Circuits Assembly - December 2008 - (Page 39) White Residue Rings What happens when paste residues and cleaning solvents are incompatible? also been through a standard immersion cleanliness s debuted in these pages last month, the National testing process for ionic residues. Some combinations Physical Laboratory’s new interactive assembly of paste residue and cleaning soland soldering defects datavents are not compatible and leave base lists problems and solutions. a white- or brown-like dust on the The database permits searching and board surface. In this case, the comviewing of countless defects and bination of 75% IPA and 25% water solutions. Users also can submit has failed to dissolve or displace the defects online for recommendations residues from around the base of at http://defectsdatabase.npl.co.uk/. the ball and pad interface and creThis month we feature one ates a most interesting image. recent submission: white residue This issue was only seen on a rings on BGA joints. All BGA solder few boards intended for a consumer joints featured a white ring around Figure 1. Following Pb-free reflow, application, and as such, there was each ball termination. The ring was solder paste residues can form white no specific corrective action. The perfectly formed and not like nor- residue rings on BGA joints. paste was a no-clean material; the mal white residue often seen from a cleanliness testing was just part of a process evaluation standard cleaning operation (Figure 1). and created these unique rings that did not prove to be In fact, the ring consisted of solder paste residues harmful to the application. found after Pb-free reflow. The sample in this case had n The Defects Database A Dr. Davide Di Maio is with the National Physical Laboratory Industry and Innovation division (npl. co.uk); defectsdatabase@npl.co.uk. Charlie Barnhart & Associates Leading Indicators Monthly Report The Industry’s Only Source for the Data that Matters Most to Global Electronics Manufacturing “Charlie Barnhart continues to provide the best data of its kind available to the industry. Anyone involved in the offshoring of electronics manufacturing would benefit from the data and insights the Leading Indicators Monthly Report contains. Charlie began his work in this area while working with me at Technology Forecasters, where it quickly became the most pertinent and valuable data we had to offer customers. I am glad to see him continuing and extending his work now that he is independent. It is current, insightful, and well organized which makes it very easy to access and utilize.” Eric Miscoll, Vice President & General Manager, TXP Corporation » » » » Overhead rates Mark-up rates Global Labor Rates Global Risk Constants Subscribe now at www.charliebarnhart.com to get on the distribution list of this valuable and cost-effective research. » www.charliebarnhart.com circuitsassembly.com Circuits Assembly DECEMBER 2008 39 http://defectsdatabase.npl.co.uk/ http://www.npl.co.uk http://www.npl.co.uk http://www.charliebarnhart.com http://www.charliebarnhart.com http://www.circuitsassembly.com
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