IR hot plate, convention air hot plate, ceramic conductive transfer from
hotplate?
How efficient is the thermal transfer, are there hot spots on the bottom
(heated) side? 
If the preheat temp on the hottest location on the heated side is 150 C or
less, I would say this is a fairly common and acceptable practice. Operating
temp is not an important piece of information for this problem. If you
exceed the storage temperature for long time. Then there is cause for
concern. 

Operating temperature allows for 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Wednesday, September 22, 2010 11:13 AM
To: [log in to unmask]
Subject: [TN] Soldering vs Storage/Operating Temperatures

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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