How to deal with the blackening of the inner layer of a multi-layer PCB board is relatively simple?

The role of blackening: passivation of the copper surface; enhance the surface roughness of the inner layer of copper foil, thereby enhancing the bonding force between the epoxy resin PCB board and the inner layer of copper foil;


Peel strength

Black oxidation method for general inner layer treatment of PCB multilayer board:

PCB multilayer board black oxidation treatment

PCB multilayer board brown oxidation method

PCB multilayer board low temperature blackening method

PCB multilayer board adopts high temperature blackening method, the inner layer board will produce high temperature stress (thermal stress), which may cause the layer separation after lamination or the crack of the inner copper foil;

1. Brown oxidation:

The product of black oxidation treatment of multi-layer boards of PCB manufacturers is mainly copper oxide, there is no so-called cuprous oxide. This is some misconceptions in the industry. After ESCA (electro specific chemical analysis) analysis, the difference between copper atoms and oxygen atoms can be determined. Binding energy, the ratio between copper atoms and oxygen atoms on the surface of the oxide; clear data and observational analysis prove that the product of blackening is copper oxide, and there are no other components;

The general composition of blackening liquid:

Oxidizing agent sodium chlorite

PH buffer trisodium phosphate

Sodium hydroxide


Or basic copper carbonate ammonia solution (25% ammonia water)

2. Relevant data

1. Peel strength (peel strength) 1oz copper foil at a speed of 2mm/min, the width of the copper foil is 1/8 inch, and the tensile force should be more than 5 pounds/inch

2. Oxide weight (oxide weight); can be measured by gravimetric method, generally controlled at 0.2—0.5mg/cm2

3. The significant factors that affect the tear strength through the relevant variable analysis (ANDVA: the analysis of variable) are:

①The concentration of sodium hydroxide

②The concentration of sodium chlorite

③The interaction between trisodium phosphate and immersion time

④The interaction between sodium chlorite and trisodium phosphate concentration

The tear strength depends on the filling of the resin to the oxide crystal structure, so it is also related to the relevant parameters of the lamination and the relevant properties of the resin pp.

The length of the acicular crystals of the oxide is 0.05mil (1-1.5um) as the best, and the tear strength at this time is also relatively large;