Vasile Surducan wrote:
> On 1/22/07, Bob Axtell <engineer@neomailbox.com> wrote:
>   
>> Brooke Clarke wrote:
>>     
>>> Hi Mike:
>>>
>>> What do  you mean by "possible failure causes"?
>>> For example are you trying to determine future reliability, like for a
>>> space mission, or . .
>>> do you have units that have failed and you want to know why, or . .
>>>
>>> Have Fun,
>>>
>>> Brooke Clarke
>>>
>>>
>>>       
>> I'll bet Mike has a legitimate reason for asking. I have gone through a
>> spate of bad crystals in the
>> past, and the experience was NOT pleasant.
>>
>> You will notice that I no longer design-in crystals, I use ceramic
>> resonators. And I have never regretted
>> the change.
>>     
>
> You are not clocking then some PLL of RF transcievers to get 5Ghz, or
> some FPGA  PLL having 1GHz main clock... because ceramic resonators
> are good only for low speed microcontrollers running at 0-30C (and not
> allways).
>
>   
Of course, ceramic resonators do not operate above 16Mhz in my 
experience, and RF requires
a crystal.

> I had very bad experiences with resonators and PIC16F676 and
> PIC16F877A, caused by an temperature/amplitude variation at the oscout
> pin, below the internal trigger limit.
>   
But ceramic resonators can handle incredible amounts of shock. For 
crystals, shock is a risk,
because the crystal chip can sustain a fracture and cause strange 
effects. Most of my clients are
military or truck-mounted industrial, and once I showed 'em how 
sensitive crystals were to
shock, they never looked back.

If I _MUST_ use a crystal, I mount it manually (on a daub of silicone 
gel) and allow the leads
to accept an 'S' curve before they are soldered. I NEVER use SMT 
versions,  they  break
easily.

Con: ceramic resonators are also hydroscopic (attract water), so some 
need a better seal: ECS
units need to be dipped or sprayed to obtain a good seal.
> I had bad experiences with some VTCXO too...I'll say it depends by your luck.
>
> greetings,
> Vasile
>   
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist