We have set up our Emulsonators with wash time of 30 minutes and rinse time of 15, but the rinse cycle will continue for up to 30 minutes if wash sump resistivity does not reach at least 1 megohm-centimeter. If this level is not met within 30 minutes, the cycle will abort. FYI to the group, this is a batch "dishwasher" style machine, with counter-rotating spray arms at top and bottom, and separate wash and rinse tanks. The wash tank contains water with 5 or 10% of wash chemistry, in our case Bioact EC-7R. Bioact is not miscible, and separates, but pumping action creates an emulsion that is pretty effective at removing RMA flux. After the wash cycle, the emulsion drains back into the wash tank, the valves close, and DI water is pumped into the cleaning chamber from a separate tank and recirculating loop. In this loop, rinse water drains from the wash chamber into a decanter, where Bioact floats to the top, and the water returns to the rinse tank. Rinse tank water is pumped through a particle filter, carbon, and mixed-bed before it flows into the wash chamber. Since water does not mix with Bioact, the rinse operation uses water to mechanically remove the solvent, basically "pushing" the Bioact residue off of the board surfaces. Any solvent left on the board will include flux and ionic residues dissolved within. In our process, boards come out with no visible flux residue, but we use these systems for gross flux removal, not final ionic cleanliness. Before conformal coat, we clean with a separate dishwasher containing 75% IPA and 25% DI water. -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Wednesday, April 16, 2003 8:12 PM To: [log in to unmask] Subject: Re: [TN] Cleaning Question - Rinse water resistivity? Hi, Jason, The resistivity setting will depend on a few factors: 1. The total area (both sides) of boards you have in the machine during any given cycle. 2. The cleanliness level you're trying to achieve for the boards. 3. The volume of water in your rinse cycle. 4. How good your machine is at correlating actual contamination levels to what it measures or reads. If you multiply your total board area by the cleanliness level you require, you will get the maximum salt equivalent total weight of contamination allowable. That amount of contamination divided by the volume of water will have some direct relationship to the resistivity delta of the water, which I guess you can either look up in tables or work out for yourself by experimentation with known volumes of water at known resistivity to which you add salt in precisely known increments and chart the resistivity drop against cumulative increments. Look up the total allowable contamination weight form your first calculation and compare it with your chart - that should give you an equivalent resistivity. Personally, I do not trust cleaning machines that give you a "cleanliness" readout for a couple of reasons: 1. It gives you a very subjective result - the best job it can give you, no matter how good or how bad, is always "clean". Why? Because it's using the same water to tell you so that it's been using for rinsing the boards. If the machine can remove no more contamination, the resistivity will be high (i.e. board = clean), but you have no idea how much contamination the machine has not been able to remove. There is no alcohol in the rinse water to dissolve other contaminants that are trapping remaining ionics. 2. The reading a cleaning machine gives you is an average cleanliness of all the boards in the machine during that cycle. It's likely that the machine does not clean entirely evenly - boards in the corners of the machine probably don't get the same pattern of cleaning water or rinse water that a board in the middle of the machine does, so cleanliness results will vary. Although your average reasult may show that your batch of boards are clean enough, it is only an average. You will thus wind up with boards that are cleaner than average and others that are dirtier - how much cleaner and how much dirtier, you cannot tell. Therefore to again have a better idea on what resistivity figure to set you machine to, you will need an independant ionic cleanliness tester to test several batches of boards using an alcohol/DI Water mix. Your tester will also have to be checked out so that you have a correlation chart for it as well (actual salt weight vs machine reading). Test each board individually and map results against the board's position in the machine. Examine the variance of the results and see how many boards are dirtier than average and where they are located in the machine. From this analysis, you should be able to determine what resistivity value you should plug into your cleaner such that all your boards come out at least as clean as you want. Hope this doesn't give you a bad weekend. Peter Wilson Jason <[log in to unmask]> 16/04/2003 06:34 PM Sent by: TechNet <[log in to unmask]> Please respond to "TechNet E-Mail Forum."; Please respond to Wilson Jason To: [log in to unmask] cc: (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group) Subject: Re: [TN] Cleaning Question - Rinse water resistivity? Hi, We do use DI water in the rinse. We use AAT Corp Emulsonator 9700. It has the feature of monitoring the rinse cycle's resistivity, and comparing that to a predetermined value. When the resistivity reaches the predetermined value the rinse stops (if the time has expired). Thus I am not sure what to enter for the predetermined rinse restivity value. Does anyone have a similar machine? We use an RMA type flux. Thanks in advance for any help, Jason >>> [log in to unmask] 04/15/03 04:31PM >>> Jason, I would recommend that you use deionized water in your cleaning for the same reason that soft water is better for cleaning clothes. DI water is a hungrier solvent. I would recommend using 2 megohm-cm resistivity water (0.5 uS/cm conductivity) as a minimum. When you get below 2 megohm, you get in RO purity water, better than tap water, but not as good a cleaner. I also recommend 140-150F for temperature. A 10 minute rinse is about normal. Doug Pauls Rockwell Collins Jason Wilson <wilson.jason@NORTHROP To: [log in to unmask] GRUMMAN.CA> cc: Sent by: TechNet Subject: [TN] Cleaning Question - Rinse water resistivity? <[log in to unmask]> 04/15/2003 01:39 PM Please respond to "TechNet E-Mail Forum."; Please respond to Jason Wilson Hi Everyone, I am a new member to the list and I have a question on cleaning. Thanks in advance for any help you can provide. It is much appreciated. What should the value be for rinse water resistivity? The cleaner we have is a AAT Corp Emulsonator 9700. We use an RMA flux (both in wave solder, and in solder paste). The solvent we use is EC7R. Also, we currently rinse for 10 min (+ time to reach resistivity). Does this seem low? We are having trouble with board cleanliness. Once again, thanks for any help provided. 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