Cracks on ceramic capacitors.

Why don't you give us the full process along with your delta T for the wave (final preheat temp to wave contact temp). Don't forget de-paneling, ICT, and other things. It could be from the supplier, but it usually is from excessive placement force and/or wave.

Russ

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We had this problem with 0805 0.1 mF also. This problem was only with this capacitor. We have replaced all these capacitor after the ninth occurrence. My opinion - it is a defect of the manufacturer. Please inform the manufacturer of your capacitor.

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Suggest you ask vendor for a failure analysis. Ceramic chips have specific signatures for mechanical or thermal shock cracking. The vast majority of failures are due to mechanical flex. Depanelization and secondary operations such as hand insertion of connectors are suspect. The symptoms you describe are often caused by flex, the crack doesn't cross all the active ceramic lays ( thus intermittent readings). The crack will appear to run from the inside edge of the termination to the bottom of the chip.

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suggest you check the preheat conditioning in the wavesolder process is sufficient, as this is the main culprit for micro-crack CAPs ?

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Are these caps on the bottom side or topside?

Bottomside could be the glue dots are too big for the caps your putting down, the glue cures and then the solder is putting force on the edges of the cap causing cracks..

Other than that agree with others comments, check the router and mechanical/handling damage..

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I've seen numerous incidences of mirror image cracking under endcaps in high dielectric material ceramic capacitors due to thermal cycling. If the cracking is deep enough to extent through the plates you can get breakdown and shorting. Section the capacitor and the cracks will look like a mirror image of the endcaps. You can induce the cracks in loose capacitors (not attached to a board) by thermal cycling over a temperature range of -65F to 160F. I'd not be surprised to find you can enduce cracking by an excursion to solder reflow temperatures. Only fix I know is don't use high dielectric constant ceramic chip capacitors in applications where there are significant temperature excursions.

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Hi, In most of the cases we are not able to detect the source of the crack.I strongly feel that component manufacturer process causes the crack in most of the cases.Only high speed turret P&P machine can cause crack and we can observe the indent on the top surface of the body.The possibility is rare as the nozzles are spring loaded.2nd ly if the PCB thickness is below 1.2 mm and de paneling is not done properly can cause crack. 3rd ly design of the PCB > if the capacitors are placed very near to the edge and their position is 90 deg than it may cause crack.4thly if the reflow ramp rate is more than 3 deg C then it may crack. 5th ly if the solderin tip temp. is very high and soldering bit is very thick can cause crack cap.

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Do you know what the maximum temperature rating is for the devices. But in my past experience you could be seeing the following. Excess thermal ramp rates typically you would like to see 2 to 3C/sec in the reflow oven, if it is greater than this i would look here. Additionally if you are using a ultasonic cleaning process be careful about the frequency setting. To low of a frequency setting will be equivalent of hitting the product with a hammer. Some other things that you may want to look at is if this occuring during your process or is it a incoming material problem. If not then you should also look at the wonderful world of how product gets stored and handled. Additionally, look at the board material and see if it is warping during the reflow process. I have seen instances where a board is warped and then screwed into a housing putting stresses on the part. And last but certainly not least is the dreades rework word. Uneven temperature heating can cause inner layer micro cracks that may only be seen in the field or during temperature cycling.

Good Luck

Larry

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