Don't let static electricity ruin your chip! These four points cannot be ambiguous at all

Latest update time：2018-06-13

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Integrated circuits that are so-called "electrostatic discharge sensitive (ESDS)" need to be protected against high voltage before being mounted on a printed circuit board. In most cases, improper handling of the IC generates environmental static electricity, which causes harmful surge voltages, i.e., discharge. Unfortunately, engineers fail to notice that the IC has been damaged and continue testing or assembly, resulting in losses.

Where does electrostatic discharge come from?

Electrostatic discharge (ESD) usually occurs in the following two situations:

1. Contact discharge - discharge of electricity through a high voltage switch after direct contact between the surfaces of two objects with different potentials

2. Air discharge - When two objects with high electrostatic fields approach each other, discharge occurs through the air.

Static charge generally accumulates on insulating materials, such as vinyl plastic, insulated plastic shoes, plastic packaging or ungrounded soldering irons. When the charge accumulates to a certain intensity on an object, it will discharge to nearby materials. The amount of accumulated charge will vary depending on the material and the surrounding environment, for example:

Walking on carpet: 15,000V

Walking on Vinyl Floor: 5,000V

Remove the bubble pack from the packaging: 20,000V

(Note: Assuming a relative humidity of 40%)

Since materials that easily generate static electricity are commonly used in the workplace, the workbench used to handle ICs needs to have good ESD control to prevent ESD from damaging the ICs being processed.

Four key points of anti-static workbench

In the process of handling IC, the electrostatic hazard prevention methods implemented will be different due to the different working environment, procedures and contact materials. The following are basic prevention facilities suggestions, as shown in Figure 1.

Figure 1. High static control IC processing workbench

ESD protection tray and diverter

Pay attention to the protective materials used in trays and diverters. According to the ANSI/ESD S541 standard, the surface resistance of the packaging material must be between 104 and 1011 ohms, so some manufacturers will also indicate this in the specification sheet, such as DESCO 's 57000 ESD protective tray series:

Figure 2: DESCO's 57000 ESD protection tray series

ESD Static Control Grounding Mat - Protect Desktop

In addition to providing an anti-static work surface area to limit the generation of static electricity, ESD protection desktop materials also remove charges from conductive objects placed on the work surface. Therefore, the grounding resistance value of the protection material will not be too high to prevent the flow of charge. According to the ANSI/ESD S4.1 standard, the surface resistance of the material should be between 106-109 ohms, such as SCS 's 8200 series products:

Figure 2: SCS's 8200 series ESD protection desktop

ESD Static Control Grounding Mat – Protect Ground

Protective floor products can generally be divided into three categories: conductive, static dissipative and insulation. According to the ANSI/ESD S20.20 standard, the surface resistance of conductive floors or mats should be less than 109 ohms, such as the product model 6836 from ACL Staticide Inc.

Figure 3: ACL Staticide Inc. 6836 conductive floor mat

Static dissipative products have a surface resistance of less than 1011 ohms, such as SCS 's AFM series:

Figure 4: SCS's AFM series classic dissipative floor mats

Surface resistance greater than this parameter can be called "insulating".

Engineering Tips

Conductive Materials: Typically used for ESD control where there is some level of insulating buildup on the floor (dirt, sand, and other insulating particles)
Static Dissipative Materials: Best used for ESD control in ideal and controlled workstations
Insulation materials: used in high voltage applications or test stations to prevent current conduction that could harm operators or equipment

Grounding wrist strap

According to the IEC61340 international standard, a 106 ohm resistor is usually used for the wrist strap grounding resistance value. If the operator touches a live conductor, this resistor will limit the current flowing through the human body to less than 500 microamperes for normal mains power. For example, the SCS company Highland series.

Figure 5: SCS's Highland series grounding wrist strap

Conclusion

In order to prevent the IC from being damaged by high ESD before assembly and during processing, it is necessary to build an electrostatically controlled workbench. The following material selection directions are recommended:

It is recommended that trays and diverters, work desks, floors or mats, and workers' bodies must have appropriate ESD protection;
Pay attention to whether the IC in the application product has an ESD sensitivity level or requirement and needs to be handled with care;
Choose appropriate conductive, static dissipative and/or insulating materials according to the working environment.