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How to avoid tombstoning in 0201 components



How to avoid tombstoning in 0201 components | 5 July, 2005

We are facing lot of problems with tombstoning in 0201 components. Ironically tomstoning in these components is not occuring while reflow but it is happening when we subject them to thermal cycling test. We have been investigating the cause and thought of conducting an experiment with PCB land patterns.

I am in the process of developing DOE for different land patterns. Can any one of you guys direct me to some papers which has stuff on 0201 land patterns. Expecting a positive response. Thanks.

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How to avoid tombstoning in 0201 components | 5 July, 2005

So your thermal cycling test is putting these solder joints into reflow (183C + if they are lead joints)? Must be quite the test!

Tell us what pad sizing and spacing you are currently using.

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How to avoid tombstoning in 0201 components | 22 July, 2005

Try using Cobar`s anti-tombstone alloy.

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Jason Fullerton


How to avoid tombstoning in 0201 components | 29 July, 2005

In the true sense of the term, tombstoning can only occur during reflow.

Now, if your solder joints are cracking during thermal cycling and opening on one end you still have a problem - it just isn't "tombstoning".

What laminate are you using on your PCBs? Lower grade laminates are less dimensionally stable. I've run 0201s on boards that are 150 degC Tg without any problems during thermal cycle (worst test condition was 150 degC air to 0 degC water for 20 cycles, as well as 50 cycles -40 to 125 degC air to air). Those tests aren't really that stressful - the joys of building Class 2 products.

My point being that if the CTE of the board, solder, and ceramic are different enough, they may be working against each other as they expand and contract.

However, I've run into a problem when we tried to go to off-shore PCB house that used a 135 degC Tg laminate. The PCB itself is so prone to warping during reflow that I was unable to reliably place 0201s on the second pass. I can only imagine what it would have done if we had subjected them to thermal cycling.

Also, what solder paste and alloy are you using? Have you done any x-rays to see if you have voids in your joints before they are thermal cycled? Have you cross-sectioned any parts to see if you are getting good intermetallics?

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