How to Choose a Solder Reflow Oven for Efficient PCB Assembly
Whether you’re an electrical engineer, like me, or an electronics hobbyist, solder reflow ovens enable fast and convenient printed circuit board (PCB) assembly. If you have assembled dense PCBs with many small surface-mount components or used ball grid array (BGA) devices in your designs, you have undoubtedly come across solder reflow ovens. While the ambitious hobbyist may choose to build a toaster oven “reflow oven”, many businesses can save time and resources by purchasing a commercial reflow oven. This post explores the factors involved in choosing a reflow oven that is right for you.
You can turn your old toaster oven into a DIY soldering reflow oven with just a microcontroller and some thermocouples.
Refresher: Solder Reflow Process
Reflow soldering can quickly assemble high-density PCBs that may pose manual hand soldering challenges to even the most experienced engineers and PCB technicians. To begin, a solder paste mixture containing both solder and flux is applied with a stencil to the fabricated PCB. The components are placed in position and are usually held in place by the adhesive nature of the solder paste. Finally, the PCB is placed inside the reflow oven to begin the heating process.
The solder reflow process is based on convection heating, similar to that in your home oven. The temperature of the hot air in the oven follows a thermal profile that provides the optimum heat and cooling rate for the given solder paste and components. Electronics manufacturers provide recommended thermal profiles that serve as a good starting point. But sometimes the thermal profile must be modified for the best soldering performance.
The four main temperature zones of the thermal profile include preheat, soak, reflow, and cooling. These temperatures should be low enough to ensure the PCB components are not damaged, yet high enough to melt the solder paste. Many companies sell reflow ovens, but let’s talk about a few factors you should consider before your purchase.
Typical solder reflow thermal profile
Save Time with Thermal Profiles
Depending on your budget, you can buy a reflow oven for $50, $50,000 or anywhere in between. I have used both a $50 “reflow oven” AKA a toaster oven and more sophisticated and expensive reflow ovens. There are advantages and disadvantages to each.
An advantage of more higher-end reflow ovens is the ability to program several custom thermal profiles and save them in the oven’s software. This feature is invaluable if you have different types of PCBs to assemble. For example, a small PCB will heat up much faster than a large PCB, and therefore a shortened thermal profile can be created to provide the fastest soldering possible.
Additionally, environmentally friendly applications may require lead-free solder paste, which has a higher melting point than traditional tin-lead based solder paste. Custom thermal profiles will give you the flexibility to efficiently solder different kinds of PCBs with various solder pastes.
Along with thermal profiles, temperature precision and sensing are an important consideration for the reflow process. Reflow ovens usually have one or more thermocouples inside them to sense the temperature. These sensors ensure the oven heats and cools as desired. Just like your cooking oven at home, reflow ovens have hot areas, cold areas, and the temperature isn’t always 100% accurate. If you purchase a reflow oven with multiple thermocouples, you can ensure all important parts of the PCB heat sufficiently and more effectively “cook” your PCBs.
Consider Your Ideal Oven Size
Now that you’ve thought about the thermal performance needed for your reflow soldering, another practical consideration is the reflow oven size. Low- and medium-end reflow ovens could be your best option if you need it to fit discretely on a table or bench in your engineering workspace. These ovens are appropriate if you do relatively low volume PCB assembly or are on a tight budget, and range anywhere from $50 to $10,000. If your budget is even tighter than $50, you could build your own reflow oven using a microcontroller and a toaster oven. Just think – you could assemble your PCBs in your pajamas from the comfort of your kitchen!
High-end reflow ovens are typically large standalone devices suited for a factory floor space and can cost $10,000 or more. These ovens usually provide higher temperature capability, tighter temperature tolerances, and the ability to solder large volumes of PCBs. These advantages are accomplished by using a conveyer belt that advances the PCBs through multiple oven compartments at varying temperatures. Further, high-end ovens achieve fast heating and cooling due to more efficient heating elements and water cooling.
In general reflow soldering is faster and more accurate than hand soldering.
Many engineers and businesses can save time and resources by purchasing a solder reflow oven. In general, reflow soldering is faster and more accurate than hand soldering, so I'd always prefer to reflow if it's available. If you’re on a budget, you can find many inexpensive reflow ovens that provide time-saving thermal profiles and moderate temperature performance. If you’ve got money to spend, a high-end reflow oven will enable large volume PCB assembly and exceptional temperature precision. If you’re torn between the two, it’s best to consider how fast and how many PCBs do you need to reflow at any given time, a more high-end oven might end up making your life easier if you expect to be working with a larger volume of PCBs.
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