Array packaging, such as BGA and CSP, has grown by nearly 25 percent over the past decade and is expected to continue to do so.At the same time, device packaging is more functional, with higher I/O number and finer pitch.Obviously the key to successful encapsulation is the degree of perfection of the solder ball used to connect the device to the substrate of the carrier.However, surprisingly, there is no global standard for ball quality, and packaging companies rely on ball manufacturers' own analysis to evaluate quality.
The new welding ball production method can provide welding ball with a certain level of quality.There are three main standards to evaluate the quality of welding ball: the production process of welding ball, the degree of oxidation of welding ball and the geometric shape of welding ball.All of these conditions will affect the yield, performance and reliability of BGA or CSP terminal products.
The new welding ball production method provides more repeatable and controllable welding ball
The traditional welding ball production method includes the mechanical process of cutting fine line or punching metal layer to get small metal particles.The particles fall into the hot oil pool and are melted into small round solder drops.As the oil cools, the droplet solidifies into a ball.This process has its inherent limitations, as each mechanical operation adds a certain amount of size and consistency deviation to the particles, resulting in unacceptable cumulative effects, resulting in rough size deviation.
Another factor that affects the properties of solder balls is the well-known defect effect.It's simply oxidation.It is well known that solder balls are blackened by collisions with each other and with the wall of the container during operation, storage and transport.If the oxidation is serious, and the reverse flow is not improved due to insufficient flow or too thick oxide layer, it will be very adverse to production.These will cause insufficient welding between the ball and its connected substrate pad.Obviously, reducing oxidation will be very important to the process.
Last but not least, the geometrical size, diameter and roundness of solder ball are important factors.Most ball suppliers measure the diameter of the ball in x and y directions.This is not optimal as it is easy to miss the maximum and minimum solder ball diameters.Roundness is also a factor to consider, but few solder ball suppliers take it into account.
The best solder ball should be almost round.The geometry of the ball is important.First of all, the equipment used to weld balls today is very accurate, and any odd shape of the ball can cause obstacles to the equipment, thus greatly affecting the output.Second, if solder balls of different diameters are used on the same BGA and vary widely, then the coplanar problem will arise.