Issue link: https://iconnect007.uberflip.com/i/806706
56 SMT Magazine • April 2017 effectiveness of cleaning. The most important factor to keep in mind when comparing clean- ing processes is the outcome. In most indus- tries, the cost of cleaning is less than the price of product failure. Current Study The MicroCare laboratory conducted clean- ing trials in order to evaluate the cleaning capa- bility of new vapor degreasing chemistries on difficult flux and solder paste formulations. The study evaluated three flux formulations and sev- en solder pastes containing leaded or unleaded ingredients. The pastes and fluxes were chosen based on customer recommendations and mar- ket trends. The flux pastes evaluated were AIM 217, AIM No-Clean Paste Flux and AIM Flux Pen. The solder pastes that were evaluated were AIM M8, AIM RMA258-15R, Loctite GC3W, Al- pha OM350, Indium 8.9HF1, Loctite GC10 and Indium SMQ92-J. The Loctite GC3W, Alpha OM350, Indium 8.9HF1 and Loctite GC10 are all lead-free, no-clean formulations. The AIM M8, AIM RMA258-15R and Indium SMQ92-J are leaded pastes. The Loctite GC3W was the only water-soluble paste chosen for this study. Two specially formulated solvents were se- lected for the cleaning trial and were compared to a more common, hydrofluorocarbon solvent. The specialty vapor degreasing solvents will be referred to as Solvent A and Solvent B*. Solvent A is composed of a blend of trans-dichloroeth- ylene, alcohol and hydrofluorocarbons with a proprietary additive to improve flux removal. Solvent B is a non-chlorinated blend of hydro- fluorocarbons, alcohol and proprietary non-vol- atile ingredients. Both chemistries can be used in modern two-sump vapor degreasers without modification, so long as the equipment has ade- quate cooling. These solvent compositions were compared to a common SNAP-approved flux- cleaning solvent with a composition of hydro- fluorocarbons, trans-dichloroethylene and an alcohol; this solvent will be referred to as "Clas- sic Solvent." Surface Insulation Resistance (SIR) testing was performed in order to evaluate the boards for failure due to dendritic growth. SIR testing is common in electronics manufacturing in or- der to verify that changes in temperature and humidity will not cause unexpected failures in the field. Many no-clean fluxes and pastes have been formulated to pass SIR evaluations, though not all. In our study, we found that most of the no-clean pastes were capable of passing SIR evaluation without cleaning; however, three of the no-clean pastes did suffer failures during the evaluations when they were not cleaned. PROCEDURE Visual Evaluation A visual analysis was preformed to compare the cleaning efficiency of Solvent A, Solvent B and the Classic Solvent. B-36 coupons were reflowed with three different no-clean solder pastes: Indium NC-SMQ 92 SAC305, Indium 8.9HF1 and Alpha OM-350 96.5sn/3.0Ag/0.5C. The boards were prepared and reflowed by Al- tek Electronics in Torrington, Connecticut. Ten boards were prepared with each paste. An addi- tional set of ten B-36 boards was prepared with AIM NC217 flux at the MicroCare laboratory according to the product's technical specifica- tions. Boards were visually examined at 15x and 40x magnification before cleaning. One set of traces was photographed for each paste type be- fore cleaning as a reference. The boards were separated by flux type and labeled to represent the flux/paste and the cleaner to be used. Three boards of each paste were cleaned in each of the solvents: Solvent A, Solvent B and Classic Solvent. The remaining boards were retained for future cleaning. Clean- ing was conducted at the MicroCare laboratory in a Branson B452R two-sump vapor degreas- er, and an Ultronix BBMLR120 with retrofitted Zero-0-Coils and an automatic hoist. No ultra- sonic agitation was used during cleaning. Each vapor degreaser was fitted with a basket of ap- VAPOR DEGREASING CHEMISTRIES Table 2: Evaluated Cleaners.