Building a Reflow Oven: Part 1 – Getting Started

27 Jul 2014

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.

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

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.

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.