• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.195-202
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• 2003

In this study, failure mechanisms of Au stud bumps/ACF flip chip joints were investigated underhigh current stressing condition. For the determination of allowable currents, I-V tests were performed on flip chip joints, and applied currents were measured as high as almost 4.2Amps $(4.42\times10^4\;Amp/cm^2)$. Degradation of flip chip joints was observed by in-situ monitoring of Au stud bumps-Al pads contact resistance. All failures, defined at infinite resistance, occurred at upward electron flow (from PCB pads to chip pads) applied bumps (UEB). However, failure did not occur at downward electron flow applied bumps (DEB). Only several $m\Omega$ contact resistance increased because of Au-Al intermetallic compound (IMC) growth. This polarity effect of Au stud bumps was different from that of solder bumps, and the mechanism was investigated by the calculation of chemical and electrical atomic flux. According to SEM and EDS results, major IMC phase was $Au_5Al_2$, and crack propagated along the interface between Au stud bump and IMC resulting in electrical failures at UEB. Therefore. failure mechanisms at Au stud bump/ACF flip chip Joint undo high current density condition are: 1) crack propagation, accompanied with Au-Al IMC growth. reduces contact area resulting in contact resistance increase; and 2) the polarity effect, depending on the direction of electrons. induces and accelerates the interfacial failure at UEBs.

• Electrical & Electronic Materials
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• v.11 no.10
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• pp.72-77
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• 1998

The effects of Al micro-bumps on the magnetic properties of CoCr(Pt)Ta/Cr films deposited on glass substrates were investigated. The coercivity increased and the coercivity squareness decreased by incorporating Cr/Al underlayers. The cause of the coercivity increase is attributed to the reduction of Co(0002) texture, the increase of magnetic isolation of CoCr(Pt)/Ta grains, and the refinement of CoCr(Pt)/Ta grains deposited on Cr/Al underlayers. The effects of an Al overlayer on the magnetic properties of CoCr(Pt)Ta/Cr films were also studied. The decrease of coercivity squareness is ascribed to the magnetic isolation of CoCr(Pt)Ta grains.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2003.11a
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• pp.99-102
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• 2003

Reactions between 48Sn-52In solder and under bump metallurgies(UBM) such as 100nm $Ti/8{\mu}m$ Cu and 300nm Al/400nm Ni(V)/400nm Cu have been investigated, and the shear strength of 48Sn-52In solder bumps on each UBM has been evaluated. While intermetallic compounds with two different morphologies were continuously thickened on Ti/Cu with repeating the reflow process, the intermetallics on Al/Ni(V)/Cu spalled into the solder with increasing the number of reflow times. The solder bumps on Ti/Cu exhibited higher shear strength than those on Al/Ni(V)/Cu.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.33-38
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• 2007

We studied a bonding at low temperature using polymer bump and Non-Conductive Adhesive (NCA), and studied the reliability of the polymer bump/Al pad joints. The polymer bumps were formed on oxidized Si substrates by photolithography process, and the thin film metals were formed on the polymer bumps using DC magnetron sputtering. The substrate used was AL metallized glass. The polymer bump and Al metallized glass substrates were joined together at $80^{\circ}C$ under various pressure. Two NCAs were applied during joining. Thermal cycling test ($0^{\circ}C-55^{\circ}C$, cycle/30 min) was carried out up to 2000 cycles to evaluate the reliability of the joints. The bondability was evaluated by measuring the contact resistance of the joints through the four point probe method, and the joints were observed by Scanning Electron Microscope (SEM). The contact resistance of the joints was $70-90m{\Omega}$ before the reliability test. The joints of the polymer bump/Al pad were damaged by NCA filler particles under pressure above 200 MPa. After reliability test, some joints were electrically failed since thinner metal layers deposited at the edge of bumps were disconnected.

• Journal of the Korean institute of surface engineering
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• v.36 no.5
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• pp.386-392
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• 2003

The electroplating process for a solder bump which can be applied for a flip chip was studied. Si-wafer was used for an experimental substrate, and the substrate were coated with UBM (Under Bump Metallization) of Al(400 nm)/Cu(300 nm)Ni(400 nm)/Au(20 nm) subsequently. The compositions of the bump were Sn-Cu and eutectic Sn-Pb, and characteristics of two bumps were compared. Experimental results showed that the electroplated thickness of the solders were increased with time, and the increasing rates were TEX>$0.45 <\mu\textrm{m}$/min for the Sn-Cu and $ 0.35\mu\textrm{m}$/min for the Sn-Pb. In the case of Sn-Cu, electroplating rate increased from 0.25 to $2.7\mu\textrm{m}$/min with increasing current density from 1 to 8.5 $A/dm^2$. In the case of Sn-Pb the rate increased until the current density became $4 A/dm^2$, and after that current density the rate maintains constant value of $0.62\mu\textrm{m}$/min. The electro plated bumps were air reflowed to form spherical bumps, and their bonded shear strengths were evaluated. The shear strength reached at the reflow time of 10 sec, and the strength was of 113 gf for Sn-Cu and 120 gf for Sn-Pb.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2004.11a
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• pp.61-61
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• 2004

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.07a
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• pp.95-99
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• 2001

Cu is considered as a promising alternative interconnection material to Al-based interconnection materials in Si-based integrated circuits due to its low resistivity and superior resistance to the electromigration. New humping and UBM material systems for solder flip chip interconnection of Cu pads were investigated using electroless-plated copper (E-Cu) and electroless-plated nickel (E-Ni) plating methods as low cost alternatives. Optimally designed E-Ni/E-Cu UBM bilayer material system can be used not only as UBMs for solder bumps but also as bump itself. Electroless-plated E-Ni/E-Cu bumps assembled using anisotropic conductive adhesives on an organic substrate is successfully demonstrated and characterized in this study

• Journal of the Microelectronics and Packaging Society
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• v.5 no.1
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• pp.7-18
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• 1998

In the flip chip interconnection on organic substrates using eutectic Pb/Sn solder bumps highly reliable Under Bump Metallurgy (UBM) is required to maintain adhesion and solder wettability. Various UBM systems such as 1$\mu$m Al/0.2$\mu$m Pd/1$\mu$m Cu, laid under eutectic Pb/Sn solder were investigated with regard to their interfacial reactions and adhesion proper-ties. The effects of numbers of solder reflow and aging time on the growth of intermetallic compounds (IMCs) and on the solder ball shear strength were investigated. Good ball shear strength was obtained with 1$\mu$m Al/0.2$\mu$m Ti/5$\mu$m Cu and 1$\mu$m Al/0.2$\mu$m ni/1$\mu$m Cu even after 4 solder reflows or 7 day aging at 15$0^{\circ}C$. In contrast 1$\mu$m Al/0.2$\mu$m Ti/1$\mu$m Cu and 1$\mu$mAl/0.2$\mu$m Pd/1$\mu$m 쳐 show poor ball shear strength. The decrease of the shear strength was mainly due to the direct contact between solder and nonwettable metal such as Ti and Al resulting in a delamination. In this case thin 1$\mu$m Cu and 0.2$\mu$m Pd diffusion barrier layer were completely consumed by Cu-Sn and pd-Sn reaction.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.456-462
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• 2002

In the present work, a low cost and fine pitch bumping process by electroless Ni/immersion Au UBM (under bump metallurgy) and stencil printing for the solder bump on the Al pad is discussed. The Chip used this experimental had an array of pad 14x14 and zincate catalyst treatment is applied as the pretreatment of Al bond pad, it was shown that the second zincating process produced a dense continuous zincating layer compared to first zincating. Ni UBM was analyzed using Scanning electron microscopy, Energy dispersive x-ray, Atomic force microscopy, and X-ray diffractometer. The electroless Ni-P had amorphous structures in as-plated condition. and crystallized at 321 C to Ni and Ni$_3$P. Solder bumps are formed on without bridge or missing bump by stencil print solder bump process.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.1
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• pp.33-38
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• 2001

We investigate the via-size dependance of as-electroplated- and reflow-bump shapes for realizing both high-density and high-aspect ratio of solder bump. The solder bump is fabricated by subsequent processes as follows. After sputtering a TiW/Al electrode on a 5-inch Si-wafer, a thick photoresist for via formation it obtained by multiple-codling method and then vias with various diameters are defined by a conventional photolithography technique using a contact alinger with an I-line source. After via formation the under ball metallurgy (UBM) structure with Ti-adhesion and Cu-seed layers is sputtered on a sample. Cu-layer and Sn/pb-layer with a competition ratio of 6 to 4 are electroplated by a selective electroplating method. The reflow-bump diameters at bottom are unchanged, compared with as-electroplated diameters. As-electroplated- and reflow-bump shapes, however, depend significantly on the via size. The heights of as-electroplated and reflow bumps increase with the larger cia, while the aspect ratio of bump decreases. The nearest bumps may be touched by decreasing the bump pitch in order to obtain high-density bump. The touching between the nearest bumps occurs during the overplating procedure rather than the reflowing procedure because the mushroom diameter formed by overplating is larger than the reflow-bump diameter. The arrangement as zig-zag rows can be effective for realizing the flip-chip-interconnect bump with both high-density and high-aspect ratio.