A Method of Selective Electroless Thick Gold Plating

Aim

To develop a selective electroless thick gold plating method and become a versatile surface treatment process

 

Goal

The selective gold thickness is above 0.3um, and the non selective gold thickness is above 0.1um

 

Problem

①The chemical gold deposition of the displacement reaction, with gold thickness of 0.03-0.05 micron, is only suitable for welding surface.

②When the surface of nickel is gradually covered by gold layer, the deposition rate slows down, and the gold thickness is difficult to be greater than 0.3 micron and dense.

③Electroplating requires additional leads, which are inconvenient to add when the networks are interwoven

 

Principle

①The nickel layer is used for catalytic reduction. The hydrogen atom is adsorbed to obtain electrons. The atomic hydrogen is provided by the reductant. The atomic hydrogen loses electrons and enters the solution to become hydrogen ions.

②The original wiring of the circuit board and the metal layer of the same bonding pad play the role of conducting electrons. Gold ions get electrons continuously on the gold surface and deposit, which is equivalent to electrogilding

 

Method and step

Step1：Carry out conventional chemical displacement gold plating, the picture is a 10000 times SEM image of gold surface, and the gold thickness is<0.02um

Aim：Expose nickel layer to obtain reducing electrons

 

Step2：Paste anti plating film to expose the bonding pad to be plated with thick gold

 

Step3：Carry out the first reduction electroless gold plating

The picture is a 10000 times gold SEM image

 

 

Step4: Remove the anti coating film

 

Step5: Reduct electroless gold plating again

The picture is a 10000 times gold SEM image

 

 

 

Results

 

Gold thickness measurement results	First replacement of chemical thin gold	First reduction plating of chemical thick gold	Second chemical reduction plating of thick gold
Selective chemical thick gold position	0.009-0.014μm	0.293-0.349μm	0.326-0.385μm
Other locations	0.009-0.014μm	Covered with anti coating film	0.105-0.111μm

 

Conclusion

The method of selective electroless gold plating can meet the target requirements.