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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


capacitor leakage

andy

#20628

capacitor leakage | 10 July, 2002

a leakage exists in the capacitor net (1206), which cause the voltage down so much. the process flow is: printing-placement-reflow-hand load-wave-depanel-FT. I find possible stress maybe exists in the depanel stage, does the extra stress cause the capacitor crack which show the leakage. another finding is when we take off the suspective capacitor from the board then re-assembly it, it is in good condition, just why? I will appreciate your suggestion

reply »

#20634

capacitor leakage | 10 July, 2002

Flex cracking under the terminations is generally regarded as one of the primary causes of failure of ceramic chips. If you can see cracks in the solder joints from board flex, those chips are certainly strongly suspect, and you must assume there is possible latent damage to other ceramic chips, even though the damage may not be readily apparent. When flex stress is present, the cracks can occur under the capacitor terminations and may be nearly invisible on the exterior surface. As a result, visual sorting cannot be relied upon to remove all damaged chips.

Such cracks may result in capacitor failure through increased leakage [or short circuits if they intersect opposed electrodes]. Also some of this damage may be latent, not readily detectable during your in-house electrical or environmental testing.

Ceramic chips mounted very near the edge of the board often see the most mechanical stress. Most ceramic capacitor suppliers give recommendations and guidelines with respect to minimizing flex stress. Primary factors include part location/orientation with respect to the board edge, depanelization techniques, connector mating, and general board handling procedures/fixtures.

reply »

andy

#20636

capacitor leakage | 10 July, 2002

i just find the gap inside the component from the cross-section, it indeed exists the interal crack, not solder joint crack. but why the failed capacitor is well after some time. and the other suspicion is the quality of the component.

reply »

#20638

capacitor leakage | 11 July, 2002

We have had failure due to a leakage in one ceramic chip capacitor. External inspection did not show any obvious damage. Cross section showed a void in the capacitor. The void was an elliptical shape and positioned longitudinal to the length of the capacitor.

Can't remember more.

reply »

andy

#20653

capacitor leakage | 12 July, 2002

thanks, Dave.

who are specialized in mechnical stress distribution? because I find the gap in the capacitor, but why? If the crack is caused by the exteral mechnical stress, which shape will be formed, zigzag or linear?

reply »

#20656

capacitor leakage | 12 July, 2002

We sent the sectioned capacitor to our supplier for analysis. So, the results of their analysis is probably in a file drawer someplace.

reply »

PCB X-Ray Inspection

Essemtec Fox Compact Automatic Pick and Place