In a message dated 02/11/2000 4:22:07 PM Central Standard Time,
[log in to unmask] writes:

> Hello technetters,
>
>  Here's a question for the HMP reflow guru's.
>  We have a board that is polyimide material, 2 layers of copper invar, and
an
> experimental paste composed of 85Pb 10Sb 5Sn. This paste goes liquidus at
255
> degrees C. Reflow is recommended at less than 45 sec above liquidus at 285
> degrees C. Adding to this is a recommended cooling rate of 4 degrees C/sec
to
> achieve a fine grain structure. Greater than 4 deg/sec cooldown will cause
a
> large grain structure, yielding a low fatigue resistance. My question is
this:
>  other than the issue of components being damaged due to this heat, will
the
> invar layers help with TCE mismatch issues and/or board warpage.
>  Any replies are GREATLY appreciated.
>
>  Jason Gregory
>  Quality Manager
>  Electrospec
>  Houston, TX.
>  (713)784-4900
>  (713)784-1194 fax

Hi Jason!

I hope you know that what you're asking is as secret as the launch codes for
the nukes that we have (with certain people)....I'm not kidding! One reason
is because of the new lead-free alloys will require reflow profiles that
exceed the recommended temperatures that most component manufacturers will
stand by.

The other reason is because there are applications that need a HMP solder,
and that the companies that utilize that technology, are very paranoid about
"their secrets" to share any information about the issues...(silly stuff, I
know).

I'm doing my own tests apart from any customer requirements. I'm doing
various experiments with different solder alloys to be prepared for the "No
lead" scenario...higher reflow temperatures will be a fact of life then....so
no matter how propietary people think this process is, I'll find out what the
details are through investigation and experimentation.

However I must say, that a 285 C. peak temperature is asking quite a
bit....maybe not from a solder alloy perspective, but what components can
stand that?

So what I'm saying, is that you won't find anybody willing to share knowledge
about this process because they're all too paranoid...(for whatever reason).
The biggest problem that I see so far is the components...creating a decent
reflow profile is the least of your worries...how can the devices survive
these temperatures is the big question.....

-Steve Gregory-

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