Skewing chip components

Sal,

Silly question: Were the parts skewed before they went into the oven? I've chased down a few similar reflow problems in my lifetime, only to find out it was a pick and place problem. Wrong nozzle size, bad nozzle, feeder not advancing all the way and giving an offset pcik point, etc.

Do traces under the components add to their propensity to skew? I've seen it on 0402's, but haven't really noticed an impact on 0603's or bigger.

Is it a profile problem? Maybe if you are ramping really fast, and the paste's solvents are boiling out on you. Do you see any solder spatter on the boards?

Is it because you changed your apertures to home plates? Doubt it. If it were a paste deposition issue, you would see tombstoning and drawbridging in addition to simple skewing.

Could it be a design issue? Like poor thermal relief on pads? Could be, but again, you would see tombstoning.

Could really close vias be sucking the solder off your pads? Better look in the scope.

They're all possibilities, but my gut says check the pick and place setup.

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Hi Sal,

I assume your homeplates are designed with the peaks towards the componentcenter. I can imagine that due to placement inaccuracy not both sides sit in the same amount of paste and that wetting difficulties prevent same force factors for both sides of the component. Actually I�m not yet a friend of this aperture design and haven�t tried it, some others swear on it. We reduce the amount of paste by an overall reduction of the aperture opening and haven�t noticed any skewing and eliminated solder balls as well. It would be interesting if this skewing also occurs with the same board and normal aperture design. From the fact that this happens randomly across the board I would say that�s not a problem of tracks and vias and for the profile, hmmm, did you try different ones ?

M2C

Wolfgang

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