The semiconductor device packages feature an electrostatic discharge (ESD) protection circuitry. To ensure the semiconductor device’s effectiveness and reliability against the ESD phenomenon, the semiconductor industry uses three test models to qualify the devices as per JEDEC standards requirements. The test models include the human body model (HBM), the charge device model (CDM), and the machine model (MM). 

A Charged Device Model (CDM) is an ESD test method used to evaluate the immunity of integrated circuits (ICs) or chips against electrostatic discharge (ESD) events that could occur during IC’s automated manufacturing, handling, and assembly. In this test, test signals are applied to charge the IC, and then the IC is discharged to a metal ground plane to simulate the ESD event. This test assesses whether the device under test (DUT) has sufficient immunity against ESD. The purpose of CDM ESD immunity testing is to ensure that the IC or chip can withstand ESD events during its manufacturing and handling processes and meet the effectiveness and reliability requirements described by ESD test standards. 

The common CDM ESD test standards include JS-002, AEC-Q101-005, AEC-Q100-011, and JESD22-C101. These standards provide guidelines, test signal levels, and procedures for testing DUT against ESD. 

What is Electrostatic Discharge (ESD)?  

Electrostatic Discharge (ESD) occurs when two objects at different electrostatic potentials come into contact or bring close together, resulting in a sudden and momentary electric current flow between them. This current flow often creates a visible spark (sometimes invisible) due to the rapid transfer of electrostatic charge (electrons) from one object to the other. An ESD event in electronics can damage sensitive components and ICs.   

The ESD event occurs due to the build-up of static electricity (charge separation) between two objects.  This static electricity can occur due to tribocharging or electrostatic induction.  

Tribocharging:   

A common cause for static electricity built-up is Tribocharging, where two objects touch and then separate, resulting in the movement of electrons from one object to the other, creating static electricity between them. One well-known example of tribochargingfor is that a person walking across a carpet accumulates static electricity. When this person touches a metal doorknob, an ESD event occurs, i.e., a sudden discharge of static charges occurs between the human and the metal doorknob, resulting in a shock or spark.  

          Figure: Static electricity built-up, ESD event, caused by Tribocharging 

Also, the person can have a static potential of 30 KV from walking on the carpet, which is enough to damage sensitive electronics if the person touches the electronics. In human-caused ESD events, the impulse current typically has a peak current magnitude greater than 30 A and with a rise time of approximately 200 ps to greater than 10 ns.  

Electrostatic induction:  

In electrostatic induction, a charged object causes polarization in a nearby conductive object (e.g., a neutral conductor). The polarization leads to a redistribution of charges within the conductive object, i.e., positive charges align on one end while negative charges align on the other end. This creates an electrostatic potential between the charged and conductive objects. An ESD event can occur if the conductive object comes into contact with a differently charged object (e.g., a metallic tool), allowing the accumulated charge to rapidly discharge.  

ESD effects and solution:  

ESD can have harmful effects in various industries, including electronics manufacturing, medical device production, and vehicle fabrication. For example, in automated electronic handling and assembly, integrated circuits (ICs) can accumulate static charges due to tribocharging or electrostatic induction. The charged IC or device subsequently discharges when it comes into contact with a person or a conductive object, leading to an ESD event. This can result in damage to the IC or semiconductor package.  

Hence, the electronics manufacturers use ESD protection techniques,  including grounding workers (use of grounded wrist straps or ankle straps), controlling humidity, providing antistatic devices, ensuring ESD-Safe workstations, and use of air Ionizers.    

ESD simulator or ESD generator can be used to perform ESD testing of electronic devices as per EMC standard requirements for the Human Body Model (HBM), Charged-Device Model (CDM), and Machine Model (MM).  

Note: 

• HBM simulates ESD caused by discharge from a human being. 
• CDM simulates ESD due to discharge from a charged device (e.g., IC) when it comes into contact with a conductive object. It can simulate ESD events that could occur during IC’s automated manufacturing, handling, and assembly.
• MM simulates ESD due to discharge from a machine to ground through a device.

How is the ESD-CDM test conducted?  

Figure shows a generic CDM testing circuit. It typically consists of an HV supply source, a field plate covered with a dielectric layer (typically FR4 dielectric), a device under test (DUT), a top ground plane, a pogo pin connected to ground through a 1 Ω disk resistor, robotic driven test head, and a 50 Ω coaxial cable. The test setup often features two small cameras to align the test head in the correct position over the DUT.   

      Figure: Generic CDM testing circuit The DUT (e.g., IC) is placed on the dielectric layer that covers the field plate. The IC is positioned with pins or balls facing upward. The high-voltage supply source applies a test voltage to the field plate. It brings the potential of the DUT nearly to the plate potential, thereby charging the DUT. Through robotic control, the grounded pogo pin touches each IC pin, one at a time, resulting in the DUT discharging. This leads to spark formation (i.e., ESD event) between a pin of DUT and the approaching pogo pin. At least one positive and one negative discharge are applied to each pin of the DUT.  If the DUT withstands the ESD event without any damage and meets its datasheet specifications, then it passes the CDM ESD test; otherwise, it is considered a test-failed unit.

The pogo pin is connected to the ground through a 1 Ω disk resistor, and there will be a current flow through the resistor during discharge. This current flow results in a voltage drop across the resistor, which is measured using a 50 Ω coaxial cable connected to an oscilloscope.  The magnitude of stress current flow through the DUT depends on the precharge voltage and the capacitance between the DUT and the field plate. For a 500-V test voltage, the current waveform rise time is usually around 400 ps with the peak current magnitude around 6 A for 1.5 to 2 ns.  For a test voltage of 1000 V, the peak current magnitude is around 12 A. 

The table shows: ESD immunity classification for CDM

Conclusion:

The Charged Device Model (CDM) is an ESD test method designed to evaluate the immunity of integrated circuits against electrostatic discharge events that occur during manufacturing and handling. By simulating real-world conditions where a charged device discharges to a grounded plane, the CDM test ensures that ICs can withstand potential ESD threats and meet industry standards for reliability. Adhering to established test protocols and standards like JS-002 and AEC-Q101-005 is essential for maintaining the integrity and performance of electronic components. Effective ESD management and robust testing practices are crucial for safeguarding sensitive electronics in various industries.