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Reflow issue with QFN

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#50925

Reflow issue with QFN | 5 July, 2007

QFN assembled on a PCB indicates paramteric fails when tested. When the QFN on PCB is reflowed a second time, it recovers and passes testing. Visual, X-ray inspection revealed no anomalies. Cross-section images of solder joint revealed no anomalies (no traces of non-wetting). Any ideas what may be causing this issue?

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#50927

Reflow issue with QFN | 5 July, 2007

Are you using a leaded or lead-free process?

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#50928

Reflow issue with QFN | 5 July, 2007

Lead-free process.

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#50929

Reflow issue with QFN | 5 July, 2007

I ran into the same thing several months ago, I increased my reflow zone temp 10 degrees and this corrected the problem. For some reason it has somthing to do with the plating on the component. I don't know what part you are running but Some of the MIMs have been this way.

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#50930

Reflow issue with QFN | 5 July, 2007

We've seen non-functional QFNs cured by touching up the toe fillets. Especially with parts that are not plated on the edge/face where you get minimal/no wetting due to oxidation of bare copper. I'm not suggesting that you touch everything up but that the second pass may promote the additional wetting to the face of the part. Increasing your TAL, as another poster suggested, may be your answer but for a different reason.

Just a thought.

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#50933

Reflow issue with QFN | 5 July, 2007

Thanks all! I'm facing this issue with one specific batch of QFNs. It could be a plating issue. But, nothing was evident from visual inspection,No sign of voiding or non-wetting. Cross-section images of solder joints were clean as well. Could this still mean the plating is contributing to this? is there a way to check for plating quality? Would a part performance very sensitive to voiding in ground pad?

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#50935

Reflow issue with QFN | 5 July, 2007

ANSI/J-STD-002, Solderability Tests for Component Leads, Terminations, Lugs, Terminals, and Wires

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#50939

Reflow issue with QFN | 6 July, 2007

Solderability testing and if possible, measure the plating thickness (XRF).

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#51039

Reflow issue with QFN | 13 July, 2007

It sounds like more has to do with plating. you may also check out the voiding issue especially if you have new FAB or the supplier. I had problems with a RF chip in QFN package due to insufficient grounding that voiding caused. This ground is often used for heat relief as well. The recommendation is min 80% solder coverage by area. QFN usually requires paste reduction to avoid open joints. It depends on the via on the pad and solder mask. difficult to avoid via if the via are plugged on bottom side due to air entrapped. I find it works good with no plugging on the via holes. Good luck! Sean

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#51040

Reflow issue with QFN | 13 July, 2007

We have had good success doing pb Free QFN work. Typically for the center pad we use ~68% coverage with 1:1 ratio on the perimeter pad. For the 68% coverage we have tried cross hatch pattern, diagonal stripes, dot series, and most successfully a cloverleaf style print. The correct pattern in the center pad area allows good outgassing during the reflow process, and helps eliminate voiding. Also for these pkgs, you cannot be afraid to get the temperatures up a little bit. They love the heat.

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