The effect of curing conditions on the low temperature relaxation behavior of catalyst-cured epoxy systems based on diglycidyl ether of bisphenol A (DGEBA) has been characterized by the thermally stimulated discharge current (TSDC) technique. In these chemically relatively simple epoxy systems, five relaxation processes, designated as y. P, P', POHI and @ ' I , have been observed: Their molecular origins are discussed in detail. The results are in agreement with prior suggestions of a n inhomogeneous cross-link density morphology.100°C at a temperature dependent on the degree of cross-linking, a P relaxation near but above -1 OOOC, and a y relaxation below -100°C; it is To and T7 with which we are concerned. As indicated, a number of suggestions have been made for the molecular mechanisms of these peaks (see Fig. 2 for a diagram of the network chemical structure). For example Chang, Carr, and Brittain (2) and Damont and Kwei (3) sug-
Optomec's patented Aerosol Jet technology is a maskless, non-contact material deposition system used to enable 3-dimensional semiconductor packaging. This presentation highlights results of printing high density, 3-D interconnects on stacked die modules which incorporate video, communication and memory chips. Such packages are critical for meeting the increasing functional requirements of SmartPhones, personal entertainment, and other mobile devices. The Aerosol Jet system is used to deposit silver nanoparticle ink connections along the staircase sidewall of staggered multi-chip die stacks. High aspect ratio interconnects with 30-micron line width and greater than 10-micron line height are demonstrated at a pitch of 61-microns. After printing, the silver inks are cured at ~200°C for ~30 minutes, which gives interconnect resistances below one-Ohm (< 5 micron Ohm*cm). The stacks can include up to 8 die, with a total stack height below 1 mm. The printing system has a working distance of several mm which means that no Z-height adjustments are required for the interconnect printing. Multiplexed print nozzles are used to achieve production throughputs of greater than two interconnects per second per nozzle. Based on cost and functional advantages, the Aerosol Jet process is emerging as an effective alternative to traditional wire bond and through-silicon-via (TSV) technologies.
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