bga Ball Grid Array Package 1

bga  Ball Grid Array Package 1

Technology principle

Principle of reflow soldering used in BGA welding. Here introduce the solder reflow mechanism in welding

process.
When the ball for a heated environment, solder reflow is divided into three stages:

Preheat:

First of all, to achieve the required viscosity and printing performance of solvent evaporation, temperature

rise must be slow (per second approximately 5 degrees C), to limit the boiling and splashing, prevent the

formation of small solder ball and some elements of internal stress is more sensitive, if external

components temperature rises too fast, resulting in fracture.
Active flux (paste), chemical cleaning operation began, water soluble flux (paste) and disposable type

flux (paste) will occur the same cleaning action, only temperature is slightly different. Remove metal

oxides and some contamination from the upcoming metal and solder particles. Good metallurgical

soldering requirements of "clean" surface.

When the temperature continues to rise, the first single melting solder particles, and liquefaction and

adsorbed on the surface of tin "rush" process. So in all possible surface coverage, and began to form

the soldering point.

When the temperature continues to rise, the first single melting solder particles, and liquefaction and

adsorbed on the surface of tin "rush" process. So as to cover all the possible surfaces, and begin

Backflow:

This stage is most important, when a single solder particles are melted, the formation of a liquid tin,

then surface tension effect began to form the weld foot surface, if the component pin and PCB solder

gap than 4mil (1 mil = 1/1000 inches), it is very likely due to the surface tension so that the pin and

the solder pad, that is, tin.

Cooling:

Cooling stage, if the cooling is fast, the tin point strength will be slightly larger, but can not be too

fast and cause the internal temperature stress element.