In a message dated 6/25/99 9:30:50, [log in to unmask] writes:

>i'm not sure that you need to have the cure temperature higher than the
>highest operating temperature if you are using a very flexible potting
>material such as rtv (room temperature vulcanizing) silicones.  Choosing a
>very rigid, high temperature curing, potting material most likely wouldn't
>be a good choice.
>phil crepeau

Hi Phil,
If the potting material fills the gap between the component and the PCB, and
if the CTE of the potting material is higher than the CTE of the attachment
material (usually the case), then the curing temperature should be at least
near the maximum use temperature. Even very 'flexible' potting material is
normally incompressible; thus a low modulus is of no help. Thus, you want the
potting material either not attached with a gap to one surface or in tension
(holding the component to the PCB and putting the component attachment
(solder) in compression).

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com