During the manufacturing or final use of electronic products, electrostatic discharge (ESD) or power surges may cause damage or malfunction of the electronic products. It is estimated that the proportion of failures caused by ESD in all component failures ranges from single digits to one-third, and the increase in circuit density and higher performance requirements exacerbate this problem.

From consumer electronic devices to expensive industrial equipment, they can all be affected by dangerous transient voltage events such as ESD. As more and more products rely on microprocessors that are susceptible to such events, it is necessary to choose appropriate ESD solutions to ensure customer satisfaction and commercial success.

When electrons are redistributed on the surface of a material, a charge imbalance phenomenon occurs. When the generated electric field is strong enough, static charges will seek equilibrium and generate electrostatic discharge. This could have a catastrophic impact on microelectronic electronic products, leading to malfunctions, product delays, revenue losses, and sometimes even damage to reputation or brand image.

Even in a clean integrated circuit manufacturing environment, components may still be affected by ESD during processing, assembly, testing, and packaging. Human Body Model (HBM) is the most widely used testing standard to ensure that integrated circuits can withstand the impact of electrostatic charges generated when a charged human body (typical ESD generator) comes into contact with the integrated circuit.

IEC 61000-4-2 is an international ESD testing standard that uses a human body model with a higher system level hardware benchmark to ensure that equipment can withstand the effects of transient events (including lightning protection) during actual use by end-users.

Transient voltage suppression
With the continuous reduction of the geometric size of integrated circuits, traditional ESD parameters are no longer sufficient to cope with system level risks. In order to protect power and high-speed data circuits, designers must utilize advances in transient voltage suppression (TVS) technology to provide additional protection beyond HBM and device built-in ESD protection measures.

For devices with HDMI, Thunderbolt, USB 2, USB 3, USB-C, antennas, and other standard interfaces, TVS is becoming increasingly important in protecting commonly used data cables from ESD. From wearable devices and keyboards to smartphones and IoT cameras, strong protective measures need to be taken to protect these products from ESD damage.

TVS diodes can be installed on power or data lines to prevent transient events by diverting surges away from the circuits they protect. In transient events, the voltage on the protected line will rapidly increase, reaching up to tens of thousands of volts. Under normal operating conditions, the TVS diode is in an open state, but it can suppress system level ESD peaks and divert high currents in less than one nanosecond.

Some key features to consider when choosing a TVS solution include:

Capacitor (C) - Inherent ability to store charge
Reverse Off State Voltage (VRMM) - The maximum operating voltage of a circuit without activating the TVS diode
Clamp Voltage (VC) - The voltage level at which TVS begins to divert excess current from the protected circuit (below VRMM)
Reverse breakdown voltage (VBR) - the voltage at which TVS enters low impedance mode
Peak Pulse Current (IPP) - The maximum current that TVS can withstand before damage
Peak Pulse Power (PPP) - Instantaneous power dissipated by TVS during event occurrence
Considerations for TVS packaging
The position of the TVS diode will affect its performance, and a position close to the ESD entry point can provide better protection. Semiconductor packaging also plays an important role in protecting precision electronic components in modern systems from ESD threats.

When designers choose TVS diodes for products, they should focus on the specific surge protection level required, the number of circuits that need to be protected, and the packaging size suitable for the available circuit board space.

Lead type integrated circuit packaging is a common choice for TVS diodes because it is easy to install on printed circuit boards (PCBs) and therefore cost-effective. In addition, this packaging can also provide excellent heat dissipation. However, due to its large size, it may occupy a large amount of printed circuit board space and often generate parasitic effects, which have a negative impact on performance.

Fortunately, the DFN (dual channel flat no lead) package has a small size and multiple functions, which may be more suitable for ESD protection. DFN packaging does not have extended leads, and its contacts are located below the component rather than distributed along the periphery of the component, thus saving space compared to lead based surface mount device (SMD) packaging.

The DFN package integrates a bare thermal pad at the bottom that can seamlessly integrate with the printed circuit board, serving as an integrated heat sink, thus providing excellent heat dissipation performance. Compared to lead SMD packages, this package also has fewer parasitic components, which helps maintain signal integrity in high-speed applications.

However, the visibility of solder joints in DFN packaging on printed circuit boards is limited, making it difficult to confirm whether the soldering is correct during the assembly process after packaging.

Overcoming DFN challenges
Semtech overcomes the DFN challenge by installing TVS diodes in DFN modules that use flip chip packaging and side wettable wings (Figure 1).

Semtech's DFN packaging image
Figure 1: A typical image of the Semtech DFN package, which uses side wettable wings to mount TVS diodes. (Image source: Semtech)

Inverted chip packaging utilizes solder bumps instead of wire bonding to achieve connection with the substrate. The side wettable side wings ensure that the solder diffuses from the bottom of the package, flows upward along the wall side, and forms visible solder connections.

With the help of this technology, automated visual inspection (AVI) systems can visually inspect the solder bumps formed between the vertical surface of the side wings and the solder pads, verify whether the printed circuit board is correctly joined, and ensure reliable connections.

The use of side wettable wings not only enhances reliability and improves productivity, but also resists vibrations and shaking that may cause separation. The copper terminal is covered with a tin plating layer to prevent copper oxidation over time.

Semtech has launched a series of 0402 size (1.0 mm x 0.6 mm x 0.55 mm) DFN packaged single channel TVS diodes using flip chip packaging and side wettable wing technology, which are specifically designed for non automotive industrial applications.

0402 DFN TVS components are designed to provide ESD protection for RF and FM antennas, touch screen controllers, 12 VDC lines, side keys and keyboards, audio interfaces, IoT devices, portable instruments, General Purpose Input/Output (GPIO) lines, and industrial equipment.

Semtech devices can provide ESD protection for the following products:

Thunderbolt 3
USB 3.0/3.2
USB Type-C on high-speed signal lines ® Connector
Configure Channel (CC) and Sideband Usage (SBU) lines (for negotiating power, data, and standby modes through USB Type-C cable connections)
VBus line
D+/D - data cable (used for transmitting differential signals of USB and other legacy protocols)
Semtech's single channel, data line, and VBUS ESD protection solutions adopt side wettable side wing packaging, providing RClamp and μ Clamp ESD protection devices. These solutions provide circuit board level protection, with lower operating voltage and clamping voltage, faster response time, and will not cause device performance degradation.