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

Abstract

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

Anisotropic Deposition of Localized Electroless Nickel for Preferential Bridge Connection

“…From the cross-sectional SEM analysis of the test pattern with the pad dimensions of W = 20 m, T = 1 m, D = 7.5 m, and T w = 5 m, deposited film was observed on the bottom surface of the trench between the facing pads. 14 The film thickness at any positions was about 200 nm. Moreover, no void and seam were observed in the films.…”

“…On the basis of several results obtained in our examinations, some probable mechanisms are discussed. [12][13][14] One mechanism is thought to be based on hydrogen generated during the electroless deposition, causing active hydrogen atoms to appear. 22,23 Moreover, the oxidization reaction of DMAB involves several elementary processes; thus, intermediate products are also generated.…”

“…[8][9][10][11] We have proposed a method of forming pad-to-pad connections using electroless metal deposition as a technique with the potential of application to flip-chip bonding technology. [12][13][14][15][16] In this method, pad-to-pad bonding was performed using a metal film formed by electroless deposition. The metal film was deposited electrolessly on organic resin to connect pads without using a seed layer or a resist pattern delineated by photolithography.…”

“…24,25 In our previous study, we developed a method of controlling the behavior of the extraneous deposition of electroless NiB films based on the selection of an appropriate pad geometry. [12][13][14][15] Moreover, we investigated the application of this method to flip-chip bonding technology known as chemical flip-chip bonding. [13][14][15][16] Hereafter, controlled extraneous deposition is referred to as localized deposition.…”

“…[12][13][14][15] Moreover, we investigated the application of this method to flip-chip bonding technology known as chemical flip-chip bonding. [13][14][15][16] Hereafter, controlled extraneous deposition is referred to as localized deposition.…”