Effect of Electromigration and Thermal Ageing on the Tin Whiskers’ Formation in Thin Sn–0.7Cu–0.05Ga Lead (Pb)-Free Solder Joints

Mokhtar, Noor Zaimah Mohd; Salleh, Mohd Arif Anuar Mohd; Sandu, Andrei Victor; Ramli, Muhammad Mahyiddin; Chaiprapa, Jitrin; Vizureanu, Petrică; Ramli, Mohd Izrul Izwan

doi:10.3390/coatings11080935

Cited by 9 publications

(4 citation statements)

References 36 publications

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“…Thus, EM has become a more and more important indicator of joints reliability, which will determine the lifetime of the service time of electronic products (Song et al, 2020;Wang et al, 2020;Yue et al, 2021). In addition, copper pillar bump needs to be joined to pad by Sn96.5Ag3.5 solder in industry, and intermetallic compound (IMC) is formed through the interfacial reaction between solder and surface-finishing pad material during joining process (Mokhtar et al, 2021) , (Xu et al, 2022). This IMC layer can affect the mechanical and electrical reliability of joints under the influence of EM.…”

Section: Introductionmentioning

confidence: 99%

Interfacial intermetallic compound modification to extend the electromigration lifetime of copper pillar joints

Yang¹,

Huang²

2023

Front. Mater.

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Electromigration is the massive metal atom transport due to electron flow, which could induce a disconnect in electronics. Due to the size of copper pillar bump reduction, the portion of interfacial intermetallic compound in solder joints is increasing obviously. However, there is lack of systematical research on the effects of intermetallic compound on the EM lifetime of solder joints. In this paper, the interfacial intermetallic compound of copper pillar joints is modified to extend the electromigration lifetime. The growth rate of intermetallic compound in solder joints sample is calculated firstly. From 230°C to 250°C, the growth rate of intermetallic compound increases from 0.09 μm/min to 0.19 μm/min. With a longer reaction time, the intermetallic compound layers continuously grow. Then electromigration tests were conducted under thermo-electric coupling loading of 100°C and 1.0 × 104 A/cm2. Compared with lifetime of thin and thick intermetallic compound samples, the lifetime of all intermetallic compound sample improved significantly. The lifetime of thin, thick, and all intermetallic compound samples is 400 min, 300 min, and 1,200 min, respectively. The failure mechanism for the thin intermetallic compound sample is massive voids generation and aggregation at the interface between solder joints and pads. For the thick intermetallic compound sample, the intermetallic compound distance is short between cathode and anode in solder joints, leading to lots of crack create in the middle of solder joints. As the all intermetallic compound sample can greatly reduce the number of voids generated by crystal structure transforming, the lifetime extend obviously.

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Section: Introductionmentioning

confidence: 99%

Interfacial intermetallic compound modification to extend the electromigration lifetime of copper pillar joints

Yang¹,

Huang²

2023

Front. Mater.

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“…In order to meet the requirements of die-attach technologies and the Restriction of Hazardous Substances (RoHS) directive, a series of die-attach materials, such as Sn-Ag, Sn-Ag-Cu (i.e., SAC) solder alloys and sintering silver paste were developed [7][8][9]. Among them, the SAC solder has become a type of widely used lead-free solder in the electronics industry by the virtue of its adequate thermal fatigue properties, strength, and wettability [10].…”

Section: Introductionmentioning

confidence: 99%

Study of Thermal Stress Fluctuations at the Die-Attach Solder Interface Using the Finite Element Method

et al. 2021

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Solder joints in electronic packages are frequently exposed to thermal cycling in both real-life applications and accelerated thermal cycling tests. Cyclic temperature leads the solder joints to be subjected to cyclic mechanical loading and often accelerates the cracking failure of the solder joints. The cause of stress generated in thermal cycling is usually attributed to the coefficients of thermal expansion (CTE) mismatch of the assembly materials. In a die-attach structure consisting of multiple layers of materials, the effect of their CTE mismatch on the thermal stress at a critical location can be very complex. In this study, we investigated the influence of different materials in a die-attach structure on the stress at the chip–solder interface with the finite element method. The die-attach structure included a SiC chip, a SAC solder layer and a DBC substrate. Three models covering different modeling scopes (i.e., model I, chip–solder layer; model II, chip–solder layer and copper layer; and model III, chip–solder layer and DBC substrate) were developed. The 25–150 °C cyclic temperature loading was applied to the die-attach structure, and the change of stress at the chip–solder interface was calculated. The results of model I showed that the chip–solder CTE mismatch, as the only stress source, led to a periodic and monotonic stress change in the temperature cycling. Compared to the stress curve of model I, an extra stress recovery peak appeared in both model II and model III during the ramp-up of temperature. It was demonstrated that the CTE mismatch between the solder and copper layer (or DBC substrate) not only affected the maximum stress at the chip–solder interface, but also caused the stress recovery peak. Thus, the combined effect of assembly materials in the die-attach structure should be considered when exploring the joint thermal stresses.

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“…The urge to use lead (Pb) or lead-based alloy-free materials in electronic packaging has become a serious problem among manufacturers since the European Union RoHS (Restriction of Hazardous Substances) regulated the minimum content of lead in products starting from 1 July 2006 [1][2][3]. Therefore, countless research has been devoted in the past two decades to replace lead in solder and surface finish materials for electronic packaging.…”

Section: Introductionmentioning

confidence: 99%

Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish

et al. 2021

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Since the use of the most stable Pb-based materials in the electronic industry has been banned due to human health concerns, numerous research studies have focused on Pb-free materials such as pure tin and its alloys for electronic applications. Pure tin, however, suffers from tin whiskers’ formation, which tends to endanger the efficiency of electronic circuits, and even worse, may cause short circuits to the electronic components. This research aims to investigate the effects of stress on tin whiskers’ formation and growth and the mitigation method for the immersion of the tin surface’s finish deposited on a copper substrate. The coated surface was subjected to external stress by micro-hardness indenters with a 2N load in order to simulate external stress applied to the coating layer, prior to storage in the humidity chamber with environmental conditions of 30 °C/60% RH up to 52 weeks. A nickel underlayer was deposited between the tin surface finish and copper substrate to mitigate the formation and growth of tin whiskers. FESEM was used to observe the whiskers and EDX was used for measuring the chemical composition of the surface finish, tin whiskers, and oxides formed after a certain period of storage. An image analyzer was used to measure the whiskers’ length using the JEDEC Standard (JESD22-A121A). The results showed that the tin whiskers increased directly proportional to the storage time, and they formed and grew longer on the thicker tin coating (2.3 μm) than the thin coating (1.5 μm). This is due to greater internal stress being generated by the thicker intermetallic compounds identified as the Cu5Sn6 phase, formed on a thicker tin coating. In addition, the formation and growth of CuO flowers on the 1.5 μm-thick tin coating suppressed the growth of tin whiskers. However, the addition of external stress by an indentation on the tin coating surface showed that the tin whiskers’ growth discontinued after week 4 in the indented area. Instead, the whiskers that formed were greater and longer at a distance farther from the indented area due to Sn atom migration from a high stress concentration to a lower stress concentration. Nonetheless, the length of the whisker for the indented surface was shorter than the non-indented surface because the whiskers’ growth was suppressed by the formation of CuO flowers. On the other hand, a nickel underlayer successfully mitigated the formation of tin whiskers upon the immersion of a tin surface finish.

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Effect of Electromigration and Thermal Ageing on the Tin Whiskers’ Formation in Thin Sn–0.7Cu–0.05Ga Lead (Pb)-Free Solder Joints

Cited by 9 publications

References 36 publications

Interfacial intermetallic compound modification to extend the electromigration lifetime of copper pillar joints

Interfacial intermetallic compound modification to extend the electromigration lifetime of copper pillar joints

Study of Thermal Stress Fluctuations at the Die-Attach Solder Interface Using the Finite Element Method

Tin Whiskers’ Behavior under Stress Load and the Mitigation Method for Immersion Tin Surface Finish

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