FR4 Board Research Articles

On the effects of temperature on the drop reliability of electronic component boards

The effects of package temperature on failure mechanisms and lifetimes under mechanical shock loading were studied with the help of five different types of high-density packages (a WL-CSP and four CSP-BGAs) assembled on both double-layer and multi-layer FR4 boards. The localized heating of the packages by means of integrated heating elements was utilized in order to produce similar hot spots to those occurring in products in service. The results showed that the temperature can have a significant effect on the lifetimes of component boards under mechanical shock loading but that the effect varied according to the structures of the component boards. The average number of drops to failure of the WL-CSP component boards increased significantly with an increase in the temperature of the package, while the average number of drops to failure of the CSP-BGA component boards generally decreased. On the other hand, the drop reliability of one out of four CSP-BGA component board types was insensitive to temperature. The failure modes and mechanisms were clarified with the help of physical failure analyses that revealed different failure modes in the component boards. Furthermore, depending on the component board type, the primary failure mode may change with temperature from that identified at room temperature. Particular attention was paid to the nucleation and propagation of cracks at different test temperatures. Computational case studies were designed in order to identify the significance of a change in temperature on three factors: (a) the stiffness of the PWB; (b) the strength and elastic modulus of the solder, and (c) the thermomechanical loads. The influences of each factor on the strains and stresses in the proximity of the solder interconnections were evaluated by means of the finite element method. The results of the statistical and physical failure analyses were rationalized with the help of the results from the finite element analyses. They showed that the effects of a change in temperature on the lifetimes of the component boards under mechanical shock loading can be explained by changes in the nucleation site and/or the propagation of cracks. The results presented in this paper point out that single-load reliability tests can form an incomplete understanding of the failure mechanisms in real service environments and modifications to the currently employed reliability test standards that are needed.

Multiband-integrated antenna/artificial magnetic conductor

An artificial magnetic conductor (AMC)-based multiband low-profile antenna for vehicle applications is designed, simulated and measured in this study. The AMC is a simple dual band structure, constructed on a 3.2 mm-thick FR-4 (e r =4.4) board, with the reflection phase and surface wave bandgaps in the 2.0 and 5.8 GHz ranges. A wideband printed circular disc monopole antenna uses this dual-band AMC as a ground plane resulting in a low-profile, multiband and platform-tolerant antenna system. The operating frequency bands covered are GPS (1.57542 GHz), DCS (1.710-1.880 GHz), PCS (1.850-1.990 GHz), UMTS (1.925-2.175 GHz), WLAN (2.4-2.485 GHz), WiFi (5.15-5.825 GHz) and V2X (5.76-5.84 GHz) using a -10 dB reflection coefficient criterion. It is demonstrated that the antenna gain increases significantly when the AMC is used over a large metal ground plane for the antenna.

A Novel Small Triple Band Rectangular Dielectric Resonator Antenna for WLAN and WiMAX Applications

A novel triple band rectangular dielectric resonator antenna is presented for satisfying wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications simultaneously. The proposed triple-band antenna operates at 2.4 GHz/3.5 GHz/5.8 GHz. By using three plexiglass dielectrics on FR4 board, a very low cost antenna is designed. In addition, a modified version of the rectangular dielectric resonator antenna, which has three-segment thin dielectrics with different sizes, provides omnidirectional radiation over the frequency bands. The antenna is fabricated, and a good agreement is achieved between the simulated and measured results. The designed triple-band antenna with extremely low cost and low profile is very suitable for multiband mobile communication systems. To the authors' knowledge, this is the first triple band dielectric resonator antennas (DRAs) presented with stable radiation patterns (nearly omnidirectional pattern) for each operating band.

Materials Selection and Processing Techniques for Small Spacecraft Solar Cell Arrays

Body mounted germanium substrate solar cell arrays form the faces of many small satellite designs to provide the primary power source on orbit. High efficiency solar cells are made affordable for University scale satellite programs as triangular devices trimmed from wafer scale solar cells. The smaller cells allow the array designs to pack tightly around antenna mounts and payload instruments, giving the board design more flexibility. We are investigating the reliability of solar cells attached to FR-4 and carbon core laminate printed circuit boards. FR-4 circuit boards have significantly higher thermal expansion coefficients and lower thermal conductivities than germanium. This thermal expansion coefficient mismatch between the FR-4 board and the components used cause major concern for the power system when considering a failure of the solar cells, such as a series of cracked cells or faulty solder joints. These failures are most likely to happen with a longer orbital lifetime and longer exposure to the harsh environment the satellite will experience while in orbit. Carbon core laminates provide an advanced alternative because the core thickness can be selected to more closely match the device substrate, or at least provide a wider thermal expansion coefficient range to match the components on the board. We are also comparing various methods of attaching the solar cells to the printed circuit boards, using solder paste alone and in parallel with a silicone adhesive, considering the application of these adhesives by comparing the solder joints under x-ray when applied by screen printing versus stencil printing, and looking closely at the cleaning processes for array assembly. Storage, vacuum exposure, thermal cycling, functional and vibration testing will be used to compare the survivability and performance of the solar arrays.

Beam Forming Networks Using Reduced Size Butler Matrix

Recent trend shows that the reduced size couplers are becoming potential building blocks and have created a continuing demand for the growing wireless communications market. Therefore, this paper presents a new design and realization for reducing the size of the branch-line coupler using eight two-step stubs that operates at 2.45 GHz. In this study, the reduced size branch-line coupler has been implemented on a 4 × 4 Butler Matrix, which generally consists of branch-line coupler, crossover, and phase shifter. The simulation results are obtained by using the advanced design system (ADS) in terms of S-Parameter analysis and the phase difference between the ports. Moreover, this design is realized on a low-cost substrate, e.g., flame resistance board (FR4 Board). The obtained results show that the proposed design has reduced the electrical length of transmission line up to 50% and consequently, the area of the branch-line coupler has been reduced up to 30% from the normal size.

Influence of the Bonding Force, Anisotropic Conductive Film (ACF) and Reflow Process on the Flip Chip Assembly

Flip chip assembly on FR4 board using anisotropic conductive films (ACFs) is gained more attention because of its many advantages. But to obtain more reliable flip chip assembly, it is necessary to control the parameters involved in the process. In this work, the effect of bonding force of ACF, as well as the kind of ACF and the parameters evolved in the reflow process on the ACF flip chip joints were investigate. It was observed a formation of the high conduction gap for ACF joints bonded with lower bonding forces after reflow. This high conduction gap can result in electrical disconnection in the worst case.

Fabrication and optical modulation of top-emitting yellow light polymer light-emitting diodes on the FR4 board

Top-emitting yellow light polymer light-emitting diodes (PLEDs) were fabricated on the FR4 board for future application in optical interconnects. A 100 μm thick glass plate with sputtered Ag films on the back side for light reflection was bonded to the board for smooth surface. The PLED had a structure of indium tin oxide /poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate)/phenyl substituted polypa raphenylene-vinylene/Ba/Ag and reached the brightness of 4528 cd/m 2 with a corresponding current efficiency of 7 cd/A. A small AC signal imposed onto a DC bias was employed to characterize the electroluminescence delay time and hole mobility in the PDY-132 super yellow films.

A Novel Time Domain Method to Extract Equivalent Circuit Model of Patterned Ground Structures

A novel and efficient time-domain method is proposed to extract the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> equivalent circuit model of the patterned ground structure. Based on time domain reflection analysis and Laplace transform, two analytical equations are derived to compute the corresponding <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> values. The non-ideal effect of the excitation source and nonzero rising time in time domain reflectometry (TDR) measurement and analysis is also considered. The equivalent <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> due to the conductor loss of the slot is obtained by the steady state DC level in TDR waveform. Two test samples are fabricated on a Duroid substrate and a FR4 board to verify the accuracy of the extracting method. The extracted <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> models for these two cases have a good agreement with the full-wave simulation and measurement results both in the time domain and frequency domain.

Board-Level Solder Joint Reliability Study of Land Grid Array Packages for RF Application Using a Laser Ultrasound Inspection System

Microelectronics packaging technology has evolved from through-hole, and bulk configuration to surface-mount, and small-profile ones. Today’s electronics industry is also transiting from SnPb to Pb-free to meet environmental requirements. Land grid array (LGA) package has been becoming popular in portable electronics in terms of low profile on the printed wiring boards and direct Pb-free assembly process compatibility. With the package profile shrinking and operating power increasing, solder joint quality and reliability has become a major concern in microelectronics manufacturing. The solder joint failure at the package level or board level will cause electronic devices not to function during service. In this paper, board-level solder joint reliability of the LGA packages under thermal loading is studied through thermal cycling tests. A novel laser ultrasound-interferometric system developed by the authors is applied to inspect solder joint quality during the thermal cycling tests. While the laser ultrasound inspection technique has been successfully applied to flip chips and chip scale packages, this study is the first application of this technique to overmolded packages. In this study, it is found out that the LGA packages can withstand 1000 temperature cycles without showing crack initiation or other failure mechanisms in the solder joints. The laser ultrasound inspection results match the visual observation and X-ray inspection results. This study demonstrates the feasibility of this system to solder joint quality inspection of overmolded packages. In particular, the devices constituting the objective of this study are radio frequency modules, which are encapsulated through overmolding and are mounted on a typical four-layer FR4 board through LGA terminations.

C‐shaped ultra‐wideband bandpass filter with WLAN notch band

AbstractA compact bandpass filter (BPF) embedded with 5.8 GHz wireless‐LAN notch is presented for 3.1–10.6 GHz ultra‐wideband (UWB) systems. The proposed UWB‐BPF based on a defect‐grounded structure is implemented with an FR4 board. Two open‐loop resonators on the top layer provide a narrow notch band whose center frequency can be easily adjusted by varying the sizes of the open‐loop. A simple C‐shaped slot on the bottom ground layer is adopted to improve the bandwidth performance. The characteristics of UWB‐BPF are analyzed and simulated using a circuit model of LC lump elements. The size of the filter is at least 34% less than those filters with the same specification. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1215–1218, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25153

UTM-LOGO WIDEBAND PRINTED MONOPOLE ANTENNA SURROUNDED WITH CIRCULAR RING PATCH

A novel of wideband monopole antenna with UTM-Logo shape is proposed to create specific wide band frequencies which can be applied in the cognitive radio. The antenna is designed to be operated between 1.98 to 6.46 GHz frequency bands (106.16%). It has been fabricated on 30£51mm2 FR4 board with thickness of 1.6mm and the dielectric permittivity and tangent loss of 4.7 and 0.019, respectively. Two slots also been attached on the ground plane for the purpose of increasing the bandwidth of antenna. Simulation and measurement results show good agreement.

Fractal Koch dipole antenna for UHF band application

AbstractThe fractal Koch curve is one of the popular fractals shape. This article discussed the analysis of the fractal Koch dipole antenna (FKDA) using log periodic technique. The effect of flare angle of the antenna has been described to reduce the antenna size. The antenna is operated at ultrahigh frequency (UHF) band frequency between 460 MHz and 4 GHz. The analysis is based on the number of elements, degree of flare angle, current distribution, and radiation pattern of the antennas. The antenna has been designed and simulated using computer simulation technology (CST) and fabricated using FR4 board. The performance of the antennas has been measured, analyzed, and discussed in this article. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2612–2614, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24702

Heat management for power converters in sealed enclosures: A numerical study

This paper compares four assembly solutions for power converters operating in sealed enclosures with tight temperature specifications. The specific application of interest is one of the DC/DC converters of a power supply system to be used in high-energy-physics experiments: the sealed case must not significantly alter the temperature of the surrounding components (detectors and their electronics). The comparison is made using 3D Finite Element thermal modeling. The standard FR4 board solution is shown not to be viable under these tight temperature specs; we therefore explore alternative assemblies for the stack connecting the active devices to the heat-sink.

Simulation based analysis of secondary effects on solder fatigue

Secondary effects on thermal fatigue of solder joints, which frequently have been neglected, were studied by means of the finite element method (FEM). Based on a semi-empirical approach to predict fatigue life by evaluating the cyclic accumulated equivalent creep strain or energy density, effects of organic boards intrinsic properties on solder joint fatigue were investigated. Aspects of more realistic FR-4 board modelling were studied, in particular concerning its in-plane anisotropy and intrinsic warpage behaviour. Intrinsic board warpage was measured on test board level as well as for boards from series production. High intrinsic warpage was in particular found for several test boards. The effects for the worst case scenario observed so far were analysed for both first level and second level interconnects. The change in predicted fatigue life varied between 30% and 500%, the latter most critical effects were found at large QFN components. Another secondary effect studied was to include the frequently neglected interfacial intermetallics into FEM. It turned out that for components with relatively large standoff like LFBGAs the effects were actually negligible, but for the highly miniaturized components like chip resistors CR0201 they are the decisive factor.

The Role of Aging on Dynamic Failure Envelopes of OSP-Sn37Pb Interconnects in Plastic Ball Grid Array (PBGA) Packages

This paper quantifies the effect of aging on the durability of printed wiring assemblies (PWAs) subjected to dynamic loading conditions. The test specimen is a FR4 board with a single 256 I/O, full grid, PBGA component at the center. The pad finish on the board and component side of the Sn37Pb eutectic solder interconnects is organic solderability preservative (OSP) and Sn15Pb, respectively. The test matrix is designed to cover one order of magnitude of PWA flexural strain (1E-3 to 1E-2), three orders of magnitude of PWA flexural strain rate (1E-3 to 1E0 s-1), and two aging conditions (as-reflowed and 125 degC for 100 h). Fatigue failure envelopes, based on a mechanics-inspired empirical rate-dependent model, are used to characterize the durability in terms of PWA flexural strain and strain rate. A failure site transition zone (FSTZ) is defined in terms of the damage parameters, beyond which the failure site changes from the solder to other parts of the PWA. The combined effect of load amplitude, loading rate, and thermal aging on the FSTZ and solder durability is quantified and presented.

Double-Layered Quad-Band Bandpass Filter for Multi-Band Wireless Systems

A compact double-layered quad-band (DLQB) bandpass filter (BPF) is presented to provide four passbands at the desired frequencies with efficient out-of-band suppression. The designed filter is verified by pattern implementation on two FR4 boards. The proposed DLQB-BPF consists of two L-shaped resonators on the first layer and two symmetrically-coupled stepped-impedance resonators (SIRs) on the second layer. The bottom of the second layer is ground plane. There are seven transmission zeros generated to perform quad-band characteristics at 1.57 GHz, 2.45 GHz, 3.6 GHz, and 5.8 GHz. An equivalent circuit model is constructed by analyzing the symmetry property of the proposed filter. A good agreement between the simulated and measured results is observed.

Evaluation and modelling of integral capacitors produced by interdigitated comb electrodes

Integral capacitors (IC) of one or two-layer printed wiring board (PWB) circuits were produced using comb electrodes fixtures and dielectric composites as the inter-electrode material. ICs were fabricated at laboratory scale, using copper comb electrodes and BaTiO3-epoxy composite materials deposited on a glass-Epoxy FR4 board. They were experimentally tested in order to obtain their electrical response. Furthermore, ICs behaviour was modelled through 2-dimensional models applying finite element method (FEM). Results showed that by this laboratory technique it was possible to obtained integral capacitors with low dielectric losses. Moreover, acceptable agreement was found between numerical and experimental capacitance results for all the different analysed ICs. In conclusion, 2D FEM models are a suitable tool to predict electric response of IC devices.

Design and Comparison of Three 20-Gb/s Backplane Transceivers for Duobinary, PAM4, and NRZ Data

A full study of three data formats including duobinary, PAM4, and NRZ is proposed to estimate the performance of the corresponding transceivers under different conditions. Transceiver prototypes designed and optimized for the three signalings are presented to evaluate their performance as well as the feasibility. The three transceivers have been tested thoroughly in Rogers and FR4 boards. Fabricated in 90-nm CMOS technology, all three transceivers achieve error-free operation with 20-Gb/s 2 31-1 PRBS data over 40-cm Rogers and 10-cm FR4 channels. General comparison reveals that the NRZ data still achieves the best performance at 20 Gb/s.

Experimental verification of negative refraction in a double cross metamaterial

We report on microwave experiments with a metamaterial composed of pairs of metallic crosses. The transmission properties of the structure show a left-handed transmission band at frequencies around 10.2 GHz. The validity of the negative effective index of refraction is verified by a Snell’s law refraction experiment performed on a wedge-shaped sample of the metamaterial. A second measurement of a similar wedge made from blank FR4 boards is done for reference. The results of the measurements show positive refraction over the whole measured frequency band for the FR4 wedge as well as the refraction of the incident radiation to negative angles within the designated left-handed frequency band for the metamaterial sample.

Quality Inspection of Flip Chip Solder Bumps Using Integrated Analytical, Numerical, and Experimental Modal Analyses

Solder bump inspection of surface mount packages has been a crucial process in the electronics manufacturing industry. A solder bump inspection system has been developed using laser ultrasound and interferometric techniques. In this research, modal analysis is important to correlate the defects with dynamic responses of packaged electronic devices under pulsed laser loading. The effect of solder bump defects on the mode frequencies and mode shapes is reported in this paper. The objective is to develop a modal analysis approach, which integrates analytical, numerical, and experimental methods. In particular, this paper discusses the analytical modeling, numerical modeling, and transient out-of-plane displacement measurements for a 6.35×6.35×0.6mm3 PB18 flip chip mounted on a FR4 board.