desktop ovens

Chat about pick and place machines, reflow ovens, assembly techniques and other SMT tips & trix

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
ralphstirling
 
Posts: 18
Joined: Fri Nov 06, 2009 2:53 pm

Re: desktop ovens

Post by ralphstirling »

We used toaster ovens for quite a few years, first with an off-the-shelf temp controller, then with an MSP430 based homemade controller programmed by students in the Assembly Language Programming class. The temp controller was limited in the time resolution for the temperature profiles. I think it had 1 minute steps, which was pretty crude for soldering profiles. The homemade controller did the job for quite a while, but started getting flaky about turning off at the end of the cycle, and after the fire alarm got set off by a smoldering pcb left in by a careless student, we shelved the toaster oven and controller and bought a commercial benchtop unit. I got a Manncorp oven, which works OK, but is quite overpriced for what it does. The controller is very limited (one profile consisting of two points).

One idea for homemade ovens that has gone through my mind is to put three or four toaster ovens in a line (front to back), cut slots in the backs, and run a conveyor through them. Each oven would just have a fixed temp PID loop, just like a commercial conveyor reflow oven. You would need to have two different 120v circuits to power it, as a single 15A circuit won't handle three toaster ovens.

-- Ralph

freaklabs
 
Posts: 37
Joined: Wed Nov 04, 2009 7:42 pm

Re: desktop ovens

Post by freaklabs »

I posted this in another thread, but there is an active community of people making their own powder coating ovens. A lot of it is also transferable to making your own reflow ovens, albeit on a smaller scale than a powder coating oven. There are links to calculators for heating element and power based on size of the oven and desired ramp speed. Here's the link:

http://forum.caswellplating.com/oven-building-forum/

@martin martin: yes, you're right. The knowledge you built by making it yourself is definitely worth more than $50. Its also nice to know that you can modify your oven to suit any particular custom need or profile you want, add extra safety features, or make a whole rack of ovens in case you start wanting to manufacture more PCBs :)

SiliconFarmer
 
Posts: 33
Joined: Sun May 31, 2009 2:07 pm

Re: desktop ovens

Post by SiliconFarmer »

Those are some SERIOUS ovens. I don't think they have the rapid temperature profiles we need, but I have no doubt that there are some real gems of info we could gleam from them.

I just took an SMT class from the author of Extreme Surface Mount Soldering Instructable http://www.instructables.com/id/Extreme ... Soldering/.

Doctek has industry experience with SMT soldering processes. He's paid a lot of attention to the recommended temperature profiles. I'm impressed with his results using a $20 hotplate for lead-free soldering. He points out that toaster ovens work OK for lead-based solder, but for lead-free, they can barely reach the melting point, which means you won't be following the profile. Hotplates don't have that limitation.

We soldered about 4 batches of boards with no catastrophic failures - neither burned nor unsoldered parts. The boards looked good, but we didn't test them.

A hotplate may not be large enough for Adafruit, but consider this: five $20 hotplates running in parallel is only $100 (plus cost of the controller).

A couple comments:
His controller could fairly easily be more automated. Several of us were suggesting connecting it to a laptop running some control software to time the heating profile steps, perhaps using Processing. Touch one button and wait for the "ding" that the boards are done.

His system is open-loop, yet works well. I believe this is because he has calibrated his hotplate carefully. He has thought about using a temperature probe, but his results are so good, he hasn't bothered. For folks using his Instructable with an unknown variety of hotplates, I think adding a temperature sensor would be very helpful.

ai_dude
 
Posts: 21
Joined: Fri Dec 11, 2009 1:49 am

Re: desktop ovens

Post by ai_dude »

FWIW, there are some lower-temp lead-free solders. See here... http://en.wikipedia.org/wiki/Solder .

gsattler
 
Posts: 48
Joined: Tue Nov 24, 2009 3:44 pm

Re: desktop ovens

Post by gsattler »

ralphstirling, what oven did you end up buying from Manncorp?

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: desktop ovens

Post by adafruit »

hotplates are pretty darn good. the $20 ones cant do tiled designs because of massive cold spots. we're looking to get a nicer plate :)

ralphstirling
 
Posts: 18
Joined: Fri Nov 06, 2009 2:53 pm

Re: desktop ovens

Post by ralphstirling »

gsattler -

We ended up buying the 850. It is very heavy duty and has no trouble heating up
quickly enough for good profiles. The control is very simple, with only one profile
consisting of two points. It is advertised as "hot air convection" (used to be advertised
as "forced air convection"), but has large heating elements above and below the pcb
in the main oven compartment. A fan at the back circulates the air. I did some
temperature profiling with a 6" x 6" pcb and five thermocouples, and it seemed to
heat solder pads pretty uniformly. We haven't tried lead-free with it yet. You can't
have a preheat plateau in your profile at less than 150C, because that is the "ready"
temperature that the oven warms up to when first turned on.

-- Ralph

freaklabs
 
Posts: 37
Joined: Wed Nov 04, 2009 7:42 pm

Re: desktop ovens

Post by freaklabs »

FYI, I'm using the Maddell QK870 hotplate and its pretty nice. It has a digital temperature controller, flat surface, and it heats up fairly quickly. So far, I'm doing all my boards on it and its okay. Temperature-wise, hotplates don't seem to be good for boards with white solder masks. They end up off-color (yellowing) past 200 deg C. I reflow my boards mostly at 210 deg C and they're noticeably off-white. At lead-free reflow temps, I think it'd be best to go with a darker color that won't show the discolor as much. Here's a shot of my hotplate.

Note: those aren't skidmarks. Did a de-soldering tutorial at Tokyo Hackerspace and that is the residue left by some of the epoxy from the bottom mounted chips.

Image

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: desktop ovens

Post by adafruit »

hmm, those plates are cheap. thinking about getting one to upgrade from my skillet. can you plug into the PID controller? i prefer not to sit around and dial in temps :) are there hot/coldspots or is it pretty uniform across the plate?

freaklabs
 
Posts: 37
Joined: Wed Nov 04, 2009 7:42 pm

Re: desktop ovens

Post by freaklabs »

To add a PID, you'd have to open it up and hack it. It doesn't look like its too difficult to open her up though and the circuitry is pretty simple. The surface is a large aluminum block with grooves on the bottom for the heating elements. Since its a fairly thick aluminum block, the temperature is pretty even for my boards. Since you're in the US, it'll be pretty easy to just order one and try it out. For my purposes, it serves me fine, although I'd prefer a solder profile controller so I don't need to use timers. One of these days, might make one, but just have no time.

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: desktop ovens

Post by adafruit »

oh so you dont set the temperature, it just has a readout?

freaklabs
 
Posts: 37
Joined: Wed Nov 04, 2009 7:42 pm

Re: desktop ovens

Post by freaklabs »

No you set the temperature through pushbuttons on the front panel. But you can probably emulate the temperature setting by hijacking the wires that go to the buttons. That would be one way to implement a PID.

freaklabs
 
Posts: 37
Joined: Wed Nov 04, 2009 7:42 pm

Re: desktop ovens

Post by freaklabs »

Just realized what I said doesn't make any sense. I meant you can hijack the signals to implement a solder profile. There's already a controller for the heating elements. Guess the solder fumes are getting to me. Since I'm posting, might as well describe it a bit more. The main block is machined flat and made of thick aluminum. On the bottom side, there are four grooves with four heating elements. Hence the temperature comes out pretty even across the plate. Actually, its not even a hot plate. Its more like a heated chunk of metal.

adafruit
 
Posts: 12151
Joined: Thu Apr 06, 2006 4:21 pm

Re: desktop ovens

Post by adafruit »

just want to mention i got one of these, its much better made than i'd expected. there's 4 heaters and a nice flat aluminum plate. the heating is nice and uniform.
the calibration is way off because of the timing, but im planning on making a controller for it. stay tuned :)

User avatar
phomann
 
Posts: 1
Joined: Thu Feb 11, 2010 8:24 pm

Re: desktop ovens

Post by phomann »

Hi,

I built a SMT toaster oven and have been using it for over 10 years now without any problems.

http://www.BANNED.com/SMDToasterOvenProject.html

One of the tips I can offer is to use a fan forced one. It helps to get even temperatures throughout the oven.

Cheers,

Peter.

Locked
Please be positive and constructive with your questions and comments.

Return to “SMT (Surface Mount Tech)”