Intermetallic growth kinetics in gold ball bonds on Al-1%Si-0.5%Cu bond pads at 175∘C

Purpose The purpose of this study is to demonstrate that isothermal intermetallic growth data for gold ball bonds can be non-parabolic with explanations of why deviation from parabolic kinetics may occur. Design/methodology/approach Intermetallic thickness measurements were made at the centre of cross-sectioned ball bonds that were isothermally annealed at 175°C. Intermetallic growth kinetics were modelled with a power law expression(x(t) − x0)2 = α1tα2. The parameters of the power law model were obtained by transformation of the response and explanatory variables followed by data fitting using simple linear regression (SLR). Findings Ball bonds made with 4 N (99.99%Au) and 3 N (99.9%Au) gold wires exhibited two consecutive time regimes of intermetallic growth denoted Regime I and Regime II. Regime I was characterised by reactive diffusion between the gold wire and the aluminium alloy bond pad, during which Al was completely consumed in the formation of Au–Al intermetallics with non-parabolic kinetics. In Regime II, the absence of a free supply of Al to sustain intermetallic growth led to the conclusion that thickening of intermetallics was caused by phase transformation of Au8Al3 to Au4Al. Ball bonds made with 2 N (99%Au) wire also exhibited non-parabolic kinetics in Regime I and negligible intermetallic thickening in Regime II. Research limitations/implications The analysis of intermetallic growth is limited to total intermetallic growth at a single temperature (175°C). Originality/value The value of this study lies in showing that the assumption that only parabolic intermetallic growth is observed in isothermally aged gold ball bonds is incorrect. Furthermore there is no need to assume parabolic growth kinetics because with an appropriate data transformation, followed by fitting the data to a power law model using SLR and with the use of statistical diagnostics, both the suitability of the kinetic model and the nature of the growth kinetics (parabolic or non-parabolic) can be determined.

Gold Jewelry with a Polychrome Inlay from a Princely Grave Dating to the Second Half of the 5th – 6th Centuries in the Zayukovo – 3 Cemetery (Republic of Kabardino – Balkaria)

В 2017 г. в могильнике Заюково 3 (Баксанский район Кабардино Балкарской Республики) была исследована катакомба 86. Катакомба была разграблена в древности, но среди сохранившегося инвентаря были обнаружены золотые предметы с полихромной инкрустацией. В их число входит гривна с замком в виде округлого медальона и декором из ложной зерни. На гривну были надеты две золотые калачевидные привески. В этом же комплексе были найдены две золотые полые шаровидные подвески, украшенные зернью и гранатовыми вставками. Данные статусные предметы, наряду с другими изделиями (фрагменты клинка железного меча с золотыми обкладками ножен, фрагменты седла и тисненой золотой поясной гарнитуры), указывают на то, что здесь мог быть похоронен представитель высшего ранга аланской аристократии. Данный факт позволяет предположить, что в Баксанском ущелье в V VII вв. находился центр власти варварского королевства , сопоставимый по уровню с такими памятниками, как Брут 1, Зарагиж, Лермонтовская Скала, и другими северокавказскими комплексами княжеского уровня. In 2017 catacomb No. 86 was excavated in the cemetery known as Zayukovo 3 (Baksan district, Republic of KabardinoBalkaria). The catacomb was looted in ancient times however, gold items with a polychrome inlay were discovered among remaining funerary offerings. Among them there was a torque with a lock shaped as a round medallion and decorated with false granulation. Two gold Ushaped hanging pendants were attached to the torque. The same association contained two gold ball shaped hollow pendants decorated with granulation and garnet insets. These prestigious artifacts along with other items (fragments of an iron sword blade with scabbard plates, fragments of a saddle and an embossed gold belt set) suggest that a high ranking representative of Alan aristocracy was probably buried here. It means that in the 5th 7th centuries the center of power of a barbarian kingdom which, in terms of its importance, may be compared with such sites as Brut 1, Zaragizh, Lermontovskaya Skala and other North Caucasus princely sites, was most likely located in the Baksan Gorge.

Bondability and Strength Evaluation of Gold Ball Bond Using Nanoindentation Approach

The evaluation of the strength and bondability of gold, Au ball bond requires a new approach to provide a more detail data. Nanoindentation test was used as a new approach to evaluate the strength distribution and bondability of Au ball. Au ball bonds that experienced different value of wire bonding parameter namely bonding force, bonding time, bonding power, and stage temperature were used as samples for the present analysis. The distribution of strength based on hardness and reduced modulus values located at the bonding area of Au ball bonds were found to be related with the values of the wire bonding parameter. Nanoindentation test was found to be a suitable approach to analyze and evaluate the bondability of Au ball bond in a localized and detailed manner. In addition, the responsible mechanism for the thermosonic Au wire bonding can be identified and analyzed by using the results obtained from the nanoindentation test.

Nanoindentation Study on Heat Treated Gold Wire Bonding

The effect of high temperature storage of gold ball bonds towards micromechanical properties has been investigated. Gold wire from thermosonic wire bonding exposed to high temperature storage at 150 °C for 10, 100 and 1000 hours. The nanoindentation test was used in order to evaluate the high temperature storage effect on wire bonding in more details and localized. Prior to nanoindentation test, the specimens were cross-sectioned diagonally. The constant load nanoindentation was performed at the center of gold ball bond to investigate the hardness and reduced modulus. The load-depth curve of nanoindentation for the high temperature storage gold wire has apparent the discontinuity during loading compared to as-received gold wire. The hardness value increased after subjected to high temperature storage. However, the hardness decreased when the storage period is extended. The decreasing in the hardness value may due to the grain size of Au metal which recrystallized after subjected to high temperature storage. The results obtained from nanoindentation is important in assessing the high temperature storage of wire bonding.

Gold Ball Wire Bonding Energy Transfer Mechanism and Experimental Studies

Because of the complexity of bonding process, the mechanism of bonding has been unable to agree. Accoding to previous research, a new bond energy transfer model is established: bond energy equals to energy caused by temperature rising and the friction energy.Then do experiment on bonding time, bonding stress and ultrasonic energy.Experimental results show that as the increase of process parameters, the bonding strength first increases then decrease, which consistent with the hypothesis.

Effect of Nanoindentation Loading Rate on Gold Ball Bond

Nanoindentation tests with loading rates of 0.05 mN/s, 0.1 mN/s, 0.5 mN/s, and 1.0 mN/s were conducted on the Au ball bond. The effect of different loading on the Au ball bond were analysed based on qualitative and quantitative results. The displacement burst was more pronounced with the increment of loading rates. The increase of hardness value and the decrease of the reduced modulus value when the loading rate was increased are due to the effect of creep. It was found that the loading rate of 0.5 mN/s is the appropriate and stable value for the nanoindentation test on the Au ball bond.