Ball Grid Array Package Assembly Research Articles

Proposal of intense pulsed light soldering process for improving the drop impact reliability of Sn–3.0Ag–0.5Cu ball grid array package

Until now, electronic packages have been manufactured using the conventional convection reflow process. However, it is becoming challenging to apply the reflow process because it is time-consuming and produces thick intermetallic compounds (IMCs) at the joint interface. In addition, the reflow process consumes a lot of power because of the preheating required and the generation of waste heat, thereby interfering with carbon neutrality. To overcome these issues, the feasibility of intense pulsed light (IPL) radiation soldering for the ball grid array package assembly process was investigated in this study. A very thin IMC was formed at the IPL-soldered joint (IMC thickness = 1.2 μm) because of the short IPL process time. However, the IMC formed during the reflow process was 6.1 μm-thick. Thus, the drop impact reliability of the IPL-soldered joint (number of drops to failure = 277) substantially improved compared with that of the reflow-soldered joint (number of drops to failure = 103). In addition, the power consumption of the IPL radiation soldering process was 17.95 kWh, considerably lower than that of the conventional convection reflow process (29.50 kWh). Therefore, we suggest that IPL soldering has a high potential to reduce process time, IMC thickness (enhancing the drop impact reliability), and power consumption.

Hygro-Thermo-Mechanical Reliability Assessment of a Thermal Interface Material for a Ball Grid Array Package Assembly

The thermal efficacy of thermal interface material (TIM) is highly dependent on its ability to adhere to the surfaces of interest. Any delamination of the TIM from the die or the lid will increase the local thermal resistance and, thus, will reduce the overall effectiveness of the TIM. Although significant amount of work has been done on understanding the thermal and moisture effects of various polymer materials used in microelectronic package assemblies, very limited work has been done to study the effect of temperature and moisture on TIM delamination. In this paper, a sequential hygro-thermal-mechanical finite-element model has been developed to mimic the loadsteps associated with package assembly as well as moisture soaking under 85°C/85RH over 500 h. The predictions from the models have been validated with a wide range of experimental data including laser Moiré data for thermomechanical loading and digital image correlation data for hygro-thermo-mechanical loading. Weight gain and coordinate-measurement machine have been used to characterize moisture diffusivity and moisture expansion coefficient of various polymer materials in the package assembly. The developed models show the evolution of normal strain in TIM during various loadsteps and provide important insight into the potential for TIM delamination under package assembly process and moisture soaking. Thus, the models can be used for developing various designs and process steps for reducing the chances for TIM delamination.

Optimization of board-level thermomechanical reliability of high performance flip-chip package assembly

In this paper, we study board-level thermomechanical reliability of a high performance flip-chip ball grid array package assembly subjected to an accelerated thermal cycling test condition. Different control factors are considered for an optimal design towards enhancement of the thermal fatigue resistance of solder joints. These factors include solder composition, underfill, substrate size, lid thickness, stiffener ring width, test board size, soldermask opening on the substrate side, and pad size on the test board. The shape of solder joints after reflow is estimated using Surface Evolver. The optimal design is obtained using an L 18 orthogonal array according to the Taguchi optimization method. Importance of these control factors on the board-level thermomechanical reliability of the package is also ranked.

Numerical evaluation of thermal cycling reliability of high performance flip‐chip package assembly using submodeling analysis

This paper applies the submodeling technique in analyzing thermal cycling reliability of high performance flip‐chip ball grid array package assemblies. The packages have one‐piece tunnel‐type heat spreaders with different lead widths, connected to chips using different thermal interface materials. The global model contains no solder bumps to simplify the analysis. The calculated displacement field of the global model is then interpolated on the boundary of the submodel that contains the critical solder bump. The submodel is solved using the prescribed displacement boundary conditions together with external thermal loads to evaluate thermomechanical reliability of the critical solder bump.

On solution schemes for time-independent thermomechanical analysis for structures containing polymeric materials

Contradicting ideas about implementing temperature-dependent Young’s modulus in a time-independent quasi-static thermomechanical analysis can be found regularly in the literature. The incremental (quasi-static evolution) and the non-incremental (Hookean) solution schemes represent simplifications of the viscoelastic behavior of polymeric materials according to different theoretical disciplines. These two schemes lead to completely different solutions when Young’s modulus is a function of the temperature. In this paper we review the ideas about implementing temperature-dependent Young’s modulus in a time-independent quasi-static thermomechanical analysis. Differences of the ideologies are highlighted using bimaterial beam solutions. Thermomechanical deformations of a bimaterial structure, which resembles a plastic ball grid array package assembly, at different temperatures are measured using shadow Moiré interferometry. Numerical solutions from different schemes are compared with measurement results.

Temperature Dependent Deformation Analysis of Ceramic Ball Grid Array Package Assembly Under Accelerated Thermal Cycling Condition

A robust scheme of moire´ interferometry for real-time observation is employed to study the temperature dependent thermo-mechanical behavior of a ceramic ball grid array package assembly. The scheme is implemented with a convection-type environmental chamber that provides the rapid temperature control required in accelerated thermal cycling. Thermal deformations are documented at various temperatures. Thermal-history dependent analyses of global and local deformations are presented. A significant nonlinear global behavior is documented due to complete stress relaxation at the maximum temperature. An analysis of solder interconnections reveals that inelastic deformation accumulates at the bottom eutectic solder fillet only at high temperatures.

Evaluation of thermal deformation model for BGA packages using moiré interferometry

A compact model approach of a network of spring elements for elastic loading is presented for the thermal deformation analysis of BGA package assembly. High-sensitivity moire interferometry is applied to evaluate and calibrated the model quantitatively. Two ball grid array (BGA) package assemblies are employed for moire experiments. For a package assembly with a small global bending, the spring model can predict the boundary conditions of the critical solder ball excellently well. For a package assembly with a large global bending, however, the relative displacements determined by spring model agree well with that by experiment after accounting for the rigid-body rotation. The shear strain results of the FEM with the input from the calibrated compact spring model agree reasonably well with the experimental data. The results imply that the combined approach of the compact spring model and the local FE analysis is an effective way to predict strains and stresses and to determine solder damage of the critical solder ball.

A study on the variation of effective CTE of printed circuit boards through a validated comparison between strain gages and Moire interferometry

The effective coefficient of thermal expansion (CTE) of printed circuit boards (PCBs) have a great deal of influence on the reliability of solder joints in microelectronic packages. In this paper we carryout a systematic characterization of nineteen circuit board samples using strain gages, further validated by moire/spl acute/ interferometry, to understand the impact of CTE variation on the reliability of solder joints. It is shown that the measured effective coefficient of thermal expansion varied in a wide range by as much as 5 PPM about the commonly used value of 17 PPM. This is shown to cause a significant reliability impact for a representative plastic ball grid array package assembly. The comparison between strain gage and moire/spl acute/ interferometry showed good overall correlation, but differed from each other by as much as 2.73 parts per million (PPM). The possible sources of error in each technique are identified and discussed.

Effect of the plasma cleaning process on plastic ball grid array package assembly reliability

Interface delamination is recognized as one of the major failures of microelectronics packaging. It can result from various factors, including stresses from mismatch of adherent materials, hygrothermal stress from the release of vapor pressure of moisture during soldering reflow process, and interface material adhesion strength. The failure mechanisms are associated with cyclic loads, temperature and moisture condition as well as interface adhesion strength degradation. This paper focuses on the evaluation of plasma cleaning on PBGA assembly, including resistance to interface delamination. Two different plasma systems, powered by radio frequency (RF) and microwave (MW) energy, are studied. The optimized plasma cleaning process parameters are obtained by surface contact angle measurements. The plasma cleaning results are also verified by scanning electron microscopy (SEM) as well as physical pull and shear tests. The test vehicles are 27/spl times/27 mm 292-ball PBGAs. The results from encapsulation peel tests, die and encapsulant pull tests, bonding wire pull tests and C-Mode SAM (C-SAM) examination are presented. It is clear that an optimal plasma cleaning process can be achieved with different plasma systems. The experimental results also demonstrate that plasma cleaning has little effect on wire bonding process and die attach pull strength for given substrates and assembly materials. In all the cases, optimal plasma cleaning steps improve PBGA resistance against interface delaminations for cases where plasma cleaning is carried out before encapsulation process. Moreover, different plasma cleaning techniques would affect the assembly productivity, investment and yield. This paper demonstrates that the optimized plasma cleaning process would enhance PBGA package qualification level and improve the process yields and productivity.

On the design parameters of flip-chip PBGA package assembly for optimum solder ball reliability

An experimental investigation of the warpage of a flip-chip plastic ball grid array package assembly is presented and a critical deformation mode is identified. The experimental data, documented while cooling the assembly from the underfill curing temperature to -40/spl deg/C, clearly reveal the effect of the constraints from the chip and the PCB on the global behavior of the substrate. The constraints produce an inflection point of the substrate at the edge of the chip. An experimentally verified three-dimensional (3-D) nonlinear finite element analysis proceeds to quantify the effect of the substrate behavior on the second-level solder ball strains. An extensive parametric study is conducted to identify the most critical design parameter for optimum solder ball reliability.