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Dendrite growth

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#53702

Dendrite growth | 18 February, 2008

Dear All,

What is the possible root causes of the dendrite growth? How long its take to cause this dendrite growth? Can dendrite growth cause electrical short? Is there any particular location on PCBA that dendrite tend to grow?

Thanks, Sean

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#53704

Dendrite growth | 19 February, 2008

While you're waiting for others to reply, search the fine SMTnet Archives for postings like http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=9328

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#53706

Dendrite growth | 19 February, 2008

The last time I encountered dendrite growth, it was within a component package. I believe we were experiencing it within a crystal. The root cause was water intrusion during in line wash. The component was supposed to have been sealed and safe for wash, however, destructive testing revealed that there was moisture intrusion. The combination of the moisture, heat, and whatever impurities got in there caused the dendrite growth. In our case, it was conductive, and caused failures.

Cheers ..rob

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#53710

Dendrite growth | 19 February, 2008

Yes dendrites can cause electrical shorts. The first stage of dendritic growth is a dark fern like pattern which reduce surface insulation between anode and cathode. In a more advanced stage the ferns transfer the plating metals of the conductors and create dead shorts.

In a previous life I did a lot of experiments with growing dendrites and my findings were that you need 4 elements to be present to create them.

1) DC low voltage +/- 10V low current

2) Humidity

3) Exposed metal conductors

4) Surface to grow

If you eliminate one of those four you can�t get dendrites.

Most books talk about Ionics as a key component, but in my experiments Co2 in the air was enough to start the process (they grew as fast on a clean board as on a contaminated board).

Also in terms of time to create dead shorts pure tin was unbeatable, another thing to think about in this lead-free world.

Hope this helps

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#53728

Dendrite growth | 20 February, 2008

We test for board cleanliness using an ionic tester. It's been my experience that if your board is clean you take away the possibility of growth even if the unit encounters moisture.

We actaully had a problem where our wash lost pressure due to a minor leak and eventually the product had growth in the field from environmental exposures and an unclean product.

Unless your using no clean-flux on everything I would defintely sample check your baords.

Oh yeah and the growth was actually under a conformal coat which was designed to keep most of the moisture out. So most conformal coatings wont even stop the dentritic growth.

my 2 cents

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#53740

Dendrite growth | 20 February, 2008

Tony,

Conformal coating will protect the board from outside moisture but will also encapsulate Ionics and moisture when present on the board.

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#53752

Dendrite growth | 21 February, 2008

what is the solde finish on the bare board is it hasl? Are you using OA flux during assembly. A little more information would be good

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#53756

Dendrite growth | 21 February, 2008

Wow, I clicked on that link. Both myself and DaveF are in it.

..and this was from the '90s! Maybe it's time to look for another line of work. :-)

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#53978

Dendrite growth | 12 March, 2008

Hi All,

Thanks for your inputs...I really appreciate it!!

Rgds, Sean

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