[TriEmbed] Now looking at the guts Re: T-962 reflow oven notes

[Pete Soper]

Thanks for the input. I wonder if these little ovens would be able to 
heat and cool the PCBs fast enough to avoid killing some of the 
components if there was 1/4" aluminum involved. I agree with you 100% 
this would probably eliminate the sensing error.

But I found the "roasted masking tape". The pictures in the popular 
"Instructables" blurb about replacing the masking tape don't really show 
the problem area. UNDER the front lip of the insulation layer is a place 
where masking tape has been put across a junction that would let hot air 
get in and overheat the control electronics. This is a couple inches 
toward the inside of the oven with virtually nothing between it and the 
heating chamber. One thin layer of one strip of this tape is burned in 
my oven and has the "now it's welded on" characteristic of old tape. A 
few minutes with a knife has gotten this off and I will be doing the 
kapton tape treatment. So I guess early on this tape burning was blended 
in with the solder paste heating when I ran the oven. But the tape is 
fully baked now. Presumably this area may be much larger with the 
T-962A, and it's probably up to the hand-assembly as far as how much 
tape gets burned.

hat appears too difficult and risky to attempt at the moment is trying 
to arrange for the existing thermocouples to come down to the PCB 
surface. If I could figure out what type they are and find affordable 
replacements I could perhaps just switch them in and out of the circuit 
in place of the ones in fixed positions. The Digikey probes on high temp 
leads are very expensive.

I will point to some pictures soon.

-Pete

On 09/24/2014 06:24 PM, Rick wrote:
> Good evening all,
>
> Pete ... I'd suggest a nice 1/4" aluminum plate upon which you place 
> your PCBs. Your thermocouples can either be taped to your board 
> (kapton is great for this), or permanently fastened to the aluminum. 
> You need some nice thermal mass to reduce your setpoint oscillation.
>
> Does your PID controller have a training mode? If so, install the 
> aluminum with the thermocouples, train it, and then run a profile with 
> an external thermocouple not tied to the system watching as well.
>
> You probably want a HEPA filter on the exhaust port ... though I'd 
> provide some cooling in the form of an aluminum vent pipe before the 
> filter ... no need to get the filter hot. You can buy a large HEPA 
> filter and cut it down to make multiple small ones if you wish (the 
> local home improvement stores carry a few HEPA filters ... beats 
> ordering and waiting for the boat from overseas). You probably don't 
> want to spend the money on an automotive "cabin" filter ... very 
> expensive for what it provides.
>
> Cooling the exhaust also helps condense the volatiles and helps reduce 
> the filter loading ('cause you can shake the filter off rather than 
> replace it every x hours).
>
> Hope this helps,
>
> Rick
>
>
>
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