On some occasions a tin lead surface finish is suggested to the OEM as an ENIG replacement. At times like this, tin lead is mostly used for the assembly of BGA-populated PCBs. Tin lead offers excellent flatness, a shelf life of up to six months, good solderability, and is relatively inexpensive. However, it is sensitive to handling, not effective for multiple reflow and assembly processes, and is prone to tin whiskers. Also, the coating depth of tin lead is critical, therefore placing high demands on process control.