Moisture induced epoxy swelling is a potential failure mechanism in nonhermetic packages. Epoxy materials used in the package absorb moisture and swell in a relatively humid environment. This will result in hygroscopic stresses in the material that can eventually lead to failure. The coefficient of hygroscopic swelling (CHS) is a material property that characterizes moisture induced swelling in the material. It is defined as the ratio of hygroscopic strain to the moisture concentration in the material. Prior research investigated the measurement of CHS experimentally using techniques such as thermo mechanical analysis (TMA) (Ardebili et al., 2003, “Hygroscopic Swelling and Sorption Characteristics of Epoxy Molding Compounds Used in Electronic Packaging,” IEEE Trans. Compon. Packag. Technol., 26(1), pp. 206–214; Mckague et al., 1978, “Swelling and Glass Transition Relations for epoxy Matrix Material in Humid Environments,” J. Appl. Polym. Sci., 22, pp. 1643–1654.), Moiré interferometry (Han et al., 2003, “Measurement of the Hygroscopic Swelling Coefficient in Mold Compounds Using Moire Interferometer Experimental Techniques,” IEEE Trans. Compon. Packag. Technol., 27(4), pp. 40–44), and digital image correlation (DIC) (Park and Zhang, 2007, “Investigation of Hygroscopic swelling of Polymers in Freezing Temperature,” ASME International Mechanical Engineering Congress and Exposition). Some of these studies recommended investigation of improved measurement techniques, while others made some procedural assumptions that may not be applicable for all materials. One of the goals of this study was to investigate an improved technique for CHS measurement and helps to better understand the various factors that affect the measurement. The DIC technique was used to measure the moisture swelling of the epoxy material considered for use in the package. Moisture loss during the measurement results in a change in moisture concentration in the sample. While it may be thought that the moisture loss during the DIC scan can be assumed negligible due to the short test time compared with other methods, this assumption did not hold well for the current epoxy material. The ramp rate chosen for the test affects the moisture loss. It introduces a level of nonuniformity in temperature and moisture distribution in the sample. A suitable value that takes into account both of these effects was determined. The moisture loss measured during the DIC scan was accounted for in the CHS computation. In addition to this, the temperature and concentration dependence of the CHS was determined. Results indicated that the temperature and concentration effects are small for the current test material within the test temperature range. The moisture loss found during the DIC measurement leads to a nonuniform moisture distribution in the sample. This was characterized by using experimental and computational methods and the effect on the measurement was determined.
This paper is a summary of a literature survey done on nonhermetic optoelectronic packages focusing on the cost and reliability aspects. The development of reliable non-hermetic lasers would not only lead to the elimination of the costs specifically associated with hermetic packaging but also lead the way for possible revolutionary low-cost optoelectronic packaging technologies. The paper starts with an introduction to the concept of hermeticity in optoelectronic packages, followed by a detailed review of the reliability issues and failure mechanisms observed in non-hermetic packages when compared to their hermetic counter parts. A hermetic seal in electronic packages is used to prevent the entry of air, foreign gases, contaminants, and most importantly moisture. To seal a package hermetically is particularly challenging and expensive. There are various techniques that have been investigated, to improve the reliability of non-hermetic packages. A few are discussed here such as facet passivation type, choosing a better optical glass and encapsulation techniques. Also accelerated testing is discussed. Some of the most common and important failure mechanisms like popcorn failure, adhesive degradation, laser misalignment and epoxy swelling are discussed.
This paper presents a performance study done on a semiconductor laser diode in a moisture condensing environment. Devices with laser diodes are used in a wide variety of electronic applications and in the various climatic conditions. The motivation behind this study is a common environmental exposure, where a device using a laser diode is brought into a relatively humid building from a dry, cold, outside environments. Under such conditions, condensation occurs on various components of the device, including the diode, which could affect the laser output power. Device performance could be affected since the laser diode and the lens are susceptible to degradation due to such repetitive condensation conditions. The test vehicle chosen for this study was an optoelectronic package using a 980 nm laser diode. These are used in products for a broad range of markets, including data communications, aerospace, material processing, scientific, and defense industries [Pliska et al., "Wavelength Stabilized 980nm Uncooled Pump Laser Modules for Erbium-Doped Fiber Amplifiers," Opt. Lasers Eng., 43, pp. 271–289; Righetti, 1996, “Amplifiers Pumped at 980 nm in Submarine Applications,” European Conference on Optical Communication, Vol. 3, pp. 75–80; Pfeiffer et al., 2002, "Reliability of 980 nm Pump Lasers for Submarine, Long-haul Terrestrial, and Low Cost Metro Applications," Optical Fiber Communication Conference and Exhibit, pp. 483–484]. These products may be used in environmental conditions that could result in condensation within the product. A hermetic package could address this concern, but it is an expensive option. Nonhermetic packaging for the laser component could help to lower the cost of these devices; however, these packages have important failure mechanisms that are a potential concern. Prior research reported performance studies conducted on similar packages at elevated temperature, humidity, and power conditions using accelerated tests [Pfeiffer et al., 2002, "Reliability of 980 nm Pump Lasers for Submarine, Long-haul Terrestrial, and Low Cost Metro Applications," Optical Fiber Communication Conference and Exhibit, pp. 483–484; Park and Shin, 2004, “Package Induced Catastrophic Mirror Damage of 980nm GaAs High Power Laser,” Mater. Chem. Phys., 88(2-3), pp. 410–416; Fukuda et al., 1992, “Reliability and Degradation of 980nm InGaAs/GaAs Strained Quantum Well Lasers,” Qual. Reliab. Eng., 8, pp. 283–286]. However, studies conducted that specifically addressed condensation measurements have not been previously reported. Hence, an attempt was made to study package performance with condensation, to address the identified concern for the current package. A test method based on a military standard specification was used for this purpose. Elevated temperature and humidity (without condensation) were found to affect the laser power. These were characterized to isolate the effect of condensation alone. The package was subjected to repetitive condensing cycles and laser output power was recorded as a function of time, temperature and humidity. The variation in laser output power due to condensation was observed and quantified. Results showed a temporary power degradation of approximately 5% with condensation. This was a repeatable effect throughout the test time. Visible water droplets were found in various areas of the package after the test cycle. This could lead to potential failure mechanisms during the device life time.
This paper presents a performance study done on semiconductor laser diodes in a moisture condensing environment. Devices with laser diodes are used in a wide variety of electronic applications and in various climatic conditions. The motivation behind this study is a common environmental exposure, where a device using a laser diode is brought into a relatively humid environment (a building) from a cold, outside environment. Under such conditions, condensation occurs on various components of the device, including the diode, and could affect the laser output power. Reliability of the device is a critical concern since the laser diode and the lens are susceptible to failure due to such repetitive condensation conditions. The test vehicle chosen for this study was a 980nm laser diode. These are used in products for a broad range of markets, including data communications, aerospace, material processing, scientific and defense industries [1–3]. These products may be used in environmental conditions that could result in condensation within the product. A hermetic package could address this concern, but it is an expensive option. Nonhermetic packaging for the laser component could help lower the cost of these devices; however reliability is a potential concern. Prior research on laser diodes consists of various reliability measurements on 980nm lasers using stress tests (e.g. accelerated aging tests; thermal cycling tests) [3–6]. Reliability analysis of laser diodes specifically addressing condensation measurements has not been previously reported. A Military Standard Specification [MIL-STD-883E Method 1004.7] titled, ‘Moisture resistance test’ was used to conduct this reliability study [10]. An experimental setup was designed and fabricated. A photonic package with a 980nm laser diode was subjected to repetitive condensing cycles and laser output power was recorded as a function of time, temperature and humidity. The variation in laser output power due to condensation was observed and quantified. The focus of this paper is on performance degradation of the laser diode. The possible mechanisms for this degradation are currently being investigated.
This paper presents an experimental and computational study done on an epoxy to determine the effect of moisture level and temperature on the Coefficient of Hygroscopic Swelling (CHS). When a non-hermetic package is exposed to a humid environment, the adhesives used in the package absorb moisture and swell. This can induce stresses in the package that can lead to failure. The Coefficient of Hygroscopic Swelling is defined as the ratio of hygroscopic strain to the moisture concentration in the material. It has been found from prior literature that hygroscopic strains are significant and have to be accounted for in reliability modeling [1]. Prior research investigated the measurement of CHS experimentally using techniques such as thermo mechanical analysis (TMA) [1] [2], moire´ interferometry [3], and digital image correlation (DIC) [4]. An experimental method using the TMA technique was used to measure the CHS [1], but further analysis using improved techniques was recommended to get a more precise measurement. One of the goals of this paper was to investigate experimental and numerical techniques that would help better understand various factors that affect the measurement. This paper focuses on measurement of CHS for an epoxy used in optoelectronic packaging. The DIC technique was chosen for measurement of CHS. Moisture loss during the test leads to a change in the moisture concentration in the sample. While it may be thought that the moisture loss during the DIC scan can be assumed negligible due to the short test time compared to other methods, this assumption did not hold well for the epoxy material tested. The ramp rate chosen for the measurement will affect the amount of moisture lost from the sample. This has to be carefully chosen to minimize the moisture loss. These effects have to be accounted for in the CHS computation. The CHS value calculated will be significantly affected if these factors are high within the range of the measurement. This paper describes the investigation to minimize such effects in the measurement of CHS and attempts to account for them using computational methods. The CHS of an epoxy material was measured and its dependence on temperature and moisture concentration was determined.
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