Enhancing the Fatigue Life of PCB Assemblies through Strategic Positioning and Novel Support Techniques for Ball Grid Array Packages

With continuing miniaturization and more prevalent use of Ball Grid Array (BGA) packages in the microelectronics industry, the mechanical strength of Printed Circuit Board Assemblies (PCBAs) with BGA packages is becoming very critical. In a variety of applications ranging from smart phones to high end switches and routers, the mechanical robustness of PCBAs is becoming the key differentiator in product reliability. To enable a standard way to benchmark mechanical reliability, the IPC/JEDEC-9702 test method was developed several years ago. The test method has helped compare different PCBAs to optimize overall mechanical reliability. However, a key challenge with mechanical testing is that by the time the testing is performed, it is too time consuming and expensive to make changes to the package if it's mechanical reliability needs improvement. In this study, bending tests for various BGA packages have been conducted based on the IPC/JEDEC-9702 standard, under different applied deflections to obtain the required data for studying the failure modes. Three-dimensional Finite Element Models (FEM) were developed to understand the relationship between PCB strain and solder joint strain. The strain values at different locations in the PCBA were estimated from the model, and compared with experimental data. Good agreement between model predictions and experimental data has been obtained. Then, a series of FEM analyses were performed with different design parameters. High performance cluster computing was used to reduce computation time without compromising accuracy. Finally, based on the results presented in this study, optimization analysis was performed to improve BGA mechanical reliability for any given geometry.

With continuing miniaturization and more prevalent use of Ball Grid Array (BGA) packages in the microelectronics industry, the mechanical strength of Printed Circuit Board Assemblies (PCBAs) with BGA packages is becoming very critical. In a variety of applications ranging from smart phones to high end switches and routers, the mechanical robustness of PCBAs is becoming the key differentiator in product reliability. IPC/JEDEC-9704 test method was developed several years ago to enable a standard way to benchmark mechanical reliability. The test method has helped compare different PCBAs to optimize overall mechanical reliability. However, a key challenge with mechanical shock testing is that by the time the testing is performed, it is too time consuming and expensive to make changes to the package if its mechanical reliability needs improvement. In this study, shock tests for various BGA packages have been conducted based on the IPC/JEDEC-9704 standard, under different applied G values to obtain the required data for studying the failure modes. Threedimensional Finite Element Models (FEM) were developed to understand the relationship between PCB strain and corner solder joint strain. The strain values on the PCB close to the package were estimated from the model and compared with experimental data. A series of FEM analyses were performed with different design parameters. Finally, based on the results presented in this study, optimization analysis was performed to improve BGA mechanical reliability for any given geometry.

This research studied the thermal fatigue life for eutectic solder balls of thermally enhanced flip-chip plastic ball grid array (FC-PBGA) packages with different lid materials under thermal cycling tests. Three FC-PBGA packages with different lid materials, i.e., Al, AlSiC, and Cu, were utilized to examine the lid material effect on solder ball reliability. The cyclic stress/strain behavior for the packages was estimated by using the nonlinear finite element method. The eutectic solder was assumed to be elastic-plastic-creep. The stable stress/strain results obtained from FEM analysis were utilized to predict the thermal fatigue life of solder balls by using the Coffin-Manson prediction model. Simulation results showed that the fatigue life of the FC-PBGA package with a Cu lid was much shorter than FC-PBGA packages with other lid materials. The relatively shorter fatigue life for the FC-PBGA package with a Cu lid was due to the complex constrained behavior caused by the thermal mismatch between the lid, substrate and the printed circuit board. The difference was insignificant in the fatigue lives between the package with an Al lid and the conventional package.

Ball grid array (BGA) package is an IC package for active devices intended for surface mount applications. It is an area array package, utilizing whole or part of the device footprint for interconnections between IC chip and printed circuits board [PCB]. The ball grid array packages increases electronic I/O counts significantly. Hence, the BGA package was mainly used in computer IT, telecommunication equipment, hand-phone, PDA as well as portable handhold electronic application. BGA packaging consisted in plastic substrate, which is to provide interconnection and mechanical platform. Substrate performance plays an important part in IC package reliability. The common quality issue and reliability issues of BGA package are delamination [popcorn], crack, warpage. All these failures are related to base material [substrate] mechanical and thermal properties. Hence, understanding and studying substrate material properties are becoming a key to development and design of an advanced electronic package. In this study, three different plastic substrates - BT, PPE and FR5 - were tested by TGA, TMA in order to obtain their mechanical, thermal behavior.

With trends in electronic devices towards more circuitry and higher pin count, Ball Grid Array (BGA) packages are now becoming popular in Integrated Circuit (IC) products. The BGA technology also provides space savings, higher yield during solder reflow attachment, and utilization of existing surface mount technology processes. This paper reviews OMPAC BGA packages, their structure and technology. In addition, we investigate the moisture sensitivity and reliability of 225 I/O 2-layered (2L) OMPAC BGA packages with Metal Oxide Semiconductor (MOS) ICs. This paper presents the experimental results of (i) percent weight gain measurements of four different BGAs that were preconditioned at various moisture levels, (ii) internal package damage as a function of ingressed moisture content, (iii) reliability concerns of BGAs, and (iv) qualification test data. Reliability performance of moisture plus solder reflow preconditioned BGAs demonstrated no failures after 1,000 hours of Temperature Humidity Bias (THB) stressing, when a low level of moisture (0.12%) was present in the BGA packages. The results of this study also suggest that 2L BGA packages with moisture content higher than 0.12% by weight exhibit serious delamination at different package interfaces during solder reflow. In addition, it was established that 4L, overmolded BGA packages appear to absorb 20-25% less moisture than a 2L BGA package.

Numerical simulation and fatigue life estimation of BGA packages under random vibration loading

It is generally known that the thermal fatigue damage is the main failure mode of ball grid array (BGA) packages, which caused by the mismatch of the coefficient of thermal expansion between low temperature co-fired ceramic (LTCC) and print circuit board (PCB). The thermal mismatch would subject the solder joints to in-plane shear and out-of-plane bending loads. To ensure the reliability of BGA packages, it must enhance the mechanical strength between solder ball and LTCC substrate, which can be improved by structure optimization. In this paper, the influence of dimpled ceramic solder mask defined (SMD) construction on the mechanical strength of solder joint in LTCC-based BGA package have been investigated using non-linear finite element analysis and experimentation. A series of dimpled ceramics SMD constructions are applied to BGA packages to carry out the ball shear tests. It could be observed that the existence of dimpled SMD has the effect of increasing the interfacial mechanical strength between pad and LTCC substrate. Averaged equivalent stress and plastic strain analyses were carried out to reveal the failure mechanisms. The results of this work can be recommended as the optimization plan for the high reliability LTCC-based BGA packages.

This paper presents a design support methods to evaluate thermal fatigue life of solder balls on ball grid array (BGA) package. Since high density packages have interactions between design factors, cluster analysis was used to extracts relations between design factors. Simplified BGA package model was proposed to evaluate thermal fatigue life quickly. Then, the mechanism generating inelastic strain falls into the difference in the coefficient of thermal expansion (CTE), Young's modulus of the package and the PCB. An estimating function to equivalent inelastic strain range was developed based on the mechanism. The function can estimate the value to a set of design factors within 20% error.

In this paper, drop reliability of various PBA (printed board assembly) mounting structures is investigated and compared. Then, we built SAC305 (Sn3.0Ag0.5Cu) interconnects for BGA (ball grid array) package failure model to evaluate the drop impact reliability of handheld devices. In order to simulate actual behavior of the solder joint under the drop impact load of handheld devices, we perform explicit full FEA (finite element analysis) modeling. However, this takes a lot of computing time because of the large aspect ratio of element size between solder joints and other structures such as PCB (printed circuit board) and electronic packages. Therefore, an effective way to represent solder interconnects for FEA is needed which would be relatively simpler yet detailed. Comparable board-level drop tests are conducted after equipping test vehicles with various fixtures considering PBA mounting structures, which make it possible to apply different loading conditions to BGA packages. The results show different drop impact life for solder interconnects depending on the mounting design of the PBA. Particularly, the solder interconnect of the component located at the middle of the PCB exhibits the shortest impact life where the highest tensile stress occurs. Also, the mounting design restraining PBA deflections shows better reliability under the drop impact loading. Sequentially, simulating with a PBA composed of the BGA package and the PCB is considered to assess the feasibility of the solder ball failure modeling when the drop impact load is applied. Especially, for the modeling of the solder balls, detailed solid model and simple beam model are compared regarding computational efficiency and numerical accuracy. We found that the simple beam model significantly shortens computational time from 110 h to less than an hour. Accordingly, the feasibility of the beam model for the solder balls is shown by correlating the stress level and the drop impact life obtained from the experiments.

There has been a dramatic proliferation of research concerned with thermal stress in electronic package for the last three decades. Moreover, reviewing the mechanical bending during printed circuit board (PCB) assembly has become important in the reliability assessment of modern electronic systems. The primary research demonstrates that the assessment approach can be applied successfully to the design model of a ball grid array (BGA) package with a more complete and accurate assessment model for solder joint fatigue life under mechanical bending. Previous research has focused mostly on the thermal analysis in electronic packages; however, most modern portable electronic products used in mobile devices, personal digital assistants, and aircraft have to endure extreme environments that involve not only thermal but also mechanical bending conditions. Initially, mechanical bending tests were conducted to demonstrate the reliability of the electronic packaging during the manufacturing and shipping process. Currently, the microelectronic packaging faces mechanical bending when everyone uses his or her Smartphones. The mechanical bending occurs when the user touches the screen on the Smartphone. Therefore, interest in the mechanical bending of BGA packaging has increased with the uptake in mobile device use. In this research, the analytical solution and finite element analysis (FEA) are both presented to investigate the solder joint fatigue life. The analytical solution is presented for a PCB assembly subjected to mechanical bending by taking the axial stress, shear stress, and moment of the solder joints with discontinuity function into account. A FEM is proposed to analyze the solder joint fatigue life and to investigate the reliability of solder joints in BGA packaging subjected to mechanical bending.

Handheld electronic devices are vulnerable to drop impacts, leading to mechanical damage and electrical failures such as PCB cracking, trace damage, solder joint fractures, and component breakage. This study investigates the reliability of solder joints in Ball Grid Array (BGA) packages by examining their dynamic response under board-level drop impacts using Finite Element methods. Explicit dynamic analysis employing the Input-G method, in accordance with JEDEC guidelines, was used to simulate the printed circuit board assembly (PCBA) model. Results reveal that solder balls on the board side are more critical than those on the package side, with corner-most solder balls near the board edges identified as the most vulnerable, experiencing maximum peel stress of 162.12 MPa and strain of 0.001048. Analysis of radial displacement and drop orientation showed that BGA packages positioned closer to PCB edges exhibit greater reliability than those at the centre. The face-down drop orientation was identified as the most vulnerable configuration. Structural optimization of the PCBA, incorporating factors such as solder ball pitch, PCB thickness, and solder ball diameter, significantly improves reliability, underscoring the importance of these parameters in ensuring the long-term durability of the assembly.

As electronic packages continue to get smaller, designing reliable solder joints is becoming an increasingly important part of the design process. The shape and height of the solder joint are major factors that can be optimized to improve the reliability of flip chip (FC) and ball grid array (BGA) packages. Optimizing the dimensions of the underlying copper pad, which influences solder height and shape, can lead to a longer time to failure for packages undergoing cyclic temperature loads. In this study, the influence of the copper pad design on the thermal fatigue life performance of an off-the-shelf BGA package is investigated. Printed circuit boards (PCBs) with different pad dimensions are employed to analyze the difference in the performance in accelerated thermal cycling (ATC) tests on a BGA package. In this article, Surface Evolver is used to predict the shape of the solder joint for different combinations of copper pad diameters on the component and PCB side, and its influence on fatigue life test performance is compared. The accumulated plastic work is used to predict the thermo-fatigue life of different solder geometries.

High-speed short-range wireless communication systems are expected to utilize the 60-GHz band. This paper presents a bonding wire loop antenna in a standard ball grid array (BGA) package for 60-GHz short-range wireless communication. The proposed antenna has a loop shape and consists of two bonding wires connecting to a complementary metal-oxide-semiconductor (CMOS) chip and a metal plate on an interposer in a BGA package. The antenna can be fabricated at low cost by a conventional BGA package fabrication process. The BGA package is mounted on a printed circuit board (PCB) that consists of resin substrate, such as FR-4. The broadband impedance characteristic is achieved by adjusting the position of the metal pad for wire bonding. The antenna gain is improved by forming cranked ledges and notches in the metal patterns of the PCB, and the wide-angle radiation characteristic is realized. The sizes of the fabricated antenna and BGA package are approximately 0.6 mm × 1.0 mm × 0.3 mm and 9.0 mm × 9.0 mm × 0.9 mm, respectively. Performing measurements, the antenna gain with the PCB is from - 2.4 to 4.9 dBi over the 57- to 65-GHz frequency range and over an angular range of 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> in the horizontal plane.

The solder-joint interconnect between an IC component and the PCB (printed circuit board) is a critical link in the system overall reliability. Trends in the automotive market are driving increased focus on solder-joint performance: (1) increasing electronics content for new functions, especially for ADAS (advanced driver-assistance systems), (2) use in safety critical systems and sub-systems, (3) decreasing interconnect pitches which reduces the stand-off and available solder, (4) increasing industry reliability expectations, and (5) package variations (ex. multi-die). In particular, BGA (Ball Grid Array) packages are used throughout the vehicle across various systems including engine control, braking, communication, infotainment, and radar to name only a few. Among these, under-the-hood applications often require high sustained operating temperatures and many heating/cooling cycles during the vehicle lifetime. The reliability of these interconnects is routinely assessed by cyclical thermal stress (temperate cycling) of components mounted to boards. While AEC (Automotive Electronics Council) offers no standards for solder-joint testing (for example, board level reliability criteria is not included in the AEC Q100 “Failure Mechanism Based Stress Test Qualification for Integrated Circuits”), IPC 9701A “Performance Test Methods and Qualification Requirements for Surface Mount Solder Attachments” can be followed. For automotive under-the-hood the specified cycle range is 40°C to 125°C (TC3). This paper summarizes the BL-TC (board level temperature cycle) performance of various BGA packages used in automotive applications. In all cases the test vehicle packages were daisy-chain versions of production devices, while maintaining critical features such as BGA footprint, physical dimensions, BOM (bill of materials), die size and thickness and substrate layer metal densities. All used Pb-free solders for both the BGA solder ball and the paste printed onto the PCB. The PCB designs were complementary to the packages establishing daisy-chain connections winding through the PCB, the solder-joint and package substrate. Each chain (net) was continuously monitored in situ during cycling. An event detector logged a failure when a net resistance exceeded 300 ohms. Wirebonded and flip chip packages were studied, ranging in size from 10mm to 29mm with BGA pitches including 0.65mm, 0.80mm and 1.00mm. In addition to these primary attributes, various other factors were found to alter the solder-joint lifetimes. For example, increasing BGA pad and solder sphere diameters improved solder-joint lifetime, but increasing the PCB pad diameter often did not. Among solder materials, eutectic SnAg typically showed longer lifetimes than other high Ag SAC alloys such as SAC305 and SAC405. The addition of Bi to the SAC alloy showed promise for further improvements. Other factors that were studied include die thickness, die size, and BGA pad finish. Both mechanical cross-section and dye penetrant analysis (dye-and-pry) were employed for failure analysis, enabling study of crack propagation and crack location within the solder-joint. Additionally, failure location (failing solder-joint) was identified for each as package corner, under the die edge, or package center in a predictable pattern depending on the package type. Examined in total, two opposing trends will force future innovation. Industry reliability requirements continue to drive expectations (i.e. cycles to failure) higher, while increasing package size and decreasing pitch will naturally reduce the solder-joint lifetimes. Solutions will be found in package design, package material and solder selections.

For critical high speed applications, system designers budget electrical performance for each individual component within the integration. During the budgeting process, each component is treated as a black box, and is assigned target performance levels. Crosstalk and switching noise levels are specified and closely watched, since they can cause episodes of false switching. SPICE simulations are performed at the IC, package, and system level to track down any signal integrity problems or issues. Obtaining accurate package models, in particular for power and ground, are the key to overall simulation accuracy. Package power and ground inductance plays a major role in determining switching noise performance. Ball Grid Array (BGA) packages are constructed with laminate substrates that provide an efficient means for achieving minimal power and ground inductance implementation. A BGA that is strategically designed will yield further enhancements in crosstalk and switching noise performance. This is accomplished by optimal implementation and location of power, ground, and signal networks. By doing so, loop inductance created at critical locations in the BGA are reduced by mutual inductance. BGA packages use power and ground rings to provide low inductance access from Integrated Circuit (IC) bond pads to package planes. These connections are typically done using many bond wires equally distributed around the perimeter of the die. Rings are used in combination with via holes, planes, and solder balls to complete the power and ground network structures. Careful attention to how the currents flow in these structures in conjunction with signal traces will yield minimal effective inductance. This paper presents a characterization methodology for creating BGA electrical models. It addresses a class of BGAs that contain power and ground planes, and the Plastic BGA package is used as a vehicle. The measurements are performed in frequency domain using a vector network analyzer. Using these models, electrical performance of BGA packages is evaluated.