How to Choose the Right Reflow Oven for Your PCB
Whether you’re an electrical engineer or an electronics hobbyist, solder reflow ovens enable fast and convenient printed 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 PCB reflow ovens. While the ambitious hobbyist may choose to build a toaster oven “reflow oven”, many businesses can save time and resources in the soldering process by purchasing a commercial bench reflow oven. This post explores the factors involved in choosing a convection reflow oven that is right for you.
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 mask 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 convection 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 printed boards 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 to $50,000 or anywhere in between. I have used both a $50 “reflow oven” (a.k.a. a toaster oven) and much more sophisticated and expensive reflow ovens. There are advantages and disadvantages to each.
An advantage of more higher-end reflow ovens is better software and parts like a better heating plate or heating element and circuit board allows the option to program several custom thermal profiles and save them in the oven’s software. This feature is invaluable if you have different types of Printed Circuit Boards to assemble and need to optimize your time. For example, the larger heating element will heat up a small PCB 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, and in so requiring an improved hot plate. Custom thermal profiles will give you the flexibility to efficiently solder different kinds of Printed Circuit Boards 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 profile. 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 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 Printed Circuit Board 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 Circuit Boards 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 Printed Circuit Board 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 a larger budget, a high-end reflow oven will enable large volume PCB assembly and exceptional temperature precision. If you’re torn between the two, consider how fast and how many PCBs you need to reflow at any given time. A high-end oven might make your life easier if you expect to be working with a larger volume of PCBs.
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