In a message dated 03/21/2000 3:08:44 PM Central Standard Time, 
[log in to unmask] writes:

<< Personally I think that if you have a 10 zone convection machine this 
should be well able to reflow Sn/Ag soldered aeemblies. If you haven't 
already, before you blow a few $0000 on VPR why not invest a few $00 on a 
data profiler and see what your max thermal excursions really are?
 
 
 Mike>>

Hi Mike!

I've got a ECD Super Mole, and I've done some experiments with a sample of 
SN96/AG04 high temp solder paste, dummy components...so I know I can create a 
profile with the paste...but I don't know what I did to the components, they 
were dummies. I peaked out at 248º C on one of my profiles and saw a max ramp 
of  3.2º per second during my final ramp into the spike zone. That was 
because I learned that you need to keep your preheat and soak down around 
traditional 63/37 temperatures, otherwise you'll fry all the activity out of 
the flux and get nothing but a bunch of solderballs when things go 
liquidous...you'll get a fillet all right, but it's just covered with solder 
balls. So my profile looks pretty normal until you get to the end, then I 
pour the coals to her! My set points are about 300-315º C at the end.

The deal is, is that the business that we may get is currently being built 
using vapor phase reflow...and seem to be getting good results and 
reliability. As you may know, you can't afford to have one of these downhole 
boards fail after you've got it 5,000 feet in the ground...takes a little 
time and money to pull everything back up again so you can repair it. So 
rather than take chances by changing the reflow process, I was just asked to 
see what it would take to give us vapor phase capability. 

I would love to be able to feel confident enough to say that the convection 
oven I have is fine, but I don't have enough experience working on the edge 
(temperature-wise) to say that one process is better than the other.

-Steve Gregory-

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