Side flexibility

The cumulative benefits to synthetic CDO structures versus cash structures, if they are all in play, amount to dramatically improved economics. For instance, if all of the asset side (flexibility, ramp-up, basis) benefits sum to only 10 bps, and the liability benefit is 40 bps on 70% of the capital structure, the savings would amount to 38 bps (= 40 x 0.7 + 10) on a 1 billion transaction. For a 5-year synthetic CDO, the PV of those 38 bps amounts to over 17 million. In a leveraged structure, of course, these benefits will primarily accrue to the equity and their impact will be magnified as shown in Exhibit 22.8. Clearly, the synthetic CDO may be an efficient vehicle for investors to use in accessing diversified tranches of risk. 

IPC-6202, IPC/JPCA Performance Guide Manual for Single- and Double-Sided Flexible Printed Wiring Boards ... 

Double-sided flexible circuits with or without through-holes... 

FIGURE 62.3 Basic structure of single-sided flexible circuit... 

FIGURE 62.5 Cross section of a single-sided flexible circuit showing (a) adhesives-based laminate and film overlay (b) adhesiveless laminate with liquid coverlay. 

FIGURE 62.7 Blind via structure of double sided flexible circuits. 

Basically, the same construction systems of coverlay, stiffeners, and surface treatments as single-side flexible circuits could be available for double-side flexible circuits. 

Basically, double-sided flexible circuits with through holes are not available for dynamic flexing. The flexibility depends on the configuration of conductors in both sides of the base substrate, as shown in Fig. 62.19 shows examples. Bending the drcuit with thin copper circuits on the outside of the flexible circuits may cause them to break, because the mechanical stresses are concentrated on the small traces. 

A dynamic flexing area of a double-sided flexible circuit should have only one conductor layer. Coverlay on the other side of conductor should also be eliminated to enable symmetrical layer constructions. Copper... 

FIGURE 62.19 Circuits configuration of double-sided flexible circhits at flexing parts, (a) Preferred, (b) Acceptable, (c) Unacceptable, (d) Meshed shield layer, (e) Crossing traces, (f) Separated shield layer for dynamic flexing, (g) Fan folded, (h) Coiled. ... 

Figure 63.2 shows standard manufacturing processes of the through holes for the doublesided flexible circuits. A mechanical numerically controlled (NC) drilling process on double-sided flexible circuits can be done similarly to that used for rigid double-sided printed circuit boards. More laminates can be stacked up in the setup because of the thin materials. 

FIGURE 43.2 Standard manufacturing process for microvia holes in double-sided flexible circuits starting with copper clad laminate (CCL). The hole is created by drilling and then copper plated. 

Another major advantage of the laser via generation systems is RTR capability compared to the traditional mechanical NC drilling systems for the volume production of the double-side flexible circuits. It needs some modifications and loader and un-loader for the RTR systems for the standard laser equipment. Several laser systems are available for RTR process. 

It is possible to produce 20-/tm-pitch traces by subtractive process (as shown in Rg. 63.15), but the process will have relatively low yields.. The advanced subtractive process can produce 60-jum-pitch traces on double-sided flexible circuits with thin copper foil plated to 20-/an-thick. 

FIGURE 63.18 Twenty micron traces on double sided flexible circuits made by semi-additive process. 

The major manufacturing steps for standard double-sided flexible circuits with through-holes are hsted here. Each step should be considered carefully to determine its contribution to the overall distortion ... 

The buried, or inner, via hole system has been introduced to optimize the space factors of the inner conductor layers as shown in Fig. 65.16. The inner layer circuits with via holes can be produced as the same process of the double-sided flexible circuits. Adhesiveless copper laminates made by the cast process or lamination process are recommended for use in minimizing the smear during the driUing and optimizing the heat resistance during the multiple high temperature processes. 

JPCA-FC 01 Single-sided flexible printed circuits JPCA-FC 02 Double-sided flexible printed circuits JPCA-FC 03 Visual defect criteria for flexible printed circuits... 

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