Circuits Assembly - April 2008 - (Page 43)

Cover Story cess parameters and materials resulted in the following conclusions: • The use of nitrogen in the reflow oven process is necessary when thick boards (0.125"-thick boards) are assembled to achieve more than 75% through-hole penetration. • Nitrogen consumption can be reduced by applying it only on the reflow areas and using higher oxygen ppm levels (up to EFD Solder Paste If You Think Our Dispensers Are Great You Should Try Our Solder Figure 15. Main effects plot for DIP – VOC-free flux. observed when components were placed on 0.125”-thick boards. Data analysis indicates unacceptable through-hole penetration on the 0.125”-thick boards assembled with the alcohol-based low rosin flux and reflowed in air. To improve results when assembling under ambient reflow condition, analysis of the data indicated the use of nitrogen in wave soldering. This is applicable only for the pins attached to six layers (based on four data points) (Figure 15). Assemblies soldered using VOC-free flux on the 0.093"-thick board resulted in unacceptable through-hole penetration when connected to six layers (Figure 15) at all atmosphere levels. In contrast, those assemblies soldered using the alcohol-based low-rosin flux resulted in acceptable through-hole penetration. DIPs showed a major challenge in comparison with other PTH components. On the 0.125"-thick boards, the lack of lead protrusion produced unacceptable through-hole penetration. During wave soldering, the component leads assist with the capillary action of solder wicking up the via.11 As mentioned for the other components, nitrogen use during reflow shows major benefits on 0.125"-thick board assembly. Nitrogen can be supplied to the reflow areas only and up to 2500 ppm of oxygen. For the 0.093"-thick board, the flux type was the major influence, and the analysis favors the low-rosin alcohol flux. Conclusions The purpose of this collaborative investigation was to provide evidence on the impact of atmosphere on solder joint formation. Materials selection provided data specific to board complexity, flux type on a CuOSP board finish. Investigation of the influence of various procircuitsassembly.com 2,500 ppm). • Flux chemistry is a very important factor that can change results dramatically. In general, alcohol-based flux selected in this study was more robust than VOC-free flux. This should be considered when optimizing for through-hole penetration. • The use of nitrogen in the wave soldering process is beneficial for reduction of bridging and when nitrogen has been used in the reflow process. • The orientation of the component with respect to the direction of the board is important and depends on component type. • When components have been reflowed in nitrogen, it is possible to obtain acceptable hole penetration using a variety of throughhole designs, while limited designs when reflow in air. ■ Acknowledgments The authors would like to thank George Oxx, Aaron Unterborn and Doug Watson for their support on the planning stage of this project; Eric Cruz for performing 5DX analysis; Roy Palhof, Norm Faucher and Jon Silin for their support on board assembly; and Linlin Yang for data collection support. The authors would also like to thank the management of Flextronics and Vitronics Soltec. Ed.: This article was first published in the SMTA Pan Pacific Symposium Proceedings and is reprinted here with permission. For a list of references, please visit circuitsassembly.com/cms/ content/view/6286. Ursula Marquez de Tino is a process and research engineer and Dr. Denis Barbini is manager of advanced technology at Vitronics Soltec (vitronics.com); umarquez@vsww.com. Wesley Enroth is with Flextronics. Request your free white paper titled “Choosing The Right Solder Paste” www.efd-inc.com/ads/ca-0308 A NORDSON COMPANY 800-338-4353 +1-401-434-1680 See us at APEX, Booth #1470 Circuits Assembly APRIL 2008 43 http://www.efd-inc.com/ads/ca-0308 http://circuitsassembly.com/cms/content/view/6286 http://circuitsassembly.com/cms/content/view/6286 http://www.efd-inc.com/ads/ca-0308 http://vitronics.com http://circuitsassembly.com

Table of Contents Feed for the Digital Edition of Circuits Assembly - April 2008

Circuits Assembly - April 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Screen Printing Better Manufacturing Design and Modeling of High-Speed, High-Density 3-D CSPs and Memory Modules The ‘Big Brush Off’ Revisited Impact of Soldering Atmosphere on Solder Joint Formation Beyond Moore’s Law ESD Control For Class 0 ESDS Devices Growing Your Brand This Year’s Model Tech Tips Reflow Soldering Process Doctor Pb-Free Lessons Learned Getting Lean Equipment Advances Apex Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - April 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.