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Skewing chip components

Sal

#3719

Skewing chip components | 22 June, 2000

Guys

Just completed a PI build. And for the first time found that some chip components are skewing. The board is approximately 8x8inches and is six layer double sided FR4. To minimise and eradicate solder balling all the chip components have been converted to the home aperture design. The skewing chip components are happening randomly across the board.There is a large concentration of tracks and vias running of these chip components, Is this having a bearing to what I,m seeing ? or is this just a profile issue? Any opinions or advice would be gratefully appreciated.

Sal.

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#3720

Re: Skewing chip components | 22 June, 2000

Sal,

Silly question: Were the parts skewed before they went into the oven? I've chased down a few similar reflow problems in my lifetime, only to find out it was a pick and place problem. Wrong nozzle size, bad nozzle, feeder not advancing all the way and giving an offset pcik point, etc.

Do traces under the components add to their propensity to skew? I've seen it on 0402's, but haven't really noticed an impact on 0603's or bigger.

Is it a profile problem? Maybe if you are ramping really fast, and the paste's solvents are boiling out on you. Do you see any solder spatter on the boards?

Is it because you changed your apertures to home plates? Doubt it. If it were a paste deposition issue, you would see tombstoning and drawbridging in addition to simple skewing.

Could it be a design issue? Like poor thermal relief on pads? Could be, but again, you would see tombstoning.

Could really close vias be sucking the solder off your pads? Better look in the scope.

They're all possibilities, but my gut says check the pick and place setup.

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#3721

Re: Skewing chip components | 22 June, 2000

Hi Sal,

I assume your homeplates are designed with the peaks towards the componentcenter. I can imagine that due to placement inaccuracy not both sides sit in the same amount of paste and that wetting difficulties prevent same force factors for both sides of the component. Actually I�m not yet a friend of this aperture design and haven�t tried it, some others swear on it. We reduce the amount of paste by an overall reduction of the aperture opening and haven�t noticed any skewing and eliminated solder balls as well. It would be interesting if this skewing also occurs with the same board and normal aperture design. From the fact that this happens randomly across the board I would say that�s not a problem of tracks and vias and for the profile, hmmm, did you try different ones ?

M2C

Wolfgang

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C.K.

#3722

Re: Skewing chip components | 23 June, 2000

Chrys:

Funny that you mention that, but here at my company, our oven is blamed on almost everything: skewing, tombstoning, solder shorts, etc....

In fact, we often have to tell the supervisors, "It's not the oven because we don't turn the skewing mechanism on in our ovens."

Often times, our soldering defects are results of placement problems...our placement guys, particularly, like to blame things on the soldering processes, but soldering guys like me prove them wrong!! ...right "BigK??!!!"

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#3723

Re: Skewing chip components | 23 June, 2000

Yeah, them soldering machines sure got some demons in them...My waves used to get blamed for wrong polarities all the time.

Sneaky little devils used to pull components out of the boards, flip them around, and get the pins back in the holes while in the preheat tunnels. Too bad we couldn't train the machines to FIX wrong polarities....

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Super K

#3724

Re: Skewing chip components | 23 June, 2000

Chrys and C.K. (or Little K from what I'm told),

Where "I" work at, our fine management staff has informed us of "Smart Solder"! Not sure who makes it, but they claim it will make all your soldering problems go away. I'll send ya more info on it once I find it - hope it comes in bar as well as paste!

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Big H

#3725

Re: Skewing chip components | 23 June, 2000

Is it just like that "smart" golf ball - where you tell it, "stop!!! stop!!!" ....or "go further!" go further!

So this smart solder, you can tell it "don't skip!! don't skew!!"

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