Circuits Assembly - October 2008 - (Page 48)

Technical Abstracts In Case You Missed It Connectors “Process Development and Reliability Study with Anisotropic Conductive Film Bonding as a Replacement for Surface Mount Connectors and Hotbar Soldering” Authors: Jonas Sjoberg, Jenson Lee, Shah Alam and Dongkai Shangguan, Ph.D.; jonas.sjoberg@ se.flextronics.com. Abstract: Flexible printed circuits (FPC) are widely used for a number of applications to enable products in a 3-D format, thereby utilizing the “dead” space within the product envelope. During the past few years, the use and complexity of FPC made of polyimide, polyester or Teflon have grown substantially and are expected to continue to grow even more. In the past, these FPCs have been connected to other FPCs or to a PCB with help of mainly connectors, but the interest of replacing these connectors with a lower cost and smaller footprint connections with help of anisotropic conductive film (ACF) is being widely explored. This paper reports the development of fine-pitch ACF bonding (down to 0.2 mm), and the mechanical and thermomechanical reliability of the ACF interconnects. The influence of different process parameters and ACF materials on the ACF process yield are discussed as well. (SMTA International, August 2008) Pb-Free Reliability “Pb-Free Feasibility Program: Assembly and Testing of a Functional Military Avionics Unit” Authors: David Hillman and Matt Hamand; ddhillma@collins.rockwell.com. Abstract: Because components used in avionics are largely common with those used in the consumer markets affected by the RoHS Directive, Rockwell Collins began addressing these issues/concerns in 2003. The objective of this investigation was to conduct a feasibility study using a full-rate production avionics product to determine printed wiring board design and potential printed wiring assembly issues/ concerns when using Pb-free soldering processes/procedures for military avionics products. The investigation results for the Control Display Units demonstrate the impact of Pb-free materials and procedures on a legacy military electronics design is minimal within the test conditions used. (SMTA International, August 2008) “A Case Study for Transitioning Class A Server Motherboards to Lead-Free” Authors: Randy Schueller, Ph.D., W. Ables, and J. Fitch, Ph.D.; randy_schueller@dell.com. Abstract: The EU RoHS legislation currently has an exemption to permit continued use of lead-based Circuits Assembly OCTOBER 2008 solder in Class A servers until at least 2010. There are industry proposals to extend this exemption to 2012 or beyond due to the added challenge of producing highly reliable Pb-free server assemblies. Dell has transitioned all recently released Class A server printed circuit board assemblies to Pb-free. This case study outlines the process followed, testing, material changes and challenges overcome in this dedicated year-long effort by a large team. A great deal of reliability testing was performed to ensure no compromise to the expected product life. The most significant challenge was selecting a PCB surface finish. Immersion silver has been ruled out because of its susceptibility to creep corrosion. OSP finish did not provide sufficient wetting capability after two surface mount passes. In the end, Pb-free HASL finish was selected because of its superior solderability and testability. However, laminate material, alloy type and process conditions had to be selected carefully to ensure compatibility with this surface finish. Since September 2007, all Dell’s newly released server motherboards have been built Pb-free and all quality targets successfully met. (SMTA International, August 2008) “Reliability of Tin-Silver-Copper Lead-Free Solder Interconnects Under Mechanical Loading with Different PWB Surface Finishes” Authors: Mohammad M. Hossain, Fahad Zahedi, Nikhil Lakhkar, Puligandla Viswanadham, Steven O. Dunford and Dereje Agonafer; mohammad.m.hossain@intel.com. Abstract: This paper shows an experimental study of Pb-free solder interconnects reliability under cyclic bend and drop impact loading. CTBGA 288 components were assembled on eight-layer test boards (JESD22-B111) with SAC (SnAg3.8Cu0.7) solder using three different PWB pad surface finishes to study the effect of the surface finish on the interconnect reliability. The pad finishes were immersion Au, immersion Ag and organic solder preservative (OSP). The test specimens were subjected to cyclic bend fatigue and board level drop tests. Strain gage measurements were taken at numerous locations across populated and unpopulated PWBs and the data used to identify variations in stress due to location and localized stiffness because of components. Results are presented with failure mode and analysis of those packages with different pad finishes and loading conditions. (SMTA International, August 2008) CirCuits Assembly provides abstracts of papers from recent industry conferences and company white papers. With the amount of information increasing, our goal is to provide an added opportunity for readers to keep abreast of technology and business trends. 48 circuitsassembly.com http://www.circuitsassembly.com

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Circuits Assembly - September 2008 Contents Letters Caveat Lector Industry News Market Watch Talking Heads Global Sourcing Screen Printing Better Manufacturing 'Checking Up' on Medical Electronics Solder Ball Attachment Using Laser Soldering Improving QFN Reliability Reflow Soldering Tech Tips Test and Inspection Process Doctor Pb-Free Lessons Learned Alternative Energies Eastern Advances Product Spotlight Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - October 2008

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