DIY reflow oven

[T4P]

few small points, thermocouples on there own generally are just the junction of 2 dissimilar metals, if you want it instead of hunting around a very tight set point to stabalise near it you add some mass to it, even say a metal beer cap, but that depends on how you want the system to function (t4p's type have high mass and will respond very slowly)

equally it is better to average out 4 thermocouples placed around the thing than a single one, to average the voltaqge of thermocouples just add them in parrellel, while this will mean there will be a tiny bit of error introduced from tiny amounts of current flow it would result in a better representation of the entire oven, and thermocouples are pretty cheap at those temperatures,

Yeah i'm aware. Only the small junction types can perform well for low thermal mass. Those thermocouples i've shown is usually used for mostly hotplates

[poorchava]

I'm also setting up a reflow equipment at the moment. I've purchased this: http://optimum.hoho.pl/index.php?lang=eng&id=821. Cost was around $35 so it's fine. It has top and bottom quartz heating elements, but they are in the center so heat distribution will not be even, because radiation will heat up stuff directly underneath the elements more than stuff in the back in front of the oven.

I plan to use some thick (1-2mm) copper or stainless steel to shield the pcbs from direct IR exposure, so that they are heated with hot air only (or the secondary IR emission from the plates).

Second problem is that stock electromechanical thermostat (i guess bimetallic type) is a total shit. When set to 175*C the temp goes up as high as 240*C (i mean temperature of PCB surface). Planning to buy or make some cheap temperature controller.

[lrai]

Cheap chinese reflow oven from 200$ ... hmm DIY doesn't look so interesting anymore
http://www.ebay.com/itm/T962-INFRARED-SMD-BGA-IC-HEATER-REFLOW-OVEN-800W-180-235MM-T-962-BRAND-NEW-k2-/180736333541?pt=UK_Home_Garden_Conservatory_Patio_bbq_Patio_Covers_Heating&hash=item2a14b996e5

Not a review but here it is what i found about it on different  forums:

(Don't use them inside, use them in a  garage or similar as they do burn off paint & of course, smelly, and most likely highly toxic solderflux gases)
There are 2 elements in the unit, mark the position of these on the bottom of the PCB drawer. Align your PCB's longitudily with these elements, ie as much in line and centered between them as possible
Always put your target PCB's on top of 2 layers of old PCB's to prevent the PCB drawers metal bottom from sinking the heat away from your PCB's
I have one of these. I've had it for about a year and a half and I've done quite a few boards with it now. It works very well. It follows the temp profiles fairly well that I choose (as monitored by an external source). I have no complaints about it and would definitely pick it up again instead of kludging together a toaster oven.

[htassell]

If you want a hardware design as a guide, as well as the software (already linked to earlier in this thread), I can reccomend the RocketScream reflow controller shield.

I use on of their shields on an Arduino with their stock code, I just made a box for the SSR's that control the heater element and cooling fan, and the arduino plus the shield and an LCD with control buttions and it has performed excellently for the last year or so with my breville toaster oven. The board is nothing special at all. Essentially it's just got a MAX6675 thermocouple sensor interface and some buttons plus a small 2x8 lcd display.

This is their main site:

http://www.rocketscream.com/shop/reflow-oven-controller-shield-arduino-compatible

All the schematics, board layouts and code are on github at:

https://github.com/rocketscream/Reflow-Oven-Controller

My apologies if this has already been brought up - I just thought I'd mention it in case.

Cheers,

Hugh

[OndraSter]

Cheap chinese reflow oven from 200$ ... hmm DIY doesn't look so interesting anymore
http://www.ebay.com/itm/T962-INFRARED-SMD-BGA-IC-HEATER-REFLOW-OVEN-800W-180-235MM-T-962-BRAND-NEW-k2-/180736333541?pt=UK_Home_Garden_Conservatory_Patio_bbq_Patio_Covers_Heating&hash=item2a14b996e5

Not a review but here it is what i found about it on different  forums:

(Don't use them inside, use them in a  garage or similar as they do burn off paint & of course, smelly, and most likely highly toxic solderflux gases)
There are 2 elements in the unit, mark the position of these on the bottom of the PCB drawer. Align your PCB's longitudily with these elements, ie as much in line and centered between them as possible
Always put your target PCB's on top of 2 layers of old PCB's to prevent the PCB drawers metal bottom from sinking the heat away from your PCB's
I have one of these. I've had it for about a year and a half and I've done quite a few boards with it now. It works very well. It follows the temp profiles fairly well that I choose (as monitored by an external source). I have no complaints about it and would definitely pick it up again instead of kludging together a toaster oven.

With all my parts I am still below $50.. yes, it looks good to me so far . (Oven was $15 shipped to me.)

Plus, DIY!

[free_electron]

For all those small toaster oven reflow systems a PID algorithm is total overkill. They don't have the heat capability or rampup speed that needs a pid regulation. a simple bang-bang controller will do. temperature can be kept constant in a 3 degree band.

now, best results are if you get a little oven thet , besides the heating elements, also has a built in fan... ( hot air) the fan creates a more uniform heat spread inside the oven. to cool down : simply shut off the heaters and leave the fan running.

i am wrapping up on a controller for such an oven. simple 2x8 lcd , two thermocouple sensors ( one for temp regulation one to monitor pcb ) usb for logging and programming , memory for 9 recipes. uses new maxim thermocouple chips
atmega328 based so you could run the arduino stack if you want ( it is not an arduino , custom board that splits in half : one front panel one power section ) uses a beefy 30 ampere relay for heater and another 2 ampere relay for the fan.

i use a 4 step duty cycle control : a cycle is 8 seconds. the duty can be programmed as 1/4 1/2 3/4 or full on
the regulation algorithm is a simple select case.
if i am low more than 20 degrees : full on
off 15 degrees : 3/4
off 10 degrees 1/2
off 5 degrees 1/4
over setpoint : heater off

works like a charm.

[Noize]

Have you got any photos of your oven and/or details of construction, I've got a breville toaster that I don't use much.

I use on of their shields on an Arduino with their stock code, I just made a box for the SSR's that control the heater element and cooling fan, and the arduino plus the shield and an LCD with control buttions and it has performed excellently for the last year or so with my breville toaster oven.
Cheers,

Hugh

[Spikee]

What about this oven (i know it does not have a fan :c )

Delonghi-eo12001b :
http://www.wehkamp.nl/huishoudapparatuur/kookapparatuur/ovens/delonghi-eo12001b-oven/C27_7G3_G35_767759/

It's 1400 w and 12,5 liter , has bottom and top heating elements.
If you calculate the watt per liter you get  1400/12,5 = 112 W/ L which is pretty good.
Maybe whit some extra insulation it will perform even better.

[george graves]

i am wrapping up on a controller for such an oven.

Would love to see the details!

[IanB]

few small points, thermocouples on there own generally are just the junction of 2 dissimilar metals, if you want it instead of hunting around a very tight set point to stabalise near it you add some mass to it

This reasoning is not very sound. You want a temperature sensor to measure the temperature of its surroundings, not the temperature of itself. Therefore a smaller thermal mass is better than a large one as it can respond to changes quicker. You put the filtering in the control circuit, not in the sensor.

Consider by analogy what happens to a voltage regulator if you put too large a capacitor on the output side in a misguided attempt to stabilize the voltage. The regulator will have all sorts of performance problems. Similarly, if you put a big thermal capacitance where the temperature is measured the temperature control loop will also have all sorts of performance problems.

So by analogy, let the temperature sensor be small and fast to respond. If you get a noisy measurement out of it you can apply carefully tuned filtering in the control system with full control over how you extract the signal from the noise.

[free_electron]

i am wrapping up on a controller for such an oven.

Would love to see the details!

Pcb can be ordered through elektor. Full plans (schematics) are in the new labworx book 'mastering surface mount technology ( there's also an uv exposure unit , a ringlight for microscope or magnifier and an led tester for smt leds's)

The sourcecode is written in mikrobasic and will be released soon ( polishing it right now ) . The board can be flashed with the arduino stack so you can go that route if you want.

[EEVblog]

Cheap chinese reflow oven from 200$ ... hmm DIY doesn't look so interesting anymore

Yes, I've been wondering this.
They are about AU$250 delivered.
Any real advantages to the DIY approach?, and has someone standardised on a kit controller board?, or is each build a unique hack?
Just temped to get the commercial one at that price and save the dicking around...

Dave.

[Noize]

As well as reflow you can have a cup of coffee whilst you are waiting 

http://www.ebay.co.uk/itm/3-In-1-Toaster-Oven-Griddle-And-Coffee-Maker-/221130568166?pt=UK_Campervan_Caravan_Accessories&hash=item337c68b1e6

[Baliszoft]

I got a $250 ebay "T-962" reflow oven (came with a complete set of spare IR tubes). They are controlled by two thermocouples (hanging from the top into the compartment), and one of them had a bad contact in its connector. My first test board was completely fried . After fixing and calibrating it (properly), now it works. Heat dirtribution is not even though, the outer 20% of the drawer area is nearly useless (has a lot lower temp).

EDIT: Maybe the drawer is a bit bigger than the specified area (did not measure it).

[tld]

i am wrapping up on a controller for such an oven. simple 2x8 lcd , two thermocouple sensors ( one for temp regulation one to monitor pcb ) usb for logging and programming , memory for 9 recipes.

I'm wondering which thermocouple for the PCB, and how you're planning to use it.  Will you simply keep it close by, or actually fastened to the PCB somehow?

Terje

[free_electron]

There's two thermouple interface. One is used to measure the air temperature in the oven and control the reflow process. Note that i am NOT useing an infrared oven ! It is a convection oven with air circulation.

Plenty of cheap reflow systems use infrared heating tubes. That is NOt what i use and this controller is NOT made for that. The problem with IR is that you 'cook; certain parts , while others are still cold... a black TQFP heats up way faster than the white ceramic resistor next to it... or the yellow trim potmeter .

My oven is a pure hot air system. the airtemperature is controlled and there is no direct IR radiation hitting the board.

The second temperature sensor is optional ( you can omit the chip if you don't want it ) the controller reads that sensor but does not use the information. You can plot the data and see how the real pcb heats up under the heating conditions. This information can be used to tune-in your particular oven.

Maybe i'll make a smarter algorithm that also monitors this sensor and can provide feedback to what is actually happening on the pcb.

I use an Oster oven that wa son sale at costco for 40$.

[jucole]

Not sure if you had seen these, might be an option if anyone wants something but can't be arsed to make something.


OSPid

http://www.ospid.com/blog/







Reflow Oven Controller Shield

http://www.rocketscream.com/shop/reflow-oven-controller-shield-arduino-compatible

[David_AVD]

We've been using a Breville BOV800 convection oven to do small batches of SMD boards.



It's not cheap (AUD $249) but has much better heating than the crappy cheap ovens.  Yet to make a controller for it.  Just using it manually for now.

[JimmyM]

Skip the Arduino and use one of these...
https://www.sparkfun.com/products/10089  or these  https://www.sparkfun.com/products/11075
Maybe an additional external board for the thermocouple converter and opto-isolated control of SSRs/relays for heaters/fans, etc. It has several ADC and Digital I/O ports as well as an SD card slot for images and thermal profiles.

[EEVblog]

We've been using a Breville BOV800 convection oven to do small batches of SMD boards.

It's not cheap (AUD $249) but has much better heating than the crappy cheap ovens.  Yet to make a controller for it.  Just using it manually for now.

That looks like the go, in convection mode.
Could probably even hack the keypad to control the thing instead of replacing all the electronics.

Dave.

[David_AVD]

That looks like the go, in convection mode.
Could probably even hack the keypad to control the thing instead of replacing all the electronics.

Yeah, the smaller el-cheapo units just don't have enough grunt.  This one is much better construction.

We normally use leaded paste, but a visiting colleague tried lead-free the other day.  The boards flowed ok apart from the ones at the edges.  We think the issue was that the inbuilt controller cut the heaters just short of the ideal temp for lead-free.

Using an external controller would allow the profile to be automated and raise the current temp ceiling.

[Short Circuit]

I got a $250 ebay "T-962" reflow oven (came with a complete set of spare IR tubes). They are controlled by two thermocouples (hanging from the top into the compartment), and one of them had a bad contact in its connector. My first test board was completely fried . After fixing and calibrating it (properly), now it works. Heat dirtribution is not even though, the outer 20% of the drawer area is nearly useless (has a lot lower temp).

EDIT: Maybe the drawer is a bit bigger than the specified area (did not measure it).

I have the bigger -A version, and I consider it garbage.
Indeed, heat distribution is terrible. But even worse is the heat distribution in height.
When you have large SMD parts such as caps or connectors, they end up fried or molten before the solder has reflowed.
Also the user interface of the thing is beyond terrible.

Perhaps performance can be improved bigtime by adding a convecion fan and
replacing the controller with a more reliable and useful thing.

[David_AVD]

I considered one of the 962 series units but saw many negative reviews, ranging from "poor heat distribution" to "caught fire" !   

I like the oven I bought as the extra height and 5 heater bars seem to give quite reasonable performance.

[Short Circuit]

We've been using a Breville BOV800 convection oven to do small batches of SMD boards.
...

...
I like the oven I bought as the extra height and 5 heater bars seem to give quite reasonable performance.

Looks nice. Bottom heater and convection fan sound good.
 
However, reading the manual, I see mention of the temperature range no more than 230 degrees.
That means the oven would be unsuitable for lead-free soldering...

[David_AVD]

However, reading the manual, I see mention of the temperature range no more than 230 degrees.
That means the oven would be unsuitable for lead-free soldering...

Yes, it regulates too low as standard.  That's why I mentioned using an external controller for lead-free use.  Works well out of the box for leaded solder though.