This section provides overview, applications, and principles of reflow ovens. Also, please take a look at the list of 11 reflow oven manufacturers and their company rankings.
A reflow oven is a heating oven for bonding printed circuit boards and electronic components with solder in unit board production.
Since the reflow oven accounts for most of the total amount of the reflow equipment, the reflow oven is sometimes referred to as a reflow device.
The reflow oven is heated to about 150°C to 230°C during board mounting. In addition, some solders contain lead, and some do not, and the operating temperature range varies depending on the solder used.
Reflow ovens are used for bonding printed circuit boards and electronic components with solder in unit board production. It is mainly used as the main function in reflow equipment.
When soldering components to a printed circuit board, there is a method of actually bonding electronic components by hand using a soldering iron, but this is a complicated process when the number of components is large or when the bonding surface is extremely small. In recent years, the miniaturization of mounted components and the densification of mounted components due to the high integration of circuits has increased, and there are concerns that insufficient adhesion or shorts may occur when soldering is done by hand. Therefore, the use of reflow equipment capable of precision surface mounting enables reliable board assembly.
First, the principle of temperature rise inside the reflow oven is explained. The temperature of the reflow oven is raised by an inflow of hot air into the oven. There are various methods for the inflow of hot air, but the reflow oven raises the temperature by blowing hot air in the form of a collision jet. By blowing hot air from a direction perpendicular to the substrate, the temperature of the substrate is raised by friction between the hot air that collides with the substrate and the air that has stopped moving.
Next, we will explain the principle of bonding a board and electronic components in a reflow oven. When a reflow oven is heated, solder is first placed on the board, and then electronic components are placed on top of the solder. From this state, the solder melts as the reflow oven is heated up, and the components on the solder adhere to the board as if they were sinking. After all, the components on the board have adhered to the board, the reflow oven temperature is lowered, the solder becomes solid, and the board and electronic components are bonded.
A flow oven is a device used for flow soldering. Flow soldering is a flow method in which soldering is performed by passing a board over a solder bath containing molten solder. Flow soldering requires a solder bath, and as a result, the equipment tends to be large.
On the other hand, reflow soldering does not require a solder bath. Paste solder, called cream solder, is applied to the surface of the board or the backside of the component beforehand. The paste solder is metalized, and the component and board are joined by passing the board through the reflow oven with cream solder applied. Cream solder looks like melted solder, but it is a mixture of fine solder and several microns in size flux. It is applied to the board through a metal mask and heated to form a metal bond between the soldiers.
Flow ovens and reflow ovens have different processes and require different types of solder.
If a lot of oxygen is present in the furnace, the heated oxygen will come in contact with the solder paste. The substance called rosin contained in the paste is easily oxidized. When the rosin is oxidized, the solder powder in the paste and eventually the leads of the component and the pads of the substrate are also oxidized. One option is to fill the furnace with nitrogen gas (N2) to reduce the oxygen concentration in the furnace.
However, even if the bonding between solder and leads is insufficient, the use of nitrogen gas may cause the fillet to pass inspection due to the clean appearance of the fillet on the surface caused by the oxygen concentration lowering effect. The decision to use nitrogen should be made in consultation with the manufacturing and design departments and in some cases, contractors.
*Including some distributors, etc.
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