Infrared and convection ovens

Reflow ovens are machines that are used to reflow solder surface mount electronic components to printed circuit boards (PCBs).

In commercial high-volume applications, reflow ovens take the form of a lengthy tunnel with a conveyor belt that transports PCBs. PCBs can be placed in a tiny oven with a door for prototyping or hobbyist use.

Multiple separately heated zones can be individually regulated for temperature in commercial conveyorised reflow ovens. PCBs are treated at a controlled rate as they pass through the oven and each zone. To obtain a given time and temperature profile, technicians modify the conveyor speed and zone temperatures. Depending on the requirements of the PCBs being processed at the time, the profile in use may change.

The heat source in infrared reflow ovens is typically ceramic infrared heaters above and below the conveyor, which radiate heat to the PCBs.

Convection ovens heat air in chambers before using it to transmit heat to PCBs via convection and conduction. The airflow within the oven can be controlled with the help of a fan. Because the infrared absorptance of PCBs and components varies, indirect heating with air provides for more precise temperature control than direct heating with infrared radiation.

Ovens that combine infrared radiative heating with convection heating are referred to as "infrared convection" ovens.

In some ovens, PCBs are reflowed in an oxygen-free environment. Nitrogen (N2) is a commonly utilised gas for this. The oxidation of the surfaces to be soldered is reduced as a result. The nitrogen reflow oven takes a few minutes to lower the oxygen concentration in the chamber to acceptable levels. As a result, nitrogen ovens often have nitrogen injected at all times, lowering failure rates.

The act of measuring multiple spots on a circuit board to determine the temperature excursion it undergoes throughout the soldering process is known as thermal profiling. SPC (statistical process control) is used in the electronics manufacturing business to determine if the process is under control, as measured against the reflow parameters established by soldering technologies and component requirements.

I've been wanting to learn to solder SMD devices in a reflow oven for a long time. I've had my eyes on that toaster oven conversion for quite a while - to the point of having the target oven in my "save for later" cart at Amazon. In the end, I chose to buy a real oven.

There are tons of them for sale from a variety of vendors with probably an equal variety of reputations. I bought this one from the sm18595638214-4 seller on ebay for no particular reason other than 97%+ reputation and over 60 units sold. Despite the profile saying "Based in China", reading the small print it actually ships from USA. My oven was shipped from Southern California and arrived in only a few days via FedEx (shipping included in price!) The manufacturer is Tai'an Puhui Electric Technology Co., Ltd (see also their T-962 product page with quite a few PCBA machines for sale).

There are actually a variety of different methods for upgrading a T-962. These are my notes as I follow along the 1bitsquared Upgrading a T962a Reflow Oven blog. My notes here are somewhat of a supplement and note-to-future-self as his documentation is quite good. Still, I had my own questions and challenges.

I'd like to extend a special thanks to @esden for giving me a heads up when he had one of his Improved Thermocouple Interface boards for sale. He's a really great guy that I had the pleasure of meeting at the Hackaday Supercon. I highly recommend supporting him by shopping at 1bitsquared. Be sure to check out his twitch stream and discord (invite).

Thanks also to Unified Eningeering for the open source design on the Better Thermocouple Interface.

It is tiny! Actually, I think it should really be a bit bigger. There's plenty of space in the oven, and I had a difficult time inserting the thermocouples (with relatively large connectors) into the green header. Note there are 4 channels available for thermocouples. The oven comes equipped with only two.

My unit had some sharp edges on the drawer. Some fine sandpaper is wise to round them a bit so fingers are not cut.

I powered up the unit to make sure it was at least operational. The first thing I noticed is that the little fan is indeed rather loud. Unless the oven is used a lot, I later learned that this fan is only used to attempt to keep the cold junction as a reasonable temperature- so it could probably be removed altogether. Probably just as well to replace it.

I had a difficult time removing the drawer. The instructions where to "lift the black latch". On my unit, the one on the left is released by pushing up. However the latch on the right is released by pushing down. I of course started on the right. Perhaps no big deal - but keep in mind the rails are also sticky with lubricant.Read More

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