Quoting Josh Koffman : > I do use two passes. I've actually been doing the bottom side first as > it has fewer semiconductors (figuring it'd stress them less to only be > heated once). The ring shows up on the bottom only, and after the > first reflow. The second time through doesn't seem to do much to the > rings. I haven't tried swapping the order, though that was something > that occurred to me earlier today too! I wonder if there's something > on the board that burns off during the first pass, thereby leaving the > second pass less ring-y. That said, if one side had to have rings, I'd > rather keep it as is, the bottom is much less populated and easier to > clean. I was actually thinking that the rings were formed when the first =20 reflowed side went back in for the second pass, so I guess that's not =20 it. Can you post a pic of what these "rings" look like. Have you profiled your reflow oven temps, and can you see at what =20 point they form? I've got a 3-zone conveyor oven and have not seen =20 that before (from what I gather these rings would look like). What are you using to clean the board & stencil? I use IPA for the =20 PCB, but that doesn't clean the (stainless) stencil properly, so I use =20 a flux remover pen and that works beautifully (though takes time). > I've been wicking with the SSOP parts as well, seems to work. I'm > using a 4 mil mylar stencil, laser cut. I think I need to reduce the > aperture size, particularly on some components where I've deliberately > made a large landing pad to facilitate hand soldering (if needed). > Resizing the aperture should allow a better relation of solder paste > to actual component size, rather than just covering most of the pad > with paste. Yes, it's a common misconception that the pad size is always the =20 perfect size for the stencil apertures, but component height makes a =20 big difference too. Considering the low height of SSOP pins, it's =20 obvious now that less solder would be great. Cheers, -Neil. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .