Up Time Magazine - February/March 2009 - (Page 43) enough current to cause failure in digital circuits. It can cause a short that can fail the equipment while leaving little or no evidence. Whiskers frequently achieve lengths of several millimeters with a typical diameter of 1 µm. In rare instances lengths of up to 10 mm have been observed. Whiskers can grow indefinitely and they can be straight, kinked, hooked or forked (see Figures 1, 2 & 3). Annual growth rates can vary between 0.03 mm and 9 mm. Figure 1 – Whiskers on a relay armature Managing your weight just got easier. Pb-free solder is, to some extent, more brittle than traditional solder. Substitute solders that have been developed may be applied too thinly or with too little heat, which results in stressing of the circuit board laminate (a contributing factor in whisker growth). Trico’s High-Viscosity Gear & Lube Oil Portable Filter Cart 10,000 SUS Introducing the Industrial Gear and Lube Oil Filtration System from Trico designed specifically for higher viscosity fluids. This recently released product features a substantial viscosity capability of 2000 cSt @ 40oC, making it one of the most versatile filtration systems available. • Conditions lubricants in use • Filters new oil before putting into service • Complements existing system filtration as part of a preventative maintenance program • Transfers new fluids from drums to storage tanks or system reservoirs ELIMINATE YOUR WEIGHT WATCHING WORRIES. CALL TRICO. up to What Causes Tin Whiskers? The removal of Pb from solder is not the cause of whisker formation - it has simply illuminated the underlying condition. Tin whiskers are Figure 2 – Magnified view of tin whiskers individual crystal growths of tin that grow spontaneously from a tinned surface. They appear to be related to residual stresses within the tin plating. Pb in solder compensates for these stresses. Exactly how and why a tin whisker grows is not completely understood and more research is needed to establish the root cause(s) and deliver a solution. However, some progress has been made in understanding this phenomenon. Factors that are reasonably well proven to contribute to whisker formation are: • External compressive stresses such as those introduced by torquing of a nut or a screw can contribute to the formation of whiskers. Figure 3 – Magnified view of a single tin whisker tip • Bending or stretching of the surface after plating has been applied. www.tricocorp.com 800-558-7008 TRICO Filter Cart_Uptime_2.9375x1 1 8/1/07 11:32:54 AM www.uptimemagazine.com 43 http://www.tricocorp.com http://www.uptimemagazine.com
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