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High Reliability Techniques For Benchtop PCB Cleaning
Analysis Lab |
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Authored By:Lindsey Shehan Techspray Amarillo, Texas SummaryThe purpose of this study is to determine whether or not aerosol benchtop cleaning can consistently and reliably clean reworked circuit boards. Different variables that play a role in the effectiveness of aerosol benchtop cleaning were examined. These variables included straw attachment, spray technique, spray angle, handheld cleaning tools, brush attachments, and a final rinse. While no approach to aerosol benchtop cleaning was found to be 100% effective all of the time, the study did yield good information that can be used as general guidelines to improve benchtop cleaning processes. ConclusionsThere is no "one size fits all" approach to aerosol benchtop cleaning. There are too many variables that prevent developing a method or formula for cleaning that appears to be 100% effective all of the time. That being said, some methods do work better than others, and selecting the correct combination and formalizing the process will reduce variability. The following information is intended to be used as a general guide to improve benchtop cleaning effectiveness. First, boards should be held in an upright position for cleaning, at a slightly backward angle (approximately 30 degrees was used in testing). As the board is cleaned, keep the board in this same upright position, do not rotate the board. This board position helps to ensure that all residues move in the same direction throughout the entire cleaning process, down, and eventually off of the board. Using an aerosol with a straw attachment helps to focus the solvent spray; thus, eliminating waste. A pre-rinse should be utilized; wetting the entire area to be cleaned from top to bottom. This step begins solvating the flux residues. The next focus should be on the corners of each of the components to be cleaned. A short burst under each corner (down into top corners and up into bottom corners) will help to break up any flux dams located there. It is important to take steps early in the cleaning process, as clearing the corners of the components of flux residue opens the number of paths the solvent can travel as it works its way under the component. Attention should be given to each side of the contaminated components by spraying back and forth across each side of the component. To keep all residues moving in the same direction, down and off, work your way around the components moving from top to bottom. For each side, keep the straw angled so that it is spraying under the component. This step is an opportunity to remove flux residues from under the components. It is better to slightly overdo this step. If you underestimate and don't use enough solvent here, you will only move the residues around, not out from under the component. Spray each component surface, angling the straw to spray away from each side of the component. This helps to move residues away from the component and ensure that no residues are trapped between the leads. The last step is the final rinse. Again, working from top to bottom spray the affected area to rinse all residues completely off of the board. Although this process seems elaborate, the total time averaged 60 seconds per board. Additional cleaning tools intuitively make sense, but did not increase cleaning performance and slowed down the process. For critical cleaning, this technique should be used to achieve an acceptable level of cleaning effectiveness and repeatability, similar to automated methods. Initially Published in the IPC Proceedings |
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