Black-brown and pink-circle process terminology manual

1. Black oxide
In order to make the multilayer board maintain the strongest adhesion after lamination, the copper conductor surface of the inner layer board must first be treated with a black oxide layer. At present, this roughening treatment has been improved to browning (Brown Oxide) or redding treatment, or brassing treatment to meet different needs.

2. Brown Oxide
Refers to the oxidation treatment layer on the surface of the copper conductor of the inner layer board before lamination. This layer has the effect of increasing the surface area, which can strengthen the adhesion of the resin after hardening, reduce the attack of the hardener (Dicy) in the epoxy resin on the bare copper surface, and reduce the probability of its by-product moisture bursting the board. Generally, the black oxide layer contains more monovalent cuprous components, while the brown oxide layer contains more divalent copper, so the properties are also more stable. However, both processes require processing in a high-temperature (80 ~ 90℃) bath (3 ~ 5 minutes), which is not only inconvenient for the inner thin board, but also causes the trouble of dimensional distortion, and there is also the possibility of causing the "pink ring" problem. Recently, a new approach has emerged in the industry, that is, only "special micro-roughening" treatment is performed on the inner copper surface to obtain a multilayer board with good fixing force. If such an improvement is really achieved, it will not only simplify the process and reduce costs, but also improve the quality of the multilayer board.

3. Pink Ring
The black or brown oxide layer on the surface of the hole ring on the inner layer of the multilayer board, where it is interconnected with the hole wall of the plated through hole, is affected by various processes of drilling and plating, so that it is eroded by the solution and diffused to become a ring-shaped bare copper surface of the original color, which is called "Pink Ring". It is a quality defect, and its cause is very complicated (see Circuit Board Information Magazine No. 37 and 38 for details).

4. Wedge Void:
The side edge of the black layer of the inner hole ring of the multilayer board is often attacked laterally by various strong acid bath solutions during the PTH process. A triangular wedge-shaped gap will appear on the cross section of the micro-slice, which is called Wedge Void. If the black layer is corroded more deeply, a "Pink Ring" that can also be seen outside the board will appear. The proportion of this type of Wedge Void is generally higher in the new "direct electroplating" than in the traditional "chemical copper". The reason is that the chemical copper bath solution and alkalinity are less likely to attack the black film, and the direct electroplating process (including palladium, polymer or carbon powder) is mostly composed of acid tanks. In the absence of a rapid deposition layer of chemical copper layer and timely protection of electroplated copper, once the black layer is attacked into a breach, a Wedge Void will appear.