Hi,
I bourght some chips"sn74hc4020n" 250 pcs from Mouser a few days before.(datecode of 17+ has 175pcs, date of 18+ has 75pcs.) When my customer received the chips, They found that the datecode of 18+ has the chip pin oxidation.There is the phenomenon of pin oxidation, poor weldability, see the attached picture, pin can not be tin.please see the attachment.