PCB News - PCB design of high-speed DSP system and research status of acid copper plating additives

introduced the characteristics of high-speed DSP system PCB board and several issues that should be paid attention to based on signal integrity design, including power line design, ground line design, impedance matching termination technology.
The test result shows that the design is reliable and reasonable, and it solves the signal integrity problem of the system well.
With the rapid development of microelectronics technology, the digital electronic system composed of IC chips is developing rapidly in the direction of large scale, small size and high speed, and the development speed is getting faster and faster. The application of new devices has led to high circuit layout density in modern EDA designs and high signal frequencies. With the use of high-speed devices, there will be more and more high-speed DSP (digital signal processing) system designs. The signal integrity problem has become an important design issue. In this design, its characteristic is that the system data rate, clock rate, and circuit density are constantly increasing, and the design of the PCB printed board shows a completely different from the low-speed design Behavioral characteristics, that is, signal integrity problems, aggravated interference problems, electromagnetic compatibility problems, and so on.
These problems can cause or directly lead to signal distortion, timing errors, incorrect data, address and control lines, system errors, or even system crashes. If they are not resolved, they will seriously affect system performance and cause immeasurable losses. Therefore, the design quality of the PCB printed board is very important.
PCB design for high-speed DSP system
This PCB board is a high-speed DSP image processing board for real-time image signal detection. The DSP chip used is TMS320DM642[2], the main frequency speed is up to 600 MHz, the off-chip data bus speed is also above 100 MHz, and the chip package uses BGA Form, the number of pins is as high as 548.
In addition, the DSP system needs to be mixed with the video A/D conversion device, which puts forward high requirements on the design of the circuit board. If the multilayer board is not used, it is impossible to connect successfully. This system uses a six-layer wiring scheme, one of which is a dedicated power layer, one is a dedicated ground layer, and the fourth is a signal layer. Whether it is a large-area ground or a ground net, its effect is not as good as a special ground layer; and when wiring, the use of ground layers can save a lot of work for device pin grounding.
But it should be noted that the through-hole pads and vias will break the ground layer, especially when the pads and vias are dense, the ground layer may produce distortion burrs, etc. This should be fully considered when laying holes and wiring. The PCB board developed is a 6-layer board, including 1 layer of ground and 1 layer of power, and 4 layers of signal. For debugging convenience, signal test points are added on the PCB board.

In PCB, acid copper plating additives have formed a relatively complete system. However, under the requirements of high thickness-to-diameter ratio of printed circuit boards and various coating indexes, the test of high temperature of the solution, strong stirring of the solution, and continuous production can really occupy There are not many products on the market, especially domestic products used for electroplating of high-end products are even rarer. In this regard, domestic efforts are still being made.
From the 1970s to the 1980s, my country and the United States, Japan, Germany, and the United Kingdom have widely adopted acid copper plating for PCB electroplating. The products include UBAC additives from the United States, HS and HS-makeup additives from Japan, Sloto-cup from Germany and PC- from the United Kingdom. 81 additives, these additives greatly improve the overall performance of the electroplating layer, they are all mixed additives.
There are 153, 154, M-N-SP and other multi-component additives in China. The number of small holes of the printed board on the basis of the current electronic component installation
More and more, the hole diameter is getting smaller and smaller, and each hole is different. In order to meet the new requirements of PCB production, corresponding finished additives have appeared, such as Ethone's CUPROSTAR○RST-2000 and CUPROSTART○RCVF1, EBARA- Udylite’s CU-BRIGHTVF, Rohm AND Haas’s ELECTROPOS-IT and ELECTROPOSITTM 1100 are imported products, while the domestic production of high-demand electronic electroplating series additives is still difficult. Imported products still have great advantages in the domestic market.
The basic composition of acid copper plating additives
Acidic copper plating additives generally include brighteners, levelers, wetting agents, etc. It usually requires the synergistic effect of several additives to achieve the desired effect.
It is difficult to control the amount of additives in the electroplating process. This is a problem in HDI (High Density Printed Board) microporous electroplating with high aspect ratio. Although foreign researchers have developed technologies that do not use additives by changing the conditions of pulse electroplating, But getting a good coating is still very dependent on additives.