Choosing Between New and Used Reflow Ovens

How to choose between a new and used reflow oven?

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Choosing between a new and used reflow oven is a decision that can significantly impact your electronics manufacturing process. Both options have their advantages and drawbacks, and the choice depends on your specific needs and circumstances.

Exploring Reflow Ovens

Let&#;s start with new reflow ovens. These shiny, state-of-the-art machines offer several benefits. First and foremost, they come equipped with the latest technology and innovations. This means you&#;ll likely get better temperature control, more precise profiling, and improved energy efficiency. Newer ovens often come with user-friendly interfaces, making them easier to operate and maintain. Additionally, they might have advanced features like automatic profiling and data logging, which can streamline your production process and improve quality control.

Considerations with New Ovens

On the flip side, new reflow ovens can be quite expensive. The initial investment cost is higher, and you&#;ll need to consider ongoing maintenance expenses. However, if you&#;re working on cutting-edge electronics and require top-notch quality and reliability, a new reflow oven is often the way to go.

Exploring Used Ovens

Now, let&#;s talk about used or older reflow ovens. These machines can be significantly more budget-friendly compared to their brand-new counterparts. If you&#;re a startup or a smaller operation with limited capital, this can be a big advantage. Used ovens can still provide reliable performance, especially if they&#;ve been well-maintained over the years.

Trade-Offs

However, there are some trade-offs. Used reflow ovens may not have the latest technology, so you might experience less precise temperature control or slower heating and cooling rates. They could also be less energy-efficient, which could increase your operational costs over time. Maintenance and repair costs might be higher as well, as finding replacement parts for older machines can be challenging.

Choosing the Right Oven

When choosing between a new and used reflow oven, consider your specific production requirements, budget constraints, and long-term goals. If you prioritize cutting-edge technology, consistency, and have the financial resources, a new oven is the way to go. But if you&#;re working within a tight budget and can compromise slightly on the latest features, a well-maintained older oven can be a cost-effective solution to get your electronics manufacturing up and running.

Machine used in circuit board production

A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCBs).

In commercial high-volume use, reflow ovens take the form of a long tunnel containing a conveyor belt along which PCBs travel. For prototyping or hobbyist use PCBs can be placed in a small oven with a door.

Commercial conveyorised reflow ovens contain multiple individually heated zones, which can be individually controlled for temperature. PCBs being processed travel through the oven and through each zone at a controlled rate. Technicians adjust the conveyor speed and zone temperatures to achieve a known time and temperature profile. The profile in use may vary depending on the requirements of the PCBs being processed at the time.

Types of reflow ovens

Infrared and convection ovens

In infrared reflow ovens, the heat source is normally ceramic infrared heaters above and below the conveyor, which transfer heat to the PCBs by means of radiation.

Convection ovens heat air in chambers, using that air to transfer heat to the PCBs by means of convection and conduction. They may be fan assisted to control the airflow within the oven. This indirect heating using air allows more accurate temperature control than directly heating PCBs by infrared radiation, as PCBs and components vary in infrared absorptance.

Ovens may use a combination of infrared radiative heating and convection heating, and would then be known as 'infrared convection' ovens.

Some ovens are designed to reflow PCBs in an oxygen-free atmosphere. Nitrogen (N2) is a common gas used for this purpose. This minimizes oxidation of the surfaces to be soldered. The nitrogen reflow oven takes a few minutes to reduce Oxygen concentration to acceptable levels within the chamber. Thus nitrogen ovens typically have nitrogen injection in at all times which decreases defect rates.[1]

Vapour phase oven

The heating of the PCBs is sourced by thermal energy emitted by the phase transition of a heat transfer liquid (e. g. PFPE) condensing on the PCBs. The liquid used is chosen with a desired boiling point in mind to suit the solder alloy to be reflowed.

Some advantages of vapour phase soldering are:

• High energy efficiency due to the high heat transfer coefficient of vapour phase media
• Soldering is oxygen-free. There is no need for any protective gas (e.g. nitrogen)
• No overheating of assemblies. The maximum temperature assemblies can reach is limited by the boiling point of the medium.

This is also known as condensation soldering.

Pressure Curing Ovens

Pressure curing ovens, or Autoclave, is widely utilized to minimize voiding and improve adhesion strength in bonding processes.  Pressure cure ovens are typically employed in die attach and underfill applications.  Increasing pressure during the curing process removes voids.

In a pressure cure process, air is pressurized in a rigid vessel or chamber while heating or cooling with forced convection.  Heaters, heat exchangers, and blowers are mounted internal to the pressure vessel, continuously circulating air across the pressure chamber providing consistent heat transfer to the product.  Upon completion of the curing process, pressure is relieved and the product cools.

Pressure cure ovens can utilize air or nitrogen as the pressurizing agent.

Vacuum Reflow Ovens

Traditional reflow can be augmented by the addition of a late-stage vacuum chamber.  Introducing a vacuum chamber to the reflow process allows voids and bubbles to escape, significantly reducing voiding in solder joints and interfaces.

During the vacuum process, the circuit board is stationary, assuring no shifting parts.  Smooth travel into and out of the vacuum chamber, minimizing vibration, is critical.

Employing heat inside the vacuum chamber allows peak temperatures to be achieved during vacuum, assuring shorter time above liquidous and greater process flexibility.  High vacuum chamber temperatures also prevent flux buildup inside the chamber.

Advanced vacuum reflow ovens employ multiple conveyor systems allowing higher throughput by optimizing transfer time into the vacuum chamber, dual rail processing, and closed-loop vacuum pumps to prevent solder and flux spatter.

Formic Acid Reflow Ovens

Formic acid reflow ovens operate similarly to a traditionally reflow oven, with the addition of formic acid vapor injection into the key soak zones for flux-free reflow and vapor soldering.  Upon injection, the formic acid removes any oxides present on the metal prior to reflow.

Formic acid concentration is maintained by a bubbler system that is monitored in real time to provide stable and consistent formic concentrations to within 0.5% in the process chamber.

Formic acid reflow ovens employ sets of double doors at the oven&#;s entrance and exit to dramatically reduce process gas consumption.  During production, only one door opens at a time, thus isolating the process chamber and lowering nitrogen and formic acid consumption.

Thermal profiling

Thermal profiling is the act of measuring several points on a circuit board to determine the thermal excursion it takes through the soldering process. In the electronics manufacturing industry, SPC (statistical process control) helps determine if the process is in control, measured against the reflow parameters defined by the soldering technologies and component requirements. [2] [3]

See also

References and further reading

General references