What does the reflow zone do in reflow soldering

When the PCB enters the reflow zone, the temperature rises rapidly and the solder paste reaches a melting state. The melting point of leaded solder paste 63SN37PB is 183, and the melting point of lead-free solder paste is 217. In this area, the temperature of the heater is set to the highest, causing the temperature of the components to rise quickly to the peak temperature.

The peak temperature of the reflow curve is usually determined by the melting point temperature of the solder, the heat-resistant temperature of the assembled substrate and components. In the reflow section, the peak temperature of the soldering depends on the different solder pastes used, generally the maximum temperature of lead-free is 230 250, and the maximum temperature of lead is 210 230. The peak temperature is too low, and it is easy to produce cold contacts and insufficient wetting; If it is too high, the epoxy substrate and plastic part are prone to coking and delamination, and excessive eutectic metal compounds will be formed, resulting in brittle weld joints and affecting the weld strength.

The reflow zone is the highest temperature of reflow soldering, and it plays the role of molten solder paste to solder the pads of the circuit board and the feet of the chip components together. The role of each temperature zone of reflow soldering equipment can be viewed in detail by Guangshengde reflow soldering.

The furnace chamber of the reflow oven is composed of four temperature zones: heating zone, constant temperature zone, welding zone, and cooling zone, which have the following functions:

1. When the PCB enters the heating zone, the solvent and gas in the solder paste evaporate, and at the same time, the flux in the solder paste wets the pads, component ends and pins, and the solder paste softens, collapses, and covers the pads, isolating the pads and component pins from oxygen;

2. When the PCB enters the insulation area, the PCB and components are fully preheated to prevent the PCB from suddenly entering the soldering high temperature area and damaging the PCB and components;

3. When the PCB enters the soldering area, the temperature rises rapidly to make the solder paste reach a melting state, and the liquid solder wets, diffuses, diffuses or reflows the pads, component ends and pins of the PCB to form solder contacts;

4. The PCB enters the cooling zone to solidify the solder joint; reflow soldering is completed.

In general, circuit board reflow soldering goes through four stages, that is, the preheating zone, the constant temperature zone, the soldering zone and the cooling zone.

1.Heating area: The preheating of the PCB and materials (components). The reflow oven indicates the heating effect of the first to two heating intervals. The higher preheating causes the solder material to be thermally balanced, the solder paste begins to move, and the flux and other components are warmed up.

The proper amount of evaporation is the heating effect of the third to fourth heating zones of the reflow oven.

2.Constant Zone: The surface oxide is removed, and some of the gas flow begins to evaporate (start welding) to reach the melting point of the solder paste (at which point the solder paste will dissolve in an undissolved state), which is the heating effect of the reflow oven for the 5673 heating zone.

3.Soldering Zone: From solder paste melting to peak to dissolving melting point, solder paste melting process, pad and solder forming soldering, which is the eighth, ninth, tenth or third addition interval heating of the reflow oven.

4.Cooling zone: From the soldering point of the solder to about 50 degrees, the forming process of the alloy solder joint, which is the cooling effect of the reflow oven on the eleventh and twelfth cooling zones.

The reflow soldering in the above ** is called channel reflow soldering, and its heating principle is: hot air convection, that is, after the heating wire is heated, the fan is used to bring the heat to the PCB board, and the PCB is heated, so that the solder paste distributed on the PCB board is heated and melted and soldered;

Nowadays, the circuit integration is getting higher and higher, and the conventional reflow soldering can not meet the welding needs of power devices, the void rate of conventional reflow soldering is 15-25%, and there is no low thermal resistance, resulting in the power device in the working process, the temperature of the body device is too high and damaged, in order to solve the above problems, many manufacturers use vacuum reflow soldering vacuum eutectic furnace to reduce the void rate of the welding layer.

Our company's self-developed vacuum reflow soldering vacuum eutectic furnace with positive and negative pressure combination has a void rate of 1%, which is suitable for large-area solder lugs and solder paste processes!

1. There are several temperature zones in the reflow oven.

2. How many temperature zones does the reflow oven have?

3. The temperature of the four temperature zones of the reflow furnace.

4. The role of each temperature zone of reflow soldering.

1.Heating zone: preheat and heat the PCB board, activate the solder paste, volatilize a part of the solvent, and evaporate the water of the PCB board and components to eliminate the stress in the PCB board.

2.Holding area: The PCB board enters the insulation area and reaches a certain temperature to prevent it from suddenly entering the soldering high temperature area and damaging the PCB board and components.

3.Keep the temperature of the components stable, so that the temperature of the different sizes of components on the PCB board is maintained all the time.