Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


about solder bridge

angela

#4498

about solder bridge | 5 April, 2000

Recently we have serious problem of our 0.5mm pitch QFP solder bridge.

I check the viscosity of the Litton Kester paster. It's roumd about 700 is it too low.

And do you have god solution about it?

thanks alot

reply »

Dean

#4499

Re: about solder bridge | 6 April, 2000

I would check their data sheet for the particular product. Thats the range I have for Some Kester products I use...

Are you seeing any slumping prior to pick-and-place? Is the bridge in the same place every time? How is your pick-and-place mounting accuracy? Are you moving the qfp after placement? How tall are the solder bricks? Can you measure the height? How thick is your stencil vs aperture width? Peaking?

Hope this points you in the right direction! Dean

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Marcus

#4500

Re: about solder bridge | 6 April, 2000

What about your printer and your stencil ? Do you have a problem with misalignment between pcb and stencil ? How often do you clean your stencil during production ? Maybe you have smearing under the stencil because there is a snapoff between stencil and pcb during printing ? Do you use a etched stencil or is it lasercut ?

I hope this gives you a little bit more information about the influences of you problem.

Good luck

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jacob lacourse

#4501

Re: about solder bridge | 6 April, 2000

I have also come across this very same problem and found that our screen vendor made a mistake on our screen. Check the thickness of your screen it should be about six thousandths if it's eight thousandths then you are most likely depositing to much paste on the pads. Good luck.

reply »

D Scott

#4502

Re: about solder bridge | 6 April, 2000

Angela

Do you see this problem on other .5mm pitch devices or is it only on the QFP? Check placement height, too low or to high can cause you problems Pad co-planarity, are your boards HASL? Is your board sagging during placement(board supports) Any environmental fluctuations? Look for something that might have changed.

A few other things to consider.

Good Luck

D. Scott

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