What Is Vapor Phase Reflow?

One of the biggest challenges of soldering components to a printed circuit board (PCB) is the distribution of heat. With components of various sizes on the board, it becomes difficult to apply heat evenly to adjoin and harden the components without fault.

In order to ensure the integrity of the board and components, and that the components adhere to the board, manufacturing companies are increasingly turning to vapor phase reflow. This specialized heating method gives you more control, as you have the ability to alter the temperatures within a vapor phase reflow oven. These ovens can solder batches of PCB at a time, creating higher efficiency and many other advantages.

Vapor Phase Reflow Defined

Vapor phase reflow, also known as condensation soldering, is the process of heating up an inert liquid to create a vapor that solders components to a circuit board. It uses a specialized oven called a vapor phase reflow oven. When heating up the gas, the vapor fills the oven. This step creates heat that condenses around the circuit board, allowing the vapor to ensure that all pieces on the PCB are soldered.

Perfluoropolyether fluorinated fluid (PFPE) is a lead-free inert liquid placed at the bottom of the chamber. The PFPE is heated to temperatures between 230 degrees Celsius and 240 degrees Celsius using the heating elements in the oven. This level of heat also has the ability to melt the solder paste. As the PFPE reaches its boiling point, the liquid will start to evaporate. The vapor fills the bottom of the oven and rises up, filling the chamber. The vapor is dense, which creates a layer in the oven.

The PCB, along with the components, are put onto a tray and lowered into the oven. The vapor will condense around the PCB and create heat. The circuit board and solder paste reach the same temperature as the vapor. This heat will melt the solder paste and join the elements together. At the same time the vapor fills the oven, it removes any oxygen from the chamber. With no oxygen, heat is distributed evenly across the board.

Once the solder paste is melted, it must cool to harden the paste onto the board. There are also cooling elements in the oven to assist in cooling down the liquid. The tray is then lifted out of the oven to allow the paste to become solid. This completes the final stage of the vapor phase reflow process.

Why Use Vapor Phase Soldering?

There are many benefits of using vapor phase reflow in surface mount technology.

• Reaches higher temperatures in the oven: Unlike a convection oven that uses hot air to heat materials, the vapor phase reflow oven uses a gas that can reach higher temperatures.
• Prevents the PCB from overheating: Regardless of the high temperatures in the oven, the PCB board and its components will not overheat.
• Maintains the integrity of the board and components: As the vapor prevents the PCB and components from overheating, it will not alter the integrity of any of the elements. This means the board will not bend or break during the process.
• Uses lead-free solder pastes: This prevents the circuit board from becoming damaged in the process while using a higher heat.
• Distributes heat even across the board: With no shadowing between big and small components, the heat is distributed evenly across the board. This ensures components adhere to the board at the same time regardless of their size.
• Improves wetting: Since there is no oxygen formed in the oven, the vapor creates better wetting of the PCB.
• Controls the temperature: Even if the circuit board cannot overheat, engineers have the ability to control the temperatures with the oven when necessary.
• Does not corrode the board: PFPE does not corrode the materials on the board, which further maintains the integrity of the board.
• Saves space: Vapor phase reflow ovens are typically smaller than convection ovens.

Vapor Phase Reflow vs. Convection Reflow Oven

Convection reflow ovens and vapor phase reflow ovens use heat to solder various components to a PCB. However, there are a few key differences between them that impact production and can yield different outcomes.

Size

Convection ovens are generally larger than vapor phase reflow ovens. They are larger to accommodate the different zones within the oven. A vapor phase reflow oven generally has one chamber within the oven, divided into three layers:

1. Base liquid layer
2. Vapor layer
3. Preheat zone

Process

A convection reflow oven has four zones. The number of zones used in the process depends on the size and complexity of the circuit board. Depending on your specific manufacturing process, you could use four, five, six, eight or 10 zones within a convection oven. The four heat stages in the process are:

1. The preheat zone
2. The soak zone
3. The reflow zone
4. The cooling zone

In comparison, the vapor phase reflow process goes through three stages. This includes heating the PFPE — which creates a vapor — heating the solder paste and PCB, joining the components, and the cooling process.

Heating

Convection reflow ovens use heated air that circulates in the oven. As the conveyor belt moves through the oven, the PCB goes through the various heating stages in the different zones. Comparatively, vapor phase ovens use an inert liquid heated up at the bottom of the oven. The PCB tray is lowered into the vapor, heating the PCB.

Get Quality BGA Rework Stations With Us Today

With over 25 years of experience, we at Precision PCB Services provide quality BGA rework stations to production and manufacturing companies. When you invest in BGA rework stations for your facility, you can benefit from cost savings, improved accuracy and many other advantages to help you streamline your PCB modification process.

Our stations come with lifetime technical support, and we provide employee training to ensure your team fully understands how to use them, increasing productivity and efficiency. When training is complete, they receive a certificate of proficiency.

To get started, contact us today!