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desktop ovens
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desktop ovens

by adafruit on Wed Nov 04, 2009 9:34 pm

right now im using a skillet. its OK but the heat is uneven and with leadfree this is a bit of a pain cause too hot and the PCB melts (its gross)
im wondering whether to go with a 'nicer' hotplate or a an oven...
akiba, from your photos i saw you have a 'desktop oven' - is that working out?

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Re: desktop ovens

by ktownsend on Thu Nov 05, 2009 3:10 am

There are a lot of opinions out there on ovens versus skillets, etc., but I've had really good results using this toaster oven controller: http://www.reflow-kit.de/rkuk/order_pro ... .html?p=15

After adjusting the temperature to 245°C (which I found gave me good results with lead-free solder without melting any parts), I've had pretty much perfect results, and with the press of a button the entire heat profile is managed to around 1 or 2°C accuracy (I was impressed by that). What's nice versus a skillet is there's no interaction on my part messing around with the temp. I just press the button, and when it beeps I open the oven door and it's done. I can keep working while it's reflowing my boards. It's 220V only, mind you (fine for me in Europe). If I was in North America I'd still stick with it, though, and just get an adapter.

I'd completely avoid the awful infrared reflow ovens on ebay. They're dangerous, and useless ... it was a scary waste of money for me and after using it a few times the thing started to scare me so much (smoke billowing out at high temps) that I just threw it out. Wish I knew about the toaster oven controller first since it's 1/2 the price and works well.

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Re: desktop ovens

by adafruit on Thu Nov 05, 2009 10:28 am

yeah have definately heard about sketch-ass 'chinese' reflow ovens. skillets can also be controlled pretty easily with an SSR/relay and microcontroller (arduino or similar)
thing im looking for is heat uniformity. the skillet is cold in the center. im thinking of putting a sheet of aluminum on it to help even out the hotspots a bit. i also want ~ 12" x 12" space

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Re: desktop ovens

by freaklabs on Thu Nov 05, 2009 8:06 pm

Actually only fired up the oven once and turned it off immediately. It kinda scared me.
I use a Madell hot plate which can get up to 300 deg C. I'm getting a little tired of the hot plate though because it forces you to only have components on the top side and the side in contact with the plate turns my solder-mask off-white from its original white color. I'm going to try to go with a reflow oven as soon as I can and will be checking out the PCB manufacturing show in Tokyo coming up in January. I'll be looking specifically for companies with small reflow ovens and should be grilling them about specs since I know pretty much what I want now.
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Re: desktop ovens

by adafruit on Thu Nov 05, 2009 8:25 pm

the elektor oven might be OK. they're a pretty rigorous zine and dutch are not wishywashy about machinery. that said, we're probably going to do 1 sided only for now

or...you could also do a skillet/plate for the tough side, and then screen and place the other and hot air?

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Re: desktop ovens

by slick on Thu Nov 05, 2009 10:45 pm

adafruit wrote:im thinking of putting a sheet of aluminum on it to help even out the hotspots a bit. i also want ~ 12" x 12" space


You have to be careful about adding mass to your skillet. I made a plate inspired by this one, but I didn't think it through. My plate is 1" thick by 8 inches long by 4 inches wide. I have a 1/2" dia by 7 inches long 500W heating element, and at full power it takes too long (ten minutes) to get hot enough to reflow solder. Then it stays hot for way too long afterward. My control is an arduino with the PID library, an LCD, a the MAX6675 TC amp with a k-type TC, and a solid state relay. (I don't have the whole reflow profile programed yet). Instead of trying to match up a heating element to an appropriate hunk of metal I'm thinking it might just make more sense to try this control in a toaster oven. If I can get the oven to work I bet it wouldn't be too difficult to rig up a conveyor.
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Re: desktop ovens

by Stynus on Fri Nov 06, 2009 6:43 am

adafruit wrote:the elektor oven might be OK. they're a pretty rigorous zine and germans are not wishywashy about machinery. that said, we're probably going to do 1 sided only for now

Elektor is from the Netherlands, not Germany.

The reflow oven they sell is a cheap oven from china with a elektor sticker on it sold for to much money. On ebay you can find the cheaper one's http://cgi.benl.ebay.be/T962-Infrared-S ... 25544b796e for example.
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Re: desktop ovens

by martinimartin on Fri Nov 06, 2009 9:37 am

Why not build one yourself?

I made one from a cheap toaster oven and a custom built PCB. Or actually, from two cheap toaster ovens because one set of heaters showed to be to little.
It works really excellent. Just put in your PCBs press the button and open it when done. Up to now I've soldered at least 200 PCBs with at without one failing.

Currently I'm working on an improved version with a larger processor. The ATmega8 seemed to be to small for all the printf libs. And it's going to have a lasercut front panel with a small display and some buttons (and USB).

If your interested I could send you a copy of the new circuitboard. My PCB manufacturer will make at least three and I only need two. It's been designed for 230V but it will probably run as well on 110V.

Once the new design is finished I will post a complete overview of the build + tutorial on my website (www.anlagelab.net)
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Re: desktop ovens

by adafruit on Fri Nov 06, 2009 11:54 am

Stynus wrote:
adafruit wrote:the elektor oven might be OK. they're a pretty rigorous zine and germans are not wishywashy about machinery. that said, we're probably going to do 1 sided only for now

Elektor is from the Netherlands, not Germany.


man

that is so embarassing

:oops:

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Re: desktop ovens

by adafruit on Fri Nov 06, 2009 11:57 am

we have a toaster oven but when we put a (larger) PCB in we had uneven heating problems. one part reflowed and another started bubbling molten epoxy! it was really really gross!!!
it could, of course, be our fault tho :)

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Re: desktop ovens

by martinimartin on Fri Nov 06, 2009 12:10 pm

No problems like that with this one.
The only thing I noticed that sometimes parts of boards show a little discoloration when accidentally left in to long. But never any serious damage. I use a self written and tuned PID control loop and an accurate Pt100 sensor in the middle of the oven (very probably overkill).

If your heat spreading is uneven you could put a deflector over your heaters (just some aluminium plate) to reduce direct radiation. If you additionally add a fan for circulation it will probably be very evenly spread, but I don't think this will be necessary.

Ps: It will also do 2-sided without any problem, as long as you take some care with supporting your board.
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Re: desktop ovens

by adafruit on Fri Nov 06, 2009 12:20 pm

ha! cute :)

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Re: desktop ovens

by westfw on Fri Nov 06, 2009 6:40 pm

If the actual toast produced is any indication (and it probably is), toasters and toaster ovens are pretty wildly variable (across brands, etc) WRT how evenly they heat ANYTHING...

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Re: desktop ovens

by adshea on Fri Nov 06, 2009 10:15 pm

I've used toaster ovens, but just ebay'd a real temperature controller (Omega, Watlow, etc.) The nice ones only run about $40-$50 and let you program in profiles. The nice thing is that they already have the PID stuff and thrermocouple amps built in. I'll get some pictures for my current setup sometime here when I remember, but it's just a K-type TC, an Omega controller and a $20 toaster oven I picked up at Target. For under $80 I can do pretty nice profiles with one button press. I've been considering adding a solenoid to open the door for a faster cool-down so I don't have to watch and open it when things are done, but that's a ways down my list.

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Re: desktop ovens

by martinimartin on Mon Nov 09, 2009 8:22 am

But by doing it yourself you learn something. :D

Now I can build a PID controller, measure temperature up to 1/100 dC accurately with a calibrated Pt100 (try that with your K-type TC), PWM control SSRs and sync the whole proces with the sine wave of the mains.
Something you cannot buy for $50. ;)

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