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  • Author Author: shabaz
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Building a Reflow Oven: Part 1 – Getting Started

shabaz

Contents

Part 1 (You're here) Introduction and Test bed setup

Part 2: Experimentation with a heating element and some basic measurements

 

Introduction

Some people (not me) can successfully solder incredibly tiny Quad Flad No-lead (QFN) parts such as the one in the photo below by hand using a soldering iron or a hot air gun (the photo below is from a commercial board, not hand soldered). For wireless devices and modern sensors, surface mount device (SMD) packages as small as QFN have become the normal, default package.

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Solder paste allows other methods to be used. A hot plate is one option. Another popular method is to use an oven.

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At work, we may purchase a small reflow oven or hot plate at some date. However, for now, I decided to attempt to create a simple oven for home use.

 

There are lots of reflow oven projects on the Internet based on modified toaster ovens, but it is difficult to replicate them because manufacturers keep bringing out new toaster ovens and the older ones become unavailable.

 

The aim was to try to create an oven from scratch, using off-the-shelf readily available heating elements. This would allow others to be able to repeat the exercise, which in theory has two huge benefits. Firstly it allows people to replicate with confidence that the same consistent results should be achievable. Secondly it allows people to share their findings and help improve everyone’s ovens!

 

Setting Expectations

Commercial reflow ovens use many clever techniques and may need a gas supply too. It will be impossible to achieve high quality results in the simple reflow oven that will be constructed. Here is an example production quality oven:

 

At best, the reflow oven that will be created might be just-about usable for prototypes. I’m not knowledgeable in thermodynamics so it is quite an experimental oven. If people have suggestions they will be gratefully received.

 

Finally this project uses mains line power which can easily kill. This project also gets hot which may cause burns, toxic smoke or a fire. Please check with a qualified expert before building this project.

 

Trying out some Heating Elements

To speed up development, the strategy was to start constructing a potential enclosure while narrowing down heating element possibilities at the same time. A couple of heating elements will be tested. If they are unsuitable, then more will be tried. The controller for the reflow oven will be based on an off-the-shelf microcontroller development board. For the initial experiments, no electronic oven control capability will be used; the heating element will be switched on/off using a mains switch. The initial tests will be in free air. The test results won’t be usable since the elements are not in an enclosure, but the aim here is to just get some experience with the heating elements and begin to see their characteristics.

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The photo above shows the setup so far. The heating element is suspended 100mm above a scrap circuit board. For now, the element is connected to the mains through an IEC connector with built-in fuse and switch, as shown in the photo below. It may need to be replaced with a hot IEC socket for the actual build.

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Here is an annotated photo of the setup:

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Another view without all the cables:

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Next Steps

The heating elements will be experimented with; some additional information on this tomorrow!

Parents

  • In my professional area, dental equipment service, we often had to deal with a piece of equipment called a dry heat sterilizer. This came in two different styles one using radiant heat, like a toaster oven, and the other using heated forced air, like the heat guns or a hot air popcorn popper, into a partially enclosed chamber. While normal operating temperatures for these pieces of equipment was only about 200 degrees C they had controllers that were fairly accurate and stable. I suspect that they could be modified into the temperature area that you are exploring. If you have a dental equipment service facility in your area you might check to see if they have an old unit where you could salvage a temperature sensor and control. I would assume that your goal is to produce something with uniform and accurate heat distribution. Most of the sterilizers had polished stainless internal chambers to reflect and scatter the radiation around the chamber. Something that might make a pretty good chamber would be a piece of stainless insulated wood stove chimney pipe. It would combine the reflectivity of stainless and include insulation.

    John

  • in reply to jw0752

    That actually would be very neat, to have a circular oven chamber - and would certainly save constructing 4 sides. I had not considered metal tubes or pipes, but it seems an incredibly good idea to save effort. I'll see what I can find.

    With the flat walled approach I was initially thinking of, I was going to use ceramic paper in-between the two walls.

  • in reply to shabaz

    Nice project.

    Be interesting to see the end result, as it is an area where technology is going.

     

    You could also look at stainless cooking trays/dishes as a possible source of upper and lower.

     

    For the stainless chimney, here is NZ they are double skinned with free flowing air in between to prevent the outer skin setting any wooden structure on fire.

    You could certainly add insulating material in-between.

    Inside the Wood Fire there is a refractory brick or tile like material that is used to stop the heat from melting the outside, that would be useful for insulation.

     

    I also ran across this which talks about mouldable material, so you could make the oven a double use and cook your pizza at lunchtime image

    Really long link to article

     

    Mark

  • in reply to mcb1

    Hey Mark,

     

    What a very interesting, and humorous article. I do like the stainless chimney idea. Actually now that you mention pizza, that seems a whole lot more useful, forget the SMD stuff : ) A guy's got to eat!

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