John H. L. Pang

Drop impact reliability testing for lead-free and lead-based soldered IC packages

Abstract Board-level drop impact testing is a useful way to characterize the drop durability of the different soldered assemblies onto the printed circuit board (PCB). The characterization process is critical to the lead-free (Pb-free) solders that are replacing lead-based (Pb-based) solders. In this study, drop impact solder joint reliability for plastic ball grid array (PBGA), very-thin quad flat no-lead (VQFN) and plastic quad flat pack (PQFP) packages was investigated for Pb-based (62Sn–36Pb–2Ag) and Pb-free (Sn–4Ag–0.5Cu) soldered assemblies onto different PCB surface finishes of OSP (organic solderability preservative) and ENIG (electroless nickel immersion gold). The Pb-free solder joints on ENIG finish revealed weaker drop reliability performance than the OSP finish. The formation of the brittle intermetallic compound (IMC) Cu–Ni–Sn has led to detrimental interfacial fracture of the PBGA solder joints. For both Pb-based and Pb-free solders onto OSP coated copper pad, the formation of Cu6Sn5 IMC resulted in different failure sites and modes. The failures migrated to the PCB copper traces and resin layers instead. The VQFN package is the most resistant to drop impact failures due to its small size and weight. The compliant leads of the PQFP are more resistant to drop failures compared to the PBGA solder joints.

Finite element formulation for a digital image correlation method

A finite element formulation for a digital image correlation method is presented that will determine directly the complete, two-dimensional displacement field during the image correlation process on digital images. The entire interested image area is discretized into finite elements that are involved in the common image correlation process by use of our algorithms. This image correlation method with finite element formulation has an advantage over subset-based image correlation methods because it satisfies the requirements of displacement continuity and derivative continuity among elements on images. Numerical studies and a real experiment are used to verify the proposed formulation. Results have shown that the image correlation with the finite element formulation is computationally efficient, accurate, and robust.

Flip chip on board solder joint reliability analysis using 2-D and 3-D FEA models

This study investigates the effects of employing different two-dimensional (2-D) and three-dimensional (3-D) finite element analysis (FEA) models for analyzing the solder joint reliability performance of a flip chip on board assembly. The FEA models investigated were the 2-D-plane strain, 2-D-plane stress, 3-D-1/8th symmetry and 3-D-strip models. The different stress and strain responses generated by the four different FEA models were applied to various solder joint low cycle fatigue life prediction relationships. The investigation shows that the 2-D-plane strain and 2-D-plane stress models gave the highest and lowest solder joint strains, respectively. The 3-D-strip and 3-D-1/8th symmetry model results fall in between the 2-D-plane strain and 2-D-plane stress model results. The 3-D-1/8th symmetry model agrees better with the 2-D-plane strain model, while the 3-D-strip model agrees better with the 2-D-plane stress model results. The results for the fatigue life prediction analyses also show similar trends.

Electromigration induced ductile-to-brittle transition in lead-free solder joints

The effect of electromigration on ductile-to-brittle transition in flip chip solder joints has been studied using one-dimensional bamboo-type samples of eutectic 95.5Sn–3.8Ag–0.7Cu solder joined by Cu wires at two ends. Both electrical current and tensile stress were applied to the samples either in serial or in parallel. In serial tests, the strain rate was 6×10−3. In parallel test, the creep stress was 7MPa. The current density applied was (1–5)×103A∕cm2. The working temperature was 100–150°C. In both tests, the authors observed the ductile-to-brittle transition in which the fracture migrates from the middle to the cathode interface of the joint with increasing current density and time. The transition is explained by the polarity effect of electromigration, especially the accumulation of vacancies at the cathode interface.

Creep and fatigue characterization of lead free 95.5Sn-3.8Ag-0.7Cu solder

The creep and fatigue properties of 95.5Sn-3.8Ag-0.7Cu lead free solders were investigated. Steady-state creep behavior for 95.5Sn-3.8Ag-0.7Cu bulk solder specimens were compared to reported creep test data for solder joints. Tests were carried out at four different temperatures (-40/spl deg/C, 25/spl deg/C, 75/spl deg/C and 125/spl deg/C) and a range of stress levels. The constitutive equation for the steady-state creep law is reported. Low cycle fatigue behavior for 95.5Sn-3.8Ag-0.7Cu bulk solder specimens were investigated over a range of test temperatures (-40/spl deg/C, 25/spl deg/C, 75/spl deg/C and 125/spl deg/C) and frequencies (1 Hz, 0.01 Hz, and 0.001 Hz). Frequency modified strain-based and energy-based low cycle fatigue models are proposed for solder fatigue life prediction analysis.

Mechanical Properties for 95.5Sn–3.8Ag–0.7Cu Lead-Free Solder Alloy

Mechanical properties for 95.5Sn–3.8Ag–0.7Cu solder alloy were derived from bulk specimen tensile test and lap shear solder joint tests specimen. The tensile tests were carried out at three temperatures (25<tex>

Isothermal and thermal cycling aging on IMC growth rate in lead-free and lead-based solder interface

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Through-wafer electroplated copper interconnect with ultrafine grains and high density of nanotwins

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Vibration reliability test and finite element analysis for flip chip solder joints

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Thermal fatigue reliability analysis for PBGA with Sn-3.8Ag-0.7Cu solder joints

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