Simply analyse ESD to protect with ESD protective device
In daily life, ESD (Electro-Static Discharge, electrostatic discharge) It is a kind of common phenomenon to us, but for electronic product, ESD is often fatal - -It may cause the components and parts in-house line to damage, the normal life time of the direct influence products, even cause the damage of the products. So, it has all been engineers' focal points of work that ESD has been protected all the time. For just beginning the electronics engineer of the career, will usually accept the training of some ESD relevant knowledge before knowing the expertise, it serves to show ESD protected position and importance.
Photo of damage within the electron microscope lower IC of Fig. 1
Generally, ESD protects and generally realizes by two kinds of routes, the first kind of method is to avoid the emergence of ESD; Second method is through on-chip or slice outside integrate internal by protective circuit or ESD protective devices specialized, thus prevent ESD from being damaged by the protective device after happening.
Avoid the emergence of ESD
Prevent method that ESD take place from appear, pay customer in the past on products more, namely course of researching and developing, producing etc.. Because at these stages, static susceptible device susceptors such as IC, circuit board,etc. may be uncovered (such as SMT process for preparing in the engineering course of production) ,It is perhaps far greater than having protective finished products of outer cover that IC is spoiled because of ESD.
Sensitive intensity of static of several kinds of different kinds of devices of Table 1
Generally speaking, avoiding the method of ESD can be divided into the following several kinds:
Surround (surround) : The static sensitive components and parts are packed with the antistatic material, or use the operculated antielectrostatic container to store; In the sensitive area of static ' Such as SMT process for preparing) The personnel of the work, will wear the clothes of static.
Ground (earth) : Earth personnel and apparatus in the work environment through different ground wire;
Impound (get rid of) : Get rid of the inner non- antielectrostatic material of all work regions; In addition, can it is working since is sensitive for static extremely station increase ion fan with in and products static that surface bring.
Fig. 2 uses the ion fan and earthes the static tablecloth in order to avoid ESD
On the other hand, the humidity is also an important doing in the test amount factor. Probability that the suitable humidity reducible ESD takes place. (see Table 2) Why one of the reasons to found the factory in the South is this an electronic works too more.
Influence to ESD of the humidity of Table 2
ESD protective device and protective circuit
Though the above-mentioned method of preventing ESD from happening has very ideal results, obviously not suitable to the terminal user - -For example, it is impossible for us to wear the static hand-ring first before using the mobile phone, converse, put the mobile phone into static bag in order to avoid ESD. In fact, because user fresh to have an opportunity to touch components and parts and circuit board inside product, so does not need so rigorous ESD safeguard procedures either, but this does not mean the problem of ESD does not exists - -First of all, ESD all right input / the outconnector (such as USB interface, interface of the charger, SIM card slot) It is the route that enters various components in circuit; Secondly, with electronic product, especially consumption electronic product towards light and thin to take, develop, lead to the fact the physical dimension of internal IC is reducing constantly, its one's own ESD protective capacity is being also weakened constantly. So, the engineer usually puts into ESD protective device during design, and there is ESD protective circuit on one within a lot of IC.
Fig. 3 is on the user, ESD may be entered by various interface of the electronic device, and cause damaging to the internal chip
ESD protective circuit on one
It is believed that all people hope ESD protects and integrates within the IC wafer completely, because can economic board-level space in this way, reduce system cost and reduce, design with cloth collinear complexity. But according to present situation, the prospect is not optimistic. Nowadays, ESD a protective great difficult problem in flakes of technological progress of IC process for preparing. On one hand, technological progress although promotes characteristic and integrated level of IC and reduces the power consumption and size, but because gate oxidation is thinner and thinner in layer thickness, IC autogenous ESD protective capacity reduced instead. On the other hand, with the constant decrease of IC size, are limited by space, so protective power is limited.
4 Fig., with the intersection of IC and constant decrease of area, very difficult in integrated the intersection of ESD and protective circuit (materials under IC
