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This study investigates the power cycling reliability of nanosilver sintered joints formed by a time-reduced sintering process, designed for use on a die bonder. A range of sintering parameters, reflecting different levels of manufacturability, were used to produce sintered joints in respect of shear strength and porosity, within a process cycle time of a few seconds. The reliability of the sintered attachments were evaluated against Pb5Sn solder joints under constant temperature swing power cycling conditions over the range 50 to 200 °C. The thermal performance and microstructural changes of the sintered joints were monitored and evaluated non-destructively at regular intervals using transient thermal impedance and X-ray computed tomography. The results show that sintered joints with higher shear strengths (>50 MPa) and lower porosities (<25 %) tend to maintain their thermal performance up to ~100k power cycles before gradual degradation occurs. Sintered joints with intermediate shear strengths (20 to 40 MPa) and with corresponding analogous porosities (35 to 51 %) also demonstrated comparable power cycling behavior; exhibiting a progressive decrease in effective thermal conductivity with increasing cycles. The evaluated lifetime of sintered joints with the highest shear strengths were found to be at least double those for the lower shear strength joints, and up to fourteen times those of a Pb5Sn solder die attachment. Even the most porous sintered joints exhibited lifetimes appreciably longer than a Pb5Sn die attachment. Degradation in thermal resistance was seen to correlate with observed microstructural changes, with a dependence on initial sintering parameters. [ABSTRACT FROM AUTHOR]

13.5 mm ${\times }\,\,$ 13.5 mm sintered nano-silver attachments for power devices onto AlN substrates were prepared at 250 °C and a pressure of 10 MPa for 5 min and compared with Pb5Sn solder joint die attachments under constant current power cycling with an initial temperature swing of 50 °C–175 °C. Both effective thermal resistance and microstructural evolution of the samples were monitored using transient thermal impedance measurement and nondestructive X-ray computed tomography at regular power cycling intervals. The results showed a gradual increase in the effective thermal resistance of the Pb5Sn solder joints from 0.047 to 0.133 K/W from zero to 41k power cycles, followed by a rapid escalation to 0.5018 K/W at 52k cycles. This was accompanied with the formation and development of oblique cracks within the Pb5Sn die attachments until delamination occurred at the solder/device and solder/substrate interfaces. By contrast, the effective thermal resistance of the sintered Ag joints remained almost constant at 0.040 K/W up to 116k power cycles. This was explained in terms of thermally induced continuation of densification of the sintered structure and the formation and development of networked vertical cracks within the sintered Ag die attachments, some of which further extended into the Cu tracks of the AlN substrate. [ABSTRACT FROM AUTHOR]

Pressure-assisted sintering processes to attach power devices using wet nanosilver pastes with time scales of minutes to a few hours have been widely reported. This article presents our work on time-efficient sintering using nanosilver dry film and an automatic die pick and place machine, resulting in process times of just a few seconds. The combined parameters of sintering temperature 250°C, sintering pressure 10 MPa and sintering time 5 s were selected as the benchmark process to attach 2 x 2 x 0.5-mm dummy Si devices. Then, the effects of either the sintering temperature (240-300°C), time (1-9 s), or pressure (6-25 MPa) on the porosity and shear strength of the sintered joints were investigated with three groups and a total of 13 experimental trials. The average porosities of 24.6-46.2% and shear strengths of 26.1-46.6 MPa are comparable with and/or even better than those reported for sintered joints using wet nanosilver pastes. Their dependences on the sintering temperature, time and pressure are further fitted to equations similar to those describing the kinetics of sintering processes of powder compacts. The equations obtained can be used to not only reveal different mechanisms dominating the densification and bonding strength but also anticipate the thermal-induced evolutions of microstructures of these rapidly sintered joints during future reliability tests and or in service. [ABSTRACT FROM AUTHOR]

Routine monitoring of the wire bonding process requires real-time evaluation and control of wire bond quality. In this paper, we present a nondestructive technique for detecting bond quality by the application of a semisupervised classification algorithm to process the signals obtained from an ultrasonic generator. Experimental tests verified that the classification method is capable of accurately predicting bond quality, indicated by bonded area measured by X-ray tomography. Samples classified during bonding were subjected to temperature cycling between −55 °C and +125 °C, and the distribution of bond life amongst the different classes was analyzed. It is demonstrated that the as-bonded quality classification is closely correlated with thermal cycling life and can, therefore, be used as a nondestructive tool for monitoring bond quality and predicting useful service life. [ABSTRACT FROM AUTHOR]

The samples of sintered Ag joints for power die attachments were prepared using paste of Ag nanoparticles at 240°C and 5 MPa for 3 to 17 minutes. Their microstructural features were quantitatively characterized with scanning electronic microscopy, transmission electron microscopy, X-ray diffraction and image analysis method. The resulting normalized thickness, pore size and porosity decreased, and grain size increased with increasing the sintering time. A time dependence of the formt1/nwithnclose to 2 or 3 can be further derived for the kinetics of the thinning, densification and grain growth within the sintered Ag joints. [ABSTRACT FROM PUBLISHER]

This paper presents a review of the commonly adopted physics-of-failure-based life prediction models for wire bond interconnects in power electronic modules. In the discussed models, lifetime is generally accounted for by loading temperature extremes alone. The influence of the time spent at temperature on bond wear-out behavior and damage removal phenomena resulting from thermally activated processes is not addressed. The phenomenological considerations based on some unusual observations highlight the need for new approaches to wire bond life prediction models and thus motivate the proposal of a new time-domain damage-based crack propagation model. [ABSTRACT FROM PUBLISHER]