In the production and processing of multi-layer boards (MLB), the surface treatment of the inner layer boards is a very important process, which directly affects the quality of the multi-layer boards and has an important impact on the functional life reliability of the assembled boards. Although there is no obvious evidence that the appearance of the pink circle will have an abnormal effect on the quality of the multi-layer board, it will also cause customers to question the stability of the production process of the manufacturer, so it also becomes Customers evaluate the potential standards of manufacturers and processors and important reasons for non-scrap returns. How to reduce the occurrence of such problems in the multi-layer board processing has also become an important control content in the multi-layer board production process. Now I have some experience in the actual production and processing of the multi-layer board for many years. Industry colleagues share together, but I hope it will be beneficial to you!

First of all, it is necessary to understand that the fundamental reason for the pink ring in the inner layer of the multilayer board is that the inner layer of copper oxide is dissolved in acid to expose the pink copper surface or reduced elemental copper at the bottom, so it is named. The black-oxide of the inner layer of the multilayer board is mainly for two reasons:

(1) The smooth inner layer of copper surface is insufficiently bonded after the multilayer board is laminated, so it is easy to produce defects such as bursting and delamination after production and processing; therefore, the surface should be micro-roughened (micro-roughening) during processing. Etch MICRO-ETCH) to increase the surface area of the inner copper foil and improve the bonding force:

(2) Without oxidation treatment on the copper surface, the inner copper surface will interact with the organic matter in the curing process of the prepreg (bonding sheet) under high temperature and high pressure (the multifunctional organic matter has a strong oxidation effect under high temperature and pressure) and volatilization The reaction of natural gas (water and other small molecular substances) causes uneven color of the inner copper surface, obvious color difference and sub-surface defects. The black oxidation treatment can effectively prevent the occurrence of such defects, and the black color is very strong. The concealing property (which can effectively cover some minor defects of the inner surface treatment), so the blackening process can be widely promoted in the industry.

The author recommends the following aspects to prevent the pink circle: 1. The use of red-browning, metal organic film, chemical tin and other new processes or post-dipping improved black oxidation process can be accepted by the customer and the production equipment funds allow , It is recommended to adopt new processes such as red-browning, metal organic film and chemical tin. At present, there are many mature products in the market that are being promoted and used. In recent years, the market reflects the effect of customer use effect. In addition, a post-dipping process can also be added to the production process. Post-processing is to reduce the needle-like structure of the excess oxide film, but it will increase the production cost and is not as cost-competitive as the new process;

2. The old production and processing technology is still used, how to control and check to prevent such problems from happening? After many years of actual production and processing experience, the author suggests to control from the following aspects:

1. When the inner layer of the multilayer board is black oxidized, pay attention to the following parameters of the blackening process:

a. The thickness of micro-etching is generally in the range of 1.5-2. 5um, which can be controlled by bath analysis and micro-etching thickness measurement;

b. The temperature of the prepreg, the temperature of the prepreg before blackening can be increased to about 30-40 degrees, the processing time is 1-2 minutes, not at room temperature, this change can effectively ensure the color of the blackened board surface Uniformity, reduce the chromatic aberration caused by uneven blackening;

c. The concentration of black oxidized AB and the ratio of AB solution, the treatment time, and the aging condition of the bath: the difference in the ratio and concentration of the blackening solution will affect the density and color uniformity of the blackened film, and the bath treatment time The length and aging of the bath will affect the length of the blackened film crystal and the physical properties of the crystal layer. After the inner layer treatment, the blackened layer is a needle-like crystal layer. The blackening treatment time is too short, the crystallization is too short, and the bonding force with the resin is insufficient; the blackening time is too long, the needle-like structure is too long and the brittleness is too large.