Difference between vacuum vapor reflow and hot air reflow

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 process has many advantages over other reflow welding methods, mainly in: high temperature control accuracy, high temperature uniformity, relatively low oxygen content control, and can weld 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 vapor-liquid boiling 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, in the welding of complex components, a series of solder with lower melting point can be used.

(2) The temperature uniformity is very high.

Vapor liquid fluid has high heat transfer coefficient. Due to condensation on all exposed surfaces, the welding temperature of the whole circuit board has good temperature 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 steam and the addition of oxygen sent to steam, and its total amount is usually ignored.

(4) Geometric correlation.

Because condensation occurs on the whole surface, the geometry of the component hardly affects the process, and the steam will penetrate into the parts under the device that cannot be seen from the outside of the welding. Especially for welding large-size BGA, transformer, shielding cover and other workpieces.

(5) Welding quality.

Because the vacuum vapor phase welding system is welded under a relatively closed and vacuum assisted condition, which is not available in the traditional hot air reflow welding, under this condition, the vapor phase welding can effectively discharge the bubbles generated by the volatilization of 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 deify vacuum vapor phase welding. It seems to be great. In fact, because the boiling point of vacuum vapor liquid itself is not high. Only low temperature solder can be welded. If there is a need for high temperature welding. In fact, vacuum vapor reflow welding is impossible. For example, gold tin, gold silicon or gold germanium, and even some high lead solders cannot be welded. If you need a wide range of welding, you should consider using a standard vacuum welding furnace. At present, the vacuum reflow soldering of comrades of Zhongke is used in many industries. Solder paste welding process, solder chip welding process and eutectic welding process can be used, with a wide range of applications.