Originally, in the early days of RoHS compliance, Maxim intended to offer DS1339C-33 as lead(Pb)-free device with orderable part number DS1339C-33+. However, it was then determined that the internal crystal is not lead-free/RoHS compliant. Maxim converted the package leadframe plating material to 100% matte tin, so the exterior of the device is lead(Pb)-free, but it contains a crystal inside that is not lead(Pb)-free. The RoHS compliance rules allow an exemption for small amount of lead that is fully encapsulated in the sealed device, and these parts are given the suffix indicator of " # "
Maxim was able to offer the DS1339C-33# which denotes parts which are not lead free but are RoHS compliant by exemption.