Full Body Hard Gold 

Full Body Hard Gold also known as Hard Electrolytic Gold,is a layer of gold with hardeners for increased durability, plated over a barrier coat of nickel using an electrolytic process. Hard gold is extremely durable, and so this material is usually applied to high-wear areas, such as edge connector gold fingers and keypads, since its hardness can withstand repeated use; however, due to the high cost of hard gold, and its relatively poor solderability, it is rarely applied to solder-able areas. 
Full Body Hard Gold is a rarely-chosen surface finish, where the full body of the PCB board is plated with hard gold. In order to apply a Full Body Hard Gold surface finish, an electrolytic process using an electric current or an immersion process is needed, depending on the PCB design. Due to the poor solder-ability of hard gold, a very active flux will be required to solder effectively to the hard-gold-plated pads.See below figure 13

Pros 

• Hard, Durable Surface

•  No Lead

•  Long Shelf Life

Cons

•  Very Expensive

•  Extra Processing / Labor Intensive

•  Use of Resist / Tape

•  Plating / Bus Bars Required

•  Demarcation

•  Difficulty with Other Surface Finishes

•  Etching Undercut Leads to Slivering / Flaking

•  Not Solder-Able Above 17 μin

•  Finish Does Not Fully Encapsulate Trace Sidewalls, Except in Finger Areas

Click here:Introduction for Surface finish choices