Jung-Lae Jo

Application of Underfill for Flip-Chip Package Using Ultrasonic Bonding

In this study, the reliability of flip-chip (FC) packages with various underfills using ultrasonic bonding was evaluated in temperature and humidity (TH) tests. Fatigue cracks began at the interface between the Au bumps and glass substrate and then propagated through the interface with increasing dwell time in the TH test. The initial electrical resistance of Au bumps with lower viscosity underfill was lower than that of Au bumps with higher viscosity underfill. Entrapped underfill between the Au bumps and glass substrate or void formation between the Au bumps in FC packages was caused by high viscosity of the underfill. As the dwell time of the TH test increased, the electrical resistance of the FC packages increased. The fatigue life of an FC package with underfill that has a higher glass transition temperature (Tg) and lower coefficient of thermal expansion (CTE) value was higher than that of an FC package with underfill with lower Tg and a higher CTE value. Therefore, the properties of underfill affect the fatigue life of FC packages with underfill using ultrasonic bonding.

Effect of Atmospheric Pressure Plasma Treatment on Transverse Ultrasonic Bonding of Gold Flip-Chip Bump on Glass Substrate

This study was focused on the effect of atmospheric pressure plasma treatment conditions on the ultrasonic bonding properties of Au flip-chip bumps on Au-finished glass substrates. The spreading test of de-ionized (DI) water was carried out on the substrate after the treatment. The plasma treatment was performed with three different gases, N2, N2 + O2, and N2 + H2, for various treatment times from 0.3 to 18 s. The surface analysis was carried out after the treatment using Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The treatment conditions greatly affected the spreading angle and joint strength. The addition of O2 and H2 gases to N2 gas was effective to improve the wettability of the Au-finished substrate and the bondability between the Au bump and substrate, respectively. The spreading angle rapidly decreased with increasing treatment time from 0.3 to 1 s and then decreased slightly with further increase in the treatment time, whereas the bonding strength peaked after the treatment for 0.5 to 2 s and then decreased.

Reliability of Fine-Pitch Flip-Chip (COG) Bonding with Non-Conductive Film Using Ultrasonic Energy

This study evaluated the reliability of fine-pitch, flip-chip bonding with ultrasonic energy and non-conductive film (NCF). The surface treatment was carried out with H2SO4 before flip-chip bonding (FCB). The electro-plated Cu bumps on the Si wafer and Cu-coated glass substrate were prepared for chip on glass (COG). The ultrasonic bonding was carried out, with and without NCF, under optimum bonding pressure and time. The mechanical properties were tested by die shear testing. The reliabilities of COG with and without NCF were evaluated with thermal shock testing, humidity and temperature (HT) testing, and high temperature storage (HTS) testing after FCB. The contact resistances of COG were evaluated for electrical reliability. To determine the variation in the initial value of the contact resistance of the flip-chip bumps according to the bonding method, the bonded interface of each sample was analyzed with scanning electron microscopy (SEM).

Effect of Surface Treatment on the Mechanical Strength of Ultrasonically Bonded Chip on Copper-Coated Glass for Ultra-Fine Pitch Application in Microelectronics

This study was focused on the effect of surface treatment on the mechanical strength of ultrasonically bonded copper chips on copper-coated glass. The plasma treatment was performed with two different gases, either N2+O2, or N2+H2, for treatment times up to 18 s. Wet treatment was also carried out with 5 vol % H2SO4. Surface analysis was carried out after the treatment using Auger electron spectroscopy (AES) and it was found that treatment conditions greatly affected the joint strength. Wet cleaning with 5 vol % H2SO4 effectively removed oxides from the Cu surface, while addition of O2 gas into N2 gas plasma was good for removing carbides. The treatment conditions greatly affected the removal of contaminants on the Cu surface and the bondability between Cu bumps and Cu-coated glass substrates.

Effect of Time and Pressure on Ultrasonic Bonding Strength of Flexible Printed Circuit Board to Glass with Nonconductive Film

This study investigates the feasibility of ultrasonic bonding of flexible printed circuit board (FPCB) on glass with nonconductive film (NCF). The glass substrate is sputtered with Cr as a diffusion barrier and Cu to form the electrodes, whereas two different surface finishes are employed for the FPCB: immersion Sn and electroless Ni/immersion Au (ENIG). The peel strengths of the joints are investigated with various parameters, such as bonding time and pressure. The study showed that bonding time of the joints was not related to the degree of curing of NCF, because almost the same curing degree resulted when bonded for 1 or 3 s. Furthermore, the bonding pressure on the joints is strongly related to the amplitude of vibration at the horn.