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QFN84 Solder Printing Issue (QFN with Inner LGA Pad)

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#79319

QFN84 Solder Printing Issue (QFN with Inner LGA Pad) | 10 November, 2017

Hi, we are experiencing insufficient solder and bridging solder. Any recommendation on the inner pad (LGA) and stencil thickness. Any suggestion will be very helpful. link: http://www.latticesemi.com/~/media/LatticeSemi/Documents/ApplicationNotes/PT/PCBLayoutRecommendationsforLeadedPackages.pdf?document_id=46898

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#79320

QFN84 Solder Printing Issue (QFN with Inner LGA Pad) | 11 November, 2017

One suggestion I have seen for packages like this is to have the device balled first.

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#79323

QFN84 Solder Printing Issue (QFN with Inner LGA Pad) | 13 November, 2017

Just a few thoughts, as we use similar quite frequently without issues.

Ensure correct support when pasting the board, especially if it is thin.

Correct support when placing the part. Is it placed correctly by the machine? If it is very slightly off, it should pull in OK. Is the bridging coming from the LGA paste? If so, then maybe your stencil is wrong. If it is bridging across the QFN pads, placement is most likely the issue.

Can you provide us with a picture of a faulty part?

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#79338

QFN84 Solder Printing Issue (QFN with Inner LGA Pad) | 15 November, 2017

IMO – Look into nano-coatings for your stencil and radius all square apertures This should help out with solder paste releasing from the stencil helping with insufficient solder

QFN LGA aperture design, try a stencil cut with a few different aperture designs to test.

I have had success with aperture reductions in “pad” width and increase in “pad” toe (almost 15%) to take care of bridging

For the larger ground center “pad” window pane aperture should aid paste to allow outgassing. Also reduce the ground aperture about 40%, check the volume of paste under the QFN ground, if the volume is too much it will lift/tilt the component too high and could cause opens or poor solder joints on outer “pad”

I hope this helps

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