Part sliding in reflow?

So, we�re talkin� �bout the smaller end of a "large" paper clip after it�s unfolded once, eh?

In keeping with your "nothin� up the sleeves" full disclosure, I�ll bet you�re feelin� a little sheepish about not tellin� us about: * Antenna pad dimensions, quantity, and location [relative to the antenna] * Results of the reduced blower volume on the SOT23 near the bent-up paper clip thingie * Effect on reflowing other SOT23 packages * Reflow profile, other than letting us fantasize what it would be using a NC paste

I hear you talkin� �bout the blowers pushin� the antenna off its pads and that makes sense [even tho you didn�t tell us, the bent-up paper clip thingie has to be soldered with two pads at the top of the U shape, because the pads have to be small, the U would the relatively long, the U would not be secured at the bottom of the U] because:

1 Bottom of the U acts like a long lever that pivots at the top of the U.

2 Alternately, the "arms" of the upper part of the U could be spreading apart during heating and then closing after the reflowed solder has cooled.

But then I hear you talkin� �bout the blowers pushin� every tenth antenna off its pads and I wonder why every tenth? Why not all of them? Yano, �cause the fans are turned-on, crankin� and doin their thing aren�t they? Could it be that

1 Blowers don�t blow at a constant volume, even though they are set at a constant rate, because they get behind [or ahead] on cooling , then need to crank up [or down] the volume every ten boards? [Didn�t someone like Glenn Campbell do a song about "cranking-up the volume"?] So as the oven compensates by firing-up the blower ever ten boards, it then blows the antenna from its pads. Coo, eh?

2 This could still be explained by the thermal expansion theory [#2 above] if the oven gets real hot to spread the legs [hey, hey, this is a family show, watch it!!!] of the U, get poor reflow bla, bla, bla AND just after that the fan kicks it up a notch [as Emeril says BAM!!!], but not such a high notch to dislodge the paper clip thingie on the next board.

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I some something like this. My package was not flat the belly of the body rested on the PCB. We found that every 4-5 part would wander to the side. What was puzzling is that the blowers would have blown it the opposite side. ultumately we proved the flux was getting under the belly and moved the part as the flux spread. We eventually fixed the problem by changing the part.

Good Luck

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