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ref: tombstoning on chip capacitors

C.Long

#4456

ref: tombstoning on chip capacitors | 12 April, 2000

anyone any ideas how to minimise my DPM as regards tombstoning..i have checked oven profile..appeture size on my stencils..placement machine etc and still problems.???????????

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Chris May

#4457

Re: ref: tombstoning on chip capacitors | 12 April, 2000

Have you checked the pad geometry, shape / size etc ??

Regards,

Chris.

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NickMata

#4458

Re: ref: tombstoning on chip capacitors | 12 April, 2000

Aside from all of what you've done I would also suggest you take a look at component specs. Some vendors recommend a certain paste composition, for example a 2% silver content.

I have found out thru experience that when using these components my tombstoning defects will increase.

Contact me and I'll share more detail.

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#4459

Re: ref: tombstoning on chip capacitors | 12 April, 2000

Chris, is right! Pad geometry is one of the biggest factors of tomb-stoning. Check Pad size against parts size.

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Micah Newcomb

#4460

Re: ref: tombstoning on chip capacitors | 12 April, 2000

Billy and Chris have a good point, pad size and geometry will affect proper aperture size and geometry and could result in tombstoning. Also I have seen chips which require special pastes but I have never found this to be the cause of tombstoning, instead the result has been poor wetting. One other thing to consider is the pad spacing. All to often a customer will lay out a board for a specific size chip and then change the part. For example, original board layout for 0603 chips but later changed to 0402 for whatever reason. I see this too much and it is especially critical the smaller your chip. Look into it, good luck.

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Christopher Lampron

#4461

Re: ref: tombstoning on chip capacitors | 13 April, 2000

I agree with Nick. You should check with the manufacturer to determine what type of plating is used on the components and see if the manufacturer has any recomendations on materials that may help. If no exotic materials are used, the culprit is most likely the profile or pad sized/geometries. Things to check: is the pad size correct for this type of component? Is the oven soak time/temperature adequate to allow thermal equalibrium across the PCB.

Just my $.02

Chris

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Michael Parker

#4462

Re: ref: tombstoning on chip capacitors | 13 April, 2000

I too have followed all of the useful suggestions provided herein. I still found some tombstoning which was specific to a manufacturers lot. I changed the reel to another brand and the problem went away. I suspect contamination or oxidation on the connections of the 0603 chip. Just last week the problem came up at the end of a reel. No problems experienced until we got down to the last 100 pcs. or so. Frustrating to solve but the short answer is the parts are very cheap- easier to scrap a couple of bucks of suspect parts than to launch a tediuos investigation with no real answer for the outcome. When all else fails, swap it and wait and see.

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Bene

#4463

Re: ref: tombstoning on chip capacitors | 17 April, 2000

Do you know the wetting speed of the solder paste you are using? Ask your vendor for this measurement. I have observed this issue on several products using pastes with wetting speeds faster than 1 second. As stated previously, smaller packages are more suseptible. You could confirm this by changing nothing but the solder paste.

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Mark

#4464

Re: ref: tombstoning on chip capacitors | 19 April, 2000

THE PROBLEM IS DEFINETLY CAUSED BY INCORRECT PAD DESIGN. A FRIEND DID A INVESTIGATION ON TOMBSTONING AND HAS THE CORRECT SIZES.HE CAN BE E-MAILLED AT NMANSON@AFTE.COOKSON .COM OR TEL. 0094 1355 276 500

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JACOB LACOURSE

#4465

Re: ref: tombstoning on chip capacitors | 21 April, 2000

I FOUND THAT ONE OF THE MANY REASONS FOR TOMBSTONING COMPONENTS IS MOISTURE IN SOLDER PASTE. ONE WAY TO CONFIRM THIS IS TO CHECK FOR EXCESIVE SOLDER BALLS AROUND THE PART IF THEY ARE PRESENT THEN YOU MAY HAVE A HUMIDITY PROBLEM. GOOD LUCK!!! JAKE

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