The root cause of black pad failure of solder joints with electroless Ni/Immersion gold plating

Zeng, Ke; Stierman, R.J.; Abbott, D.C.; Murtuza, Masood

doi:10.1007/s11837-006-0187-5

Cited by 82 publications

(38 citation statements)

References 22 publications

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“…As the immersion coating of Au is dependent on the efficient removal of Ni from the surface, these plating solutions are typically run at an acidic pH which means the conventional aqueous immersion gold process fundamentally contributes to the formation of these defects and control over when and where they form is difficult. 14 To address these issues, Deep Eutectic Solvents (DES) have shown promise in the immersion coating of other metals, such as copper, from acid free formulations [15][16][17] and so our strategy has been focused on the development of alternative processes using DES media.…”

mentioning

confidence: 99%

Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Ballantyne

Forrest

Frisch

et al. 2015

Phys. Chem. Chem. Phys.

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In this study we compare the electrochemical and structural properties of three gold salts AuCl, AuCN and KAu(CN)2 in a Deep Eutectic Solvent (DES) electrolyte (Ethaline 200) in order to elucidate factors affecting the galvanic deposition of gold coatings on nickel substrates. A chemically reversible diffusion limited response was observed for AuCl, whereas AuCN and KAu(CN)2 showed much more complicated, kinetically limited responses. Galvanic exchange reactions were performed on nickel substrates from DES solutions of the three gold salts; the AuCN gave a bright gold coating, the KAu(CN)2 solution give a visibly thin coating, whilst the coating from AuCl was dull, friable and poorly adhesive. This behaviour was rationalised by the differing speciation for each of these compounds, as evidenced by EXAFS methods. Analysis of EXAFS data shows that AuCl forms the chlorido-complex [AuCl2] − , AuCN forms a mixed [AuCl(CN)] − species, whereas KAu(CN)2 maintains its [Au(CN)2] − structure. The more labile Cl − enables easier reduction of Au when compared to the tightly bound cyanide species, hence leading to slower kinetics of deposition and differing electrochemical behaviour. We conclude that metal speciation in DESs is a function of the initial metal salt and that this has a strong influence on the mechanism and rate of growth, as well as on the morphology of the metal deposit obtained. In addition, these coatings are also extremely promising from a technological perspective as Electroless Nickel Immersion Gold (ENIG) finishes in the printed circuit board (PCB) industry, where the elimination of acid in gold plating formulation could potentially lead to more reliable coatings. Consequently, these results are both significant and timely. IntroductionGold plating processes are widely used in the materials finishing, decorative and electronics industries due to their high reliability, electrical conductivity and corrosion resistance. 1 The key characteristic feature of these noble metal coatings is the lack of insulating surface oxides. 2 Electrolytic, 3 electroless, 4 and immersion plating 5 are the three common electrochemical methods used for the coating of conducting substrates with gold films. In each of these processes the conventional/commercial plating bath chemistry is dominated by the choice of the dicyanidoaurate anion [Au(CN) 2 ] − as the gold source 6 due to its high stability 7 and the ability to yield fine grained deposits. 8 In electroplating experiments, acidic plating baths around pH 5 are used to produce soft gold coatings, whilst alkaline and neutral baths are used to produce hard gold. 8 However, there are significant safety concerns, as well as issues regarding the disposal of waste, where cyanide based processes are present. In addition, the requirement of large negative reduction potentials can also lead to the coreduction of hydrogen ions. 9 As such, there have been cyanide free gold plating solutions developed, primarily based upon sulphite and thiosulfate complexes, however these are limited to...

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confidence: 99%

Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Ballantyne

Forrest

Frisch

et al. 2015

Phys. Chem. Chem. Phys.

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“…Before the studies, however, we examined the UBMs without soldering in order to preclude the involvement of pre-existing defects, such as nodular cracks or spike penetration, that could cause black pad failure of the solder joint. [26][27][28] Figure 7a shows the Ni-P pad surface after removing the thin Au layer by cyanide etching. The surface has a smooth nodule structure with a diameter of about 2.1 lm.…”

Section: Growth Of Imcs After Reflow Soldering and Agingmentioning

confidence: 99%

Inhomogeneous Consumption of the Electroless Ni-P Layer at the Solder Joint Formed with Sn-3.5Ag-0.7Cu

2009

Journal of Elec Materi

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This report investigates the phenomenon of interfacial serration at the joint between Sn-3.5Ag-0.7Cu solder (SAC) and electroless Ni-P underbump metallization (UBM) during aging. For comparison, the interface between SAC and electrolytic Ni UBM was also examined under similar aging conditions. The joint in the electrolytic Ni/SAC sample showed a smooth, flat interface between the Ni and intermetallic compounds, even after a long aging time. In contrast, electroless Ni-P/SAC exhibited an irregular interface, the irregularity of which became more severe with increased aging time. This observed roughness was initiated by large breaks across the P-rich layer. The breaks were filled with the overlying Ni-Sn-P phase material, which provided an easier interdiffusion path for Ni and Sn in the opposite direction. As a result, the local consumption of the Ni(-P) layer was accelerated, and the interface was serrated. The local maximum consumption rate of the Ni-P layer, as calculated from the minimum thickness of this layer in each sample with aging time, was similar to that of an electrolytic Ni layer.

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“…In most cases unsoldered substrates from the same batch as the failures are not available for failure analysis, making it difficult to determine the correct root cause. One noted exception has been reported recently by Zeng et al 4 The failure rate due to embrittled ENIG solder joints is typically low when averaged over long time intervals, but brittle failure is unpredictable and can periodically affect a large quantity of devices in a short period of time. ''Black pad'' failure is typically sporadic in that very few substrate lots of devices fail.…”

Section: Introductionmentioning

confidence: 97%

“…[1][2][3][4][5] In addition to having desirable solder wetting characteristics, ENIG provides a low-cost and longshelf-life surface finish that is easily adopted for use on fine-pitch BGA substrates without complicating the design layout. 6 Unfortunately, although ENIG solder joints are generally robust, brittle solder joint fractures are sometimes found in assembly and testing.…”

Section: Introductionmentioning

confidence: 99%

ENIG Corrosion Induced by Second-Phase Precipitation

Osenbach¹,

Amin

Baiocchi³

et al. 2009

Journal of Elec Materi

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Materials analysis of a flip-chip package lot with solder bump interconnect failures revealed a new mechanism for corrosion of electroless nickel immersion gold surface finish. Detailed scanning and transmission electron microscopy (SEM and TEM) in conjunction with focused ion beam microscopy and electron dispersion analysis of the unsoldered ball grid array substrate pads on packages that exhibited flip-chip solder bump interconnect failures revealed an unusual and subtle defect in the original Ni(P) layer, which was ultimately responsible for flip-chip joint failure. Detailed TEM analysis of the defect regions showed that they consisted of Ni(P) particles of slightly different composition than the bulk Ni(P) layer. Microstructure changes around these incorporated particles indicated that the second-phase particles were deposited from the plating bath during the Ni(P) growth stage. The second-phase particles provided additional surface area for nucleation and growth of Ni(P). Ultimately, a low-density boundary region in the growing Ni(P) layer formed where the particle-induced growth front and the planar Ni(P) film growth front intersected. This low-density interface eventually terminated at the surface of the Ni(P) layer. In addition the growth from the second-phase particle created localized surface topology that was different than that of the surrounding Ni(P) layer. The low-density interfaces as well as the surface topology led to enhanced corrosion of the Ni(P) layer when exposed to the immersion gold plating process. In some cases the corrosion was severe enough to create voids in the Ni(P) layer. The exposed, oxidized Ni(P) surfaces in and around these enhanced corrosion regions did not wet when exposed to solder. This led to degradation in the strength of the solder joint and subsequent solder interconnect failure.

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The root cause of black pad failure of solder joints with electroless Ni/Immersion gold plating

Cited by 82 publications

References 22 publications

Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Inhomogeneous Consumption of the Electroless Ni-P Layer at the Solder Joint Formed with Sn-3.5Ag-0.7Cu

ENIG Corrosion Induced by Second-Phase Precipitation

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The root cause of black pad failure of solder joints with electroless Ni/Immersion gold plating

Cited by 82 publications

References 22 publications

Electrochemistry and speciation of Au+in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Electrochemistry and speciation of Au+in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Inhomogeneous Consumption of the Electroless Ni-P Layer at the Solder Joint Formed with Sn-3.5Ag-0.7Cu

ENIG Corrosion Induced by Second-Phase Precipitation

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Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings

Electrochemistry and speciation of Au⁺in a deep eutectic solvent: growth and morphology of galvanic immersion coatings