Gold ball bumping versus E-less Ni/Au remetallization for chemical sensor integration using lead-free soldering for flip chip assembly

The use of analytical systems capable of performing analysis of high amount of chemical parameters is growing up. These microsystems known as μ-TAS (Micro Total Analysis Systems) can replace many steps carried out in laboratories allowing a more accurate and autonomous process. The sensors based in the microelectronic technology has a lot to offer to μTAS due to its small size and mass production. To reach a high level of miniaturization these devices are integrated in its bare die shape. However, the bonding pads finish in these devices is made of aluminum, which do not allow a direct soldering process using solder pastes for a flip chip assembly method. This work addresses this issue, evaluating the solderability using lead-free solder pastes for two solder bump processes: the SBB (Stud Ball Bumping) and Electroless Ni/Au UBM (Under Bump Metallurgy) in order to allow the interconnection between different sensors and substrates.