Re: lua-users.org down

[Lorenzo Donati <lorenzodonatibz@...>]

On 09/10/2014 00:05, Rob Kendrick wrote:
> On Wed, Oct 08, 2014 at 05:45:45PM -0400, Jay Carlson wrote:
>> On Oct 8, 2014 5:15 PM, "Rob Kendrick" <rjek@rjek.com> wrote:
>>
>>> This should now be up again. Hilarious unleaded solder failure involving
>> the south bridge heat sink. The whole system has now been totally replaced
>> and data transferred.
>>>
>>> https://www.rjek.com/octopus-heatsink.jpeg
>>
>> That is awesome.
>>
>> Is that red stuff on other chip corners...hot glue?
> 
> Probably epoxy used for stability: the ATI graphics chip seems also
> covered in it!  You'll find that lots of ICs in smaller devices (like
> phones) will have epoxy for this reason.  No idea why  in a server,
> though.
> 
Those ICs seem to be BGA (Ball Grid Array) packages. They tend to suffer
of mechanical strain problems related to thermal expansion, so
they compensate by injecting epoxy between the BGA PCB and the main PCB.

This is called "underfill". The specific technique is "corner bonding".
See [1] for some additional info.

Cheers!

-- Lorenzo


[1]
http://www.embedded.com/design/system-integration/4235387/Underfill-revisited--How-a-decades-old-technique-enables-smaller--more-durable-PCBs




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