Plating process (11)

Let's take a look at the defects in electroless plating.

 

First, let's review the mechanism of electroless plating.

 

Initially, due to the diffusion theory, deposition on the surface is inhibited, and the center of the through-hole (TH) connects. Next, according to the memory effect, deposition in the center of the TH is promoted, resulting in a smoother surface.

 

Diffusion Theory: Due to strong exchange, Leveler (which inhibits deposition) adsorbs heavily on the thin surface diffusion layer, strongly suppressing surface deposition. As a result, deposition underneath the hole is promoted, and filling occurs.

 

Memory Effect: Brightener (which promotes deposition) uniformly adsorbs regardless of the diffusion layer but is deposited only where it is adsorbed. As the density of Brightener under the hole increases, the deposition rate under the hole gradually accelerates, and filling takes place.

 

Influence of TH Filling Agitation:

If agitation is weak, the diffusion layer near the entrance of the hole becomes thick, and the connection between the centers of the THs becomes the first to occur, leading to void defects.

If agitation is strong, the adsorption density of leveler on the surface and inside the hole becomes equal, delaying the connection of the center of the hole, resulting in dimple defects.

 

Let's once again remind ourselves of the roles of additives that greatly influence defects.

 

Brightener: Facilitates small particle plating, provides gloss to the plated surface, improves plating quality, and promotes plating growth.

 

Carrier: Transports and regulates Brightener, Leveler, Cl-, etc., necessary for Cu reduction reaction, improves uniform deposition by hindering Cu ion supply near the cathode.

 

Leveler: Hinders Cu ion supply, improves current distribution, and reduces defects in plating.