Large-Area Chip Attachment by Sintering Nanosilver Paste: Process Improvement by Nondestructive Characterization

Xiao, Kai; Calata, J.N.; Ngo, Khai D. T.; Ibitayo, Dimeji; Lü, Gongxuan

doi:10.5104/jiepeng.4.101

Cited by 9 publications

(7 citation statements)

References 9 publications

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“…Although the use of this X-ray CT has been prevalent within other scientific fields for a number of decades, its emergence within power electronics packaging reliability studies is relatively recent (Xiao et al, 2011;Padilla et al, 2012;Agyakwa et al, 2014;Li et al, 2014;Agyakwa et al, 2016;Feng et al, 2016;Regalado et al, 2019). There are a number of reasons for this.…”

Section: Figmentioning

confidence: 99%

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Agyakwa

Dai

et al. 2019

Journal of Microscopy

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Summary A time‐lapse study of thermomechanical fatigue damage has been undertaken using three‐dimensional X‐ray computer tomography. Morphologies were extracted from tomography data and integrated with data from microscopy modalities at different resolution levels. This enables contextualization of some of the fine‐scale properties which underpin the large‐scale damage observed via tomography. Lateral views of crack development are presented, which show networks analogous to mud‐cracks. Crack fronts which develop in the most porous regions within the sintered attachment layer travel across the boundary into the copper substrate. The propagation characteristics of these cracks within the substrate are analysed. Evidence is provided of heterogeneous densification within the sintered joint under power cycling, and this is shown to play a major role in driving the initiation and propagation of the cracks. Examination of the texture (differing levels of X‐ray absorption) of virtual cross‐sectional images reveals the origins of the nonuniformity of densification. Finally, cracks within the sintered joint are shown to have a negligible impact on the conduction pathway of the joint due to their aspect ratio and orientation with respect to the assembly. Lay Description This paper concerns the use of three‐dimensional (3D) X‐ray tomography, a nondestructive technique, to perform cradle‐to‐grave studies of sintered nanosilver die‐attachments under operation. Sintered nanosilver die‐attachments have been proposed as a more reliable and environmentally friendly alternative to solder alloy joints for emerging power electronics module designs. However, their degradation mechanisms are not as well understood. This same sample‐study is about observing how the fine‐scale structure of a sintered attachment evolves and degrades over time. Using 3D tomography affords otherwise infeasible perspectives, such as virtual cross‐sections in the lateral plane of the attachment. These perspectives provide qualitative information which elucidates the degradation mechanisms. They demonstrate, for example, that the structure of the sintered attachment densifies under operation, and a consequence of this is the formation of shrinkage cracks in the most porous regions, much like mud‐cracks. Other imaging techniques (metallographic etching and scanning electron microscopy) have been used in correlation with 3D renderings of these cracks to analyse their propagation and reveal their relationship both with the internal structure of the sintered attachment itself, and the structure of the substrate to which it is joined. It is shown that the cracks develop within the sintered attachment layer and eventually cross over into the substrate. A comparison of two sintered attachments with contrasting bulk porosities allows the effect of initial bond quality on crack development to be examined.

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Section: Figmentioning

confidence: 99%

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Agyakwa

Dai

et al. 2019

Journal of Microscopy

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“…The experimental results of external pressure effect on bonding quality have already been reported in our previous study, indicating that external pressure helps to eliminate the defects in the joint layers in chip attachments, 26 The analysis also indicates that the internal stresses of the nanosilver paste between the chip and the substrate decrease with increasing external applied pressure during drying. At any given location, a lower vertical internal stress implies a lower possibility of debonding in the paste, and a lower x-y in-plane internal stress implies a lower possibility of crack formation in the paste, both leading to higher bonding quality.…”

Section: Effect Of External Pressure During Chip Attachment Dryingmentioning

confidence: 52%

A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line

2014

Self Cite

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The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer-or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C11 programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.

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“…Using LTJT, different materials can be joined. It is possible to directly join Cu base substrate with Si element; however, surfaces of such material usually are metallized with noble metals through different ways (Kisiel et al , 2012; Xiao et al , 2011). If, for example, a Cu substrate coated with a Ni sublayer and a Au final layer is joined with Si element metallized with Ag, and Au and Ag should be treated as joined surfaces.…”

Section: Joined Elementsmentioning

confidence: 99%

Technological aspects of silver particle sintering for electronic packaging

Felba

2018

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Purpose This paper aims to find proper technological parameters of low-temperature joining technique by silver sintering to eventually use this technique for reliable electronic packaging. Design/methodology/approach Based on the literature and author’s own experience, the factors influencing the nanosized Ag particle sintering results were identified, and their significance was assessed. Findings It has been shown that some important technological parameters clearly influence the quality of the joints, and their choice is unambiguous, but the meaning of some parameters is dependent on other factors (interactions), and they should be selected experimentally. Originality/value The value of this research is that the importance of all technological factors was analyzed, which makes it easy to choose the technological procedures in the electronic packaging.

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Large-Area Chip Attachment by Sintering Nanosilver Paste: Process Improvement by Nondestructive Characterization

Cited by 9 publications

References 9 publications

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

Three‐dimensional damage morphologies of thermomechanically deformed sintered nanosilver die attachments for power electronics modules

A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line

Technological aspects of silver particle sintering for electronic packaging

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