DfM

“The Effect of Design Parameters on PTH Barrel Fill in High Complexity Assembly”

Authors: Jinda Songninluck, et al; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Through-hole barrel fill, especially for high-complexity thick PCBs, is an issue in Pb-free soldering. Many experimenters have identified that inadequate hole fill can be improved by optimized preheat profiles, higher pot temperatures, and more aggressive fluxes. However, processing temperatures are limited by the thermal tolerances of the laminate and components. Even Pb-free-compliant laminates cannot withstand extended exposures to liquid solder, and flux chemistries limit preheat temperatures. The application of more aggressive fluxes with high solid contents often leads to undesirable residues that can affect AOI, pin probability at downstream testing, and a host of other problems associated with reduced cleanliness. This work explores the optimization of through-hole solder fill by design for manufacture. The focus is on investigating design factors affecting barrel fill of high-complexity thick boards (>0.120", >10 layers) populated with high-thermal-mass components. Assembly processes, test methods, analysis and selected results are discussed. (SMTA International, October 2011)

Chip Packaging

“Processing Strategies and Reliability of 3D Wafer Level CSPs”

Authors: Daniel F. Baldwin, Ph.D.; Paul N. Houston; Brian J. Lewis; and Fei Xie; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: A 3D wafer level CSP packaging architecture that provides a cost-effective, rapid time to market alternative to emerging 3D die to wafer integration technologies has been previously introduced. This paper focuses on the second-level assembly process development and reliability performance assessment of the 3D WLCSP packages. Second-level assembly to date shows robust yield and solid reliability performance through 1500 air-to-air thermal cycle testing on packages under various assembly process conditions. Manufacturing process challenges such as underfill encroachment, underfill voiding and Pb-free CSP reflow profile parameters, as well as different underfill methodologies are discussed. The impact of the parameters on overall reliability is covered. A detailed analysis of the yield on both fine pitch and coarser pitch WLCSP structures is detailed, in addition to reviewing different underfill processing schemes used to resolve underfill encroachment on fine-pitch first-level packages. Some material selections and their impact on yield and reliability are covered. The reliability assessment on second-level package assemblies shows that the structured 3D-WLCSP packages can be fabricated with robust yields and demonstrates high reliability. (SMTA International, October 2011)

Solder Joint Reliability

“Quality, Reliability and Metallurgy of ENEPIG Board Finish and Tin-Lead Solder Joints”

Author: Mike Wolverton; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Electroless nickel electroless palladium immersion gold (ENEPIG) board finish was evaluated for soldering to ball grid array and chip components using highly reliable SnPb solder. Five palladium thicknesses, ranging from 5 to 30 microinches, from two PCB suppliers were evaluated. Several conditions were compared, namely, the as-soldered, post-solder assembly thermal exposure, reworked, coated and temperature-cycled conditions. Maximum global and local solder joint palladium weight percentages and cross-sectioned intermetallic compound morphology requirements were derived for high quality and reliability in a typical mil-aero application. Visual, electrical continuity, x-ray and shear strength data, plus scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) compositional and metallurgical data and analysis are provided. Wire bond ball shear strength results also are given for the range of palladium thicknesses tested. (SMTA International, October 2011)

Wave Soldering

“iNEMI Lead Free Wave Soldering Project: An Investigation of Reliability of Through-Hole Electrical Interconnects”

Authors: Denis Barbini, Quyen Chu, Denis Jean, Stuart Longgood, Keith Howell and Jian Miremadi; This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Abstract: Previous investigations of Pb-free wave soldering, as well as standards development, focused on process optimization, material selection, through-hole fill, coverage requirements, etc. However, few published investigations focus on the reliability of surface mount and through-hole solder joints assembled with various board finishes and thicknesses, component types and alloys. This iNEMI collaboration studied and reports on the behavior and performance of various solder alloys and solder joints after long-term thermal cycle testing. (SMTA International, October 2011)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.