Cu/epoxy interface enhancement and characterization with thiol treatment

This paper aims at the study of the copper/epoxy interface enhancement with the thiol-based self-assembled treatment. The objectives of this work are to study the interfacial adhesion improvement with different thiol materials as well as investigate the interfacial fracture behavior and reliability performance. The motivation is using the thiol-based self-assembled materials to improve the reliability of the electronic packages. The rationale is to build chemical linkage between the copper substrate and epoxy to improve the adhesion and utilizes the hydrophobic nature of the thiol-based material to impede the moisture diffusion through the interface. In order to study the adhesion strengthening by different thiol materials, two groups of thiol-based materials were selected with different backbone structure, TA group and TB group with alkane chain and benzene ring respectively. Both of the two backbone structures are hydrophobic. Chain length effect of TA group on adhesion is evaluated with different molecule chain length. To build covalent with copper, thiol group is chosen. For the reaction with epoxy, three different end groups are selected for the TB group, named TB-A, TB-B, and TB-C. Systematic study on the treated surface is carried out. SEM pictures show no obvious change in morphology, while XPS and ToF-SIMS proofs the chemisorbed thiol on copper substrate. DI water contact angle test is applied to measure the surface hydrophobicity. Angle-resolved XPS is carried out to evaluate the thickness of thiol coating layer. Interfacial fracture toughness (G_IC) is assessed by the tapered double cantilever beams (TDCB) setup. Maximum adhesion of 244.4±39.5Jm^-2 is recorded, which shows about 50 fold enhancement compared with control sample. With the reliability study, high temperature is found to be a dominant factor for adhesion degradation. Yet, best adhesion of 115.7±8.7Jm^-2 is measured after MSL1 preconditioning.