Laminates Cyanate ester

Martin et al. (1989b) focus on cure of epoxies and cyanate ester resins for lamination of prepregs into multilayered circuit boards. The following dual Arrhenius engineering model was fitted to viscosity profiles ... 

As mentioned earlier, the cyanate-epoxy systems find many commercial applications. Many multifunctional formulations, principally based on CE/epoxy, have been claimed. Generally, the properties of epoxies are improved on co-cur-ing by cyanate ester and the blend is more cost-effective than cyanate alone. The applications of these blends, as covered by patents, has been referred to in a review by Penczek and Kaminska [184]. Most of their applications are in copper clad laminates [185-191], fire resistant formulations [192], aircraft structures [193], and in semiconductor devices [194-196]. Due to the commercial significance of the blends, the information on the epoxy-cyanate systems is still covered by patents and some of the most relevant and recent ones have been referred to in this review. 

For the production of base materials for circuit boards with higher performance (e.g., glass/epoxy or graphite/cyanate ester combinations) and of multilayer boards, the laminating resin acts as adhesive or special bonding prepregs must be used. The requirements for the resins, which act as adhesive, depend on both the processing conditions and the desired properties of the final circuit board and are similar to those described above. 

Ablefill UF 8807/ Ablestik Labs. Moisture-resistant cyanate ester (silica filled) 10 Plastic, ceramic, andPWB laminates Dispense, capillary underfill CSP or BGA packages and high-density interconnect substrates... 

Epoxy/cyanate ester thermoset blend-based composites have low dielectric constant desirable for advanced radomes, microwave anteimas, and stealth aircraft composite applications. Other applications include its use in copper clad laminates, semiconductor devices, and fire-resistant aircraft structural composites. 

The resin systems primarily used for laminates are bismaleimides, epoxies, melamines, polyesters, polyimides, silicones, and phenolics and cyanate esters. These resins are described in Sec. 2.7.8, and the reinforcements are described in Sec. 2.6.3. 

Common laminating resins used are phenolic and epoxy, although cyanate esters, polyimides, and other resins are used in specialty applications. The copper foil used is 99.5 percent pure and may contain some silver. Generally, electrodeposited foil is used rather than rolled copper, and the foil is usually treated to improve the adhesion of the laminating resin to the foil surface. 

Cyanate esters are used in circuit boards because of their low dielectric constant of 2.91 and a high Tg of 290°C. Prepregs and laminates are made with conventional technology, and they are tougher and more moisture resistant than FR-4 copper clad. Laminates are also used in radomes, antennas, and aerospace structures. 

There are numerous industry standard laminate constructions, and one of the leading sets of standards is that established by the National Electrical Manufacturers Association (NEMA). Some of the most commonly used resins are epoxies, polyesters, polyimides, cyanate esters, and phenohcs. Some of the most common reinforcements are paper, glass fiber, glass fabric, and certain plastic fibers and fabrics. 

PPE has been used in thermosets. In particular, PPE is used in the resin formulations to make GETEK copper-clad laminates for high-end, high-performance printed wiring boards. GETEK laminates were developed by GE Electromaterials. Epoxy-PPE based laminates were commercialized in 1991 [28]. In 2002, PPE-cyanate ester based laminates were... 

CyanatG Ester Curing Agents. Cyanate esters can be used to cure epoxy resins to produce highly cross-linked thermosets with high modulus and excellent thermal, electrical, and chemical resistance properties. They are used in high performance electrical laminate and composite applications. Cure involves oxazoline formation catalyzed by metal carboxylates in addition to homopolymerization of both cyanate ester and epoxy (122). The high costs of cyanate esters however limit their uses. 

A modified epoxy matrix for Kevlar FRP composites was produced from ep>oxy/polyphenylene oxide (PPO) blends cured with multifunctional cyanate ester resin [94]. The effects of the PPO content on the cme behavior in the cyanate ester-cmed epoxy were investigated with FTIR. The cme reaction in the ep>oxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanate fimctional group reactions were accelerated by adding PPO and that several co-reactions had occurred. Thermal mechanical analysis showed that the thermal stability of the epoxy/PPO matrix is improved by adding PPO. In the respective compursites, the ISS values between Kevlar fiber and the epoxy/PPO blends are almost the same as those between Kevlar fiber and neat epoxy. The ILSS in the respective laminates increases with the PPO content, which was attributed to an increase in the composites ductility. 

Similarities to epoxy resin include no volatile polymerization byproducts stable B-stage resins possible low shrinkage, high adhesion and void free structures. High purity makes cyanate esters very attractive for use in electronic applications. The performance of bisphenol A dicyanate resins in printed wiring board laminates was described by Weirauch et al(4). Mobay Chemical (and Bayer) introduced products of this type for PWB applications in the United States in 1976-78. These "Triazine A resins were not commercially successful and were withdrawn from the market about 1979. 

Kubens (9) found cyanate ester resins were compatible and reactive with epoxy resins. We have confirmed this in our laboratories. Such combinations can be formulated to yield cured materials containing both triazine and oxazoline ring structures. If brominated epoxy resins are employed in such blends, flame retardant materials can be obtained containing as low as 12% bromine versus 20% bromine required to flame retard epoxy systems. Such products show promise for use in printed wiring board laminates. 

Comprehensive Index Cyanate Ester - Laminating Resins... 

These blends include epoxy-polyphenylene oxide (PPO) (see Fig. 7.7), epoxy-cyanate ester, and epoxy isocyanurate (see Fig. 7.8). While these materials have been developed to minimize impacts to common printed circuit manufacturing processes, they can affect productivity in multilayer lamination and drilling and can require special desmear and hole wall conditioning processes, depending on the design of the printed circuit and fabrication process used. On the other hand, they typically have less of an impact to these processes when compared to the even higher performance materials. 

Laminates contain different reinforcement materials (woven/non-woven glass/organic fibers, expanded PTFE, etc.), resin types (phenolic, epoxy, cyanate ester, polyimide, BT, etc.), resin formulations (blended, functionality, etc.), hardeners (dicyanodiamide [dicy],phenol-novolak, cresol-novolak, p-aminophenol, isocyanurate, etc.), and sometimes fUler particles (ceramic or organic). The ratio of aU of these individual components can vary widely.To define a test strategy for laminates, it is important to understand the different main components of the materials as well as the conditions during manufacturing, as these wiU have a large influence on their properties and quality. 

Polyimide, cyanate ester, BT epoxy, high-Tg laminates... 

Cyanate Ester Blends. The second most stable resin system is the triazine or cyanate ester family. In its pure form, the cyanate ester resin is brittle and is difficult to drill without cracking. Low peel strengths are typically associated with its use. In addition, cyanate ester is an expensive resin system. As a result, cyanate ester resin is often blended with epoxy and a small amount of polyimide. This blend, called BT (after its two ingredients, bis-maleimide and triazine), can be coated on conventional glass cloth to produce a laminate. 

Some fabricators use bakes both before and after lamination. The bake before lamination is designed to ensure moisture removal from cores after the apphcation of the adhesion promotion chemistry follow the recommendations of the laminate manufacturer carefully. The bake is also needed if innerlayers are stored at high humidity prior to lamination, or as a standard process for hygroscopic materials such as some of the LFAC laminates or polyimide. Other fabricators use a bake after lamination to complete the cure, reduce warp, and relieve stress. Although a post bake will achieve these goals, it is usually unnecessary in a controlled lamination process. In the case of high-temperature materials such as polyimide, cyanate ester, and PPO, a post bake is a useful way to achieve a full cure in a process where the maximum press temperature is limited. 

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