In case you missed it.This month's abstracts come from papers presented at Apex, February 2005 (ipc.org). Soldering "Lead-Free Solder Flip Chips on FR-4 Substrates with Different Assembly Processes and Materials" Authors: David Geiger, Dongkai Shangguan, Jonas Sjoberg and Todd Castello; dongkaishangguan@flextronics.com. Abstract: This study is on using different assembly options such as dip fluxing, flux jetting and reflow (1) The process of heating and melting the solder that has been screen printed onto a printed circuit board in order to bond chips and other components to the board. Surface mount chips (SMT) use the reflow method. Contrast with wave soldering. See also reflowable text. encapsulate en·cap·su·late v. 1. To form a capsule or sheath around. 2. To become encapsulated. en·cap for 200-250 [micro]m pitch lead-free (SnAgCu) flip chips on FR-4 substrates. The impact of different PCB PCB: see polychlorinated biphenyl. PCB in full polychlorinated biphenyl Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. surface finishes (OSP (Online Service Provider) See online service. OSP - Optical Signal Processor and ENIG ENIG Electroless Nickel Immersion Gold (printed circuit board manufacturing process) ) was investigated from an assembly perspective. Different underfill materials, including acid anhydrate and non-acid anhydrate based materials, were evaluated for compatibility with the flux and lead-free solder bumps and process. A reflow encapsulate designed for lead-free soldering is also studied. "Maximizing Lead-Free Wetting" Author: Richard Lathrop; rlathrop@4cmd.com. Abstract: Wetting of lead-free solder pastes is surfacing as the major paste performance tradeoff. Global efforts to significantly increase lead-free wetting chemically have proven unproductive to date. With respect to wetting, a drop-in lead-free paste looks improbable. This paper reports the findings of numerous studies using quantitative wetting gauges to measure solder paste wetting to the PCB surfaces. Wetting results with various lead-free profiles, reflow atmosphere oxygen concentrations and lead-free PCB surface metalizations are compared and contrasted for their contribution to maximizing lead-free wetting. This paper concentrates on the SAC (SnAgCu) alloy, specifically 95.5/4/0.5 in a no-clean paste. Solder defects and voiding are also included in the comparisons to reveal the best overall lead-free reflow process. Solder Joint Reliability "Vibration Fatigue Evaluation on Solder Joints of Under-Filled BGA (Ball Grid Array) A popular surface mount chip package that uses a grid of solder balls as its connectors. Available in plastic and ceramic varieties, BGA is noted for its compact size, high lead count and low inductance, which allows lower voltages to be used. " Authors: T. E. Wong, Ph.D., and Ray-Chung Yu, Ph.D.; tes_e_wong@raytheon.com. Abstract: A previously developed BGA solder joint vibration fatigue life prediction model, which was experimentally validated by Test Vehicle One (TV1) test data for BGAs with and without underfilled materials, has been used to determine solder joint integrity of BGAs. However, newly obtained TV2 test results show that this life prediction model has a tendency to underestimate the fatigue life of BGA solder joints. The need to revalidate re·val·i·date tr.v. re·val·i·dat·ed, re·val·i·dat·ing, re·val·i·dates To declare valid again. re·val the life prediction model is the object of this study. A TV2, with various sizes of BGA daisy-chained packages with/without underfilled materials (including nonreworkable and reworkable), was designed, fabricated and subjected to random vibration In mechanical engineering, random vibration is motion which is non-deterministic, meaning that future behavior cannot be precisely predicted. The randomness is a characteristic of the excitation or input, not the mode shapes or natural frequencies. tests with continuous monitoring of solder joint integrity. Based on the measurement results, a destructive physical analysis is conducted to further verify the failure locations and crack paths of the solder joints. The previous model combined with a finite element analysis Finite element analysis (FEA) is a computer simulation technique used in engineering analysis. It uses a numerical technique called the finite element method (FEM). There are many finite element software packages, both free and proprietary. is recalibrated by the TV2 test results. This updated model is then recommended to serve as an effective tool to determine the solder joint integrity of the BGAs (with/without underfilled materials) during vibration. The relationship between BGA solder joint fatigue life and the elastic modulus elastic modulus or elastic constant In materials science and physical metallurgy, any of various numbers that quantify the response of a material to elastic or springy deflection. of underfilled material is illustrated. The analysis results show that BGA fatigue life exponentially increases as the elastic modulus of underfilled material increases to a certain threshold value and this relationship can be used to select the underfill for improving BGA solder joint vibration fatigue life. Rework/Repair "Perspectives on Repaired Lead-Free Solder Joints" Authors: Richard Colfax, Matthew O'Keefe, Patricia Amick, David Kleine, Steve Vetter and Dale Murry; mjokeefe@umr.edu. Abstract: Processing conditions during soldering can significantly affect the microstructure mi·cro·struc·ture n. The structure of an organism or object as revealed through microscopic examination. microstructure Noun a structure on a microscopic scale, such as that of a metal or a cell and reliability of the joint. While methods for repairing assemblies using SnPb solders are established, limited data are available for rework and repair of lead-free solder processing, especially when the resulting joint is a combination of SnPb and lead-free solders. This study investigates the influence of repair processing conditions on the microstructure of lead-free solders. Processing parameters such as soldering conditions and solder composition were used to simulate manufacturing operations Manufacturing operations concern the operation of a facility, as opposed to maintenance, supply and distribution, health, and safety, emergency response, human resources, security, information technology and other infrastructural support organizations. . Temperature cycling of components soldered to PCBs between -55 and +125[degrees]C with SnPb, lead-free and mixtures of SnPb and lead-free solders was performed. Analyses of the phases present, chemical composition and microstructure of the solder joints before and after temperature cycling were conducted using optical and electron microscopy electron microscopy Technique that allows examination of samples too small to be seen with a light microscope. Electron beams have much smaller wavelengths than visible light and hence higher resolving power. to correlate processing conditions to the resulting microstructure. Shear testing of surface-mounted capacitors prior to and after temperature cycling demonstrated a significant drop in shear strength For the shear strength of soil, see . Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. after temperature cycling. Implications of processing conditions on the reliability and long-term stability of the solder joints are discussed. 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. |
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