I can answer this one. For the AC line connections… no. Opto-isolators don’t handle much current, and the Bipolar transistor (BJT) cannot do reverse blocking (or at least not more than a few volts before breaking). Unless you know of a really really beafy opto (like made out of an Insolated Gate Bipolar Transistor (IGBT) or what not), I’d stick to a relay.
The one I’m using on mine is a L90-5W ( 20A 277VAC, 20A 30VDC). I think Sparky was thinking about using it, but then re-evaluated his life and opted for something beefier. I’m gonna take some safety precautions, and just take the manufacturer on his word, since I’m a broke college grad who wouldn’t mind seeing things blow up. If it survives and seems ok, then I just saved a buck or two. It’s really small. There are pics of it, and the over worked protoboard on my website. (Projects-> Reflow Oven).
I had concerns about the ramp up/down times as well as the uneven heat of the benchtop oven so I converted a 2 slice bread toaster. I removed the middle element , added a couple of ‘u’ channels for a piece of al mesh to hold the boards then added some feet for the toaster to lie on it’s side. I made up a small stainless fan which is attached to the rear (bottom) of the toaster for cooling. I did cheat on the control by buying a cal controls process controller to control the heating and cooling profiles (NZ$450). Its easy to program, has failsafe modes and you can enter multiple profiles. With it’s small volume and low thermal mass it can heat to 225 degrees C in 75 seconds. I only make small boards so it does the job nicely.
I know there are some people out there who just have to build it for themselves. So this post is not for them.
I have been using the “Temptell Reflower” to turn a toaster oven into a reflower for about 6 months. It works very well and you don’t have to modify the oven at all. You simply plug the oven into the unit and the internal relay will handle up to 1800 watts. All aspects of the reflow cycle from the drying ramp to the reflow cycle are easy to control.
For $245.00 for the unit and the software it’s hardly worth building your own device.
This particular one can be programmed for all sorts of profiles. I was able to use the alarm outputs to control a convecton fan and the oven light.
Be prepared to spend a few hours reading the manual. It is thorough and correct, but this thing has a LOT of configurability and the way it’s presented it pretty dense.
You’d also need an SSR and thermocouple- then you’re in business. One thing about the thermocouples on this site- they seem to all have fairly heavy metal fittings on the end. You want something more along the lines of what SparkFun sells- just the bare bead. I was able to rip the fitting off the one I bought from Auber, though I wouldn’t necessarily recommend doing that.
What’s the state of this project? The v2 kit looks nice, but are there any success stories? Has anybody posted additional example code. I’ve probably just missed the post. Could somebody point me in the right direction? Thanks!
On the topic of reflow ovens, I would like to find out if this oven method is good enough for doing very small parts with pads on the under side. In particular, there are many parts I cannot use right now that come in packages whos pads are on the bottom of the chip (BGA, LGA, DFN). I would like to be able to lift this restriction from my designs, and am wondering if a low cost oven reflow method would allow me to use these parts. Or for such parts is a professional oven required?
The cost of these parts are also much more expensive, so if the process has a moderate failure rate, it would almost be cheaper to have them professionaly placed on my prototypes.
Basically it comes down to the unit cost and I am not quite sure how much that is.
Are stencils required? Thats $150.
Do I need to use a batch of solder paste each time? How much does that cost? As much as $50 after shipping?
Basically it looks like each run with a stencil would cost about $200. That means if I had to do two batches of the same board, the repeating cost would be the solder paste @ $50. If I mess up, it would be the cost in parts for that entire board.
It starts to approach the cost of having the parts professionally placed. What are your suggestions and how do you recommend working with small parts? Prototyping already requiers a PCB, how can I start using BGA, LGA, and DFN parts effectively in my designs?
I guess that price range may be out side the budget for a lot of people, but this seems like a much cheaper solution to getting a functional reflow unit.
The question is does anyone have experience with these and have any comments suggestions on using these units?
mooreaa:
On the topic of reflow ovens, I would like to find out if this oven method is good enough for doing very small parts with pads on the under side. In particular, there are many parts I cannot use right now that come in packages whos pads are on the bottom of the chip (BGA, LGA, DFN). I would like to be able to lift this restriction from my designs, and am wondering if a low cost oven reflow method would allow me to use these parts. Or for such parts is a professional oven required?
The cost of these parts are also much more expensive, so if the process has a moderate failure rate, it would almost be cheaper to have them professionaly placed on my prototypes.
Basically it comes down to the unit cost and I am not quite sure how much that is.
Are stencils required? Thats $150.
Do I need to use a batch of solder paste each time? How much does that cost? As much as $50 after shipping?
Basically it looks like each run with a stencil would cost about $200. That means if I had to do two batches of the same board, the repeating cost would be the solder paste @ $50. If I mess up, it would be the cost in parts for that entire board.
It starts to approach the cost of having the parts professionally placed. What are your suggestions and how do you recommend working with small parts? Prototyping already requiers a PCB, how can I start using BGA, LGA, and DFN parts effectively in my designs?
Yes, a cheap, err, inexpensive reflow oven should work well with those pin packages.
You can also check out www.smtstencils.com for inexpensive stencils as well. Stencils aren’t required if you can put a consistent amount of paste on the pads. For a prototype I personally don’t bother with stencils until I know the design works, and is done changing.
So after about 2 years of using a hot plate to make boards I finally had to make a 2 sided pcb and needed a reflow oven. I went to Target and picked up this Sweet Oster 6-Slice Toaster Oven. The cool thing about it is that it has a glass top! You can easily check on the progress of your boards through the window!
I set the temp to 420F and place the board on the inside rack. I usually keep both the top and bottom heating elements on. But do place both the rack and the “cookie sheet” below the pcb. I did 20 panels of 4 pcbs last night with no problems.
If you are looking to make stencils for your design we are now offering a service similar to the pololu folks. However, we are offereing a $20 flat rate and allow you to do multiple designs. Only limitation is that the design fit into a 8.5"x11" area. You can check out details at www.ohararp.com/Stencils.html
Our laser uses a 1.5" Focus Lens to produce the smallest spot size possible. To this end we can cut surface mount pads that are 15 mils x 15 mils or larger.
We can pretty much do any package. However, high pin count TQFP 64 pin and higher packages cause some problems since they require long thin pads. These pads require resizing since they fall below the pitch specs.
Otherwise, if you have had stencils cut with pololu we can match their specs no problem.
