| Field Report : Top |
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| The Mechanism of Solder Cracking |
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| Soldered jointings are indispensable to high-density surface mounting of electronic equipment. Maintaining the reliability of soldered jointings is going to become a major problem that must be overcome to accurately mount miniaturized electronic parts. These soldered jointings deteriorate with exposure to long-term heat and mechanical stress, causing cracking which leads to part failure. In this paper we shall report on reliability testing to confirm the mechanism of solder cracking due to heat stress.
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| An analysis of solder cracking mechanisms
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Hiroko Inoki* Hirokazu Tanaka* Yuuichi Aoki* Shigeharu Yamamoto*
High-density mounting of circuit parts on electronic equipment makes the reliability of solder joints more crucial than ever. To grasp trends and improve reliability in solder joints, studies must be undertaken on printed circuit boards, mounted parts, and mounting technology. Solder cracking is directly involved in equipment failure, and controlling its occurrence has become a major problem. This report looks at one cause of solder cracking -the roughening of the solder grain boundary field- and verifies the relation of the problem to both thermal and mechanical stress. The results indicate that the solder grain boundary experiences roughening from both types of stress, although thermal stress exerts the greater influence. Degradation of solder strength due to roughening was also confirmed.
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| Investigating the effects of packaging materials on products
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| Modern packaging materials emit naturally-occurring gas that can corrode the metal parts of the products. To investigate this problem, we developed methods for testing and evaluating the Outgas. Our investigation revealed the source of corrosion to be sulfuration due to hydrogen sulfide (H2S) emitted by the packaging materials. Sulfuration varies with temperature, set-up conditions, and the quantity of the Outgas. To insure product reliability, care must be taken with the type of packaging materials used, the packaging method, and the temperature during shipping.
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The affects of adsorbed water on printed circuit boards,
and the process of ionic migration
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Hiroko Katayanagi* Hirokazu Tanaka* Yuichi Aoki* Shigeharu Yamamoto*
This report considers the insulation resistance characteristics of printed circuit boards (PCBs) and the effects of ionic migration in environmental testing. By measuring insulation resistance in a variety of environmental test conditions, the authors have determined that the initial changes in insulation resistance values is caused by water adsorption *1 and electrolysis. While investigating the occurrence of ionic migration, the authors were able to confirm that metal ions eluted in response to changes in the pH near the electrodes. These changes in pH were determined to have been caused by the electrolysis of water, which affected both pH and applied voltage.
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Evaluation validity in systems with continuous, automatic measurement
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Kunikazu Ishii*
Rapid strides are being made in miniaturizing electronic equipment while simultaneously offering improved functions and performance. Companies are under pressure to reduce product development time, while equal pressures demand that product safety and reliability be maintained. To handle these opposing demands, both the effectiveness and the accuracy of environmental testing require further improvement. To meet such requirements, we at ESPEC CORP are incorporating measurement of electrical characteristics in our environmental test equipment. This arrangement enables us to continually measure specimen characteristics under environmental conditions, and thus grasp real time characteristics when determining malfunction modes. We are currently developing a full line of automatic measuring systems. This report will introduce some aspects of Evaluation Systems and discuss the effectiveness of automatic measurement systems. |
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