An investigation of the thermal cure reactions and the hydrolysis reactions involved in the degradation of polyimide films under temperature and humidity stress using nitrogen-15 solids nuclear magnetic resonance (NMR) is herein reported. Nitrogen-15 labeling was used in combination with dipolar decoupled, cross polarization magic angle spinning (CPMAS) NMR techniques as a means of monitoring chemical reactions as these occur in solid state polyimide. The relative concentration of each nitrogen-containing functional group was calculated using standard NMR methods based on determination of the values of the cross polarization time constant, Thn. the proton rotating frame time constant, , , and observed spectral line intensities. The polyimides were derived from an oligomeric poly(amic acid) precursor [pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA)], a high molecular weight poly(amic acid ester) precursor (PMDA m-diacyl chloride diethyl ester and ODA), and a polyisoimide oligomer [3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and l,3-bis(3-aminophenoxy)benzene (APB) endcapped with (3-aminophenyl)acetylene (APA)]. The number of "defect sites" or imide-precursor groups where imidization does not occur was estimated to be between 6 and 9% of the total nitrogen and varies with the type of precursor used. The degree of imidization or cure was found to vary between 91 and 94% following a cure at 400 °C. Residual isoimide groups were detected after an extended 400 °C bake of the polyisoimide precursor. Cured films were subjected to temperature and humidity stress at 85 °C and 81% relative humidity for 450 h. Estimates of hydrolysis range from as little as 1 % of total nitrogen for the BTDA-APB-APA derived material to approximately 13 % for the PMDA-ODA poly(amic acid ester) precursor. About 30% of the amide acid groups formed during stress react with water in a second hydrolysis reaction with chain cleavage to yield a terminal diacid and a terminal amine group. Hydrolysis from temperature and humidity stress is almost completely reversed if the stressed polyimide is heated at 400 °C after stress. The data obtained in this study are consistent with previously reported macroscopic observations in which polymer properties degrade during temperature and humidity stress and are recovered after post temperature and humidity bakes.
This paper summarizes the adhesion test standard and technique developed collectively by groups from the IBM Research Division, Yorktown Heights, and the Development Laboratory of IBM Microelectronics Division at East Fishkill. This activity was initiated since the increased complexity of interconnection technologies require a large number of interfaces to maintain their integrity while being subjected to a large variety of processes. For example, reliable adhesion of polymer layers to metals and ceramics plays a vital role in several IBM key product technologies, such as the recently announced Glass-Ceramic Module multichip packaging technology used in the system 390ES9000, models 820, 900 and 9021, computers and the Metallized Ceramic Polyimide (MCP) products. During the course of these product development cycles, it was noted that, sample preparation and measurement techniques can strongly affect the measured adhesion strength of a multi-component structure such as that found in multichip and multilayer modules. As a result of the observed variability in a multitude of adhesion measurements from many IBM laboratories, it was decided that standardization of the sample preparation and adhesion measurement techniques was required. During the course of collective work between a large number of participants, it became clear, that once a certain number of rules are followed, data collected from different workers can be compared. These rules form the basis of the peel standard which is discussed here. Once the standard measurement of adhesion is implemented, various adhesion promotion techniques can be directly compared, which lead to a swift and facile improvement in the reliability of products and in their development cycle time.
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