Purity: epoxy adhesives

Fig. 31.3 Cathodic delamination potential profiles of an unmodified epoxy adhesive layer (adhesive as in Fig. 31.2, about 50 pm thick) on an iron substrate (purity 99.99%) with 0.5 M NaCI as electrolyte measured (a) 20 h after the addition of the electrolyte (b) 50 h after the addition, x increases positively with distance from the electrolyte-filled defect.

Fig. 31.6 SKP potential profiles of the delamination of an epoxy adhesive (as in Fig. 31.2, about 50 pm thick) from an iron substrate (99.99% purity) coated with an HMDS/O2 plasma polymer layer about 5 nm thick. Electrolyte 0.5 M NaCI [51].

Polyimides became popular for die-bonding adhesives because they are cleaner (in terms of ionic contaminants) than equivalent epoxy products. The market at present, however, is dominated by high-purity epoxy adhesives. Polyimides are always applied from solvent solution and require higher curing temperatures than epoxies. They are stable to higher temperatures. Solvent-borne thermoplastics pastes (or cast-film preforms) have been used for some lower reliability die-attachment applications. 

The resins, solvents and curing agents used in modem conductive epoxy adhesives are chosen to minimize residual vapors which can be released after cure. Modem epoxy adhesives generally consist of high purity Bis-A epoxies cured with a phenolic novolac resin. These mixtures do not contain boron or fluorides, and generate less ammonia or other corrosive vapors than epoxies available before 1982. 

High purity 4-dodecylphenol is used to produce specialty surfactants by its reaction with ethylene oxide. The low color of high purity 4-dodecylphenol is important in this appHcation from a standpoint of aesthetics. 4-Dodecylphenol is also used to produce phenoHc resins which are used in adhesive appHcations and printing inks. 4-Dodecylphenol is also used as an epoxy curing catalyst where the addition of 4-dodecylphenol accelerates curing of the epoxy resin to a hard, nontacky soHd. 

The paints were spray applied to a number of substrates. Two coatings gave a final dry film thickness between 85 to 130 microns. For ac impedance studies the coatings were applied to shot (steel) blasted cold rolled steel plates. For interface metal-loss studies by electrical resistance the coatings were applied to 10 micron Fe foils (99.85 purity), adhesively attached by Araldite 2003 epoxy paste on one side to grit blasted glass plates. 

Silicones and epoxy-silicone (9) hybrids have also been used. The silicones are naturally flame retardant, have excellent electrical characteristics, good purity and good thermal stability. But they have poor mechanical strength and poor adhesion to the lead-frames. The poor strength has resulted in an excessive amount of... 

Fig. 31.2 Measurement of the interfacial diffusion of hydrated ions by means of the scanning Kelvin probe on a polished iron substrate (purity 99.99%) coated with an adhesive layer about 70 pm thick (hot-curing, two-component epoxy resin adhesive with amine-based hardener) containing an aminosi-lane adhesion promoter (3-(tri-methoxysilyl) propylamine).

First use of electrically conductive epoxies Premixed, frozen adhesives introduced by Ablestik Laboratories, Epoxy Technology, and Amicon Reduced ion content epoxies and polyimides Introduction of epoxy preforms First high-purity RTV silicone adhesives from G.E. and Dow Coming... 

CAS 14464-46-1 EINECS/ELINCS 231-545-4 Uses Filler, extender for architectural and traffic paints, powd. coatings, protective coatings, wire and cable coating compds., adhesives/seal-ants, ceramic, high-temp, insulation, epoxy castings semireinforcing filler for silicone rubber filler in thermosets incl. polyester and epoxy Features High purity... 

Underfill adhesive (snap cure) Epoxy resins (high purity Bisphenol-A and cycloaliphatic resins) 45-60% Resin modifier 1—5% Curing agents (amine) 3-5% Filler (amorphous silica) 50-80% Loctite 3563, Ablebond 7811... 

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. 

FireShield HPM Series High Purity antimony oxide is used as a catalyst, chemical Intermediate and flame retard2uit in specialty applications requiring low levels of lead, arsenic and other trace metals. FireShield HPM is available in tvro grades. The 1.0 to 1.6 micron average particle size is suitable for many sensitive electronic applications, while the 0.2 to 0.4 submicron grade is used in liquid systems such as epoxies, urethanes, adhesives, paints, solvents and colloids where dispersibility or surface area is ing>ortant. 

Conductive adhesives are used for many other electronic assembly operations, in addition to die attach. Epoxy paste adhesives are used for capacitor and other component attach in hybrid components or on printed circuit boards. In general, these electronic assemblies require high purity adhesives which do not give off im-... 

---