PCT Test Purpose and Application (1)
PCT test is generally known as pressure cooker cooking test or saturated steam test, the most important is to test the product to be tested under harsh temperature, saturated humidity (100%R.H.)[saturated water vapor] and pressure environment, test the high humidity resistance of the test product, for printed circuit board (PCB&FPC), used to carry out material moisture absorption test, high pressure cooking test... For the purpose of the test, if the product to be tested is a semiconductor, it is used to test the moisture resistance of the semiconductor package. The product to be tested is placed in a harsh temperature, humidity and pressure environment. If the semiconductor package is not good, moisture will penetrate into the package along the colloid or the interface between the colloid and the conductor frame. Popcorn effect, open circuit caused by corrosion of dynamic metallized area, short circuit caused by contamination between package pins... And other related issues.
Pressure Digester test (PCT) Structure:
The test chamber consists of a pressure vessel, including a water heater that can produce a 100% (wetting) environment. The different failures of the product to be tested after PCT test may be caused by a large amount of water vapor condensation and penetration.
Bathtub curve:
Bathtub curve (Bathtub curve, failure period), also known as bathtub curve, smile curve, mainly shows the failure rate of the product in different periods, mainly including early death period (early failure period), normal period (random failure period), wear period (degradation failure period), according to the reliability test box of environmental test. It can be divided into screening test, accelerated life test (durability test) and failure rate test. "Test design", "test execution" and "test analysis" should be considered as a whole when conducting reliability tests.
Common failure periods:
Early failure (early death, Infant Mortality Region) : imperfect production, defective materials, unsuitable environment, imperfect design. Random failure period (normal period, Useful Life Region) : external shock, misuse, changes in environmental conditions fluctuations, poor compression performance. Degradation failure period (Wearout Region) : oxidation, fatigue aging, performance degradation, corrosion.
Environmental stress and failure diagram description:
According to the statistical report of Hughes Airlines, the proportion of environmental stress caused by electronic products failure, height accounted for 2%, salt spray accounted for 4%, dust accounted for 6%, vibration accounted for 28%, and temperature and humidity accounted for up to 60%, so the impact of electronic products on temperature and humidity is particularly significant, but due to the traditional high temperature and humidity tests (such as: 40℃/90%R.H., 85℃/85%R.H., 60℃/95%R.H.) takes a long time, in order to speed up the material's hypersonic rate and shorten the test time, accelerated test equipment (HAST[High accelerated life testing machine], PCT[pressure pot]) can be used to carry out relevant tests. It is also called (degenerate failure period, wear period) test.
PCT Test Purpose and Application (2)
θ 10℃ rule:
When discussing product life, the expression of [θ10℃ rule] is generally used, and a simple explanation can be expressed as [10℃ rule], when the ambient temperature rises by 10℃, the product life will be reduced by half; When the ambient temperature rises by 20 ° C, the product life will be reduced to a quarter. This rule can explain how the temperature affects the life of the product (failure), the opposite product reliability test, can also be used to increase the ambient temperature to accelerate the failure phenomenon, a variety of accelerated life aging tests.
Causes of failure caused by moisture:
Water vapor infiltration, polymer material depolymerization, reduced polymer bonding ability, corrosion, cavitation, wire solder joint detachment, leakage between leads, wafer and wafer bonding layer detachment, pad corrosion, metallization, or short circuit between leads. Effect of water vapor on the reliability of electronic packaging: corrosion failure, delamination and cracking, changing the properties of plastic sealing materials.
PCT failure mode for PCB:
Blister, Crack, SR de-lamination.
PCT testing of semiconductors:
PCT is mainly to test the moisture resistance of semiconductor packaging, the product to be tested is placed in a harsh temperature and humidity and pressure environment test, if the semiconductor packaging is not good, moisture will penetrate into the package along the colloidal or colloidal and wire frame interface into the package, common reasons for installation: Popcorn effect, open circuit caused by corrosion of dynamic metallized area, short circuit caused by contamination between package pins... And other related issues.
PCT reliability assessment for IC semiconductors:
DA Epoxy, wire frame material, sealing resin corrosion failure and IC: corrosion failure (water vapor, bias, impurity ions) will cause electrochemical corrosion of IC aluminum wire, resulting in open circuit and migration growth of aluminum wire.
Failure phenomena caused by moisture corrosion of plastic-sealed semiconductors:
Because aluminum and aluminum alloys are cheap and simple to process, they are usually used as metal wires for integrated circuits. From the beginning of the integrated circuit molding process, water and gas will penetrate through epoxy resin to cause corrosion of aluminum metal wires and thus open circuit phenomenon, which becomes the most headache for quality management. Although various efforts have been made to improve product quality through various improvements, including the use of different epoxy resin materials, improved plastic sealing technology and the improvement of inactive plastic sealing film, with the rapid development of miniaturization of semiconductor electronic devices, the corrosion problem of plastic sealed aluminum metal wire is still a very important technical topic in the electronics industry.
Corrosion process in aluminum wire:
① Water permeates into the plastic sealing shell → moisture permeates into the gap between the resin and the wire
② Water permeates the surface of the wafer to cause aluminum chemical reaction
Factors that accelerate aluminum corrosion:
① The connection between the resin material and the wafer frame interface is not good enough (due to the difference in expansion rate between various materials)
② When packaging, the packaging material is contaminated with impurities or impurity ions (due to the appearance of impurity ions)
③ The high concentration of phosphorus used in the inactive plastic encapsulation film
(4) Defects in inactive plastic encapsulation film
The Popcorn Effect:
The original refers to the IC encapsulated in the plastic outer body, because the silver paste used in the wafer installation will absorb water, once the plastic body is sealed without prevention, when the downstream assembly and welding encounter high temperature, the water will burst due to the vaporization pressure, and it will also emit a sound like popcorn, so it is named, when the absorbed water vapor content is higher than 0.17%, The [popcorn] phenomenon will occur. Recently, P-BGA packaging components are very popular, not only the silver glue will absorb water, but also the substrate of the serial board will absorb water, and the popcorn phenomenon often occurs when the management is not good.
PCT Test Purpose and Application (3)
The way water vapor enters the IC package:
1. Water absorbed by IC chip and lead frame and silver paste used in SMT
2. Moisture absorbed in the plastic sealing material
3. The device may be affected when the humidity in the plastic sealing room is high;
4. After the encapsulation of the device, water vapor permeates through the plastic sealant and the gap between the plastic sealant and the lead frame, because there is only a mechanical combination between the plastic and the lead frame, so there is inevitably a small gap between the lead frame and the plastic.
Note: As long as the gap between the sealant is greater than 3.4*10^-10m, water molecules can pass through the sealant protection Note: The airtight package is not sensitive to water vapor, generally do not use accelerated temperature and humidity test to evaluate its reliability, but to measure its air tightness, internal water vapor content, etc.
PCT test description for JESD22-A102:
It is used to evaluate the integrity of non-airtight packaged devices against water vapor in water vapor condensation or saturated water vapor environments. The sample is placed in a condensed, high-humidity environment under high pressure to allow water vapor to enter the package, exposing weaknesses in the package such as corrosion of the delamination and metallization layers. This test is used to evaluate new package structures or updates of materials and designs in the package body. It should be noted that there will be some internal or external failure mechanisms in this test that do not match the actual application situation. Since absorbed water vapor reduces the glass transition temperature of most polymer materials, an unreal failure mode may occur when the temperature is higher than the glass transition temperature.
External pin tin short circuit: The ionization effect caused by moisture in the package external pin will cause abnormal growth of ion migration, resulting in short circuit between pins.
Moisture causes corrosion inside the package:
The cracks caused by the moisture through the packaging process bring external ion contamination to the surface of the wafer, and after passing through the surface defects such as: protective layer pinholes, cracks, poor covers... Etc., into the semiconductor original, causing corrosion and leakage current... Such problems, if there is applied bias then the fault is more likely to occur.
PCT test conditions:
(Collate PCB, PCT, IC semiconductor and related materials have relevant test conditions on PCT[steam pot test]) PCT test purpose and application
Test name
temperature
humidity
time
Check items & add notes
JEDEC-22-A102
121 ℃
100%R.H.
168h
Other test time: 24h, 48h, 96h, 168h, 240h, 336h
Tensile stripping strength test of IPC-FC-241B-PCB copper laminated laminates
121 ℃
100%R.H.
100 h
The strength of the copper layer should be 1000 N/m
IC-Auto Clave test
121 ℃
100%R.H.
288h
Low dielectric high heat resistant multilayer board
121 ℃
100%R.H.
192h
PCB plug agent
121 ℃
100%R.H.
192h
PCB-PCT test
121 ℃
100%R.H.
30min
Check: Layers, bubbles, white spots
Lead-free solder accelerated life 1
100 ℃
100%R.H.
8h
Equivalent to 6 months under high temperature and humidity, activation energy =4.44eV
Lead-free solder accelerated life 2
100 ℃
100%R.H.
16h
Equivalent to a year of high temperature and humidity, activation energy =4.44eV
IC lead-free test
121 ℃
100%R.H.
1000h
Check every 500 hours
Liquid crystal panel adhesion test
121 ℃
100%R.H.
12h
Metal gasket
121 ℃
100%R.H.
24h
Semiconductor package test
121 ℃
100%R.H.
500, 1000 hours
PCB moisture absorption test
121 ℃
100%R.H.
5, 8h
FPC moisture absorption test
121 ℃
100%R.H.
192h
PCB plug agent
121 ℃
100%R.H.
192h
Multilayer material with low dielectric power and high heat resistance
121 ℃
100%R.H.
5h
Water absorption is less than 0.4 ~ 0.6%
High TG glass epoxy multilayer printed circuit board material
121 ℃
100%R.H.
5h
Water absorption is less than 0.55 ~ 0.65%
High TG glass epoxy multilayer printed circuit board - Heat resistance test after hygroscopic reflow welding
121 ℃
100%R.H.
3h
Heat resistance test of reflow welding after PCT test is completed (260℃/30 seconds)
Micro-etching Horizontal Browning (Co-Bra Bond)
121 ℃
100%R.H.
168h
Automotive PCB
121 ℃
100%R.H.
50, 100h
PCB for the main board
121 ℃
100%R.H.
30min
GBA carrier board
121 ℃
100%R.H.
24h
Accelerated wet resistance test of semiconductor devices
121 ℃
100%R.H.
8h
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