>The problems is that some packages can absorb moisture, and when they get
reflow-soldered, it boils
>out, causing cracking

I think it is referred to in the industry as 'pop corning' or the 'popcorn
effect'.


Regards,

Ken Pergola


-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Mike Harrison
Sent: Saturday, August 09, 2003 5:55 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [AD]: A carload of SMD Parts on EBAY


On Sat, 9 Aug 2003 23:05:03 +0200, you wrote:

>Bob Axtell wrote:
>> I've been told by a vendor or two that semis can also absorb moisture
thru
>> their tiny cases. This makes a case for PCB coatings, which we used to do
>> years ago frequently.
>
>
>A couple of months ago, I ordered some samples from National.
>I'v done this before, and I always got them in a sticks
>in standard (soft) envelopes. This time *one* of the ICs
>was sent in a sealed plastic bag, with one of these anti-
>moist things "SIEVE PAK(tm)" together with a small
>thing with three circles that would turn pink
>at 5, 10 and 15% rel humidity. And there was a separate
>document attached with instructions and recomendations
>about "baking" the ICs before mounting/soldering
>if the marks had turned pink. This was "ADC12138" in
>normal "SOIC-WIDE" packing :
>http://www.national.com/pf/AD/ADC12138.html.
>
>So, for *some* reason, these chips seems much more
>sensitive to humidity then all other chips *I* have
>seen so far...
>
>Jan-Erik.

moisture-proof packing (with dessicants and indicators has been standard
practice for SMD ICs for
many years with some distributors.
The problems is that some packages can absorb moisture, and when they get
reflow-soldered, it boils
out, causing cracking

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