Miniature Reflow Oven... New Photo Added 09/19/20: "A Little Perspective" :)

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  • idbruceidbruce Posts: 6,164
    edited 2020-09-19 - 11:48:32
    While fitting the 45s for the viewport frame, I set my coffee cup down next to the project and thought it would provide a nice visual for size representation, so here is a new photo for you guys :)

    perspective.jpg
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  • Ray

    For these thermistors coming out the door/drawer, how are you insulating the wires/leads from shorting? PTFE?
  • I think your little oven looks fantastic.
    Thanks for sharing the photo.
  • idbruceidbruce Posts: 6,164
    edited 2020-09-19 - 12:21:11
    Thanks Duane

    The question is, will it do the job for which it is intended? :)

    I think it should :)

    EDIT: If not, then perhaps this little oven could be used as a cookie warmer or some other application :)
  • Yes, my thermistors have insulation - some woven high temp material
  • idbruceidbruce Posts: 6,164
    edited 2020-09-20 - 14:18:44
    I am almost done with the viewport frame and the base mounting brackets, and while the 45 degree angles look nice, they are very time consuming, so I do believe that I am going to change directions.

    My main goal in designing and making this miniature reflow oven was to make something small, inexpensive, and functional. In 20/20 hindsight, I went way overboard when designing the viewport frame and base mounting brackets, and definitely out of the scope of my original intentions.

    In my opinion, there is not much to the structure, so structural integrity is not of major concern. Additionallly, I do not believe that the oven needs to be air tight, but it does need to contain and control the heat as required by the purpose of the oven.

    That being said, the viewport actually only needs four retaining clips (angle aluminum), although eight would be better, but eight of them would require more labor and money, and the oven can be mounted to the base with two short pieces of angle aluminum, but I will make it four short pieces, just because I like symmetry. :)

    In an effort to reduce both the labor and the money required to make this miniature reflow oven, and to eliminate the tedious work of making and fitting 45 degree angles, I will now be creating a new design, incorporating the changes just discussed, and I will be implementing these changes in my prototype.

    It certainly won't look as nice as it could have, with a beautiful viewport frame, but the new design will be much easier for the average maker to create :)
  • idbruceidbruce Posts: 6,164
    edited 2020-09-20 - 13:53:44
    Concerning my last post relating to the time consuming 45 degree angles and another post further back pertaining to one main terminal block for the heating elements and thermistors, I am now attaching an image which shows the changes in the design and what the furnace will look like.

    Various%20Views.jpg
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  • idbruceidbruce Posts: 6,164
    edited 2020-09-20 - 17:26:06
    Before proceeding with this post, let me just state for the record that I am no expert at heating and cooling :)

    As previously discussed and as shown in the various drawings, within this discussion, there will be a fan mounted to the bottom of the oven. While this fan is running, the hot air must have a route of escape, and this is the intended purpose of the viewport/ventilation plate. I originally thought about putting a 1/2" diameter hole in the center of the ventilation plate, but after more in depth thought, I have decided to put numerous 1/8" diameter holes in the ventilation plate. There will be 17 of them to be exact, and the total area covered by these holes, will be slightly larger than the area of a 1/2" diameter hole.

    Of course it will be more time consuming to drill (17) 1/8" diameter holes as compared to (1) 1/2" diameter hole, but I believe cooling and ventilation will be more efficient with this arrangement. Additionally, I am fairly certain that a 1/2" drill bit capable of drilling through Pyrex would be quite expensive, whereas a 1/8" drill bit is quite common and inexpensive.

    Okay, since you can probably guess what I will most likely say next, I will just post a drawing of what "I" intend to do :)

    viewport.jpg
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  • I question the use of ventilation holes. Toaster ovens and professional SMD ovens do not have ventilation. You can cover the holes during heat profile and uncover during cool down but that may cool down too quickly.
  • idbruceidbruce Posts: 6,164
    edited 2020-09-20 - 17:23:25
    Toaster ovens and professional SMD ovens do not have ventilation.

    Well..... Some toaster ovens do have fans and ventilation and they are convection toaster ovens. From what I have read, convection ovens provide better heating than conventional ovens.
    You can cover the holes during heat profile and uncover during cool down but that may cool down too quickly.

    OR.... This is my plan.... Create my profile using both heating elements and the fan. There is no rule saying that I cannot have the heating elements energized during the cooling period :wink:

    EDIT:
    PWM will be my friend :) PWM for the heating elements and PWM for the fan :)
    Don't forget that I changed the power supply and that I can get those heating elements up to 1000 degrees fahrenheit if necessary.
  • Sounds like you have a plan.
  • idbruceidbruce Posts: 6,164
    edited 2020-09-22 - 08:44:45
    I have another design change for you folks.

    Instead of drilling the viewport, which could prove to be difficult, the 1/8" ventilation holes will now be relocated around the top perimeter of the square tubing, and instead of (17) holes, there will now be (16) of them, with (4) per side. Drilling aluminum is certainly a lot easier than drilling glass. :)

    Another change is the intended direction of ventilation. Originally I was going to push the air out through the top, but after more in depth thought, I have come to the conclusion that this is a very bad plan. If I need serious rotation of the fan, there is a high potential of lifting the PCB off of the drawer, whereas if I draw the air downward, it will pull it against the drawer. :)

    I am now providing a new set of drawings showing the new location of the holes.

    Various%20Views.jpg
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  • "Rule Of Thumb" - Never cut your metal until all design changes have been made :(

    With all the design changes, I had one major oversight. Now I must make compensation in all of my drawings :(
  • idbruce wrote:
    Well..... Some toaster ovens do have fans and ventilation and they are convection toaster ovens. From what I have read, convection ovens provide better heating than conventional ovens.
    I can verify this, albeit only from a negative standpoint. The toaster oven I use for SMT soldering does not have a fan. It tends to overheat sections of a largish board and underheat other sections. I believe a fan would remedy this problem. Of course you don't want one strong enough to blow components off of the board!

    -Phil
  • idbruceidbruce Posts: 6,164
    edited 2020-09-23 - 20:31:00
    It tends to overheat sections of a largish board and underheat other sections.

    As we all know, I am just diving in, but as I previously mentioned, I read a pretty informative article that stated when building a reflow toaster oven, you should definitiely begin your build with a convection toaster oven, because it provides more uniform heating and it is more efficient. Whether it is true or not, I surely don't know :)

    EDIT: But as a result of reading that article, I decided to build a convection oven, mostly because I believe you can have better control over the profile with ventilation.
  • IIRC fan-forced ovens were invented to circulate the air to make the temperatures even throughout the oven???
  • idbruce wrote: »
    "Rule Of Thumb" - Never cut your metal until all design changes have been made :(

    With all the design changes, I had one major oversight. Now I must make compensation in all of my drawings :(

    Measure Twice. Cut once.
    Working backwards, by numerical extrapolation, "Design" should therefore happen Thrice.
  • @Tubular

    The #1 rule of Mr.Thumb.... "Rule #1 - Do not hit me with a hammer!" :)
  • Just out of curiousity, how much time would you guys estimate that you put into modifying a toaster oven into a reflow oven?
  • As a side note, if anyone was interested in attempting to make the reflow oven discussed here, instead of making the PCB drawer like I did, by bending steel rod, a person could use aluminum plate instead, and just cut out the center area.
  • As we all know, the images displayed on the internet can be very misleading, when pertaining to the size of specific items. For those that may be interested in the "actual size" of this prototype, I have created a PDF file which accurately depicts the "actual size" (except for the fan, which is an extremely close approximation). If you print this file, just remember to select "Actual Size" in the print properties.
  • idbruce wrote:
    Just out of curiousity, how much time would you guys estimate that you put into modifying a toaster oven into a reflow oven?
    Zero.

    I use mine as is. It has quartz infrared elements and digital temp controls with a timer. The only thing I have to do by hand is change the time/temp settings when the timer goes to zero in order to get the correct profile. Although it lacks a fan, that's not a problem with small boards.

    -Phil
  • idbruce wrote: »
    Just out of curiousity, how much time would you guys estimate that you put into modifying a toaster oven into a reflow oven?
    A number of hours pulling it apart (free from kerbside trash), and some hours working out the smarts and ordering the parts.

    Then I bought a commercial reflow oven for $5K because I had a commercial project that needed proven assembly techniques. So I threw out the toaster and parts.

    What’s your time worth? At the time I was semi-retired so time was free. But if it takes valuable time from a commercial project, then it’s an expensive detour.
  • idbruce wrote: »
    Just out of curiousity, how much time would you guys estimate that you put into modifying a toaster oven into a reflow oven?

    Yeah you're not going to like my answer either, but like Phil, zero.

    My first oven was/is a Tiffany toaster oven that "just works" and has a natural 5 minute heating and cooling cycle (that repeats). I put the boards in at the bottom of the temperature cycle and they do their solder reflow thing. The temp cycle is around 140 to 240C, so their preheating cycle is a bit harsher than usual, as the boards are brought in along with their woft of ambient air, and probably quickly rise to the ~140. After the heating light turns off, i open the door for the cooling part.

    For a larger board I bought a larger oven, which was an aggressive disaster, killed a board with $500 worth of parts on it, blistered a top copper plane (too much radiation, not enough convection) and got thrown out the same day in disgust. I kept the charred board in a sealed plastic bag as evidence of what not to do.

    I went back and put some science into finding out why the original Tiffany worked so well, and it turns out it naturally heats at around the desired 0.5C per second ramp time, which is about ideal.

    I bought a third oven, Delonghi, like the first (Tiffany) but with required larger area, that also works.

    What I don't get using the natural 0.5 C per second rise is the sharper peak temperature, but it hasn't mattered for what I've done so far. Some of the prototypes we have successfully done in those ovens have had around 500 hand-placed components that take the most part of a day to place, before the few minutes of soldering grand finale towards the end of the day

    My suggestion for your design is get running with some cycles now, to determine the natural thermal cycle that your design has. There's a good chance you won't need ventilation holes because when the heat is turned off you'll probably fall (cool) faster than the nominal soldering profile curve. I suggest this based on the AL walls and I don't think you have much insulation.

    Also you don't need to worry about PWM at this stage especially if you have a lab supply. If you can get your natural thermal cycles close to the ideal then it'll save work on the control strategy later. Or even potentially eliminate the need for a control strategy altogether if you can get the natural cycle close to ideal
  • Tubular wrote: »
    ...
    Some of the prototypes we have successfully done in those ovens have had around 500 hand-placed components that take the most part of a day to place, before the few minutes of soldering grand finale towards the end of the day
    Make sure you don't trip on the way to the oven ;)
  • Cluso99 wrote:
    Make sure you don't trip on the way to the oven ;)
    I've done that -- or something similar: banging the board into the oven rack on the way into the oven. 'Hate being such a klutz!

    -Phil
  • sam_sam_samsam_sam_sam Posts: 2,194
    edited 2020-10-11 - 11:58:30
    idbruce

    Have you finished this project I have been watching this post

    If you finished this project how well does it work
  • I can verify this, albeit only from a negative standpoint. The toaster oven I use for SMT soldering does not have a fan. It tends to overheat sections of a largish board and underheat other sections. I believe a fan would remedy this problem. Of course you don't want one strong enough to blow components off of the board!
    -Phil
    That makes me wonder if a hair dryer's blower motor could be combined with a toaster oven for convection.
  • lardom wrote: »
    I can verify this, albeit only from a negative standpoint. The toaster oven I use for SMT soldering does not have a fan. It tends to overheat sections of a largish board and underheat other sections. I believe a fan would remedy this problem. Of course you don't want one strong enough to blow components off of the board!
    -Phil
    That makes me wonder if a hair dryer's blower motor could be combined with a toaster oven for convection.

    I doubt it. The hair dryer motor and fan are pulling in cold air which keeps them relatively cool. The air then goes over the heating coils. You need a metal fan blade to recirculate the toaster oven air and for the fan motor to be mounted outside the oven.
  • kwinn wrote: »
    I doubt it. The hair dryer motor and fan are pulling in cold air which keeps them relatively cool. The air then goes over the heating coils. You need a metal fan blade to recirculate the toaster oven air and for the fan motor to be mounted outside the oven.

    I agree it's not a great idea. I checked Walmart's website. I can get a convection toaster oven for $50. I want one because an IC that I want is only available in a QFN package.
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