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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


HELP ( SOLDERING ISSUE)

Sal

#2637

HELP ( SOLDERING ISSUE) | 26 October, 2000

Guys! witnessing a problem i've never seen before.Manufacturing a mixed technology with HASL finish, BGA,QFP's,fuses etc..etc. I've profiled the product, but what i'm witnessing is really weird. I've got a 0.020" QFP which is at the edge of the board, and under close scrutiny what I've seen is that the solder fillet has a toe, it has a fillet,.....get ready for this !!! the main body of the fillet doesn't seem to have formed, and the paste doesn't seem to have reflowed just on that mid-section. The worst thing is that it's not on everyboard, but when it does happen it's always the same lead.Like I said the profile which is product specific seems fine, the convection oven is extremely stable and there is no evidence of any contamination on the pad itself, every other device and lead on the product seem fine. The worst thing about this is we have a customers inspector on site who found the problem, and is seeking anwers. All I've done so far is scratch by head, HELP!!!

SAL.

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#2638

Re: HELP ( SOLDERING ISSUE) | 26 October, 2000

Sal: Two things: 1 Duct tape the scope to the back of your customer�s head so he / she can�t find stuff like this. 2 Profile that lead.

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#2639

Re: HELP ( SOLDERING ISSUE) | 26 October, 2000

No vias or other nasties near or under pad? Check the cad file of middle layers if applicable. Not being programmed on site or by customer with contamination in programmer? Most unusual. Let us all know if ( when ) you find out.

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JohnW

#2640

Re: HELP ( SOLDERING ISSUE) | 27 October, 2000

Sal,

check the spec of the components, what are the leads made of?? also check what's happening under the pad, is there a large ground plain or a heavy track running there??

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#2641

Re: HELP ( SOLDERING ISSUE) | 27 October, 2000

1) Na, I wouldn�t give my scope out of hand, need it to much. 2) Profiling for that pin is a good thing.

I don�t know your oven but some will react to exessive external air flow ( means windows and doors wide open ) with sudden loss of temperature to such an extend that normal reflow will not take place. This occurs or is seen on the leads that need the most heat for proper soldering first. I too was scratching my head until we found out the cause for this only-sometimes-occuring mess.

Good luck

Wolfgang

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#2642

Re: HELP ( SOLDERING ISSUE) | 30 October, 2000

Sal,

I kind of assume you have paste there to start with... Because sometimes the edge components do not have paste applied caused by the bottom support in the screen printer etc. And if that is the case for one direction, the other direction applies the paste OK and around 50% of the boards come out with problems...

Again, assuming you had enough paste there to wet, I also would wanna know what's happening on that lead but I have one suggestion...

If the oven flow rates are not adequate, the amount of heat transfered to that lead will depend on the number of boards you have in that section of the oven. The boards will be acting as heatsinks, and if a board goes through all by itself, the heat will be enough to wet the solder... However, if 2-3 boards are sent through all at once, they will have to share the heat blows on them, where non-wetting may occur.

So, if/when you run the MOLE profiler through, I would make sure same amount of boards are being sent through, one with the sensor to simulate the real life case... The profiling unit may also absorb some heat too, so it's good to keep it away from the experiment board...

I stopped smelling the oven fumes almost a year ago, so I hope my suggestions help...

Erhan

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