Surface and Buried Interfacial Structures of Epoxy Resins Used as Underfills Studied by Sum Frequency Generation Vibrational Spectroscopy

Abstract

Flip chip technology has greatly improved the performance of semiconductor devices, but relies heavily on the performance of epoxy underfill adhesives. Because epoxy underfills are cured in situ in flip chip semiconductor devices, understanding their surface and interfacial structures is critical for understanding their adhesion to various substrates. Here, sum frequency generation (SFG) vibrational spectroscopy was used to study surface and buried interfacial structures of two model epoxy resins used as underfills in flip chip devices, bisphenol A digylcidyl ether (BADGE) and 1,4-butanediol diglycidyl ether (BDDGE). The surface structures of these epoxies were compared before and after cure, and the orientations of their surface functional groups were deduced to understand how surface structural changes during cure may affect adhesion properties. Further, the effect of moisture exposure, a known cause of adhesion failure, on surface structures was studied. It was found that the BADGE surface significantly restructured upon moisture exposure while the BDDGE surface did not, showing that BADGE adhesives may be more prone to moisture-induced delamination. Lastly, although surface structure can give some insight into adhesion, buried interfacial structures more directly correspond to adhesion properties of polymers. SFG was used to study buried interfaces between deuterated polystyrene (d-PS) and the epoxies before and after moisture exposure. It was shown that moisture exposure acted to disorder the buried interfaces, most likely due to swelling. These results correlated with lap shear adhesion testing showing a decrease in adhesion strength after moisture exposure. The presented work showed that surface and interfacial structures can be correlated to adhesive strength and may be helpful in understanding and designing optimized epoxy underfill adhesives.

Probing the interfacial molecular packing in TIPS-pentacene organic semiconductors by surface enhanced Raman scattering

“…5,6 Several techniques have been utilized for probing buried interfaces, such as near-edge X-ray absorption ne structure spectroscopy (NEXAFS) combined with delamination techniques 7,8 and vibrational sum frequency generation (SFG) spectroscopy. 9,10 Nonetheless, a more readily accessible method is needed for direct structural characterization of such interfacial layers in semiconductor thin lms.…”

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

“…reported a study using SFG-VS to derive molecular orientations of epoxy molecules cured on surfaces of various substrates. 113 However, SFG-VS signal from the buried epoxy/polymer interface was so weak that the vibrational peaks can barely be resolved. 113 Zhang et al.…”

“…In 2011, Vázquez et al reported a study using SFG-VS to derive molecular orientations of epoxy molecules cured on surfaces of various substrates. 113 However, SFG-VS signal from the buried epoxy/polymer interface was so weak that the vibrational peaks can barely be resolved. 113 Zhang et al improved the SFG-VS technique for the study of buried epoxy interfaces by using a near TIR geometry which allowed to detect weak signal contributed by the interface molecules.…”

“…113 However, SFG-VS signal from the buried epoxy/polymer interface was so weak that the vibrational peaks can barely be resolved. 113 Zhang et al improved the SFG-VS technique for the study of buried epoxy interfaces by using a near TIR geometry which allowed to detect weak signal contributed by the interface molecules. 114 Furthermore, the interfacial molecular structures of cured epoxies incorporated with silane molecules were 110 (c) The scheme of epoxy adhesion to PET when amine was used as a cross-linker.…”

“…One example is the interfaces between polymer and adhesives, which have been reviewed previously. [102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120] Another example is the rubbing and sliding between two polymers, which will be discussed in the following section.…”