Au Bump Interconnection in 20 µm Pitch on 3D Chip Stacking Technology

Nomura

Transactions of The Japan Institute of Electronics Packaging

et al. 2009

The formation of Au microbump arrays for flip-chip bonding was investigated using an electroless Au plating bath. Generally, electroless Au deposition gives a low deposition rate, preventing the fabrication of Au bumps with heights of more than 5 μm. To overcome this problem, we developed a new electroless Au deposition process that employs a non-cyanide bath. This process delivers a high deposition rate, especially for fine bump patterns (bumps of less than 10 μm in diameter). Au bumps with a diameter and height of 10 μm each could be fabricated with a high deposition rate using the new electroless Au plating bath. Moreover, Au microbump arrays were successfully fabricated on Cu wiring. The practical feasibility of this technique was demonstrated by forming arrays with bump heights and bump diameters of 10 μm each and an array pitch of 30 μm. All film-formation processes were performed under cyanide-free conditions; thus, this process has a high industrial potential for fabricating ultra-fine Au microbump arrays.

Section: Introductionmentioning

confidence: 99%

Formation of Au Microbump Arrays for Flip-Chip Bonding Using Electroless Au Deposition from a Non-Cyanide Plating Bath

Nomura

Transactions of The Japan Institute of Electronics Packaging

et al. 2009

“…In recent years, the bump size for flip-chip bonding between a silicon die and a package has reached a value of the order of 10 µm [1,2,3,4]. With the downsizing of the interconnect bumps for flip-chip bonding, mechanical issues such as stress concentration in a bump due to thermal mismatch after bonding, or misalignment among bump junctions due to a limited alignment accuracy are becoming more serious.…”

Section: Introductionmentioning

confidence: 99%

Chemical flip-chip bonding method for fabricating 10-.MU.m-pad-pitch interconnect

IEICE Electron. Express

Kikuchi

et al. 2008

Abstract:A flip-chip bonding method has been developed for fabricating ultrafine-pitch pad-to-pad interconnects. The method utilizes the preferential growth of Ni-B bridge layers on resin walls in a microscale cavity structure fabricated in the underfill resin between copper pads facing each other under some conditions of electroless Ni-B plating. In this method, the interconnect can be fabricated without loading and/or heating. By controlling the growth of the bridge layer on the resin walls in the microscale cavity under optimized plating conditions, the feasibility of ultrafine-pitch flip-chip bonding with a 10-µm pad pitch is experimentally demonstrated at a temperature of 60 • C. Keywords: interconnect, flip chip, electroless plating, Ni-B, fine pitch Classification: Science and engineering for electronics References

“…4 Many researchers have investigated this method. 5,6 However, fine-pitch arrays of bumps of the order of micrometers in height and width are not easy to fabricate. Moreover, insufficient accuracy in alignment in the chip-to-substrate bonding is becoming a serious problem in dealing with finer bumps.…”

mentioning

confidence: 99%

Interconnection of Micropad Electrodes by Controlled “Extraneous” Deposition of Electroless NiB Film

Electrochem. Solid-State Lett.

Oosato

et al. 2007

A method of interconnecting micropad electrodes was developed by using the electroless deposition of NiB for application to the flip-chip bonding technology. The phenomenon of "bridge" formation by the so-called "extraneous deposition" was utilized as a technique to perform selective deposition of NiB on noncatalytic surfaces. The process of extraneous electroless deposition was controlled by optimizing deposition conditions so that the deposit grew anisotropically along the surface between the facing pads. Practical feasibility of this technique was demonstrated by forming an interconnection between pads separated by 5 m and measuring 5 m in both height and width. This method was applied successfully to interconnecting the pads forming an array with a pitch of 20 m.To meet the strong demand for high performance electronic packaging, interconnection technology involving chip-to-chip and chip-to-substrate bonds is a key element controlling the performance of electronic instruments. 1-3 In this packaging technology, the reliability of interconnection of high-density pad electrodes in three dimensions is very important. Currently, several methods, including wire bonding, tape automated bonding ͑TAB͒, and flip-chip bonding, are being used widely. Especially, the method of flip-chip bonding with small metal bumps is used more widely than other methods for fine-pitch bonding, as the former technology is more compatible with a higher packaging density with a shorter electrical path because of the use of a fine-bump array with a fine pitch. 4 Many researchers have investigated this method. 5,6 However, fine-pitch arrays of bumps of the order of micrometers in height and width are not easy to fabricate. Moreover, insufficient accuracy in alignment in the chip-to-substrate bonding is becoming a serious problem in dealing with finer bumps. 1 Furthermore, chip damages caused by pressure and heat treatment during bump bonding are also becoming a problem. 1,2 For solving these problems, several researchers have investigated the chip-to-substrate connection using the "surface activated bonding" method at room temperature 7 and the electroless deposition method. 8,9 In this article, we propose a method of pad interconnection using electroless metal deposition as a technique with a potential of application to flip-chip bonding technology. In this method, a metal is deposited electrolessly on organic resin to connect pads without using a seed layer and a resist pattern delineated by photolithography. No heat treatment nor pressure application is required, and the temperature during this fabrication process is as low as 60°C. This method is believed to be useful as a process for forming interconnections in technologies including three-dimensional system integration.Generally, it is known that electroless deposition, especially electroless NiB deposition, can occur not only on catalytic surfaces but also on noncatalytic surfaces near a catalytic area. 10-18 This phenomenon is called "extraneous deposition," and it is known to cause ...