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LGA... where to start?

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LGA... where to start? | 8 May, 2014


We are about to start building a new PCBA using a LGA, we have not used such components in the past, is there any recomendations you can provide me? I've found some articles saying that stencil thickness is the key, what is your experince using LGAs? Any special care when printing, placing, soldering? what about rework?


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LGA... where to start? | 8 May, 2014

There are many different style LGA packages, but don't sweat it. Stick with the manufacturers recommendations for PWB pad geometry for a start. Voiding can be reduced by careful profiling, and also by pre-tinning the devices. QFN style packages can be pre-bumped prior to SMT process too. For QFN style packages, you might reduce the solder at the center ground pads by about 40%, and leave the perimeter pads at 1:1, both to ensure a good connection and to reduce voiding at the ground pad. Plenty of experience wiht these packages here, so continue to post questions and the group will provide knowledge, I am sure. 'hege

You'll zero in the process quickly.

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LGA... where to start? | 9 May, 2014

REduction of center pad is the key as well as the stencil thickness. Having too big opening on your stencil will sometimes lift the part from the pads. Always try to make windowpane and shoot for about 60% of the thermal pad to be covered as start point(as suggested in the earlier post).

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LGA... where to start? | 9 May, 2014

we are placing small QFNs with no major issues, but this one may not seem like a QFN with thermal pad... I'm attaching a picture of the component.


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LGA... where to start? | 9 May, 2014

I might start with the equivalent 4 or 5 mil stencil and 1:1 on the apertures.

If voids are too prevalent, then I would tin the pads of the device, remove the solder, and then solder as above.

You may have another hurdle, in that the resulting standoff height may not be sufficient for your cleaning process.

This looks like it could turn out to be a No Clean process, or it might require some augmentation to your cleaning in order to remove residues from beneath the part when assembled to the PWB. Best of luck. Don't over think it. 'hege

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