> > I was a little bemused to receive Jerry's comment and have re-read my > posting. > > Perhaps I should have worded it more clearly, particularly in view of > Karen's reply. As I conduct this correspondence late in the evening, so my > communications are sometimes not as I would intend Maybe Jerry was playing internet in the late evening, also. > of course RF > circuits use AC not DC and that the real issue with flux residues will be > dielectric influences. I would think so. > > I do not agree that AC will not cause dendrites. You have gazillions of > reverse biasing going on at any moment which will certainly limit the > ability of dendrites to form but over time they surely will, particularly if > there is something present to help them. I am very doubtful that purely AC voltage will allow electrochemical migration. However, I am willing to change my opinion if decent experimental proof is given. AC on top of appropriate DC may indeed allow electrochemical migration and dendrite formation to occur. I also doubt that there would be a synergy of AC and DC combined, I would guess that the DC voltage will grow dendrites like the AC voltage wasn't there. > > Many examples of RF circuitry that I have seen, are incorporated near to DC > inputs and other DC circuitry. Such as power inputs for IC's etc., which are prime sites for electrochemical migration to occur. > I am not sure how or why, one would > selectively leave solder residues on an RF circuit where they would > certainly compromise performance and not on the other areas (if present) > where dendrites will form more readily. Gloppy RMA residues (like good old Reliacore 15 (if Graham can do it, so can I)) are not particularly "dendro-genic", nor do they degrade DC and low frequency SIR, like certain no-clean, organic-acid-type residues. They tend to be hydrophobic and act like quasi conformal coatings. However, their residues have dielectric properties that may have a deleterious affect on RF circuits. Adding another layer of dielectric material near a stripline, resonator, etc., may mess up its designed function. > > As to the application of SIR testing, we are looking at developing the > measurement aspects of our system to include for AC circuitry testing which > Karen asked about in an earlier posting. > AC measurements could be a very interesting way of studying SIR and electrochemical reactions in the thin moisture film on circuit board with hygroscopic residues at high humidities. ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################