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Thursday, 01 April 2010 00:00

ESD

“Electrostatic Discharge (ESD) – Sources of Electrostatic Charge in a Production Line (SMT)”

Author: Hartmut Berndt; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: It is necessary for everyone who handles electrostatic-sensitive devices to know the reasons of ESD failures. This paper gives an overview about possible causes for ESD in a SMT production line. Automated production lines have some processing steps where electrostatic charges increasingly are generated. So far, mitigation has focused on the operator. This is controllable. Measurements in production lines show electrostatic charges at the following processing steps: screen printer, component assembly (automated and manual pick-and-place), labeling, optical and electrical tests. Electronics components are always assembled directly, without covering the PCB. Thus, wire bonding can lead to component damage. This process step is a critical part in the production line, during which electronic devices will be directly contacted with a metal needle. (SMTA Pan Pac Symposium, January 2010)

Solder Joint Reliability

“Parametric Acceleration Transforms for Lead-Free Solder Joint Reliability Under Thermal Cycling Conditions”

Authors:  Mudasir Ahmad, Xie Weidong, Kuo-Chuan Liu, Xue Jie and Dave Towne; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: A significant factor in the slow transition to Pb-free solders is the absence of industry-accepted Pb-free acceleration transforms that can translate lab test results into field reliability life data. Without such industry-accepted acceleration transforms, it is difficult to translate lab test data into reliable predictions of field-life performance. In this study, a comprehensive set of test data have been generated over a wide spectrum of package types, solder joint metallurgies, joint size, pitch, die sizes, PCB thicknesses and thermal cycling conditions. The effect of aging on acceleration transforms also was included. The data have been analyzed to compare with existing Pb-free and SnPb acceleration transform models. The data help explain contradictions in the existing literature, and offer more comprehensive acceleration transforms for Pb-free solders. Some publications indicate the acceleration transforms for Pb-free solders are the same as SnPb acceleration transforms. Comprehensive results of this study also show that in specific conditions, Pb-free acceleration transforms could even be lower than SnPb acceleration transforms. In addition, the acceleration transforms for backward-compatible (Pb-free solders attached with SnPb paste) assemblies are presented as a function of assembly peak temperature. Finally, finite element analysis also has been performed to better understand the effects of the different package design variables on the experimental acceleration transforms. The results have been used to derive recommendations on what package design variables to consider in ensuring good long-term Pb-free reliability. (Electronic Components and Technology Conference, May 2009)

“Quality and Reliability Analysis of Lead-Free PCBs in Simulated Production Conditions and Long-Term Use”

Authors: Sammy Shina, Ph.D., et al; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: The New England Lead-free Electronics Consortium is a collaborative effort of New England companies spanning the electronics supply chain, created by the University of Massachusetts Lowell in 1999 and sponsored by the Toxics Use Reduction Institute and the US EPA. The consortium has completed and published the results of three phases of manufacturing and testing of lead-free PWBs, with the goal of achieving zero-defect Pb-free soldering processes with comparable or superior reliability to that of leaded solder processes. In this fourth phase of testing, which began in 2007, several simulated conditions of assembly and rework processes were evaluated in a matrix of multiple levels of components, PWB lead-free surface finishes and solders, and compared to a baseline of leaded equivalent materials and processes. Plated through-hole and surface mount technologies were evaluated.

All quality and reliability testing was performed with industry standard methodologies, using specially trained production inspectors for the quality evaluation, and extreme thermal cycling and vibrations for reliability testing. Results indicate that with proper selection of currently available (2009) materials and finishes, and careful control of the assembly processes, successful Pb-free assembly and rework can be achieved. Comparison of different strategies for rework, and recommendations for least copper dissolution for PTH technology processes, are discussed in Chapter 6 of a book published by the authors. Reliability testing showed inflection points for leaded versus Pb-free reliability currently being investigated. (SMTA Pan Pac Symposium, January 2010)

Tin Whiskers

“Local, Submicron, Strain Gradients as the Cause of Sn Whisker Growth”

Authors: Matthias Sobiech et al; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: It has been shown experimentally that local in-plane residual strain gradients occur around the root of spontaneously growing tin whiskers on the surface of tin coatings deposited on copper. The strain distribution has been determined with synchrotron white beam micro Laue diffraction measurements. The observed in-plane residual strain gradients in combination with recently revealed out-of-plane residual strain-depth gradients provide the driving forces for whisker growth. (Applied Physics Letters, June 2, 2009)

Last Updated on Friday, 26 March 2010 10:53
 

Columns

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Parity emerges among EMS Factories from Asia, Mexico and the US.

For the first time in years we see parity in the Eastern US among EMS factories from Asia, Mexico and the US. This EMS market condition will permit American OEMs (the EMS industry refers to OEMs as customers) to have more EMS pathways to choose from. Now more than ever, such EMS assignments will require deeper investigation relating to the OEMs’ evaluation of manufacturing strategies.

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Circuits Disassembly: Materials Characterization and Failure Analysis

A systematic approach to nonconventional methods of encapsulant removal.

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