Toshihiro Iwasaki

Development of 30 micron pitch bump interconnections for COC-FCBGA

We developed the flip-chip bonding technology on chip-on-chip (COC) package with ultra-fine pitch bump, which leads advanced high performance devices. On this package, the realization of the metallographic behavior in the micro-bump interconnection is the substantial issue for achieving good bondability and reliability. In this paper, to implement flip-chip BGA package with COC structure (COC-FCBGA), the metal systems of micro-bump and the dimension especially metal plating thickness have been optimized by precise analysis. And it is confirmed that the specification we fixed on this package would meet sufficient quality level for fine pitch bonding. This COC-FCBGA technology will meet demands for high-end system solutions in very near future

Variable-Size Solder Droplets by a Molten-Solder Ejection Method

We have developed a molten-solder ejection method by which molten-solder droplets from a 13- (1 pL) to 450- mum (48 nL) diameter could be realized. This method has been developed as a technique to supply small solder balls. The authors have developed a newly designed solder ejection head and confirmed that solder balls with almost no surface oxidation can be formed by using this method. The diameter of the molten-solder droplets using an advanced head is 13 mum, which is much smaller than the 35 mum of a conventional minimum droplet. As the relative positioning accuracy, a standard deviation of 0.81 mum was achieved when the diameter of the solder droplets was 13 mum. Furthermore, by changing the drive waveform of the conventional head, we enlarged the diameter of the solder droplets to 450 mum, which was much larger than 200 mum of a conventional maximum droplet. In this case, the standard deviation of 26 mum as the relative positioning accuracy was also achieved when the diameter of the solder droplets was 450 mum.

High thermal sintering die attach for power device

Solder paste material is widely used for power devices as a standard die attach adhesive. But current solder paste material is not suitable to support high power devices which are requiring large current and high voltage application because it has low thermal and electrical conductance property. The characteristics of good die attach material should have high thermal conductance and low coefficient of thermal expansion (CTE) to minimize thermo-mechanical stresses, high electrical conductance to handle large current, high temperature stability, high mechanical strength and resistance to fatigue failure. Solders of the Pb-Sn and Lead-free have relatively low electrical and thermal conductivity. We have performed evaluations to find optimum material with silver sintering concept to replace solder paste.

The fine pitch Cu-pillar bump interconnect technology utilizing NCP resin, achieving the high quality and reliability

In the field of high-end server or network systems, the Flip Chip Ball Grid Array (FCBGA) package has been applied to achieve high performance on the device for data processing. And recently, global IT network and cloud markets, which require high-speed data processing, are rapidly expanding, so that further development of FCBGA package with high performance is strongly needed to realize such market demands. This time, we have developed Flip Chip technology with very fine pitch of 30 um staggered pitch Cu-pillar Bump, utilizing Non Conductive Paste (NCP) resin to adapt to high pin count device including high-speed signal interface. The keys of this flip chip technology are to optimize the condition of the reaction of NCP resin under the die and the phenomena of solder melting for interconnection. And, in order to confirm of the level of package reliability, the effectiveness of the height of solder joints was studied. The above technology and reliability is reported on this paper.

One picoliter ejection of solder droplets by an advanced molten solder ejection method

We have developed an advanced molten solder ejection method which realizes to eject 1 picoliter molten solder droplets. The molten solder ejection method has been developed as a technique to supply small solder balls. The authors have developed a newly designed solder ejection head and have confirmed that solder balls with almost no surface oxidation can be formed by using this head. The size of the molten solder droplets using this newly developed method is 1 picoliter, which is much smaller than the previous minimum droplet size of 22 picoliters. A standard deviation in position accuracy of 0.81 mum was achieved.