Blackening factor of inner layer of multi-layer PCB board

In the production process of multilayer boards, there is a very difficult problem - the inner layer of multilayer boards is blackened. Which method of black oxidation is most effective? And what is the effect of inner blackness?

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Black oxidation of the inner layer: passivate the copper surface; improve the surface roughness of the inner layer copper foil, thereby improving the adhesion between the epoxy resin board and the inner layer copper foil.

Multilayer PCB general inner layer treatment black oxidation method:

1. Multilayer PCB?black oxidation treatment
2. Multilayer PCB?brown oxidation method
3. Multilayer PCB?low temperature blackening method
4. The PCB multi-layer board adopts high-temperature blackening method, and the inner layer board will generate high-temperature stress (thermal stress), which may cause delamination after lamination or cracking of the inner layer copper foil;

Brown oxidation:

The black oxidation treatment products of PCB manufacturers' multilayer boards are mainly copper oxide, not the so-called cuprous oxide, which is some erroneous statements in the industry. Through ESCA (electro-specific-chemical analysis) analysis, the binding energy of copper atoms and oxygen atoms on the oxide surface and the ratio of copper atoms to oxygen atoms can be determined; clear data and observation analysis show that the blackened product is copper oxide. contain other ingredients;

The general composition of blackening liquid:

1. Sodium chlorite
2. PH Buffer Trisodium Phosphate
3. sodium hydroxide
4. Surfactant
5. Or basic ammonium cupric carbonate solution (25% ammonia water)

Relevant information:

Peel strength (peel strength) 1oz copper foil at a speed of 2mm/min, the width of the copper foil is 1/8 inch, the pulling force should be greater than 5 lbs/inch

Oxide weight; it can be determined by gravimetric method, generally controlled at 0.2---0.5mg/cm2

The important factors affecting the tear strength through correlation variable analysis (ANDVA: variable analysis) are:

1. Concentration of sodium hydroxide
2. Concentration of sodium chlorite
3. Interaction between trisodium phosphate and soaking time
4. Interaction between sodium chlorite and trisodium phosphate concentration

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

The length of the oxide needle-like crystals is 0.05 mil (1-1.5um) is the best, and the tear strength is relatively high at this time.

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