Technical Library | 2015-10-22 17:37:28.0
The objective of this study is to evaluate conformal coatings for mitigation of tin whisker growth. The conformal coatings chosen for the experiment are acrylic, polyurethane and parylene. Also included in this paper are tin whisker inspection results of tin-plated braiding and wire that was exposed to an environment of 50°C with 50% relative humidity for over five years.
Technical Library | 2012-08-16 22:38:05.0
First published in the 2012 IPC APEX EXPO technical conference proceedings. The physical mechanisms behind tin whisker formation in pure tin (Sn) films continue to elude the microelectronics industry. Despite modest advances in whisker mitigation techniqu
Technical Library | 2023-02-13 19:23:18.0
Spontaneously forming tin whiskers, which emerge unpredictably from pure tin surfaces, have regained prevalence as a topic within the electronics research community. This has resulted from the ROHS-driven conversion to "lead-free" solderable finish processes. Intrinsic stresses (and/or gradients) in plated films are considered to be a primary driving force behind the growth of tin whiskers. This paper compares the formation of tin whiskers on nanocrystalline and conventional polycrystalline copper deposits. Nanocrystalline copper under-metal deposits were investigated, in terms of their ability to mitigate whisker formation, because of their fine grain size and reduced film stress. Pure tin films were deposited using matte and bright electroplating, electroless plating, and electron beam evaporation. The samples were then subjected to thermal cycling conditions in order to expedite whisker growth. The resultant surface morphologies and whisker formations were evaluated.
Technical Library | 2011-03-03 16:54:47.0
Most of the electronics industry by now knows about tin whiskers. They know whiskers are slim metallic filaments that emanate from the surface of tin platings. They know these filaments are conductive and can cause shorts across adjacent conductors. And they know that these shorts can cause some really bad failures (see nepp.nasa.gov/whisker/ for a list longer than you need). But, with all of this knowledge, the industry is still struggling on how to predict and prevent these "Nefarious Needles of Pain".
Technical Library | 2013-08-22 14:28:58.0
Tin-rich solders are widely applied in the electronic industry in the majority of modern printed circuit boards (PCBs). Because the use of lead-tin solders has been banned in the European Union since 2006, the problem of the bridging of adjacent conductors due to tin whisker growth (limited before by the addition of Pb) has been reborn. In this study tin alloys soldered on glass-epoxy laminate (typically used for PCBs) are considered. Scanning ion microscopy with Focused Ion Beam (FIB) system and energy-dispersive X-ray spectroscopy (EDXS) were used to determine correlations between spatial non-uniformities of the glass-epoxy laminate, the distribution of intermetallic compounds and whisker growth.
Technical Library | 2010-09-23 18:22:39.0
If you've been in electronics for any length of time, the phenomenon of tin whiskers is something you've likely heard discussed (maybe in scared whispered tones). Tin whiskers certainly aren't a new problem. In fact, some of the first published reports of the occurrence date back to the 1940’s and 1950's. But, over half a century later, we're still talking about it.
Technical Library | 2023-02-13 19:04:25.0
The tin whisker phenomenon is a failure mode associated with all electronic devices that use a number of low melting point elements (e.g., Sn, Cd, In) in operations such as soldering. Recognized many years ago, the problem was minimized by adding lead, now identified as a hazardous substance and banned
Technical Library | 2022-01-26 15:22:33.0
Reliability of conformal coatings used to mitigate tin whisker growth depends on their ability to contain tin whiskers. Two key material properties required to assess the reliability of a polyurethane coating are documented experimentally: adhesion strength and puncture strength. A modified blister test using a predefined blister area is employed to assess the adhesion strength and a puncture test is employed to evaluate the puncture strength of the coating. After measuring the properties at time zero, the coatings are subjected to accelerated testing conditions (high temperature/humidity storage and temperature cycling) and the degradations of the coating properties are documented.
Technical Library | 2023-02-13 18:56:42.0
This paper describes the results of an intensive whisker formation study on Pb-free assemblies with different levels of cleanliness. Thirteen types of as-received surface-mount and pin-through-hole components were cleaned and intentionally contaminated with solutions containing chloride, sulfate, bromide, and nitrate. Then the parts were assembled on double-sided boards that were also cleaned or intentionally contaminated with three fluxes having different halide contents. The assemblies were subjected to high-temperature/high-humidity testing (85_C/85% RH). Periodic examination found that contamination triggered whisker formation on both exposed tin and solder fillets. Whisker occurrence and parameters depending on the type and level of contamination are discussed. Cross-sections were used to assess the metallurgical aspects of whisker formation and the microstructural changes occurring during corrosion.
Technical Library | 2023-02-13 19:14:03.0
Technology Focus: Develop and evaluate nanoparticle filled conformal coatings designed to provide long term whisker penetration resistance and coverage on tin rich metal surfaces prone to whisker growth in commercial lead-free electronics used in modern DoD systems. Research Objectives: Identify the fundamental mechanisms by which conformal coatings provide long-term tin whisker penetration resistance and inhibit nucleation/growth. Correlate mechanical properties and coverage thickness to whisker penetration resistance. Project Progress and Results: Functionalized nanosilica and non-functional nanoalumina enhanced polyurethane conformal coatings have shown improved spray coating coverage characteristics and crack resistance during thermal cycling fatigue testing. Lead-free assembly whisker mitigation validation testing is in process. Technology Transition: Current project partners provide coating materials to industry. SERDP test data will be considered during updates to the DoD adopted IPC standards for coating materials and coverage.
