Epoxy adhesives moisture sensitivity

Carboxylic acids are used as heat-curing coreactants in epoxy adhesives with reasonable room temperature latency. The cured adhesives typically demonstrate high heat resistance and relatively low moisture sensitivity. Epoxy cures with carboxylic acid curatives are generally somewhat sluggish, requiring high cure temperatures and/or base activators to achieve cures in reasonable time periods. 

Bullions TA, Loos AC, McGrath JE (2003) Moisture sorption effects on and properties of a carbon fiber-reinforced phenylethynyl-terminated poly(etherimide). J Compos Mater 37(9) 791-809 Carpenter IF (1973) Moisture sensitivity of epoxy composites and structural adhesives. 

The most important types of two-component adhesives are moisture-sensitive polyurethane, comprising polyol resin and isocyanate catalyst, and heat-sensitive epoxy, comprising bisphenol A or F resins and polyamine catalyst. Both single- and two-component adhesive systems are available in the market. Single-component reactive adhesives, which include cyanoacrylate and silicone, are also widely known, with the latter often being used as a sealant. 

Moisture absorption can influence the reliability of conductive adhesive interconnection joints. Moisture in polymer composites is known to have an adverse effect on both the mechanical and electrical properties of epoxy laminates [54,55]. Studies relating to the reliability and moisture sensitivity of electronic packages indicate similar degrading effects. It was determined that moisture absorption can cause an increase in contact resistance, especially if the metallization on the bond pads and components is not a noble metal [56]. Effects of moisture absorption on conductive adhesive joints are summarized in Table 2. In order to achieve high reliability, conductive adhesives with low moisture absorption are required. High adhesion strength to pad... 

Sihcones (qv) have an advantage over organic resias ia their superior thermal stabiUty and low dielectric constants. Polyurethanes, when cured, are tough and possess outstanding abrasion and thermal shock resistance. They also have favorable electrical properties and good adhesion to most surfaces. However, polyurethanes are extremely sensitive to and can degrade after prolonged contact with moisture as a result, they are not as commonly used as epoxies and sihcones (see Urethane polymers). 

In addition to the test above, the adhesive sensitivity as a function of the moisture take-up is evaluated. It is well known that plasticization phenomenon occurs in epoxy polymers which affects the overall characteristics but also the bonding properties. 

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