Multilayer Processing

Two general types of multilayer process may be distinguished, depending on whether they use oxygen reactive ion etching (RIE) (4) or optical exposure (5-11) to transfer the pattern into the resist. Optical pattern transfer may suffer from some limitation due to substrate reflections, but has an advantage in the simplicity of the equipment compared to RIE. 

The dendrimer tubes prepared by this multilayer process have only one open end and probably show a mechanical stability gradient, indicating that the effective number of layer-deposition steps in the proximity of the closed end is lower than elsewhere because the ionic dendrimer to be precipitated has limited access there. Production of uniform tubes would therefore require templates with two openings. 

Technologies, such as coextrusion and coinjection, allow PET and other plastics to package foods and other products.225 226> 227 Care must be taken to control the process so that the melt when blown will not have micro-voids in the container walls or will delaminate. Coextrusion and coinjection (or multilayer processes) are essential technique in the production of high performance BM products (Chapters 4 and 5). The parison or preform is coextruded with a number of different layers, each of which contributes an important property to the finished product. Increasingly, a mid layer may consist of recycled material which is encapsulated between inner and outer layers of virgin plastics. 

The general tendency toward synthesis of thinner films, driven both by applications and by the more microscopic analytical techniques, is well illustrated in this group of compounds. The interdiffused multilayer process deposits alternate layers of metal and chalcogenide, which are heated to promote direct reaction. An example is the growth of NbsSe4 from films of tens of nanometers This procedure is also successful for MoSc2. Because of the volatility of selenium, the last layer is metal, used as a cap. ... 

Extrusion, lay flat tubing, calendering, casting, solvent or aqueous dispersion coating, etc. for single layer materials. Multilayer processes—wet or dry bonding (lamination), extrusion coating, coextrusion, etc. 

The most commonly used process is electroplating, either by electrochemical or by electroless deposition. For nearly aU conditions, these methods provide a corrosion-protective solution, either consisting of the deposition of a one layer or a multilayer process. Because electroplating also provides the most economical solution for metallic coatings, we will concentrate on this method in this article. The main advantage of an electrochemicaUy prepared metaUic coating is the mechanism of... 

In the absence of complicating factors such as capillary condensation and competitive adsorption, the process of physical adsorption has no activation energy that is, it is diffusion-controlled and occurs essentially as rapidly as vapor molecules can arrive at the surface. The process will be reversible and equilibrium will be attained rapidly. Because the forces involved are the same as those involved in condensation, physical adsorption will generally be a multilayer process—that is, the amount of vapor that can be adsorbed onto a surface will not be limited simply by the available solid surface area, but molecules can stack up to a thickness of several molecules in a pseudoliquid assembly (Fig. 9.3). If the vapor pressure of the gas reaches saturation level, in fact, the condensation and adsorption processes overlap and become indistinguishable. The fact that physical adsorption can be a multilayer process is very important to the mathematical modeling and analysis of the process, as will be seen below. 

Figure 23 Lap shear strength determination (a) test specimen recommended in ASTM D1002 standard (b) multilayer process used to bond titanium alloy coupons with thermoplastic Larc TPI polyimide adhesive.

Discrete wire is a method for forming the wiring layers by rolling round wire into a soft insulating material coated onto the outsides of power plane cores.This method is often referred to as multiwire. It is available from only a very small number of manufacturers and offers few advantages over conventional multilayer processing. It is described more fully in Sec. 13.2.3. 

New structures or advancements on existing structures are then needed to make these interconnections. These structures—such as blind and buried vias, multi-lamination (sub-laminations), and build-up technologies—directly impact multilayer processing. Deeper bhnd vias and buried vias have caused a major increase in the demand for reliable via filling materials and methods. Relatively new materials, equipment, and processes have and are being developed to address this need. A new section in this chapter, Filled Via Processing and Sequential Lamination, addresses filled vias internal to the PCB. 

The multilayer process begins with the accumulation of the innerlayer clad dielectric laminate. 

Substrates made by the multilayer process from tape cast alumina have received considerable attention in recent years for multichip module (MCM) applications. An MCM consists of an array of closely packed chips on an interconnect board several inches on a side. Cofired ceramic is attractive relative to organic laminates because its thermal conductivity is almost 2 orders of magnitude higher, an important consideration in high-density circuitry. In addition both alumina and aluminum nitride ceramics are more closely matched to silicon in CTE than are organic boards. For similar reasons, alumina and AIN are attractive for ball grid array (EGA) mounting of chips. ... 

Aluminum nitride has been demonstrated to be suitable for blank substrates for high power and high frequency applications. Substrates from many sources are available for thick or thin film metaUization. Thick film paste manufacturers now supply pastes formulated for aluminum nitride. The multilayer process described in the previous section has also been adapted for aluminum nitride. Both multilayer substrates and packages are available commercially. 

The process that produces these 3D structures begins with an electronic, three-dimensional solid model file, generally called a CAD model. The 3D printer uses an inkjet printhead to deposit controlled droplets of specially formulated binder onto thin layers of powdered material. The binder forms the desired part, which is built in a multilayer process, one digital slice at a time. Once the printing is complete, the shapes are removed from the unbound, loose powder and chemically or mechanically bonded or solidified. 

Initially, multilayer coextrusion was considered as a new technology for creating PP nanocomposites with potentially well dispersed OMM. The three master batches were prepared and Irt down into the multilayer process in a 1 4 ratio with homopolymer PP so that the final samples contained between 2-5 wt% clay and a constant 5 wt% PP-g-MA compatibilizer. These samples all contained 20 layers and TEM analysis was used to determine the extent... 

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