PBGA Package Research Articles

Analyses on the large size PBGA packaging reliability under random vibrations for space applications

Large size commercially available plastic ball grid array chip packaging was tested and analyzed under random vibration to access its application feasibility on satellite electronics. Two types of the PBGA of 16 mm × 16 mm and 10 mm × 10 mm were chosen, and the chips were surface mounted without underfill on a daisy chained polyimide printed circuit boards. Then the boards were installed to an aluminum frame, a common type used to fix the boards to satellite structure, and undergone the random vibration tests. Two extreme levels of the random vibrations, the power spectrum of which were 22.48 grms and 31.78 grms, were applied sequentially to investigate the sustainability. It was found that the test results did not show any solder failure under the test conditions, indicating the robust structural integrity and providing the evidences justifying the PBGA packaging feasibility to the aerospace applications. Numerical analyses were also performed to analyze the PCB vibration behaviors and stress development mechanisms. The analyses results showed that, unlike usual expectation, the first natural mode may not be the dominant contribution to the solder stress developments, and higher natural modes could induce the maximum stress depending on the chip size and its location.

인공위성 임의진동에서의 PBGA 패키징 신뢰성

인공위성 임의진동에서의 PBGA 패키징 신뢰성

PBGA packaging reliability assessments under random vibrations for space applications

In this study, experimental and numerical analyses on the solder joint reliability of plastic ball grid array under harsh random vibration and thermal loadings were presented. The chips were assembled on the daisy chained circuit boards for the test samples preparation, and a half of the samples were processed for underfill to investigate the underfill effects on the solder failures. Two consequential steps of the random vibrations, named as acceptance level and qualification level, were applied. Overall required root mean square (rms) of the power spectrum densities of the steps were 22.48grms for one minutes and 31.78grms for two minutes, respectively. A thermal shock test was then performed after the vibration tests. It was found that the samples did not show any solder failure under the test requirements, demonstrating the robustness of the packaging structure for potential space applications. The samples were further tested to induce the failures, and finite element analyses were performed to analyze the sample vibration behaviors and the solder stresses to compare the results with the test data. Finally, a simple analytical calculation for the natural frequency estimations was introduced to overcome the complex finite element modeling efforts.

Ag wire and Ag alloy wire reliability and molding compounds

Ag wire and Ag alloy wire reliability experiments were conducted on both 28-lead SOP and 96-pin PBGA packages. Biased HAST (b-HAST) of Ag-wired packages with higher ion content molding compouds generated obvious defects promoted by ion accumulation mechanism. Intermetallic compounds (IMCs) at the corroded interface are identified using cross-sectional TEM/EDX. Ion selective affinity of intermetallic compound is rationalized using ab initio molecular dynamics simulation.

Design of experiments to investigate reliability for solder joints PBGA package under high cycle fatigue

This paper emphasizes a rapid assessment methodology using by the design of experiments (DOE) to determine fatigue life of ball grid array (BGA) components in the random vibration environment. The most critical dynamic loading occurs when the dominant frequency approaches the natural frequency of the printed wiring board (PWB) assembly. This research has chosen to work within the PWB clamped on two opposite edges. One only needs to think of commercial personal portable electronic products such as cell phones, personal data assistants, and entertainment devices (as exemplified by the I-pod) to realize that electronic products are no longer exclusively used in a relatively benign office environment. The approach in this paper will involve global (entire PWB) and local (particular component of interest) modeling approach. In the global model approach, the vibration response of the PWB will be determined. This global model will give us the response of the PWB at specific component locations of interest. This response is then fed into a local stress analysis for accurate assessment of the critical stresses in the solder joints of interest. The stresses are then fed into a fatigue damage model to predict the life. The solution is achieved by using a combination of finite element analysis (FEA) and physics of failure to BGA damage analysis.

Warpage Analysis of Flip-Chip PBGA Packages Subject to Thermal Loading

The aim of this paper was to measure and simulate the warpage of flip-chip PBGA packages subject to thermal loading (from room temperature to 260?C). In the experiments, a full-field shadow moirE? was used to measure real-time out-of-plane deformations (warpages) on the substrate and chip surfaces of the flip-chip packages under thermal heating and cooling conditions. A finite-element method (FEM) and Suhir's die-assembly theory, together with the measured material data (elastic moduli and coefficients of thermal expansion (CTEs) for organic substrates), were used to analyze the thermally induced deformations of the packages to gain insight into their mechanics. The strain gauge data used to determine the CTEs of the substrates also indicated that there was nearly no bending strain under thermal loading. The full-field warpages on the substrate surface of the packages from the shadow moirE? were documented under temperature loading. It was also found that there were different zero-warpage temperatures (which resulted in a variation of warpages at room temperature) for the four test packages during thermal loading, but they had similar warpage rates (the slope of warpage with respect to temperature). This might have been due to the creep of the underfill and the solder bumps in the packages at the solder reflow temperature. Regardless of the zero-warpage temperature, the warpage of the packages can be well simulated or predicted by FEM and Suhir's theory. The key material properties (elastic moduli and CTEs for the substrate and underfill) that affect the maximum warpage of the package were thoroughly studied. It was found that, among these material properties, a low elastic modulus for the underfill can significantly reduce the maximum warpage, while its CTE is much less sensitive to warpage. Moreover, the substrate CTE affects the warpage of a package only with noncompliant underfills, while a typical substrate elastic modulus (ranging from 10 to 30 GPa) is insensitive to warpage, unless its value is lower than a few gigapascals.

A Rapid Life-Prediction Approach for PBGA Solder Joints Under Combined Thermal Cycling and Vibration Loading Conditions

While some electronic products are routinely subjected to concurrent vibration and temperature cycle loading, the ability to accurately model and estimate life expectancy of hardware under such conditions still presents a unique challenge. For combined vibration and temperature cycling, one of the most likely causes of failure is the fatigue of solder interconnects. This paper presents an approach to predict solder joint life under combined thermal cycling and vibration loading conditions, by taking into account temperature effects and loading interactions. Combined loading experiment on a test vehicle populated with PBGA packages was used to demonstrate this approach.

Design of Experiments for Board-Level Solder Joint Reliability of PBGA Package Under Various Manufacturing and Multiple Environmental Loading Conditions

A design of experiments was conducted to determine the reliability of plastic ball grid array packages under various manufacturing and multiple environmental loading conditions. Parameters included conformal coating methods, underfill, solder mask defined, and non-solder mask defined pads. Board-level temperature cycling, vibration, and combined temperature cycling and vibration testing were performed to quantify the reliability and identify preferred design parameters. Through the main effects and interaction analysis, test results show underfill is the key parameter related to the solder joint reliability improvement. Conformal coat method and printed circuit board pad design are not main effects on solder joint reliability. No interactive relationship exists among these three factors under temperature cycling loading, but some interactive relationship between printed circuit board pad type and the conformal coating method exists under vibration and combined loading conditions.

Reliability and Failure Analysis of Lead-Free Solder Joints for PBGA Package Under a Cyclic Bending Load

Nowadays, interest in the bending reliability of ball grid array packages has increased with the increase in mobile devices. Initially, bending tests were conducted to certify the safety of an electronic package during the manufacturing and shipping processes. But recently, the purpose of the bending test has changed: cyclic bending tests are being used to evaluate the electronic package's endurance against handling damage such as bending, twisting and key pressure. Furthermore, the bending test is being adopted as an alternative to a drop test. In this study, a four-point cyclic bending test was performed under various loading levels to investigate the fatigue behavior of solder joints with chemical compositions of 95.5Sn4.0Ag0.5Cu and 63Sn37Pb. It was found that the lead-free solder has a longer fatigue life than the lead-contained solder when the applied load is low. A finite element analysis (FEA) with plasticity and creep constitutive equations was conducted because there are no suitable sensors to measure stress and strain of solder ball joints directly. From the analysis results, it was found that the inelastic energy dissipation could be used as a good damage parameter. Also, from the inspection of the failure site and the FEA, it was found that the fatigue crack initiated at the exterior solder joints and propagated into the inner solder joints.

The Measurement of Residual Deformation in PBGA Package after Reflow Process Using A Newly Developed Laser Profiler

For measuring deformation of electronic packages, various techniques have been used. Each technique has some merits and demerits. Some techniques have very high resolution but small measuring area. On the contrary, other techniques have large measuring area and low resolution. So the judicious selection of techniques with a trade-off between the resolution and available measuring area is important. In this research, a new laser profiler was developed by integrating high resolution laser displacement sensor into the x-y scanner. This system has 10nm vertical resolution and 100nm horizontal resolution with a measurement area up to 25mm by 25mm. The residual deformation of a lead-contained and lead-free PBGA package after reflow process was measured by the newly developed system. And the effect of aging was evaluated.

Effect of Size of Lid-Substrate Adhesive on Reliability of Solder Balls in Thermally Enhanced Flip Chip PBGA Packages

Six design cases of lid-substrate adhesive with various combinations of widths and heights were analyzed to investigate how the size of the adhesive affects the reliability of the solder balls of thermally enhanced flip chip plastic ball grid array (FC-PBGA) packages in thermal cycling tests. Analysis results were compared with data on the reliability of conventional FC-PBGA packages. Thermal-mechanical behavior was simulated by the finite element (FE) method and the eutectic solder was assumed to exhibit elastic-viscoplastic behavior. The temperature-dependent nonlinear stress/strain relationship of the adhesive was experimentally determined and used in the FE analysis. Darveaux's model was employed to obtain the predicted fatigue life of the solder ball. Simulation results reveal that the fatigue life of the solder balls in thermally enhanced FC-PBGA packages is much shorter than that in conventional FC-PBGA packages, and the life of solder balls increases with both the width and the height of the adhesive. However, the effect of the width of the adhesive on the reliability of the solder ball is stronger than that of the height. Moreover, increasing either the width or the height reduces the plastic strain in the adhesive at critical locations, indicating that the reliability of the adhesive can be improved by its size. The predicted results of the life of solder balls for some selected studied packages are also compared with experimental data from thermal cycling tests in the paper

Fracture Mechanic Analysis for Package Delamination

Delamination and crack were considered as significant failures in electronic packaging. For these circumstances, Modified Crack Closure Integral method was tested and applied to determine crack growth rate and for the purpose to understand failures. TQFP package was successfully verified by using the method. A PBGA package was modeled for thermal distribution and moisture concentration in order to calculate vapor pressure acted on crack. The energy release rate was the main concern among fracture parameters, which had been proven fully related with vapor pressure and crack length ratio in popcorn cracking.

Stability of the warpage in a PBGA package subjected to hygro-thermal loading

The CTE and CHE mismatch between materials in a thin PBGA package is primarily attributed to the warpage which occurs when the package is being mounted on to a PCB, especially when the moisture content reaches a specified value. In this paper, the stability equations for the warpage in a PBGA package without the solder balls being subjected to hygro-thermal loading, by modeling it as an initially perfect/imperfect composite plate, have been developed. The analytical closed-form solutions are found and used to compute not only the critical moisture content but also the warpage occurring before the critical loads are reached. The buckling of the PBGA package, at the solder reflow peak temperature, occurs when the theoretical moisture content reaches 0.259–0.283 wt.%. This theoretical critical moisture content accurately predicts the experimental critical moisture content (0.25–0.30 wt.%) derived from our previous work. The results, from comparison between theoretical and experimental critical moisture content, indirectly indicate that the PBGA package has little imperfection. However, the large initial imperfect structure of the package does not easily reach the buckling stage because of moisture absorption. In addition to this, the structure of the PBGA package before buckling become stress-free at the moisture level of 0.077 wt.% and at room temperature during moisture conditioning.

Thermal resistance analysis and validation of flip chip PBGA packages

This work proposes a finite element numerical methodology to predict the thermal resistance of both flip chip-plastic ball grid array (FC-PBGA) with a bare die and FC-PBGA with a metal cap. The 3D finite element model was initially constructed to simulate the thermal resistance of FC-PBGA. A thermal resistance experiment was performed to verify the FEM results, following the construction of specimens of FC-PBGA with a bare die and with an aluminum cap, using six-layered substrate. The verified finite element model was employed to determine the thermal resistance of FC-PBGA with a copper cap using four-layered and six-layered substrates. Experimental results demonstrated that FC-PBGA with a metal cap improves thermal performance by 35% over with a bare die. FC-PBGA with a copper cap slightly improves thermal performance from 2% to 2.8% over that of FC-PBGA with an aluminum cap. The thermal resistance of FC-PBGA with a four-layered substrate is reduced by 4.0% to 5.9% from that of FC-PBGA with a six-layered substrate, since the four-layered substrate contains less metal. The finite element numerical results negligibly differ from the experimental results by 6% to 8.1%. A finite element numerical methodology is here proposed to predict the thermal resistance of FC-PBGA. The methodology is effective in researching and developing new products or improving existing packages.

814 薄型電子機器筐体モデル内の熱性能と流れ(オーガナイズドセッション5 電子機器の熱問題)

814 薄型電子機器筐体モデル内の熱性能と流れ(オーガナイズドセッション5 電子機器の熱問題)

ベンチマーク筐体内で強制空冷されるPBGAパッケージの熱性能(J01-5 筐体放熱設計,J01 エレクトロニクス実装における熱制御および信頼性評価)

This paper presents the experimental results regarding the thermal performance of a PBGA package model mounted on a printed circuit board in a thin compact casing. The casing exit was linked with an exhaust duct that has an orifice plate for flow rate measurement and an exhaust fan. The effect of the relative position of the PBGA package and a cooling air inlet on the thermal performance was examined. It is confirmed that air flow through a narrow inlet diffuse slightly and that increasing the streamwise distance between the package and the inlet has a limited effect.

The impact of moisture in mold compound preforms on the warpage of PBGA packages

The moisture in the mold compound preforms influenced the resultant mechanical properties as well as the warpage of IC packages after the molding and post mold curing (PMC) process. Moisture will diffuse into the mold compound preforms (compound pallet) after thawing from cold room and exposing to clean room condition before molding process. The moisture will cause the package to swell, and combine with thermal stress, and finally result in the warpage of molded package after molding process. The main objective of this paper is to address the impact of moisture in the compound preforms on the warpage of the PBGA packages and explain the change in mechanical properties under different moisture conditions, e.g., the variations of the flexural modulus, Tg, and CTE with respect to moisture level. The compound preforms exposure to a clean room condition were simulated by a series of experiments. The warpage of PBGA packages were measured by the moiré test. The moisture control during the IC manufacturing process was highlighted in terms of the mechanical properties variation and warpage measurement due to the moisture effects on the mold compound preforms.

1837 ベンチマーク筐体内で強制空冷される BGA パッケージの熱性能(筐体内充填率の影響)

This paper presents the experimental results concerning the effects of packaging density to the thermal performance of a PBGA package model mounted on a printed circuit board in a thin compact casing. The casing exit was linked with an exhaust duct, which has an orifice plate for flow measurement in the middle, and an exhaust fan at the end. The thermal resistance values of the package were plotted against the ratio of the obstacle volume to the casing volume and the ratio of obstacle sectional area to the inlet. The results demonstrate that there exist different temperature rise distributions even when both the ratio of the obstacle sectional area to the inlet area and the ratio of the obstacle volume to the casing volume are the same.

An Accurate Transient Analysis of High-Speed Package Interconnects Using Convolution Technique

An accurate transient analysis of a package interconnect requires the modeling and analysis of conductor and dielectric losses, as well as other high-frequency effects of 3D structures. The skin effect and dispersion of interconnects are more accurately modeled in frequency domain. Consequently, an accurate time-domain simulation of such a system is only possible using convolution techniques. Although the convolution method is well understood, the application of windowing for frequency-dependent interconnect analysis is less so. In this paper, we present the practical considerations of window selection and its application to improve the accuracy of convolution simulators. We introduce the Tukey window and study the tradeoff between how smoothly data can be set to zero to avoid aliasing and suppress ripples and how much information tapering will discount at the edge of the window in order to obtain meaningful results. The bandlimiting effects of the Tukey window and other well-known windows are also compared. Finally, to verify the validity and accuracy of the proposed method, a wirebond PBGA package and a PCB-connector system are analyzed using the scattering parameters obtained from simulation and measurement, respectively.

Influences of the moisture absorption on PBGA package’s warpage during IR reflow process

The coefficient of temperature expansion mismatch between materials in a thin plastic ball grid array package is primarily attributed to the warpage when mounting the package to a printed circuit board, especially when the moisture concentration reaches a specified value. The influence of variations in storage conditions on warpage was investigated in this paper. The effects of the reflow parameters on warpage were also examined. Taguchi’s method was implemented for experimental design and data analyses. A critical relative moisture absorption between 0.25% and 0.30% was found for a considerable warpage response.