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SMT Reflow (Toaster) Oven - Introduction

This article, is part of a set of articles, that demonstrates the conversion of a compact  electric oven, popularly known as a toaster oven, into a surface mount technology (SMT) reflow oven. This construction has been inspired by the one described in  Conversion of a toaster oven into a SMT reflow oven .

Health and Safety Message: Most websites that explain the toaster oven to reflow oven conversion process have some type of health and safety warning attached to them so I'd better do the same! In the U.K the mains voltage is 240V and like the mains voltage in most  countries can be extremely dangerous. Modifying a toaster oven could involve encountering a voltage that  could cause you or your nearest and dearest great distress. This conversion should be performed by a trained and certified electrician that knows what they are doing. [N.B Plugs in the U.K are fused which is not the case in some countries. The conversion process demonstrated here uses a fused plug.]


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Figure 1: A Hobbyist Reflow Toaster Oven Comprises Of A Compact Oven  and  PID Controller. The aim of converting a toaster oven (1), (2) into a SMT reflow oven is to provide a temperature controlled enclosure to enable hobbyists design engineers to assemble Printed Circuit Boards (PCBs) containing Surface Mount Devices (SMDs). In this case, a 230V, 50Hz 600W 6L signature toaster oven has been used.

  

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Figure 2 : A Typical Solder Reflow Profile. A solder reflow  temperature profile,  is used to control the process by using a Proportional Integral Derivative (PID) controller. The PID ensures that the soldering process goes through a gradual preheating stage and a brief duration of soldering temperature followed by a cooling stage. The cooling stage is typically performed manually by partially opening the toaster oven door! [Taken from the Application Note AN081 - Reflow soldering Guidelines for Surface-Mount Devices, June 2002 Ver 4, Altera Corp].

 

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Figure 3 : A Typical Conversion Includes Some Of The Components Shown In The Figure. (1) A Solid State Relay (SSR) is used to control the on/off switching of the heating elements and hence control the heat profile of the oven. (2) A replacement front panel is typically need to mount any "added" instrumentation. In this case acrylic has been temporarily used. (3) A commercial PID controller is used to produce the soldering temperature profile. (4) A thermocouple is the sensor used to monitor the instantaneous temperature of the toaster oven. (5) Insulation of the instrumentation compartment, is required to ensure that the instruments are operated within their operating temperatures. In this case two layers of soldering mat has been used.