Difference between vacuum vapor phase reflow soldering and hot air reflow soldering

The difference between vapor phase reflow welding and hot air reflow welding is that vapor phase liquid steam is used to heat the key. Vapor phase reflow welding has many advantages over other reflow welding methods, mainly in the following aspects: high temperature control accuracy, high temperature uniformity, relatively low oxygen content control, and welding in low oxygen environment.

(1) High temperature control accuracy.

During welding, the temperature of the workpiece to be welded depends on the boiling temperature of the fluid because the welding is carried out by the steam after the boiling of the gas-phase liquid during heating. Because the boiling range of vapor phase fluid is very narrow, the welding temperature can be accurately controlled. This is very advantageous for welding temperature sensitive elements, because various gases with different boiling temperatures can be obtained. Therefore, a series of low melting point solders can be used in the welding of complex components.

(2) The temperature uniformity is very high.

Vapor liquid fluid has a high heat transfer coefficient. As condensation occurs on all exposed surfaces, the welding temperature of the whole circuit board has a good uniformity on the surface of the circuit board.

(3) Low oxygen welding.

Since the density of initial steam is about 20 times that of air, oxygen is fully removed from the system. In fact, trace amounts of oxygen are always present in steam. This is probably due to the inherent solubility of oxygen in the steam and the addition of oxygen to the steam, and the total amount is usually ignored.

(4) Geometric dependence.

Since condensation occurs on the entire surface, the geometry of the component hardly affects the process, and steam may even penetrate into the parts under the device that cannot be seen from the outside of the welding. In particular, it is very advantageous for welding large-size BGA, transformer, shield cover and other workpieces.

(5) Welding quality.

Since the vacuum vapor phase welding system is welded under a relatively closed and vacuum assisted condition, which is not available for the traditional hot air reflow welding, under this condition, the vapor phase welding can effectively discharge the bubbles generated by the volatilization of the flux in the solder, greatly reduce the void rate of the welding surface, and effectively improve the welding quality.

Of course, vacuum vapor phase reflow welding also has great shortcomings. Many companies have deified vacuum vapor phase welding. It seems to be very good. In fact, the boiling point of vacuum vapor phase liquid itself is not high. Only low temperature solder can be welded. If high temperature welding is required. In fact, vacuum vapor phase reflow welding is impossible. For example, gold tin, gold silicon or gold germanium, and even some high lead solders cannot be soldered. If a wide range of welding is required, a standard vacuum welding furnace should be considered. At present, vacuum reflow soldering is used in many industries. Solder paste welding process, solder chip welding process and eutectic welding process can be used in a wide range of applications.