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QFN soldering

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QFN soldering - 03-/29-12 by johnnysmt

QFN soldering - 03-/29-12 by Bill Axler

QFN soldering - 03-/29-12 by Nguyen ducThanh

QFN soldering - 04-/04-12 by Reese

QFN soldering - 04-/05-12 by aj

QFN soldering - 04-/05-12 by Reese

QFN soldering - 04-/06-12 by umair

QFN soldering - 04-/06-12 by Cadco

QFN soldering - 04-/20-12 by Th. Meier

johnnysmt

#66081

QFN soldering | 29 March, 2012

My company is doing a project with a lot of QFN. The question that we are not sure is how to properly solder a QFN on a PCB. QA says The alignment tab on the side of the QFN should have a physical solder from the board, like a leaded chip. After reflow the QFN do have contact with the board already but no solder on the alignment tab. So we have no manually solder. Does anybody who works with QFN have any input on how to treat soldering a QFN?

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Bill Axler

#66084

QFN soldering | 29 March, 2012

In the IPC-A-610E standard QFNs are classified as BTC (bottom termination components). Most QFNs do not have a solder-able surface on the outside of the part. Usually the lead that you can see on the outside is copper and classified is not solder-able. On these type of parts no toe solder is required. The only way to truly inspect these type of parts is with an x-ray.

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Nguyen ducThanh

#66086

QFN soldering | 29 March, 2012

Your QA don't know nothing about QFN.
look at Bill Axler post, he was 100% corrected.

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Reese

#66111

QFN soldering | 4 April, 2012

I agree, the only way to "truly" inspect a QFN is with an X-ray. But this might be over-kill for him. He asked about soldering, not inspection. We use QFN's regularly and you can inspect these parts from the side to see if they are soldered. Unfortunately, most AOIs are not capable of solder inspection for these parts. So Bill is correct. He is also correct about referring to the IPC standard for QFN components. This is something your design Engineer should do when laying out the pcb. Refer to it for land patterns and dimensions.

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#66118

QFN soldering | 5 April, 2012

if you want to get some sort of a joint even to allow AOI to inspect you can overprint on on the outer lead by 3 thou or so. This will give you a joint that can be seen from the side for inspection purposes.

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Reese

#66119

QFN soldering | 5 April, 2012

Yes, but no guarantee of solderability. This just puts more paste on the pads. From my experience, unsoldered QFN parts are not due to lack of solder, but reflow.

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umair

#66124

QFN soldering | 6 April, 2012

Agree with Reese with my experience with QFN parts it is the reflow.

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Cadco

#66125

QFN soldering | 6 April, 2012

We are a PCB design house/CM and we have found that if you elongate the QFN pads to the outside of the part by .025 to .030 you then have the opportunity of doing touch-up manually with a soldering iron should there be a voiding issue. This would have to be done at the CAD/Gerber level before PCB manufacturing.

Regards to all.
JR

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Th. Meier

#66191

QFN soldering | 20 April, 2012

If you extend the pads you get the effect that the solder below the component is pushed to the outside land which results in a very low standoff of the component, deteriorate the overall quality of the solder joint.
Hot air (pencil or some of the semiautomated rework stations) helps with rework.
We use Ersascope and x-ray for verifying the solder joint quality (Hi-Rel).
Regards, Thorsten

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