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![Solder Joint Void Classifications [4]](profile/Ross-Wilcoxon/publication/303120904/figure/fig1/AS:407100921532416@1474071831528/Solder-Joint-Void-Classifications-4.png)
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![Figure 1. Solder Joint Void Classifications [4]](profile/Ross-Wilcoxon/publication/303120904/figure/fig1/AS:407100921532416@1474071831528/Solder-Joint-Void-Classifications-4_Q320.jpg)
![Figure 2. Failure Data Weibull Plot from Banks [5]](profile/Ross-Wilcoxon/publication/303120904/figure/fig2/AS:407100921532417@1474071831602/Failure-Data-Weibull-Plot-from-Banks-5_Q320.jpg)
The impact of voiding on the solder joint integrity of ball grid arrays (BGAs)/chip scale packages (CSPs) can be a topic of lengthy and energetic discussion. Detailed industry investigations have shown that voids have little effect on solder joint integrity unless they fall into specific location/geometry configurations. These investigations have f...
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The impact of voids on the mechanical behaviour of a BGA solder joint can be evaluated by simulation. The Finite Element (FE) method is adapted to achieve such a task where an infinite number of different void distributions is possible. A tool is proposed in this paper with a modelling process involving a global calculation of a thermal load and a refined sub model. The global model represents a quarter of an electronic package soldered to a piece of PCB while the submodel is limited to a single ball with copper pads and defects under investigation i.e. intermetallic compounds (IMC) and voids. Creep properties are taken into account to model mechanical response of the lead-free solder SAC 305. The simulation of a thermal cycle is performed on the global model with only elastic properties. The nodal displacements are extracted from the results to be applied to the submodel's mesh. True viscoplastic mechanical behaviour is simulated in this refined model to get the solder material response with respect to different defects' considerations. The void distribution is handled with 4 parameters driving the height and thickness of the layer of distribution, the size and the proximity of voids. Simulating the effects of these parameters can afford to sort them for future reliability assessments via Finite Element methods.
With the introduction of lead-free solder alloys, the effect of voids on solder joint reliability has rapidly gainedimportance. In this study, a first analysis of X-rayed CR0805 solder joints shows a significant reduction in void content, from 20% down to 2.5%, after vacuum soldering. The statistical analysis of the void distribution demonstrates that the vacuum option reduces number of voids and median diameter of voids in comparison to the convection soldering process. A subsequent accelerated thermal cycling test of these analysed test vehicles, according to JESD22-A104D, indicates the tendency of a higher characteristic life time for higher void content. In contrast to these findings, the 1% to failure criterion reveals a higher reliability for lower voiding. During the finite element method (FEM) modelling part of this study, two modelling approaches of void implementation into solder joint geometry are investigated: modelling with a constant volume of the standoff for different void contents, and a modelling approach with a random combination of void content and volume of standoff. The modelling approach with the random combination reveals that voids can reduce the lifetime in the “worst case” parameter combination. In particular, the 1% time to failure rate indicates a quantitative correlation with the experimental results. Furthermore, the FEM results suggest a higher impact on reliability for a single void in comparison to a distribution of multiple voids with similar void content. Finally, the FEM study shows a high sensitivity of predicted life time with respect to the standoff height. Based on this finding, the CR0805 solder joint geometry is examined using optical inspection and cross-section polishes with the outcome that the better wetting behaviour during vacuum soldering causes a reduction of the solder alloy volume and consequently further decreases the standoff height.
Since the introduction of lead-free solder alloys, the impact of voids in solder joints has rapidly gained in importance. Particularly in power electronics, voids in solder joints can reduce their reliability due to less heat dissipation and a significant reduction of the cross-sectional area. While void formation in the printed circuit board (PCB) technology has been the focus of many research projects, the increasing application of molded interconnect devices (MIDs) demands a vivid understanding of void formation and its impact on reliability. This report will show that those processes specific to MID technology do not significantly influence the void formation in SAC305 solder deposits. The processed different roughness levels on Vectra, Vestamid, and FR4 substrate materials show no significant impact on void formation. The surface finish metallization was detected as the most important factor. Especially, the chemical-Sn (iSn) surface finish is inclined to having more voids compared to a nickel–phosphor–gold (NiP-Au) finish. Furthermore, three solder processes were investigated: convection, condensation, and vacuum-condensation soldering. The vacuum-condensation processes significantly reduced the voids in the Sn–3.0Ag–0.5Cu (simplified as SAC305) solder joints of CR0805, MLF20, and switches on all the investigated substrates. An accelerated thermal cycling test of these components according to JESD22-A104D demonstrates no significant effect of the void content of <19% on the solder joints’ reliability. Finally, the result of accelerated thermal cycling shows the possibility to achieve an equivalent lifetime of the solder joints on Vectra in comparison to the FR4 substrate.
This article is focused on both macro and microvoids in soldered joints and the use of additional flux to reduce their frequency and minimize their negative effect on the soldered joint reliability. In total five fluxes were used, three were gel based (NC559, MTV-125R, TSF-6516) and two of them were liquid based (Topnik G-5, JBC FL-15). They were used within two solder pastes, both lead and lead-free. The reflow process was identical for all of the combinations and was within the range of manufacturer recommended profiles. The amount of voids was evaluated using X-ray analysis. It was found that the use of increased amount of proper flux, specifically flux with higher activity, in the solder paste may significantly lower the void occurrence.
