by Chris Anglin, Dr. Ronald C. Lasky , Ed Briggs
The explosive growth of personal electronic devices such as mobile phones and personal music devices has driven the need for smaller and smaller passive and active electrical components. Not too long ago, 0401 (40 x 10 mils) passives were seen as the ultimate in miniaturization, but recently 0201 and now 01005 passives have arrived, with rumors of even smaller sizes to come. For active electrical components, the 0.4mm pitch component has become commonplace with 0.3mm already in the works. What effect does this miniaturization have on the stencil printing process? Can it meet the challenge? This paper takes a preliminary look at some of the work that has been performed to evaluate the capability of the stencil printing process to print these fine feature components. Discussed is the stencil printing of the small features and efforts to obtain consistent volume in the printed solder paste deposit.
miniaturization, stencil printing, solder paste
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Posted on 4 Mar 2010
by Dr. Ning-Cheng Lee , Dr. Arnab Dasgupta, Dr. Runsheng Mao, Dr. Yan Liu
Electronic industry has been driven toward lead-free by RoHS (Restriction of Hazardous Substances Directive) which is in force since 2006. Recently REACH (Registration, Evaluation and Authorization of Chemicals) further drives the industry toward halogen-free. As a result, solder pastes for PCB assembly are required or desired to be both lead-free and halogen-free. Lead-free solder alloys in general wet poorer than tin-lead due to the higher surface tension of the former alloys. In the mean time, halogen-free fluxes typically also wet poorer than the more powerful halogen-containing fluxes. Consequently, the lead-free and halogen-free solder paste products that emerged inevitably suffer from a considerably inferior soldering performance than that of conventional halogen-containing tin-lead solder pastes. The deficiencies include poor wetting, solder balling, voiding, graping, head-in-pillow, etc. This gap is particularly significant for fine-pitch applications where the impact of oxidation is more profound. Furthermore, the higher soldering temperature of the higher melting lead-free alloys also aggravates the challenge of in-circuit test for no- clean processes, mainly due to the difficulty for probe to penetrate through the toughened flux residue. Although use of inert reflow atmosphere may alleviate some of the problems, the higher cost of it is prohibitive for most of the manufacturing firms. In this work, a halogen-free lead-free no-clean solder paste system, Indium8.9HF series, has been developed. It exhibits superior oxidation tolerance, thus assures superior resistance against graping, head-in-pillow, solder balling, voiding, and poor wetting for miniaturized electronic applications. In spite of the immense challenge in material science, this system also shows outstanding probe testability, in addition to its very good printability, non- slump, SIR, and ECM performance. The superior performance of this Indium8.9HF system effectively sealed the gap caused by lead-free and halogen-free requirements.
lead-free, halogen-free, no-clean, solder, solder paste, miniaturization, graping, head-in-pillow, voiding, solder balling, probe testability, ICT, oxidation
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Posted on 1 Jan 2009
