Publication: Effect of molecular structures and concentration of hardener on thermal characteristics of epoxy underfill
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Date
2024-08-02
Authors
Nor Rashikin Binti Abd Khalid
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Abstract
The reliability and performance of electronic packaging is greatly dependant on the underfill material. The underfill material operate as a barrier to keep out environmental elements like moisture, pollutants, and mechanical harm. On the other hand, variables like curing temperature and molecular structure could have an impact on the curing rate of the underfill materials which determines its qualities and performance. In this work, the effect of different molecular structures (i.e. linear and aromatic) and anhydride hardener’s concentration (i.e. 1.0 and 1.5 weight ratio) of the underfill materials on the thermal behaviour were compared, characterised and studied in anhydride-epoxy curing system. The chemical, physical, and thermal properties of the underfill material were evaluated using Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), hardness test, and optical image. It could be observed that all epoxy underfills in this study were completely cured by the disappearance of peaks at 1848 – 1774 cm-1 and 887 cm-1 in the FTIR spectrum that correspond to the anhydride and epoxy respectively. From the DSC and TGA analyses, it was found that the molecular structure (i.e. aromatic and linear) contributes to the thermal stability and flexibility of the epoxy underfill in the DSC. The glass transition temperature (Tg) could be observed at -2oC for EPM (Epoxy-Polyethylene Glycol-Maleic Anhydride) and none in the EHM (Epoxy-Hydroquinone-Maleic Anhydride) for the temperature range of 25 to -40 oC. This is due to the linear molecular structure that contributing to the easier chain segment movement between the crosslinks while the aromatic restricted the chain movement thus increasing the Tg. Moreover, hardness studies indicate that aromatic structure (EHM) is harder than linear structure (EPM). This is further supported by the optical picture, which indicates that EPM is more flexible than EHM. Additionally, it has been determined by DSC, TGA, and hardness tests that the presence of aromatic and linear structures would affect the thermal and physical performance.