On Sun, May 22, 2011 at 12:51 AM, PICdude wrote: > I was actually thinking that the rings were formed when the first > reflowed side went back in for the second pass, so I guess that's not > it. =A0Can you post a pic of what these "rings" look like. I'm finished my current batch of PCBs, but I will take a picture next time I run a board. > Have you profiled your reflow oven temps, and can you see at what > point they form? =A0I've got a 3-zone conveyor oven and have not seen > that before (from what I gather these rings would look like). I hadn't thought of that, but I will try to figure that out. I'm just using a thermocouple and controlling the oven manually so I doubt I'm right on the correct profile. > What are you using to clean the board & stencil? =A0I use IPA for the > PCB, but that doesn't clean the (stainless) stencil properly, so I use > a flux remover pen and that works beautifully (though takes time). Same here. It seems to clean my stencil fairly well. I just keep wiping each side until nothing comes through the other side. > Yes, it's a common misconception that the pad size is always the > perfect size for the stencil apertures, but component height makes a > big difference too. =A0Considering the low height of SSOP pins, it's > obvious now that less solder would be great. I think it's a combination of component height and pad size. I'd have to check, but I think the landing pattern that I'm using for the SSOP is long under the chip, meaning there's a lot of solder that then gets wicked up by the pins. I think I mentioned it in a previous email, but I also have some pads deliberately oversized to help with manual soldering. I generated the stencil by using an Eagle script that writes to DXF. I then took that to my laser cutter's and had them cut it out of mylar. It exported the pads as a blocked shape. I think I need to convince it to export as an outline, as then I'd be able to move the lines around to resize things. I don't want to just shrink the pads by some amount, in the SSOP example above I want to move the inner edge of the aperture out. Overall, for my first paste/reflow experience, I'm pretty happy with how this is going. Some room to improve, but it isn't too bad! Josh --=20 A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. =A0 =A0 =A0 =A0 -Douglas Adams --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .