Failure mechanism of FBGA solder joints in memory module subjected to harmonic excitation

doi:10.1016/j.microrel.2011.11.015

Microelectronics Reliability

Volume 52, Issue 4, April 2012, Pages 735-743

https://doi.org/10.1016/j.microrel.2011.11.015 Get rights and content

Abstract

This paper investigates the failure mechanism of Fine-pitch Ball Grid Array (FBGA) solder joints of memory modules due to harmonic excitation by the experiments and the finite element method. A finite element model of the memory module was developed, and the natural frequencies and modes were calculated and verified by experimental modal testing. Modal damping ratios are also obtained and used in the forced vibration analysis. The experimental setup was developed to monitor resistance variation of FBGA solder joints due to the harmonic excitation under Joint Electron Devices Engineering Council (JEDEC) standard service conditions. Experiments showed that the failure of the solder joints of the memory module under vibration mainly occurs due to resonance. Forced vibration analysis was performed to determine the solder joints having high stress concentration under harmonic excitation. It showed that failure occurs due to the relative displacement between PCB and package and solder joints are the most vulnerable part of the memory module under vibration. It also showed that cracked solder joints in the experiments match those in the simulations with the highest stress concentration.

Introduction

Memory modules are composed of a number of packages or dynamic random access memory integrated circuits modules mounted on a printed circuit board (PCB), designed for use in personal computers, workstations, and servers. There are various types of memory modules, such as Single In-Line Memory Module (SIMM), Dual In-Line Memory Module (DIMM), and Small Outline Dual In-Line Memory Module (SO-DIMM). Packages are mounted on PCBs through solder balls called ball grid arrays (BGAs). Solder balls are further used to provide the electrical signals between package chips and the PCB. Memory modules are exposed to vibration over various frequency ranges [1], which may result in the malfunction of products. Reliability and performance of memory modules are standardized by the Joint Electron Devices Engineering Council (JEDEC). Performance and fatigue life time of the memory modules mostly depend on the solder joints. According to a report released by a semiconductor company, solder joint cracks reflected approximately 40% of total failure of memory modules. Therefore, it is important to understand the dynamic behavior of memory modules, as well as the behavior of solder joints subjected to vibration.

Many researchers have investigated the fatigue life reliability of packages or memory modules due to thermal load by experiment and simulation [2], [3], [4]. Once vibration was realized to be one of the dominant failures for electronic components, the electronic packaging industry began to show interest in understanding its failure mechanism under vibration. Basaran and Chandaroy [5] presented a study based on a viscoplastic model to compute damage mechanics of a solder joint with Pb40/Sn60 solder alloys under different dynamic load conditions. They showed that fatigue life of solder alloys is greatly affected by dynamic loads and the frequency ranges of applied loads. Kim et al. [6] investigated the high cycle vibration fatigue life characteristics of Pb-free and Pb packages under various mixed mode stresses by experiment and FEM. They observed the failure process of a solder ball at low frequency during the fatigue test by using an optical microscope. Wu [7] utilized the global–local modeling concept to calculate von Mises stress in solder joints of interest under random vibration loading. Then, she predicted the fatigue life of solder joints by using a damage model, called the Basquin power-law relation. Che and Pang [8] studied flip chip solder joints under out-of-plane sinusoidal vibration load with constant and varying amplitudes and they used Miner’s cumulative damage law to estimate fatigue life of flip chip solder joints. Zhou et al. [9], [10] investigated the vibration durability of Sn3.0Ag0.5Cu (SAC305) and Sn37Pb solder interconnects under narrow-band harmonic vibration and random vibration. They found that SAC305 interconnects have lower fatigue durability than Sn37Pb interconnects. However, prior researchers did not investigate failure mechanism of the solder joint in terms of resistance variation over high frequency ranges, as well as the most vulnerable solder joint of the memory module under vibration.

This paper investigates the failure mechanism of Fine-pitch Ball Grid Array (FBGA) solder joints in daisy chains assembled memory module with double-sided packages due to harmonic excitation by using the experiments and the finite element method. The experimental setup was developed to monitor resistance variation of FBGA solder joints due to the harmonic excitation of the JEDEC standard service condition 1 [11]. A finite element model of the memory module was developed, and the natural frequencies and modes were calculated and verified by experimental modal testing. Forced vibration analysis was performed to correlate the cracked solder joints in experiments with the solder joint of high stress concentration in simulation.

Section snippets

Analysis model

Fig. 1 shows a double-data-rate three synchronous dynamic random access memory (DDR3 SDRAM) type memory module used in this research. It is mainly composed of a PCB, packages and package register, and solder balls. The PCB is composed of 10 layers of copper conductor and FR-4, while the packages and package register are composed of many integrated circuits (ICs). This memory module has 36 packages and 1 package register. Table 1 shows the mechanical dimensions of PCB, package, and package

Free vibration analysis

A finite element model of the memory module was developed, as shown in Fig. 3. Table 2 shows the material type, properties, element type and number of each component. The PCB, packages, package register, and solder balls are modeled by the linear brick elements with eight nodes, and each node has three degrees of freedom. The total number of elements was 208,853. In the finite element model, packages, solder balls and PCB were connected by node sharing. DDR type memory modules are usually

Experiment to detect failure mechanism of memory module

Failure mechanism of the solder joints can be observed by monitoring the resistance increase of the memory module with daisy chain assembly, because failure of solder joints due to crack increase resistance. Except package register, every package on the memory module was assembled with daisy chains. The daisy chains of the packages in the front and back side of the memory module were connected in series. Total resistance of daisy chain of the memory module was measured to be around 35–40 Ω. A

Finite element forced vibration analysis

The dynamic response of a memory module subjected to harmonic excitation was investigated by using the finite element method and mode superposition. The damped global finite element equation of the memory module due to harmonic excitation is given by $[M] {\ddot{x} (t)} + [C] {\dot{x} (t)} + [K] {x (t)} = {P (t)}$ where [M], [C], [K] and {P(t)} are the mass, damping, stiffness matrices and excitation force vector, and ${\ddot{x} (t)}$ , ${\dot{x} (t)}$ and {x(t)} are the nodal acceleration, velocity and displacement vectors. In the large

Conclusion

This paper presents an investigation of failure mechanism of FBGA solder joints of memory modules due to harmonic excitation by using the experimental and finite element methods. The experimental setup was developed to monitor and to characterize the failure mechanism of FBGA solder joints due to the harmonic excitation of JEDEC standard service condition 1. Results showed that the crack of the solder joints of the memory module under vibration mainly occurs due to resonance. A finite element

Acknowledgments

This research has been supported by Samsung Electronics, and Y. Cinar thanks the Korean National Institute for International Education (NIIED) for a scholarship supporting his Ph.D work.

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The fatigue life prediction of solder joints under random vibration load is one of the most important aspect in design of packaging. A fatigue-life estimation in the frequency domain is proved to have advantages in comparison to the time-domain estimation. This paper presents a comparison of the fatigue life prediction of solder joints under random vibration load by several popular frequency domain methods, including the narrow-band, the Wirsching–Light, the single-moment, the Empirical α_0.75, the Tovo–Benasciutti, the Zhao–Baker, and the Dirlik methods. The comparison between these selected frequency domain methods and the traditional Steinberg method was investigated with the help of the relative error. Results indicate that most spectral methods are accurate than the Steinberg method, the Tovo–Benasciutti method is proved to be the best method for the life estimation of solder joints suited not only to the BGA package but also to the PoP package.
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Once the event detector has considered a daisy chain failed, failed times are recorded in the WinDatalog software. The critical solder joints are the critical part for the packages under vibration [18–20], thus the response of the critical solder joints under vibration loading is a major focus for the vibration reliability research. In order to find the critical solder joints of the PoP, the typical von Mises stress distribution of solder joints under 6 G harmonic excitation was obtained by means of the FE simulation method, as shown in Fig. 6.
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In the analysis and experiment, the maximum displacement occurred near the center of the SSD and the frequency difference was 0.649%. Since the first natural frequency had a major influence on the vibration-induced fatigue fracture, global finite element analysis was conducted around the first natural frequency [20]. A mode superposition method using 40 natural modes was applied in the transient analysis of the global finite element model after confirming the convergence of the proposed global finite element model.
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The total resistance of the memory module daisy chain was measured to be around 35–40 Ohm. A failure of the solder joint is assumed to occur when the total resistance is greater than 100 Ohm [16,25]. The experimental setup shown in Fig. 11 was used to determine the fatigue life of the memory modules.
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Failure mechanism of FBGA solder joints in memory module subjected to harmonic excitation

Abstract

Introduction

Section snippets

Analysis model

Free vibration analysis

Experiment to detect failure mechanism of memory module

Finite element forced vibration analysis

Conclusion

Acknowledgments

Theor Appl Fract Mech

Appl Math Model

Microelectron Reliab

Microelectron Reliab

Mech Sys Signal Process

Vibration analysis for electronic equipment