Thickness product design

In the reinforced RIM (RRIM) process a dry reinforcement preform is placed in a closed mold. Next a reactive plastic system is mixed under high pressure in a specially designed mixing head. Upon mixing, the reacting liquid flows at low pressure through a runner system to fill the mold cavity, impregnating the reinforcement in the process. Once the mold cavity is filled, the plastic quickly completes its reaction. The complete cycle time required to produce a molded thick product can be as little as one minute. 

Preliminary consideration of candidate materials, processes and tooling factors, configuration, thicknesses in section, ribs, bosses, holes, surface characteristics, color, graphics, decoration, and assembly methods will begin to impose some discipline on the product design as it evolves. In the middle and latter phases of the design cycle, two or three concepts should make their validity apparent to all involved. With luck (logic), one will... 

For epitaxial silicon wafers, product design focuses on optimizing the geometry of the plasma-enhanced, chemical-vapor-deposition (PECVD) reactor. To increase productivity, and maintain acceptable thickness uniformity, on the order of 5%, a simple optimization strategy locates a design that completes the deposition in 62 s. Then, for a standard manufacturing process, the economics are driven by the wafer costs, which are provided by a vendor at 206/wafer. At a sales price of 260/epitaxial wafer, the investor s rate of return is 18.3% and the return on investment is 25.3%. 

Fig. 6 Examples of poor (on left) and improved extrusion product designs (on right) to achieve uniform product thickness (1) profile (A) made into a hollow profile and (2) profile (B) made into an open profile.

CMP remains hampered by systematic and random interlayered dielectric (ILD) thickness variation at the wafer and die level. Pattern dependencies within the die, in particular, have been of concern for both manufacturability and product design. 

If FEA shows that some ribs buckle, the product can be redesigned with thicker or shorter ribs. The latter can be achieved by having crossribs at closer intervals. These add to mould construction costs, but add very little to the materials costs or the process cycle time. The productivity of an injection mould for the ribbed plate will be controlled by the solidification time given by Eq. (5.4). It will be 3 s for the ribbed plate and 19 s for the 5 mm thick original design. The increase in mould productivity is usually more important than the materials saving from product mass reduction. 

Products which benefit most from wide rollforming equipment will follow some basic considerations. The product designer should keep in mind that the complexity and size of any profile is directly related to the cost of equipment required. The most economical situation is a dedicated rollformer to make one product, in one width, and with little thickness variation. When this is not possible, the designer should look first at variations in panel width between forms to accomodate his requirements. Any variations in the edge forms themselves between products is difficult, as with any roll set. The degree of difficulty will depend on changes required, from roll pressure adjustments to an entirely new roll set. 

Product B, while having aTg of 150°C, is better suited for lead-free assembly than product C, with its 175°CTg.This is due the fact that product B has a decomposition temperature approximately 25°C higher than product C. In addition, as shown in Table 11.3, products B and C exhibit approximately the same total amount of thermal expansion in the range from 50 to 260°C. The charts for the different peak temperatures are shown to be the same for product B in Fig. 11.9.This is partly due to the hmited experience to date with this product in thick PWB designs. In addition, at lower peak temperatures, the number of reflow cycles that this product... 

Embedded capacitors may also be present. All boards exhibit capacitance between various traces, and especially between planes. The amount of capacitance is determined by the parallel surface area of the conductors, the thickness of the insulator between them, and the dielectric constant of the insulating material. Some product designs seek to maximize the desirable noise suppression benefits of capacitance between power and ground planes by making the intervening insulator thin. Some go further and use special insulating cores for these layers. 

---