Semi conductor reliability analysis PCT Accelerated Aging Test

Generally, the failure of plastic-encapsulated devices can be divided into early failure and lifetime failure. The former is mostly caused by quality defects caused by design or process errors, which can be judged by conventional electrical performance testing and screening. The latter is caused by latent defects of the components. The behavior of latent defects is related to time and stress. Experience has shown that failures caused by moisture, corrosion, mechanical stress, electrical overstress and electrostatic discharge dominate.

The PCT high-pressure accelerated aging test is mainly to test moisture resistance of the semiconductor package. The product to be tested is placed in a specific temperature, humidity and pressure environment to test the pressure resistance and air tightness of the sample. If the semiconductor package not good condition, the moisture will follow the glue or the glue and the wire. The interface of the rack penetrates into the package. The common causes of failure include popcorn effect, open circuit caused by corrosion in the metalized area, and short circuit between the pins of the package due to pollution.

PCT high pressure accelerated aging test concept

The PCT high pressure accelerated aging test is also called the pressure cooker cooking test or the saturated steam test. The product to be tested (placed in a specific temperature,saturated humidity (100%R.H. saturated water vapor and pressure environment). resistant to high humidity ability. For printed circuit boards (PCB&FPC), it is used for test purposes such as material moisture absorption test and high pressure cooking test. If the test product is a semiconductor, it is used to test the moisture resistance of the semiconductor package. The product to be tested is tested in a harsh temperature, humidity and pressure environment. If the semiconductor package is not good, moisture will penetrate into the package along the interface between the gel or the gel and the lead frame.?Reasons for failure: popcorn Related issues such as the disconnection caused by corrosion in the moving metallization area, and the short circuit between the package pins due to contamination.

PCT High Pressure Accelerated Aging Test Standard

IEC60068-2-66, JESD22-A102-B, EIAJED4701, EIA/JESD22

Failure phenomenon of PCT high pressure accelerated aging test

1. Corrosion failure and IC

Corrosion failure (water vapor, bias voltage, impurity ions) will cause electrochemical corrosion of the aluminum wire of the IC, which will lead to open circuit and migration and growth of the aluminum wire.

2. The failure of plastic-packaged semiconductors due to moisture corrosion

Because aluminum and aluminum alloys are cheap and simple in processing technology, they are usually used as metal wires for integrated circuits. From the beginning of the integrated circuit plastic packaging process, water vapor will penetrate through the epoxy resin to cause corrosion of the aluminum metal wire and cause an open circuit phenomenon, which has become the most headache problem for quality management. Although various efforts have been made to improve production and quality through various improvements including the use of different epoxy resin materials, improved plastic packaging technology and increased inactive plastic packaging films, with the rapid development of the miniaturization of semiconductor electronic devices, plastic aluminum metal wires have been corroded The problem is still a very important technical issue in the electronics industry.

3. θ10℃ rule

When discussing product life, generally use expression of θ10°C rule. ?simple description can be expressed as 10°C rules. When the ambient temperature rises by 10°C, the product life will be reduced by half; when the ambient temperature rises by 20°C , The product life will be reduced to 4/1 .This rule can explain how temperature affects product life (failure). On the contrary, in the reliability test of the product, also use increasing the ambient temperature to accelerate the failure phenomenon, and conduct various accelerated life aging tests.

4. The cause of failure caused by moisture

Water vapor penetration, polymer material depolymerization, decreased polymer bonding ability, corrosion, voids, wire solder joint disconnection, leakage between leads, chip and die bonding layer separation, pad corrosion, metallization or short circuit between leads influence the electronic packaging reliability. Corrosion failure delamination and cracking change the properties of plastic packaging materials.

5. Corrosion process in aluminum wire

1) Moisture penetrates into the plastic shell → moisture penetrates into the gap between the resin and the wire

2) Water vapor penetrates into the surface of the chip to cause a chemical reaction of aluminum

Factors that accelerate aluminum corrosion:

1) The connection between the resin material and the chip frame interface is not good enough (due to the difference in expansion rate between various materials)

2) When packaging, the packaging material is doped with impurities or contamination by impurity ions (due to the appearance of impurity ions)

3)?High concentration of phosphorus used in inactive plastic film

4) ?Defects in inactive plastic film

6. Popcorn effect

Originally refers to the IC packaged with a plastic outer body, because the silver paste used for chip mounting will absorb water. Once the plastic body is sealed without precautions, when the downstream assembly and welding encounter high temperatures, their moisture will be caused by vaporization pressure. The bursting of the enclosure also makes a popcorn-like sound, hence the name. When the absorbed water vapor content is higher than 0.17%, the popcorn phenomenon will occur. Recently, P-BGA package components are very popular. Not only the silver glue will absorb water, but the substrate of the carrier board will also absorb water. Popcorn often occurs when the management is poor.

7. The way water vapor enters the IC package

1) Water absorbed by the silver paste used in IC chip and lead frame and SMT

2) Moisture absorbed in the molding compound

3) High humidity in the plastic packaging workshop may affect the device

4) After encapsulation of the device, water vapor penetrates through the plastic compound and through the gap between the plastic compound and the lead frame. Because there is only a mechanical bond between the plastic and the lead frame, it is inevitable that there will be a small gap between the lead frame and the plastic. .

Remarks: As long as the gap between the sealants is greater than 3.4*1^-10m, water molecules can pass through the sealant's protection. Hermetic seals are not sensitive to water vapor. Generally, accelerated temperature and humidity tests are not used to evaluate their reliability, but to determine their airtightness and internal water vapor content.

8. External pin tin short circuit

The ionization effect caused by moisture on the external leads of the package will cause abnormal growth of ion migration, which can lead to short circuits between the leads.

9. Moisture causes internal corrosion of the package

The cracks caused by the moisture passing through the packaging process bring external ion pollution to the surface of the chip. After passing through the surface defects such as: pinholes, cracks, and poor coatings, it enters the semiconductor element, causing corrosion and Leakage current, etc., if a bias voltage is applied, the fault is more likely to occur.

PCT high pressure accelerated aging test conditions

Test equipment: KOMEG brand PCT pressure cooker testing chamber

Temperature range: +105℃ to +162.5℃, humidity range: 100%R.H