Ok guys, I need help. Here's the deal. We're getting micro solder balls under discreets on the bottomside of the board. Here's my set up...
MPM screener w/vacuum plate 6 mil metal screen with 90% circular (rounded) apertures 7 mil (measured) paste Paste = Kester CENTCH 0445 R256 (63%/37%) No Clean Visc. Ps. 1100-1800 Humidity is normal (whatever that actually is) Part placement with a CP-643E. Reflow with an Electrovert OmniFlow 7 with 7 zones: 130, 160, 160, 170, 190, 240, 240 for both top and bottom convection, moving at 26 in/min, using Air environment.
We're building to class 2 requirements, the board is 8"X11" with 682 discreets being put on the bottomside. What happens is that tiny solder balls are all over the board right next to the component body. IPC has "imbedded" in the paste standard. So, theoretically, were OK, but I just KNOW the customer is going to have fits. Going to the stencil with round aperatures helped but didn't fix it. I ran a bare board thru to see if the masking was the problem; not one solder ball. The nozzle placement of the CP is also good, it's not coming down too far. What's everyones take on this?
Thanks in advance, Antonio
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