Search

(3-Aminopropyl)triethoxysilane (APTES) silane possesses one terminal amine group and three ethoxy groups extending from each silicon atom, acting as a crucial interface between organic and inorganic materials. In this study, after APTES was deposited on the aluminum alloy AA2024-T3 as a primer for an optional top coating with polystyrene (PS), its role with regard to stability as a protection layer and interaction with the topcoat were studied via combinatorial experimentation. The aluminum alloy samples primed with APTES under various durations of concentrated vapor deposition (20, 40, or 60 min) with an optional post heat treatment and/or PS topcoat were comparatively characterized via electrochemical impedance spectroscopy (EIS) and surface energy. The samples top-coated with PS on an APTES layer primed for 40 min with a post heat treatment revealed excellent performance regarding corrosion impedance. A primed APTES surface with higher surface energy accounted for this higher corrosion impedance. Based on the SEM images and the surface energy calculated from the measured contact angles on the APTES-primed surfaces, four mechanisms are suggested to explain that the good protection performance of the APTES/PS coating system can be attributed to the enhanced wettability of PS on the cured APTES primer with higher surface energy. The results also suggest that, in the early stages of exposure to the corrosion solution, a thinner APTES primer (deposited for 20 min) enhances protection against corrosion, which can be attributed to the hydrolytic stability and hydrolyzation/condensation of the soaked APTES and the dissolution of the naturally formed aluminum oxide pre-existing in the bare samples. An APTES primer subjected to additional heat treatment will increase the impedance of the coating system significantly. APTES, and silanes, in general, used as adherent agents or surface modifiers, have a wide range of potential applications in micro devices, as projected in the Discussion section. [ABSTRACT FROM AUTHOR]

Underfill is usually modeled as an isotropic medium containing uniformly distributed filler particles. However, filler particles tend to settle (or segregate) and thus alter the mechanical response of the flip chip die attachment package. The integrity of such flip chip attachment is different from that with an ideal isotropic underfill with very uniform distribution of filler. We analyzed the thermomechanical implications of filler settling to the stresses along the die/underfill interface by considering different profiles for the local concentration of filler and calculating their effective material properties by employing the Mori-Tanaka method. As the worst-case scenario, direct silicon die attach with solder bumps was assumed to analyze the interfacial stresses, which were predicted in trend by a simplified multilayered stack model and calculated in detail by finite element simulation. The filler settling has a localized but strong influence on the interfacial peeling stress near the edge of the die. The extent of this influence is determined by the profile of filler settling: (1) if the filler is assumed to settle in the form of a bilayer, then the peeling stress near the die's edge increases and it is directly proportional to the average volume fraction of the filler; (2) if the filler is assumed to settle gradually, then the magnitude of the peeling stress near the edge of the die becomes smaller as the local filler volume fraction near the die interface increases. The filler settling has no significant effect on the other components of the interfacial stresses. The edge fillet of underfill in pure resin can locally reverse the direction of the interfacial peeling stress and increase the interfacial shearing stress near the die's edge. [DOI: 10.1115/1.2957324] Keywords: filler settling, flip chip, interfacial stresses, bilayer, peeling stress

The fracture energy, toughness and failure modes of air plasma oxidized polydimethylsiloxane (PDMS) bonding are evaluated in this paper. Each PDMS-PDMS bonded specimen was subjected to T-peel testing at a constant-displacement rate. The load-extension curve from each test was analyzed by the principle of energy balance in linearly elastic fracture mechanics, to calculate the fracture energy (critical strain energy), which is the maximal strain energy a bonded specimen can withstand without losing its assembly integrity, and toughness (surface energy), which is the bonding energy at the interface. A distribution of calculated values against the air plasma treatment parameters shows the predominant range of 0.1 to 0.4 N/mm for fracture energy and 0.1 to 0.2 N/mm for toughness. Together with an analysis of three failure modes (cohesive, adhesive, and mixed), the results suggest 0.1 N/mm as the threshold of the fracture energy for weak bonding, below which a specimen will be likely to fail through debonding. A set of treatment parameters are recommended for using air plasma to achieve strong bonding. [ABSTRACT FROM AUTHOR]