DIY Reflow Oven

[rlaury]

Well I'm going to have to build a SMD reflow oven. Anyone have any recommendations on a good
system. I need to be able to do small productions of 25 - 50 boards in a run.
I see a lot on YouTube using the Black and Decker oven. I thought about using a more commercial
type. Maybe the kind you would see in a SUB Shop. There are some good controllers available on
Ebay. I'll use one of them I guess.

Any suggestions

RonL

 

[ruairioflaherty]

Has everyone been taken care of?

https://groupdiy.com/index.php?topic=64819.0

 

[joaquins]

  In addition of a PID (or more comprehensive control system) taking care of the temp profile you should be careful spreading the heat evenly, for so many boards might be tricky to get the desired thermal profile for all of them simultaneously. You should probably add some fans to do so but you cant just put any fan in there, probably a hole with the motor outside and the fan inside could do so. In a single axis you could use more than one fan to improve air recirculation.

  The other trick is this ovens usually doesn't cool down fast enough for most standard profiles, so you should add a vent forcing cool air in or sometimes opening the lid right after the peak does the trick, you could automate that but I don't know, is not the most controlled way of doing so. I'd use a fan forcing air in. Most comercial ovens have fixed temp regions and move the board across the oven, once it's done it takes them out to finish the cooling. Is not a very DIY friendly, so you have to work around.

JS

 

[rlaury]

good food for thought.

Thanks

 

[Martin Griffith]

I keep thinkng about this http://www.whizoo.com/index#reflowwizard

 

[ruairioflaherty]

good food for thought.

Thanks

But my post is not?

 

[rlaury]

Thanks.
I think this is where I'll start.

 

[hitchhiker]

But my post is not?

Your post should be food for thought because in fact it's a very good question!

 

[Monte McGuire]

I've thought about this too, but one of the issues that comes up is not only the need to cool the contents somewhat rapidly, but also the need to provide a relatively fast positive temperature ramp.

Essentially, a soldering profile will bring up parts above ambient, and do a simple moisture bake / soak / preheat, but then when the real ramp starts, the total time of the profile cannot take too long. The solder paste needs to heat, liquefy, and react with the PCB and component metals, and then transition to the liquidus temperature before all of the flux has volatilized. I forget the exact number, but IIRC you need around 3 degrees C per second of temperature slew to be able to do a good profile.

If you do not have enough energy to do 3 degrees per second, your preheat and soak take so long that the flux in the solder paste will have volatilized before liquidus happens, so you will not have optimal surface tension, and may have cleanliness or 'flux junk problems' in the finished boards. Additionally, this will subject the parts to a longer cycle, which is sometimes damaging.

While this should be also a function of the chamber insulation, from what I could determine, one needs 220V power to get this to happen. Much more than a kilowatt is needed, and this sort of a ramp is not so easy (or possible at all) with simple 'hacked toaster ovens' plugged into a 15A 110V household outlet.

Now, I'd love to be proven wrong, but for me, 220 wiring would be difficult, so I have not pursued this.

So, I'd have to dig into the specs to work it out, but having a relatively fast, controlled rate ramp is really crucial to getting this to work, both going up in temperature and going down. Going down can be easy if you have liquid Nitrogen, but that's also a hardship for small labs.

So, I know people have made this work, but it seems on the ragged edge. Any promising thoughts?

 

[rlaury]

Good info there. This seems to be the J-STD-020 standard on reflow.
I'm in the process of building mine now. I'm using 900 watts on bottom and 650 watts on top.
2 elements top and 2 elements bottom. I bought the ControlLeo2 kit after studying all links
I could find. I'll keep us posted on my progress. Here's the link to the controller kit.

http://www.whizoo.com/index#reflowwizard

 

[3nity]

Hey Buddy.
Do you know when my Optos are gonna be shipped?
Its been over 4 months or even more!

Please keep us updated.

 

[Andy Peters]

So, I know people have made this work, but it seems on the ragged edge. Any promising thoughts?

I've seen a lot of "hackaday" type projects that purport to work, and I've thought about doing it, and then I look at the reflow oven in the production area of the office and I realize why the toaster-oven idea isn't great. The real reflow ovens put the boards on a moving track, and the timing for the various cycles is determined by the speed of the track.

A toaster oven's heating elements are wildly variable, and cooling is difficult unless you put a fan or something in it to blow the hot air out.

 

[deva]

I've thought about this too, but one of the issues that comes up is not only the need to cool the contents somewhat rapidly, but also the need to provide a relatively fast positive temperature ramp.

[...]

So, I'd have to dig into the specs to work it out, but having a relatively fast, controlled rate ramp is really crucial to getting this to work, both going up in temperature and going down. Going down can be easy if you have liquid Nitrogen, but that's also a hardship for small labs.

So, I know people have made this work, but it seems on the ragged edge. Any promising thoughts?

FWIW, at my university lab we have a cobbled-together reflow oven (was a junkyard rescue, actually...).
It is rather small, some 15 x 20 x 20cm and I'd assume it's not really powerful, as it was not meant for baking stuff.

It does not have enough power to meet the ramp-up specs, and we're really unable to meet ramp-down by just opening the doors. The standard profile is way too fast for the oven: we begin liquid phase when the standard curve is already cooling down.
So, we basically let the PID follow the curve as much as possible, then we just switch it in manual mode and keep it at peak-ish temperature "for a bit" before turning it off and letting it cool with the door open. Very, very much imprecise and guesswork.

As much as I wouldn't advocate this setup for anything resembling production, we've been able to reliably solder 1mm and 0.8mm BGAs, 0.4mm QFN and so on, with minimal need for rework, except some occasional tombstoning on 0402 components. Actives (power devices, FPGAs, fast SiGe logic andRF stuff, and so on) seem to get thru the process with no damage/deterioration; same goes for passives, connectors and reflow compatible plastic parts.

Bottom line, in my experience, if you are doing small or single quantities and can afford to test each board and fix the occasional issue, you can maul the standard curve quite significantly and still get away with it.

Caveats:
- We still use leaded solder (research, not sale, so RoHS doesn't bother us)
- My definition of "reliably solder" is: all the pins we use (e.g. in FPGAs not all are used) make electrical contact, and we don't observe performance degradation or failures that we can relate to bad soldering or overcooked components.
- Can't comment on long-term (> 1-2 year) reliability as we got that thing just a couple years ago.

 

[Monte McGuire]

That sounds very similar my experience with 'home reflow'. I use a Hakko FR810 hot air wand with a Hakko FR872 IR pre-heater, along with a nice PCB, a nice stencil and 63/37 lead solder paste. With this, I can more or less get a ramp that sorta works, but I have to carefully orient the board relative the IR elements and then be very methodical with the hot air to make sure that all areas of the PCB have flowed properly, without taking too long.

Using lead makes it a bit easier, since it'd be hard to get 260 degree C to properly flow SAC305 paste. The time it takes just to get to lead reflow temperatures tends to 'use up' the flux in the paste before I can get all parts of the board to flow. A partial fix for this is to apply Kester 959 flux to the PCB and bake that dry before screening the paste. This adds a bit of extra flux that helps out. This is also a great idea if I ever have to use the IR heater for rework - having extra 'new' flux keeps the existing work from getting crusty or oxidized. As long as you don't overheat, you can re-flux, heat, and clean between cycles without problems (obviously only up to a point).

With really awesome footprints (that I designed with PCB Library Expert software), and really awesome boards from Advanced Circuits, I can get this hodgepodge to work, but it's not foolproof, and requires too much skilled intervention to get it to work well. And, in the end, since the ramp is so long, the flux has a slight 'rainbow oxide' sheen to it and doesn't look at nice as it should. Still, the parts align to the pads beautifully, and pretty small features worked beautifully. I have a DFN with very low clearance from the die attach pad to the DFN pins, and because the PCB was so good, that part did not fail, ever. Good footprints are essential!

So, yeah... I guess we struggle along with the kludges that we have worked out, and a real oven would be great, but 220V is gonna be tough for me, as would shop nitrogen. There still could be a way to get this work for a small reflow chamber, but it's right on the edge, so it'd have to be tightly engineered.

Thanks for chiming in, and if anyone else has any success or failure stories, I'd like to hear about it! When reflow works, it's gorgeous, but getting there is unfortunately difficult to do at home.

 

[Andy Peters]

That sounds very similar my experience with 'home reflow'. I use a Hakko FR810 hot air wand with a Hakko FR872 IR pre-heater, along with a nice PCB, a nice stencil and 63/37 lead solder paste. With this, I can more or less get a ramp that sorta works, but I have to carefully orient the board relative the IR elements and then be very methodical with the hot air to make sure that all areas of the PCB have flowed properly, without taking too long.

Using lead makes it a bit easier, since it'd be hard to get 260 degree C to properly flow SAC305 paste. The time it takes just to get to lead reflow temperatures tends to 'use up' the flux in the paste before I can get all parts of the board to flow.

We have to use lead-free at work, so I use it at home too. One trick we use with the small IR preheaters and hot-air tools is when pre-heating, cover the work with a Pyrex casserole dish. It keeps the heat in and helps.

 

[Monte McGuire]

Nice idea! I have a large Pyrex casserole that I've used for etching - would be perfect for this use.

Thanks!

 

[buildafriend]

without having the proper time to read all of the above -

You can use a hot air gun, you can get an SMD rework gun, you can get hot weezers, you can get low temp melting solder for popping off things like CPLD , FPGA, or microcontroller/CPU chips, you can keep flux around, solder braid, and use extremely fine point soldering tips. In my experience reflow ovens haven't been anywhere near as useful as a good set of eyes and a continuity meter. But to each his own. If you're populating boards that's a whole different story. I don't know exactly what you're tackling though..

best of luck