>What is different about these capacitors that they cannot take the thermal
>shock of wave soldering.  I have experienced over the past few years the
>cracking of 1206 and 0805 capacitors due to various stresses, and solved
>various stress related issues with said capacitors (thanks to all the
>consultants who have helped me with this issue, you know who you are!!  :-}
>). Since I have never used this specific size capacitor, i would like to
>know if this is a problem so it can be added to a list of do's and don'ts
>for design guidelines.   Is the size the problem, or what?
>
>Thanks
>
>Ed Holton
>Hella Electronics
>

Multilayer ceramic capacitors are complex structures of interleaved metal
electrodes and ceramic dielectric surrounded by ceramic cover layers. These
metal/ceramic layers are not truly bonded during the firing process
resulting in a fragile structure that becomes increasing sensitive to
thermal and mechanical stress as size is increased. As size and active area
is increased the chance or probability of a flaw or defect between
dielectric layers also increases making the part even more sensitive to
mechanical and thermal stress. Once there is a crack between opposing
electrodes failure follows. Failure is accelerated by the presence of
humidity and DC voltage but the part will always fail when a crack between
electrodes is present.

The simplest solution is to minimize exposure of large chip capacitors to
thermal stress by restricting their use to reflow soldered processes only.
By large chip I am referring to 1812 and larger chips.

Please contact me by direct e-mail if there are further questions.

Regards,


John Maxwell

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