What is HAST testing for chips?

This method is widely used in PCBs, IC semiconductors, connectors, circuit boards, magnetic materials, polymer materials EVA、 Used in industries such as photovoltaic modules to evaluate the sealing, moisture absorption, and aging performance of products. HAST has become a standard in certain industries, especially in products such as PCBs, semiconductors, solar panels, and display panels, as a fast and effective alternative to high-temperature and high humidity testing.

The principle and purpose of chip HAST testing

HAST testing is a commonly used reliability testing method in the integrated circuit (IC) industry. It simulates the harsh conditions that the chip may face in practical applications by placing the chip in a high temperature and high humidity environment, in order to evaluate the stability and reliability of the chip. HAST testing can help manufacturers identify potential issues with chips and ensure that they can function properly in harsh environments.

The main principle of HAST testing is to accelerate the aging process of chips through high temperature and high humidity. High temperature and high humidity environments can trigger a series of physical and chemical reactions, such as thermal expansion, thermal stress, and corrosion. These factors have a negative impact on the performance and reliability of the chip. In the HAST test, the chip is exposed to a high temperature and high humidity environment, which accelerates the aging process and exposes potential problems earlier.

The purpose of HAST testing is threefold: firstly, to evaluate the stability of the chip in high temperature and high humidity environments, to ensure that the chip can operate stably for a long time in harsh application environments; Secondly, detect issues that may be caused by high temperature and humidity, such as welding rupture or metal wire breakage caused by thermal expansion, as well as electrical connection problems caused by corrosion; Finally, verify the reliability of the chip to provide reliable product performance data to manufacturers and customers.

Failure mechanism of chip HAST testing

HAST can quickly trigger specific failures in PCBs and chips, such as delamination, cracking, short circuits, corrosion, and popcorn effects.

The causes of faults caused by moisture include water vapor infiltration, polymer material depolymerization, decreased polymer bonding ability, corrosion, voids, detachment of wire solder joints, leakage between leads, detachment of chip to chip adhesive layers, pad corrosion, metallization or short circuit between leads.

The way water vapor enters IC packaging:

The moisture absorbed by the silver paste used in IC chips, lead frames, and SMT;

Moisture absorbed in the plastic sealing material;

When the humidity in the plastic packaging workshop is high, it may have an impact on the components;

After packaging, water vapor penetrates through the plastic packaging material and the gap between the plastic packaging material and the lead frame. Because there is only mechanical bonding between the plastic and the lead frame, small gaps are inevitable between the lead frame and the plastic

Note: As long as the gap between the seals is greater than 3.4 * 10- ¹⁰ m or more, water molecules can pass through the protection of the seals. Airtight packaging is not sensitive to water vapor, and generally does not use accelerated temperature and humidity tests to evaluate its reliability. Instead, its airtightness and internal water vapor content are measured.

Corrosion process in aluminum wire:

Moisture seeps into the plastic casing → Moisture seeps into the gap between the resin and the wire;

Water vapor seeps into the surface of the chip, causing an aluminum chemical reaction.

Factors that accelerate aluminum corrosion:

The connection between the resin material and the chip frame interface is not good enough (due to differences in expansion rates between various materials);

During packaging, the packaging material is contaminated with impurities or impurity ions (due to the presence of impurity ions);

High concentration phosphorus used in non active plastic encapsulation films;

Defects present in non active plastic encapsulation films.

Chip and PCB distribution: Due to the inconsistent thermal expansion coefficients of the packaging body, disk, and lead frame materials, stress concentration will occur at the connections of different materials inside the plastic encapsulated device under thermal stress. If the stress level exceeds the yield strength or fracture strength of any of the packaging materials, the device will be delaminated. Moreover, generally speaking, the glass transition temperature of epoxy resin for plastic sealing materials is not high, and its thermal expansion coefficient and Young's modulus are very sensitive to temperature changes in the vicinity of the glass transition temperature. Under extremely small temperature changes, the thermal expansion coefficient and Young's modulus of epoxy plastic sealing materials will undergo particularly significant changes, making it more prone to reliability issues for plastic sealing gifts.

Plastic encapsulated components are semiconductor devices packaged with resin based polymers. Resin based materials themselves are not dense and have the characteristic of adsorbing water vapor. Moisture is also introduced into the plastic encapsulated components at the bonding interface between the package and the lead frame. When the water vapor content in the plastic encapsulated components is too high, it can cause corrosion on the chip surface and dissociation of the resin at the interface between the package and the lead frame, which in turn accelerates the entry of source gas into the interior of the plastic encapsulated components, ultimately leading to delamination.

In harsh environments with high temperature, high humidity, and bias voltage, accelerating the penetration of moisture through the external protective layer or along the interface between the metal and the external protective layer can cause the failure of the sample.

Popcorn effect: Originally referring to ICs packaged in plastic outer bodies, the silver paste used for chip installation absorbs water. Once the package is not properly protected and subjected to high temperatures during downstream assembly and welding, the moisture will cause the package to burst due to vaporization pressure, while also making a sound similar to popcorn. Therefore, it is named after the popcorn phenomenon. When the water vapor content absorbed is higher than 0.17%, popcorn phenomenon will occur. Recently, P-BGA packaging components have become very popular. Not only does the silver glue absorb water, but the substrate of the carrier board also absorbs water. Poor management often leads to popcorn phenomenon.

Moisture causes internal corrosion of the package: The cracks caused by moisture during the packaging process bring external ion contamination to the surface of the chip. Through surface defects such as pinholes, cracks, and poor coating, it enters the semiconductor components, causing corrosion and leakage current problems. If a bias voltage is applied, faults are more likely to occur.

Corrosion: Corrosion failure (water vapor, bias voltage, impurity ions) can cause electrochemical corrosion of aluminum wires in ICs, leading to wire opening and migration growth. Due to their low prices and simple processing techniques, aluminum and aluminum alloys are commonly used as metal wires for integrated circuits. From the beginning of the integrated circuit plastic packaging process, water vapor will penetrate through epoxy resin, causing corrosion of aluminum metal wires and making it difficult to generate open circuits, becoming one of the most headache inducing problems in the chip industry. Although various efforts have been made to improve the quality of materials, including the use of different epoxy resin materials, improved encapsulation technology, and increased non active encapsulation films, with the rapid development of miniaturization in semiconductor electronic devices, corrosion of encapsulated aluminum metal wires remains a very important technical issue in the electronics industry to this day.

Applicable standards for chip HAST testing

IEC60749-4 (High Acceleration Stress Test)

ED-4701/100A (Unsaturated Steam Pressure Test)

JESD22-A118 (unbiased high acceleration stress test)

JESD22-A110E (High Acceleration Stress Test)

JESD22-A102E (unbiased high-pressure cooking test)

AEC-Q100 Version H (Biased High Acceleration Stress Test/Unbiased High Acceleration Stress Test)

JPCA-ET08 (Unsaturated Pressurized Steam Test)