Reza Ghaffarian

Accelerated Thermal Cycling and Failure Mechanisms for BGA and CSP Assemblies

This paper reviews the accelerated thermal cycling test methods that are currently used by industry to characterize the interconnect reliability of commercial-off-the-shelf (COTS) ball grid array (BGA) and chip scale package (CSP) assemblies. Acceleration induced failure mechanisms varied from conventional surface mount (SM) failures for CSPs. Examples of unrealistic life projections for other CSPs are also presented. The cumulative cycles to failure for ceramic BGA assemblies performed under different conditions, including plots of their two Weibull parameters, are presented. The results are for cycles in the range of -30 C to 100 C, -55 C to 100 C, and -55 C to 125 C. Failure mechanisms as well as cycles to failure for thermal shock and thermal cycling conditions in the range of -55 C to 125 C were compared. Projection to other temperature cycling ranges using a modified Coffin-Manson relationship is also presented.

Thermal Cycle Reliability and Failure Mechanisms of CCGA and PBGA Assemblies With and Without Corner Staking

Area array packages (AAPs) with 1.27 mm pitch have been the packages of choice for commercial applications; they are now starting to be implemented for use in military and aerospace applications. Thermal cycling characteristics of plastic ball grid array (PBGA) and chip scale package assemblies, because of their wide usage for commercial applications, have been extensively reported on in literature. Thermal cycling represents the on-off environmental condition for most electronic products and therefore is a key factor that defines reliability. However, very limited data is available for thermal cycling behavior of ceramic packages commonly used for the aerospace applications. For high reliability applications, numerous AAPs are available with an identical design pattern both in ceramic and plastic packages. This paper compares assembly reliability of ceramic and plastic packages with the identical inputs/outputs (I/Os) and pattern. The ceramic package was in the form of ceramic column grid array (CCGA) with 560 I/Os peripheral array with the identical pad design as its plastic counterpart. The effects of the following key parameters on reliability of both CCGA and PBGA assemblies were investigated:(1) thermal cycle ranges, -50degC/75degC, -55degC/100degC, and -55degC/125degC; (2) corner staking on failure mechanisms for two thermal cycle profiles, -55degC/125degC and -50degC/75degC; (3) package interchangeability, i.e., using PBGA package on CCGA pad design with a larger pad. Packages were assembled on polyimide boards and their daisy chains were continuously monitored. Optical photomicrographs were taken at various thermal cycle intervals to document damage progress and behavior. Representative samples along with their cross-sectional photomicrographs at higher magnification, taken by scanning electron microscopy and analyzed by energy dispersive X-ray, are also presented. The inspection documents were used to determine crack propagation and failure analyses for packages with and without corner staking. In assemblies with corner staking adhesive, a transition in failure from corner columns to center columns was observed when maximum temperature in thermal cycling profiles changed. This is a new failure mechanism not reported on in literature. Finite element analysis (FEA) was used to predict such global failure mode changes. FEA findings are also presented.

Chip Scale Package Assembly Reliability

Emerging chip scale packages (CSPs) and miniature versions of ball grid arrays (BGAs), are competing with bare die flip chip assemblies. CSP is an important miniature electronic package technology utilizing low pin counts, without the attendant handling and processing problems of low peripheral leaded packages such as thin small outline packages (TSOPs) and high-I/O (input/ output) quad flat packages (QFPs). Advantages include self-alignment capability during assembly reflow process and better lead (ball) rigidity. Reliability data and inspection techniques are needed for CSP acceptance especially for high-reliability applications.

Qualification approaches and thermal cycle test results for CSP/BGA/FCBGA

Abstract Qualification of newly developed multifunctional electronic packages, e.g. system in a package (SIP), are becoming complex at the package level and even more at the assembly and system levels. After many years of data collection, just recently industry agreed to release an industry-wide specification for single die area array package assembly qualification. Probability risk assessment, being implemented by NASA for space flight missions, may be narrowed at the element level for advanced electronic systems and SIP, and further narrowed at the electronic subsystem level. This paper will review the key elements of an industry-wide specification recently published by the IPC (association connecting electronics industries). It will report on a few other unique qualification approaches that are currently being either implemented or developed for risk reduction in high reliability applications. Risk level assessment based 2-P, 3-P, and LogNormal distributions will be compared for plastic ball grid array (PBGA) and flip chip BGA (FCBGA). For this case, risks are compared using cycles-to-failures (CTFs) test results for temperature ranges of −30 to 100 °C and 0 to 100 °C (two profiles). In addition, CTFs up to 1,500 cycles in the range of −55 to 125 °C for a 784 I/O FCBGA (flip chip BGA, a 175 I/O FPBGA (fine pitch BGA)), and a 313 I/O PBGA (plastic BGA) are compared. Inspection results along with scanning electron microscopy and optical cross-sectional photos revealing damage and failure mechanisms are also included.

Ball grid array reliability assessment for aerospace applications

Abstract Reliability of ball grid arrays (BGAs) was evaluated with special emphasis on space applications. This work was performed as part of a consortium led by the Jet Propulsion Laboratory (JPL) to help build the infrastructure necessary for implementing this technology. Nearly 200 test vehicles, each with four package types, were assembled and tested using an experiment design. The most critical variables incorporated in this experiment were package type, board material, surface finish, solder volume, and environmental condition. The packages used for this experiment were commercially available packages with over 250 I/Os including both plastic and ceramic BGA packages. The test vehicles were subjected to thermal and dynamic environments representative of aerospace applications. Two different thermal cycling conditions were used, the JPL cycle ranged from −30°C to 100°C and the Boeing cycle ranged from −55°C to 125°C. The test vehicles were monitored continuously to detect electrical failure and their failure mechanisms were characterized. They were removed periodically for optical inspection, scanning electron microscopy (SEM) evaluation, and cross-sectioning for crack propagation mapping. Data collected from both facilities were analyzed and fitted to distributions using the Weibull distribution and Coffin–Manson relationships for failure projection. This paper will describe experiment results as well as those analyses.

Shock and thermal cycling synergism effects on reliability of CBGA assemblies

BGAs are now packages of choice especially for higher I/O counts for commercial applications and are also being considered for use in military and aerospace. Thermal cycling characteristics of BGA assemblies have been widely reported. Thermal cycling represents the on-off environmental condition for most electronic products and therefore is a key factor that defines reliability. As a result, much data is available for accelerated thermal cycle conditions, but very limited data is available on vibration and shock representative of aerospace applications. Test vehicles with daisy chain plastic and ceramic BGAs (CBGAs) ranging from 256 to 625 I/O count were subjected to random vibration/shock representative of a spacecraft launch environment. The effect of board rigidity on behavior was also investigated by adding strips to or bonding of board to an aluminum plate. This paper compares accelerated thermal cycles-to-failure data under four temperature ranges before and after thermal random vibration for CBGAs with 361 and 625 I/Os. Stress and strain projections by finite element analysis are also presented.

Simulation of fatigue distributions for ball grid arrays by the Monte Carlo method

Abstract Any approach to qualification of advanced technologies during product development must include an assessment of variation expected in product life over the life cycle. However, testing product design options in development, to approach an optimal design is costly and time consuming. Hence, simulation of product life distributions for virtual qualification can be a valuable tool to evaluate and qualify design options. This paper presents a physics of failure-based approach to virtual qualification of advanced area array assemblies against solder fatigue failure. The approach applies Monte Carlo simulation to evaluate solder joint fatigue life distributions, given material property variations and manufacturing capabilities. Preliminary results using the simple Engelmaier model as the basis of simulations are presented. Simulation results are compared to data accumulated from two test environments and two ball grid array product types. The results reveal some of the limitations of the Engelmaier model as a basis for simulation. They also show the potential of this approach to virtual qualification for design and manufacturing capability assessment in development.

Thermal shock and drop test performance of lead-free assemblies with no-underfill, corner-underfill and full-underfill

A wide array of lead-free alloys is available in the market and distinguishing one over the other is not an easy task. Several factors have to be considered before making a choice. Reliability under both thermal and mechanical conditions is one such factor. This experimental research aims at making a comparison of the different lead-free solder ball alloys for area array and advanced packages, assembled using lead-free solder paste. Package reliability will be compared for No-underfill, Corner-underfill and Full-underfill. Assembly reliability was evaluated by subjecting the assemblies to 30 mechanical drops in the as-assembled(AS) condition and after 200 and 500 thermal shock cycles (TS). The scope of this paper is limited to the performance evaluation for area array packages (UCSP, PBGA676, PBGA1156, PoP, CVBGA). Solder ball alloy for the area array packages include SAC305, SAC405, SAC105 and SnAg. The solder paste used for the assembly is SAC305 with Type 3 solder particle size. Three different PCB surface finishes, electroless nickel immersion gold (ENIG), SnPb hot air solder level (HASL), and immersion silver (ImAg) are used. Different solder ball alloys and surface finish combinations will provide data to compare intermetallic thickness. Assembly reliability was evaluated by subjecting the assemblies to 30 mechanical drops in the as-assembled condition and after 200 and 500 thermal shock cycles. After each drop the components were checked for the continuity of the total daisy chain. The number of drops for the first failure was used in analyzing the performance of the components for various combinations. Since each component had many independent daisy chains, the failure of the individual daisy chains was later used in determining the location of the failure and how it progressed. Test results gathered for no-underfill, corner-underfill and full-underfill assemblies indicate SnAg alloys for the solder balls to be performing better than the SAC305 and SAC405 alloys for PBGA676, irrespective of the PCB pad surface finish. The location on the PCB could have had an influence on these packages. An improvement in drops to failure was also observed for some packages with corner-underfill. But with full-underfill the improvement was observed for all packages. It was also observed that UCSP failed to withstand 500 thermal shock cycles for no-underfill and corner-underfill assemblies. But the package was able to withstand 500 cycles of thermal shock for full-underfill assemblies. Solder joint analysis reveals pad cratering and crack formation to be the root cause for failure. These packages were also cross-sectioned in order to record the changes in intermetallic thickness. This paper will provide a detailed analysis of the findings.

CSP assembly reliability and effects of underfill and double-sided population

The JPL-led MicrotypeBGA Consortium of enterprises representing government agencies and private companies have jointed together to pool in-kind resources for developing the quality and reliability of chip scale packages (CSPs) for a variety of projects. In the process of building the Consortium CSP many challenges were identified regarding aspects of technology implementation. Last year, ball shear test results before and after isothermal aging were presented and compared to ball grid array packages. These package were assembled on single- and double sided printed circuit board (PWB) without and with underfill. These test vehicles are subjected to various environmental tests including four thermal cycling conditions. These cycles represent the extreme harsh accelerated testing in the range of -55 to 125/spl deg/C to a commercial requirement in the range of 0 to 100/spl deg/C. This paper presents the thermal cycling test results to 2,000 cycles performed under different environmental conditions for single- and double-sided assemblies with and without underfill.

Reliability Issues of COTS MEMS for Aerospace Applications

During the last decade, research and development of microelectromechanical systems (MEMS) has shown a significant promise for a variety of commercial applications including automobile and medical purposes. For example, accelerometers are widely used for air bag in automobile and pressure sensors for various industrial applications. Some of the MEMS devices have potential to become the commercial- off-the-shelf (COTS) components. While high reliability applications including aerospace require much more sophisticated technology development, they would achieve significant cost savings if they could utilize COTS components in their systems. This paper reviews the current status of MEMS packaging technology from COTS to specific application provides lessons learned, and finally, identifies a need for a systematic approach for this purpose.