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Solder balls high on IC

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Solder balls high on IC | 26 September, 2019

Experiencing some solder balls on an SSO-36 package. Things I am planning on checking are as follows: (not necesarilly in this order)

I am just looking for a sanity check to see if you would try other things to help ?

1) Reflow profile. I have heard increasing the soak zone time to allow for full outgassing may help ? 2) Stencil design. Making sure aperture design matches pad design and is not overprinting onto masking. 3) Part height setting at PNP. Making sure excessive force is not used when placing component. 4) Part to pad design. Unfortunately the datasheet that I found does not show recommended pad design for part ?? Any idea where I would search it down ?

Thanks for your assistance ahead of time.


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Solder balls high on IC | 26 September, 2019

Excellent X-ray picture, very helpful!

It looks like you have a lot of voiding on the center thermal pad. My guess is that outgassing is pushing solder off the pad which is forming solder balls outside the body of the component package.

The first thing I would look at is the stencil design for the thermal pad. A window pane type design will provide channels for outgassing without pushing out solder.

There are a lot of voids on your other solder joints as well. Normally this isn't a big deal, but I'd be concerned about the large voids in the heal filets of the IC.

Tweaking the reflow profile might help. Make sure you are using fresh paste. Also make sure you don't have excessive humidity in your plant. Some solder pastes are very hygroscopic and will absorb moisture in a humid environment. Voiding is often the result. If all else fails, try using a different solder paste formulation.

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Solder balls high on IC | 27 September, 2019

Thank you DWL for this input. I will include this info on my investigation.

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Solder balls high on IC | 30 September, 2019

Hi Scot,

What X-ray machine are you using? that's a pretty good image.



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Solder balls high on IC | 30 September, 2019

I am not quite sure. The analysis came from our sub-supplier. I can find out though. I agree it is a very good image.

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