Circuits Assembly - December 2008 - (Page 35) The impact of solder temperature was minor relative to its effect on bridging, while for through-hole penetration a higher solder temperature was preferred (275 oC). However, this option could potentially damage components during soldering. Therefore, a solder pot temperature between 265 o and 270 oC was chosen. In addition, shorter contact time yielded better results. This might be attributable to the characteristics of the flux, which were compromised at the higher preheat and solder pot settings. The champion setting was 1.8 sec. In terms of preheating, a setting of 110 oC was the champion for this process. Calrod IR elements were used in the first heating zone, which provided the adequate heat to start the flux activity without forcing the water to boil out. Forced convection heaters were used in the second and third zones to eliminate excess water before entering the solder wave and to inhibit solder balling. For the flux, a wet flux amount of 474 mg/dm 2 was the champion setting. A continuous and uniform spray across the board is essential. Higher settings may cause a droplet bouncing effect rather than improved wetting of the board surface. All these settings were validated with confirmation runs. Reduced bridging and good through-hole penetration were achieved. Optimal Pb-free assemblies are not a simple replacement of fluxes and materials. This review can be done in a proper and fast way by conducting Partial Factorial, Taguchi or Response Surface experiments. The outcome of the experimentation will provide a practical understanding of important factors and settings by using just a small number of test boards, reducing cost and minimizing resource use. n circuitsassembly.com Life can be tough. Attending a trade show shouldn’t be. February 24-25, 2009 The first and only truly interactive, web-based event for designers, fabricators and assemblers Network – learn – participate – from the comfort of your home or office! www.virtual-pcb.com 35 Circuits Assembly DECEMBER 2008 http://www.envisionrules.org http://www.virtual-pcb.com http://www.circuitsassembly.com
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