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DPAK's sliding off pad during reflow

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DPAK's sliding off pad during reflow | 11 August, 2015

We have had two jobs that have the same issues with DPAK's sliding off their pads during reflow. We tried to resolve this by placing epoxy on the side of the component to create a "dam". However this is not repeatable enough to be a quality resolution.

Has anyone had a similar situation? If so how did you resolve it?

Thanks Sam

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DPAK's falling off pad during reflow | 11 August, 2015

I assume that these parts are falling off during second-side reflow?

The easy solution, of course, is to not build high-mass components on first-side reflow. If this isn't practical, however, you can try using epoxy/glue under the component. We've tacked the sides of components before as well, and, as you noted, it's not wholly repeatable.

You could also consider assembling the parts by hand, depending on the number of parts to be assembled, and/or the number of boards to be run.

Cheers, ..rob

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DPAK's sliding off pad during reflow | 13 August, 2015

Hi Sam,

I have a feeling that what you're trying to communicate is that your DPAK's are skewing off the pad during reflow. This is caused by a thermal "mismatch" where the solder paste on one side of the DPAK becomes molten before the other, then the surface tension of the solder adhering to the part causes the part to shift in position. You can control these by several means. My first recommendation is to examine the part's corresponding pads on the PCB as well as the solder paste aperture's on the stencil. Check to see that they follow the part manufacturer's recommendations. You can also adjust aperture sizes to control the amount of solder paste deposit being applied.

If all of the above checks out to be okay, try turning your PCBs 180 degrees before reflow. See if this changes the thermal footprint enough to have an effect. You should also profile your oven and use this PCB with thermocouples applied to either side of this part. That way you can measure which side reaches the melting point of the solder faster. You can always increase your soak time to try and get both sides to go molten at the same time.

Anyway... that's my six cents worth of opinions.

Good luck, please let us know how it turns out.

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DPAK's sliding off pad during reflow | 13 August, 2015

Loctite 3609. Just a small dot under the D-Pak and it works 100%.

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On-board Dispensing of Dots & Lines

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