Not to Touch PCB Boards by Hands

Dated:2017-12-05      Popularity:1456

It is the common sense for PCB engineers that man can not touch the circuit boards directly by bare hands, but why? In this article, let’s find the reasons together.

1.The dangers of static electricity

Not touch PCB by hand

Under different circumstances, electrostatic voltage carried by human body vary from several volts to hundreds volts to tens of thousands of volts. Touch electronic components directly by bare hands will generate electrostatic discharge, then devices are easily damaged and reliability are reduced; even worse, electrostatic discharge can make causes the device breakdown at once.

In addition, the electrostatic discharge process simultaneously radiates radio waves at a certain frequency and interferes with peripheral microprocessors, causing the application to run in disorder and seriously affecting the normal operation of the device.

Therefore, try to avoid direct human contact with electronic components in the daily work, especially in the charged state.

static electricity

2.Effect by static electricity on the core board feedback loop

Human touch (the introduction of human equivalent resistance and other interference) can change the characteristic of feedback loop (including the pole offset), resulting in feedback loop oscillation and instable DC-DC output voltage.

Instable DC-DC output voltage can make the system restart (DC-DC automatically reduce the output voltage), even worse, it will burn out the main circuit board (DC-DC automatically adjusts the output voltage), thus the charged motherboard is not allowed to touch.

3.How to prevent the static electricity

a.anti-static cordless wrist band

anti-static cordless wrist band
According to the corona discharge effect and the principle of the tip discharge, when the accumulated charge exceeds a certain value, the potential difference is discharged to the space to achieve the purpose of eliminating static electricity. Static dissipative time: less than 0.5s; features: convenient, reliable.

b.anti-static wrist strap

anti-static wrist strap
Human skin contacts with the wrist strap made from the static conductive material directly, thus when the wrist strap grounding, discharge static electricity generated by human can be quickly discharged. Electrostatic discharge time is less than 0.1s.

c.anti-static PU coating gloves

anti-static PU coating gloves
Anti-static PU coating gloves can further prevent static electricity from being transmitted to printed circuit boards by hand contact. Hand back conductive wire spacing is 10mm.

4.Hardware protection

Electrostatic discharge immunity: air discharge ± 15KV, contact discharge ± 8KV;

Electrical fast transient burst: interference frequency is 5KHz or 100KHz, pulse group time 300 (1 ± 20%) ms;

Lightning (surge) immunity: 2KV capacitive coupling and gas discharge tube coupling, 1 time/min;

Conducted harassment immunity: 3V capacitive coupling and gas discharge tube coupling, test frequency is from 150KHz to 80MHz.

5.Software protection

The operating system is usually stored in Flash. Static interference of the Flash and unexpected power-off are prone to make the operating system lost and the file system damaged. Except the normal operation system, design a backup system in the normal flash storage area is necessary, thus when something wrong goes about the Flash, the backup system starts automatically to ensure that the product is still able to work stable.

Now you must understand why it is not allowed to touch the printed circuit board by hand, right?

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