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Ceramic substrate. What is ESD of PCB?

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 Ceramic substrate.Recently,we are doing ESD test of electronic products.From the test results of different products,we find that this ESD is a very important test:if the circuit board is not well designed,when static electricity is introduced,it will cause product crash and even damage to the component equipment.In the past,we only noticed that ESD would damage the equipment,but we didn't expect that we should attach great importance to electronic products.

  ESD is what we often call electrostatic discharge.From the knowledge learned,we can know that static electricity is a natural phenomenon,which generally occurs through touch,conflict,induction between electrical appliances and other ways.It is characterized by long-term accumulation,high voltage(which can generate thousands of volts or even tens of thousands of volts of static electricity),low electricity,small current and short acting time.For electronic products,if the ESD Design is not well designed,the operation of electronic and electrical products is often unstable or even damaged.

  Two methods are generally used in ESD discharge test:touch discharge and air discharge.Touch discharge is the discharge of the equipment to be tested directly;air discharge,also known as direct discharge,is the coupling of strong magnetic field to the nearby current loop.The test voltage of these two types of tests is generally 2kv-8kv,and the requirements of different regions are different.Therefore,before design,it is necessary to find out the market for products.

  The above two conditions are the fundamental tests for the electronic products that cannot be operated due to the electrified human body or other reasons when the human body touches the electronic products.

  Humidity is different all over the world,but at the same time,if the air humidity is different,the static electricity will be different.The following table is the collected data,from which we can see that the static electricity increases with the decrease of air humidity.This is also a direct explanation of the northern winter,depilation occurred when the electrostatic spark is very large.

  Since static electricity is such a great hazard,how can we protect it?We usually take three steps in the design of static electricity protection:to avoid the damage caused by external charge flowing into the circuit board;to avoid the damage caused by external magnetic field to the circuit board;and to avoid the harm caused by static electricity field.



Ceramic substrate


  In the actual circuit design,we will choose one or more of the following methods for electrostatic maintenance:

  1.Avalanche diode for static maintenance.This is also a method often used in the design.The typical method is to connect an avalanche diode to the ground in parallel in the key signal line.

  This method uses avalanche diode to respond quickly and has the ability of stable clamping.It can consume high voltage in a short time and then maintain the circuit board.

  2.Use high voltage capacitor for circuit maintenance.

  In this method,the ceramic capacitor with a voltage withstand of at least 1.5kV is generally placed in the direction of I/O connector or key signal,and the connecting line is as short as possible,so as to reduce the inductive reactance of the connecting line.If a low voltage resistant capacitor is selected,it will cause damage to the capacitor and lose the function of maintenance.

  3.Ferrite beads are selected for circuit maintenance.

  Ferrite beads can attenuate ESD current and restrain radiation.When faced with two problems,a ferrite bead is a good choice.

  4.Spark gap method.

  This method is seen in a document.The specific method is to use the triangle copper skin whose tips are aligned with each other to form the microstrip line layer composed of copper skin.One end of the triangle copper skin is connected to the signal line and the other triangle copper skin is connected to the ground.When there is static electricity,it will discharge at the tip and consume electric energy.

  5.Choose LC filter to maintain the circuit.

  Ceramic substrate.The filter composed of LC can effectively reduce the high-frequency static electricity into the circuit.The inductive reactance of the inductor can restrain the high frequency ESD from entering the circuit,while the capacitance can divert the high frequency energy of ESD to the ground.At the same time,this type of filter can also smooth the signal margin and reduce the RF effect.In terms of performance,the signal integrity has been further improved.

  6.ESD protection shall be provided for multilayer boards.

  When the fund allows,choosing multilayer board is also a useful way to avoid ESD.In the multi-layer board,because there is a good ground plane close to the line,it can make ESD more quickly coupled to the low impedance plane,and then maintain the role of key signals.

  7.Maintenance method of keeping maintenance belt around circuit board.

  Ceramic substrate.This method is generally to draw lines around the circuit board without welding layer.Under the condition that the conditions permit,connect the cable to the shell,and at the same time,pay attention that the cable cannot form a closed ring,so as to avoid the formation of a ring antenna and the introduction of larger costs.

  8.Choose CMOS equipment with clamp diode or TTL equipment for circuit maintenance.

  This method is to use the principle of isolation to maintain the circuit board.Because these devices have the maintenance of clamp diode,the design complexity is reduced in the practical circuit design.

  9.Choose decoupling capacitor.

  These decoupling capacitors need low ESL and ESR values.For low-frequency ESD,decoupling capacitors reduce the area of the loop.Because of the role of ESL,the role of electrolyte is weakened,which can better filter out high-frequency energy.

  In a word,although ESD is terrible and even has serious consequences,as long as the power supply and signal wire on the circuit are well maintained,ESD current can be effectively prevented from flowing into PCB.Ceramic substrate.Among them,my eldest brother often said,"a good board grounding is the king's way".I hope this sentence can also bring you the role of breaking the skylight.

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