In this technique, described in IPC 7711/21 Procedure 5.7.3, mechanical tools and fixtures are used in order to replace solder balls. BEST has further developed this technique to include high temperature plastic stencils in order to augment the stainless stencils typically used. While both stainless steel and high temperature plastic stencils will precisely hold the balls in place, the lower cost, faster processing time of the plastic stencils makes for a faster turnaround time. Larger lot sizes are well-suited for the use of the metal stencils. The stencils are custom designed and fabricated inhouse for your patterned device on one of the BEST lasers. More process considerations including analytical testing considerations can be found here.
The process below is generic in nature and is adopted to the customer specifications, lot size and the type of component being reballed
The stencil/fixturing technique is straightforward and is used when a moderate number of the same component needs to be reballed. The tooling and stenciling can accommodate several BGA reballing cycles. Many times since the tooling is created in house the lead time for customers is shortened. When a very large lot size of moderate ball count devices is to be reballed, “multi up” metal stencils can help speed the throughput of reballing components.