This paper investigates the impact of isothermal aging on the long-term reliability of lead-free solder joints. The full experimental matrix contains SAC105 and SAC305 solder alloys assembled in ball grid arrays (BGAs) with package sizes ranging from 19mm, 0.8mm pitch to 5mm, 0.4mm pitch, and three surface platings (ImAg, ENIG, and ENEPIG). The test specimens were subjected to isothermal aging at temperatures 25°C, 55°C, 85°C to 125°C with aging times of 0, 6 months, 12 months and 24 months, followed by accelerated thermal cycling from −40°C to 125°C. A two-parameter Weibull plot shows the reliability degrades up to 70% after two years of aging at elevated temperature. The degradation rate slows with aging time. The degradation is greater with smaller solder joints and perimeter ball arrangements when compared to large-diameter solder balls and full array ball arrangements. The thickness of the Cu-Sn intermetallic layer (IMC) layer during the testing grows with an approximate ~ t0.5 dependence (diffusion-controlled reaction) during isothermal aging + thermal cycling.

A methodology was developed to correlate field life with observed degradation for electronics modules. This procedure was developed by identifying common deterioration characteristics in field units, modeling observed trends and then developing a model to predict future deterioration trends. This particular method focused on the deterioration of solder joint strength due to solder fatigue and comparing these values with a threshold based on known electrical failures. A conditional probability density function was formulated and quantified for both random shear strength and the minimum shear strength within a module. The conditional probability density function characterized both the changing mean and variance for a normally distributed random shear strength. With this methodology, time or mileage (life) prediction is based on the probability that the minimum performance response is less than a defined failure threshold. The methodology described herein promises to be an effective product development tool as the effect of design changes on product life can be more quickly and easily evaluated. While the technique developed herein is applicable to all electronic designs, the method was developed with a particular focus on understanding these relationships for automotive (harsh environment) applications. Copyright © 2005 John Wiley & Sons, Ltd.

The solder joint reliability of ceramic chip resistors assembled to laminate substrates has been a long time concern for systems exposed to harsh environments such as those found in automotive and aerospace applications. This is due to a combination of the extreme temperature excursions experienced by the assemblies along with the large coefficient of thermal expansion mismatches between the alumina bodies of the chip resistors and the glass-epoxy composites of the printed circuit boards (PCBs). These reliability challenges are exacerbated for components with larger physical size (distance to neutral point) such as the 2512 resistors used in situations where higher voltages and/or currents lead to power dissipations up to 1 Watt. In this work, the thermal cycling reliability of several 2512 chip resistor lead free solder joint configurations has been investigated. In an initial study, a comparison has been made between the solder joint reliabilities obtained with components fabricated with both tin-lead and pure tin solder terminations. In the main portion of the reliability testing, two temperature ranges (-40 to 125/spl deg/C and -40 to 150/spl deg/C) and five different solder alloys have been examined. The investigated solders include the normal eutectic SnAgCu (SAC) alloy recommended by earlier studies (95.5Sn-3.8Ag-0.7Cu), and three variations of the lead free ternary SAC alloy that include small quaternary additions of bismuth and indium to enhance fatigue resistance. For each configuration, thermal cycling failure data has been gathered and analysed using two-parameter Weibull models to rank the relative material performances. The obtained lead free results have been compared to data for standard 63Sn-37Pb joints. In addition, a second set of thermally cycled samples was used for microscopy studies to examine crack propagation, changes in the microstructure of the solders, and intermetallic growth at the solder to PCB pad interfaces.

The solder joint reliability of ceramic chip resistors assembled to laminate substrates has been a long time concern for systems exposed to harsh environments. In this work, the thermal cycling reliability of several 2512 chip resistor lead‐free solder joint configurations has been investigated. In an initial study, a comparison has been made between the solder joint reliabilities obtained with components fabricated with both tin‐lead and pure tin solder terminations. In the main portion of the reliability testing, two temperature ranges (−40‐125°C and −40‐150°C) and five different solder alloys have been examined. The investigated solders include the normal eutectic Sn‐Ag‐Cu (SAC) alloy recommended by earlier studies (95.5Sn‐3.8Ag‐0.7Cu), and three variations of the lead‐free ternary SAC alloy that include small quaternary additions of bismuth and indium to enhance fatigue resistance.

The underhood automotive environment is harsh and current trends in the automotive electronics industry will be pushing the temperature envelope for electronic components. The desire to place engine control units on the engine and transmission control units either on or in the transmission will push the ambient temperature above 125/spl deg/C. However, extreme cost pressures, increasing reliability demands (10 year/241 350 km) and the cost of field failures (recalls, liability, customer loyalty) will make the shift to higher temperatures occur incrementally. The coolest spots on engine and in the transmission will be used. These large bodies do provide considerable heat sinking to reduce temperature rise due to power dissipation in the control unit. The majority of near term applications will be at 150/spl deg/C or less and these will be worst case temperatures, not nominal. The transition to X-by-wire technology, replacing mechanical and hydraulic systems with electromechanical systems will require more power electronics. Integration of power transistors and smart power devices into the electromechanical actuator will require power devices to operate at 175/spl deg/C to 200/spl deg/C. Hybrid electric vehicles and fuel cell vehicles will also drive the demand for higher temperature power electronics. In the case of hybrid electric and fuel cell vehicles, the high temperature will be due to power dissipation. The alternates to high-temperature devices are thermal management systems which add weight and cost. Finally, the number of sensors in vehicles is increasing as more electrically controlled systems are added. Many of these sensors must work in high-temperature environments. The harshest applications are exhaust gas sensors and cylinder pressure or combustion sensors. High-temperature electronics use in automotive systems will continue to grow, but it will be gradual as cost and reliability issues are addressed. This work examines the motivation for higher temperature operation, the packaging limitations even at 125/spl deg/C with newer package styles and concludes with a review of challenges at both the semiconductor device and packaging level as temperatures push beyond 125/spl deg/C.

The paper describes an optimization model for allocating solder-paste printing inspection that explicitly considers the economic tradeoff between board yield and inspection accuracy. The paper also shows that the use of a heuristic solution method for solving the post-printing inspection allocation model is effective and efficient for high-volume electronics manufacturing. The model has been developed using real production and visual inspection data provided by a high-volume electronics manufacturer located in Huntsville, AL. In addition, randomly generated problems are used to evaluate the performance of the proposed heuristic. Results from a large case study show that when compared with a full post-printing inspection, the heuristic approach provides a solution that can increase the total expected gains by 15%.

In this work, the under-the-hood reliability of smaller PBGA packages has been evaluated in the automotive thermal cycling environment. Various methods of enhancing reliability have been explored including increased BT substrate thickness, the utilization of NSMD pads on the BGA component, alternative PCB plating finishes, and the use of underfill encapsulants. A set of test boards was assembled with several 15 and 17 mm body size BGA components from two different vendors. In addition to non-underfilled parts, the enhancements achieved with four different underfill encapsulants have been explored. Larger 23 mm BGAs have also been included in the test matrix as a control/reference. The assembled test vehicles have been subjected to 6000 thermal cycles over the range -40 to 125 °C, and the daisy-chain resistances of the various components were monitored throughout the testing. Logged failures have been statistically analyzed using two parameter Weibull models. The analysis results have allowed the board level reliabilities of the examined BGA components to be compared and ranked, and the reliability enhancements achieved with various underfills to be accessed. Detailed failure analyses have also been performed to find the locations of solder joint fatigue crack growth, and to identify other failure modes occurring in underfilled parts.