Research On Template Jetting Technology For Areal Array Bumping

Area array package is now the mainstream IC packaging technology. Its bumping processattracted a large research in which droplet spray technology is one of hottest directions.Template nozzle based pneumatic diaphragm-piston bump printing technology was proposedafter the study of present droplet spray technologies. The whole area array bumping can becompleted within only one spray process, using compressed air as the drive.First of all, a multi-field coupling mathematic model was established based on the airdynamics, structural mechanics, fluid mechanics, acoustic and heat transfer theory, according tothe order of printing process. This model can be used to predict the droplet diameter when thepulse pressure of the compressed air is given. The solder jetting device and the bump printingsystem was also set up under the direction of the model.Using the bump printing system, the effects on solder spray behavior of nozzle diameter,drive pressure, solenoid valve open time, jet frequency and solder superheat wereinvestigated through experiments. The experimental results showed that, nozzle diameterdetermines the formed solder ball diameter; driving pressure and solenoid valve openingtime are relevant factors, who have a certain range of appropriate values; the device canonly spray droplets under a cetern frequency for there must be enough time for thecompressed air to escape from the driving chamber; the solder superheat only determinswhether the solder can be ejected from the nozzle and almost has no effect on the formedsolder ball diameter.The solidification of solder droplets was also studied through experiments. The resultsrevealed that, the substrate temperature is the single dominant parameter that determines thefinal bump height when the substrate possesses a high effusivity; when the effusivity of asubstrate is relatively low, both the substrate temperature and the droplet temperature at impactplay important roles in determining the final bump height.Finally, area array bump printing experiments were carried out using the template nozzle.The height uniformity of the printed area array bump was considerable, while the positionprecision was poor. Reasons for the poor position accuracy were discussed.