Produce Custom Printed Circuit Board Fabrication Promotions Company


Printed Circuit Board Fabrication

The two major difficulties in the field of microelectronics lie in the processing of high frequency signals and weak signals. In this respect, PCB production level is particularly important. PCB made by different people with the same principle design and the same components has different results. Based on our past experience, I would like to share my views on the following aspects:

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The test of the board should also be considered in the design stage. The physical location of the test point, isolation of the test point and other factors should not be ignored, because some small signals and high frequency signals cannot be directly added to the probe for measurement. In addition, some other related factors should be considered, such as the number of layers on the board, the packaging appearance of the components, and the mechanical strength of the board. Before making PCB board, we should know the design target of the design.

We know that some special components have special requirements for layout and wiring, such as the analog signal amplifiers used by LOTI and APH, and the analog signal amplifiers have stable and small ripple requirements for power supply. The analog small signal part should stay away from the power device as far as possible. On the OTI board, the small signal amplification part is specially equipped with a shield to shield stray electromagnetic interference. NTOI board using the GLINK chip is ECL process, power consumption is large and heat is severe, heat dissipation must be in the layout of the problem must be taken into special consideration, if the use of natural heat dissipation, GLINK chip in the air flow is relatively smooth place, and the spread out of the heat can not constitute a large impact on other chips. Attention should also be paid to the possibility that speakers or other high-power devices on the boards may cause serious contamination of the power supply.

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The layout of components to consider a factor is the electrical performance, the close connection to the components as far as possible to put together, especially for some high-speed lines, layout will make it as short as possible, power signal and small signal components to separate. On the premise of meeting the circuit performance, we should also consider the neat and beautiful arrangement of components for easy testing, the mechanical size of the board, and the position of the socket.

The delay time of grounding and interconnect in high speed system is also the first consideration in system design. Signal on the transmission time had a great influence on the overall system speed, especially for high-speed ECL circuits, although high speed integrated circuit block itself, but as a result of on the floor with common interconnect (every 30 cm long, about the delay of the 2 ns) bring the increase of the delay time, can make the system speed is greatly reduced. Like a shift register, synchronous counter this synchronization working parts on the same piece of card, best because of the different transmission delay time of the clock signal on the board is not equal, could lead to a shift register main production errors, if not on a plate, where synchronization is the key, The length of the clock lines connected from the common clock source to each plug-in board must be equal.

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With the completion of the design of OTNI and star fiber network, there will be more boards with high-speed signal lines above 100MHz to be designed in the future. Some basic concepts of high-speed lines will be introduced here. Any "long" signal path on a printed circuit board can be considered a transmission line. If the transmission delay time of the line is much shorter than the signal rise time, then the reflection of the producer during the rise time of the signal will be drowned. Overshooting, recoil and ringing are no longer present. For most MOS circuits at present, the rise time is much larger than the delay time of line transmission, so the route length can be measured in meters without signal distortion. For fast logic circuits, especially ultra-high speed ECL.

In the case of integrated circuits, because of the increased edge speed, if nothing else, the length of the wiring must be greatly reduced to maintain signal integrity. Strictly speaking, he said, transmission lines are not very necessary for conventional TTL and CMOS devices with slower edge speeds, nor are they always needed for high-speed ECL devices with higher edge speeds. But when using transmission lines, they have the advantage of being able to predict wire delays and control reflections and oscillations through impedance matching.

1. The following five basic factors determine whether to adopt the transmission line, which are: (1) the system signal along the speed, (2) the connection distance, (3) the capacitive load (how much fan out), (4) the resistive load (the wire termination mode); (5) allowable recoil and overshoot percentage (reduction degree of ac noise immunity).

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