Ball Layout Research Articles

A digital image processing model for characteristics capture and analysis of irregular electronic components

Amid diversification, high performance, high integration, and low-cost development in consumer electronic products, the conventional system on board function integration model is giving way to system on chip (SoC). Layout of solder balls under ball grid array (BGA) is getting irregular as system in package (SiP) is integrating multi-chip module and couple of active and passive components along with more complex circuit design. Due to the shortening life cycles of consumer electronic products and frequent new product launches, the incoming inspection operation of electronic components is getting tedious, let alone the component database updates required by mounter are also getting more frequent and time consuming due to increasingly complex and diversified components and soaring demands in characteristic measurement and identification difficulties. This study is aimed at building automated characteristic capture and analysis image processing model for BGA packages of irregular solder ball layout. It employs edge detection to get component body looks and dimensions by enhanced component edge characteristics. A image pre-processing model is used to identify consistency of individual solder ball characteristics with median filter, highlight image characteristics with binary conversion, remove noise with morphology, and connected component labeling to segment area covered by individual characteristic. In addition, a roundness and aspect ratio of the least rectangle-based solder ball characteristics identification method is proposed to determine number of, diameter of, and coordinates of center of border solder balls. The component characteristics acquired by the model comes in ± 3% difference against the actual one in terms of dimension. The model appears a good reference for system packaging operator in component database creation for the launch of new products in terms of reduced time for manual measurement and error as well as loss in mounter capacity. It also serves for electronic components incoming inspection to reduce inspection operation time and simplify the process.

A 28-channel coil array for improved imaging of the optic nerve

This work describes the design and construction of a radio-frequency (RF) coil optimized for imaging the optic nerve on a Siemens 3T TIM Trio MRI scanner. The specific goals were to optimize signal sensitivity from the orbit to the optic chiasm and improve SNR over previous designs. The optic nerve (ON) coil was constructed using two fiberglass formers that fit together in a clamshell arrangement to maintain a high filling factor for any head size. This design maintains close coil-to-sample coupling near the eyes and around the entire head to eliminate the air void regions that occur between coil and sample when heads are imaged in one-piece rigid head coils. The anterior mask former holds 26 overlapping coil elements in a soccer ball layout. The posterior former supports the neck and head and houses two additional overlapped coil elements, totaling to 28 elements. Signal-to-noise-ratio (SNR) measurements on a custom-made homogeneous head phantom using the optic nerve coil showed a 310% increase in SNR near the orbits and 60% increase at the optic chiasm compared to the 12-channel Siemens head coil. Inverse g-factor maps show that the ON coil performs well for parallel imaging over the region of the optic nerve, providing a possible reduction of eyeball motion artifacts. Images from volunteer studies demonstrate that high-resolution imaging of the optic nerve can be achieved using 3T MRI with advanced imaging coils, leading to improved patient care for optic neuritis patients. © 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 41B: 73–84, 2012

Enhancing the Reliability of Wafer Level Packaging by Using Solder Joints Layout Design

During the design and manufacturing processes of electronic packaging, solder joints are fabricated using a variety of methods to provide both mechanical and electrical connections for different applications. They include flip chip, wafer level chip scale packaging (WLCSP), fine pitch ball grid array (BGA), and chip scale packaging (CSP). The solder joint shape prediction methods have been incorporated as a design tool to enhance the reliability of the WLCSP. However, the reliability of solder joints for a large chip size such as 10mmtimes10mm without underfill remains questionable. In this research, a hybrid method combining an analytical algorithm with the energy-based approach is applied to predict standoff heights and geometry profiles of the solder joints. In addition, a hybrid-pad-shape system is proposed to design the solder ball layout, and to enhance the reliability of the solder joints. Next, a nonlinear and parametric finite element analysis is conducted to investigate the reliability issues that result from several design parameters. In addition, an experimental validation is completed to verify the correctness and feasibility of the solder joint shape prediction methods and finite element analysis procedures. The design parameters considered in this study include solder joint layout, solder volume, pad diameter, as well as the ratio and orientation of the elliptical pad. With regards to solder joint layout design, the solder joints located in the corner areas can be considered as structural dummy balls with no electrical signals passing through them. The results reveal that when the WLCSP has large round pads, or properly oriented elliptical solder joint pads at the corner areas underneath the chip, then the maximum equivalent plastic strain of the solder joints will be effectively reduced. As a result, the solder joint fatigue life under thermal loading will be greatly enhanced. Furthermore, the findings of this research can be used as a design guideline for electronic packaging with area array interconnections such as CSP, flip chip packaging, Super CSP, and fine pitch BGA

A testing method for assessing solder joint reliability of FCBGA packages

A brittle solder joint at the interface between a solder ball and a substrate metal pad could result in an open joint failure after the solder ball is attached to a motherboard. Existing metrologies, such as ball shear, do not always detect the weak solder joint strength. A peel test for solder joint strength evaluation of substrate was developed. Several problems were observed during the initial stages of the development for this metrology. These included solder bridging and inconsistency of the test results. Solder bridging was reduced by changing the stencil design to have stencil openings that match the solder ball layout and using a jig to align the coupon and substrate while assembling the peel test samples. The paste printing and peeling methods were modified and the coupon quality was carefully monitored to make the sample preparation and testing more consistent. The impact of the physical aging and reflow on the solder joint strength was investigated. It showed that the peel strength did not decrease with physical aging, but did decrease with an increased number of reflows. The peel test results correlated with the performance of the substrates. The substrate with low peel strength had weak solder joints and failed under use conditions. The substrates with high peel strength demonstrated stronger solder joints and performed well under use conditions. The metrology provides a gross check about the presence of brittle solder joints on flip chip ball grid array substrates and is successfully used in monitoring the solder joint strength.

Board level solder joint reliability modeling and testing of TFBGA packages for telecommunication applications

For thin-profile fine-pitch BGA (TFBGA) packages, board level solder joint reliability during the thermal cycling test is a critical issue. In this paper, both global and local parametric 3D FEA fatigue models are established for TFBGA on board with considerations of detailed pad design, realistic shape of solder joint, and nonlinear material properties. They have the capability to predict the fatigue life of solder joint during the thermal cycling test within ±13% error. The fatigue model applied is based on a modified Darveaux’s approach with nonlinear viscoplastic analysis of solder joints. A solder joint damage model is used to establish a connection between the strain energy density (SED) per cycle obtained from the FEA model and the actual characteristic life during the thermal cycling test. For the test vehicles studied, the maximum SED is observed at the top corner of outermost diagonal solder ball. The modeling predicted fatigue life is first correlated to the thermal cycling test results using modified correlation constants, curve-fitted from in-house BGA thermal cycling test data. Subsequently, design analysis is performed to study the effects of 14 key package dimensions, material properties, and thermal cycling test condition. In general, smaller die size, higher solder ball standoff, smaller maximum solder ball diameter, bigger solder mask opening, thinner board, higher mold compound CTE, smaller thermal cycling temperature range, and depopulated array type of ball layout pattern contribute to longer fatigue life.

Physical Properties of the“Once Through Then Out” Pebble-Bed Reactor

A new and promising operating modus for the pebble-bed reactor has been investigated. Instead of circulating the fuel balls several times through the core they are moved only once slowly from the top to the bottom. Due to the increasing depletion toward the lower core area, there is a substantial axial tilt of the power density, and the downward flow of the cooling gas ensures for the system an optimal heat removal. The reduced power generation in the hot core area and the absence of hot spots enable achievement of a higher power density than in the known pebble-bed type and make possible a rise in the average gas outlet temperature up to 950°C.For a UO2-fueled reactor the life history is followed for several years by means of a two-dimensional calculational approach. Apart from the advantages in thermodynamics, the new system is marked by a very short and smooth running-in period, by a high sensibility of reactivity to control poison changes inside the upper reflector, and by an ideal accommodation of the burnup in the balls running with different flow speeds in different radial positions. The spatial distribution of the power density can be flexibly manipulated by changes in the fuel cycle speed, in fuel ball layout, or by the use of a higher feed enrichment in the outer core region. A brief parameter study and a discussion of technological aspects give an outline of the developing potential of that new type.