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SOT23s and paste + glue

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#57663

SOT23s and paste + glue | 22 December, 2008

We changed paste manufacturers rather recently and are now seeing SOT23s falling off after wave solder. These parts have a dual process... we stencil print paste, apply glue, populate then reflow. Only SOT23s fall off, chips are fine. We do not believe we've had this problem with the previous SMT solder paste. Anyone else experience this issue or provide some suggestions? PS - we're using paste and glue to overcome design issues with solder shadowing with SOT23s.

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#57664

SOT23s and paste + glue | 22 December, 2008

Hi,

it seems like a glue problem to me. If you don't have enough glue on SOT23, you have no contact and the part is holded only by the paste, which results bad in the waver machine. So first I would check is the glue amount under the SOT. The second is the profile. You changed the paste and probably changed your profiles. May be that is not good for your glue and it doesn't harden. We usually run only glue and than wave. Regards, Emil

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#57667

SOT23s and paste + glue | 22 December, 2008

As Emil says, it's 100% the glue! Your paste is not designed to hold parts on at wave solder. Reflow is MUCH hotter than glue, so I doubt you're not adequately heat-curing it. Possibly, the glue cure is "too hot" and maybe making the material brittle and/or degrading its bonding properties - you'll need to consult with the glue manufacturer's Chemist/Tech. Apps guy.

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#57668

SOT23s and paste + glue | 22 December, 2008

We run our process like that all the time paste then glue we use same profile as if we were just reflowing paste once in a while we have A plastic bodied part that has that problem we asume it was some mold relase still on the part basicly comtamenation on the body of the part we don't place sot-23 but do place some other plastic bodied diodes with j leads. just look at your glue dot where the sot-23 feal off and see if the glue dot is flat on top or not that will tell you if the part touched the glue.

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#57671

SOT23s and paste + glue | 22 December, 2008

The first question in solving the "ol' SMT component loss after second-side wave operation" problem is: So, what makes you think the components actually came-off in the wave and not during some previous 'handling'?

Putting that aside, we'll play this game straight-up. That chips stick and only SOT fall off, makes us: * Believe the glue and cure are OK * Wonder what's the deal with the SOT.

Residual mold release on the SOT [that Wrongway suggests above] is a good explanation, if the SOT are from the same source and date code and the glue is still on the board and not on the SOT. Other possible explanations are: * Board warp across the wave is snapping the SOT from the board. * Chimney or other wave innards are tall enough to bump the thicker SOT from the board, but not the thinner chips.

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#57681

SOT23s and paste + glue | 24 December, 2008

Oh,I consider the process is wrong,it is stencil print paste-mount-reflow -apply glue-reflow,then wave solder. it must pass twice reflow,also the first reflow profile is different and the second .

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