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SMT electronics assembly manufacturing forum.


Solder Balls on 0805 capacitors

Bill Bannister

#3683

Solder Balls on 0805 capacitors | 27 June, 2000

We've been experiencing solder balls on 0805 caps. We have modified the reflow profile and had some success, but some balling still persists. The balls always form from under the cap between the lands. I measured the distance between the lands at .031". Is this too small a distance? I tried the IPC land pad calculator and it actually said I could go even smaller. Is there a down side to increasing this distance aside from maybe creating a smaller zone for placement accuracy? If I go to .040" can I expect any reduction in solder balling between lands?

Thanks Bill Bannister

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Ioan

#3684

Re: Solder Balls on 0805 capacitors | 27 June, 2000

Hi Bill,

there are a couple of things you should check. Most likely you have too much paste which is squashed at the insertion of the cap. - the paste height, around 7 mils should do. Too much paste will cause shorts under the cap at insertion which turn into beading during reflow - stencil apertures, about 80% of the area of the pad is a good idea - the placing force at the insertion machines. This could squash the paste also. If you are also using 0805 resistors with no problem, check this, since the thickness of the caps is bigger.

Hope this helps, Ioan

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CL

#3685

Re: Solder Balls on 0805 capacitors | 27 June, 2000

Hello Bill, Ioan's idea's are good. One more thing that you may want to consider is using a "Home Plate" aperture on your stencil for the aforementioned caps. The idea is to put a smaller amount of solder paste directly underneath the component. This reduces the amount of squeeze out under the components at placement and reduces the amount of solder beading.

Hope this Helps

Chris

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TOOLMANTIM

#3686

Re: Solder Balls on 0805 capacitors | 4 July, 2000

HELLO BILL I HAVE SOME QUESTIONS FOR YOU 1:HOW ARE YOU CLEANING YOUR STENCIL 2:ARE YOU SINGLE OR DOUBLE PRINTING. 3:ARE YOU USEING VACUUM FIXTURES OR NOT?

HERE ARE SOME OTHER THINGS TO TRY. IF YOU ARE CLEANING YOUR STENCIL OFTEN BECAREFUL OF USEING IT TO SOON AS IT HAS TO DRY .WE HAD ONE CUSTOMER THAT USED IT WET AND HIS VACUUM JIG WAS SO GOOD THAT THE FLUID EXITED VIA THE VIAS ON THE PCB SOAKED THE VIAS AND BECAUSE THE OVEN WAS SO SMALL CAUSED A POP UNDER THE COMPONENT AND IT WAS NOT EVEN THE PASTES FAULT. IF YOU ARE TWO STROKING ON THE M/C MAKE SURE YOUR BLADES ARE MATCHED. OR YOU WILL GET UNDERFILL OR LEACHING

WE HAVE A PCB WITH ABOUT 650 0805 AND 0603 ON BOARD AND SOLDERMASKING IS VERY IMPORTANT

HOPE THIS WILL HELP?

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