There is no reason to believe that the laws of physics do not apply to
ceramic caps. This would mean that the coefficient of linear expansion
is considered as essentially linear, until there is a phase change in
its structure, which I believe would not occur until it reached temps
well in excess of soldering temps. I can't think of any substance that
does not expand on increased temp within a phase structure, except water
between 0°C and 4°C, or whose TCLE drops to negligible levels, as you
suggest. I'd be interested to know of any.
Brian
Dehoyos, Ramon wrote:
> Werner:
> Is the coefficient of expansion for ceramic components
> linear or exponential? If it is exponential, components may reach a point
> where the expansion still exists but it is negligible. What are your
> thoughts?
> Regards,
> Ramon
>
>
>>-----Original Message-----
>>From: Werner Engelmaier [SMTP:[log in to unmask]]
>>Sent: Monday, November 17, 2003 10:05 PM
>>To: [log in to unmask]
>>Subject: Re: [TN] Not that our process is out of control or anything,
>
> but --
>
>>In a message dated 11/17/2003 16:52:11, [log in to unmask]
>
> writes:
>
>>>It is the preheat it the wave that is controlled (the infamous 2C/sec)
>>>to prevent thermal shock.
>>
>>---This is correct.
>>
>>>Once the chip has achieved a specified temp, all the materials have
>>
> expanded
>
>>equally and >after this point the rapid thermal change of hitting the wave
>>does not affect the chip.
>>---Sorry, but there is no such condition; different materials will always
>>have a differentiasl thermal expansion, unless they have identical CTEs.
>>
>>>It is the different expanding properties of the two materials that cause
>>
> the
>
>>chip
>>
>>>to crack.
>>
>>---Quite correct.
>>
>>>Once they have both expanded to their maximum state, the temperature
>>
> curve
>
>>is irrelevant.
>>---Sorry again, but there is no such state; as long as you raise the
>>temperature materials will expand, unless they have a negaqtive CTE.
>>
>>Regards,
>>Werner Engelmaier
>>Engelmaier Associates, L.C.
>>Electronic Packaging, Interconnection and Reliability Consulting
>>7 Jasmine Run
>>Ormond Beach, FL 32174 USA
>>Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
>>E-mail: [log in to unmask], Website: www.engelmaier.com
>>
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