Evaluation of Environmental Tests for Tin Whisker Assessment

Tin whiskers are electrically conductive crystalline structures of tin that over time may grow outward from tin-rich surfaces and present a reliability hazard to electronic systems. While the problem has been known for decades, no satisfactory explanation of whisker growth mechanisms exists, leaving the industry to create whisker-assessment tests based on empirical data gathered under various environmental storage conditions controlled for temperature, humidity and temperature cycling. The long-term predictability of these environmental storage tests has not been addressed and the accuracy of these tests in foreseeing whisker growth is unclear. In this thesis, different tin finishes are assessed for whisker growth in accordance with existing environmental test standards and compared to growth seen in ambient storage conditions. The results indicate that environmental tests may over-predict, under-predict, or show little distinguishable growth as compared to ambient-stored tin finishes. In conclusion, environmental tests are not a reliable method of assessing future whisker growth

A Screening Method Using Pulsed-Power Combined with Infrared Imaging to Detect Pattern Defects in Bulk Metal Foil or Thin Film Resistors

Bulk metal foil and thin film resistors occasionally contain localized defects within the etched resistor pattern. Common defects of this type include in-line constrictions referred to as notches, unremoved resistor material bridges between adjacent pattern lines, and embedded non-conductive particles in the resistor material. Such defects are prone to fracture due to thermomechanical fatigue during powered operation, especially power cycling, resulting in positive resistance change and open circuit failure modes. Common screening methods of optical microscopy, short time overload power tests (e.g., 6.25x rated power for 5 seconds) and burn-in (e.g., 1.5x rated power for 100 hours) are useful, but they are not always effective at removing devices with such defects. An improved method has been developed to screen for localized resistor pattern defects. The method involves the application of brief, high power electrical pulses at a low duty cycle while inspecting the resistor with a high resolution, high speed infrared camera. The following test conditions were found to be suitable for this purpose: 6.25x rated power, 1 to 5 pulses, 50 ms pulse width and 10% duty cycle. During the power pulsing, localized constrictions in the resistor pattern are identifiable as hot spots via the infrared camera. Reject criteria can be established based on observations of hot spots. To assess its effectiveness, a total of two hundred eighty (280) surface mount foil resistors (40 each from 7 different lots) were screened using this infrared technique. The screening identified twenty-nine (29) resistors with significant hot spots in the resistor pattern. All 280 resistors were then subjected to an industry standard 10,000 hour life test at 1x rated power at 70C with power cycled for 90 minutes on and 30 minutes off. During life testing, three resistors exhibited positive resistance change failure mode. All three failures were due to thermomechanical fatigue failure of localized bridge defects at the locations identified via infrared screening. The results of this evaluation illustrate the benefits of the pulsed-power infrared detection screening technique to identify reliability suspect foil or thin film resistors that may escape common screening methods

NASA Electronic Parts and Packaging (NEPP) Hermeticity Task. NEPP Program Task 13-294: MSFC/GSFC Joint Hermeticity Instrument Correlation Study of TO-5, TO-18, and UB Style Packages

No abstract availabl

Long Term Investigation of Urethane Conformal Coating Against Tin Whisker Growth

No abstract availabl

NEPP Program Task 16-294: Gross Leak Standard Development

No abstract availabl

NEPP Program Task 14-294: Joint Hermeticity Correlation Study

No abstract availabl

Thermal Signature of a Resistor and Problems Encountered Along the Way

No abstract availabl

NASA Electronic Parts and Packaging (NEPP) Hermeticity Task Overview, NEPP Program Task 13-294: Hermeticity Correlation Study

No abstract availabl

Development of Stable, Low Resistance Solder Joints for a Space-Flight HTS Lead Assemblies

The solder joints in spaceflight high temperature superconductor (HTS) lead assemblies for certain astrophysics missions have strict constraints on size and power dissipation. In addition, the joints must tolerate years of storage at room temperature, many thermal cycles, and several vibration tests between their manufacture and their final operation on orbit. As reported previously, solder joints between REBCO coated conductors and normal metal traces for the Astro-H mission showed low temperature joint resistance that grew approximately as log time over the course of months. Although the assemblies worked without issue in orbit, for the upcoming X-ray Astrophysics Recovery Mission we are attempting to improve our solder process to give lower, more stable, and more consistent joint resistance. We produce numerous sample joints and measure time- and thermal cycle-dependent resistance, and characterize the joints using x-ray and other analysis tools. For a subset of the joints, we use SEMEDS to try to understand the physical and chemical processes that effect joint behavior

Rating of consumption of materials and electric energy in electroslag welding

Translated from Ukrainian (Avtom. Svarka 1997 (4) p. 46-50)Available from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8267)T / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo