Лако-красочные материалы — производство

A U. S. military hybrid specification (MIL-A-87172 of MIL-STD-883) established the selection and qualification requirements for polymeric adhesives used in military hybrid circuits and is used as a guide for die attach materials for nonmilitary applications as well.

Table 2 lists the requirements for a type I (electrically conductive) adhesive and test results of a typical current generation isotropically conductive adhesive as reported by Estes [44]. These requirements specify test ranges for characteristics that will establish processing, performance, and reliability.

In the process category, viscosity and pot life determine the suitability of a material for a specific application technique (e. g., stencil and screen printing, syringe dispensing, and pin transfer printing) and the length of time the material can be used. Shelf life is important from an inventory control point of view as well as a cost factor. Cure schedule will govern the product flow during the manufacturing process and also the compatibility

with temperature-sensitive components. The thermogravimetric analysis specification is an attempt to limit volatile evolution during cure. This can be very important in preventing voids in the conductive adhesive which will adversely affect electrical and thermal conductivity, joint strength, and die cracking [5]. In addition, the evolution of volatiles has been correlated to surface contamination of the die bonding pads and poor wirebonding yields [45].

The other test requirements shown in Table 2 deal with performance and reliability. The outgassed materials test in part is concerned with residual solvent and moisture in the starting adhesive, as well as by-products of thermal degradation. Ionic impurities and corrosivity have been associated with damage to the active die and thus poor reliability where found in excess. Bond-strength requirements are necessary to ensure processibility during subsequent manufacturing steps such as wirebonding and overmold­ing (plastic packages). The aged bond strength is intended to be another measure of thermal degradation resistance. Coefficient of linear thermal expansion and Tg relate to stresses in a bonded assembly; however, the significance of the value is not indicated by the requirements. Thermal conductivity is another check on void formation, while volume resistivity, especially after aging, is a measure of adequate particulate content, sufficient particle to particle contact, and a stable particle-matrix-particle structure in the adhesive.