Some help please!!

I have recently become involved in a program that has to meet a temperature
cycling criteria of -40C to +140C, 30 minute dwell times, 10sec transition
time, for 1000 cycles.  We have already made some units, and they are
failing at various points in the temp. cycling.  The failure mechanism
appears to be the solder joint itself, however, there are some joints that
are so strong we break the components, while others pop right off.  The
unit is being developed by another firm for us.  There is discussion as to
wether the problem is solder related or process related (cleanliness, etc.)

The unit thus far is a ceramic substrate, silver palladium pads.  The
components are commercial grade resistors, capacitora and SOIC's.  One
problem appears to be the reflow temperature.  With some of the high temp
solders, the reflow temperatures are exceeding the component max.
temperatures (ex. 250C for 30 seconds).  Higher temp components may be the
solution, but this is an automotive application, and cost is a big factor.

Questions:
What type of high temp solder is best for us,   tin based, lead based, or
gold based?

Where can I find published papers?

Component/terminal plating suggestions?

Who are the experts in this field ( I have searched various archives to no
avail)

Is there a conference on high temperature soldering/applications coming up?

What do you think about not soldering at all, instead glue all components
to the board and attach to the substrate with wire bonding and encapsulate
the whole thing(chip and wire)?

Are there any conductive epoxies that might be used to replace the solder?

Thanks for your help

Ed Holton
Hella Electronics
734-414-0944

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