Bromine resin

TetrabromobisphenolA. TBBPA is the largest volume reactive flame retardant. Its primary use is in epoxy resins (see Epoxyresins) where it is reacted with the bis-glycidyl ether of bisphenol A to produce an epoxy resin having 20—25% bromine. This brominated resin is typically sold as a 80% solution in a solvent. TBBPA is also used in the production of epoxy oligomers which are used as additive flame retardants. 

Secondly, whereas 26-30% chlorine is required to make the resin effectively fire retardant, only 13-15% of bromine is required. It is therfore possible to achieve a greater flexibility in formulation with the bromine resins, which may be blended with other resins and yet remain effectively fire retardant. 

Principles and Characteristics Combustion analysis is used primarily to determine C, H, N, O, S, P, and halogens in a variety of organic and inorganic materials (gas, liquid or solid) at trace to per cent level, e.g. for the determination of organic-bound halogens in epoxy moulding resins, halogenated hydrocarbons, brominated resins, phosphorous in flame-retardant materials, etc. Sample quantities are dependent upon the concentration level of the analyte. A precise assay can usually be obtained with a few mg of material. Combustions are performed under controlled conditions, usually in the presence of catalysts. Oxidative combustions are most common. The element of interest is converted into a reaction product, which is then determined by techniques such as GC, IC, ion-selective electrode, titrime-try, or colorimetric measurement. Various combustion techniques are commonly used. 

Gopalakrishnan, G., Kasinath, V., Singh, N.D.P., Krishnan, V.P.S., Solomon, K.A. etal, Microwave assisted regioselective bromomethoxylation of alkenes using polymer supported bromine resins, Molecules, 2002, 7,412. 

Standard epoxy resins are usually blended with brominated epoxy resins to provide the concentration of bromine required to provide ignition temperature resistance. Brominated resins have also been used as flame-retardant additives in thermoplastic compounds. 

In order to provide the required flame retardancy to the molding compound, an encapsulated formulation usually contains brominated resins and antimony oxide. The brominated resins used in the encapsulated formulation are mainly tetrabromobisphenol A (TBBA) based epoxy resin or brominated epoxy novolac. These bromine-containing additives were reported to cause bond degradation at high temperature through accelerated void formation in the gold-aluminum intermetallic phases (1-4). 

For the purpose of identifying the cause of this detrimental effect of the brominated resins on the wirebond reliability, the diglycidyl ether of tetrabromobisphenol A (TBBA) was exposed to 150° or 180° C for two hours, and the resultant resins were analyzed for the hydrolyzable halide content. A hydrolyzable halide is the halogen adjacent to a hydroxyl group and hence can be easily dehydrohalogenated (Table II). 

Chemical stability of the m-bromo phenol containing epoxy resin was compared with commercially available brominated resins. Epoxy resins were refluxed in N-methyl-pyrrolidinone with 1 N KOH for 15 minutes. Results in Table IV clearly demonstrated the extraordinary chemical stability of the m-bromo-phenol containing epoxy resin over the commercial product. 

Cresol Epoxy Novolac (CEN) and the epoxy derivative of tetrabromo-bisphenol-A (TBBA) are the resins typically employed to encapsulate microelectronic devices in molding compounds. The brominated resin, which is utilized as a flame-retardant additive to impart a degree of ignition resistance to the encapsulant, contains many unstable hydrolyzable bromides. These bromides, along with the presence of chloride impurities, are detrimental to the life of the electronic component. Specifically, bromine has been suspected and proven to cause wire bond failure (1-31. 

However, there are still unanswered questions about the mechanism leading to the generation of intermetallic alloys, and an explanation is yet to be provided for the difference in degradation rates among IC devices containing like amounts of brominated resin. 

Degradation of the Brominated Resin. From past studies, it is believed that the generation of intermetallic alloys is triggered by methylbromide (or hydrogen bromide) (1-3). The generation of these substances from brominated epoxy resin is discussed below. 

The purpose of this work was to study the role of the organic bromide in causing failure at the Au-Al bimetallic junction, and to establish any possible relationship between thermal stability of the brominated resin and wirebond failure. Special emphasis was placed on the identification of any contaminants other than inorganic ionic species that might be responsible for accelerated failure. 

Aqueous extractions of bromide and chloride ions were done at various temperatures ranging from 120- to 250°C. This was done to verify the thermal stability of brominated resins in aqueous medium at elevated temperatures. The total level of alkali metal ions and NH4+ combined was nearly an order of magnitude lower than either bromide or chloride this indicated that the halides were mostly derived from organic sources. Arrhenius plots of bromide... 

Effects of Brominated Resins. Wirebonds under high-temperature bake endured a remarkably longer life when coated with the experimental resins as compared to the standard. Uncoated wirebonds, of course, still had longer... 

Effects of Brominated Materials. Failure data presented in Table II shows that even at 250°C, resistive wirebond failure is strongly accelerated by the brominated resin. Uncoated wirebonds at this temperature had a failure time of 100 h, compared to 19- to 20 h for wirebonds coated with brominated resins. This finding confirmed that the rate of degradation of the interface between gold and the intermetallic phase could be accelerated by a brominated resin at any practical design temperature. 

Mechanism of Wirebond Failure. By considering the apparent activation energy of wirebond failure in the presence of brominated resins, the overall wirebond degradation process appeared to be controlled by a diffusion step. The activation energy values ranged from 21- to 23 kcal/mole for various... 

The brominated resins are more effective than the chlorinated resins and have become more predominant commercially. The ability of the resins to retard or extinguish burning is due to the evolution of hydrogen halide at elevated temperatures. Brominated epoxy resins are generally blended with other epoxy resins to impart flame retardance in such applications as laminates and adhesives. 

Where fire retardancy is an issue, vessels can be made entirely from brominated resins, or more commonly (particularly in Europe), just the outer millimetre or two can be made from the fire retardant grade. If a... 

Bromination of vinyl-ester resin imparts fire retardancy as manifested by flame spread and lower RHR [50]. However, this fire-retardant system functions primarily in the gas phase causing incomplete combustion. As such, brominated resins produce dense smoke, and an increase in the yield of CO and HBr. Recent interest in the use of non-halogenated organic-matrix composite materials in US Navy submarines and ships has generated the requirement for significant improvement in the flammability performance of these materials including reduction in the amount of smoke, CO and corrosive combustion products. 

The thermal stability of FR4 brominated resins is poorer than non-brominated (GIO), although it has been improved over the years. Limitations of FR4 can be overcome by using a GIO resin with ATH and the effect of heat ageing this combination provides a V-0 performance. 

In a PRCB factory, Bruze and Almgren (1989) found 6 workers of the 19 tested were sensitized to epoxy resin. During the production of manufactured articles (made of copper sheets and rolled fiberglass soaked with epoxy brominated resins), subjects were exposed mainly to such nonpolymerized resins and to powders from fiberglass tissues soaked with resins. 

Post-functionalization is usually carried out by electrophilic aromatic substitution in the presence of a Lewis acid (27) or by metallation of a brominated resin (Fig. 1) (28). 

The tensile modulus and flexural modulus property values of phenol-resorcinol resin are reinforced with 35% glass fiber and are greatly superior to the properties of a 35% glass fiber-reinforced brominated resin bisphenol in bisphenol A-polyester resin. 

Useful brominating resins (containing vinylpyridinium hydrobromide per bromide units) were prepared by functionalizing terpolymers of styrene, 4-vinyl-pyridine and divinylbenzene with bromine and HBr. The resins were stable over long periods and gave excellent yields in the bromination of alkenes and ketones. The spent reagent was readily removed after reaction and could be regenerated easily. ... 

Epoxy resins containing bromine atoms are particularly useful in circuit boards, electrical laminates, and potting and encapsulation applications in which flame-retardant properties are desired. Brominated resins that contain bromine atoms ortho or para with respect to a glycidyl ether group or a hydroxyl group have been proved to be the cause of inferior thermal stability and wire bond failure [25]. 

Brominated resins in which the bromine atom is in meta position to the phenolic hydroxyl or glycidyl ether group have been shown to be more hydrolytically and thermally stable than their ortho- or para-brominated counterparts [26,27],... 

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