Wire-bonded Plastic Ball Grid Array Research Articles

Thermo‐mechanical behavior of ball grid packages with different solder ball grid patterns investigated through moiré interferometry

AbstractPlastic ball‐grid array (PBGA) package assembly comprises various materials with different thermo‐mechanical properties, and the solder ball‐grid patterns can significantly influence the package deformation and solder ball stress. This study utilizes moiré interferometry to investigate the deformation behavior of wire bonded plastic ball‐grid array (WB‐PBGA) packages under varying temperatures. Real‐time moiré interferometry experiments were conducted to capture fringe patterns representing package deformation at different temperature stages. Experiments were conducted for three different wire bonded plastic ball‐grid array packages with distinct solder ball array configurations: full grid patterns (WB‐PBGA‐FG) and perimeter patterns with/without central connections (WB‐PBGA‐PC/P). The analysis revealed considerable variations in thermal strain distribution and positioning of the critical solder ball within the package assembly, depending on the solder ball‐grid pattern. Among these wire bonded plastic ball‐grid array packages, WB‐PBGA‐P/C exhibited the most substantial bending deformation, experiencing the highest effective strain, which directly impacts solder ball failure. These findings emphasize the importance of solder ball‐grid patterns in understanding the deformation behavior and reliability of WB‐PBGA packages under varying temperature conditions.

40-Gb/s Package Design Using Wire-Bonded Plastic Ball Grid Array

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> A 40-Gb/s packaging solution that uses low-cost wire-bonded plastic ball grid array (WB-PBGA) technology is presented. Since such a high speed was beyond the reach of conventional package designs, a new design methodology was proposed—discontinuity cancellation in both signal-current and return-current paths. The 3-D structures of bonding wires, vias, solder ball pads, and power distribution networks were optimized for the discontinuity cancellation. Two versions of four-layer WB-PBGA packages were designed; one according to the proposed methodology and the other conventionally. The proposed design methodology was verified with full-wave simulation, passive bandwidth measurement, time domain reflectometry (TDR), eye diagram measurement, and jitter analysis. </para>

Electrical approach to Nondestructive Analysis on WB-PBGA with TDR Technology

Time Domain Reflectometry (TDR) is a powerful measurement technique that uses the reflection of a pulse sent down a transmission line to characterize the impedance of that line. The voltage of a reflection will vary depending on the distance to the fault and on the amount of energy reflected. In this paper we develop a simple and effective electrical nondestructive analysis (NA) system for the evaluation of the interconnection of wire-bonded plastic ball grid array (WB-PBGA) package. An open-end fixture (OEF) was employed to connect fast rising edge signals to the package which was monitored for its time delay and reflection voltage parameters. This technology represents a valuable new method for the NA of WB-PBGA packages, and it has enabled the rapid and efficient detection and location of faults. Comparative TDR measurements accurately predicted the location of opens and short circuits in the copper traces of the substrate, bond wire, and solders balls. The TDR analysis was verified by using X-ray analysis. The paper establishes the use of a TDR system incorporating an open-end fixture for locating opens and shorts in WB-PBGA packages.

Characterization of flexural and thermo-mechanical behavior of plastic ball grid package assembly using moiré interferometry

Flexural and thermo-mechanical behavior of a wire-bond plastic ball grid array (WB-PBGA) package assembly is characterized using moiré interferometry. Fringe patterns are recorded and analyzed at several bending loads and temperatures. Detailed global and local deformations of the assembly are investigated. The deformations caused by the thermally induced bending are compared with those caused by the mechanical bending. The results reveal that global bending modes are similar but the deformations at the critical locations are significantly different; the sign (direction) of the shear strain caused by the mechanical bending is the opposite of that caused by the thermal loading. The implication of the opposite bending on board level reliability is discussed.

Prediction of Thermal Performance of Wire-Bonded Plastic Ball Grid Array Package for Underhood Automotive Applications

Thermal performance of a three chip, overmolded wire-bonded plastic ball grid array (WB-PBGA) package with four layer substrate attached to a 1.52-mm-thick, four-layer (2s2p), FR4 printed wiring board (PWB) has been evaluated under horizontal natural convection conditions for underhood automotive applications as a function of ambient temperature, package design parameters, and thermophysical properties of the package and PWB materials. A two-tier modeling approach, which accurately accounts for multidimensional heat transfer effects caused by substrate features such as vias and C5 solder joints, has been developed and implemented. In this methodology, the effect of small features is first characterized using a detailed micromodel from which an effective thermal conductivity is computed. The effective thermal conductivity is implemented in the global model thereby excluding the small features in the global model. The actual stackups of the package and PWB have been used in the computations to accurately determine the in-plane heat spreading. Using this methodology for automotive underhood applications, a parametric study of thermal performance of the WB-PBGA package has been carried out. This study shows that: 1. The maximum junction temperature rise above ambient, ΔT, decreases with increase in ambient temperature by 30% as the ambient temperature increases from 23 to 125°C. 2. ΔT decreases by 20% as the emissivity of the molding compound and the PWB surfaces increases from 0 (no radiative loss) to 0.8 under natural convection conditions. 3. The decrease in ΔT is small (∼7%) as the thermal conductivity of the die attach material varies over a wide range. 4. ΔT decreases by 30% as the thermal conductivity of the molding compound is varied over a wide range. 5. ΔT decreases by 45% as the thermal conductivity of the substrate increases (i.e., as the number of vias in the substrate increase) from no vias case to densely populated vias.

무아레 간섭계를 이용한 WB-PBGA 패키지의 온도변화 및 굽힘하중에 대한 거동해석

Thermo-mechanical and flexural behavior of a wire-bond plastic ball grid array (WB-PBGA) package are characterized by high sensitive moire interferometry. Moire fringe patterns are recorded and analyzed Cor several bending loads and temperatures. At the temperature higher than 100℃, the inelastic deformation in solder balls become more dominant, so that the bending of the molding compound decreases while temperature increases. The deformation caused by thermally induced bending is compared with that caused by mechanical bending. The strain results show that the solder ball located at the edge of the chip has largest shear strain by the thermal load while the maximum average shear strain by the bending moment occurs in the end solder.

THERMAL STRATEGY FOR MODELING THE WIREBONDED PBGA PACKAGES

The Plastic Ball Grid Array (PBGA) package attracts considerable interest, being one of the most promising packaging technologies of the moment. Thermal analysis of a package and a Printed Circuit Board (PCB) stack-up is performed for a better understanding of package constitutive elements, allowing an enhanced thermal coupling of package and board for cost effective thermal management. A commercial Computational Fluid Dynamics (CFD) software was applied for thermal simulation. The study focuses on detailed thermal modeling of a 256 Wirebonded PBGA (depopulated bump array) package in a natural convection setup. The model was refined to include all the features, and the calculated junction-to-ambient thermal resistance for each simulation was compared to available experimental data. The order of creating the internal structures in the model has a strong impact on the package thermal characteristics. The calculated errors varied from 5% (detailed model) to 43% (simplified model).

Overmold technology applied to cavity down ultrafine pitch PBGA package

The transfer molding technology is normally used for leadframe type packages and chip-up plastic ball grid array (PBGA) packages. This technology has been applied to cavity down PBGA packages where, normally, a liquid epoxy is dispensed by a needle in the cavity in order to cover the device and gold wires without exceeding the solder ball height plane. The new encapsulation approach using transfer molding process as well as the debug/qualification method and results using an ultrafine pitch wirebond PBGA process will be described.