Single layer package

Ordinary textiles in a single layer packaging give almost no protection against vapor and liquid. 

Mass Transfer in Liquid Food from a Single Layer Package... 

Theoretical for a Single Layer Package in Contact with Liquid Food... 

The problem is different from the case shown with the single layer package. 

Secondary packaging components are not intended to make contact with the dosage form. Examples are cartons, which are generally constructed of paper or plastic, and overwraps, fabricated from a single layer of plastic or from a laminate made of metal foil, plastic, and/or paper. In special cases, secondary packaging components provide some additional measure of protection to the drug product. In such cases it could be considered a potential source of contamination and the safety of the raw materials should be taken into consideration. 

The presence of a second layer of primary packaging material will reduce transfer compared to situations where a single layer only of the material is employed. The use of an air space between primary and secondary packaging could be used to reduce transfer of less volatile substances. It will not reduce transfer of more volatile substances (boiling points <250 °C) if these substances can transfer through the primary packaging when there is no air space. 

Ethylene vinyl alcohol barrier resins are never used as single layer films in packaging but rather are utilized in coextruded structures combined with less expensive structural polymers. 

Multichip packaging involves the attachment and interconnection of a variety of chip devices on an interconnect substrate that may be single layer or multilayer. There are two basic types of multichip packaging hybrid microcircuits and multichip modules. 

The substrates that we have been describing are single-layer substrates. There are a wide variety of multilayered packages that perform the same function as the single-layer substrate—that is, as a carrier for components that also provide insulation of one component from another, but which occupy a smaller area since some of the layers are internal to the package. The next section will discuss these multilayered ceramic packages in some detail, since they are manufactured primarily by tape casting. 

For interconnecting IC substrates with hundreds of I/O terminals, a single layer of microvia holes may not be sufficient to satisfy interconnection requirements. Double, triple, or even quadruple microvia hole layers may be necessary whether the board is a motherboard or a chip package substrate. When microvia holes are made only between adjacent layers (see Fig. 22.6), all three microvia processes— photovia, plasma via, and laser via—can be used. However, when a design requires microvia holes that must connect beyond adjacent layers—such as LI and L3 (skipvia)—laser via processing is the only practical option. 

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