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Date: | Thu, 06 Jun 1996 13:53:47 -0700 |
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ROGER HELD wrote:
>
> To TechNet,
>
> I have had a problem with a sample PCB evaluation and I hope someone
> can help me with some supporting data.
>
> The problem is that the evaluation board had a shear crack in the
> barrel of a 12mil small via hole after 100 cycles of thermal shock.
> What we discovered is that the hole had been plugged on both sides
> with soldermask (not my idea). We feel like the expansion of the
> trapped air eventually caused the barrel to shear. What I need is
> some confirming data to show that the theory is correct.
>
> In the past, we had some boards which were plugged on both sides with
> mask (but not thermal shocked). The resultant after reflow was that
> one side of the plug popped (outgassing) and that the barrel did not
> crack. Was the difference in resultants due to the cycling at lower
> temperature (-65C ~ +125C) vs. short term exposure at high temp (270C
> for ~7 secs.)?
>
> Any opinions or sources of data would be greatly appreciated. Thanks
> in advance for all your responses.
>
> Roger Held
> Hitachi Computer Products (America), Inc.
> [log in to unmask]
> (405) 360-5500 x142
We often observe barrel cracking in small vias after thermal shock.
This is a fairly common failure mechanism, and is observed particularly
after thermal shock and not thermal stress (solder float). I don't have
any data to offer, but since you asked for opinions, I doubt the trapped
gas is the problem. I'd be more concerned about the copper ductility,
and plating quality.
--
John Moylan
Delsen Testing Laboratories, Inc.
1024 Grand Central Ave.
Glendale, CA 91201
Phone: 818 247 4106
FAX 818 247 4537
email: [log in to unmask]
URL: http://www.primenet.com/~delsen/
Delsen Testing Laboratories, Inc. is an independent testing
laboratory primarily engaged testing advanced materials.
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