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Voids with LGAs

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#67948

Voids with LGAs | 17 January, 2013

We have got lots of voids at ALL LGA. Anyone has ideas to get rid of this issue or just minimize the size of voids ?. With the same paste, same reflow oven, looking good profile, we don't have that problem with BGA. Thanks.

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#67950

Voids with LGAs | 18 January, 2013

Just because a certain profile works good for a board with a BGA does not mean it is automatically the correct profile to use for a different board that contains an LGA. Have you run a separate profile check with the board containing the LGA?

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#67953

Voids with LGAs | 18 January, 2013

Yes, I have. think I have pretty good reflow profile. We use Lead-Free,No-Clean,SAC305 Solder Paste. The problem is at LGA design.The pad size is alot bigger than BGA. They are totally flat and do not have balls/spheres which melted and collapsed through reflowing process. Also, there is no space enough to allow gas/air to be escaped. I am trying to contact some reps in South California area to get some different brands of solder paste to be able to test all of them. Thank you for your reply.

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#67957

Voids with LGAs | 18 January, 2013

Main issues with LGA voiding are: * Design * Material selection * Thermal recipe

For design, loo here http://blogs.smtnet.com/smt/other/qfn-btc-design-guidelines-thermal-pads-etc/

BR, davef

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#68080

Voids with LGAs | 1 February, 2013

We have had some success in void reduction with LGA by pre-tinning or "bumping" the devices before placement. The extra solder seems to allow a slightly higher standoff, and allows better outgassing, is my guess. A lot more labor , but the results are notable. You can also experiment with your stencil aperture shapes in an effort to create an outgassing path for the solder paste at reflow. Try small squares or dots, stripes, or something similar when you print the board, that too can help get the voids out. As mentioned earlier, your reflow profile is important too, dwelling at peak for as long as the solder pase spec allows can also help with void reduction. Just some ideas that have worked for me in the past. 'hege

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#68083

Voids with LGAs | 2 February, 2013

The keys to avoiding the voids we have found are: 1. Proper reflow profile 2. Proper stencil design 3. Prebumping using either a metal stencil or StencilMate stencils (and then using paste flux to attach later) http://www.solder.net/products/stencilmate

Using these techniques there are nearly no voids, a greater standoff height for better heat dissipation and ability to get underneath and clean residues.

BWET

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