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Old 5th March 2004, 08:00 AM   #1
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Exclamation Moisture Sensitive!

Hello,

I've received my LM1084IS-5.0 samples from NSC today...

But, there was something unfamiliar with it....

It says on the package that the devices are moisture sensitive.

It's specially wrapped with conductive bag in a vacuum condition, to prevent any ESD or moisture entering...

It even says on the package that the devices have to be "baked" before mounting , if the relative humidity on the surrounding is too high.

There were no warnings In the data sheet.
http://cache.national.com/ds/LM/LM1084.pdf

Can anybody explain me how an I.C can be "MOISTURE" sensitive.

And has anybody ever tried this regulator chip before?
I think I've seen someone who tried this I.C before...
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Old 5th March 2004, 11:30 AM   #2
cyr is offline cyr  Sweden
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IC packages can absorb moisture, and when heated suddenly (during soldering, in some kind of oven) they can pop.

Don't think it's a problem with hand soldering.
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Old 5th March 2004, 11:50 PM   #3
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And as an addition, they have a shelf-life of 24months (2years) if the devices are kept within the package, without any single openings.

This means the devices have to be soldered straight away, if the packaged is opened.

The devices are in TO-263 SMD package.

Any other comments on handling these devices?
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Old 6th March 2004, 01:57 AM   #4
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Yeah, could be that... Like you have to dry pottery real slow otherwise it cracks up... and I think stick welding electrodes have similar problems.

I figure it sounds good because when the heat hits the heatsink/main tab, the chip is going to suddenly get very hot, very fast...

Tim
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Old 6th March 2004, 02:49 AM   #5
tiroth is offline tiroth  United States
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You really, really don't need to worry about any of this if you are hand soldering.
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Old 6th March 2004, 02:52 AM   #6
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Quote:
Originally posted by tiroth
You really, really don't need to worry about any of this if you are hand soldering.

Agreed. I've only had to worry about those things when I've worked on projects that were put through hot air assembly or reflow ovens. Large chips like 960pin BGAs (Ball Grid Arrays).

I've never seen an issue on a hand soldered device.

Scott
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Old 7th March 2004, 12:42 AM   #7
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Thumbs up Sweet!

Thanks!

And do you think all other TO-263 SMD devices will have the same kind of warnings on their wrappings?

I was going to use the chip for a tube heater regulator.

They can handle up to 5A.

Better than buying an expensive LM338, but it's really hard to cool them down, because they are in SMD pack.

I don't like to use the copper track as a heatsink, because it increases the size of PCB. There's no reason to use a SMD device then..
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Old 7th March 2004, 06:36 AM   #8
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Any other comments?
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Old 9th March 2004, 07:25 AM   #9
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Old 9th March 2004, 09:44 AM   #10
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Itīs right, all plastic packages are somewhat hygroscopic, BGA and packages alike are verry sensitive.
For hand soldering itīs not an issue, but on the other hand smd devices are designed for reflow soldering. The only advantage of smd is machine assembly, use throug hole devices for small series, soldering and reliability will be better.
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