热膨胀系数不匹配导致的塑封器件失效

塑封器件使用过程中由于塑封材料和芯片之间热膨胀系数的不匹配,导致在外界温度变化时的应力释放对芯片造成损伤。文中通过VLSI失效分析,对这种应力造成的芯片损伤进行了研究,并提出利用环境应力试验和可靠性分析的方法暴露热膨胀系数不匹配导致芯片损伤的技术。     

Demonstrated reliability of plastic-encapsulated microcircuits formissile applications

For the past decade, overall reliability improvement and product availability have enabled plastic encapsulated microcircuits (PEM) to move from consumer electronics beyond the relatively large and reliability-conscious automotive market, into the military market. Based on the analysis of the worst-case PEM scenario for military applications, demonstrating the moisture reliability under long-term (20 years) dormant storage environments has become the last hurdle for PEM. Studies have demonstrated that PEM can meet the typical missile environments in long-term storage. To further validate PEM reliability in missile applications, Texas Instruments (TI) conducted three separate studies involving 6 years of PEM moisture-life monitoring and assessment, testing of the standard PEM electrical characteristics under the military temperature ranges (-55°C to +125°C), and assessing their robustness in moisture environments after the assembly processes. These TI studies support the use of PEM in missile (or similar) applications. Effective focus on part and supplier selection, supplier teaming, and process monitoring is necessary to maintain the PEM reliability over the required environments at the lowest cost. This paper assesses PEM reliability for a selected missile storage environment using the industry-standard moisture testing, such as biased HAST or 85°C/85%RH (relative humidity), for demonstrating the PEM moisture survivability. The moisture reliability (MTTF) or average moisture lifetime of PEM is assessed to correlate PEM capability to anticipated field-performance environments     

Qualification of plastic encapsulated microcircuits (PEM) for avionicsBased on ``Plastic Encapsulated Microcircuits (PEM) Qualification Testing'''', by J. A. Scalise, which appeared in the Proceedings of the 46th Electronic Components and Technology Conference, Orlando, FL, U.S.A., 28–31 May 1996, pp. 392–397. © 1996 IEEE.

Microcircuit package qualification testing is used to establish the reliability of integrated circuit processes and devices as they relate to part packaging. This paper presents the results of package qualification tests conducted on plastic encapsulated microcircuits (PEMs) and plastic discrete devices (diodes, transistors) used in avionics applications. Highly accelerated stress test (HAST) and temperature cycle (TC) test results, including part failure mechanisms and associated failure rates, are provided. A variety of plastic package styles and integrated circuit functions have been tested. Examples of package styles tested include small outline (SO), plastic leaded chip carrier (PLCC), thin small outline package (TSOP), plastic quad flat package (PQFP) and plastic dual-in-line (PDIP).Manufacturers' devices have been evaluated and various plastic compounds have been compared to determine which provide optimum reliability. The testing showed that package qualification performance of PEMs is affected by type of compound, passivation (including die coat) and die size. HAST failures are caused by moisture penetration of the package while temperature cycle failures result from coefficient of thermal expansion (CTE) mismatch effects.     

塑封器件失效机理及其快速评估技术研究

针对影响塑封器件可靠性的五种失效机理,即腐蚀失效、爆米花效应、低温/温冲失效、闩锁以及工艺缺陷等方面进行分析和讨论,并提出利用高温潮热和温度冲击试验对塑封器件的可靠性进行评估.还介绍了美国航天局Goddard空间飞行中心提出的对塑封器件进行高可靠性筛选的方案.     

Reliability comparisons for plastic-encapsulated microcircuits

This paper briefly compares reliability test data obtained from plastic encapsulated microcircuits (PEM) purchased from various manufacturers. Tests include biased humidity, temperature cycling, autoclave, and life tests. The results indicate differences in reliability associated with PEM from the various manufacturers. These data highlight the need for a thorough understanding of supplier quality and reliability     

Degradation of adhesion between Cu and epoxy-based dielectric during exposure to hot humid environments

Degradation of adhesion between Cu and epoxy-based dielectric build-up film (EDF), which is used for fan-out wafer level packaging applications, was investigated by the reliability test. The samples were composed of four layers: epoxy molding compound substrate, laminated EDF, electroless Cu, and electrolytic Cu. Adhesion was evaluated by the 90° peel test before and after the temperature and humidity (T&H) test and the highly accelerated temperature and humidity stress test (HAST). The effects of the peel strip width and humidity exposure of the peeled edges on adhesion were determined. It was found that adhesion gradually decreased during the reliability tests. The adhesion reduction mechanism was explained by the combinatorial effect of the loss in chemical bonding and the degradation of mechanical interlocking due to moisture. A black strip was observed along the edges of the peeled Cu strips (herein referred to as the black band, BB). AES revealed the BB as the superficial oxidation of the Cu strip. HAST and the T&H test showed the effect of the BB in an additional adhesion loss. SEM revealed a local cohesive fracture of the polymer, which led to an additional loss due to an early failure of the degraded polymer. Furthermore, BB growth showed a linear correlation with the square root of time and was accompanied with adhesion reduction. Since the modern packages have micro-sized Cu lines, the formation of BB should be avoided for better reliability of devices.     

Compound semiconductor activation energy in humidity

Product reliability investigations typically include accelerated humidity testing. Originally, the “standard” test was a biased 85 °C/85% relative humidity (RH) lifetest for 1000 h. Recently, a substitute accelerated version of this test has been used. The accelerated version is called highly accelerated stress test (HAST). The HAST conditions are also biased, at 130 °C, 85%RH, and approximately 18 PSI overpressure. The duration of the HAST test is normally 96–100 h – to be equivalent to the 85/85 test. This study is intended to investigate thermal acceleration and show that equivalent HAST tests on compound semiconductors are more highly accelerated and could be conducted with much shorter durations.     

Plastic encapsulated microcircuit reliability predicition: why?

Reliability prediction models for microcircuits have been a function of steady-state temperature. Failure rates generated from accelerated temperature tests were extrapolated to predict system reliability at system use temperatures. This is now known to be completely inaccurate. Attempts are now being made to predict the reliability of plastic encapsulated microcircuits (PEMs) based on accelerated temperature/humidity testing. Failure rates generated due to corrosion failure mechanisms at these high stress levels are then extrapolated and used to predict system reliability at used temperature/humidity conditions.This paper discusses the fallacy of this approach. A new concept for the assurance of PEM corrosion resistance is proposed. It will be shown that today's best commercial practice suppliers have already addressed the design, materials, and processing issues of molded packaged microcircuits, and corrosion is no longer a mechanism of concern to the user.     

Influence of underfill materials on the reliability of coreless flip chip package

A flip chip package was assembled by using 6-layer laminated polyimide coreless substrate, eutectic Sn37Pb solder bump, two kinds of underfill materials and Sn_3.0Ag_0.5Cu solder balls. Regarding to the yield, the peripheral solder joints were often found not to connect with the substrate due to the warpage at high temperature, modification of reflow profile was benefit to improve this issue. All the samples passed the moisture sensitive level test with a peak temperature of 260 °C and no delamination at the interface of underfill and substrate was found. In order to know the reliability of coreless flip chip package, five test items including temperature cycle test (TCT), thermal shock test (TST), highly accelerated stress test (HAST), high temperature storage test (HTST) and thermal humidity storage test (THST) were done. Both of the two underfill materials could make the samples pass the HTST and THST, however, in the case of TCT, TST and HAST, the reliability of coreless flip chip package was dominated by underfill material. A higher Young’s modules of underfill, the more die crack failures were found. Choosing a correct underfill material was the key factor for volume production of coreless flip chip package.     

Evaluation of standard plastic integrated circuits reliability after accelerated sequential testing

We present here in this paper main results obtained during the first phase of a work plan which aim is to allow the use of plastic encapsulated devices (PED’S) in some military equipments. This phase (called feasibility) was conducted in order to evaluate the risk an equip-ment maker takes when using standard PED’S. TO do that a large number OF PED’S (about 1000) were characterized. Main features of performed tests are that they were se-quential file of tests and better suited to assessment of PED’S reliability. Moreover one file included an extremely severe damp heat test, at high temperature and high hu-midity, called HAST. Results we get show a large disparity in PED’S behaviour under rugged environments. Fine fail-ure analysis have shown what are major defect modes and indicated that classical corrosion is not the only failure mechanism which occurs at high temperature and high humidity conditions. Failure rate derived from these results can be compared favourably with those computed following reliability prediction models.     

Automatically Controlled 2-Vessel Pressure-Cooker Test-Equipment

A highly accelerated humidity test for plastic encapsulated IC reliability short-term evaluation has been studied. 2-Vessel pressure cooker test (PCT) equipment capable of controlling relative humidity and temperature independently, and of keeping specimens free from water droplet condensation, has been designed. This equipment consists of a test chamber and a vapor chamber. Humidity conditions are set by controlling the temperature difference between the test chamber and the vapor chamber. Humidity levels are controlled with the direct pressure adjustment. The whole test chamber is heated in an oven, thereby obtaining temperature stability and uniformity. Using this equipment, humidity tests were carried out on plastic molded ICs. As a result, good test reproducibility and excellent correlation in test results between PCT and conventional humidity test such as 85°C/85%RH, were obtained. As a consequence, it was found possible, in a short time, to evaluate plastic molded IC reliability quantitatively in humidity ambients using this 2-vessel PCT equipment. This equipment can be used for quality assurance testing of plastic-encapsulated ICs in a short time.     

Plastic-encapsulated microcircuit reliability andcost-effectiveness study

This study evaluates the reliability and cost-effectiveness of using commercial plastic-encapsulated microcircuits (PEM) in a typical military system, with a view to increasing their acceptability in military applications. The cost comparison indicates an average 6-fold decrease in cost when commercial devices are used. Assurance testing did not reveal any special problems with commercial parts. Thus, if commercial PEM were proven to be sufficiently reliable for an intended military application, large cost savings would be gained by using them instead of hermetic packages. The 4.5 sigma enhanced inspection program and the process-control methods suggested here would enhance the manufacturing yield of the PLGR (precision lightweight global positioning system receiver) by encouraging improvements in the manufacturing process while simultaneously cutting the cost of a 100% rescreen to qualify the final product. Neither the requirements assurance tests (including the step-stress test-analyze-and-fix test), nor the reliability demonstration test, nor the operational test, showed more failures than are typical for any new development, and no problems unique to PEM were observed. Thus, the use of PEM did not lead to any special problems that caused PLGR-use specifications to be violated. Complete failure analysis of the isolated parts is in progress, and the results will help to understand the specific reliability issues involved with the use of PEM in military systems. These issues can then be addressed to improve the acceptability of such devices in future military applications     

智能手机用薄印制电路板技术与可靠性考虑

下一代智能手机为进一步减少其产品厚度,将需要非常薄的多层印制板。文章叙述了薄的任意层积层HDI板之三种不同的制造方法,对用这三种不同方法制造的测试样板进行相关可靠性测试,以确认制造高端智能手机用PCB技术的有效性。三种试验板均为八层积层板,整体厚度小于0.5mm。进行了再流焊试验、高低温循环试验、高加速应力试验,比较它们的可靠性优劣。     

A plastic LCD design with high reliability and color-free readability

A new design has been developed for a plastic substrate twisted nematic LCD. The design results in color-free optical performance and high reliability as measured by accelerated life tests at high temperature and humidity. The crystalline nature of most chemically stable plastics has a biaxial birefringence which can produce dramatic interface colors in the twisted nematic geometry. Optically isotropic plastics are generally amorphous and, therefore, chemically incompatible with the liquid crystal which is a good organic solvent. This dichotomy has been solved by using a special form of polyester whose optic axes are controlled to lie at an angle from the normal which is considerably larger than the largest angle which can be reached by light entering the high index plastic. A fabrication process was developed to be consistent with the 150°C glass transition temperature for the polyester as opposed to the 500°C transition temperature of typical LCD glass substrates. Display materials were designed to be water tolerant, since all plastics transmit water. It was established on a laboratory scale that a plastic LCD design will pass consumer type reliability criteria for high-temperature and humidity stresses. Displays as large as 50 in²were fabricated and preliminary operational tests were encouraging. The plastic LCD process has been shown to be a technologically feasible manufacturing method and may hold promise for significant cost reduction over glass technology.     

Lifetime acceleration model for HAST tests of a pHEMT process

We report the results of DC biased life tests performed on gallium arsenide pseudomorphic high electron mobility transistor (GaAs pHEMT) switches under elevated temperature and humidity conditions. The goal of this work was to determine whether the acceleration factors typically reported for silicon technologies are also appropriate for GaAs technologies. Toward that end we performed tests at three different temperatures and two different humidity conditions. Failure distributions were generated for each life test, and the results applied to an acceleration model commonly used for HAST. We determined the activation energy for the failures observed during these tests to be 0.81 eV; similar to values commonly reported for HAST tests of silicon technologies. In contrast, our results show significantly stronger stress acceleration due to relative humidity (RH^−10.7) than is typically reported for silicon (RH^−3.0). Examples of typical visual and electrical device failure signatures are shown.     

A Reliability Evaluation of Plastic Packaged Semiconductor Components

Qualification testing programs have been developed for assessing the reliability of commercial grade discrete semiconductors for use in office business machines. These programs include accelerated stresses of high temperature storage (HTS) and high temperature reverse bias (HTRB) for 1000 hours, and a sequence test of thermal cycle and thermal shock followed by storage at 85°C and 85% RH (85/85) for 1000 hours. Both hermetic and plastic encapsulated parts have been tested more than 15 million part hours. HTRB and 85/85 are about twice as effective as HTS in identifying potentially unreliable parts. Plastic packaged semiconductors are inherently capable of withstanding 85/85 for 1000 hours without parameter degradation. The value of qualification testing against the 85/85 environment is demonstrated by the observed correlation of machine failure rates in the field with the relative humidity in the use environment. The observed failure rate of plastic parts is not more than 3.2 times that of hermetic parts. Plastic parts are capable of reliable operation, but the marked differences in reliability between different vendors and between different part types from the same vendor require increased process and materials control in order to achieve the potential of which plastic parts are capable.     

Accelerated life test of high power white light emitting diodes based on package failure mechanisms

Accelerated life tests of high-power white light emitting diodes (LEDs) were conducted under an unbiased highly accelerated temperature and humidity test (HAST) and a normal aging test. The conditions in the unbiased HAST were 110 °C-85% RH, 130 °C-85% RH without bias. During the aging, the degradation mechanisms of optical power reduction and degradation of 455 mm blue wavelengths that were better than phosphors related yellow emission bands were observed. The microscopy analysis showed that this effect could be ascribed to the bubbling and discoloration of the silicone encapsulating material of the package. It is thought that these features are also responsible for the optical power reduction and thermal resistance increase.     

应用PDCA实现湿度敏感器件的有效控制

伴随信息技术快速发展与电子产品的普及和应用,电子产品的使用寿命和可靠性越来越成为人们关注的焦点。在电子产品的制造过程中,ESD(静电放电)和MSD(湿度敏感器件)成了威胁电子产品质量的两大重要因素,直接影响产品测试的直通率和产品的可靠性。MSD器件的失效像ESD破坏一样,具有一定的隐蔽性。MSD失效在测试过程中,也不一定会表现为完全失效。在各种诱发器件失效的机制中,MSD失效在电子制造过程中占据相当高的比例。在审核多家SMT工厂过程中发现,MSD的控制远比ESD的防护要薄弱。文章从工作实践出发,探讨应用PDCA全面质量管理的思路来实现电子产品制造过程中湿度敏感器件的有效控制。     

A review on discoloration and high accelerated testing of optical materials in LED based-products

Reduction of intensity of light output is one of the most common degradation modes in light-emitting diode (LED) systems. It starts from the failure of the various components in the system, including the chip, the driver, and optical components (i.e. phosphorous layer). The kinetics of degradation in real life applications is relatively slow and in most cases it takes several years to see an obvious deterioration of optical properties. Highly Accelerated Stress Testing (HAST) set-up and a methodology to extrapolate the results to real time applications are therefore needed to test the reliability of LED packages and lens materials. Using HAST concept in LED industry is inevitable due to the necessity of assessing the reliability of new products in a short period of time. This paper aims at briefly clarifying the degradation mechanisms of optical components in LED packages and explaining how they contribute to the depreciation of light output of the LED systems. The concept of HAST and the way the reliability of LED packages can be evaluated will also be discussed.     

Influence of bias humidity testing and application on time-dependent,Arrhenius-law-based stability predictions for thin film resistors

The time dependence of the drift phenomena in thin film resistors has been shown in a previous paper, which described the conditions in a “dry heat” environment. However, the conditions when using electronic equipment in areas of the world or applications with high relative humidity are still a challenge for component reliability. Therefore, industry standard AEC-Q200 requirements include the biased humidity test 85 °C/85% RH for passive components as well. Qualified thin film resistors are designed with an appropriate stable R-layer and electro-isolation lacquer systems that are capable of passing the 85/85 test.The following questions arise:

• (1)What does passing the 1000 h biased 85/85 test mean for real world applications of thin film resistors?
• (2)Is it possible to predict the worst case drifts of resistors under load and environmental conditions over the time of use from the 85/85 or HAST data?

To answer these and other test-related questions, an experimental long-time comparison study was made at 40 °C/93% RH and 85 °C/85% RH; the usual standard tests. These were extended to 4000 h at approximately 0.5% and 10% of maximum specified operating power using our most sensitive thin film resistive layer systems. In addition to that, tests at 70 °C/90% RH, 90 °C/40% RH, and HAST130 were performed, enabling a check of the linearity of temperature, humidity, and voltage influence on drift.This paper will show the results of this comparison study, whose data points enabled us to give answers about acceleration factors of applied temperatures and voltages. The results will be compared with available prognosis models. These findings are the basis for the formulation of a new general model covering all aging conditions in the whole temperature–humidity–time expanse, system characterization, and components’ health prognosis.