Direct measurement of temperature distribution in flip-chip micro-bumps under current stressing by using infrared microscopy

Recently, the dimensions of the flip-chip solder bumps reduce to about 20-30 micrometers, also known as "micro-bumps" sandwitched between two Si chips. In such a structure, electromigration and thermomigration behaviors in the micro-bumps are not clear now. In this study, the temperature map distribution of Al traces and Al pads in CoC and C4 structures during current stressing was directly examined by using infrared microscopy. When the Joule heating power of the 8.3-ohm circuits was 0.14 watt supported by 0.13-A current stressing at 100°C, the temperature increases of Al trace in CoC and C4 structure were 0.7°C and 5.5°C, respectively. During current stressing by 1.77×10⁴ A/cm² at 100 °C, the Joule heating of Al trace heated up the temperature of Al pad to 116.6°Cin the C4 structure, while there was no temperature increase in the Al pad in the CoC structure at such a stressing condition. According to Black\´s equation, the micro-bumps will have a longer MTTF as a result.