Any comments are welcome


Customers can be really irritating....

.....but more seriously, operating temperature is not relevant because 
the devices are not operating. When they are operating they dissipate 
heat and rise in temperature above the local ambient, this isn't 
happening during assy. Also things like migration can occur when the 
parts are switched on but won't happen when they aren't. Further, 
maximum  operating temperature may be defined by some aspect of 
performance of the device going out of spec but returning in spec when 
the temperature drops again.

Storage temperature is more relevant but a look at the test spec to 
which the device complies will show you that this temperature can be 
endured by the device for many many hours, much longer than your 
assembly process. Therefore if you're soldering below the storage 
temperature you should have plenty of margin.

Good luck.





On 22/09/2010 16:13, Phil Bavaro wrote:
> I have a process where a metal backed PWA is being put on a hot plate in
> order to preheat the assembly high enough (140 C) so that a soldering
> iron can be used to solder (2-5 seconds) hand installed parts as well as
> to touch up any reflow defects.
>
> One customer has raised questions relative to the hot plate temperature
> overstressing the devices due to the extended time necessary to solder
> all the devices.   Subsequently all the Storage and Operating
> temperatures for the components needed to be presented.
>
> Across all of the devices, Storage Temperature maximum is either 150 C
> or 200 C.
>
> The Operating temperature rating for most of the devices is below 140 C
> (70, 125, 150).
>
> One can see how there might be some concern incorrectly focused on the
> assembly soldering temperatures violating this parameter.
>
> I know that soldering requires temperatures which exceed the operating
> and storage temperature rating ranges for our components, but how do I
> explain this to a customer who is asking such questions about the
> assembly soldering process.
>
> Certainly I can show the typical reflow curves listed by the SMT device
> manufacturer's, but since this application is post reflow hand solder,
> the manufacturer's don't have recommended hand soldering profiles to
> show the customer.  And certainly the preheated cycles are not reflected
> in a device curves.
>
> Any comments are welcome.
>
>
> Phil
>
>
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Eric Christison
Consumer&  Micro group
Imaging Division

STMicroelectronics (R&D) Ltd
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United Kingdom

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