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Ceramic capacitors cracking

#23251

Ceramic capacitors cracking | 4 February, 2003

I am haveing some trouble with ceramic capacitors breaking on a couple of boards I am running. The boards I have trouble with are in a 6 up and 12 up array and the caps are near the score lines where the individual boards are broken apart. Has anybody run into this out there? If so how did you work around the problem?

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#23252

Ceramic capacitors cracking | 4 February, 2003

If you are physically breaking the boards apart and not using a depanelizer you will always have this problem. I have a machine shop that can make you one for about $3,000.00. You can buy one for around $5K new. Cab,FKN and some others make them. Be carefull of the ones with motors. If the boards are not aligned perfectly you will have a lot of scrap.

The caps can still pass electrical test sometimes after cracking but in time will become opens. It can be a serious problem.

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Rajinder Sharma

#23260

Ceramic capacitors cracking | 5 February, 2003

If you are facing problem of craked capacitor only after breaking of the panel into individual PCB's, this may be due to stress being generated on the capacitors terminals. The stress may be due excess pressure being applied on the panel for breaking, which in turn may be due to insufficient depth of the V-score line. In this case you just ask your PCB manufacturer to in craese the depth of V-score line. It will make the breaking easier. There is no need for buying any depannling machine for this purpose only. No body is today using depannling machines.

Rajinder Sharma

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#23267

Ceramic capacitors cracking | 5 February, 2003

Thanks for responding. Do you think I could have my oven profile too aggressive

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Stephen

#23274

Ceramic capacitors cracking | 5 February, 2003

Don't forget placement. I"ve seen chips broken when they are being placed because they were thicker than the parts data used for them. This is not an issue on Panasonic machines because they measure the thickness of parts but I have seen it happen on another machine. Although even on a Panasonic machine if you have the table height set wrong, you could put stress on the parts during placement. Even if the parts aren't getting broken there, maybe they are getting weakened.

Stephen

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#23275

Ceramic capacitors cracking | 5 February, 2003

Increasing the score depth enough to make manual depaneling safe may very well make the panel useless, depending on your automated processes and handling requirements and methods.

We use depanelers daily, hourly, even.

We prefer to route the boards out where there are fragile parts in close proximity to the score line.

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Hans Koerner, Germany

#23410

Ceramic capacitors cracking | 15 February, 2003

It is a serius problem with that mulilayer ceramic caps! In automotive applications you have to use 2 in series for one single cap. During depanelizing you create a mechanically wave in the board, so 3.. 4 mm. Best way is not to do such a wrong design. You can NOT test it really. Moisture and dust will increase the problem over time and you can get a burning cap. I got it!! With a recall of some automobiles. One good idea is to seal the caps.

Have a nice troublefree time

Hans

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Neil

#23504

Ceramic capacitors cracking | 24 February, 2003

Brad,

This is a common problem and may relate to the design of the board. In all cases when a device such as a capacitor is place near the edge of the board and the board must be de-panelled, the capacitor must be parallel to the break line. If the device is perpendicular to the break line it has the opportunity to fracture the dielectric. If you have devices that run perpendicular you will need to educate your design engineers to ensure they avoid this in the future.

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#23571

Ceramic capacitors cracking | 28 February, 2003

Thanks for all the input on this thread. My company bought an FKN depanalizer and that solved our problem. I am also working with our design engineers on laying out the boards without the caps near the edges.

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genny

#23583

Ceramic capacitors cracking | 28 February, 2003

If you can't get rid of all caps near the edges, don't forget Neil's advice above regarding parallel vs. perpendicular. I have seen a 90 degree rotation make a huge improvement in the reliability of some caps.

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Kelly

#23594

Ceramic capacitors cracking | 3 March, 2003

We just had this issue a couple months ago with a single sided FR-4 board which was scored. We found that the design was a factor but also the depth of the v-score. Since then we have re-designed the part further away from the score line. At the same time, I had to get the PCB supplier to score with the proper material remaining. We specify .014" +/-.003" web remaining. Our boards were coming in with .020" web remaining and it caused problems. Now that the web remaining is lower, averaging .011" to .014", the problem is now gone. I orded a V-Score checker through one of my PCB suppliers which measures web remaining. This tool has been great! It is made by Accuscore - ask your board suppliers about this. Good Luck!

Kelly

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