![]() Eliminating this tape from the dicing process solved the problem. A specific contaminant that caused solderability problems was a silicone residue left behind from a tape used during dicing of the ceramic assemblies to their proper size. Defects that did occur were primarily due to incoming chip/ceramic carriers being contaminated and process or tooling errors. The change to the no-clean system allowed IBM to eliminate half of the process steps previously required for joining, while maintaining yields and product quality comparable to the old process (defect rates were 0.05% with the no-clean process versus 0.03-0.06% for the rosin-based process). ![]() This hydrogen-flux combination system was used because the standard no-clean fluxes will not withstand the high temperature reflow cycle required for flip-chip on ceramic assembly. The flux also almost completely decomposes after processing in the hydrogen atmosphere, thereby leaving minimal residue. The flux and hydrogen both clean solder surfaces and reduce oxidation in this system. This was done by combining a mildly activated, no-clean fluxing material in combination with a hydrogen reflow reducing atmosphere. IBM successfully converted from rosin-based flux to a no-clean flux for the flip-chip process (a method used to attach dies to ceramic carriers), resulting in the elimination of perchloroethylene and xylene in the process.Electrical performance was not compromised with the no-clean paste. It found that yields with the no-clean pastes used were equal to those achieved with the aqueous pastes, and that only a minimal visual residue was left by the pastes. Solectron Corporation of Milpitas, California reported on making a successful transition to no-clean solder pastes from aqueous-based solder pastes for both oven reflow and wave soldering processes.However, the researchers observed that most of these defects stemmed from printing, as opposed to IR reflow. The researchers observed that the most frequently observed defects found in no-clean processed boards were bridges, coplanarity, insufficient solder, no-joint made and misregistration. Processing with no-clean pastes resulted in boards that passed both electromigration and SIR tests, even though some quantity of residue was visible on all boards processed using the no-clean pastes. Next, tests were conducted on four types of boards similar to those actually used in military assemblies made at Martin Marietta (Lockheed Martin). First, the pastes were all chemically analyzed, tested for corrosivity, screen printed onto standardized test boards, and processed (reflowed) in a five-zone infrared (IR) oven. Department of Defense-funded tests were conducted at Binghamton University on 10 different no-clean solder pastes for use in military applications.Some examples from the literature include: It also lead to a major effort by the Department of Defense to test no-clean fluxes and prove their acceptability for military applications. This lead to some collaborative efforts between vendors and manufacturers where vendors have adjusted no-clean flux formulations while working with a manufacturer on no-clean implementation. The need for alternatives to be available quickly once the Montreal Protocol went into effect forced many no-clean fluxes into the marketplace before their use was completely understood or optimized. It is also clear from these reports that the technology is rapidly changing and evolving. It is clear from these reports that no-clean technology is a technically viable alternative for many soldering applications, using either wave soldering or oven reflow soldering. Both laboratory, pilot-scale, and full-scale implementation studies have been reported on in the literature. In addition, the United States government, especially the Department of Defense, has funded a number of tests and investigations of the no-clean fluxes. No-clean approaches for soldering in electronics manufacturing are already used successfully by a number of manufacturers (primarily the larger ones, such as IBM, AT&T, etc.) in full-scale production. Return to the first page of the No-Clean Cleaning Technology Review NO-CLEAN FLUX DOES NOT MEAN NO CLEANING AT ALLĪN ALTERNATIVE ATMOSPHERE, SUCH AS NITROGEN, CAN HELP VISIBLE RESIDUES: NOT NECESSARILY DETRIMENTAL TECHNICAL FEASIBILITY OF NO-CLEAN APPROACHES
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