
Building a Reflow Oven - mindcrime
https://whizoo.com/reflowoven
======
Stratoscope
This is cool! I can buy a $30 Black & Decker toaster oven and turn it into a
reflow oven.

There are a few worrisome steps, like this section:

> _Ceramic fibers are very fine and sharp. They don 't penetrate though thick
> skin, but can irritate thin tissue like eyes, nostrils and lungs. If you
> exercise precautions you won't have any problems. The blanket has amazing
> insulating properties, and the top of your oven will be barely warm during a
> reflow._

> _Things to keep in mind:_

 _• Unwrap the ceramic fiber blanket just before you use it - not earlier._

 _• Clean up your workspace immediately after applying the blanket and closing
the oven_

 _• If possible, wear a face mask (we recommend using N95 masks)_

 _• Wear shoes. Our preference is flip-flops that we can easily wash
afterwards_

 _• Take care not to touch your eyes, lips or ears_

 _• Keep the area free of drinks, and use the restroom (toilet) before
starting_

 _• Work in a draft-free environment. Don 't use fans_

 _• Make slow movements to minimize dust_

 _• Make sure you have all your tools and parts close by (you need to close up
the oven too)_

 _• Make sure pets, kids and neglected spouses don 't come into your work
area_

 _• Immediately after working with the blanket you should take a shower and
wash your clothing_

> _Scared? Don 't be. Ceramic fiber is easy to work with as long as you take a
> few precautions._

OK! I am not scared at all.

I do have to wonder about the cost effectiveness, at least for myself. It
sounds like a solid couple of days work to make this thing.

Suppose I were looking for a ready-to-go reflow oven at some kind of
reasonable price. Where would I start? Any recommendations?

~~~
mindcrime
_Suppose I were looking for a ready-to-go reflow oven at some kind of
reasonable price. Where would I start? Any recommendations?_

Here's the rub... there _are_ relatively inexpensive, COTS reflow ovens out
there[1], and they do work - more or less. The problem is that many people
find them to be more on the "less" side of that spectrum, without putting
considerable work into upgrades and mods anyway. And once you take a cheap
T962 off the shelf and start modding it, you might start to ask "why not just
build my own from a toaster oven?"

The toaster oven conversion winds up being cheaper, or - at worst - a wash,
from a price standpoint. And many people find that they get better results
from the converted ovens than they do from a T962.

Unfortunately, the next "hop" up in quality in terms of commercial ovens winds
up being a pretty big jump price wise.

I haven't tried this myself yet, but I have a friend who has both a T962 and a
conversion oven (made from a Black and Decker convection oven, so a little
pricier than the model cited in TFA), and he only actually uses his converted
oven. I trust his opinion a lot, so if/when I decide to get a reflow oven, I'm
leaning hard towards doing this.

[1]: [https://www.amazon.com/Happybuy-Soldering-Machine-
Infrared-A...](https://www.amazon.com/Happybuy-Soldering-Machine-Infrared-
Automatic/dp/B01LZYEF90/ref=asc_df_B01LZYEF90/?tag=hyprod-20&linkCode=df0&hvadid=312128028232&hvpos=1o1&hvnetw=g&hvrand=10004436235525553708&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9009670&hvtargid=pla-526334860728&psc=1)

~~~
fest
I've also had less screwups using the regular toaster oven instead of T962. I
suspect that's because T962 uses IR heaters instead of convection.

I've regularly had slightly charred or even molten connectors on boards
reflown with T962. The most extreme case was broken inner layer traces (on a
board with black soldermask, which apparently had a bit too much moisture
inside- the board layers visibly popped).

An interesting side note- large LEDs don't like being reflown in IR ovens. The
lens on large LEDs also works in reverse- it happily damages the bond wires by
focusing incoming IR radiation to a point.

~~~
mindcrime
_I 've also had less screwups using the regular toaster oven instead of T962.
I suspect that's because T962 uses IR heaters instead of convection._

I suspect so. Especially if one follows the advice of adding an extra heating
element to their converted oven. It's not just about having more raw heating
power, it's about having the heat coming from multiple places, so you get more
even heating.

------
Animats
Finding a good reflow oven is frustrating. The Puhui T962 series units,
available since 2014, were around $150, but they had wildly nonuniform
temperature inside. I've had boards scorched at the center and failure to
solder properly at the edges. There's an open source mod to those which makes
them reasonably usable. New firmware that runs the cooling fan a bit during
heating to distribute the hot air, and a proper cold end reference for the
thermocouples.[1] With those mods, those things are usable. These things have
been cloned in China; you'll see "T962" units that don't have a Puhui logo on
Amazon and eBay. None of the cloners seem to have made these well-known
improvements and delivered a good out of the box experience.

The next step up costs much more. A nice little prototyping convection oven
from Germany costs about $3500. There's not much in between the $200 units and
the $2000 units.

The article is really an ad for Whizoo's Controleo3 board, which is $249 with
all the parts you need. So this isn't that great a deal.

Most of the cheap solid-state relays on eBay and Amazon are fake. The current
ratings on the unit are far beyond what the electronics inside can handle.
Google "Counterfeit Fotek SSR" for details.[2] Since the failure modes are 1)
fail in the ON state and 2) catch fire, this is not good for anything that
draws significant current. The real ones are a lot more expensive than the
fakes, and cost goes up with current rating.

[1] [https://hackaday.com/2014/11/27/improving-
the-t-962-reflow-o...](https://hackaday.com/2014/11/27/improving-
the-t-962-reflow-oven/) [2]
[https://www.ul.com/node/81246](https://www.ul.com/node/81246)

~~~
CamperBob2
[https://www.estechnical.co.uk/](https://www.estechnical.co.uk/) has a very
nice modification kit for the T962 that makes it quite usable, as well as
controllable via USB.

Unfortunately it's about as expensive as the oven itself, but the end result
works very well and no longer torches boards.

------
matt_trentini
An alternative controller is the Reflow Master by the Unexpected Maker:

[https://www.tindie.com/products/seonr/reflow-
master/](https://www.tindie.com/products/seonr/reflow-master/)

US$89 on Tindie (just add Toaster+SSR!)

It's been used to reflow _thousands_ of boards including the majority of the
TinyPICO's:

[https://www.crowdsupply.com/unexpected-
maker/tinypico/](https://www.crowdsupply.com/unexpected-maker/tinypico/)

------
natvert
I also designed and built a reflow oven! My goal was to make it simpler /
smaller: [https://nathan.vertile.com/blog/2019/04/24/fluxlamp-the-
sold...](https://nathan.vertile.com/blog/2019/04/24/fluxlamp-the-soldering-
reflow-over-for-hackers/)

Email me if anyone wants control boards and I can try to make some more.

~~~
thatcat
I like the light housing based design, pretty clever!

------
kurthr
Hrrmmm... I like SMT. It's cheap, easy, and performs well. I haven't tried the
ceramic paper, but I've only tried single sided reflow, and it worked fine
without. I'd also worry a bit about fumes during reflow so doing it under a
vent or hood (they recommend no drafts?)

The challenge I saw was with silk screening the solder paste with the right
alignment and thickness. Placement with tweezers and a binocular microscope
(or young eyes) went fine once you do a couple. Post reflow rework
substantially increased yield from ~80-90% to 99%.

Make sure you have a test for those parts before you put then all together
wrong!

------
kennywinker
I recently did a smd reflow using a cast iron pan and a few handfuls of sand.
Worked like a charm.

Got the idea here: [https://hackaday.com/2014/02/15/smd-soldering-on-hot-
sand/](https://hackaday.com/2014/02/15/smd-soldering-on-hot-sand/)

Granted that was for fairly large, hearty components, but for many hobbyists
it seems to me an oven is a bit overkill.

~~~
bcaa7f3a8bbc
Does your method work for QFN and DFN? I currently find them to be the biggest
headache in prototyping. If you coat some solder on the chip and board using
an iron and then reflow with a hot air station, it's easy to miss a few pins
underneath due to uneven solder distribution; on the other hand, if you use
solder paste and reflow with hot air, again, due to uneven solder
distribution, you'll short some pins and miss others, and there is no
straightforward way to fix it, the thing gets even worse when solder on the
ground pad suddenly melts and causes unwanted movements (during rework) that
misaligns the chip. I got my board working only by pure luck. I'd like to hear
your recommendation.

~~~
elcritch
QFN/DFN are pain, but I've had decent luck with them using the toaster oven
method. Of course that's using a solder mask from JLC PCB, as without the mask
you just end up with the incorrect amount of solder. Still you get the
occasional missed pin you need to re-solder but it works.

~~~
bcaa7f3a8bbc
> _Still you get the occasional missed pin you need to re-solder but it
> works._

How? Did you mean to remove all the existing solder, reapply the paste, and
reflow again (can that even be done on an already populated board, where do
you place the mask/stencil?), or it's something else?

~~~
elcritch
More of just putting a bead of solder on a soldering iron tip and fixing that
pin (best with a microscope setup). If you get the technique just so, you can
do a form of "drag soldering" to fix a missing pin or two. Otherwise you can
do a quick dab with a bead of solder since with most QFN's you can still see
the side of the pin but you may need to rotate the board. I think there are a
bunch of great youtube videos on doing that.

Getting a proper solders for QFN's really does best with a proper metal
stencil. If you use JCL PCB, use their "electropolishing" option otherwise on
fine pins the paste sticks more.

Removing and reflowing the part is tricky and often damages the part. Also to
not ruin other parts of the board, a heat gun is often easier. We've never
really tried reflowing parts unless a board didn't "bake" properly.

------
jwr
I would not follow the tip about connecting multiple thermocouples in
parallel. The voltages involved are very small and the Maxim chips are very
sensitive to noise.

Source: myself, as I had to put in a diff 10nF capacitor between T+/T- of the
31855 to get good consistent readings. Maxim confirmed this is a known
solution and they were supposed to put the recommendation in the datasheet.

So, be careful with those thermocouples.

------
BrooklynRage
When I was a student, pretty much every student organization that did PCBs had
one of these (FSAE Electric, Robotics clubs, etc.)

This + boards from OSHPark or Advanced Circuits' 33/66 each deal were a great
way to cheaply get started with PCB design.

------
unfoldedCravat
I've got a Zallus reflow controller off an old kickstarter - finally installed
it this weekend into an old oven but haven't had a chance to try it properly.
They seem quite a bit cheaper than the whizoo controller although it's much
more limited. Mine doesn't control the door or heating elements independently.

Apparently a popular use case for these is roasting your own coffee beans.

[http://www.zallus.com/](http://www.zallus.com/)

------
1asterisk
Instead of that nasty ceramic blanket and that reflective tape why not just
use ceramic tile? Its cheap, easy to find locally, and will work better. True,
it will be heavier, but it would be easier to maintain a consistent
temperature. Another alternative would be the ceramic cement products like
FiberFrax. It dries solid, so no floating fibers to be concerned with.

------
contingencies
Puhui T-962A @ $250 does the job if you don't want to DIY.

~~~
ycui1986
I have both the Puhui T-962A and DIY conversion oven. The Puhui T962A will
consistently burn your board. You solder joint will come out black as the
temperature goes way beyond proper lead-free temp. You will never be able to
solder any film capacitor. Any film cap you put into T962A will come out
melted/exploded. It actually save your time to build you own oven then by the
off-the-shelf T962.

~~~
contingencies
Works fine for us! Haven't had any issues to date, must have done over 100
different boards. There is third party firmware[0] for better control
including an active fan if you run in to issues. Thanks for the tip though.

[0]
[https://github.com/UnifiedEngineering/T-962-improvements](https://github.com/UnifiedEngineering/T-962-improvements)

