Ball Grid Array Ball Research Articles

SPROUT—Smart Power Routing Tool for Board-Level Exploration and Prototyping

The board-level power network design process is governed by system-level parameters, such as the number of layers and the ball grid array (BGA) pattern. These parameters influence the characteristics of the resulting system, such as power, speed, and cost. Evaluating the impact of these parameters is however challenging. To estimate the reduction in impedance if, for example, additional BGA balls are dedicated to the power delivery system, adjustments to the board layout, and an additional impedance extraction process are required. These processes are poorly automated, requiring significant time and labor. Automating power network exploration and prototyping can greatly enhance the board-level power delivery design process by increasing the number of possible design options. With power network exploration and prototyping, the effects of the system parameters on the electrical characteristics can be better understood, providing valuable insight into the early stages of the design process. SPROUT—an automated algorithm for prototyping printed circuit board (PCB) power networks—is presented here. This tool includes the first fully automated algorithm for board-level power network layout synthesis. Two board-level industrial power networks are synthesized using SPROUT. The impedance of the resulting layouts exhibits good agreement with manual PCB layouts while significantly reducing the design time. The tool is used to explore area/impedance tradeoffs in a three-rail system, providing useful data to enhance the PCB design process.

A Statistical Approach to Three-Dimensional Shape Inspection of Micro-Solder Balls

This article presents an optical technique for the three-dimensional (3D) shape inspection of micro-solder balls used in ball grid array (BGA) packaging, before attaching them to a board or film. This technique uses an optical source comprising spatially arranged light-emitting diodes (LEDs), and the results are derived based on the specular reflection characteristics of the BGA balls. A vision system is designed to acquire the reflected image from the micro-solder balls. For shape inspection, the locations of the LED point-light-source reflections are determined via image processing, and defects in 3D BGA shapes are detected using statistical information of the relative positions of multiple BGA balls captured in the images. Experiments were conducted to validate our proposed method, and the results revealed that it allows for simultaneous inspection of multiple BGA balls placed arbitrarily in a glass dish, without the need for precise ball-position control.

5층 링 조명에 의한 BGA 볼의 검사 방법

Fast inspection of solder ball bumps in ball grid array (BGA) is an important issue in the flip chip bonding technology. Particularly, semiconductor industry has required faster and more accurate inspection of micron-size solder bumps in flip chip bonding, as the density of balls increase dramatically. In this paper, we describe an inspection approach of BGA balls by using 5-step ring illumination device and normalized cross-correlation (NCC) method. The images of BGA ball by the illumination device show unique and distinguishable characteristic contours by their 3-D shapes, which are called as iso-slope contours. Template images of reference ball samples can be produced artificially by the hybrid reflectance model and 3D data of balls. NCC values between test and template samples are very robust and reliable under well-structured condition. The 200 samples on real wafer are tested and show good practical feasibility of the proposed method.

Could thermal stresses in a BGA/CGA-system be evaluated from a model intended for a homogeneously bonded assembly?

An analytical stress model is developed for the evaluation of thermal stresses in an inhomogeneously bonded assembly of the ball-grid-array (BGA) or column grid array (CGA) type. It is shown that one can get away with employing a simpler model intended for an assembly with a homogeneous bond, if the gaps between the supports (BGA balls or CGA columns) are small, so that the ratio \( \frac{p}{2l} \) of the pitch p (the distance between the joint centers) to the joint widths 2l is below 5, and the product kl of the parameter k of the interfacial shearing stress and half the assembly length l in the equivalent homogeneously bonded assembly is above 2.5. This is indeed the case for actual BGA and CGA systems. This finding can be used also in other areas of engineering, such as, say, mechanical or structural, when there is an intent to simplify the calculations by replacing a model for beams on separate supports by using a model intended for a beam on a continuous elastic foundation.

Reflow Optimization Process: Thermal Stress Using Numerical Analysis and Intermetallic Spallation in Backwards Compatibility Solder Joints

This study applies the reflow optimization process to investigate the phenomenon of spalling in aerospace backward compatibility solder joints when utilized with a Ni substrate [electroless nickel immersion gold, printed circuit board surface finish, and ball grid array (BGA) pads]. The backward compatibility assembly comprised a lead-free tin–silver–copper (96.5Sn3.0Ag0.5Cu/SAC 305 alloy) solder ball assembled with tin–lead paste. The soldering of the lead-free BGA was conducted using two reflow temperature profiles and two conveyor speeds under a nitrogen atmosphere in a full convection reflow oven. The optimized reflow profile has peak temperatures ranging from 237.06 to 237.09°C for 68.94–69.36 s. Scanning electron microscope reveals intermetallic compound formation with maximum thicknesses which are lower than 12 μm as per aerospace requirement. Intermetallic compound spalling of solder ball interface components was not observed. However, spalling between printed circuit board and solder bulk was noted. Nevertheless, at both reflow temperature profiles, the composition and phase distribution of the lead-free BGA ball and tin–lead solder paste were fairly uniform across all joints. This work also presents a finite element-based simulation of backward compatibility assembly in reflow process. A growing number of manufacturers are changing their components to lead-free types without notifying customers. If an aerospace production line is still running a tin–lead-based process, understanding how these lead-free components are processed with tin–lead solder becomes essential. This paper will serve as a reference for manufacturing engineers, particularly those involved in surface mount technology application.

Influence of the Hybrid BGA Residual Stress after Reflow on the Thermal Cycling Reliability

Thermal cycle reliability in Sn3.0Ag0.5Cu lead-free solder joints of ball grid array(BGA) package assembled with eutectic SnPb paste is investigated under the residual stress induced by reflow soldering. According to the mixed BGA package, the finite element model of lead-free and mixed BGA package is established. The residual stress and strain of BGA solder bumps are obtained after loading the different reflow profiles. The peak temperature ranges from 220 ℃ to 265 ℃, while the cooling rate is from 1 ℃/s to 6 ℃/s. The thermal cycling loads are applied on the BGA package model with the 243 ℃ peak temperature and 3 ℃/s cooling rate. The solder joint lifetime is calculated based on the equation of Coffin-Manson. In the reflow analysis, the cooling rate has a greater influence to the residual stress which increases from 27.9 MPa to 32.5 MPa with the cooling rate adding, while the highest temperature in the reflow curve has obvious impact on the residual strain. In the thermal recycle analysis, the most dangerous locationis is the upper-left corner of the BGA ball as the high stress and strain. The prediction life of the hybrid BGA could be compatible to the SnPb solder joints. Compared to the reflow curve load the life prediction among them has almost no difference.

Prognostics Model Development of BGA Assembly Under Vibration Environment

Application of electronic devices on automotive vehicles keeps increasing, and adoption of ball grid array (BGA) package is inevitable in the industry. Vibration loading to a vehicle provides another hazardous stress to the BGA assembly in addition to thermal one. In this paper, random vibration test on a daisy-chained BGA assembly is conducted with a real-time monitoring of resistance. BGA assemblies with leaded and lead-free solders are tested at once in the test. The changes of resistance before the occurrence of failure are investigated and a precursory resistance pattern before the failure of BGA assemblies is identified at the both solder types. Analyses on the failure locations confirm the localized failures on the BGA ball matrix. To investigate the generating mechanism of the precursory resistance pattern in the BGA assemblies, a numerical model of the mechanism is suggested and experimentally demonstrated. Based on the studies, a noble design of BGA assembly is suggested for the implementation of prognostics and health monitoring in vibration environment.

Life cycle assessment of integrated circuit packaging technologies

Background, aim and scope Nanostructured polymer particles are produced to be used in ball grid array (BGA) and chip scale packaging (CSP). The technology could replace conventional BGA and CSP metal balls, and the hypothesis is that the shift could be eco-efficient as polymer core particles increase the reliability. For the first time, these particles are environmentally evaluated.

Effects of multiple BGA rework on strength of solder joints

PurposeThe purpose of this paper is to investigate effects of the multiple rework of ball grid array (BGA) components on mechanical strength of BGA balls, as well as any possible intermetallic (IMC) embrittlement, and obtain data correlated with possible estimation on the maximum permitted limits of BGA rework.Design/methodology/approachIn this paper, mechanical strength of BGA components assemblies with multiple numbers of rework operations was evaluated. Mechanical evaluation was conducted using BGA ball shear tests and four‐point bending tests of BGA assemblies. Test samples were prepared under the following conditions: virgin, one, two, three and five BGA reworks. Failure mechanism was evaluated using cross‐section and SEM analysis.FindingsThe results show that both ball shearing tests and four‐point bending tests indicates that strength of BGA solder ball itself was not reduced significantly after repair/rework operation from one to five cycles. The IMC structure layer after rework is a mixture of IMC, Sn‐rich and Pb‐rich phases. This mixture layers with thickness even more than 10 μm in thickness does not show reduction of strength of BGA solder balls and do not cause premature embrittlement. However, the bonding strength of the copper pads to the laminates is reduced with rework/repair operation, with the great reduction coming from the first and second rework operation.Practical implicationsIn general, the industry recommends two rework cycles for BGA components on the same spot. This study indicates that further rework (up to five) causes little degradation, therefore there is room to increase the total rework cycle limit beyond recommended two for plastic BGA components.Originality/valuePresented test results shows that in most cases industry overestimates risks associated with increased embritlement of the BGA solder joints due to the intermetallics growth after multiple BGA rework operations. Strength reduction of BGA assemblies is mostly associated with reduction of bonding strength of the copper pads to the laminates is reduced with rework/repair operation and number of reworks could be increased in most cases.

Pinout Optimization for 10 Gbps+ Serial Link Routing

Definition and optimization a BGA (ball grid array) package pinout is a complicated process. Multiple factors must be considered, such as chip level floorplan, board placement of the component, the board stackup, escape routability, and signal and power integrity constraints. These tradeoffs and decisions impact package body size and board real estate, therefore overall system cost. At high frequencies, such as >10 Gbps, the BGA to board via transitions cause visible impedance and noise mismatches and becomes a critical factor in the end to end channel design. Determining BGA pin assignments and their PCB transitions must meet the package crosstalk constraints within the required commodity PCB technology manufacturing rules. This paper describes a methodology of extracting 4 differential signal pairs in the board file from BGA ball to its PCB via transitions through BGA pin field into 3D field solver. The extracted geometry is simulated to determine near-end and far-end crosstalk noise levels between a single victim pair and its associated aggressors. Different pin assignment designs will have different number of aggressors to consider. Different routing layers will also produce different signal via stub lengths (specific resonant frequency) and signal via coupling contributing to far-end crosstalk noise. This may require back drilling of differential signal via stubs to minimize this noise. The aggregated crosstalk noise level must be equal to or better than what the package can deliver. Once these design rules are determined, they can be leveraged across all channels running at the same frequency.

Faraday Cage를 이용한 900 MHz RFID 소형 LTCC 패키지 리더 안테나의 설계

본 논문에서 제안된 패키지 안테나는 900 MHz RFID 대역에 적용하기 위하여 미엔더 라인과 단락 핀을 부설하고 LTCC(Low Temperature Cofired Ceramic) 층의 공동 내부에 RFID BGA(Ball Grid Array) 칩을 장착하였다. BGA 칩과 안테나 사이에 발생되는 커플링과 혼신을 감소시키기 위한 격리 특성을 확보하기 위하여 접지면과 비아 펜스를 부설하여 Faraday Cage를 구현하였다. 제안된 안테나는 낮은 주파수 대역에서 패키지 단계의 안테나 구현에 관점을 두었다. 제안된 안테나의 크기는 <TEX>$13mm{\times}9mm{\times}3.51mm$</TEX>이며, 측정된 안테나의 공진 주파수는 0.893 GHz, 임피던스 대역폭은 9 MHz, 최대 방사 이득은 -2.36 dBi를 나타내었다. In this paper, the proposed package antenna, which is meander line structure with short pin, is miniaturized to realize RF-SoP at 900 MHz RFID band. The RFID BGA(Ball Grid Array) chip is put in a cavity of LTCC Layers. The coupling and cross talk, which are happen between BGA chip and proposed package antenna, are reduced by faraday cage, which consists of ground and via fences, is realized to enhance the isolation between BGA chip and antenna. The proposed antenna structure is focused on the package level antenna realization at low frequency band. The novel proposed package antenna size is <TEX>$13mm{\times}9mm{\times}3.51mm$</TEX>. The measured resonance frequency is 0.893 GHz. The impedance bandwidth is 9 MHz. The maximum gain of radiation pattern is -2.36 dBi.

Reliability Investigation of Mixed BGA Assemblies

The effect of different reflow profiles on the reliability of lead-free (LF) Sn-3.0 Ag-0.5 Cu (wt.%) (SAC 305) ball grid array (BGA) devices assembled with a SnPb eutectic paste was investigated. The memory modules in a back-to-back configuration were reflowed on standard graphic cards finished with immersion silver (IAg) or hot air solder leveling (HASL) coatings. The reflow peak temperatures ranged from 209 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C to 227 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C, while the time above liquidus (TAL) varied from 45 to 80 s. Depending on the reflow conditions, the solder interconnects displayed varied degrees of SnPb and LF solders intermixing. It was established that in order to receive a homogeneous solder alloy, the reflow peak temperature had to be in the 218 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C–222 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C range. The reliability of solder interconnects of memory modules was assessed by subjecting the cards to 1500 cycles of accelerated thermal-cycling with a profile from 0 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C to 100 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$^circ$</tex> C. It was found that the control SnPb/SnPb assemblies displayed superior reliability to that of the mixed assemblies. Regardless of the degree of homogeneity of the BGA balls, the predominant failure mode of the mixed solder joints was interfacial cracking through a Pb-rich phase near the intermetallic layer. In contrast, only partial cracks propagating diagonally through the bulk solder were present on the control boards. It was concluded that a combination of state of stress and segregation of the Pb-rich phase at the interface was responsible for the shortened thermal–mechanical fatigue life of the mixed solder interconnects.

Lead-free ball-grid array balls: Production method and properties

Production method and properties of lead-free ball-grid array (BGA) balls in comparison to standard BGA balls with the eutectic Sn-Pb composition are presented. Lead-free BGA balls can also be produced by an innovative process that allows the production of solder balls directly from the melt. In contrast to Sn-Pb solder balls, the surface of lead-free balls is not perfectly shiny but appears partly rough. This is caused by a different solidification behavior. The stability of Sn-based solder balls against darkening caused by oxidation effects during movement is far more pronounced than for Sn-Pb balls. The patent situation concerning Sn-based soft solders is not critical any more because of an existing “older” patent that covers comparable alloy types.

A Novel Frequency-Shift Moir&amp;eacute; Fringe Method for 3D Inspection of BGA Packaging

BGA (ball-grid array) is an advanced electronic packaging technology that has increasingly become more important and demanding in microelectronic industry. However, no effective technique is available to inspect the performances of the welding points and its co-planarity. The moire fringe method is often employed to measure the three-dimensional (3D) shape of the welding spot on BGA, and a high-resolution CCD camera is utilised to capture the deformation stripe image. In order to gain high measuring accuracy, a frequency-shift moire fringe technique is proposed in this paper, in which three light-sources are deployed to create the fringe. The system parameters are designed to ensure the BGA ball height within exactly one grade moire fringe. By using zero-maximum equation transformation, the measuring range can be segregated into eight subsets. Equal-step interpolation and indexed table approaches are also introduced to greatly improve the measurement speed, so it may be useful for industrial on-line application. Finally, the predicted results based on the simulated images are presented, demonstrating that its measuring accuracy can be achieved to 5 micron.