SAC305 solder balls are widely used in lead-free BGA packaging. During assembly, the solder balls are placed between the package substrate and the corresponding PCB pads, and the reflow process transforms these individual balls into solder joints.
Understanding what happens during reflow helps explain why solder ball specifications and assembly conditions need to work together.
What Happens During Reflow?
Before reflow, the solder balls remain solid and maintain their original spherical shape. Once the assembly enters the appropriate temperature range, the solder alloy begins to melt.
The molten solder wets the corresponding pad surfaces and forms the connection between the package and PCB. After cooling, the solder solidifies and creates the final solder joint.
The final joint shape is therefore influenced not only by the solder ball itself, but also by the pad design, surface finish, flux, temperature profile, and other assembly conditions.
Why SAC305 Is Commonly Used
SAC305 is a lead-free tin-silver-copper alloy containing approximately 96.5% tin, 3.0% silver, and 0.5% copper.
Its established use in lead-free electronic assembly makes it a common choice for applications such as BGA and CSP packages.
However, SAC305 is not automatically suitable for every package. The required ball diameter, tolerance, package pitch, and assembly process still need to be considered.
The Importance of Consistent Solder Balls
A BGA package may contain hundreds or even thousands of solder ball connections. Consistency between individual balls is therefore important.
Variation in ball diameter can influence the amount of solder available at each connection. Surface condition and cleanliness can also affect wetting during reflow.
For this reason, solder ball manufacturing typically involves dimensional inspection and quality control before the balls are packaged for assembly.
Reflow Is Part of the Complete Process
A solder ball cannot be evaluated independently from the assembly process.
For example, even when the solder alloy and ball diameter are correctly specified, an unsuitable reflow profile or poor pad surface condition can still affect the final solder joint.
A reliable BGA interconnection therefore depends on the combination of solder ball characteristics, package design, PCB design, materials, and process parameters.
For engineers working with BGA packaging, understanding this relationship can make solder ball selection more practical and help identify potential assembly issues before mass production.
