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Optimization of the process parameters remains a challenging task in thermosonic wire bonding due to relatively poor understanding of the bonding mechanism. The purpose of…
Optimization of the process parameters remains a challenging task in thermosonic wire bonding due to relatively poor understanding of the bonding mechanism. The purpose of this paper is to understand initial bond formation in thermosonic gold wire bonding on aluminium metallization pads and the effect of bonding time on the initiation of bonding.
A gold wire (20 μm diameter/99.99 per cent wt%) was bonded to aluminium metallization pads (1 μm thick) on a silicon chip using a commercial ball/wedge automatic bonder. Bonding parameters were selected specifically to produce underdeveloped ball bonds so that ball lift‐off occurred during looping process. The lift‐off footprints on the aluminium metallization pads and their evolution were carried out using optical microscopy and scanning electron microscopy. A model is proposed to elaborate the effect of bonding time on initiation of bonding.
The obtained results showed that metallurgical bonding initiated at the peripheral areas of the contact area situated along the direction of ultrasonic vibration. Those areas extended inwards with bonding time, eventually covering the entire contact area.
This paper describes how bond initiation and its evolution in thermosonic gold wire bonding on aluminium metallization is ascertained by observing lift‐off footprints. The understanding of bonding mechanism benefits the optimization of process parameters and improvement of bondability in thermosonic wire bonding.
This paper explores breakthroughs or ‘lift‐off’ moments in learning involving several teacher/researchers and their students in China. The data come from teaching and research situations centring on teaching and learning English as a foreign language (EFL). An analysis of the language features of the data and their effects explores learning by tracing movement from initial impasses to breakthrough moments, as participants interact, shift ground and discover new learning. Definition of these lift‐off moments and ways of knowing centres in a sense of discovery that pushes learning forward and simultaneously pulls together life experiences in new directions for specific pedagogical insights, self‐assessment and identity conclusions, and recognition of the power of inquiry. In particular, the paper explores the potential contribution of narrative forms of collaborative inquiry in learning, as evident in two contrasting exemplars, the first coconstructed in face‐to‐face interviews or conversational settings, and the second, thesis supervision by the distance learning one‐to‐one format of emailing. These documented interchanges between two Chinese postgraduate EFL teachers and their research coursework teacher and supervisor come from a wide data bank of exemplars collected over many years, and from linguistically diverse contexts.
A study was undertaken to correlate macroscopic profile variations in the photoresist duringlift‐off procedures with changes in material properties. It was established…
A study was undertaken to correlate macroscopic profile variations in the photoresist during lift‐off procedures with changes in material properties. It was established that soaking in chlorobenzene, which gave rise to negative slopes, was accompanied by hardening of the top layer of the photoresist and caused the surface to become hydrophobic. FTIR measurements did not yield new information about variations in chemical bonding.
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models…
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models with the same geometries and cross-section areas of film holes’ exits at three typical blowing ratios (M = 0.5, 1 and 1.5). The two models are an elliptical model and a cylindrical model with 90° compound angle, respectively.
Three different cases are considered in this work and the baseline is the model with a cylindrical film hole. The same boundary conditions and a validated turbulence model (realizable k-ε) are adopted for all cases.
The results show that both the elliptical and cylindrical models with 90° compound angle can enhance the film cooling effectiveness compared with the baseline. However, the elliptical model performs well at lower blowing ratios and in the near region at each blowing ratio because of the wider width of the film hole’s exit. The cylindrical model with 90° compound angle provides better film cooling effectiveness in the further downstream area of the film hole at higher blowing ratio because of the less lift-off and better coolant coverage in the larger x/D region along the mainstream direction.
Overall, it can be concluded that although the elliptical and cylindrical models with 90° compound angle have identical hole exits, the different inlet direction and cross-sectional geometry affect the flow structures when the coolant enters, moves through and exits the hole and finally different film cooling results appear.
UNITED STATES: December rates 'lift-off' gets closer
Although wire‐bonding is an established and well‐known technique for micro‐joining on leadframes, direct die‐attach without housing on printed circuit boards has some new…
Although wire‐bonding is an established and well‐known technique for micro‐joining on leadframes, direct die‐attach without housing on printed circuit boards has some new requirements for the surface of the bond pads and the PCB itself. The best choice of material for the bond pads is a pure gold metallisation. The quality of the surface can be tested during wire‐bonding using the ultrasonic‐power process window. It will be shown that the surface and the PCB itself have a considerable influence on the ultrasonic and thermosonic bonding process.
UNITED STATES: Lift-off decision to be data-dependent