Issue link: https://iconnect007.uberflip.com/i/806706
April 2017 • SMT Magazine 57 VAPOR DEGREASING CHEMISTRIES proximately 500in 3 in size. The three boards of the same paste were cleaned simultaneous- ly. The three boards were stacked vertically in the baskets with wire boundaries on each side to keep the boards from touching. The clean- ing cycle remained consistent for each set: 30 seconds in the vapor zone, five-minute immer- sion in the boiling liquid, five minutes in the rinse liquid and 30 seconds in the vapor zone. The timing was controlled and monitored by an operator or by a timed automatic hoist when available. After the final 30-second vapor rinse, the boards were held in the cooled freeboard area for approximately 30 seconds to allow for any excess solvent to drip off. After cleaning, the boards were immediately inspected at 15x and 40x magnification and evaluated for clean- liness. One representative set of traces was pho- tographed for each paste and each cleaner. SIR Evaluation The two advanced solvent formulations, Sol- vent A and Solvent B, were selected for clean- ing evaluation with visual inspection and SIR analysis. The Classic Solvent was omitted from the second round of visual analysis and the SIR testing due to the poor cleaning results of the first visual evaluation. A selection of three flux- es and seven solder pastes were evaluated. A total of 98 B-24 boards were prepared for the SIR testing: six boards were supplied without flux—three were cleaned in Solvent A and three were cleaned in Solvent B; 60 boards were re- flowed with flux/paste—30 were cleaned in Sol- vent A and 30 were cleaned in Solvent B; three boards of each flux/paste were reflowed and left un-cleaned as controls; two boards were sup- plied with no flux/paste and were un-cleaned as blanks. Each of the boards contains four pads of traces. No components were attached to the pads. All of the B-24 boards were prepared and reflowed by the AIM Solder lab in Montreal, Canada, per IPC-J-STD-004A controls. Cleaning was again conducted at the MicroCare laborato- ry 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. All boards were vi- sually inspected before any cleaning was per- formed. The boards were visually examined at 15x and 40x magnification and one of the four pads was photographed for each representative paste/flux. The boards were separated by flux type and labeled to represent the flux/paste and the cleaner to be used. Three boards of the same flux type were cleaned simultaneously in one of the solvents. The cleaning process used for all solvents was the same as the visual evalu- ation cleaning: 30 seconds in the vapor zone, five minute immersion in the boiling liquid, five minutes in the rinse liquid and 30 seconds in the vapor zone. The timing was controlled and monitored by an operator or by a timed au- tomatic hoist when available. After the final 30-second vapor rinse, the boards were held in the cooled freeboard area for approximately 30 seconds to allow for any excess solvent to drip off. The boards were im- mediately inspected again at 40x magnifica- tion, photographed, packaged in ESD anti-stat- ic bags and labeled. Visual evidence was record- ed with photographs and an overall assessment of the cleanliness was determined. The pack- aged boards were boxed and shipped out to the National Technical Systems laboratory in Balti- more for SIR evaluation. The SIR method fol- lowed IPC-TM-650 Method 2.6.3.3, require- ments per IPC J-STD-004A, paragraph 3.2.4.5. After testing, all boards were sent back to the MicroCare laboratory for disposal. Results Visual analysis of the boards prior to and after cleaning showed positive effectiveness of the cleaners. Visual analysis was conducted on each pad of traces on each board at 15x and 40x magnification. The visual results were approx- imately quantified using a percentage system: if all three boards of the same paste set had no visible residue after cleaning they were desig- nated 100%; if one-three visible contaminat- ed traces were found on the three boards of a paste set they were designated 90%; if more than a total of three contaminated traces were found on the three boards of a paste set they were designated 50%; if boards contained most- ly contaminated traces with softened or dried residues they were designated 10%. Contamina-