barcode scanner programming asp.net SOLDERING MATERIALS AND METALLURGY in Software

Encoder Quick Response Code in Software SOLDERING MATERIALS AND METALLURGY

SOLDERING MATERIALS AND METALLURGY
Decoding QR In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Make QR-Code In None
Using Barcode drawer for Software Control to generate, create QR Code 2d barcode image in Software applications.
When fresh, tin has reasonable solderability, but also tends to oxidize quickly. There are two important phenomena that are associated with Sn platings: tin whiskers and tin pest. 45.6.6.1 Sn Whiskers. Not to be confused with corrosion dendrites, whiskers are crystallites (see Fig. 45.6) that grow from pure tin surfaces into free space whereas corrosion dendrites grow on ionic contaminated, hydrated surfaces between two charged conductors. Although whiskers have been studied since the 1940s, their root cause is yet to be fully understood.
Decode QR Code In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
QR Code JIS X 0510 Drawer In C#
Using Barcode maker for .NET Control to generate, create QR Code image in .NET framework applications.
FIGURE 45.6 Scanning electron microscope (SEM) micrograph of Sn whiskers growing from a pure Sn surface.When whiskers break, they pose danger of shorting between fine-pitch conductors. Whiskers can also grow long enough to bridge to a nearby conductor. (Courtesy of H. Hsu, Mitac Corporation, ShunDe, China).
Making QR Code 2d Barcode In Visual Studio .NET
Using Barcode encoder for ASP.NET Control to generate, create Denso QR Bar Code image in ASP.NET applications.
Denso QR Bar Code Printer In VS .NET
Using Barcode creation for .NET Control to generate, create QR Code image in VS .NET applications.
The concern over whisker growth is related to electrical short circuits. If a tin whisker is long enough, it may break due to mechanical shock or vibration. The broken whisker may bridge two closely spaced contacts or traces on a component or PWB. Whiskers need not break to cause a short circuit, as they can grow long enough to bridge two adjacent, closely spaced conductors. In 1998, the Galaxy IV communications satellite failure was traced back to tin whiskers. Spare boards for that satellite stored on Earth clearly showed whisker growth. It is ironic that the first whisker issue occurred in 1946 on Bell telephone equipment, causing another telecommunications disruption. Theories abound with regard to tin whisker formation. There are lattice dislocation theories and grain boundary diffusion theories. But the most prevalent theory for whisker generation relates their origin to compressive stresses within the tin lattice and perhaps weak spots in the overlying natural oxide on the tin surface (see Fig. 45.7). When tin grains are compressed against each other, and particularly when there are large compressive forces against a small, near-surface grain, the small grain may start to recrystallize or extrude in the least stressful direction, outward through a weak spot in the native oxide layer. Growth will continue until the lattice energy reaches equilibrium. Tin whiskers can grow to a diameter of approximately 1 micrometer and their length can reach tens of micrometers.
QR Code JIS X 0510 Drawer In Visual Basic .NET
Using Barcode generation for VS .NET Control to generate, create QR Code 2d barcode image in VS .NET applications.
Code 128 Code Set C Encoder In None
Using Barcode generation for Software Control to generate, create Code 128 Code Set B image in Software applications.
PRINTED CIRCUITS HANDBOOK
Data Matrix 2d Barcode Generator In None
Using Barcode creation for Software Control to generate, create DataMatrix image in Software applications.
Bar Code Maker In None
Using Barcode drawer for Software Control to generate, create barcode image in Software applications.
FIGURE 45.7 Compressive stress within the tin lattice may cause whisker formation. The picture sequence depicts a likely mechanism for tin whisker growth and risk to printed circuit assembly: (a) A tin lattice with small, near-surface grain between two large grains. (b) Compressive stresses cause recrystallization of grain. A thin spot in the oxide layer allows rudimentary whiskers to penetrate the surface. (c) The whisker continues to grow. (d) The whisker continues to grow. (e) The whisker breaks due to mechanical shock or vibration. Whisker fragment poses a shorting risk to the PCA.
Barcode Drawer In None
Using Barcode creator for Software Control to generate, create barcode image in Software applications.
Painting UPC - 13 In None
Using Barcode creation for Software Control to generate, create EAN 13 image in Software applications.
Now that Europe s RoHS legislation restricts Pb to a level of less than or equal to 1,000 parts per million by weight in electrical and electronic assemblies, there is much more focus on tin whiskers. Traditionally, many electrical components had tin-lead surface finishes, as did printed wiring boards (HASL). In cases where pure tin finishes were used on components, small additions of lead were added. The resulting lead-doped tin lattice imparted some compliance to the structure and reduced the risk of tin whisker formation. For the vast majority of electrical and electronic products, that is no longer an option for many classes of components. Where tin and copper are in contact with one another, copper is found to diffuse into tin faster than tin into copper. The disruption to the tin lattice results in compressive strains, which sets the stage for whisker initiation. The solution is the addition of a thick, non-porous nickel barrier layer over the copper. Tin is then plated over the nickel. The thick nickel deposit is generally under tension and the tin diffuses into the nickel faster than the nickel into the tin. Since the nickel exerts no compressive influence on the tin lattice, tin whiskers are less likely to form. Note that an added RoHS exemption allows the addition of Pb to Sn plated component leads if the component lead pitch is <0.65 mm (<0.025 in.). Besides metallic dopants, there are other ways to mitigate the growth of tin whiskers. Brighteners in tin-plating baths should be avoided and matte tin is preferred to minimize whisker growth. Annealing tin coatings is known to reduce whisker growth as recrystallization minimizes lattice stress. Ensuring that the reflow temperature during PCA soldering is above the melting point of tin (232 C) will reduce whisker risk. Additionally, the use of a barrier metal between copper and tin is recommended whether for circuit board or component surface finish.
USPS POSTNET Barcode Encoder In None
Using Barcode creator for Software Control to generate, create Postnet image in Software applications.
Data Matrix 2d Barcode Generation In C#
Using Barcode creation for Visual Studio .NET Control to generate, create ECC200 image in .NET applications.
Generate Barcode In Java
Using Barcode generation for Android Control to generate, create barcode image in Android applications.
Read GTIN - 128 In VB.NET
Using Barcode reader for Visual Studio .NET Control to read, scan read, scan image in VS .NET applications.
Painting 1D Barcode In Visual Basic .NET
Using Barcode generation for .NET Control to generate, create 1D Barcode image in Visual Studio .NET applications.
USS Code 39 Printer In None
Using Barcode generation for Office Word Control to generate, create USS Code 39 image in Word applications.
Making Barcode In .NET
Using Barcode generation for .NET framework Control to generate, create bar code image in VS .NET applications.
GS1 - 12 Creation In C#.NET
Using Barcode generator for .NET framework Control to generate, create Universal Product Code version A image in Visual Studio .NET applications.
Copyright © OnBarcode.com . All rights reserved.