Issue link: https://iconnect007.uberflip.com/i/1545666
62 SMT007 MAGAZINE I JULY 2026 have been aware of package moisture sensitivity levels (MSL) for many years and have procedures in place to treat components prior to their use in the reflow process. With the move to lead-free solders, which have substantially higher reflow temperatures, BGA packages are more susceptible to popcorn. This is due to the peak temperature a BGA is exposed to, with lead-free alloys approximately 20°C higher than tin-lead solders. As a result, it is suggested that a typical MSL will increase between one and three levels for the same device when used in a lead-free process. Common Causes for Rejection Several anomalies can occur during the assembly of a PCB containing BGA devices. The most common are incomplete solder melting, excessive voids, misalignment, or missing solder balls. • Partial reflow or cold solder: Incomplete melt- ing of solder balls during the solder reflow process, resulting from inadequate time-tem- perature profile or insufficient dwell time • Excessive voids: Large or clustered excessive voids within solder balls, greater than 30%. Alternatively, this voiding requirement can be as low as 10% for mission-critical applications such as aerospace, defense, and medical products, etc. • Misaligned or shifted BGA: Device package should be located over its intended PCB land/ pad with no gross offset that risks contact with K N O C K I N G D OW N T H E B O N E P I L E Figure 2: BGA popcorning caused by moisture absorption. K N O C K I N G D OW N T H E B O N E P I L E