NWSA Journal

Lists the reviewers who have contributed to IEEE Transactions on Components and Packaging Technologies during the period of October 2009 through October 2010.

Misra P., Nagaraju J.

This paper describes the electrical contact resistance (ECR) measurements made on thin gold plated (gold plating of ≤ 0.5 μm with a Ni underlayer of ~2 μm) oxygen free high conductivity (OFHC) Cu contacts in vacuum environment. ECR in gold plated OFHC Cu contacts is found to be slightly higher than that in bare OFHC Cu contacts. Even though gold is a softer material than copper, the relatively high ECR values observed in gold plated contacts are mainly due to the higher hardness and electrical resistivity of the underlying Ni layer. It is well known that ECR is directly related to plating factor, which increases with increasing coating thickness when the electrical resistivity of coating material is more than that of substrate. Surprisingly, in the present case it is found that the ECR decreases with increasing gold layer thickness on OFHC Cu substrate (gold has higher electrical resistivity than OFHC Cu). It is analytically demonstrated from the topography and microhardness measurements results that this peculiar behavior is associated with thin gold platings, where the changes in surface roughness and microhardness with increasing layer thickness overshadow the effect of plating factor on ECR.

This index covers all technical items - papers, correspondence, reviews, etc. - that appeared in this periodical during the year, and items from previous years that were commented upon or corrected in this year. Departments and other items may also be covered if they have been judged to have archival value. The Author Index contains the primary entry for each item, listed under the first author's name. The primary entry includes the coauthors' names, the title of the paper or other item, and its location, specified by the publication abbreviation, year, month, and inclusive pagination. The Subject Index contains entries describing the item under all appropriate subject headings, plus the first author's name, the publication abbreviation, month, and year, and inclusive pages. Note that the item title is found only under the primary entry in the Author Index.

Yan B., You J.P., Tran N.T., He Y., Shi F.

In this paper, the influence of the die attach adhesive (DAA) layer on the thermal performance of high power light emitting diodes was first investigated by using finite element analysis, and some key results were verified by the experimental data. Effective thermal management of the studied light emitting diode package can be achieved by selecting a DAA material with a proper thermal conductivity and by manipulating the geometry parameters of the DAA layer, such as the DAA area, and the bond-line thickness. The significance of DAA thermal conductivity to heat dissipation was further demonstrated by an analysis of the bottleneck to heat transfer.

Arik M., Sharma R., Jackson J., Prabhakaran S., Seeley C., Utturkar Y., Weaver S., Kuenzler G., Han B.

Light-emitting diode (LED)-based solid-state lighting (SSL) products have been exceeding the predicted performances especially at the chip and package levels. This has led to new SSL-based products for energy savings and long lifetimes. Large amounts of government funding and private investments have been made during the last decade to accelerate and guide the technology. This paper focuses on the development of an LED-based high-lumen luminaire technology. The critical subcomponents of the luminaire are the LED light engine (LED chips and optical system), thermal management, and driver electronics. Each of these subcomponents will be discussed in detail for a 100 W incandescent replacement technology. The paper addresses system integration of each of the subcomponents. While the design of new products evolve, the lack of reliability data poses a risk of premature failure of LED-based products. Premature failures would trigger customer rejection and may delay market penetration. Therefore, luminaire reliability is an important aspect of luminaire design. In cohort with this notion, finally, the luminaire reliability has been discussed.

Chang C., Liang N., Chen S.

This paper experimentally investigated the thermal performance of a miniature vapor compressor refrigeration system using a thermal resistance model for electronic cooling. The evaporator, compressor, expansion valve, and condenser are the four main devices forming the refrigeration system with R-134a as a working fluid. The experimental parameters considered were the openings of the expansion valve and input heating power. The results indicated that the system in this paper had the largest cooling capacity of 150 W and coefficient of performance of 4.25 at the 8th and 9th openings of the expansion valve, respectively. The results also showed that correlations of the thermal resistance of the evaporator and the condenser are developed with experimental data and their precision, compared with the experimental data, was about 4.42% and 12%, respectively. Besides the adjustment of the compressor speed could decrease the possibility of the occurrence of condensation phenomena near the inlet and outlet of the evaporator. Also, the smallest dimension of the combination of the evaporator and condenser is presented at the input heating power of 150 W and the 8th opening of the expansion valve.

Christiaens W., Bosman E., Vanfleteren J.

Flexible materials, today, are being used already as base substrates for electronic assembly. A lot of mounted components could be integrated in flexible polyimide (PI) substrates. Very interesting advantages of integrating components into the flex are compactness and enhanced flexibility; not only the interconnection but also the components themselves can be mechanically flexible. This paper describes a PI-based embedding technology for integrating very thin silicon chips in between two spin-on PI layers, the ultra-thin chip package (UTCP). This paper discusses the different process steps in the UTCP production and also presents the interconnection test results realized with this technology.

Liu Z., Liu S., Wang K., Luo X.

Effects of variations of yttrium aluminum garnet:Ce phosphor thickness and concentration on optical consistency of produced white light-emitting diodes (LEDs) including the consistency of brightness and light colors were studied by optical simulation. Five packaging methods with different phosphor locations were compared. Optical models of LED chip and the phosphor were presented and a Monte Carlo ray-tracing simulation procedure was developed. Both color binning and brightness level were used to sort the simulated LEDs to evaluate their optical consistency. Results revealed that the optical consistency of white LEDs strongly depends on how the phosphor thickness and the concentration vary. To obtain desired color binning, conformal phosphor coating is not a favorable packaging method due to its low brightness level and poor brightness consistency by large shifts of the brightness level as the phosphor thickness and concentration varying. Planar remoter phosphor improves the brightness level and its consistency, but realization of high color consistency becomes more difficult due to its smaller variation ranges of the phosphor thickness and concentration. Hemispherical remoter phosphor can fulfill the requirements of both high color consistency and high brightness consistency due to its capability of larger variation ranges of the phosphor thickness and concentration. By applying this method with thick phosphor thickness or high phosphor concentration, this method can be a promising packaging method for the low cost production.

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Lu S., Chen W.

Future applications of flexible displays and wearable electronics will need 3-D stacked flexible interconnects. The interconnection of an ultrathin chip-on-flex (UTCOF) that can provide flexibility is one approach that meets this requirement. Therefore, thermally induced warpage of UTCOF interconnects using anisotropic conductive adhesive (ACA) is investigated. In this paper, the effects of the ACA joint material properties, bonding temperature, and chip thickness on warpage of ACA-bonded UTCOF interconnects are examined experimentally and numerically. Two film types of ACA materials, ACA-P and ACA-F, are assembled under different bonding temperatures to study the effects of bonding temperature on warpage via out-of-plane deformation measurements using a micro figure measurement instrument. Micro Au-bump and compliant-bump assemblies in 80-μm-pitch dummy test vehicles are evaluated. Moreover, ultrathin chips with 25-50 μm thickness were assembled onto polyimide flex substrates to study the effects of chip thickness on thermally induced warpage. The 85°C/85% relative humidity thermal humidity storage test (RH THST) was also conducted for 1000 h for the UTCOF assembled with the selected process parameters. The interfaces between the ultrathin silicon chip and substrate are inspected in cross-sectional scanning electron microscopy (SEM) images. To validate the results of the experiments, a rigorous 3-D finite element (FE) analysis model integrating both thermal and thermal-mechanical behaviors of the UTCOF is established and performed using the ANSYS program. Experimental and numerical results indicate that the warpage of the micro compliant-bump assembly is less than that of the micro Au bump. Furthermore, the averaged warpage of the ACA-P-bonded samples with the Au bump using a 50- μm-thick chip is around 50.3 μm at a bonding temperature of 160°C whereas that of the ACA-F-bonded samples is 64.4 μm at 190°C. Additionally, both thermal expansion mismatch and the thermal gradient between the ultrathin silicon chip and substrate strongly affect the thermal-mechanical behaviors of the UTCOF interconnects. As expected, warpage increases as thickness of an ultrathin silicon chip decreases. A strong correlation exists between FE analysis results and experimental results. The manufacturing technology for high-density and flexible UTCOF interconnects with ACA joints is thus established.

Ming-Yi Tsai, Chun-Hung Chen, Wan-Lin Tsai

The light emitting diode (LED) packaging problems associated with high cost, high junction temperature, low luminous efficiency, and low reliability have to be resolved before the LED gaining more market acceptance. In this paper, chip-on-plate (CoP) LED packages with and without phosphors are evaluated in terms of thermal resistance and reliability under wet and high-temperature operation life (WHTOL) and thermal shock tests. The WHTOL test is with the condition of 85°C/85%RH and 350 mA of forward current for 1008 h, while thermal shock test is with 200 cycles at temperature ranging from -40°C to 125°C. The thermal behavior of the CoP packages was analyzed by 1-D thermal resistance circuit (1-D TRC) with and without spreading angle, 3-D TRC method, and 2-D axisymmetric finite element method. The feasibility of these analyses was evaluated and discussed in detail by comparing those results with experimental measurements. The reliability results indicated that all CoP packages with phosphors in the silicone encapsulant failed after 309 h in the WHTOL test, but all those without phosphors still survived after 1008 h. The failure modes were found to be the debonding of the aluminum wire from the chip or copper pad of the substrate. However, after the aluminum wire was replaced by gold wire, all the packages with and without phosphors passed after 1008 h. For these survival packages in the WHTOL test, their thermal resistances of junction-to-air and junction-to-aluminum substrate increased by about 12 and 9°C/W, respectively. Moreover, it was also found that there is a difference of 38°C/W in the junction-to-air thermal resistances for the packages between under natural and forced convections in the chamber during the WHTOL test. This might yield the different reliability data, unless the flow conditions in the test chamber are specified in this standard test. Furthermore, all the packages with and without phosphors could pass 200 cycles in thermal shock test, with minor changes in the thermal resistances. However, the degradation of luminous flux in the packages with phosphors was found to be greater than those without phosphors by 14% vs. 9%.

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Kuramot M., Ogawa S., Niwa M., Kim K., Suganuma K.

Die-bonding for a nitride light-emitting diode (LED) by sintering of micrometer size Ag particles in air at 200°C was investigated. Micrometer size Ag particles absorb oxygen remarkably well at 200°C and above, and on sintering, they form a porous layer. The activating temperature of the sintering is in good agreement with the oxygen adsorption temperature. Sintering does not progress in the absence of oxygen. A reduction of thermal resistance and an improvement of reliability are achieved by the sintered layer as a die attach to a surface-mount-type LED. This mounting method is useful in the die bonding of electronic components, and is an alternative technique to high-temperature lead soldering.

Lin Y., You J.P., Lin Y., Tran N.T., Shi F.G.

Silicone materials with a relatively high-refractive index have been introduced for the encapsulation of high-power light-emitting diodes (LEDs), and LEDs with relatively short wavelengths. However, most of those existing silicone encapsulants still suffer from thermal and radiation induced degradations and thus lead to reliability issues and a shorten lifetime. A new high-performance silicone has been developed and its performance is compared with other commercial silicone and optical grade epoxy in high-power white LEDs. The new materials had been found to suffer less loss in the lumen output during the aging test and high-temperature/high-humidity test, as well as the Joint Electron Devices Engineering Council (JEDEC) reliability test. It is concluded that this material is excellent for the packaging of high-power white LEDs and high-power colored LEDs, because of its ability in maintaining high-transparency and great radiation/thermal resistance.