Mesh Classification
Categorization of solder spheres based on their diameter identifies material suitable for ultra-fine-pitch printing and dispensing applications. Type 6 powder consists of particles ranging from 5 to 15 microns in size, which is significantly smaller than the standard types used in general assembly. It is required for components such as micro-BGAs and 008004 chip resistors where aperture sizes are extremely restricted.
Standards set by J-STD-005 define the percentage of particles that must fall within this specific micron range.
Solder Geometry
Small particle size allows more spheres to fit into a tiny aperture, which improves the flow and release characteristics. Using type 6 powder ensures that at least five spheres can span the width of the smallest opening to create a stable brick. This fine resolution is necessary for high-density interconnect designs that push the limits of traditional screen printing.
The paste must be formulated with specialized flux to handle the increased surface area of the metal. If the particles are too large for the hole, the aperture will clog and result in missing solder joints.
Oxidation Surface
Increased surface-to-volume ratio makes the material more susceptible to oxidation during the reflow process. Type 6 powder requires careful storage and a controlled atmosphere, such as nitrogen, to prevent wetting issues. It is more expensive than larger powders due to the intensive sieving and manufacturing processes needed to produce such uniform spheres.
The use of this grade is generally limited to the most advanced electronic assemblies.
