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0402 tombstones

Views: 6644

#58607

0402 tombstones | 15 April, 2009

Hi,

I am trying to reduce some 0402 cap tombstones.

The main cause is the pad spacing is a little too far apart and the parts are as tall as they are wide .5mm I am stuck with the pad spacing for a while.

All other parts are soldering well, even 0201 resistors.

Has anyone encountered this and reduced the defects?

Screen print and pick and place has been checked.

I was asking if someone had any ideas for the oven reflow that had helped. We have a 10 zone Heller oven.

Like longer soak, higher bottom preheat on pcb, less degree change between zones etc...???

rob

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kpm

#58609

0402 tombstones | 16 April, 2009

I've had some luck with longer soak. Of course that was on a board with severe thermal mismatches so I don't know if it will help your problem or not.

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#58612

0402 tombstones | 16 April, 2009

We know virtually nothing about your process, but here's some guesses: * Turn-off the nitrogen * Change from Sn63 to Sn62 * Change to a low-tombstone paste * Change the thermal recipe: slower ramp, longer soak * Do a better job of placing components spot-on * Thermal couple the pads * Purchase components with plating on both terminals

If all else fails, glue the little blanks in place.

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#58622

0402 tombstones | 17 April, 2009

have you try to change the stencil apertures to another figure like the one that look like a baseball home? I was having that problem and some solder beads and with that I was able to decrease the tombstones

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#58623

0402 tombstones | 17 April, 2009

Hi, follow up,

Thanks to everyone that responded.

We finished the build, the sun burst thru the clouds and the birds sang. Well that was a slight exageration.

Sorry for lack of detail on the original post, I was frazzled.

Since the 0201's were placing and soldering well and the 0402's were tombstoning I was searching for any oven profile suggestions. I think the profile is good as the board is large and has about 3500 parts on the bottom side

It was mostly one part a panasonic 0402 cap. I have ordered some from a different vendor to try since the problem transfers to some other boards with that cap.

Again new pad spacing is in the works, but we all know that takes time.

Any suggestions for lower tombstone paste? Like brand and version.

This product was not lead free but most of our products with the same problem are. I would like to get a different paste brand that is available in both lead free and leaded.

rob

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#58625

0402 tombstones | 18 April, 2009

I have a solution.... contact me by mail Vapor phase gives a solution to that problem

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#58626

0402 tombstones | 18 April, 2009

Low tombstone pastes have been around for 8-10 years. Talk to your paste supplier about suggestions of the "latest and greatest." Usually these pastes: * Are a blend of alloys with slightly different melting points * Have a mid-level activity flux * Use mixture of powder particle sizes

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#58627

0402 tombstones | 18 April, 2009

I like this suggestion the best as a "band aid", check out some of the low tombstoning solder pastes. I've seen these work.

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#58634

0402 tombstones | 21 April, 2009

Home plate design is great for avoiding beads and tombstoning in some cases, but it will not help you when the spacing is too far apart. It will make it worse. You need a good even screen and accurate placement.

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#58653

0402 tombstones | 24 April, 2009

TOMBSTONING OF 0402 AND 0201 COMPONENTS: "A STUDY EXAMINING THE EFFECTS OF VARIOUS PROCESS AND DESIGN PARAMETERS ON ULTRA-SMALL PASSIVE DEVICES" Michael Yuen, Heather Benedict, Kris Havlovitz, and Tim Pitsch, Plexus Electronic Assembly Corporation, Neenah, WI and Andy C. Mackie, Ph.D., Praxair, Inc., Tarrytown, NY: http://www.xs4all.nl/~tersted/PDF_files/Plexus/tombstoning.pdf

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#58654

0402 tombstones | 24 April, 2009

I haven't seen those names in a while. I used to work with them; the ones from Plexus anyway. That must be from about 2000 or 2001, I think that's about when Michael Yuen left the company.

I haven't read through this yet, but Mr. Yuen is a very sharp guy so I'm sure it is good information.

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