ESD Systems - Questions And Answers

When we don't know if the electric static voltage will destroy the compents, we must design some different models to test it, such as HBA model, Machine model, e.g. Now, could you tell me how many models there are in electronic industry field and the details to design? - Anonymous

There are three models to simulate an ESD event in the electronics industry.
1- Human Body Model (HBM), [100 pF @ 1.5 kilohms], ESD STM5.1
2- Charge Device Model (CDM), [4 pF/30 pF], ESD DS5.3.1
3- Machine Model (MM), [200 pF @ 0 ohms], ESD STM5.2

The most well understood and often used model for controlling an ESD control program is the HBM. The least understood and often overlooked model is the CDM. The CDM is important to understand as well. A device may charge on its own during transportation, kitting, etc. and discharge when brought into contact with any conductor, whether grounded or not.

The ESD Association has standards for all 3 models which may be obtained directly from them at: [ http://esda.org/standards.html ]

There are 3 classifications based on 3 different ESD models which are detailed standards from the ESD Association: [ http://esda.org/ ]

HBM
=====
The most common model is the HBM. This model simulates when a discharge occurs between a human (hand/finger) to a conductor (metal rail). The equivalent capacitance is 100 picofarads (100 x 10^-12 Farads) and equivalent resistance is 1,500 ohms to simulate a human body. The typical rise time of the current pulse (ESD) through a shorting wire averages 6 nanoseconds (6x10^-9 s) and larger for a higher resistant load. The peak current through a 500 ohm resistor averages 463 mA for a 1,000 volt pre-charge voltage.

HBM ESDS Component Classification
Class Voltage Range (V)
0 < 250
1A 250 to < 500
1B 500 to < 1000
1C 1000 to < 2000
2 2000 to < 4000
3A 4000 to < 8000
3B > or = 8000

CDM
=====
The most neglected of models that can compromise your ESD control program. Here, it is the ESDS device itself that becomes charged (sliding out of a tube/bag/sorter/etc) and when contacting a grounded conductor (table top/hand/metal tool) will discharge to that conductor and may result in damaging ESD. Using a 4 pF or 30 pF verification module which can simulate from 2 to 30 Amps peak current for non-socked and up to 18 amps for socketed devices.

CDM ESDS Component Classification
Class Voltage Range (V)
C1 < 150
C2 150 to < 250
C3 250 to < 500
C4 500 to < 1000
C5 1000 to < 1500
C6 1500 to < 2000
C7 > or = 2000

MM
======
Testing components to the Machine Model (MM). The tests replicate MM failures and tell you the MM ESD sensitivity levels for your Devices. The criteria (200 pF @ a nominal 0 ohms).

7.1.2. Machine Model Sensitivity:
A source of damage for the MM is a rapid transfer of energy from a charged conductor to the conductive leads of the device. This ESD model is a 200 pF capacitor discharged through a 500 nH inductor directly into the device with no series resistor. Due to the lack of a series current limiting resistor, this model approximates a voltage source. In the real world this model represents a rapid discharge from items such as, charged board assembly, charged cables, or the conduction arm of an automatic tester. The discharge itself is a sinusoidal decaying waveform with a rise time of 5-8 nanoseconds and a period of approximately 80 nanoseconds.
Control to this model would entail knowing the ESD sensitive devices MM ESD component classification and keeping all voltages below their MM Classes voltage range.

MM ESDS Component Classification
Class Voltage Range (V)
M1 < 100
M2 100 to < 200
M3 200 to < 400
M4 < or = 400

Related Categories: