> Ceramics:
> Definition: Inorganic nonmetallic materials characterized by high melting
points, high compressive strength, good strength retention at high
temperatures (1650°C) and excellent resistance to oxidation. Disadvantages
include relatively low tensile strength, poor impact resistance and poor
thermal shock. Reinforcements are used to overcome these deficiencies of
ceramics.
> I did some digging and found out that, yes, for the
processing temps the expansion is linear. As it was explained by Brian
Ellis, preheating softens the temp shock. Also I found out that the CTE
varies quite a bit between different types of ceramic materials. That
explains why some ceramic caps do not have a problem being soldered by
soldering irons without preheting and some can not be done that way.
> 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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