A necessary welding process in PCBA DIP plug-in

In the production link of SMT patch proofing processing, there is a procedure called DIP plug-in processing, which requires welding, and welding can be divided into soft brazing and hard brazing according to the melting point of the solder. Generally speaking, soft brazing is the welding with melting point lower than 450 degrees Celsius, and the solder used in smt patch processing soft brazing is naturally called soft solder. At present, various welding methods commonly used in electronic processing plants are generally soft brazing.

smt patch processing soft brazing related technology

1. Characteristics of soft brazing
① The melting point of the solder is lower than the melting point of the solder.
② Heat until the solder melts and wets the welds.
③ The weldment does not melt in the welding process.
④ In order to remove the oxide layer on the metal surface, the welding process needs to add flux.
⑤ The welding process is reversible, can be welded, can be repaired.

2. Brazing process
No matter it is manual welding, dip welding, wave soldering or reflow welding, the welding process must go through several stages of surface cleaning, heating, wetting, diffusion and dissolution, cooling and solidification of the weldment interface.

(1) Surface cleaning
Brazing welding can only be done on clean metal surfaces.

The function of this stage is to clean the welding interface of the weldment, and clean the oxide film and attached dirt on the interface. The surface cleaning is completed after the solder is activated by flux to react with the oxide film on the solder surface before melting during heating.

(2) Heat
Only at a certain temperature can metal molecules have kinetic energy, which can complete wetting, diffusion, dissolution and formation of binding layer in a very short time. So heating is a necessary condition for brazing welding.

For most alloys, the ideal brazing temperature is 15.5 ~ 71℃ above the liquidus of the filler metal.

(3) Wetting
Only when the molten liquid filler metal is diffused on the metal surface, can the metal atoms be freely close to each other. Therefore, the wetting of the molten filler metal on the weldment surface is the primary condition for the diffusion, dissolution and formation of the bonding layer.

(4) Capillary action, diffusion and dissolution, metallurgical combination to form a binding layer
After the molten filler metal wets the surface of the weldment, under the action of capillary phenomenon, diffusion and dissolution, the bonding layer (weld) is formed after a certain temperature and time. The tensile strength of the solder joint is related to the structure and thickness of the intermetallic bonding layer.

(5) Cooling, welding completed
Cooling to the solid phase temperature below, after solidification to form a certain tensile strength of the solder joint.

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