Buffers coating

Since the invention of integrated circuits (ICs), polyimides as heat-resistant organic polymers have been applied to insulation materials in electronics devices such as flexible printed circuit boards (FPCs), interlayer dielectrics, buffer coatings, and tape automated bonding (TAB). A polyimide thin layer is easily... 

Blocking buffer Coating buffer containing 0.05% Tween-20, 5% bovine serum albumine (BSA) and 20% heat inactivated serum (see Note 9). 

Figure 11. Master curves of the dynamic tensile moduli at -40 C for three representative types of primary buffer coatings for optical fibers.

Because the integrity of the core-cladding interface is critical to beam guiding, the clad fiber is encased typically in a tough but flexible protective fluoropolymer buffer coat. 

Buffer coat n. A finishing material appUed over an old coating to protect it from solvent action of the new finish. 

Stress buffer coats are applied to semiconductor devices by two commonly used methods. The first method is termed glob-top coating and involves... 

Fig. 9. A stress buffer coat pattern formed in PMDA-ODA polyamic acid using the bilayer process shown in Figure 8. Courtesy of Arch Chemicals, Inc.

A compilation of commercially available nonphotosensitive stress buffer coat materials is shown in Table 3 (29-34). Table 4 provides selected physical data for some of the materials shown in Table 3. 

Table 3. Non-photosensitive Stress Buffer Coat Formulations Available from Various Suppliers...

Fig. 19. Chemical basis for image contrast in positive tone buffer coat materials based on DNQ-PAC chemistry.

Table 6. Selected Physical Properties of Stress Buffer Coat Films Derived from Photosensitive Precursors...

Tight buffered cables were the first generation of premises cables. The name tight buffered is derived from the layer of thermoplastic or elastomeric material that is applied directly over the fiber coating as discussed earlier. The buffer coating on the fiber makes it easier to handle and supports direct termination with fiber optic connectors (Fig 9.31). 

At present most commercial fibers possess a dual coating, a soft buffer coating surrounded by a stiff external coating (Fig. 3). Typical diameters of fibers with their soft and hard coatings are 185 and 250 pm, respectively. Both can be cured in situ by means of photopolymerization. 

In electronics, polyimides are now extensively used in the form of self-standing films for flexible circuitry, deposited films for interlayer dielectrics, passivation and buffer coatings, moulding thermoplastic powders for PCBs, and adhesive pastes or tapes. The basic polyimide chemistry has been adapted to fulfill the specific requirements of these applications. A series of books provides complete information not only on the chemistry of polyimides but also on their utilization in electronics [4,23,24]. The following figures summarize the chemical formulae of the most important categories of polyimide precursors or precyclized polymers that are commonly used in electronics. 

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