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Tomb-Stoning. What's going on here?

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#39131

Tomb-Stoning. What's going on here? | 17 January, 2006

Got a wierd one here, 0402's tomb-stoning.

Scenerio---- Double sided PCB, paste both sides, 0402 on both sides.

Reflow bottom side first--- no problems.

Reflow topside next----no problems with topside components, BUT, the bottom side that was reflowed first now has some 0402's that have tomb-stoned ?? How can this happen ?? Any one out there experience this problem?

Thanks

Paul M.

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GEB

#39136

Tomb-Stoning. What's going on here? | 17 January, 2006

Tombstoning is usually caused by one joint heating to melting point before the other. Is it possible to have a lower temperature for the heat zones on the underside of the panel, so the paste is less likely to reach melting point. Does there appear to be enough/ equal amounts of paste on the pads, and are the components located centrally to the pads.

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#39143

Tomb-Stoning. What's going on here? | 17 January, 2006

Here's a page on tombstoning:

http://www.tkb-4u.com/defects/reflow/tombstoning/tombstoning.php

Be sure to see this on the bottom of the page:

For more info about this item look at the Articles / Newsletter: (Causes and Cures of Tombstoning Chip Components)

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#39144

Tomb-Stoning. What's going on here? | 17 January, 2006

GEB,

The parts that are tombstoning have all ready been through reflow once with no problems, so I assume the paste and the positioning was correct the first time, since they did not tombstone through the first reflow. This is very strange.

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#39153

Tomb-Stoning. What's going on here? | 18 January, 2006

Good morning,

This isn�t very strange. Bottom side components are prone to tombstoning more than topside ones. Try to reduce oven�s bottom heaters temperature slightly to prevent solder paste melting on bottom side. This can help.

BR, Pavel

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#39158

Tomb-Stoning. What's going on here? | 18 January, 2006

I had the same exact problem recently. I did exactly as the gentlemen said, and reduced the B/S zones 20 or so degrees, AND changed to medium convection. I'd like to point out that the B/S components still go liquidous (such is the Physics of convection heating), and the part was a high mass/high profile cap with "funky looking" terminations, but I was able to get rid of the tombstoning.. It worked!

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URL

#39159

Tomb-Stoning. What's going on here? | 18 January, 2006

Samir brings up a good point with convection ovens. The flow rate of the fans can move parts, which can cause tombstoning to very light/small components.

Also, check you conveyor and or chain. If it is not running smoothly, even a slight shake or jerk can cause tombstoning.

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#39161

Tomb-Stoning. What's going on here? | 18 January, 2006

Thanks folks !!

I'll experiment with the bottom side heaters. Unfortunatly I don't think our Vitronics-Soltec oven has the option for adjusting the heater fan speeds. And I'll check the conveyor chains. This is our first project using 0402 parts, what a pain in the arss !!!!

Thanks for your valued inputs.

Paul M.

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Bjorn Kerkin Durk

#39163

Tomb-Stoning. What's going on here? | 18 January, 2006

Jurkin' derkin jerkin ged-dern twoomb stone is a cornspeerwacy!

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URL

#39165

Tomb-Stoning. What's going on here? | 18 January, 2006

Hi Bjorn,

Yes that can also add to tombstoning, but if maticulate your stencil to a high sanalot, you shouldn't see any tombstoing.

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Burgandy

#39166

Tomb-Stoning. What's going on here? | 18 January, 2006

Your right on the money there Peter. Steve, over to you!!!!

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Darnell

#39189

Tomb-Stoning. What's going on here? | 18 January, 2006

Samir brings up uh pimp-tight point wiff convection ovens. The flow rate o' da fans can move parts, which can cause tombstoning ta very light/small components.

Also, check ya conveyor an' or chain. If it iz not running smoothly, even uh slight shake or jerk can cause tombstoning.

with muh beeotch

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URL

#39206

Tomb-Stoning. What's going on here? | 19 January, 2006

Finny dat Darnel.

Guess this proves that jerks can cause tombstoning.

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