One of the problems in the modern microelectronics is the environmental protection of Integrated Circuits (IC). Especially, Chip-on-the-Board systems are sensitive to the temperature and relative humidity changes. Currently, IC can be protected as flip-chip with epoxy underfill; hermetic or semihermetic housing or polymer resin encapsulation. The last method offers simplicity, good environmental protection and can be applied directly to the chip without cavities, ceramic packages. Environmental protection of used glob-top encapsulation can be improved when the IC surface is modified by deposition of a coupling monolayer or multilayer system prior to the polymer resin coating.
Molecules forming the coupling monolayer or multilayer system can be applied for the IC encapsulation by using two methods. In the first one, molecules can be applied to form a separate film deposited by the Langmuir-Blodgett transfer or self-assembly (S.A.) technique. In this case crucial role is played by the chemical nature of coupling molecules and thickness of the deposited film. In the second method, coupling molecules can be added directly to the encapsulating resin and the coupling film is formed due to their diffusion to the interface region and surface enrichment. Two sets of experiments were performed. In the first one, special electronic testers "PW-ITE 5" with resistors lines of different widths and spacings were modified with LBT deposited 1, 10, 20 or 50 stearic acid monolayers. Therefore, testers were modified with thin organic films with the thicknesses equal to respectively 1.5, 4.5, 10 or 23 nm. In the second set of experiments, "PW-ITE 5" testers were modified with different compounds forming S.A. monolayers like 9,10-dialkylantracene-di(15-crown-5 ethers) or such simple molecules as anthranilic acid added in the 1% w/w amount directly to the epoxy encapsulating resin. Next, all modified "PW-ITE 5" testers were subjected to the highly accelerated aging procedure (100% RH; 85 C). Then, resistivity changes of both testers and number of "living" structures were measured. The best results, i.e., the highest number of "living" structures after accelerated aging test, were obtained for the anthranilic acid molecules added directly to the encapsulating epoxy resin. The lowest values of resistivity changes were obtained for ICs protected only with 20 monolayers of stearic acid molecules (film thickness about 10 nm). Both for thinner nad thicker films, poorer environmental protection was observed (faster raise of the resistivity changes in the electronic tester structures). The results obtained suggest the best environmental protection with the film only about 10 nm thick.