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Fine Pitch QFP Bowing after reflow


DCK

#17922

Fine Pitch QFP Bowing after reflow | 17 October, 2001

The fine pitch QFP is a 240 pin one being loaded with other components on a 2.0mm thick FR4 PCB. There are 6 of this Qfp's on this PCB showing the same charactristic of bowing therfore the solder fillets are vary from the center to the end of the package.

The reflow profile used was a generic one being used for another 8 PCB types of the same complexity.

What caused this problem and how to solve this?

Rgds, Daniel/Manny

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#17929

Fine Pitch QFP Bowing after reflow | 17 October, 2001

Dear Daniel,

I assume that these components are moisture-sensitive. If they have absorbed too much moisture prior to reflow you might be experiencing popcorning. This typically shows up as a bulge over the surface of the die, in the center of the package. The bulge can be on the top side or bottom side of the component. If it is on the bottom and the component has a fairly low standoff (distance between body of component and bottom of leads) this can be enough to lift some leads off the pads on the PCB. In most cases these deformations are on the bottom side and thus impossible to detect with a normal lead standoff.

In any case, to verify if moisture is causing this problem, simply bake your components prior to assembly, at 125C for 48 hours or less, based on moisture sensitivity level and body thickness (ref. joint IPC/JEDEC standard J-STD-033, available for free at http://www.jedec.org).

Please note that if you are experiencing popcorning you should be concerned about other assemblies that can contain damaged component. The parts that do exhibit popcorning represent the most severe case of internal delamination and they may still pass electrical test. However, partial cracks and delaminations that cannot be detected may also cause potential field failures.

If the problem is not related to moisture then it is most likely a design issue with the component and you should consult your supplier.

Good luck !

Fran´┐Żois Monette Cogiscan Inc. 450-534-2644 fmonette@cogiscan.com

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#17931

Fine Pitch QFP Bowing after reflow | 17 October, 2001

Help us understand your situation better:

ARE THE QFP BOWED? If so, * Where are the QFP bowed? * Is the QFP body bowed or is it just the leads? * How much are the QFP bowed? * Are all QFP the same part number, from the same supplier, date code, etc? * What is your experience with this QFP?

ARE THE LEADS OF THE QFP MISMATCHED WITH THE PADS ON THE BOARD? If so, * Describe what you see when you place a QFP on the pads of the board with no paste. * Is the spacing between all QFP leads equal? * Is the spacing between all board pads equal? * What measuring unit does the fabricator of the QFP use? * What measuring unit does the fabricator of the board use? * What measuring unit does the designer of the board use?

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Hussman

#17938

Fine Pitch QFP Bowing after reflow | 17 October, 2001

Moisture has done this to me in the past. Try baking a few QFPs first and then place and reflow. I had to remove them from the tape and reel and place them from a tray - but it was moisture related.

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