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'[EE]: Small reflow ovens -- source'
2007\10\03@210511 by Vitaliy

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Hi List,

First of all, a question: when making small batches of RoHS boards in a
toaster oven, should we expect to stink up the lab and the rest of the
office? It seems that at the temperatures required to melt the solder, the
PCB material itself starts to emit very strong chemical odor.

Assuming that the answer is yes, can someone recommend a small reflow oven
we can get for small-volume production? It needs to be something we can vent
to the outside.

Vitaliy

2007\10\04@012652 by Matthew Bajor

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Vitaliy,

Your right about the odor. I have done a few boards using a toaster  
oven and found the best way to not stink up my basement, or destroy a  
board for that matter, is to always use double sided PCB.
If you are making a quick prototype and are only using one sided PCB,  
then the exposed backside will burn pretty badly. Also, putting a  
piece of fire-brick right above the board is also good in terms of  
getting more uniform melting.
My former supervisor did this in a small commercial oven to get a  
better reflow and it worked.


Matt

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> --

2007\10\04@140342 by Steve Baldwin

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Did you measure the temperature profile that your oven can achieve ?
I found that if I ran a profile pretty close to the solder manufacturers
suggestion, I get very little fuming. If you just put it on to bake and it ramps
up to the peak slowly, it gets smelly and sometimes the board discolours.

My oven could get to the RoHS final temp but just didn't have enough power
to get the risetime. It sounds like you're getting the same thing.

I didn't buy one, but Essemtec make a nice batch oven that has no problem
with RoHS. You might want to be sitting down when the bill arives though.

Steve.


On 3 Oct 2007 at 18:03, Vitaliy wrote:

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> --

2007\10\04@141721 by Martin Klingensmith

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I won't claim that it would work because I haven't done it, but I would
think that you could add some glass fiber insulation in relevant places
to get a quicker heat-up time if that's what you require. In any case I
wouldn't leave a hot toaster oven unattended.
--
Martin K

Steve Baldwin wrote:
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2007\10\04@144038 by Marcel Duchamp

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Martin Klingensmith wrote:
> I won't claim that it would work because I haven't done it, but I would
> think that you could add some glass fiber insulation in relevant places
> to get a quicker heat-up time if that's what you require. In any case I
> wouldn't leave a hot toaster oven unattended.
> --
> Martin K


You might be successful in pre-heating your oven if you are not doing
that now.

I set mine to "bake" at 250F and let it preheat for a minimum of 15
minutes.  At that point, all the cold sheet metal is heated up and that
allows the ramp up to proceed apace.

Only then do I put in the boards and set the controls to "broil" which
turns off the lower element and turns on the overhead element.  At this
point, I start a 3 minute stopwatch.  Depending on the size and quantity
of boards, the solder usually melts between 1:30 and 2:30 into the run.
 After I see all the paste shiny, I turn off the power and after 30
secs more, I open the door to cool.


2007\10\04@200427 by Vitaliy

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Marcel Duchamp wrote:
{Quote hidden}

We're using an electronic temp control unit, so the oven is never really
"unattended" :)

I have a feeling that you guys may be right about the long bake time and
pre-heating the oven. We'll try that tomorrow, to see if we can bake the
boards without producing the fumes.

Thank you for your feedback.

Vitaliy

2007\10\04@202855 by Marcel Duchamp

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Vitaliy wrote:
> Marcel Duchamp wrote:
>>
>> You might be successful in pre-heating your oven if you are not doing
>> that now.
>>
>> I set mine to "bake" at 250F and let it preheat for a minimum of 15
>> minutes.  At that point, all the cold sheet metal is heated up and that
>> allows the ramp up to proceed apace.
>>
>> Only then do I put in the boards and set the controls to "broil" which
>> turns off the lower element and turns on the overhead element.  At this
>> point, I start a 3 minute stopwatch.  Depending on the size and quantity
>> of boards, the solder usually melts between 1:30 and 2:30 into the run.
>>  After I see all the paste shiny, I turn off the power and after 30
>> secs more, I open the door to cool.

I just noticed an omission in my details.  After pre-heating the oven at
250F, the board to be soldered is then inserted and allowed to pre-heat
for 90 seconds.  THEN the oven goes to broil, etc.  This lets the board
come up to 250F so the ramp up from there is more tightly controlled.
For the oven we use, I stuck a thermocouple into it and made a temp vs
time curve that looks fairly close to the ones seen in data sheets.

It ain't perfect but works well for prototypes.

>
> We're using an electronic temp control unit, so the oven is never really
> "unattended" :)

That's a good solution too.

> I have a feeling that you guys may be right about the long bake time and
> pre-heating the oven. We'll try that tomorrow, to see if we can bake the
> boards without producing the fumes.
>
> Thank you for your feedback.
>
> Vitaliy
>

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