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Broken capacitors

jmlasserre

#2336

Broken capacitors | 1 December, 2000

I just started an analysis concerning broken capacitors (0603 ceramic).

My first question concern the standard used to determine the maximum force a capacitor 0603 can support on a pcb. Some capacitors suppliers use the die sheer test of MIL-STD-883 some of them use a torque test: where is the true and whitch test can I use ?

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#2337

Re: Broken capacitors | 1 December, 2000

JM,

Be sure to include in your analysis to check the caps before placement. We had some problems w/ EPCOS caps being already cracked in the tape. I don't know about max force permitted for a given cap.

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Steven J

#2338

Re: Broken capacitors | 3 December, 2000

Greetings to all. We are currently experiencing cracking of the ceramic capacitors, on both primary and secondary sides of the PWB. The components range in size from 1206, 1210, to 1815s. The cracks do not appear to alter the electrical properties (PWBs pass in circuit testing), but we are concerned with long term reliability. Thermal profiling of all processes, and copying same in defect lab, has not reproduced the defect! The cracking appears randomly, and is spread across several vendors. Any helpful suggestions out there? Thanx for your time. Steven J

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Michael Nguyen

#2339

Re: Broken capacitors | 3 December, 2000

Wow. And I thought I was the only one having problem with ceramic capacitors.I too am having problem with cracking ceramic capacitors 1206 package.We changed vendors and still having the same problem. I had to reverify my entire process and I had to get all the specs from both vendors on their ceramic capacitors. I inspected the parts after reflow and then inspected them again after the secondary reflow.I did this to verify that it is not caused by the reflow oven with too much heat. Since the PCB's are in panels we had to depanel them into strips by using a score machine and then handbreaking the individual since the board is just 1in x .25in ..This is where we find the ceramic parts cracking.I wouldn't think hand breaking will cause that much board stress to make the ceramic capacitors to have cracks at the terminal end. Then we try to use the score machine to depanel them into individual instead of handbreaking our defect went down but we were still seeing some cracked capacitors but not as much. Any help will be greatly appreciated. I am wondering are the ceramic capacitors cracking at the terminal ends or on the body of the part? Thanks.!

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jmlasserre

#2340

Re: Broken capacitors | 4 December, 2000

Hello,

When we discover the broken caps, there are missing and we can observe only either the 2 terminaisons or a small part of ceramic. The defect is due to a shock during the process but it's possible that the caps are fragilized during an operation like the depanalization.

I would like to find a standard to perform some shear test on the caps but I not sure that the Shear test of the MIL 883 method 2019 is the good one (used for die shear strenght on semi conductor) but it seems the caps manufacturers use this one, is there someone to confirm or not ?

Thanks for your help.

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JimH

#2341

Re: Broken capacitors | 4 December, 2000

All, For what it's worth the only time I have experienced this phenom was when board support pins were misplaced on our chip shooter and these components (previously placed) were resting on the pins and cracking when we populated the other side of the board. I have also seen through hole clinching machines crack and even break off ceramic chips. Any investigation been done to find ceramic pieces in other parts of your process? Finally, the only time I have used a torque test was to prove the curing strength of our adhesive not the craking point of a component package. Just my 2 cents worth. Good luck and I'll be watching for follow up posts. Jim

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#2342

Re: Broken capacitors | 6 December, 2000

To the post on the depaneling system. Almost any smt component can (and will according to Murphy's law) be damaged during hand breakout. Our company began using SMT a few years ago, and our primary customer absolutely will not allow us to hand break out SMT boards for this reason. We've proven this more than once on engineering samples that we do not have a depaneling fixture for. For a while we used a pizza cutter to depanel our scored boards, but this is too dependent upon the diligence of the operator. We finally ended up with a press system from Pioneer Dietecs. Thus far it has worked better than anything else we've tried.

John

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LeeKibler

#2343

Re: Broken capacitors | 8 December, 2000

Beware the foam fluxer. I had a problem with cracked caps that just about drove me off the deep end. I discovered that my foam fluxer air knife was not turned on resulting in excessive flux. The excessive flux (VOC free) was not properly dried off by the convection preheater resulting in large solder balls being deposited on the top side of the Panel where ever there was a gap. The solder balls built up on the surface of the singulation press dies and hold down punches. You guessed it....flexing the pcb and cracking the caps every time the press cycled. What did we do....moved all the SMT/Mixed Technology PCB's to a router and left the thru-hole only PCB's on the singulation press. We also used this as a justification to remove the foam fluxer and replace it with a spray fluxer.

Remember cap vendors round the corners of caps in a tumbler. If they leave them in too long -- cracks!

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