How to deal with the blackening of the inner layer of the multi-layer automotive rigid-flex board

In the production process of multi-layer automotive flexible and rigid boards, there is a very difficult problem - blackening of the inner layer of the multi-layer board. What black oxidation method is the most effective? And what is the effect of inner blackening?

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

Black oxidation method for general inner layer treatment of automotive flexible and rigid multi-layer boards:

●Black Oxidation Treatment of Multilayer Board of Automotive Rigid and Rigid Board

●Brown Oxidation Method of Multilayer Board of Automotive Rigid and Rigid Board

●Low temperature blackening method of multilayer board of automobile flexible and rigid board

The high-temperature blackening method used in the multi-layer automotive rigid-flex board will generate high-temperature stress on the inner layer, which may cause interlayer separation after lamination or cracks in the inner copper foil.

1. Brown oxidation:

The black oxidation treatment products of the multi-layer boards of the automotive flexible and rigid board manufacturers are mainly copper oxide, not the so-called cuprous oxide, which is some wrong statement 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 observational analysis show that the blackening product is copper oxide, not copper oxide. Contains other ingredients.

The general composition of blackening liquid:

●Oxidant Sodium Chlorite

●PH Buffer Trisodium Phosphate

●Sodium hydroxide

●Surfactant

●Or ammonia solution of basic copper carbonate (25% ammonia)

2. Relevant data

(1) Peel strength (peel strength) of 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 lbs/inch;

(2) The weight of the oxide; it can be measured by the gravimetric method, and is generally controlled at 0.2---0.5mg/c㎡;

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

①Concentration of sodium hydroxide

②Concentration of sodium chlorite

③Interaction between trisodium phosphate and immersion time

④Interaction of 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 lamination and the relevant properties of the resin pp.

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

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