to tailor and control the CTE, and the low dielectric thin film layers provide more controlled impedance and reduced crosstalk than other substrate materials. In addition to MLBs, ordered polymer films can be used to advantage in multichip molecules where silicon chips are directly bonded to the interconnect substrate. The very low permeability of PBO and PBZT films will protect the chips from moisture. Flexible circuitry is another promising application area for these films. 

However, a series of additional mechanisms are superimposed on the general scheme above, which can significantly control, impede or enhance subsurface pollutant transport ... 

Compliant layer between silicon and rigid redistribution substrate Controlled impedance, low inductance and resistance, no underfill required Wave (Tessera) Large die size and small I/O apphcations (memory base hand, ASIC)... 

Electrical parameters of interconnects (controlled-impedance design, cross talk, clock skew, signal propagation delay, electromagnetic interference for RE circuits, etc.)... 

The package has superior electrical performance in that the total lead length is short, controlled impedance interconnects can be designed in, and low-dielectric constant and low-loss materials can be used for the substrate. 

Information This drawing describes the unpopulated printed board and all features that become part of the board. It may contain specific design requirements such as material requirements, multilayer stack-up diagram, dielectric separation between layers, controlled impedance requirements, solder mask type, nomenclature color, location, size requirements for the fabricator s ID,... 

Custom constructions based on defined electrical property constraints, such as controlled impedances, cross-talk, or capacitance. These custom constructions are typically defined via equations or software models provided with certain product parameters. 

Conductor width (W) The finished width of the conductor can produce variance, which is likely to occur from lot to lot. Therefore, process control measures are necessary when producing controlled impedance circuits.The density of neighboring circuits will have an effect on the final etch. Often it is advantageous to modify the artwork line width at phototool generation for predicted variance. 

A good lamination cycle produces a flat ML-PWB that is free of moisture or voids and has a fully cured substrate. All layers must be well registered. The ML-PWB must be free of warp and the thickness must be within the specification. Any controlled impedance layers mnst have the correct pressed dielectric separations above and below the signal layer. Each of these requirements puts special demands on the lamination process. To assist in setting control measures, the following process indicators (see Table 27.6) should be monitored with a Statistical Process Control (SPC) method. 

Backlog blindsplanners and controllers, impedes schedule effectiveness, causes capital tie-up in inventory to skyrocket and cements the much too long throughput times that are difficult to calculate ... 

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