PCB Technical - High-precision double-layer PCB circuit board production

With the rapid development of the mobile phone, computer, electronic and digital industries, the PCB circuit board industry is also constantly meeting the needs of the market and consumers, which has promoted the continuous increase of industry output value. However, the competition in the PCB circuit board industry is increasing, and many PCB manufacturers are not hesitating Reduce prices and exaggerate production capacity to attract a large number of customers. However, low-priced PCB boardsmust use cheap materials, which will affect the quality of the product, have a short service life, and the product is prone to surface damage, bumps and other quality problems. High-precision double-layer PCB circuit board production

In fact, the test points after wave soldering will also have the problem of poor probe contact. Later, after the popularity of SMT, the misjudgment of the test was greatly improved, and the application of test points was also given a great deal of responsibility, because the parts of SMT are usually very fragile and cannot withstand the direct contact pressure of the test probe. Use test points. This eliminates the need for the probe to directly contact the parts and their solder feet, which not only protects the parts from damage, but also indirectly greatly improves the reliability of the test, because there are fewer misjudgments. Double layer PCB circuit board

Why do all circuit boards use serpentine traces?

The serpentine trace is to maintain the same delay of the same type of signal line. If you follow a straight line, the length is different, the frequency of the signal on the line is high, and the speed is fast, which may cause confusion when reading.
Especially for the PCB wiring of the DRAM interface, where there is a very high requirement for interface signal synchronization (G on the clock), it is necessary to ensure that each line is the same length. Therefore, some wiring must be lengthened deliberately and arranged in a serpentine shape, even if it could be connected to a short place, so that the delay is consistent with other wiring. The length and interval of the lines are restricted, not arbitrary, so they are related to the clock frequency, delay relationship, and even hardware device technology. High-precision double-layer PCB circuit board
Snake-shaped wiring can carry out long wiring in a short space, so it saves area, and it also has a certain inhibitory effect on electromagnetic interference (make full use of the overlapped part of the wiring to cancel it). Some are to prevent electromagnetic interference and prevent parasitic interference. Too many parallel lines will have a capacitive effect, and they cannot be flushed. The circuit board wiring of high-frequency lines needs to consider these, mainly considering how to deal with the sudden changes of current or voltage. Isolation of high-frequency parts, separation of high-frequency and low-frequency, insertion of power lines and ground wires, and avoiding large loops in the wiring are some methods. It is also necessary to avoid sharp corners in the design, so sharp corners must be made obtuse. Double layer PCB circuit board
In addition, it will form a right angle when turning in a straight line, low frequency does not matter, high frequency is easy to cause reflection, the most important thing is that it is easy to lift up during 90 degree processing, especially easy to break.

Impedance type:

(1) Characteristic impedance. In electronic information products such as computers and wireless communications, the energy transmitted in the PCB circuit is a square wave signal (called pulse) composed of voltage and time. The resistance encountered is called the characteristic impedance.

(2) Differential impedance Two identical signal waveforms with opposite polarities are input at the drive end, which are respectively transmitted by two differential lines, and the two differential signals are subtracted at the receiving end. The differential impedance is the impedance Zdiff between the two wires.

(3) Odd Mode Impedance The impedance value of one of the two wires to the ground is Zoo, and the impedance value of the two wires is the same.

(4) Even mode impedance The drive end inputs two identical signal waveforms with the same polarity, and the impedance Zcom when the two wires are connected together. High-precision double-layer PCB circuit board vias are an important factor in the design of blind and buried multi-layer circuit boards. A via is mainly composed of three parts, one is the hole; the other is the pad area around the hole; the third is POWER Layer isolation area. The process of making a via on a double-layer PCB circuit board is to plate a layer of metal on the cylindrical surface of the hole wall of the via by chemical deposition to connect the copper foils that need to be connected in the middle layers, and the upper and lower sides of the via It is made into a common pad shape, which can be directly connected to the upper and lower sides of the circuit, or not connected. Vias can play the role of electrical connection, fixing or positioning devices.