Thanks, Chunks. That's the one point of the experiment that we haven't tried yet. Though, we came to the same conclusion just yesterday.
Dave, so far, the most help we've gotten was from the paste manufacturer. I've involved the board house, but the argument almost always goes the same way. Call paste manufacturer, take suggestions, make no progress, told to call the board house. Call board house, get hemming and hawing, have the process blamed, or the paste blamed. Try new paste, ad nauseum.
We agree that 2 minutes in reflow is excessive. And, can't find any logic in that helping. When AIM suggested we increase the front end temperatures, it made some sense...activate the flux earlier in reflow, to help in cleaning the pads of any potential contamination, to allow better reflow. The end result, though, seems to have pushed us towards too long in reflow, and, potentially, exceeding the paste recommended max temperature. Neither of which, we think, is good for the solder joint.
Last night and this morning, we conducted a separate set of trials, aimed at our wash process. We first flipped and ran product without washing it, to see how the paste flowed. Things looked pretty nice; so, we took the next step, and hand washed the boards (same deionized water, and even same intake lines, just removing the actual wash machine from the process). Those boards appeared to run well, as well. Finally, we took a board and washed it in our wash machine (AS900 batch washer), and ran it. This final board exhibited some dewetting, as we had been seeing previously. We removed the inline strainer on the wash, and observed what we believe to be a fair amount of lime-scaling. When a finger is wiped across the strainer, a fine powder is left on the finger. Our working theory at this point is that there's excessive lime-scale (or some other such deposit) in the wash machine, and that this foreign substance is getting onto our boards during wash/dry cycles, and from there causing our dewetting problem (which, we initially thought to be contaminated boards). I'm off to pick up some CLR, and do some machine scrubbing later today, to see if that helps to improve things.
cheers ..rob
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