| Dear Al, | Are these reworked, double-sided boards? | | If you attempt to clean side #2 of double-sided misprint in a "spray" type cleaner, millions of solder balls can be broadcast throughout the same chamber as the populated side #1. Or, if this is a single-sided PCB, the walls of the chamber and the sump of a spray type cleaner will be contaminated with solder balls if a misprint has been previously cleaned in the spray cleaner. We have an article that was published in EP&P on our Web Site by Dick Clouthier formerly of AMTX stencils. He refers to this practice as a "solder ball nightmare." You can down load this article at: | http://www.smartsonic.com Click on the "Recommended Reading" button. | | | We have problems with solder balls after reflow. Anybody have any ideas as to what causes them? | | | | Al,
Assumming your solderball's are from the origonal process there are a number of thing's that could cause them. For Screen Printing - is the screen clean ? also if you set up is wrong you could be either leaving toom much of a gap and the paste is getting onto the resist or too much paste is being deposited which could lead to slumping. If your board thickness isn't set up right e.g. you think it's 1.6 mm but it's actually 1.7mm you could be stressing the stencil and letting solder blead under. If you placement machine is using too high a placement for or the board thickness isn't right that could cause a 'splashing' effect. Misplacement isalso a problem. Assumming that's alright how is your oven profile - ramps rates and so on and how does it tie in with the solder paste manufacturer's 'ideal' profile ?
One thing you could check is that as bill say's for boards that have been cleaned there is the posibility of solder being left on the board or even in pth / via holes.
You could go the whole hog and reflow a board with no paste on it ( and no components) and one with only paste. Is the bare board has solder balls you are probably looking at a bad PCB manufactring process or more likely a bad profile / oven. This would be backed up by the second board with paste but no components, no solderball's on the first card but on this one point'sto the oven / paste compatibility so it's profile etc, no solderballs here either and you may be wanting to look at pplacement pressures etc on you machine. One last thought..are your components alright and are you getting random / nonrandom solderballs
Tuffty
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We have problems with solder balls after reflow. Anybody h...
- Feb 17, 1999
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